Patent Application
20230279194
The invention is generally in the field of upcycling of hydrocarbon polymers; particularly methods for upcycling of waste hydrocarbon polymers.
Over the past 70 years, global production of synthetic, petroleum-based plastics has risen sharply, from less than 2 Mt in 1950 to 359 Mt in 2018 (PlasticsEurope, “Plastics—The facts 2019: An analysis of European plastics production, demand and waste data”, 2019). Production is projected to double again in the coming decade (Pravettoni, United Nations Environment Programme, GRID-Arendal, 2018). Plastics have become indispensable in many facets of modern life, enhancing the security of our food and health care systems, the performance of textiles, the versatility of consumer electronics, and the energy efficiency of transportation. About 40% of these plastics are destined for short-term use, and most (in the US: >90%) are not recycled (Geyer, et al., Sci. Adv. 3, e1700782 (2017)). The vast bulk of this plastic waste ends up in landfills or being incinerated. However, the embodied energy that can be recovered by combustion is far less than that used in the original manufacturing of the plastic (Eriksson, et al., Energ. Environ. Sci. 2, 907-914 (2009)). Furthermore, a significant fraction of the waste is mismanaged, ending up in rivers and oceans, where its chemical inertness leads to extremely slow degradation and visible accumulation in the natural environment (Jambeck, et al., Science 347, 768-771 (2015); Chamas, et al., ACS Sustain. Chem. Eng. 8, 3494-3511 (2020)).
Efforts to develop closed-loop lifecycles for synthetic plastics by relying on collection, separation, and mechanical recycling have had limited success. The inferior properties of the recycled materials, relative to virgin plastics, contribute to the economic challenges of the “downcycling” model (Rahimi, et al., Nat. Rev. Chem. 1, 0046 (2017)). New types of polymers that degrade rapidly in the environment are being investigated (Zhu, et al., Nature 540, 354-362 (2016)), although such materials do not currently have either the physical properties or the cost structure to displace existing commodity plastics. Degradable plastics can also contaminate recycling streams, and may encourage single-use product design. Depolymerization (also known as chemical or feedstock recycling) can recover the original monomer subunits whose subsequent repolymerization gives materials with properties identical to those of the original plastic (Vollmer, et al., Angew. Chem. Int. Ed., DOI:10.1002/anie.201915651 (2020)). However, this strategy requires prohibitive amounts of energy for polyolefins, such as polyethylene (PE) and polypropylene (PP). Controlled partial depolymerization could convert post-consumer waste plastics directly into more valuable chemicals (“upcycling”), although few such processes have yet been developed.
High and low density polyethylenes currently represent the largest fraction (36% by mass) of all plastic waste (Geyer, et al., Sci. Adv. 3, e1700782 (2017)). Their depolymerization by pyrolysis at temperatures above 400° C., with or without a catalyst, generates complex, low-value mixtures of gas, liquid hydrocarbons and char (Ignatyev, et al., ChemSusChem 7, 1579-1593 (2014); Sharuddin, et al., Energ. Convers. Manage. 115, 308-326 (2016)). US 2020/0017772 by Ramamurthy, et al. discloses a process for producing propylene and cumene from plastics via a complex multi-unit operation. Somewhat more selective disassembly can be achieved at lower temperatures via catalytic hydrogenolysis (Dufaud, et al., Angew. Chem. Int. Ed. 37, 806-810 (1998); Celik, et al., ACS Cent. Sci. 5, 1795-1803 (2019)) or tandem catalytic alkane metathesis (Jia, et al., Sci. Adv. 2, e1501591 (2016)), but the low-value alkane products are unlikely to recoup the costs of recovery, separation, and processing using large amounts of a co-reactant (H2 or liquid alkanes, respectively).
Aromatics are more attractive target products from partial depolymerization. The conventional process for making aromatics is naphtha reforming. This energy-intensive process generates a mixture known as benzene-toluene-xylenes (BTX) at 500-600° C. (Rahimpour, et al., Appl. Energ. 109, 79-93 (2013)). In a subsequent step with a large environmental footprint, BTX is alkylated to give linear alkylbenzenes (LAB), which can be used to make surfactants. The most widely-used processes require linear olefins (typically, C10-C16) and liquid HF or AlCl3—HCl as the acid catalyst (Perego, et al., Catal. Today 73, 3-22 (2002)). Manufacturing BTX by aromatization of shale gas-derived light alkanes requires harsher reaction conditions (propane: 550-700° C.; ethane: 600-800° C.; methane: 900-1000° C.) (Kanitkar, et al., Natural Gas Processing from Midstream to Downstream, Wiley, pp. 379-401, 2019), and the catalysts tend to deactivate rapidly. New zeolite-based catalysts can use either methanol (Yarulina, et al., Nat. Catal. 1, 398-411 (2018)), or syngas (Cheng, et al., Chem 3, 334-347 (2017)), to make BTX aromatics at lower temperatures, 300-400° C. Biomass-based routes include oxidative coupling of ethanol to aromatic alcohols and aldehydes (Wang, et al., ACS Catal. 9, 7204-7216 (2019)), hydrogenolysis/hydrodeoxygenation of bio-oils or lignin to give propylbenzene (Maneffa, et al., ChemSusChem. 9, 2736-2748 (2016)), and Diels-Alder reactions of carbohydrate-derived furanics to give p-xylene (Williams, et al., ACS Catal. 2, 935-939 (2012)). However, slow rates, low yields, and high H2 requirements would make them expensive to operate and none are practiced commercially. BTX is also formed in the catalytic pyrolysis of PE at 400-600° C., although deactivation of the zeolite catalysts by coking is severe (Lopez, et al., Renew. Sust. Energ. Rev. 73, 346-368 (2017)). The yields are moderate (up to 50 wt %), and large amounts of low-value gases (C1 to C5, >50 wt %) are formed.
There remains a need for improved processes for upcycling hydrocarbon polymers.
Therefore, it is the object of the present invention to provide a process for upcycling plastic waste containing hydrocarbon polymers to more valuable materials, such as alkylaromatic compounds.
It is a further object of the present invention to provide an improved depolymerization process to produce more valuable materials.
It is a further object of the present invention to provide compositions formed from depolymerization processes.
It is a further object of the present invention to provide compositions formed from upcycling plastic waste.
Processes for upcycling plastic waste containing one or more hydrocarbon polymers to alkylaromatic compounds are described herein. The process typically includes (i) feeding a plastic waste containing a hydrocarbon polymer, optionally more than one hydrocarbon polymer, into a reactor and (ii) operating the reactor at a sufficient temperature for a sufficient period of time to convert the hydrocarbon polymer(s) to a product in the form of a liquid and/or wax that contains an alkylaromatic compound, such as a dialkylbenzene, optionally more than one alkylaromatic compound. Typically, the mol % of the alkylaromatic compound, optionally the total mol % of the more than one alkylaromatic compound, in the product (i.e. selectivity) is at least 50 mol %, such as between 50 mol % and 95 mol %.
The reactor contains a catalyst therein. The catalyst includes a transition metal. Typically, the catalyst is in the form of atoms, nanoclusters, or nanoparticles, or a combination thereof. Optionally, the catalyst is dispersed in the form of atoms, nanocluster, or nanoparticles, or a combination thereof on the surface of a support.
Typically, the reactor operates at a temperature of up to 500° C. or up to 350° C., such as between 250° C. and 300° C.
Process for upcycling a plastic waste material is described herein. Generally, the term “upcycling” refers to the depolymerization of a waste material to more valuable chemicals, such as aromatic compounds. The waste contains a hydrocarbon polymer, optionally more than one hydrocarbon polymer. In the process, the hydrocarbon polymer in the waste is generally upcycled to form one or more aromatic compounds, such as one or more alkylaromatic compounds.
The process can also be a process for manufacturing aromatic compounds, such as alkylaromatic compounds.
The upcycling process includes a depolymerization reaction. Optionally, the depolymerization reaction is solvent-free or hydrogen gas-free, or a combination thereof. Optionally, the depolymerization reaction is hydrogen gas-free. For example, no hydrogen gas is added to the reactor for the depolymerization reaction. Optionally, the process is solvent-free. For example, the waste material is in a solid form and is not dissolved in a solvent prior to or during the depolymerization reaction. Generally, the depolymerization reaction is performed at a temperature≤500° C., optionally at a temperature≤350° C.
The process generally includes (i) feeding the waste material containing hydrocarbon polymer(s) into a reactor, where the reactor contains a catalyst therein; and (ii) operating the reactor at a sufficient temperature for a sufficient period of time to convert the hydrocarbon polymer(s) to a product.
The product contains an alkylaromatic compound, optionally more than one alkylaromatic compound, and is generally in the form of a liquid, a wax, or a combination thereof. Typically, the mol % of the alkylaromatic compound, optionally the total mol % of the more than one alkylaromatic compound, in the product is at least 50 mol %, such as between 50 mol % and 95 mol %. The mole % of the alkylaromatic compound or the total mole % of the more than one alkylaromatic compound in the product is also referred herein as “the selectivity to alkylaromatic compound”, when one alkylaromatic compound is present in the product, or “the total selectivity to alkylaromatic compounds”, when more than one alkylaromatic compound is present in the product.
An exemplary process for upcycling a waste material is illustrated in
Without being bound by theory, it is believed that hydrogenolysis and aromatization via dehydrocyclization occur in tandem, i.e. together, during this reaction to covert polyethylene to the resulting liquid and/or wax product.
Optionally, the process does not include a hydrocracking step, an olefin metathesis step, or a benzene alkylation step, or a combination more than one of these steps.
A. Feed a Waste Material into a Reactor.
Generally, the waste material is fed into the reactor. Optionally, the waste material is in the form of a solid. The waste material contains a plastic, optionally a mixed plastics. Examples of suitable plastics that can be upcycled using the process include, but are not limited to, non-chlorinated plastics, such as polyolefins, polyethylene, polypropylene, polystyrene, and copolymers thereof; and chlorinated plastics, such as polyvinylchloride (PVC), polyvinylidene chloride (PVDC), etc. In the reactor, the waste material is in contact with the catalyst in the reactor. Reactors that can be used to upcycle a plastic waste material are known. For example, the reactor can be an autoclave reactor, such as a pressure reactor system, a flow reactor, a fixed-bed reactor, a packed-bed reactor (PBR), a continuous stirred tank reactor (CSTR), or a semi-batch reactor.
1. Hydrocarbon Polymers
The waste material contains a hydrocarbon polymer. The hydrocarbon polymer in the waste can be polyethylene, polypropylene, polystyrene, a copolymer of polyethylene, a copolymer of polypropylene, a copolymer of polyethylene and polypropylene, or acrylonitrile butadiene styrene (ABS). For example, the waste material contains polyethylene or polypropylene. Optionally, the waste material contains more than one hydrocarbon polymer described above, i.e. a mixture of two or more hydrocarbon polymers described above. For example, the waste material contains a mixture of polyethylene and polypropylene.
Optionally, the waste material contains a hydrocarbon polymer, which is a mixture of different densities of the same hydrocarbon polymer. For example, the waste material can contain polyethylene, which is a mixture of high density polyethylene (HDPE) and low density polyethylene (LDPE).
LDPE generally has a density in the range of 917 to 930 kg/m3. It is not reactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. LDPE has more branching (on about 2% of the carbon atoms) than HDPE.
The density of HDPE generally is in the range of 930 to 970 kg/m3. Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength than LDPE. The difference in strength between HDPE and LDPE exceeds the difference in density, giving HDPE a higher specific strength (a material's strength (force per unit area at failure) divided by its density; also known as the strength-to-weight ratio).
Optionally, the waste material contains a hydrocarbon polymer of different molecular weights (weight average molecular weight Mw or number average molecular weight Mn). For example, the waste material contains polyethylene, which is a mixture of high molecular weight polyethylene and medium molecular weight polyethylene, a mixture of high molecular weight polyethylene and low molecular weight polyethylene, a mixture of medium molecular weight polyethylene and low molecular weight polyethylene, or a mixture of high, medium, and low molecular weight polyethylene. Generally, a hydrocarbon polymer of low Mw is in the range from 1000 g mol−1 to 10,000 g mol−1; a hydrocarbon polymer of medium Mw is in the range from 10,000 g mol−1 to 200,000 g mol−1; a hydrocarbon polymer of high Mw is in the range from 200,000 g mol−1 to 500,000 g mol−1; and a hydrocarbon polymer of ultrahigh Mw is in the range from 500,000 g mol−1 to 7,500,000 g mol−1.
a. Average Molecular Weight
Typically, the hydrocarbon polymer in the waste material has a weight average molecular weight (Mw) of at least 1×103 g mol−1, 2×103 g mol−1, at least 2.5×103 g mol−1, at least 3×103 g mol−1, at least 3.5×103 g mol-, at least 4×103 g mol−1, up to 7.5×106 g mol−1, 5×106 g mol−1, 1×106 g mol−1, 5×105 g mol−1, up to 1×105 g mol−1, up to 9.5×104 g mol−1, up to 9×104 g mol−1, up to 8.5×104 g mol−1, up to 8×104 g mol−1, up to 7.5×104 g mol−1, up to 7×104 g mol−1, up to 6.5×104 g mol−1, up to 6×104 g mol−1, up to 5.5×104 g mol−1, up to 5×104 g mol−1, between 1×103 g mol−1 and 7.5×106 g mol−1, between 1×103 g mol−1 and 5×106 g mol−1, between 1×103 g mol−1 and 1×106 g mol−1, between 1×103 g mol−1 and 5×105 g mol−1, between 2×103 g mol−1 and 1×105 g mol−1, between 2×103 g mol−1 and 1×105 g mol−1, between 3×103 g mol−1 and 1×105 g mol−1, between 4×103 g mol−1 and 1×105 g mol−1, between 4×103 g mol−1 and 9.5×104 g mol−1, between 4×103 g mol−1 and 5.5×104 g mol−1, or between 4×103 g mol−1 and 5×104 g mol−1.
Optionally, the hydrocarbon polymer in the waste material has a number average molecular weight (Mn) of at least 1×102 g mol−1, at least 5×102 g mol−1, at least 1×103 g mol−1, at least 1.5×103 g mol−1, at least 2×103 g mol−1, at least 2.5×103 g mol−1, at least 3×103 g mol−1, at least 3.5×103 g mol−1, at least 4×103 g mol−1, up to 2×104 g mol−1, up to 1.5×104 g mol−1, up to 1×104 g mol−1, between 1×103 g mol−1 and 2×104 g mol−1, between 1.5×103 g mol−1 and 2×104 g mol−1, between 1.8×103 g mol−1 and 2×104 g mol−1, between 2×103 g mol−1 and 2×104 g mol−1, between 3×103 g mol−1 and 2×104 g mol−1, between 4×103 g mol−1 and 2×104 g mol−1, between 1.5×103 g mol−1 and 1.5×104 g mol−1, or between 1.8×103 g mol−1 and 1.5×104 g mol−1.
For example, the waste material contains a polyethylene having a Mw of at least 3×103 g mol−1 and a Mn of at least 1.5×103 g mol−1, such as a Mw in a range between 3×103 g mol−1 and 1×105 g mol−1 and a Mn in a range between 1.5×103 g mol−1 and 1.5×104 g mol−1, such as a Mw of 3.52×103 g mol−1 and a Mn of 1.85×103 g mol−1.
Optionally, the waste material contains a hydrocarbon polymer of different average molecular weights (also referred herein as “molecular weight”). Generally, a low molecular weight hydrocarbon polymer has a Mw in a range from 1000 g mol−1 to 10,000 g mol−1 and a Mn in a range from 100 g mol−1 to 1,000 g mol−1; a medium molecular weight hydrocarbon polymer has a Mw in a range from 10,000 g mol−1 to 200,000 g mol−1 and a Mn in a range from 1,000 g mol−1 to 20,000 g mol−1; a high molecular weight hydrocarbon polymer has a Mw in a range from 200,000 g mol−1 to 500,000 g mol−1 and a Mn in a range from 20,000 g mol−1 to 50,000 g mol−1; and an ultrahigh molecular weight hydrocarbon polymer has a Mw in a range from 500,000 g mol−1 to 7,500,000 g mol−1 and a Mn in a range from 50,000 g mol−1 to 750,000 g mol−1. For example, the waste material contains polyethylene, which is a mixture of high molecular weight polyethylene and medium molecular weight polyethylene, a mixture of high molecular weight polyethylene and low molecular weight polyethylene, a mixture of medium molecular weight polyethylene and low molecular weight polyethylene, or a mixture of high, medium, and low molecular weight polyethylene.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.
b. Number of Carbon Atoms in Hydrocarbon Polymer
Typically, the hydrocarbon polymer(s) in the waste material contains at least 70 carbon atoms, at least 100 carbon atoms, at least 120 carbon atoms, at least 150 carbon atoms, at least 200 carbon atoms, at least 250 carbon atoms, at least 300 carbon atoms, at least 350 carbon atoms, at least 400 carbon atoms, at least 450 carbon atoms, at least 500 carbon atoms, at least 550 carbon atoms, at least 600 carbon atoms, at least 650 carbon atoms, at least 700 carbon atoms, at least 750 carbon atoms, at least 800 carbon atoms, at least 850 carbon atoms, at least 900 carbon atoms, at least 950 carbon atoms, at least 1000 carbon atoms, up to 500,000 carbon atoms, up to 100,000 carbon atoms, up to 50,000 carbon atoms, up to 10,000 carbon atoms, up to 7000 carbon atoms, up to 6500 carbon atoms, up to 6000 carbon atoms, up to 5500 carbon atoms, up to 5000 carbon atoms, up to 4500 carbon atoms, up to 4000 carbon atoms, up to 3500 carbon atoms, between 70 and 500,000 carbon atoms, between 100 and 100,000 carbon atoms, between 120 and 50,000 carbon atoms, between 120 and 10,000 carbon atoms, between 120 and 7000 carbon atoms, between 200 and 7000 carbon atoms, between 500 and 7000 carbon atoms, between 500 and 6500 carbon atoms, between 500 and 6000 carbon atoms, between 500 and 5500 carbon atoms, between 500 and 5000 carbon atoms, between 500 and 4500 carbon atoms, between 500 and 4000 carbon atoms, between 500 and 3500 carbon atoms, or between 3500 and 7000 carbon atoms.
c. Density
Optionally, the waste material contains a hydrocarbon polymer of ultra-low density, very low density, linear low or low density, linear medium or medium density, or high density or a combination thereof. For example, the waste material contains a hydrocarbon polymer with a mixture of low and high densities. Generally, a hydrocarbon polymer of ultra-low density is in the range from 0.867 g cm−3 to 0.889 g cm−3. A hydrocarbon polymer of very low density is typically in the range from 0.890 g cm−3 to 0.914 g cm−3. A hydrocarbon polymer of linear low or low density is typically in the range from 0.919 g cm−3 to 0.925 g cm−3. A hydrocarbon polymer of linear medium or medium density is typically in the range from 0.926 g cm−3 to 0.940 g cm−3. A hydrocarbon polymer of high density is typically in the range from 0.941 g cm−3 to 0.970 g cm−3. For example, a polyethylene of ultra-low density is typically in the range from 0.867 g cm−3 to 0.889 g cm−3; a polyethylene of very low density is typically in the range from 0.890 g cm−3 to 0.914 g cm−3; a polyethylene of linear low or low density is typically in the range from 0.919 g cm−3 to 0.925 g cm−3; a polyethylene of linear medium or medium density is typically in the range from 0.926 g cm−3 to 0.940 g cm−3; and a polyethylene of high density is in typically the range from 0.941 g cm−3 to 0.970 g cm−3.
For example, the waste material contains a linear low-density or low-density hydrocarbon polymer, such as a linear low-density or low-density polyethylene having a weight average molecular weight (Mw) in a range from 8.9×104 g mol−1 to 4.7×105 g mol−1, such as 94.5×103 g mol−1 and a density in a range from 0.919 g cm−3 to 0.925 g cm−3. Exemplary waste material that contains a low-density polyethylene includes freezer bags.
For example, the waste material contains a high-density hydrocarbon polymer, such as a high-density polyethylene having a Mw in a range from 103 g mol−1 to 107 g mol−1, such as 53.5×103 g mol−1 and a density in a range from 0.941 g cm−3 to 0.970 g cm−3. Exemplary waste material that contains a high-density polyethylene includes plastic bottles and plastic packaging, such as a plastic non-biodegradable grocery bags.
Optionally, the waste material contains a hydrocarbon polymer of different densities. For example, the waste material can contain a mixture of high density polyethylene and low density polyethylene.
d. Dispersity
Typically, the waste material contains hydrocarbon polymer having a high dispersity of >1.5, at least 2, at least 2.2, at least 2.5, at least 3, at least 3.5, up to 7.5, up to 7, between 1.8 and 7.5, between 2 and 7.5, or between 3.5 and 7.5, such as at least 1.9, at least 3.6, or at least 7.4.
2. Catalysts
The reactor contains a catalyst therein. The catalyst is generally in the form of a solid. Catalysts suitable for upcycling the waste material generally include a transition metal, optionally more than one transition metal. The term “transition metal” refers to a single transition metal or a transition metal that is an element in a compound, such as metal oxide or metal carbide. For example, the catalyst is a transition metal, a mixture of two or more metals containing at least one transition metal, a metal oxide of a transition metal, or a metal carbide of a transition metal, or a combination thereof. The transition metal of the catalyst acts as the catalytic active sites that react with the hydrocarbon polymer of the waste material.
Optionally, the hydrocarbon polymer and transition metal of the catalyst has a ratio (by mass) in a range from 20 to 200, from 30 to 200, from 30 to 150, from 35 to 200, or from 35 to 150, such as about 39 or about 133.
a. Transition Metals
Optionally, the catalyst is or contains a transition metal, such as platinum, palladium, ruthenium, iridium, rhenium, rhodium, iron, cobalt, nickel, copper, molybdenum, or tungsten.
Optionally, the catalyst is or contains a mixture of two or more metals containing a transition metal, such as a bimetallic or a trimetallic. For example, the catalyst is a mixture of two or more metals and each metal in the mixture of metals is a transition metal, such as platinum, palladium, ruthenium, iridium, rhodium, iron, cobalt, nickel, copper, molybdenum, or tungsten. For example, the catalyst is a bimetallic of platinum and cobalt.
For example, the catalyst is or contains a mixture of two or more metals containing a first group of transition metal(s) and a second group of metal(s). The first group of transition metals in the mixture of metals contains one or more transition metals, and each of the first group metals is platinum, palladium, ruthenium, iridium, rhodium, iron, cobalt, nickel, copper, molybdenum, or tungsten. The second group of metal(s) in the mixture of metals contains one or more metals that are different from the metals of the first group, and each of the second group metals can be a transition metal or a non-transition metal. For example, each of the second group metals is different from each of the transition metals in the first group and is rhenium, tin, lead, tungsten, molybdenum, chromium, manganese, or zinc. For example, the mixture of metals is a bimetallic containing platinum and rhenium or platinum and tin. For example, the mixture of meals is a trimetallic, and optionally contains platinum, rhenium, and tin.
b. Metal Oxides
Optionally, the catalyst is or contains a metal oxide of a transition metal. The metal oxide can contain a single transition metal or a mixture of two or more metals where at least one of the mixture of metals is a transition metal. For example, the catalyst is a metal oxide of a single transition metal, such as platinum, palladium, ruthenium, iridium, rhodium, iron, cobalt, nickel, copper, molybdenum, or tungsten.
For example, the catalyst is or contains a metal oxide of a mixture of two or more metals and each metal in the mixture of metals is a transition metal, such as platinum, palladium, ruthenium, iridium, rhodium, iron, cobalt, nickel, copper, molybdenum, or tungsten.
For example, the catalyst is or contains a metal oxide of a mixture of two or more metals containing a first group of transition metal(s) and a second group of metal(s) as described above.
Optionally, the catalyst is or contains a metal oxide having a perovskite structure. For example, the catalyst is a metal oxide of a transition metal, such as titanium, niobium, iron, or zirconium, and the catalyst further contains calcium and/or sodium, where the elements of the metal oxide are arranged in a way such that it has the same type of crystal structure as CaTiO3.
c. Metal Carbides
Optionally, the catalyst is or contains a metal carbide of a transition metal. The metal carbide can contain a single transition metal or a mixture of two or more metals where at least one of the mixture of metals is a transition metal. For example, the catalyst is a metal carbide of a single transition metal, such as platinum, palladium, ruthenium, iridium, rhodium, iron, cobalt, nickel, copper, molybdenum, or tungsten. For example, the metal carbide is molybdenum carbide or tungsten carbide.
For example, the catalyst is or contains a metal carbide of a mixture of two or more metals and each metal in the mixture of metals is a transition metal, such as platinum, palladium, ruthenium, iridium, rhodium, iron, cobalt, nickel, copper, molybdenum, or tungsten.
For example, the catalyst is a metal carbide of a mixture of two or more metals containing a first group of transition metal(s) and a second group of metal(s) described above.
Optionally, more than one catalyst is used in the process. Any catalysts described above may be used. For example, the reactor contains more than one metal oxide described above therein. Each of the metal oxides in the reactor contains a transition metal that is different from the other. For example, the reactor contains more than one metal carbide described above therein. Each of the metal carbides in the reactor contains a transition metal that is different from the other. For example, the reactor contains a metal oxide and a metal carbide therein. The metal oxide in the reactor contains a transition metal that is different from the metal carbide.
d. Form of the Catalyst
The catalyst can be in a variety of suitable forms, such as atoms, nanoclusters, nanoparticles, or a combination thereof.
When the catalyst is in the form of nanoclusters, the nanoclusters can have an average diameter of up to 2 nm, up to 1.5 nm, up to 1 nm, in a range from 0.5 nm to 2 nm, from 0.5 nm to 1.5 nm, from 0.5 nm to 1 nm, or from 1 nm to 2 nm.
When the catalyst is in the form of nanoparticles, the nanoparticles can have an average diameter of up to 50 nm, up to 20 nm, up to 10 nm, up to 5 nm, at least 2 nm, in a range from 2 nm to 50 nm, from 2 nm to 45 nm, from 2 nm to 40 nm, from 2 nm to 35 nm, from 2 nm to 30 nm, from 2 nm to 25 nm, from 2 nm to 20 nm, from 2 nm to 15 nm, from 2 nm to 10 nm, or from 2 nm to 5 nm.
3. Optional Components
Optionally, the catalyst is dispersed on the surface of a support to form a catalytic system. When a support is present, the catalyst is dispersed on the surface of the support in the form of atoms, nanoclusters, or nanoparticles, or a combination thereof. For example, the catalyst is platinum nanoparticles and the platinum nanoparticles are dispersed on the surface of an aluminum oxide support. The support is generally understood to separate the catalyst atoms, nanoclusters, and/or nanoparticles apart and/or adsorb the hydrocarbon polymer(s), thereby improve the efficiency of the depolymerization reaction.
Additionally, some supports, such as acidic support materials or acid-modified support materials, can be included in the catalytic system to increase the efficiency of the catalyst therein. For example, a catalytic reaction using a catalytic system that includes an acidic support produces a liquid and/or wax product with a similar or higher yield and a similar or higher total selectivity to alkylaromatic in a shorter time period, compared to the same catalytic reaction using a catalytic system that does not include the acidic support, under the same reaction conditions. The term “same reaction conditions” means that the catalytic reaction is performed under the same temperature, same pressure, same atmosphere, etc. For example, depolymerization of polyethylene using a catalytic system that includes an acidic support produces a liquid and/or wax product with a similar or higher yield with a similar or higher total selectivity to alkylaromatic in a time period that is at least 2-time shorter, at least 3-time shorter, at least 5-time shorter, at least 10-time shorter, at least 15-time shorter, or at least 20-time shorter, compared to the same catalytic reaction using a catalytic system that does not include the acidic support, under the same reaction conditions. Optionally, these support materials are catalytic on their own.
Optionally, more than one support is used for forming a catalytic system with the catalyst. When two or more supports are present, the catalyst is dispersed on the surface of at least one of the supports in the form of atoms, nanoclusters, or nanoparticles, or a combination thereof. For example, when two supports are used for forming a catalytic system, the catalyst is platinum nanoparticles and the platinum nanoparticles are dispersed on the surface of a first support; the platinum nanoparticles dispersed first support is mixed with a second support that is different from the first support to form the catalytic system. For example, when two supports are used for forming a catalytic system, the catalyst is platinum nanoparticles and the platinum nanoparticles are dispersed on the surface of a first support and the surface of a second support that is different from the first support; the platinum nanoparticles dispersed first support and second support are mixed to form the catalytic system.
Optionally, when two or more supports are present, a first catalyst can be dispersed on the surface of at least one of the supports in the form of atoms, nanoclusters, or nanoparticles, or a combination thereof, and a second catalyst can be dispersed on the surface of at least one of the supports that is different from the support having the first catalyst dispersed thereon, in the form of atoms, nanoclusters, or nanoparticles, or a combination thereof. For example, when two supports are used for forming a catalytic system, a first catalyst is platinum nanoparticles and the platinum nanoparticles are dispersed on the surface of a first support and a second catalyst that is different from the first catalyst is dispersed on the surface of a second support that is different from the first support.
When two or more supports are present, the weight percentage of each support in the catalytic system is selected based on the specific catalyst and the material of each support. For example, when two supports are used for forming a catalytic system, a first support having platinum nanoparticles dispersed thereon is mixed with a second support without any catalyst dispersed therein, where the second support is different from the first support. The weight percentage of the second support in the catalytic system is in a range from 2% to 90%, from 2% to 50%, from 2% to 35%, from 10% to 90%, from 10% to 80%, from 10% to 70%, from 10% to 60%, from 10% to 50%, from 10% to 30%, from 15% to 40%, from 20% to 50%, from 20% to 40%, or from 20% to 35%, such as about 20% or about 33%, with the balance of the components in the catalytic system being the weight of first support and the weight of the catalyst dispersed thereon.
a. Materials for Support
The material for the support is typically chemically stable when subject to the operating conditions of the reactor for the depolymerization of the waste material. For example, the material for the support does not react with common chemicals (e.g. hydrogen gas, saturated C1-C5 alkane, benzene, or toluene, etc) at the reaction temperature and pressure and for a period of time described below. For example, the material for the support does not react with common chemicals (e.g. hydrogen gas, saturated C1-C5 alkane, benzene, or toluene, etc) at a temperature of 500° C. or less and at a pressure in a range from 1 atm to 2 atm.
Examples of suitable materials for the support include, but are not limited to, oxide compounds, halogenated oxide compounds, metal carbides, metal phosphates, and carbon-based materials, and acid modified oxides, metal carbides, metal phosphates, and carbon-based materials. The material for the support is a different material than the transition metal or mixture of metals in the catalyst.
Optionally, the material for the support is an oxide compound, such as a metal oxide or a non-metal oxide. For example, the oxide compound for the support is silicon dioxide, aluminum oxide (e.g. γ-alumina, amorphous alumina, etc.), halogenated alumina, such as Cl-alumina and F-alumina, silica-aluminum oxide, silica (e.g. silica gel, mesoporous silica, etc.), acid-modified silica, CeO2, acid-modified CeO2, TiO2, acid-modified TiO2, WO3, MoO3, Re2O7, a perovskite, clays (dealuminated clays, clays modified with organic or inorganic acids, clays ion exchanged with H+, NH4+, Fe3+, Na+, etc.), or a zeolite (e.g. ZSM-5, dealuminated zeolites, zeolites modified by organic and/or inorganic acids, zeolites modified by organic and/or inorganic bases, etc.), or a combination thereof.
Examples of acids that are suitable for modifying the above-mentioned support materials include, but are not limited to, Keggin-type heteropoly acid (H3PW12O40, H4SiW12O40, etc.) and their acidic salt thereof (e.g. Cs2.5H0.5PW12O40, etc.). Methods for modifying the support materials are known in the art, such as chemical modifications (e.g. covalently attaching an acid/base on the material) or non-chemical modifications (e.g. physical loading of an acid/base on or entrapping an acid/base in the material). For example, Keggin-type heteropoly acid (H3PW12O40, H4SiW12O40, etc.) or an acidic salt thereof (e.g. Cs2.5H0.5PW12O40, etc.) can be physically loaded on a silica support, a TiO2 support, or a carbon-based material.
Optionally, the material for the support is a metal carbide. For example, the metal carbide forming the support is any metal carbide described above, such as molybdenum carbide or tungsten carbide.
Optionally, the material for the support is a metal phosphate. The metal phosphate forming the support can contain a transition metal or a mixture of metals described above for metal oxides.
Optionally, the material for the support is a carbon-based material. A carbon-based material generally refers to a material where the number of carbon atoms are at least 50% of the total number of atoms in the material. Examples of suitable carbon-based materials for the support include, but are not limited to, graphite, graphite oxide, activated carbon, carbon nanotubes, carbon nanosheet, graphene, and graphene oxide, and an acid modified version thereof, or a combination thereof. Suitable acids for modifying these carbon-based materials can be any of the inorganic acids described above, such as Keggin-type heteropoly acid (H3PW12O40, H4SiW12O40, etc.) and their acidic salt thereof (e.g. Cs2.5H0.5PW12O40, etc.).
Optionally, the material for the support is a Keggin-type heteropoly acid (H3PW12O40, H4SiW12O40, etc.) or an acidic salt of the Keggin-type heteropoly acid (Cs2.5H0.5PW12O40, etc.).
The material for the support may be catalytic or non-catalytic. For example, the support is formed from a catalytic material that can participate in the depolymerization reaction. In these cases, the catalytic material for the support may be a transition metal, a mixture of metals containing at least one transition metal, a metal oxide containing a transition metal, or a metal carbide containing a transition metal as described above as suitable materials for the catalyst. However, the catalytic material for the support is different from the metal in the catalyst. Optionally, the material for the support is a material that does not participate in the depolymerization reaction, such as silica oxide or a carbon-based material. For example, the material for the support is γ-alumina or silica-alumina.
Optionally, the material for the support is an acidic material. Typically, the acidic material is strong enough to protonate pyridine, as determined by known methods. Whether a given material is able to protonate pyridine, and therefore considered to be an acidic material can be shown using the following test. First the, material is dehydrated at about 400° C. under vacuum; then the dehydrated material is dosed with an excess of pyridine vapor at room temperature, followed by desorption, typically at about 150° C. under vacuum for suitable time period, such as about 20 minutes. If the IR spectra of the resulting material shows a peak at 1545 cm−1, strong Brønsted acid sites are present, and thus demonstrates its acidity for protonating pyridine. Examples of suitable acidic materials that can be used for the support include, but are not limited to, halogenated oxide compounds (e.g. Cl-alumina and F-alumina), WO3, MoO3, Re2O7, acid modified oxide compounds, such as acid-modified zeolites, silica, CeO2, TiO2, clays, etc., and acid modified carbon-based materials (e.g. acid-modified activated carbon, carbon nanotubes, graphene, etc.), where the acid can be any of the acids described above. When the material for the support is a halogenated oxide compound, such as Cl-alumina or F-alumina, the weight percentage of the halogen in the support can be in a range from 0.1% to 5%, from 0.5% to 3%, from 0.5% to 2%, from 0.5% to 1.5%, such as about 0.7% or about 1.3%.
Optionally, when a single support is used for forming a catalytic system, such as any one of the oxide compounds, halogenated oxide compounds, metal carbides, metal phosphates, and carbon-based materials, and their acid modified versions thereof described above, the weight percentage of the support in the catalytic system is in a range from 90% to 99.9%, from 90% to 99.8%, from 90% to 99.5%, from 90% to 99%, from 98% to 99.9%, from 98% to 99.8%, from 98% to 99.5%, from 98% to 99%, from 98.5% to 99.9%, from 98.5% to 99.8%, from 98.5% to 99.5%, or from 99% to 99.9%, with the balance of the components in the catalytic system being the weight of the catalyst dispersed thereon.
Optionally, when two or more supports are used for forming a catalytic system, at least one of the supports is an acidic support as described above, such as a halogenated oxide compound (e.g. Cl-alumina and F-alumina). In these catalytic systems, the catalyst can be dispersed on the surface of the acidic support(s) and/or on the surface of the support material that is different from the acidic support(s).
For example, when two supports are used for forming a catalytic system, a first support is γ-alumina or silica-alumina having the catalyst dispersed thereon and a second support is an acidic support as described above, such as F-alumina, that does not have the catalyst dispersed thereon. The weight percentage of the acidic support in the catalyst system is in a range from 2% to 90%, from 2% to 50%, from 2% to 35%, from 10% to 90%, from 10% to 80%, from 10% to 70%, from 10% to 60%, from 10% to 50%, from 10% to 30%, from 15% to 40%, from 20% to 50%, from 20% to 40%, or from 20% to 35%, such as about 20% or about 33%, with the balance of the components in the catalytic system being the weight of the first support and the weight of the catalyst dispersed thereon.
For example, when two supports are used for forming a catalytic system, a first support is γ-alumina or silica alumina having the catalyst dispersed thereon and a second support is an acidic support as described above, such as F-alumina, that also has the catalyst dispersed thereon. The weight percentage of the acidic support in the catalyst system is in a range from 2% to 90%, from 2% to 50%, from 2% to 35%, from 10% to 90%, from 10% to 80%, from 10% to 70%, from 10% to 60%, from 10% to 50%, from 10% to 30%, from 15% to 40%, from 20% to 50%, from 20% to 40%, or from 20% to 35%, such as about 20% or about 33%, with the balance of the components in the catalytic system being the weight of the first support and the weight of the catalyst dispersed on the first and second supports. The catalyst dispersed on the first support can be the same as or different from the catalyst that is dispersed on the second support.
b. Forms of the Support
Typically, the support has a surface area having a dimension sufficiently large to allow the catalyst to be dispersed hereon. When calculating surface area of the support, any surface that the reactants are able to contact is typically included. Surface area of the support can be measured by techniques known in the art, for example, by nitrogen physisorption. Typically, the support has a surface area of at least 50 m2 g−1, at least 100 m2 g−1, or at least 150 m2 g−1, in a range from 50 m2 g−1 to 1000 m2 g−1, from 50 m2 g−1 to 900 m2 g−1, from 50 m2 g1 to 800 m2 g−1, from 50 m2 g1 to 700 m2 g1, from 50 m2 g−1 to 600 m2 g−1, from 50 m2 g1 to 500 m2 g−1, from 50 m2 g−1 to 400 m2 g−1, from 50 m2 g1 to 300 m2 g−1, from 50 m2 g1 to 200 m2 g−1, or from 50 m2 g−1 to 1000 m2 g−1. For example, the support has a surface area of at least 150 m2 g−1, such as 186 m2 g−1.
The support can be in a form of a mesoporous sheet or microparticles, or a combination thereof. For example, the support can be in the form of aluminum oxide microparticles. In some embodiments, the support can be in the form of a carbon sheet (e.g. graphene sheet), carbon powders, carbon particles, or carbon nanoparticles (e.g. carbon nanotubes).
The support is generally understood to separate the catalyst atoms, nanoclusters, and/or nanoparticles apart and/or adsorb the hydrocarbon polymer(s), thereby improve the efficiency of the depolymerization reaction. For example, when the catalyst is a metal or a mixture of metals dispersed on the support in the form of atoms, each atom is displaced a distance or different distances from the other atoms of the metal or mixture of metals. For example, when the catalyst is dispersed on the support in the form of nanoclusters, each nanocluster is displaced a distance or different distances from the other nanoclusters of the catalyst. For example, when the catalyst is dispersed on the support in the form of nanoparticles, each nanoparticle is displaced a distance or different distances from the other nanoparticles of the catalyst.
c. Weight Loading
Generally, the total weight loading of the one or more metals of the catalyst is present on the support in an amount less than 10 wt % of the total weight of the catalyst and the support. For example, when the catalyst includes one or more transition metals, the total weight loading of the metals present in the catalyst on the support is calculated as the sum of the weights of the transition metals in the catalyst divided by the sum of the weight of the support plus the weights of the transition metals and non-transition metals multiplied by 100. When the catalyst includes only one transition metal, the total weight loading of the metals present in the catalyst on the support is simply calculated as the weight of the transition metal in the catalyst divided by the sum of the weight of the support plus the weight of the transition metal multiplied by 100. Similarly, when the catalyst includes both one or more transition metals and one or more non-transition metals, the total weight loading of the metals present in the catalyst on the support is calculated as the sum of the weights of transition metals and non-transition metals in the catalyst divided by the sum of the weight of the support plus the weights of the transition metals and non-transition metals multiplied by 100.
For example, the total weight loading of the one or more metals of the catalyst is present on the support in an amount of less than 10 wt %, less than 8 wt %, less than 5 wt %, less than 4.5 wt %, less than 4 wt %, less than 3.5 wt %, less than 3 wt %, less than 2.5 wt %, less than 2 wt %, less than 1.5 wt %, less than 1 wt %, in a range of from 0.1 wt % to 10 wt %, from 0.1 wt % to 8 wt %, from 0.1 wt % to 5 wt %, from 0.2 wt % to 5 wt %, from 0.5 wt % to 10 wt %, from 0.5 wt % to 8 wt %, from 0.5 wt % to 5 wt %, from 1 wt % to 10 wt %, from 1 wt % to 8 wt %, from 1 wt % to 5 wt %, from 0.1 wt % to 4.5 wt %, from 0.1 wt % to 4 wt %, from 0.1 wt % to 3.5 wt %, from 0.1 wt % to 3 wt %, from 0.1 wt % to 2.5 wt %, or from 0.1 wt % to 2 wt %, from 0.1 wt % to 1.5 wt %, from 0.1 wt % to 1 wt %, or from 0.1 wt % to 0.5 wt % of the total weight of the catalyst and the support, such as about 0.2 wt %, about 1 wt %, or about 1.5 wt % of the total weight of the catalyst and the support.
Methods for preparing the disclosed catalysts are known. For example, the disclosed catalysts may be prepared using the methods described in Garcia and Goto, Mater. Trans., 44(9):1717-1728 (2003).
B. Operate the Reactor to Convert the Hydrocarbon Polymer to a Product.
The reactor is operated at a sufficient temperature for a sufficient period of time to convert the hydrocarbon polymer to a product containing an alkylaromatic compound, optionally more than one alkylaromatic compound. The product is in the form of a liquid, a wax, or a combination thereof. Typically, the mol % of the alkylaromatic compound in the product, optionally the total mol % of the more than one alkylaromatic compound in the product is at least 50 mol %.
Typically, the reactor is operated at a low temperature, such as less than or equal to 500° C., optionally less than or equal to 450° C., less than or equal to 400° C., or less than or equal to 350° C. The temperature at which the reactor operates is sufficient to convert the hydrocarbon polymer to the product containing one or more alkylaromatic compounds, such as dialkylbenzene.
An exemplary upcycling process, which includes the steps of (i) feeding a waste material containing hydrocarbon polymer(s) into a reactor; and (ii) operating the reactor at a sufficient temperature for a sufficient period of time to convert the hydrocarbon polymer to a product, is schematically illustrated in
The product stream 110 contains a liquid and/or wax containing an alkylaromatic compound or more than one alkylaromatic compound. The mol % of the alkylaromatic compound or the total mol % of the more than one alkylaromatic compound in the product stream 110 is at least 50 mol %. The product stream 110 contains other unsaturated compounds and/or C6-C10 alkanes in addition to the one or more alkylaromatic compound(s). In addition to the liquid/wax stream, gas products also exit the reactor. Additionally, some unreacted solid waste may remain. The solid waste can be removed from the reactor 10 via the organic solid stream 130. The gas product containing hydrogen gas and/or a short-chain hydrocarbon(s), such as a saturated C1-C5 alkane, benzene, or toluene, or a combination thereof exits the reactor via gas stream 120. Optionally, the product stream 110 is fed to a separation unit 20 where the product is separated into short-chain (i.e. C6-C10) alkane and/or aromatic compound stream 111, alkane stream 112 containing a mixture of alkanes with carbon numbers in a range from 11 to 80, thus the alkane stream contains alkanes with an average carbon number of 30, and/or alkylaromatic compound stream 113 containing alkylaromatic compound(s) with average carbon numbers described below, such as alkylaromatic compound(s) with an average carbon number of 30.
1. Product
Following steps (i) and (ii), product in the form of a liquid, a wax, or a combination thereof, is formed. The product in a liquid and/or wax form is identified as stream 110 in
The product contains an alkylaromatic compound, optionally more than one alkylaromatic compound. For example, the product contains a mixture of two alkylaromatic compounds, a mixture of three alkylaromatic compounds, a mixture of four alkylaromatic compounds, a mixture of five alkylaromatic compounds, and optionally contains more than five different alkylaromatic compounds. Optionally, the product contains other unsaturated compounds, alkanes with a carbon number in a range from 11 to 80, from 15 to 80, from 20 to 80, from 11 to 70, from 11 to 60, from 11 to 50, from 20 to 50, such as a mixture of alkanes with carbon numbers in a range from 11 to 80, thus the alkane stream contains alkanes with an average carbon number of 30, and/or C6-C10 alkanes in addition to the alkylaromatic compound(s). Optionally, the product does not include tetramethylbenzene, butylbenzene, dimethylnaphthalene, or biphenyl, or a combination thereof.
a. Aromatic Compounds
The liquid and/or wax product contains an alkylaromatic compound, and optionally contains more than one alkylaromatic compound. For example, the product contains a mixture of two alkylaromatic compounds, three alkylaromatic compounds, four alkylaromatic compounds, or five alkylaromatic compounds, and optionally contains more than five different alkylaromatic compounds. The alkylaromatic compound or each alkylaromatic compound in the mixture of alkylaromatic compounds can be monocyclic or polycyclic alkylaromatic hydrocarbons, or partially hydrogenated analogs of polycyclic alkylaromatic hydrocarbons. The alkylaromatic compounds can be monocyclic aromatic hydrocarbons or polycyclic aromatic hydrocarbons, or partially hydrogenated analogs of polycyclic aromatic hydrocarbons. In polycyclic aromatic hydrocarbons, the rings can be attached together in a pendant manner or can be fused. After exiting the reactor, the alkylaromatic compounds can be separated from the other compounds in the liquid and/or wax product stream in a separation unit. For example, in the exemplary process shown in
Exemplary alkylaromatic compounds that can be in the liquid and/or wax product include alkylbenzene, an alkyl-polycyclic aromatic compound (e.g. alkylnaphthalene, alkylanthracene, alkylphenanthrene) or a partially hydrogenated analog of an alkyl-polycyclic aromatic compound (e.g. a partially hydrogenated analog of alkylnaphthalene, alkylanthracene, or alkylphenanthrene), such as a partially hydrogenated analog of alkylnaphthalene (i.e. alkyltetralin), or a combination thereof. For example, the product contains dialkylbenzene and/or dialkylnaphthalene, and optionally alkyltetralin, alkylanthracene, and/or alkylphenanthrene.
Optionally, the liquid and/or wax product does not include tetramethylbenzene, butylbenzene, dimethylnaphthalene, or biphenyl.
i. Number of Carbons
Typically, each alkylaromatic compound in the liquid and/or wax product contains at least 10 carbon atoms, at least 12 carbon atoms, up to 50 carbon atoms, up to 45 carbon atoms, up to 40 carbon atoms, up to 35 carbon atoms, up to 30 carbon atoms, up to 25 carbon atoms, in a range of from 10 to 50 carbon atoms, from 10 to 45 carbon atoms, from 10 to 40 carbon atoms, from 10 to 35 carbon atoms, from 10 to 30 carbon atoms, from 10 to 25 carbon atoms, from 12 to 50 carbon atoms, from 12 to 45 carbon atoms, from 12 to 40 carbon atoms, from 12 to 35 carbon atoms, from 12 to 30 carbon atoms, from 12 to 25 carbon atoms, from 15 to 50 carbon atoms, from 15 to 45 carbon atoms, from 15 to 40 carbon atoms, from 15 to 35 carbon atoms, from 15 to 30 carbon atoms, from 15 to 25 carbon atoms, from 20 to 50 carbon atoms, from 20 to 45 carbon atoms, from 20 to 40 carbon atoms, from 20 to 35 carbon atoms, from 20 to 30 carbon atoms, or from 20 to 35 carbon atoms.
Optionally, the alkylaromatic compound in the liquid and/or wax product contains from 10 to 50 carbon atoms, from 12 to 50 carbon atoms, from 15 to 50 carbon atoms, 15 to 25 carbons, 20 to 40 carbons, or from 20 to 35 carbon atoms.
For example, the alkylaromatic compound in the liquid and/or wax product contains from 10 to 50 carbon atoms, from 12 to 50 carbons, from 15 to 50 carbon atoms, 15 to 25 carbons, 20 to 40 carbons, or from 20 to 35 carbon atoms. For example, the aromatic compound in the product is a C10-C50 alkylbenzene, a polycyclic C10-C50 aromatic, or a C10-C50 alkyl-polycyclic aromatic, optionally a C15-C50 alkylbenzene, a polycyclic C15-C50 aromatic, or a C15-C50 alkyl-polycyclic aromatic, optionally a C15-C25 alkylbenzene, a polycyclic C15-C25 aromatic, or a C15-C25 alkyl-polycyclic aromatic, optionally a C20-C40 alkylbenzene, a polycyclic C20-C40 aromatic, or a C20-C40 alkyl-polycyclic aromatic, optionally a C20-C35 alkylbenzene, a polycyclic C20-C35 aromatic, or a C20-C35 alkyl-polycyclic aromatic.
Optionally, the liquid and/or wax product does not include tetramethylbenzene, butylbenzene, dimethylnaphthalene, or biphenyl or a combination thereof.
ii. Average Molecular Weight
Typically, the alkylaromatic compound in the liquid and/or wax product has a Mw less than 800 g mol−1, less than 750 g mol−1, less than 700 g mol−1, less than 650 g mol−1, less than 600 g mol−1, less than 550 g mol−1, less than 500 g mol−1, at least 300 g mol−1, at least 200 g mol−1, at least 150 g mol−1, in a range of from 150 g mol−1 to 800 g mol−1, from 200 g mol−1 to 800 g mol−1, from 200 g mol−1 to 600 g mol−1, from 200 g mol−1 to 500 g mol−1, from 300 g mol−1 to 800 g mol−1, from 300 g mol−1 to 600 g mol−1, or from 300 g mol−1 to 500 g mol−1.
Optionally, the alkylaromatic compound in the liquid and/or wax product has a Mn less than 700 g mol−1, less than 650 g mol−1, less than 600 g mol−1, less than 550 g mol−1, less than 500 g mol−1, at least 300 g mol−1, at least 200 g mol−1, at least 150 g mol−1, in a range of from 150 g mol−1 to 700 g mol−1, from 200 g mol−1 to 700 g mol−1, from 200 g mol−1 to 600 g mol−1, from 200 g mol−1 to 500 g mol−1, from 300 g mol−1 to 700 g mol−1, from 300 g mol−1 to 600 g mol−1, or from 300 g mol−1 to 500 g mol−1.
For example, the alkylaromatic compound in the liquid and/or wax product has a Mw less than 800 g mol−1, less than 750 g mol−1, less than 700 g mol−1, less than 650 g mol−1, less than 600 g mol−1, less than 550 g mol−1, less than 500 g mol−1, at least 300 g mol−1, at least 200 g mol−1, at least 150 g mol−1, in a range of from 150 g mol−1 to 800 g mol−1, from 200 g mol−1 to 800 g mol−1, from 200 g mol−1 to 600 g mol−1, from 200 g mol−1 to 500 g mol−1, from 300 g mol−1 to 800 g mol−1, from 300 g mol−1 to 600 g mol−1, or from 300 g mol−1 to 500 g mol−1.
Optionally, the alkylaromatic compound in the liquid and/or wax product has a Mw or Mn that is at least 5-times less than the Mw or Mn of the hydrocarbon polymer (reactant) in the waste material before depolymerization, at least 10-times less than the Mw or Mn of the hydrocarbon polymer, at least 15-times less than the Mw or Mn of the hydrocarbon polymer, at least 20-times less than the Mw or Mn of the hydrocarbon polymer, at least 25-times less than the Mw or Mn of the hydrocarbon polymer, at least 30-times less than the Mw or Mn of the hydrocarbon polymer, at least 35-times less than the Mw or Mn of the hydrocarbon polymer, at least 40-times less than the Mw or Mn of the hydrocarbon polymer, at least 45-times less than the Mw or Mn of the hydrocarbon polymer, at least 50-times less than the Mw or Mn of the hydrocarbon polymer, at least 55-times less than the Mw or Mn of the hydrocarbon polymer, at least 60-times less than the Mw or Mn of the hydrocarbon polymer, at least 65-times less than the Mw or Mn of the hydrocarbon polymer, at least 70-times less than the Mw or Mn of the hydrocarbon polymer, at least 75-times less than the Mw or Mn of the hydrocarbon polymer, at least 80-times less than the Mw or Mn of the hydrocarbon polymer, at least 85-times less than the Mw or Mn of the hydrocarbon polymer, at least 90-times less than the Mw or Mn of the hydrocarbon polymer, at least 95-times less than the Mw or Mn of the hydrocarbon polymer, at least 100-times less than the Mw or Mn of the hydrocarbon polymer, at least 120-times less than the Mw or Mn of the hydrocarbon polymer, at least 150-times less than the Mw or Mn of the hydrocarbon polymer, or at least 200-times less than the Mw or Mn of the hydrocarbon polymer.
For example, the alkylaromatic compound in the liquid and/or wax product has a Mw at least 5-times less than the Mw of the hydrocarbon polymer (reactant) of the waste material before depolymerization, at least 10-times less than the Mw of the hydrocarbon polymer (reactant), at least 20-times less than the Mw of the hydrocarbon polymer (reactant), at least 50-times less than the Mw of the hydrocarbon polymer (reactant), at least 100-times less than the Mw of the hydrocarbon polymer (reactant), at least 150-times less than the Mw of the hydrocarbon polymer (reactant), or at least 200-times less than the Mw of the hydrocarbon polymer (reactant).
For example, the alkylaromatic compound in the liquid and/or wax product has a Mn at least 5-times less than the Mn of the hydrocarbon polymer (reactant) of the waste material before depolymerization, at least 10-times less than the Mn of the hydrocarbon polymer (reactant), at least 20-times less than the Mn of the hydrocarbon polymer (reactant), at least 50-times less than the Mn of the hydrocarbon polymer (reactant), at least 100-times less than the Mn of the hydrocarbon polymer (reactant), at least 150-times less than the Mn of the hydrocarbon polymer (reactant), or at least 200-times less than the Mn of the hydrocarbon polymer (reactant).
iii. Dispersity
Generally, the dispersity (polydispersity index, PDI) of the distribution of the molecular weight of the alkylaromatic compound in the liquid and/or wax product is smaller than the dispersity of the distribution of the molecular weight of the hydrocarbon polymer (reactant) prior to depolymerization.
Typically, the alkylaromatic compound in the liquid and/or wax product has a dispersity of less than 4.0, less than 3.5, less than 3.0, less than 2.5, less than 2.0, less than 1.5, less than 1.3, less than 1.2, between 1.1 and 1.5, between 1.1 and 1.4, between 1.1 and 1.3, or between 1.1 and 1.2.
iv. Structure of the Alkylaromatic Compounds
The alkylaromatic compound in the liquid and/or wax product can contain two alkyl groups, three alkyl groups, four alkyl groups, five alkyl groups, six alkyl groups, or more, attached to the aromatic ring or partially hydrogenated ring of a polycyclic aromatic compound.
Generally, the alkyl group of the alkylaromatic compound in the product can be linear, branched, or cyclic. The alkyl group of the alkylaromatic compound in the product can be a linear C1-C20 alkyl, a branched C4-C20 alkyl, or a cyclic C3-C20 alkyl, optionally, a linear C1-C15 alkyl, a branched C4-C15 alkyl, or a cyclic C3-C15 alkyl, optionally a linear C1-C12 alkyl, a branched C4-C12 alkyl, or a cyclic C3-C12 alkyl, optionally a linear C1-C10 alkyl, a branched C4-C10 alkyl, or a cyclic C3-C10 alkyl, optionally a linear C1-C5 alkyl, a branched C4-C5 alkyl, or a cyclic C3-C5 alkyl.
Optionally, the alkyl group of the alkylaromatic compound in the product is a linear C1-C20, C1-C15, C1-C12, C1-C10, C1-C8, C1-C5, C2-C20, C2-C15, C2-C12, C2-C10, C2-C8, C2-C5, C3-C20, C3-C15, C3-C12, C3-C10, C3-C8, C3-C5, C4-C20, C4-C15, C4-C12, C4-C10, C4-C8, C4-C5, C5-C20, C5-C15, C5-C12, C5-C10, or C5-C8 alkyl group.
Optionally, the alkylaromatic compound contains two alkyl groups attached to the aromatic ring of the alkylaromatic compound, or aromatic ring and/or partially hydrogenated ring in case of a polycyclic aromatic compound. The two alkyl groups can have any suitable relative positions. The second alkyl group may be at the ortho-, para-, or meta-position relative to the first alkyl group. The second alkyl group may be in the same ring or different rings in case of the polycyclic aromatic compound. For example, a biaryl compound contains two alkyl groups, where the first alkyl group is attached to a first aromatic ring and the second alkyl group is attached to a second aromatic ring. For example, an alkyltetralin contains two alkyl groups, where the first alkyl group is attached to a first aromatic ring and the second alkyl group is attached to a second partially hydrogenated ring.
Optionally, the alkylaromatic compound in the product is a dialkylbenzene. Optionally, the dialkylbenzene has a structure of Formula (I).
where R1 and R1′ are independently a C1-C20 alkyl group, a C1-C15 alkyl group, a C1-C12 alkyl group, a C1-C10 alkyl group, or a C1-C5 alkyl group, and where the sum of the carbon atoms in R1 and R1′ is at least 10.
Optionally, R1 and R1′ of Formula (I) are independently a linear C1-C20 alkyl group, a linear C1-C15 alkyl group, a linear C1-C12 alkyl group, a linear C1-C10 alkyl group, or a linear C1-C5 alkyl group, and where the sum of the carbon atoms in R1 and R1′ is at least 10.
Optionally, the alkylaromatic compound in the product is a polycyclic aromatic compound. The polycyclic aromatic compound can contain two aromatic rings, three aromatic rings, four aromatic rings, five aromatic rings, or six aromatic rings. For example, the alkylaromatic compound in the product is alkylnaphthalene, alkylanthracene, or alkylphenanthrene. Optionally, the alkylaromatic compound in the product is a partially hydrogenated analog of a polycyclic aromatic compound. For example, the alkylaromatic compound in the product is a partially hydrogenated analog of alkylnaphthalene, i.e. alkyltetralin.
Optionally, the polycyclic aromatic compound is a dialkylnaphthalene. Optionally, the dialkylnaphthalene has a structure of Formula (II).
where R2 and R2′ are independently a C1-C20 alkyl group, a C1-C15 alkyl group, a C1-C12 alkyl group, a C1-C10 alkyl group, or a C1-C5 alkyl group, and where the sum of the carbon atoms in R2 and R2′ is at least 4, optionally at least 5.
Optionally, R2 and R2′ of Formula (II) are a linear C1-C20 alkyl group, a linear C1-C15 alkyl group, a linear C1-C12 alkyl group, a linear C1-C10 alkyl group, or a linear C1-C5 alkyl group, and where the sum of the carbon atoms in R2 and R2′ is at least 4, optionally at least 5.
b. Other Compounds
Optionally, the liquid and/or wax product further contains other unsaturated compounds, alkanes with a carbon number in a range from 11 to 80, from 15 to 80, from 20 to 80, from 11 to 70, from 11 to 60, from 11 to 50, from 20 to 50, such as a mixture of alkanes with carbon numbers in a range from 11 to 80, thus the alkane stream contains alkanes with an average carbon number of 30, and/or C6-C10 alkanes in addition to the alkylaromatic compound(s). The total mol % of the other compounds in the liquid and/or wax product is typically less than 50 mol %, such as less than 45 mol %, less than 40 mol %, less than 35 mol %, less than 30 mol %, less than 25 mol %, less than 20 mol %, less than 15 mol %, or less than 10 mol %.
For example, the liquid and/or wax product contains an aromatic compound that is not an alkylaromatic compound. For example, the product contains a polycyclic aromatic compound (e.g. naphthalene, anthracene, phenanthrene, or a partially hydrogenated analog of naphthalene, anthracene, or phenanthrene, such as tetralin) or an alkylaromatic compound (e.g. alkylbenzene, alkylnaphthalene, alkylanthracene, alkylphenanthrene, or a partially hydrogenated analog of alkylnaphthalene, alkylanthracene, or alkylphenanthrene, such as alkyltetralin), or a combination thereof.
For example, the liquid and/or wax product contains an olefin, such as a dienen or a cycloalkene. Olefins are unsaturated hydrocarbons that contain at least one carbon-carbon double bond. The olefin in the product can be linear, branched, or cyclic. For example, the unsaturated compound in the product is diene or a cycloalkene.
The other unsaturated compounds can contain any number of carbons described above for the alkylaromatic compound. The other unsaturated compounds can have a Mw or Mn as described above for the alkylaromtic compound.
The other unsaturated compounds can be separated from the alkylaromatic compounds in the liquid and/or wax product. For example, after exiting the reactor, the liquid and/or wax product stream can be fed into a separation unit. For example, as shown in
c. Exemplary Products
An exemplary product that is in the form of liquid and/or wax contains alkylbenzene (e.g. dialkylbenzene), alkylnaphthalene (e.g. dialkylnaphthalene), alkyltetralin (e.g. dialkyltetralin), alkylanthracene, ankylphenanthrene, partially hydrogenated alkylanthracene, and partially hydrogenated ankylphenanthrene. For example, the liquid and/or wax product stream 110 contains alkylbenzene (e.g. dialkylbenzene), alkylnaphthalene (e.g. dialkylnaphthalene), alkyltetralin (e.g. dialkyltetralin), alkylanthracene, ankylphenanthrene, partially hydrogenated alkylanthracene, and partially hydrogenated ankylphenanthrene as shown in
2. Gas
The process described herein may also produce other compounds that are not in the form of a liquid or wax. For example, depolymerization of the solid waste using the process described herein may also produce a gas. Generally, the gas contains a saturated compound, optionally more than one saturated compound, such as a saturated C1-C5 alkane, hydrogen, benzene, or toluene, or a combination thereof.
Optionally, the saturated C1-C5 alkane in the produced gas can be linear, branched, or cyclic. For example, the saturated alkane is a linear C1-C5 saturated alkane, a branched C4-C5 saturated alkane, or a cyclic C3-C5 saturated alkane, optionally a linear C1-C4 saturated alkane, a branched C4-C5 saturated alkane, or a cyclic C3-C5 saturated alkane.
For example, the gas produced from depolymerization of the solid waste contains C1-C5 saturated alkanes, such as methane, ethane, and propane, hydrogen, benzene, and toluene.
3. Operation Conditions
The reactor is operated at a temperature for a period of time sufficient to convert the hydrocarbon polymer forming the waste material to the product in liquid and/or wax form that contains one or more alkylaromatic compounds.
a. Temperature, Pressure, and Period of Time
Typically, the operation temperature for the reactor is low, for example, the operation temperature does not exceed 500° C. Such low operation temperatures allow energy-efficient depolymerization of waste hydrocarbon polymers.
Optionally, the temperature sufficient to convert the waste hydrocarbon polymer to the product in the form of liquid and/or wax is up to 500° C., up to 450° C., up to 400° C., up to 380° C., up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 250° C. and 500° C., between 250° C. and 450° C., between 250° C. and 400° C., between 320° C. and 500° C., between 320° C. and 450° C., between 320° C. and 400° C., between 350° C. and 500° C., between 350° C. and 450° C., between 350° C. and 400° C., between 250° C. and 360° C., between 250° C. and 350° C., between 250° C. and 330° C., between 250° C. and 320° C., or between 250° C. and 300° C., such as about 250° C., about 280° C., about 330° C., or about 360° C.
The temperature is selected based on the hydrocarbon polymer(s) in the waste material and/or the catalyst. For example, when a Pt/γ-Al2O3 catalyst is used for depolymerization of the waste material, the temperature sufficient to convert the hydrocarbon polymer to the liquid and/or wax product is up to 380° C., up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 320° C. and 380° C., between 320° C. and 360° C., between 330° C. and 360° C., between 280° C. and 360° C., between 250° C. and 360° C., between 250° C. and 350° C., between 250° C. and 330° C., between 250° C. and 320° C., or between 250° C. and 300° C., such as about 250° C., about 280° C., about 330° C., or about 360° C. For example, when a Pt/γ-Al2O3 catalyst is used for depolymerization of polyethylene, the temperature sufficient to convert the hydrocarbon polymer to the liquid and/or wax product is up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 250° C. and 350° C., between 250° C. and 320° C., or between 250° C. and 300° C., such as about 250° C. or about 280° C.
For example, when a Pt/silica-Al2O3 catalyst is used for depolymerization of the waste material, the temperature sufficient to convert the hydrocarbon polymer to the liquid and/or wax product is up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 250° C. and 350° C., between 250° C. and 320° C., between 250° C. and 300° C., or between 250° C. and 280° C., such as about 250° C. For example, when a Pt/silica-Al2O3 catalyst is used for depolymerization of polyethylene, the temperature sufficient to convert the hydrocarbon polymer to the liquid and/or wax product is up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 250° C. and 350° C., between 250° C. and 320° C., between 250° C. and 300° C., or between 250° C. and 280° C., such as about 250° C.
For example, when a mixture of Pt/γ-Al2O3 and F-γ-Al2O3 is used as the catalyst for depolymerization of the waste material, the temperature sufficient to convert the hydrocarbon polymer to the liquid and/or wax product is up to 380° C., up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 320° C. and 380° C., between 320° C. and 360° C., between 330° C. and 360° C., between 280° C. and 360° C., between 250° C. and 360° C., between 250° C. and 350° C., between 250° C. and 330° C., between 250° C. and 320° C., or between 250° C. and 300° C., such as about 250° C., about 280° C., about 330° C., or about 360° C. For example, when a mixture of Pt/γ-Al2O3 and F-γ-Al2O3 is used as the catalyst for depolymerization of polyethylene, the temperature sufficient to convert the hydrocarbon polymer to the liquid and/or wax product is up to 380° C., up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 320° C. and 380° C., between 320° C. and 360° C., between 330° C. and 360° C., between 280° C. and 360° C., between 250° C. and 360° C., between 250° C. and 350° C., between 250° C. and 330° C., between 250° C. and 320° C., or between 250° C. and 300° C., such as about 250° C., about 280° C., about 330° C., or about 360° C.
Typically, the operation pressure for the reactor to convert the waste hydrocarbon polymer to the product in the form of liquid and/or wax is in a range from 0.01 atm to 50 atm, from 0.1 atm to 50 atm, from 0.5 atm to 40 atm, from 0.1 atm to 40 atm, from 0.1 atm to 30 atm, from 0.1 atm to 20 atm, from 0.1 atm to 10 atm, from 0.1 atm to 5 atm, or from 0.5 atm to 5 atm, such as from 1 atm to 2 atm.
Typically, the period of time sufficient to convert the hydrocarbon polymer to the product is up to 6 hours, up to 5.5 hours, up to 5 hours, up to 4.5 hours, up to 4 hours, up to 3.5 hours, up to 3 hours, up to 2.5 hours, up to 2 hours, up to 1.5 hours, up to 1 hour, up to 55 minutes, up to 50 minutes, up to 45 minutes, up to 40 minutes, up to 35 minutes, up to 30 minutes, up to 25 minutes, up to 20 minutes, up to 15 minutes, up to 10 minutes, up to 5 minutes, in a range from 5 minutes to 6 hours, from 5 minutes to 5.5 hours, from 5 minutes to 5 hours, from 5 minutes to 4.5 hours, from 5 minutes to 4 hours, from 5 minutes to 3.5 hours, from 5 minutes to 3 hours, from 5 minutes to 2.5 hours, from 5 minutes to 2 hours, from 5 minutes to 1.5 hours, from 1 minute to 1 hour, from 5 minutes to 1 hour, from 10 minutes to 1 hour, from 15 minutes to 1 hour, from 20 minutes to 1 hour, from 30 minutes to 1 hour, from 1 minute to 55 minutes, from 1 minute to 50 minutes, from 1 minute to 45 minutes, from 1 minute to 40 minutes, from 1 minute to 35 minutes, or from 1 minute to 30 minutes.
For example, the depolymerization reaction can be performed at a suitable temperature, such as up to 500° C., up to 450° C., up to 400° C., up to 380° C., up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 250° C. and 500° C., between 250° C. and 450° C., between 250° C. and 400° C., between 320° C. and 500° C., between 320° C. and 450° C., between 320° C. and 400° C., between 350° C. and 500° C., between 350° C. and 450° C., between 350° C. and 400° C., between 250° C. and 360° C., between 250° C. and 350° C., between 250° C. and 330° C., between 250° C. and 320° C., or between 250° C. and 300° C., such as about 250° C., about 280° C., about 330° C., or about 360° C., for a suitable period of time, such as from 5 minutes to 6 hours, from 10 minutes to 6 hours, from 20 minutes to 6 hours, from 30 minutes to 6 hours, from 5 minutes to 5 hours, from 10 minutes to 5 hours, from 20 minutes to 5 hours, from 30 minutes to 5 hours, from 5 minutes to 4 hours, from 10 minutes to 4 hours, from 20 minutes to 4 hours, from 30 minutes to 4 hours, from 5 minutes to 3 hours, from 10 minutes to 3 hours, from 20 minutes to 3 hours, from 30 minutes to 3 hours, from 5 minutes to 2 hours, from 10 minutes to 2 hours, from 20 minutes to 2 hours, or from 30 minutes to 2 hours that are sufficient to convert the hydrocarbon polymer to the product in a liquid and/or wax form.
For example, the depolymerization reaction can be performed at a suitable temperature, such as up to 500° C., up to 450° C., up to 400° C., up to 380° C., up to 350° C., up to 320° C., up to 300° C., up to 290° C., between 250° C. and 500° C., between 250° C. and 450° C., between 250° C. and 400° C., between 320° C. and 500° C., between 320° C. and 450° C., between 320° C. and 400° C., between 350° C. and 500° C., between 350° C. and 450° C., between 350° C. and 400° C., between 250° C. and 360° C., between 250° C. and 350° C., between 250° C. and 330° C., between 250° C. and 320° C., or between 250° C. and 300° C., such as about 250° C., about 280° C., about 330° C., or about 360° C., under a suitable pressure, such as from 0.01 atm to 50 atm, from 0.1 atm to 50 atm, from 0.5 atm to 40 atm, from 0.1 atm to 40 atm, from 0.1 atm to 30 atm, from 0.1 atm to 20 atm, from 0.1 atm to 10 atm, from 0.1 atm to 5 atm, from 0.5 atm to 5 atm, or from 1 atm to 2 atm, for a suitable period of time, such as from 5 minutes to 6 hours, from 10 minutes to 6 hours, from 20 minutes to 6 hours, from 30 minutes to 6 hours, from 5 minutes to 5 hours, from 10 minutes to 5 hours, from 20 minutes to 5 hours, from 30 minutes to 5 hours, from 5 minutes to 4 hours, from 10 minutes to 4 hours, from 20 minutes to 4 hours, from 30 minutes to 4 hours, from 5 minutes to 3 hours, from 10 minutes to 3 hours, from 20 minutes to 3 hours, from 30 minutes to 3 hours, from 5 minutes to 2 hours, from 10 minutes to 2 hours, from 20 minutes to 2 hours, or from 30 minutes to 2 hours that are sufficient to convert the hydrocarbon polymer to the product in a liquid and/or wax form.
b. Atmosphere
Optionally, the depolymerization reaction is operated in the reactor in an atmosphere filled with an inert gas. Exemplary inert gas includes, but is not limited to, argon, nitrogen, helium, neon, krypton, xenon, and radon. For example, the depolymerization reaction is operated in an atmosphere filled with argon or nitrogen.
In some embodiments, the depolymerization reaction is operated in an atmosphere that is hydrogen gas-free.
4. Characterization of the Depolymerization Process
The disclosed process for depolymerizing a solid waste containing hydrocarbon polymer(s) can be characterized by product yield and selectivity to the unsaturated compounds.
a. Yield
Typically, the liquid and/or wax product has a yield of at least 50 wt %, at least 55 wt %, at least 60 wt %, at least 65 wt %, at least 70 wt %, at least 75 wt %, at least 80 wt %, at least 85 wt %, at least 90 wt %, at least 95 wt %, between 50 wt % and 95 wt %, between 60 wt % and 95 wt %, between 70 wt % and 95 wt %, or between 75 wt % and 95 wt %.
Optionally, the alkylaromatic compound(s) in the liquid and/or wax product has a total yield of at least 40 wt %, at least 45 wt %, at least 50 wt %, at least 55 wt %, at least 60 wt %, at least 65 wt %, at least 70 wt %, at least 75 wt %, at least 80 wt %, between 40 wt % and 85 wt %, between 45 wt % and 85 wt %, between 50 wt % and 85 wt %, between 55 wt % and 85 wt %, or between 60 wt % and 85 wt %. The term “total yield” refers to the weight of the alkylaromatic compound or the total weight of the alkylaromatic compounds when the product contains more than one alkylaromatic compound, relative to the total weight of the hydrocarbon polymer(s) of the waste material.
b. Selectivity
The process disclosed herein may produce other compounds that are not alkylaromatic compounds, such as other unsaturated compounds, alkanes, and/or a gas. For example, depolymerization of polyethylene using the disclosed process produces alkylaromatic compound(s), such as one or more alkylaromatic compounds described above and/or one or more other unsaturated compounds described above in the liquid and/or wax product.
The selectivity of the disclosed process to convert the hydrocarbon polymer to the alkylaromatic compound(s) described above can be measured by NMR, such as 1H NMR or 13C NMR. Exemplary methods for determining the selectivity to the alkylaromatic compound(s) in the liquid and/or wax product, are shown in Example 1.
Typically, the disclosed process is able to convert the hydrocarbon polymer to the liquid and/or wax product with a total selectivity to the alkylaromatic compound(s) described above of at least 25 mol %, at least 30 mol %, at least 35 mol %, at least 40 mol %, at least 45 mol %, at least 50 mol %, at least 55 mol %, at least 60 mol %, at least 65 mol %, at least 70 mol %, at least 75 mol %, at least 80 mol %, at least 85 mol %, at least 90 mol %, at least 95 mol %, between 25 mol % and 95 mol %, between 30 mol % and 95 mol %, between 35 mol % and 95 mol %, between 40 mol % and 95 mol %, between 50 mol % and 95 mol %, or between 60 mol % and 90 mol %. The term “total selectivity to the alkylaromatic compound(s)” refers to the total moles of the one or more alkylaromatic compounds in the product relative to the total moles of the liquid and/or wax product. For example, the disclosed process to convert the hydrocarbon polymer to the product has a total selectivity to alkylaromatic compounds including alkylbenzene, alkyltetralin, alkylnaphthalene, alkylanthracene, alkylphenanthrene, a partially hydrogenated alkyanthracene, and a partially hydrogenated alkylphenathrene, of at least 50 mol %, at least 55 mol %, at least 60 mol %, at least 65 mol %, at least 70 mol %, at least 75 mol %, at least 80 mol %, at least 85 mol %, at least 90 mol %, at least 95 mol %, between 50 mol % and 95 mol %, or between 60 mol % and 90 mol %. For example, the disclosed process to convert the hydrocarbon polymer to the product has a total selectivity to alkylaromatic compounds including alkylbenzene and alkylnaphthalene, of at least 35 mol %, at least 40 mol %, at least 45 mol %, at least 50 mol %, between 35 mol % and 95 mol %, or between 35 mol % and 90 mol %.
For example, as shown in
Optionally, the disclosed process to convert the hydrocarbon polymer to the product has a total selectivity to the monoaromatic compound(s) of at least 10 mol %, at least 20 mol %, at least 25 mol %, at least 30 mol %, at least 35 mol %, at least 40 mol %, at least 45 mol %, at least 50 mol %, at least 55 mol %, at least 60 mol %, at least 65 mol %, at least 70 mol %, between 40 mol % and 70 mol %, between 10 mol % and 60 mol %, between 10 mol % and 40 mol %, between 20 mol % and 60 mol %, between 20 mol % and 40 mol %, between 40 mol % and 60 mol %, or between 45 mol % and 60 mol %. The term “total selectivity to the alkylbenzene(s)” refers to the total mole of the one or more alkylbenzene(s) in the product relative to the total mole of the product. For example, the disclosed process to convert the hydrocarbon polymer to the product has a total selectivity to alkylbenzene(s) and alkyltetralin(s), of at least 10 mol %, at least 20 mol %, at least 25 mol %, at least 30 mol %, at least 35 mol %, at least 40 mol %, at least 45 mol %, at least 50 mol %, at least 55 mol %, at least 60 mol %, at least 65 mol %, at least 70 mol %, between 20 mol % and 60 mol %, between 20 mol % and 40 mol %, between 40 mol % and 70 mol %, between 40 mol % and 60 mol %, or between 45 mol % and 60 mol %.
Optionally, the disclosed process to convert the hydrocarbon polymer to the product has a total selectivity to the polycyclic aromatic compound(s) of at least 20 mol %, at least 25 mol %, at least 30 mol %, at least 35 mol %, at least 40 mol %, at least 45 mol %, at least 50 mol %, at least 55 mol %, at least 60 mol %, at least 65 mol %, at least 70 mol %, between 40 mol % and 70 mol %, between 20 mol % and 60 mol %, between 20 mol % and 40 mol %, between 20 mol % and 30 mol %, between 40 mol % and 60 mol %, or between 45 mol % and 60 mol %. For example, the disclosed process to convert the hydrocarbon polymer to the product has a total selectivity to alkylnaphthalene(s) of at least 20 mol %, at least 25 mol %, at least 30 mol %, at least 35 mol %, at least 40 mol %, at least 45 mol %, at least 50 mol %, at least 55 mol %, at least 60 mol %, at least 65 mol %, at least 70 mol %, between 20 mol % and 60 mol %, between 20 mol % and 40 mol %, between 20 mol % and 30 mol %, between 40 mol % and 70 mol %, between 40 mol % and 60 mol %, or between 45 mol % and 60 mol %. The term “total selectivity to the alkylnaphthalene(s)” refers to the total mole of the one or more alkylnaphthalene(s) in the product relative to the total mole of the product.
C. Optional Steps
1. Processing the Waste Hydrocarbon Polymer
The process optionally includes a step of processing the waste material containing one or more hydrocarbon polymers to a suitable form prior to step (i) or subsequent to step (i) and prior to step (ii). Generally, the waste material containing one or more hydrocarbon polymer(s) is processed to a form that improves the contact between the polymer and the catalyst.
For example, the waste material is in the form of a solid and the solid waste is processed by shredding, cutting, and/or grinding the waste hydrocarbon polymer to small parts prior to feeding it into the reactor, such that the contact between processed solid waste and the catalyst is improved compared with the solid waste prior to processing.
Optionally, the waste material is in the form of a solid and the solid waste is dissolved in a solvent, optionally in a hydrocarbon solvent, prior to feeding it into the reactor or the waste is dissolved in the solvent in the reactor after feeding it into the reactor and prior to the depolymerization reaction, such that the contact between the dissolved solid waste and the catalyst is improved compared with the solid waste without dissolving. For example, the solvent is fed into the reactor, and the solid waste is subsequently fed into the reactor and dissolved in the solvent. Alternatively, the solid waste is fed into the reactor and the solvent is subsequently fed into the reactor and dissolves the solid waste. Optionally, the solid waste and the solvent are fed into the reactor simultaneously or substantially simultaneously, and the solid waste is dissolved in the solvent in the reactor.
Typically, the hydrocarbon solvent is a small hydrocarbon solvent, i.e. a hydrocarbon solvent containing less than 11 carbon atoms. Suitable hydrocarbon solvents for dissolving the solid waste include, but are not limited to, hexane, cyclohexane, isopentane, a mixture of n-pentane and isopentane (e.g. pentane 60/40 and pentane 80/20), toluene, TOPSol (e.g. TOPSol 60/145, TOPSol A100, TOPSol A150, TOPSol A150ND, TOPSol BF, TOPSol X2000, and TOPSol 2046), a mixture of paraffins, cycliparaffins, and aromatics (WS 200), xylene, benzene, ethylbenzene, and a mixture of xylene and ethylbenzene.
For example, as shown in
2. Cooling the Reactor to Room Temperature
The process optionally includes a step of cooling the reactor to room temperature after step (ii). The reactor may be cooled by any suitable method. For example, the reactor can be cooled in an air-flow or in a water bath of room temperature (i.e. 25° C.).
3. Recycling the Catalyst
The method may include a step of recycling the catalyst after step (ii). Typically, the catalyst can be recycled and reused for the depolymerization reaction without significant loss of activity. For example, the catalyst can be recycled and reused for the depolymerization reaction with less than 5%, less than 10%, or less than 20% decrease in product yield. Optionally, the selectivity of the process to form the one or more unsaturated compounds using a recycled catalyst is the same or substantially the same as that using a fresh catalyst. The catalyst can be recycled and reused at least 2 times, at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 9 times, or at least 10 times.
Catalyst may be recycled by oxidation with an oxidizing gas and then optionally reduced with a reducing gas.
a. Oxidation
After step (ii), the catalyst is recycled. For example, the catalyst is exposed to an oxidizing gas to oxidize the catalyst. Examples of suitable oxidizing gas for oxidizing the catalyst include, but are not limited to, oxygen and air. For example, the oxidizing gas is oxygen.
Generally, the catalyst is oxidized with an oxidizing gas at a temperature at least 200° C., at least 250° C., at least 300° C., up to 450° C., up to 400° C., from 200° C. to 450° C., from 250° C. to 450° C., or from 300° C. to 450° C., such as from 350° C. to 450° C.
Generally, the catalyst is oxidized with the oxidizing gas for a time period at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, at least 1 hour, up to 5 hours, up to 4 hours, up to 3 hours, up to 2 hours, between 10 minutes and 2 hours, between 30 minutes and 2 hours, or between 1 hour and 2 hours.
For example, the oxidation is performed at a temperature at least 200° C., at least 250° C., at least 300° C., up to 450° C., up to 400° C., from 200° C. to 450° C., from 250° C. to 450° C., or from 300° C. to 450° C., for a time period at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, at least 1 hour, up to 5 hours, up to 4 hours, up to 3 hours, up to 2 hours, between 10 minutes and 2 hours, between 30 minutes and 2 hours, or between 1 hour and 2 hours. For example, the oxidation is performed at a temperature from 250° C. to 450° C. for a time period between 10 minutes and 2 hours or between 30 minutes and 2 hours.
b. Reduction
Optionally, after oxidation the oxidized catalyst is reduced with a reducing gas. Examples of suitable reducing gas for reducing the oxidized catalyst include, but are not limited to, hydrogen, carbon monoxide, ammonia, methane, and nitric oxide. For example, the reducing gas is hydrogen.
The reduction temperature can be at least 150° C., at least 200° C., at least 250° C., up to 400° C., up to 350° C., up to 300° C., between 150° C. and 400° C., between 150° C. and 350° C., or between 150° C. and 300° C., such as between 200° C. and 300° C. Typically, the reduction temperature is lower than the oxidation temperature. For example, the catalyst is oxidized at 400° C. and then reduced at 250° C.
The period of time for the reduction step can be the same, substantially the same, or different than the period of time for the oxidation step.
For example, the reduction step is performed at a temperature at least 150° C., at least 200° C., at least 250° C., up to 400° C., up to 350° C., up to 300° C., between 150° C. and 400° C., between 150° C. and 350° C., or between 150° C. and 300° C. for a period of time at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, at least 1 hour, up to 5 hours, up to 4 hours, up to 3 hours, up to 2 hours, between 10 minutes and 2 hours, between 30 minutes and 2 hours, or between 1 hour and 2 hours. For example, the oxidation is performed at a temperature from 250° C. to 450° C. for a time period between 10 minutes and 2 hours or between 30 minutes and 2 hours, and the reduction is performed at a temperature between 200° C. and 300° C. for a time period between 30 minutes and 3 hours or between 1 hour and 3 hours.
Optionally, the period of time for the reduction step is different than the period of time for the oxidation step. The period of time for the reduction step may be longer or shorter than the period of time for the oxidation step. For example, the period of time for the oxidation step is 2 hours, and the period of time for the reduction step is 3 hours.
4. Separating the Liquid and/or Wax Product
The upcycling process optionally includes a step of separating the liquid and/or wax product subsequent to step (ii). For example, as shown in
Suitable separators that can be used for the step of separating the liquid and/or wax product are known. For example, the liquid and/or wax product can be separated by distillation as described in U.S. Pat. No. 2,848,387 to Glazier, et al. and U.S. Pat. No. 3,308,060 to Ellis.
5. Feeding Catalyst into the Reactor
The process optionally includes a step of feeding the catalyst into the reactor prior to step (i), or subsequent to step (i) and prior to step (ii), or simultaneously or substantially simultaneously with step (i). The catalyst in the reactor is in contact with the hydrocarbon polymer of the waste material. For example, as shown in
The disclosed methods can be further understood through the following enumerated paragraphs.
The preceding ranges are intended to be made clear by context, and no further limitation is implied. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
The present invention will be further understood by reference to the following non-limiting examples. Although the Examples described below are bench scale reactions, the conditions can be scaled up for use in industrial scale reactors to produce alkylaromatics with the yield and selectivity that are similar to or substantially similar to those produced in the bench scale reactions described below.
Materials and Methods
Materials
Trimethyl(cyclopentadienyl)platinum (CpPtMe3, 99%) and γ-alumina (Lot 29481900, 186 m2 g−1, pore volume 0.50 cm3 g−1) were both purchased from Strem. Chloroform (HPLC, OmniSolv®, CX1054-6) was obtained from EMD Millipore Corp. HPLC-grade water, dichloromethane (≥99.9%, GC Resolv™), triethylamine (HPLC-grade) and 1,2,4-trichlorobenzene (HPLC-grade) were obtained from Fisher Chemicals. H2 (4.0% in Ar, Airgas) was purified by passage through 13× molecular sieves and BTS catalyst (Sigma Aldrich) before use. H2 (10.0% in Ar, Airgas) was used for calibration of the TCD response. Propene (99.8%) was obtained from PRAXAir. 1,1,2,2-Tetrachloroethane-d2 (TCE-d2, ≥99.5 atom % D), KBr (FT-IR grade), triacontane (n-C30H62, 98%), dodecylbenzene (97%) 1,4-didodecylbenzene (95%), di-tert-butylhydroxytoluene (>99%), and chloroplatinic acid hexahydrate (≥37.5 wt % Pt) were all purchased from Sigma Aldrich and used as received. Dichloromethane-d2 (99.8 atom % D) was purchased from Cambridge Isotope Laboratories. A standard mixture of saturated alkanes (C7-C40, certified reference material, 1000 μg/mL each component in hexane) and a standard Pt solution containing (976±2) mg Pt/kg in 5% HCl and high-purity water were obtained from Sigma Aldrich. Tetraammineplatinum (II) nitrate (Pt(NH3)4(NO3)2, >50.0% Pt basis) was purchased from Sigma Aldrich. Amorphous silica-alumina (ASA, Davicat 3113, 7.6 wt % Al, 573 m2 g−1) was purchased from Grace-Davison.
Catalyst Synthesis and Characterization
Synthesis of Pt/γ-Alumina
γ-Alumina was calcined in flowing air at 500° C. for 4 h, followed by evacuation (10−4 Torr) at 450° C. for 12 h. Volatile trimethyl(cyclopentadienyl)platinum (32±1 mg) was deposited onto the dry alumina (1.000±0.020 g) by vacuum sublimation (ca. 10−4 Torr) at room temperature (Gozum, et al., J. Am. Chem. Soc. 110, 2688-2689 (1988); Garcia, et al., Mater. Trans. 44, 1717-1728 (2003)). The reactor was shaken vigorously during the procedure to promote uniform deposition, then was evacuated at room temperature for 1 h to remove physiosorbed PtCp(CH3)3. The resulting solid was reduced in flowing H2 (4.0% in Ar, 30 mL/min) as the temperature was ramped to 250° C. at a rate of 2° C./min. The reactor was held at this temperature for 2 h, then cooled to room temperature and evacuated for 15 min. The reduced catalyst was stored in an Ar-filled glovebox until use to avoid re-oxidation in air.
Synthesis of Pt/Silica-Alumina
˜1 wt % Pt/silica-alumina was prepared by incipient wet impregnation of 1.0 g silica-alumina with 0.5 ml aqueous solution containing 20 mg of Pt(NH3)4(NO3)2, followed by drying at 80° C. overnight and finally calcination at 400° C. for 3 h under static air. The catalyst was then reduced under 4% H2 in Ar at 350° C. for 2 h and then stored in the Ar-filled glovebox before use.
Synthesis of F-γ-Al2O3
1.5 g of calcined γ-Al2O3 was impregnated with 0.6 ml aqueous solution containing 87.6 mg of NH4F, followed by drying in the oven at 80° C. overnight and calcination at 550° C. for 5 hours under static air. The resulting materials were then evacuated under ca. 10−4 Torr at 400° C. for 8 hours. The fresh synthesized catalyst was stored in an Ar-filled glovebox before use or characterization. The fluorine content was determined to be 1.3 wt % based on elemental analysis, which was performed by flask combustion followed by chromatography. A lower content of fluorine on γ-Al2O3 was synthesized using the same procedure with half the amount of NH4F, giving 0.7 wt % F-γ-Al2O3 based on elemental analysis.
Characterization
TEM images of the catalyst were obtained on either a FEI Titan 80-300 kV S/TEM or ThermoFisher Talos F200X. Pt particle sizes were measured from the high angle annular dark field (HAADF) images. The fresh catalyst contains particles with an average size of (0.9±0.2) nm (
Metal analyses were performed by Inductively-Coupled Plasma (ICP)—Optical Emission Spectrometry (ICP-OES) on a Thermo iCAP 6300. A calibration curve was constructed using standard Pt solutions, prepared using a commercial Pt standard with a mixture of aqua regia in HPLC-grade water (4% v:v). Pt was extracted from solid catalyst samples at 75° C. in aqua regia under magnetic stirring for 30 min, based on a slight modification of a previously described procedure (Marinho, et al., J. Hazard. Mater. 192, 1155-1160 (2011)). The resulting suspensions were allowed to stand at room temperature for 24 h, then filtered. The solid residue was washed three times with HPLC-grade H2O. The combined filtrates were diluted with aqua regia (4% v:v in water) and analyzed by ICP-OES, using the spectral lines at 214.423 and 203.646 nm. The fresh catalyst contains 1.5 wt % Pt.
Procedures for Catalytic Reactions
Initial screening reactions and time-resolved experiments were conducted in unstirred stainless-steel mini-autoclaves made from Swagelok junctions (Macala, et al., ChemSusChem. 2, 215-217 (2009)), each with an internal volume of ca. 10 mL. In a typical procedure, the reduced catalyst (1.5 wt % Pt/γ-Al2O3, 0.200 g) and a sample of the appropriate PE material (0.118 g) were loaded into an autoclave reactor inside an Ar-filled glove-box. The reactor was sealed, removed from the glove-box and placed in a temperature-controlled muffle furnace (Thermo Scientific Lindberg/Blue M BF51848C) that was pre-heated to the desired temperature. When the furnace door was opened to insert the autoclave, the temperature decreased by 20-30° C., but returned to the desired temperature within ca. 5 min. Reaction timing started when the temperature stabilized. During the 24 h reaction time, the furnace temperature fluctuated by ±5° C. After the specified reaction time, the reactor was removed from the oven and cooled rapidly in a jet of compressed air to quench the reaction.
At the end of the reaction, the reactor was opened inside a fume hood and the gases were vented. The remaining material was transferred onto a fine glass frit (4.0-5.5 μm), washed with hot (50° C.) chloroform, and filtered to remove insolubles. Soluble hydrocarbons were recovered by evaporating the chloroform under reduced pressure (0.1 Torr) overnight. The insoluble material, including the catalyst and hydrocarbons insoluble in hot chloroform, was recovered from the frit. After removing the chloroform residue by evacuating under reduced pressure (0.1 Torr) overnight, the insoluble material was weighed. The yield of insoluble hydrocarbons was calculated as the difference between the total mass of recovered solid and the initial mass of the catalyst. Since volatiles were not recovered in these experiments, their yield was calculated as the difference between the initial mass of PE and that of the recovered soluble and insoluble hydrocarbons.
To characterize volatile reaction products, a mini-autoclave was modified with a gas outlet made from a Swagelok hose connector sealed with a hexagon socket head screw cap containing a Cu O-ring. The total internal volume of the reactor and the gas outlet, 13 mL, was measured by filling with water. The mini-autoclave and a Schlenk flask capped with a white rubber septum were connected via Tygon tubing to a glass vacuum line equipped with a pressure gauge and a port for gas sampling. The Schlenk flask and the lines were evacuated under reduced pressure (10−4 Torr), then isolated from the pumping system. The gases in the autoclave were expanded into the line by loosening the screw cap, and the pressure was measured. The volatiles yield was estimated using the total volume of the gas line and the Schlenk flask as measured by gas expansion (152 mL), and the ideal gas law. An aliquot of gas (400 μL) was removed via the sampling port for analysis of H2 by GC-TCD, using a gas-tight syringe. The Ar present in the autoclave at the start of the reaction (1 atm) was used as the internal standard. Propene, which is not a reaction product, was injected into the Schlenk tube as an internal standard for hydrocarbon analysis by GC-FID. An aliquot (0.2 mL) was then removed for analysis. The total GC yields of H2 and light hydrocarbons are consistent with the total yield of gases based on pressure measurement, with a precision of ±10%.
To analyze volatile hydrocarbons that may have been lost during solvent removal from the chloroform-soluble fraction, the reactor contents were transferred with the aid of chloroform (5 mL) into a Schlenk flask. The contents were distilled at 150° C., while condensing volatile products and chloroform in a receiving flask cooled in a dry ice/acetone bath. The clear, colorless distillate was transferred to a 10 mL volumetric flask, 2 mg mesitylene was added as an internal standard, and the flask was filled to the 10 mL mark with chloroform. The solution was analyzed on an Agilent 6890N Network Gas Chromatograph equipped with a DB-5 column and an FID detector, using response factors measured for toluene and light n-alkanes (C7-C11) relative to mesitylene. The total mass of recovered volatile products from distillation is small (ca. 1.5 mg, measured by GC-FID), with toluene being the major product.
Some reactions were conducted in a larger autoclave reactor (Parr Series 5000 Multiple Reactor System, internal volume ca. 100 mL, stainless steel). The contents were stirred at 678 rpm, using a magnetic stir bar encapsulated in Pyrex. Timing of the reaction began when the internal temperature reached the set temperature, 250° C.; reported reaction times do not include the time (ca. 30 min) needed to heat the reactor from room temperature. Since the internal thermocouple is located above the solids in the reactor, it reads the temperature of the gas phase rather than the solid/liquid phase. The temperature of the autoclave wall was also measured externally with a thermometer and stabilized at (280±5) ° C. during the reaction time.
The autoclave was cooled to room temperature prior to opening, by immersing the bottom of the vessel in 25° C. water for 15 min. Gases were collected as described above. When the autoclave lid was removed, an oily liquid was observed to have adhered on the lid and separated from the catalyst at the bottom of the vessel. It was recovered by dissolving in hot chloroform, then evaporating the solvent under reduced pressure overnight. The solid products were transferred onto a fine glass frit, then washed with hot chloroform. The solvent was removed from the filtrate by evaporation overnight at 0.1 Torr at room temperature. The insoluble material remaining on the frit, including the catalyst and insoluble hydrocarbons, was recovered and weighed. The mass of insoluble hydrocarbons was calculated by subtracting the initial mass of the catalyst. Some hydrocarbons were not recovered during workup, due to the difficulty in washing the dead volumes in the connectors and valves of the autoclave.
Product Analysis
Gas Chromatography
Hydrocarbons in the gas fraction (C1-C9) were analyzed quantitatively on a Shimadzu GC-2010 gas chromatograph equipped with a capillary column (Supelco Alumina Sulfate plot, 30 m×0.32 mm) and a flame ionization detector (FID). Propene was added as an internal standard. Relative carbon response factors were assumed to be 1.0 (Dietz, J. Gas Chromatogr. 5, 68-71 (1967); Tong and Karasek, Anal. Chem. 56, 2124-2128 (1984)). The injector and detector temperatures were 200° C. The temperature ramp program was: 90° C. (hold 3 min), ramp 10° C./min to 150° C. (hold 20 min).
Hydrocarbons in the gas fraction (C1-C9) were analyzed qualitatively on a Shimadzu GC-2010 gas chromatograph equipped with an Agilent DB-1 capillary column (dimethylpolysiloxane, 30 m×0.25 mm×0.25 μm) coupled to a QP2010 Mass Spectrometer. The injector and detector temperatures were 250° C. The temperature ramp program was: 40° C. (hold 3 min), ramp 25° C. per min to 250° C. (hold 10 min).
H2 was quantified on a Shimadzu GC-8AIT gas chromatograph equipped with a packed column (ShinCarbon ST 80/100, 2 m×2 mm) and a thermal conductivity detector (TCD), using Ar as the internal standard. The linear response of the TCD signal to the injected volume of H2 and Ar was confirmed using standard H2/Ar gas mixtures. The response factors for H2 (fH2) and Ar (fAr) were obtained as the slopes of fitted lines. The column, injector and detector temperatures were 130° C. The TCD current: 70 mA and the head pressure were 300 kPa (N2).
Hydrocarbons in the liquid fraction (C6-C30) were quantitatively analyzed on an Agilent 6890N Network gas chromatograph equipped with an Agilent DB-5 capillary column (fused silica, 30 m×0.25 mm×0.25 μm) and FID. The inlet and detector temperatures were 300 and 280° C., respectively. The temperature ramp program was: 40° C. (hold 3 min), ramp 25° C./min to 320° C. (hold 10 min). The flow rate was 1.0 mL/min (He) with a split ratio of 5:1.
Gel Permeation Chromatography
Molecular weight distributions of hydrocarbon products were analyzed on an Agilent PL-GPC 220 gel permeation chromatograph, equipped with a PL-Gel Mixed B guard column, three PL-Gel Mixed B columns, and a refractive index (RI) detector. Samples were dissolved in 1,2,4-trichlorobenzene (TCB) containing di-tert-butylhydroxytoluene (BHT, 0.01 wt %), by heating at 150° C. for at least 1 h. Elution was achieved using TCB (with BHT) at 150° C. and 1.0 mL min−1. The molecular weight response was calibrated with monomodal, linear polyethylene standards (Varian). To ensure accurate measurement of low molecular weight materials (Mw<1000 g mol−1), PE standards with peak molecular weights Mp of 507 and 1180 g mol−1 (Polymer Standards Services) were included in the calibration.
To examine the distribution of chromophores, selected product mixtures were also analyzed by GPC with UV detection. Analysis was conducted on a Waters 2695 HPLC equipped with three Acquity APC XT Columns (45+200+450 pore sizes, 4.6×75 mm) and a guard column (XT, 450 pore size, 4.6×30 mm), a Waters 2410 refractive index (RI) detector and a Waters 2998 photodiode array detector (PDA). Chloroform with 0.25 vol % triethylamine was used as the mobile phase at room temperature and 0.35 mL/min. Calibration was achieved using polystyrene standards (Agilent EasiVial kit, linear response for the range 200<molecular weight<400,000 g/mol).
NMR Spectroscopy
Spectra were recorded in 1,1,2,2-tetrachloroethane-d2. 1H NMR spectra were acquired at 600 MHz on a Varian Unity Inova AS600 spectrometer, and were analyzed using MestReNova (v11.0.1, Mestrelab Research S. L.). 13C NMR spectra were acquired on a Bruker AVANCE III Ultrashield Plus 800 MHz (18.8 T) spectrometer, and were analyzed using Topspin (v4.0.6, Bruker Biospin). A Bruker TXI HCN cryoprobe was used to enhance sensitivity for direct 13C detection. 13C spectra were recorded using a long relaxation delay (10 s) to ensure quantitative intensities. Chemical shifts (δ, ppm) were calibrated using the residual proton signals of the solvent and referenced to tetramethylsilane (TMS).
IR Spectroscopy
Spectra were recorded on a Shimadzu Prestige-21 spectrometer. Samples (2 mg) were ground with a mortar and pestle, mixed with KBr (100 mg), and pressed into 15 mm diameter pellets using a force of 4 tons. IR spectra were measured with a resolution of 1.0 cm−1 over the range 400-4000 cm−1. A background spectrum of a KBr pellet was subtracted from each sample spectrum.
Field Desorption Mass Spectroscopy (FD-MS)
Spectra were obtained on a Waters Micromass GCT Premier Time of Flight mass spectrometer, operating with an extraction rod voltage of 12 kV. Samples were dissolved in dichloromethane and loaded directly onto a CARBOTEC FD emitter, consisting of a 10 μm tungsten wire carrying a pyrocarbon coating of microneedles (ca. 120 μm diameter). Nominal mass data were acquired while employing a data-dependent ramp of the emitter current from 0-90 mA, pausing the ramp when more than 30 counts per scan were observed in the base peak ion. The extraction rods were cleaned between acquisitions by slowly raising the extraction rod current to 3 A while maintaining a 12 kV charge. The emitter was cleaned between acquisitions by raising the emitter current to 95 mA for 5 s. The calibration range is 400<m/z<1200, with a maximum mass error of 0.2 m/z. A mixture of triacontane (C30H62), and 1,4-didodecylbenzene (C30H54) in a molar ratio of 1:1.02 was analyzed to assess sensitivity and accuracy for detecting and quantifying different types of hydrocarbons. Each compound gave its molecular ion as the major peak. The similar peak heights confirm that this data is suitable for the semi-quantitative analysis of their relative abundance.
Determination of Selectivity to Alkylaromatics
NMR Method
Although the 1H and 13C NMR spectra are complex due to the presence of multiple isomers, they can be integrated for various functional group regions. The sample calculations below correspond to analysis for the CHCl3-soluble liquid hydrocarbon fractions recovered from the autoclave after depolymerization of 0.118 g PE (Mw=3.52×103 g mol−1, Ð=1.9) with 0.200 g Pt/γ-Al2O3 (1.5 wt % Pt) at 280° C. for 24 h. Results for other product fractions and reaction conditions are summarized in Tables 2A, 2B, and 2C. In Table 2A, standard deviations for selectivities are represented inside the parentheses.
To estimate selectivities for each type of aromatic products, it is assumed that the major aromatic products are dialkylbenzenes and dialkylnaphthalenes. Integration of the aromatic line region gives a ratio of monoaromatic protons to polyaromatic protons, Hmono/Hpoly, of 1.6. Thus, the molar ratio of dialkylbenzenes (each with 4H) to dialkylnaphthalenes (each with 6H) is 2.4. Consequently, if dialkylnaphthalenes represent x mol % of all products, then dialkylbenzenes represent 2.4x mol %, and the selectivity to alkylaromatics (SAr) is the combination of the two fractions, 3.4x mol %. The remainder, (1-3.4x) mol %, corresponds to saturated alkanes (since olefins were not detected in significant amounts by 1H NMR).
According to GPC analysis, the liquid hydrocarbon products have an Mn value of 466 g mol−1 (corresponding to an averaged carbon number C34, in good agreement with the FD-MS result), with a narrow dispersity (Ð=1.12). The aromatic protons (HAr) in the products are distributed as dialkylnaphthalenes (6x mol %) and dialkylbenzenes (4×2.4x mol %). Furthermore, the total protons (Htotal) are distributed as dialkylnaphthalenes (C34H56, 56x mol %), dialkylbenzenes (C34H62, 62×2.4x mol %), and saturated alkanes (C34H70, 70×(100-3.4x) mol %). The ratio HAr/Htotal (0.037 observed in 13C NMR spectra) is given by eq S1:
The resulting dialkylnaphthalene mole fraction is x=15.4, while the dialkylbenzene mole fraction is 2.4x=36.9. The total selectivity to aromatics in the CHCl3-soluble hydrocarbons is therefore 52.3 mol %.
A similar assessment was undertaken by integrating the aromatic region (120-150 ppm) and the aliphatic region (10-40 ppm) of the corresponding 13C NMR spectrum. The fraction of aromatic carbons is (0.10±0.01). Since carbon atoms associated with naphthalene and benzene rings are difficult to distinguish by 13C NMR, the ratio from the 1H NMR analysis (1:3.5) is used. In addition, the average total carbon number in the hydrocarbon products is C34 according to GPC. Since dialkylnaphthalenes contribute 10x mol % CAr, while dialkylbenzenes contribute 6×(2.4x) mol % CAr, the ratio CAr/Ctotal is given by eq S2:
The resulting dialkylnaphthalene mole fraction, x, is 0.139, similar to the value obtained by analysis of the 1H NMR spectrum (0.155). The dialkylbenzene mole fraction is 0.334, for a total aromatic selectivity of 47 mol %. This value is slightly smaller than the value estimated by 1H NMR (52 mol %), presumably due to experimental uncertainty.
These estimated aromatic selectivities depend on the average carbon number. Due to differences in the hydrodynamic radii of dialkylaromatics compared to linear PE, the experimental values for Mn are lower than the actual Mn values. For example, a dodecylbenzene standard (246 g mol−1) gave a measured Mn of 166 g mol−1, and a di-dodecylbenzene standard (414 g mol−1) gave a measured Mn of 345 g mol−1. Therefore, the GPC method underestimates the mass by ca. 17%. Using an average carbon number 16% higher (C40) instead of C34 to assess the alkylaromatic selectivity would result in a slightly higher total aromatic selectivity, 61 mol % by 1H NMR and 56 mol % by 13C NMR. Thus, considering the uncertainty in the average carbon number derived from Mn, the overall alkylaromatic selectivity in the liquid fraction is estimated to be (57±5) mol % by 1H NMR, and (52±4) mol % by 13C NMR.
The 1H NMR analysis described above was applied to the liquid hydrocarbons recovered after 24 h reaction of n-C30H62 in a mini-autoclave reactor at (280±5) ° C., yielding the values for Hmono/Hpoly and HAr/Htotal shown in Table 5. However, due to the lower molecular weights involved, the average carbon number in the liquid products was obtained by GC-FID (instead of GPC). Based on the peak areas and response factors for each species, the product distribution for the liquid products was obtained. The average carbon number (20, on a molar basis) was calculated using on the following formula:
The alkylbenzene selectivity was determined by combining this number with the 1H NMR results.
FD-MS Method
Peaks were separated into several series based on mass and carbon number (n) as shown in Table 1.
The yield of paraffins includes alkanes, cycloalkanes, and dicycloparaffins. The yield of monoaromatics includes alkylbenzenes, benzocycloparaffins, and benzodicycloparaffins. In the benzocycloparaffins, it is most likely to be alkyltetralins. The yield of polyaromatics includes alkylnaphthalenes, alkylanthracenes, and alkylphenanthrenes. To estimate selectivities, the heights of the peaks corresponding to each series were summed and divided by the total height for all peaks. The results are shown in
H2 Balance
In Exp. 2 (
In Exp. S4e (Table 5), converting n-C30H62 (0.23 mmol) gives hydrocarbons ranging from C1 to C29 (0.47 mmol), requiring 0.24 mmol H2. Including the remaining H2 in the reactor (0.064 mmol) gives a total of 0.30 mmol H2. According to 1H NMR, the mole fractions of alkylbenzene and alkylnaphthalene are 0.11 and 0.035, respectively. The alkylbenzene yield is 0.045 mmol, while the alkylnaphthalene yield is 0.011 mmol. The total H2 generated is 0.26 mmol. This value is similar to the value obtained by mass balance (0.30 mmol).
Results
Scheme 1. One-pot synthesis of linear dialkylbenzenes from polyethylene (PE).
Catalytic Reaction Using Pt/γ-Al2O3
A one-pot, low temperature catalytic method to convert various grades of PE directly to liquid alkylaromatics over a simple heterogeneous catalyst is described. A low molecular weight PE (0.118 g, Mw=3.5×103 g mol−1, Ð=1.90) was combined with Pt/γ-Al2O3 (0.200 g, containing 1.5 wt % Pt dispersed as ca. 1 nm nanoparticles,
To obtain a more complete mass balance and to characterize the volatile reaction products, the exploratory experiment was repeated in a mini-autoclave equipped with a gas port. The recovered gases represent a small fraction of the original polymer mass (9 wt %), and include H2 (0.2 mg) and light hydrocarbons (C1-C8, 9.0 mg). The latter are primarily methane, ethane and propane, with minor amounts of n-hexane, cyclohexane, methylcyclopentane, benzene, and n-heptane. Additional volatile hydrocarbons (C7-C11, 1.5 mg) were recovered by distillation from the autoclave at 150° C. Their major component is toluene (47 wt %). Together, the light hydrocarbons, the CHCl3-soluble liquids/waxes (89 mg) and the insoluble organic residue (14 mg) represent an overall mass balance of 96% (
When the reaction was conducted in a larger, stirred autoclave (internal volume 90 mL), most of the PE (70 wt %) was converted at 280° C. to high-boiling liquids/waxes (
The process resulted in a high yield of liquid alkylaromatics. Such compounds find widespread application as surfactants, lubricants, refrigeration fluids, and insulating oils (Luo, et al., in Synthetics, mineral oils, and bio-based lubricants: chemistry and technology., L. R. Rudnick, Ed. (CRC press, 2020), pp. 161-180), and their manufacture from waste polyethylene could displace fossil fuel-based routes.
The 1H NMR spectrum reveals more information about the alkyl substituents. Protons associated with an aliphatic carbon directly bonded to an aromatic ring (Cα) resonate in the region 2-4 ppm. The overall ratio Hα/Haromatic=1.1 indicates that the major species are, on average, dialkylaromatics (
Using the aromatic carbon fraction (0.10, according to 13C NMR) instead results in a similar estimate for the alkylaromatic selectivity, (52±4) mol %. Many of the alkyl substituents are unbranched at the Ca position, judging by the intense 1H signals at 2.35-2.85 ppm. The paraffinic —CH2—/—CH3 ratio, 7.5, demonstrates that each alkyl substituent possesses, on average, <1 branch point.
aReaction conditions: 118 mg reactant, 200 mg catalyst (Pt/γ-Al2O3, 1.5 wt %), 280° C.
b Calculated as Mn/14. Where two entries are present for the same experiment, the liquid/wax hydrocarbon products were collected and analyzed separately.
c Selectivity to alkylaromatics (SAr) calculated based on analysis of 1H NMR spectrum.
d Selectivity to alkylaromatics (SAr), as defined above, calculated based on analysis of 13C NMR spectrum. Uncertainties are propagated from the uncertainty in the average carbon number.
eSame reaction conditions as a expect for the catalyst, i.e. reaction with γ-Al2O3 support only.
%
aReaction conditions: 200 mg of PE (Mn = 1.85 × 103 g mol−1, Ð = 1.90), 100 mg reduced catalyst (Pt/γ-Al2O3, 1.5 wt % Pt), mPE/mPt = 133.3, in 13 ml unstirred mini-autoclaves under Ar.
bCalculated as Mn /14.
cSelectivity for alkylaromatics (SAr), as defined above, calculated based on analysis of 1H NMR spectrum.
dReaction was conducted using 118 mg of PE (Mn = 1.85 × 103 g mol−1, Ð = 1.90), 200 mg reduced catalyst (Pt/γ-Al2O3, 1.5 wt % Pt), mPE/mPt = 39.3.
aReaction conditions: 120 mg PE (Mn = 1.85 × 103 g mol−1, Ð = 1.90), 200 mg Pt/γ-Al2O3 (1.5 wt %) and 100 mg F—Al2O3 (1.3 wt %), 280° C.
bCalculated as Mn/14, where two entries are present for the same experiment, the liquid/wax hydrocarbon products were collected and analyzed separately.
cSelectivity to alkylaromatics (SAr) calculated based on analysis of 1H NMR spectrum.
dReaction conditions: 120 mg PE (Mn = 1.85 × 103 g mol−1, Ð = 1.90), 200 mg γ-Al2O3 and 100 mg F—Al2O3 (1.3 wt %), 280° C.
eReaction conditions: 120 mg PE (Mn = 1.85 × 103 g mol−1, Ð = 1.90), 200 mg Pt/γ-Al2O3 and 50 mg F—Al2O3 (1.3 wt %), 280° C.
fReaction conditions: 120 mg PE (Mn = 1.85 × 103 g mol−1, Ð = 1.90), 200 mg Pt/γ-Al2O3 and 100 mg F—Al2O3 (0.7 wt %), 280° C.
Individual molecular components in the liquid fraction were identified using field desorption-mass spectrometry (FD-MS). Each mass series shows a log-normal distribution with a maximum intensity at ca. C30 (
According to FD-MS, the selectivity for mono-aromatic products (including both alkylbenzenes and alkyltetralins) is ca. 40 mol %, consistent with the 1H NMR analysis described above.
The alkylnaphthene products, which have intrinsic value as solvents and hydrogen donors (Zhu, et al., Energ. Environ. Sci. 8, 478-512 (2015)), could be further dehydrogenated to alkylaromatics by active control of P(H2) in the reactor. The total yield of cyclic products (both alkylaromatics and alkylnaphthenes) in the liquid products is 88 mol % (Table 3).
aExp. 3.
b Based on peak heights.
c Based on peak areas.
dThe ratio 1Hmono/1Hpoly = 1.6 was used to calculate the fractional contribution of alkylnaphthalenes in the (14n + 2) mass species.
When the reaction time was extended from 24 to 36 h at 280° C., similar products were formed (Table 2A, Exp. S1), although the molecular weight distributions of both liquid and wax fractions shifted to slightly lower values (
Alkylaromatic yields are also strongly temperature-dependent. A low molecular weight PE (0.118 g, Mw=3.5×103 g mol−1, Ð=1.90) was combined with Pt/γ-Al2O3 (0.200 g, containing 1.5 wt % Pt dispersed as ca. 1 nm nanoparticles,
When the polymer to catalyst ratio increases from mPE/mPt=39.3 (0.118 g of PE, 0.200 g of 1.5 wt % Pt/alumina) to mPE/mPt=133.3 (0.200 g of PE, 0.100 g of 1.5 wt % Pt/alumina), the reaction at 280° C. for 24 hours (Table 2B, Exp. S8) converted 31 wt % of PE to wax with a limited decrease in molecular weight (Mn=706 g mol−1, Ð=3.32, Cavg=50) and a small aromatic content (Haromatic/Htotal=0.015). However, the reaction at 360° C. for 8 hours (Table 2B, Exp. S9) converted 80 wt % of PE to liquid with a much lower molecular weight (Mn=262 g mol−1, Ð=1.89, Cavg=19) and a higher aromatic content (Haromatic/Htotal=0.042). These results indicate that a reasonably higher temperature can significantly increase the rate of the tandem hydrogenolysis/aromatization of PE to the desired products. The temperature for alkylbenzene formation from low molecular weight PE (0.118 g, Mw=3.5×103 g mol−1, Ð=1.90 in a reactor containing Pt/γ-Al2O3 as the catalyst support is 250° C.≥T≤360° C.
The time course of PE depolymerization was studied at 280° C. (Table 4, Exp. 1a-f). A short induction period, lasting about 1 h, corresponds in large part to the thermal equilibration of the reactor (ca. 45 min). After this time, the liquid hydrocarbon fraction increased (
Catalytic Reaction Using Pt/Silica-Alumina
As noted above, when a low molecular weight PE (0.118 g, Mw=3.5×103 g mol−1, Ð=1.90) was combined with Pt/γ-Al2O3 (0.200 g, containing 1.5 wt % Pt dispersed as ca. 1 nm nanoparticles,
When Pt/silica-alumina (0.200 g, containing ˜1 wt % Pt, with metal dispersion of 43%) was applied as catalyst, the reaction at 250° C. after 24 hours converted 76 wt % of PE (0.118 g, Mw=3.5×103 g mol−1, Ð=1.90) into wax (Mn=415 g mol−1, Ð=6.18, Cavg=30), with aromatics content of Haromatic/Htotal=0.033 and an alkylaromatic selectivity of 35 mol % (10 mol % is monoaromatics, i.e 10 mo % alkylbenzene and 25 mol % of alkylnaphthalene). The depolymerization using Pt/silica-alumina catalyst produced alkylnaphthalene, which is a valuable alkylaromatic that can be used as intermediates for producing advanced polymers (e.g. short-chain alkylnaphthalene) and in the synthesis of alkylated naphthalene sulfonic acids and as lubricating base oils (e.g. short-chain alkylnaphthalenes) (Li, et al., Chemistry Select, 4:5284-5290 (2019)).
Catalytic Reaction Using a Mixture of Pt/γ-Al2O3 and F-γ-Al2O3
A low molecular weight PE (0.120 g, Mw=3.5×103 g mol−1, Ð=1.90) was combined with Pt/γ-Al2O3 (0.200 g, containing 1.5 wt % Pt dispersed as ca. 1 nm nanoparticles,
To avoid heat and mass transfer limitation, the reaction was conducted in a larger, stirred autoclave (internal volume 90 mL). As a result, the product distribution shifted toward lower molecular weight products, where 40 wt % of PE was converted to gaseous products, along with a lower yield of liquid hydrocarbons (32 wt %), with a much higher aromatic content (Haromatic/Htotal=0.123) and alkylaromatic selectivity (63 mol %, of which 21 mol % is monoaromatics) compared to the products obtained from the reaction after 12 hours in an unstirred mini-autoclave (Table 2C, Exp. 2 and 5).
As depolymerization of PE was accelerated with the addition of F-γ-Al2O3, less time was required to achieve high yield of desired products. While the reaction catalyzed by 0.200 g Pt/γ-Al2O3 showed no apparent reactivity in 1 hour (Mn=1758 g mol−1, Cavg=126), the reaction using a physical mixture of 0.200 g Pt/γ-Al2O3 and 0.100 g F-γ-Al2O3(Table 2C, Exp. 6) converted PE to gaseous (27 wt %) and liquid hydrocarbons (38 wt %) with an estimated alkylaromatic selectivity of 22 mol % in liquid hydrocarbons and 32 mol % in wax hydrocarbons. The gaseous products were composed of mostly propane, butane and pentane, which have higher values than methane and ethane that were produced as the major products in PE reaction using Pt/γ-Al2O3(
To minimize the formation of gases and increase the yield of liquid hydrocarbons, the reaction was conducted with a lower number of acid sites (0.050 g 1.4 wt % F-γ-Al2O3) (Table 2C, Exp. 7) compared to the reaction using 0.100 g of 1.3 wt % F—Al2O3(Table 2C, Exp. 6). By lowering the number of acid sites, the yield of liquid hydrocarbons increased by 17 wt %; however, with a higher alkylaromatic selectivity (38 mol %) in wax hydrocarbons; however, alkylaromatic selectivity decreased by 4 mol % in liquid hydrocarbons. Another experiment using 0.100 g of 0.7 wt % F-γ-Al2O3 increased the alkylaromatic selectivity in both liquid (28 mol %) and wax (59 mol %) hydrocarbon products (Table 2C, Exp. 8).
a Reaction conditions: 118 mg PE (Mn = 1.85 × 103 g mol−1, Ð = 1.90), 200 mg catalyst (Pt/γ-Al2O3, 1.5 wt % Pt), 280° C., 10 mL mini-autoclave. Each experiment was performed independently (not as continuous sampling from one experiment).
b Calculated as Mn/14.
c GPC analysis was performed on the crude reaction mixture.
d This experiment is the same as Exp. 1 in FIG. 3 and Table 2A.
Materials and Methods
Depolymerization of polyethylene is performed as described above.
Catalytic conversion of n-C30H62 is performed as follows.
A mixture of 0.120 g n-C30H62 and 0.200 g Pt/γ-Al2O3 was heated at (280±5) ° C. under Ar for 24 h in mini-autoclaves. After the reaction, the gas products were analyzed by GC-TCD and GC-FID as described above. The remaining material was extracted with CHCl3 at room temperature, separated from the insoluble catalyst as a yellow liquid, then, mesitylene (2.0 mg) was added as an internal standard. The solution was analyzed on an Agilent 6890N gas chromatograph equipped with a DB-5 column and an FID detector.
Peak assignments were made by comparing retention times to a standard mixture of n-alkanes (C7-C40), standard mesitylene, as well as by matching to peaks identified by GC-MS with the aid of a mass spectral library (NIST 107). Among the liquid products, the major species are n-alkanes (C7-C30). The minor products are mostly branched alkanes, with smaller contributions from cycloalkanes and alkylbenzenes. The presence of multiple isomers with overlapping peaks hindered more complete analysis. Nevertheless, hydrocarbons that elute together have the same carbon number and very similar response factors (within 3%) (Dietz, J. Gas Chromatogr. 5, 68-71 (1967); Tong and Karasek, Anal. Chem. 56, 2124-2128 (1984)). Therefore, based on the mass of mesitylene, the peak areas and response factors for each species, the absolute amount of each species could be obtained. Since there is a negligible amount of insoluble hydrocarbon in the solid phase (less than 0.1% by mass), the species detected in both gas and liquid phases (89% yield) were combined to obtain a total distribution (
For 1H NMR analysis, undeuterated CHCl3 was removed by evaporation overnight at 0.1 Torr, resulting in a ca. 70 wt % yield of liquid products consisting only of molecules larger than C9. Mesitylene was also mostly removed (<0.1 mol % remaining) as evidenced by GC-FID analysis.
Thermodynamic Analysis of Tandem Hydrogenolysis/Aromatization
The thermodynamic feasibility of the tandem reaction was assessed using data computed using Benson group increment theory for gas phase alkanes and alkylbenzenes (Stein and Brown, NIST Chemistry WebBook, NIST Standard Reference Database Number 69, P. J. Linstrom, W. G. Mallard, Eds. National Institute of Standards and Technology, Gaithersburg Md., 20899, doi.org/10.18434/T4D303). Increment values are compiled in Table 6. The thermodynamic contributions to a linear alkane CnH2n+2 are:
g
A,n=(n−2)g1+2g2 (S4)
The thermodynamic contributions for the alkane hydrogenolysis reaction (eq S5), i.e. gHy, are given in eq S6:
Note that the linearity of the Benson group contributions eliminates the chain length dependence according to eq S8, since changes in the number of methylene carbons (−2g1) and the number of methyl chain ends (+2g2) are independent of the initial chain length.
The thermodynamic contributions to an ortho-dialkylbenzene CnH2n−6, i.e. gB,n, are given in eq S7:
g
B,n=(n−10)g1+2g2+2g3+4g4+2g5+g6 (S7)
The thermodynamic contributions to the aromatization reaction (eq S8), i.e. gAr, are given in eq S9:
Note that the linearity of the Benson group contributions also removes the chain length dependence from eq S9, since the change in the number of methylene carbons (−8g1) is independent of the initial chain length.
Derivation of Rate Model for Tandem Hydrogenolysis/Aromatization
In the simplified kinetic model, it is assumed that the hydrocarbon products contain only two types of carbon: aliphatic, and aromatic. Furthermore, the kinetic model is comprised of only two reactions, hydrogenolysis (eq S5) and aromatization (eq S8). Once an aromatic ring is formed, it is assumed it does not undergo further reaction. However, the aliphatic substituents on an aromatic ring can continue to undergo hydrogenolysis and aromatization.
Since there is no solvent in the reactor, each surface Pt atom is in contact with either an aliphatic carbon (i.e., methyl or methylene) A, or an aromatic carbon B. It is assumed that the two types of carbon compete for adsorption sites according to eq S10, where Aads and Bads are adsorbed aliphatic and aromatic carbons, respectively.
A
ads
+B
A=B
cds (S10)
Adsorption is governed by the equilibrium expression, eq S11, where θA and θB are the surface coverages of A and B, respectively:
The site balance and mass balance require:
θA+θB=1 (S12)
n
A
+n
B
=n
C (S13)
where nA and nB are the number of aliphatic and aromatic carbons at any time, and nC is the total number of carbons in the system. If the amounts of adsorbed A and B are small relative to the total amounts of A and B (true except in the earliest stages of reaction, when nB is very small), then the equilibrium expression for θA is solved as follows:
Since one aromatization reaction (eq S8) forms 6 aromatic carbons and removes 6 aliphatic carbons, the rate of aromatization is:
The rate of aromatization, relative to the rate of hydrogenolysis, is constrained by two factors: the observed mass balance on hydrogen and the observed aromatic product fraction. The model cannot simultaneously satisfy both constraints, as the mass balance on hydrogen is distorted by contributions of significant non-aromatic, nonlinear molecules, and the aromatic fraction is distorted by the presence of large amounts of light hydrocarbon gases. These gases represent a large portion of the scission products on a molar basis, even if they account for a relatively small portion of the mass in the system. To avoid introducing additional complexity to the model, the light hydrocarbons and hydrogen balance is ignored, focusing solely on the liquid products.
The experimental 1H NMR, 13C NMR and GPC results indicate an overall selectivity for aromatic molecules in the liquid product of ca. 50%. The number of molecules consisting only of aliphatic carbons is denoted as NA, and the number of molecules with at least one aromatic carbon is denoted as NB. Each hydrogenolysis (eq S5) reaction results in a net increase of one solely aliphatic molecule, and each aromatization (eq S8) reaction converts one aliphatic molecule to one aromatic molecule. Assuming the number of initial molecules is small and the reaction rates are approximately constant over a short period of time, the number of molecules of each time evolve with time t as
N
A
=r
Hy
t−r
Ar
t (S17)
N
B
=r
Ar
t (S18)
The molar selectivity among the products s can be written as
This shows that the rate of aromatization (eq S8) is half that of the rate of hydrogenolysis (eq S5). Therefore, the rate of hydrogenolysis can be written in terms of the rates of formation of either aromatic or aliphatic carbons:
The rate law for hydrogenolysis is assumed to follow first-order in both the mass of catalytic Pt, mPt, and the coverage of active Pt sites by aliphatic carbons, OA, with a second-order rate constant k (dimensions gPt−1 s−1):
Integration of eq S22 leads to the following expressions:
For K>>1, the integrated rate law simplifies to:
where τ is a dimensionless time. This equation can be solved for the fraction of aliphatic carbon, nA/nC, using the Lambert W function:
The shape of this function is shown in
Eq S27 can predict the evolution of the number-average chain length of all chains, Mn. The loss of mass to light hydrocarbons is assumed to be negligible. First, note that the number of aromatic carbons is given by nB=nC−nA, and that six aromatic carbons correspond to one aromatization event. The number of hydrogenolysis events is nB/(6s), or nB/3 for s=1/2. Each hydrogenolysis event results in a new chain, therefore the total number of chains present at time t, Nt, is:
where N0 is the initial number of polymer chains in the system. The number-average chain length, Mn, evolves in time as:
Rearranging eq S29 for nA/nC and substituting into eq S25 yields the relationship between M1 and reaction time:
Plotting the inverse number average molecular weight in terms of dimensionless time yields
The example above pertains to a system with no aromatic carbons initially present, nB(0)=0. If this is not the case, the algebra becomes more complicated, but an expression for the evolution of the average chain length may still be found. As aromatic carbons occupy catalytic sites without participating in hydrogenolysis, their presence slows down hydrogenolysis. When nB(0) is large relative to mPt, no aliphatic carbons adsorb, and no hydrogenolysis takes place.
An additional effect not included in the model is the ability of aromatics to consume hydrogen for their own hydrogenation. This may become significant at sufficiently high aromatic concentrations.
Finally, a model is considered in which aromatization (eq S8) does not occur. This is the case when the H2 partial pressure is very large, and the reaction equilibrium disfavors further H2 production via aromatization. Thus, assuming no initial aromatics (nB(0)=0) and no aromatization (rAr=0), the rate of formation of new aliphatic chains is written as:
Integration of eq S32 leads to
N
t
=N
0
+km
Pt
t (S33)
Analogous to eq S28, the number-average chain length evolves in time as:
Rearranging and noting that nC/N0=Mn(0) yields an expression similar to eq S31:
where τH is an alternative dimensionless time for the case of hydrogenolysis without aromatization.
Both models (i.e., with and without the contribution of the aromatization reaction) display similar behaviors. In both, the evolution in average chain length slows and appears to halt, due to the constant rate of new chain production. Since the number of chains increases at a constant pace, chains made later in the reaction have a smaller impact on the average chain length. When aromatization is possible, the kinetics of chain cleavage are slowed even more, because the active sites become progressively occupied by strongly adsorbed aromatics. This has a more severe effect on the leveling of the average chain length, relative to the model without aromatic formation.
Results
The thermodynamics of n-alkane aromatization was assessed. The temperature needed to achieve appreciable aromatic yields for this endothermic reaction (eq 1) decreases as the molecular weight increases (Pradhan, et al., Chem. Sci. 3, 2958-2964 (2012)).
CmH2m+2→CmH2m−6+4H2 (1)
Nevertheless, direct PE conversion to aromatics involves very mild conditions, relative to the much higher operating temperatures generally used for making BTX from molecular n-alkanes (Scheme 1). Thermodynamic values for converting linear PE chains to alkylaromatics at 280° C. in 1 atm H2, estimated using Benson group contributions for long-chain n-alkanes (Stein and Brown, NIST Chemistry WebBook, NIST Standard Reference Database Number 69, P. J. Linstrom, W. G. Mallard, Eds., National Institute of Standards and Technology, Gaithersburg Md., 20899, https://doi.org/10.18434/T4D303), are ΔH1°=246 kJ/mol and ΔG1°=31 kJ/mol. Aromatization alone is indeed disfavored. However, the reaction occurs when coupled with hydrogenation of a suitable hydrogen acceptor. In solventless PE depolymerization, the PE chains themselves serve as an internal hydrogen sink, (see
Cm+nH2(m+n)+2+H2→CmH2m+2+CnH2n+2 (2)
Consequently, aromatization becomes allowed at 280° C. (ΔG°=0) when even 10% of the H2 generated is consumed in PE hydrogenolysis.
Based on the alkylaromatic yield, the aromatization in Exp. 2 (
To explore whether polyethylene is necessary to produce long-chain alkylaromatics by tandem catalytic hydrogenolysis/aromatization, the reaction of n-C30H62 under the same conditions was investigated (Table 5, Exps. S2 and S3). Compared to PE, the n-C30H62 chains experience only half as much hydrogenolysis (consuming just 0.25 mmol H2 based on
aReaction conditions: 118 mg reactant (triacontane or PE, Mn = 1.85 × 103 g mol−1, Ð = 1.90), 200 mg reduced catalyst (Pt/γ-Al2O3, 1.5 wt % Pt), 280° C. for 24 h.
b Calculated as Mn/14.
c Selectivity for alkylaromatics (SAr), as defined above, calculated based on analysis of 1H NMR spectrum. Uncertainties are propagated from the uncertainty in the average carbon number.
dReaction in thick-walled glass reactor using fresh catalyst.
eReaction in thick-walled glass reactor using recycled catalyst.
fReaction with 1.1 g PE reactant and 1.8 g catalyst at 280° C.. Liquid/wax hydrocarbon products were collected and analyzed separately.
g Calculated based on GC-FID analysis using eq S3, as shown above.
Although there are far too many individual reactions and products to formulate a precise kinetic model, a simplified model captures the main features of the tandem reaction. It is assumed that the Pt surface is covered with molten PE and/or PE-derived hydrocarbons at all times, and that the hydrogenolysis turnover frequency is constant on sites not occupied by aromatic hydrocarbons. As the latter form, they adsorb more strongly than alkanes (Xu, et al., J. Phys. Chem. 98, 585-593 (1994)), occupying active sites and reducing the hydrogenolysis rate accordingly. Hydrogenolysis is assumed random, i.e., all aliphatic C—C bonds are equally likely to be cleaved (Carter, et al., J. Catal. 20, 223-229 (1971)). The sole adjustable parameter, k/K, is the ratio of the rate constant for hydrogenolysis (k) and the equilibrium constant for competitive adsorption of aromatics and aliphatic chains (K, eq S11). Eq 3 predicts the evolution of the average chain length as a function of the reaction time, initial total carbon amount nc, and total platinum mass mPt.
The curvefit of eq 3 to an experimental dataset is shown in
Materials and Methods
The solid material was recovered from two parallel PE depolymerization reactions conducted at 280° C. for 24 h in mini-autoclave reactors, combined and calcined in flowing O2 (50 mL/min) at 400° C. for 2 h to remove organic residues. The absence of hydrocarbons was verified by the complete disappearance of the C—H stretching modes in the IR spectrum (
Results
The Pt/γ-Al2O3 catalyst can be recovered and recycled. In the spent catalyst, the Pt NPs had increased in size slightly, from 0.8 to 1.2 nm (
Materials and Methods
A low molecular weight polyethylene (Lot SKU-427772, Mn=1.85×103 g mol−1; Mw=3.52×103 g mol−1; Ð=1.9) was purchased from Sigma Aldrich. Low density polyethylene (LDPE) was obtained from a discarded plastic packaging bag (Mn=12.8×103 g mol−1; Mw=94.5×103 g mol−1; Ð=7.4), and was cut into mm-size pieces before use. High density polyethylene (HDPE) was the cap of a disposable PET water bottle (Mn=14.8×103 g mol−1; Mw=53.5×103 g mol−1; Ð=3.6). It was cut into mm-size pieces, frozen in liquid N2, and the particle size was further reduced in a coffee-grinder before use. The reaction was conducted larger autoclave reactor (Parr Series 5000 Multiple Reactor System, internal volume ca. 100 mL, stainless steel), as described in Example 1.
Results
To investigate how a tandem catalytic process could be deployed to convert waste polyethylene without large energy input, solvent-free depolymerization of two different commercial grades of PE: an LDPE plastic bag (Mw=9.45×104 g mol−1, Ð=7.37), and an HDPE water bottle cap (Mw=5.35×104 g mol−1, Ð=3.61) was performed. These higher molecular weight polymers behaved similarly to the low molecular weight polyethylene, giving liquid/wax products with an average carbon number of ca. C30. After 24 h at 280° C., the overall liquid yields were 69 and 55 wt % for LDPE and HDPE, respectively (
Shorter residence times should also improve the selectivity for monoaromatic hydrocarbons relative to naphthalenes, etc., and suppress the already low gas yields even further. Alkylbenzene selectivity may be further improved by active control of P(H2), which is high enough to promote PE hydrogenolysis, but low enough to suppress aromatic hydrogenation. The alkylbenzenes with their linear side-chains could be sulfonated to produce biodegradable surfactants. This type of commodity polymer upcycling leading to chemical products that displace fossil carbon-based feedstocks, while simultaneously incentivizing better management of plastic waste and recovering considerable material value that can be recirculated into the global economy.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of skill in the art to which the disclosed invention belongs. Publications cited herein and the materials for which they are cited are specifically incorporated by reference.
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.
This application claims the benefit of and priority to U.S. Provisional Application No. 63/052,227 filed Jul. 15, 2020, which is hereby incorporated by reference in its entirety.
This invention was made with government support under DE-AC02-07CH11358 awarded by the United States Department of Energy. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/041812 | 7/15/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63052227 | Jul 2020 | US |
