Patent Application
20240368052
The present disclosure is directed to a method for carbon dioxide reduction, and particularly, to a method for chemically reducing carbon dioxide using red mud and modified red mud as catalyst.
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Red mud is an industrial by-product of the Bayer process for aluminum oxide manufacture. Aluminum oxide manufacture production forms a considerable amount and disposing of the resultant red mud poses a significant challenge. This is a world-wide issue that needs an immediate remedy in terms of recycling or reuse rather than land fill. Red mud generally contains various transition metals, such as iron and aluminum, which are of interest and may have potential as catalysts in various industrial catalytic processes.
The emission of greenhouse gases, such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases, has become a major concern for energy sector industries across the globe. Efforts have been made to explore methods to minimize the emission of these gases into the atmosphere and improve the capture of such compounds. CO2 is one of the most significant greenhouse gases, and it is crucial to capture and utilize it effectively, preferably at the source of its release. Conversion of CO2 to value-added chemicals not only reduces CO2 release into the atmosphere but also leads to economic benefits for investors. In the meanwhile, feasible catalytic processes can be developed to convert CO2 into hydrocarbons, syngas, and oxygenates Lower olefins are the starting material for various plastics and polymers. Aromatics like benzene, toluene, and xylenes (BTX) are starting materials for many commodities and fine chemicals. Oxygenates like dimethyl ether and methanol also hold value in chemical industries. Syngas is widely used in industry as a source of energy and process raw material. Large-scale industries are seeking practical methods to add value to CO2.
Studies have been conducted to evaluate the effective utilization of different materials for catalytic applications, such as CO2 valorization [Pawelec B, Guil-López R, Mota N, Fierro J L G, Navarro Yerga R M. Catalysts for the Conversion of CO(2) to Low Molecular Weight Olefins-A Review. Mater (Basel, Switzerland). 2021; 14(22)], ketonization [Weber J, Thompson A, Wilmoth J, Batra V S, Janulaitis N, Kastner J R. Effect of metal oxide redox state in red mud catalysts on ketonization of fast pyrolysis oil derived oxygenates. Appl Catal B Environ. 2019; 241:430-441], and adsorption [Wang S, Ang H M, Tadé MO. Novel applications of red mud as coagulant, adsorbent and catalyst for environmentally benign processes. Chemosphere. 2008; 72(11):1621-1635]. CO2 hydrogenation [Russkikh A, Shterk G, Al-Solami B H, Fadhel B A, Ramirez A, Gascon J. Turning Waste into Value: Potassium-Promoted Red Mud as an Effective Catalyst for the Hydrogenation of CO2. ChemSusChem. 2020; 13(11):2981-2987] is also reported to be an effective process of converting CO2 into hydrocarbons.
Although methods have been developed in the past for CO2 reduction, there still exists a need to develop a simple and cost-effective method for converting CO2 into valuable chemicals.
In view of the foregoing, an objective of the present disclosure is to describe a method for chemically reducing carbon dioxide (CO2) with a red mud catalyst composition. A second objective of the present disclosure is to describe a method of making a red mud catalyst composition and a modified red mud catalyst composition.
In an exemplary embodiment, a method for chemically reducing carbon dioxide (CO2) with a red mud catalyst composition is described. The method includes introducing a gaseous mixture of CO2 and H2 into a reactor containing red mud catalyst particles of the red mud catalyst composition. The method further includes reacting at least a portion of the CO2 and the H2 in the gas stream in the presence of the red mud catalyst composition at a temperature of 200 to 800° C., and under a pressure of 5 to 100 bar to form a gaseous product comprising a chemical reduction product of CO2. In some embodiments, a volume ratio of the CO2 to the H2 in the gaseous mixture is in a range of 1:10 to 10:1. In some embodiments, the gaseous product comprises 20 to 50 wt. % methane, 1 to 20 wt. % ethane, 0.5 to 10 wt. % propane, 0.01 to 1 wt. % methanol, 1 to 70 wt. % dimethyl ether (DME), and 1 to 50 wt. % carbon monoxide, each wt. % based on a total weight of the gaseous product.
In some embodiments, the reactor is at least one selected from the group consisting of a fixed-bed reactor, a trickle-bed reactor, a moving bed reactor, a rotating bed reactor, a fluidized bed reactor, and a slurry reactor.
In some embodiments, the reactor is a fixed-bed reactor in the form of a cylindrical reactor which includes a top portion, a cylindrical body portion, a bottom portion, a housing. The housing has an open top and open bottom supportably maintained with the cylindrical body portion. The cylindrical reactor further includes at least one propeller agitator disposed in the bottom portion of the reactor. In some embodiments, the red mud catalyst composition is supportably retained within the housing, permitting fluid flow therethrough. In some embodiments, the bottom portion is cone-shaped or pyramidal. In some embodiments, a plurality of recirculation tubes fluidly connects the bottom portion of the cylindrical reactor with the cylindrical body portion of the cylindrical reactor.
In some embodiments, the volume ratio of the CO2 to the H2 is in a range of 1:1 to 1:5.
In some embodiments, the gas stream further comprises carbon monoxide (CO).
In some embodiments, the method includes reacting at least a portion of the CO2 and H2 in the gaseous mixture in the presence of the red mud catalyst composition at a temperature of 300 to 400° C., to form the gaseous product.
In some embodiments, the method includes reacting at least a portion of the CO2 and H2 in the gaseous mixture in the presence of the red mud catalyst composition under a pressure ranging from 30 to 40 bar to form the gaseous product.
In some embodiments, the method chemically reduces 10 to 25% of the CO2 based on a total weight of the gaseous mixture.
In some embodiments, the red mud catalyst composition is a waste product from an aluminum extraction process.
In some embodiments, the red mud catalyst composition contains 10 to 30 wt. % Al, 2 to 20 wt. % Fe, 0.02 to 1 wt. % Mg, 1 to 20 wt. % Na, 0.02 to 1 wt. % P, 0.2 to 8 wt. % Ti, 0.02 to 1 wt. % V, 1 to 5 wt. % Ca, 2 to 15 wt. % Si, and 0.02 to 1 wt. % K, each wt. % based on a total weight of the red mud catalyst composition by energy dispersive X-ray fluorescence (ED-XRF).
In some embodiments, the red mud catalyst composition includes particles having a specific surface area in a range of 5 to 30 square meter per gram (m2/g).
In some embodiments, the red mud catalyst composition includes particles having a cumulative specific pore volume in a range of 0.01 to 0.1 cubic centimeter per gram (cm3/g).
In some embodiments, the red mud catalyst composition has a temperature-programmed desorption of ammonia (NH3-TPD) of 0.001 to 0.1 mmol/g.
In some embodiments, the red mud catalyst composition has a temperature-programmed desorption of carbon dioxide (CO2-TPD) of 0.01 to 0.5 mmol/g.
In some embodiments, the red mud catalyst composition is an alkali modified red mud catalyst composition or an alkaline modified red mud catalyst composition. In some embodiments, the alkali modified red mud catalyst composition has an alkali content of from 0.001 to 10 wt. % based on the total weight of the red mud catalyst composition. In some embodiments, the alkaline modified red mud catalyst composition has an alkaline content of from 0.001 to 10 wt. % based on the total weight of the red mud catalyst composition.
In some embodiments, the gaseous product further comprises ethylene, propylene, a hydrocarbon containing C4-C9, and aromatics, and wherein the C4-C9 hydrocarbon comprises butane, butene, butyne, pentane, pentene, pentyne, hexane, hexene, hexyne, cyclohexane, cyclohexene, heptane, heptene, heptyne, octane, octene, octyne, nonane, nonene, and nonyne.
In some embodiments, when the red mud catalyst composition comprises about 13.1 wt. % Al, about 14.7 wt. % Fe, about 0.18 wt. % Mg, about 9.7 wt. % Na, about 0.5 wt. % P, about 4.8 wt. % Ti, about 0.16 wt. % V, about 2.9 wt. % Ca, about 7.1 wt. % Si, and about 0.23 wt. % K, each wt. % based on the total weight of the red mud catalyst composition as determined by ED-XRF, the gaseous product comprises 20 to 25 wt. % methane, 4 to 9 wt. % ethane, 1 to 3 wt. % propane, 0.05 to 0.15 wt. % methanol, 45 to 55 wt. % dimethyl ether (DME), and 5 to 15 wt. % carbon monoxide, each wt. % based on the total weight of the gaseous product.
In some embodiments, when the red mud catalyst composition comprises about 18.77 wt. % Al, about 4.98 wt. % Fe, about 0.07 wt. % Mg, about 4.47 wt. % Na, about 0.19 wt. % P, about 0.49 wt. % Ti, about 0.05 wt. % V, about 2.4 wt. % Ca, about 6.4 wt. % Si, and about 0.15 wt. % K, each wt. % based on the total weight of the red mud catalyst composition as determined by ED-XRF, the gaseous product comprises 35 to 45 wt. % methane, 9 to 15 wt. % ethane, 3 to 9 wt. % propane, 0.1 to 0.25 wt. % methanol, 1 to 10 wt. % dimethyl ether (DME), and 25 to 35 wt. % carbon monoxide, each wt. % based on the total weight of the gaseous product.
In some embodiments, the method further includes preparing the red mud catalyst composition. The method of preparing the red mud catalyst composition includes drying a red mud material and pulverizing to form a pulverized red mud material. The method further includes calcining the pulverized red mud material at a temperature of at least 600° C. to form the red mud catalyst composition.
In some embodiments, the calcining is performed at a ramping rate of 1 to 10 degrees Centigrade per minute (° C./min).
In some embodiments, the method further includes preparing a modified red mud catalyst composition. The method of preparing the modified red mud catalyst composition further includes impregnating the red mud catalyst composition by soaking particles of the red mud catalyst composition in a potassium salt solution and mixing to form the modified red mud catalyst composition as a crude mixture. Additionally, the method of preparing the modified red mud catalyst composition includes separating the modified red mud catalyst composition from the crude mixture, and drying to obtain the modified red mud catalyst composition.
In some embodiments, the potassium salt solution includes at least one salt selected from the group consisting of potassium fluoride (KF), potassium chloride (KCl), potassium bromide (KBr), potassium nitrate (KNO3), potassium sulfate (K2SO4), potassium carbonate (K2CO3), potassium phosphate (K3PO4), and potassium hydroxide (KOH).
In some embodiments, the salt is present in the salt solution at a concentration of 0.5 to 10 wt. % based on a total weight of the salt solution.
The foregoing general description of the illustrative present disclosure and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.
A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a,” “an” and the like generally carry a meaning of “one or more,” unless stated otherwise.
Furthermore, the terms “approximately,” “approximate,” “about,” and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values there between.
Aspects of the present disclosure are directed to a method for chemically reducing carbon dioxide (CO2) with a red mud catalyst composition. The red mud catalyst composition, also referred to as composition, is used as a catalyst or a catalyst carrier for CO2 conversion to produce valuable chemicals such as hydrocarbons and oxygenates.
Red mud is a caustic waste material of bauxite ore processing for the alumina extraction/aluminum refinement process (Bayer's process) and is utilized here as a catalyst for chemically reducing carbon dioxide (CO2). Sources of the red mud catalyst composition include the cement industry. Although the composition of the red mud may vary depending on the source, at a broad range, the red mud catalyst composition of the present disclosure has the following elemental composition as determined by ICP-OES and ED-XRF.
In some embodiments, the red mud catalyst composition of the present disclosure includes 10 to 30 wt. %, preferably 11 to 25 wt. %, preferably 12 to 20 wt. %, and more preferably 13 to 19 wt. % of Al. In some embodiments, the red mud catalyst composition includes 2 to 30 wt. %, preferably 3 to 20 wt. %, preferably 3.5 to 19 wt. %, preferably 4 to 18 wt. %, preferably 4.5 to 16 wt. %, and more preferably 5 to 15 wt. % of Fe. In some further embodiments, the red mud catalyst composition includes 0.02 to 1 wt. %, preferably 0.05 to 0.8 wt. %, and more preferably 0.07 to 0.4 wt. % of Mg. In some preferred embodiments, the red mud catalyst composition includes 1 to 20 wt. %, preferably 3 to 15 wt. %, preferably 3.5 to 10 wt. %, preferably 4 to 8 wt. %, and more preferably 4.4 to 7.7 wt. % of Na. In some more preferred embodiments, the red mud catalyst composition includes 0.02 to 1 wt. %, preferably 0.04 to 0.8 wt. %, and more preferably 0.05 to 0.4 wt. % of P. In some furthermore preferred embodiments, the red mud catalyst composition includes 0.2 to 8 wt. %, preferably 0.3 to 6 wt. %, preferably 0.4 to 4 wt. %, and more preferably 0.49 to 3.86 wt. % of Ti. In some preferred embodiments, the red mud catalyst composition includes 0.02 to 1 wt. %, preferably 0.03 to 0.8 wt. %, preferably 0.04 to 0.6 wt. %, and more preferably 0.05 to 0.4 wt. % of V. In some preferred embodiments, the red mud catalyst composition includes 1 to 5 wt. %, preferably 1.5 to 4.5 wt. %, preferably 2 to 4 wt. %, preferably 2.5 to 3.5 wt. %, and more preferably 2 to 3 wt. % of Ca. In some even more preferred embodiments, the red mud catalyst composition includes 2 to 15 wt. %, preferably 4 to 13 wt. %, preferably 6 to 11 wt. %, and more preferably 8 to 9 wt. % of Si. In some even more preferred embodiments, the red mud catalyst composition includes 0.02 to 1 wt. %, preferably 0.04 to 0.8 wt. %, preferably 0.06 to 0.6 wt. %, and more preferably 0.08 to 0.4 wt. % of K, each wt. % based on a total weight of the red mud catalyst composition by ED-XRF. In some most preferred embodiments, Mn is preferably absent from or substantially absent from the red mud catalyst composition.
In one embodiment, the red mud catalyst composition contains 10 to 30 wt. % Al, 2 to 20 wt. % Fe, 0.02 to 1 wt. % Mg, 1 to 20 wt. % Na, 0.02 to 1 wt. % P, 0.2 to 8 wt. % Ti, 0.02 to 1 wt. % V, 1 to 5 wt. % Ca, 2 to 15 wt. % Si, and 0.02 to 1 wt. % K, each wt. % based on a total weight of the red mud catalyst composition by ED-XRF. In a further embodiment, the red mud catalyst composition contains about 13.1 wt. % Al, 14.7 wt. % Fe, 0.18 wt. % Mg, 9.7 wt. % Na, 0.5 wt. % P, 4.8 wt. % Ti, 0.16 wt. % V, 2.9 wt. % Ca, 7.1 wt. % Si, and 0.23 wt. % K, each wt. % based on the total weight of the red mud catalyst composition as determined by ED-XRF. In yet a further embodiment, the red mud catalyst composition contains about 18.7 wt. % Al, 4.98 wt. % Fe, 0.07 wt. % Mg, 4.47 wt. % Na, 0.19 wt. % P, 0.49 wt. % Ti, 0.05 wt. % V, 2.4 wt. % Ca, 6.4 wt. % Si, and 0.15 wt. % K, each wt. % based on the total weight of the red mud catalyst composition as determined by ED-XRF. Other ranges are also possible.
In some embodiments, the red mud catalyst composition may be used without any modifications. In some embodiments, the red mud catalyst composition may be used along with other conventionally used catalysts that are known in the art. In some embodiments, the red mud catalyst composition is an alkali-modified red mud catalyst composition (in other words—the red mud catalyst composition with an alkali metal such as (Li, Na, or K) or an alkaline-modified red mud catalyst composition (in other words—red mud catalyst composition modified with an alkaline earth metal—such as magnesium or calcium). In certain other embodiments, the red mud catalyst composition may be modified with transition metals such as, Ni, Ag, Mn, V, Pt, Pd, Fe, Mo, Co, Cu, Cr, and alloys thereof.
One of the key factors that affect the catalyst performance is the surface area. A higher surface area corresponds to greater sites for binding the reactant, and greater conversion. In some embodiments, the red mud catalyst composition includes particles having a specific surface area in a range of 5 to 30 m2/g, preferably 8 to 27 m2/g, preferably 11 to 24 m2/g, and yet more preferably 14 to 21 m2/g. Other ranges are also possible. As used herein, the term “specific surface area” refers to the property of solids defined as the total surface area of a material per unit of mass, or solid or bulk volume. The red mud catalyst composition includes particles having a cumulative specific pore volume in a range of 0.01 to 0.1 cm3/g, preferably 0.02 to 0.08 cm3/g, and yet more preferably 0.03 to 0.07 cm3/g. Other ranges are also possible. As used herein, the term “pore volume” refers to the total volume of openings in a bed of adsorbent particles. In some embodiments, the red mud catalyst may be of any shapes and any configurations such as spherical, cubic, rod-shaped, irregular, fibrous, plate-like, and polyhedral. Referring to
In some embodiments, binder materials such as alumina, silica, alumino silicates, clay, carboxy methyl cellulose, polyethylene glycol and a combination thereof may be added during the shaping step.
The crystalline structure of the red mud catalyst is characterized by X-ray diffraction (XRD). In some embodiments, the XRD patterns are collected in a Rigaku diffractometer (Miniflex) equipped with a Cu-Kα radiation source (λ=0.15406 nm) for a 2θ range extending between 5 and 90°, preferably 20 and 70°, further preferably 30 and 60° at an angular rate of 0.005 to 0.04° s−1, preferably 0.01 to 0.03° s−1, or even preferably 0.02° s−1.
In some further embodiments, the red mud catalyst RM-2 has a first intense peak with a 2 theta (θ) value in a range of 12 to 15°, preferably about 13.9° in the XRD spectrum, a second intense peak with a 2θ value in a range of 18 to 20°, preferably about 18.5°, a third intense peak with a 2θ value in a range of 20 to 22°, preferably about 21.3°, a fourth intense peak with a 2θ value in a range of 23 to 25°, preferably about 24.7°, a fifth intense peak with a 2θ value in a range of 25 to 27.5°, preferably about 26.3°, a sixth intense peak with a 2θ value in a range of 27 to 30°, preferably about 28.1°, at least one seventh intense peak with a 2θ value in a range of 30 to 40°, preferably 32 to 38°, or even more preferably about 32 to 35°, at least one eighth intense peak with a 2θ value in a range of 40 to 45°, preferably 41 to 43°, or even more preferably about 42°, at least one ninth intense peak with a 2θ value in a range of 50 to 55°, preferably 51 to 54°, or even more preferably about 53°, at least one tenth intense peak with a 2θ value in a range of 55 to 60°, preferably 56 to 59°, or even more preferably about 57 to 58°, at least one eleventh intense peak with a 2θ value in a range of 60 to 65°, preferably 62 to 65°, or even more preferably about 63 to 65°, at least one twelfth intense peak with a 2θ value in a range of 65 to 80°, preferably 67 to 70°, or even more preferably about 68 to 69°, in the XRD spectrum as depicted in
At step 102, the method 100 includes introducing a gas stream comprising CO2 and H2 into a reactor containing red mud catalyst particles of the red mud catalyst composition. Optionally, the gas stream may also include inert gases, such as N2 (nitrogen) or Helium (He), and/or other gases like CO, in addition to CO2 and H2. In some embodiments, the gas stream, including CO2 and H2, is introduced into the reactor in a volumetric ratio of 1:10 to 10:1, preferably in a range of 1:1 to 1:6, preferably 1:5, preferably 1:4, and more preferably 1:3. Other ranges are also possible. In some embodiments, a total amount of CO2 and H2 is present in the gas stream at a concentration of at least 1% by volume, preferably at least 10% by volume, preferably at least 30% by volume, preferably at least 50% by volume, preferably at least 60% by volume, preferably at least 70% by volume, preferably at least 80% by volume, preferably at least 90% by volume, or even more preferably at least 99% by volume. Other ranges are also possible. In some embodiments, the red mud catalyst composition comprises the red mud catalyst particles having an average particle size of 1 to 800 micrometers (μm), preferably 10 to 400 μm, preferably 20 to 200 μm, preferably 30 to 100 μm, or even more preferably 40 to 60 μm.
The reactor is at least one selected from the group consisting of a fixed-bed reactor, a trickle-bed reactor, a moving bed reactor, a rotating bed reactor, a fluidized bed reactor, and a slurry reactor. In an embodiment, the reactor may be an inclined tumbler reactor. In the present disclosure, the reactor is a fixed-bed reactor in the form of a cylindrical reactor which includes a top portion, a cylindrical body portion, a bottom portion, a housing. As used herein, the term ‘fixed-bed reactor’ refers to the cylindrical tube filled with catalyst pellets with reactants flowing through the bed and being converted into products. In some embodiments, the housing has an open top, and open bottom supportably maintained with the cylindrical body portion. The red mud catalyst composition is supportably retained within the housing, permitting fluid flow therethrough. In some embodiments, the cylindrical reactor further includes at least one propeller agitator disposed in the bottom portion of the reactor. In some embodiments, the main function of the propeller agitator is homogenization, dispersion, and suspension of low-viscosity products. In some embodiments, the bottom portion is cone-shaped or pyramidal. In an embodiment, the bottom portion may have a cylindrical, cubical, cuboidal, or rhombic shape. In some preferred embodiments, a plurality of recirculation tubes fluidly connects the bottom portion of the cylindrical reactor with the cylindrical body portion of the cylindrical reactor. In an embodiment, the cylindrical reactor may be a vertical cylindrical reactor, or a horizontal cylindrical reactor. In an embodiment, the fixed-bed reactor may be made up of a material such as stainless-steel, iron, aluminum, copper, lead, iron, zirconium, or another alloy.
Optionally, the red mud catalyst may be mixed with at least one material to form a catalyst composite for chemically reducing carbon dioxide (CO2). In some embodiments, the at least one material is selected from the group consisting of carbon nanotubes, activated carbon, metal organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs), different inorganic oxides, clays, covalent organic polymers (COPs) and their combinations. Examples of catalyst composite include carbon nanotube-complexed red mud catalyst, activated carbon-complexed red mud catalyst, MOF-complexed red mud catalyst, ZIF-complexed red mud catalyst, and COP-complexed red mud catalyst.
In general, the carbon nanomaterial may be any suitable carbon nanomaterial known to one of ordinary skill in the art. Examples of carbon nanomaterials include carbon nanotube, carbon nanobud, carbon nanoscroll, carbon dot, activated carbon, carbon black, graphene, graphene oxide, reduced graphene oxide, and nanodiamonds. In some embodiments, the carbon nanomaterial is at least one selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, carbon nanotube, carbon dot, and activated carbon.
In some embodiments, the carbon nanomaterial is a carbon nanotube. The carbon nanotube may, in general, be any suitable carbon nanotube known to one of ordinary skill in the art. Carbon nanotube may be classified by structural properties such as the number of walls or the geometric configuration of the atoms that make up the nanotube. Classified by their number of walls, the carbon nanotube can be single-walled carbon nanotube (SWCNT) which have only one layer of carbon atoms arranged into a tube, or multi-walled carbon nanotubes (MWCNT), which have more than one single-layer tube of carbon atoms arranged so as to be nested, one tube inside another, each tube sharing a common orientation. Closely related to MWNTs are carbon nanoscrolls. Carbon nanoscrolls are structures similar in shape to a MWCNT, but made of a single layer of carbon atoms that has been rolled onto itself to form a multi-layered tube with a free outer edge on the exterior of the nanoscroll and a free inner edge on the interior of the scroll and open ends. The end-on view of a carbon nanoscroll has a spiral-like shape. For the purposes of this disclosure, carbon nanoscrolls are considered a type of MWCNT. Classified by the geometric configuration of the atoms that make up the nanotube, carbon nanotubes can be described by a pair of integer indices n and m. The indices n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of a single layer of carbon atoms. If m=0, the nanotubes are called zigzag type nanotubes. If n=m, the nanotubes are called armchair type nanotubes. Otherwise, they are called chiral type nanotubes. In some embodiments, the carbon nanotubes are metallic. In other embodiments, the carbon nanotubes are semiconducting. In some embodiments, the carbon nanotubes are SWCNTs. In other embodiments, the carbon nanotubes are MWCNTs. In some embodiments, the carbon nanotubes are carbon nanoscrolls. In some embodiments, the carbon nanotubes are zigzag type nanotubes. In alternative embodiments, the carbon nanotubes are armchair type nanotubes. In other embodiments, the carbon nanotubes are chiral type nanotubes.
In some embodiments, the carbon nanomaterial is graphene. In some embodiments, the carbon nanomaterial is graphene nanosheets. Graphene nanosheets may consist of stacks of graphene sheets, the stacks having an average thickness and a diameter. In some embodiments, the stacks comprise 1 to 60 sheets of graphene, preferably 2 to 55 sheets of graphene, preferably 3 to 50 sheets of graphene.
In some embodiments, the graphene is in the form of graphene particles. The graphene particles may have a spherical shape, or may be shaped like blocks, flakes, ribbons, discs, granules, platelets, angular chunks, rectangular prisms, or some other shape. In some embodiments, the graphene particles may be substantially spherical, meaning that the distance from the graphene particle centroid (center of mass) to anywhere on the graphene outer surface varies by less than 30%, preferably by less than 20%, more preferably by less than 10% of the average distance. In some embodiments, the graphene particles may be in the form of agglomerates.
In some embodiments, the graphene is pristine graphene. Pristine graphene refers to graphene that has not been oxidized or otherwise functionalized. Pristine graphene may be obtained by methods such as exfoliation, chemical vapor deposition synthesis, opening of carbon nanotubes, unrolling of carbon nanoscrolls, and the like. In alternative embodiments, the graphene is functionalized graphene. Functionalized graphene is distinguished from pristine graphene by the presence of functional groups on the surface or edge of the graphene that contain elements other than carbon and hydrogen. In other alternative embodiments, the graphene is graphene oxide. Graphene oxide refers to graphene that has various oxygen-containing functionalities that are not present in pristine graphene. Examples of such oxygen-containing functionalities include epoxides, carbonyl, carboxyl, and hydroxyl functional groups. Graphene oxide is sometimes considered to be a type of functionalized graphene.
In other alternative embodiments, the graphene is reduced graphene oxide. Reduced graphene oxide (rGO) refers to graphene oxide that has been chemically reduced. It is distinct from graphene oxide in it contains substantially fewer oxygen-containing functionalities compared to graphene oxide, and it is distinct from pristine graphene by the presence of oxygen-containing functionalities and structural defects in the carbon network. Reduced graphene oxide is sometimes considered to be a type of functionalized graphene. In some preferred embodiments, the carbon nanomaterial is reduced graphene oxide. The reduced graphene oxide may exist as nanosheets, particles having a spherical shape, or may be shaped like blocks, flakes, ribbons, discs, granules, platelets, angular chunks, rectangular prisms, or some other shape as described above, agglomerates as described above, or any other shape known to one of ordinary skill in the art.
In some embodiments, the carbon nanomaterial is activated carbon. Activated carbon refers to a form of porous carbon having a semi-crystalline, semi-graphitic structure and a large surface area. Activated carbon may be in the form of particles or particulate aggregates having micropores and/or mesopores. Activated carbon typically has a surface area of approximately 500 to 5000 m2/g. The activated carbon particles may have a spherical shape, or may be shaped like sheets, blocks, flakes, ribbons, discs, granules, platelets, angular chunks, rectangular prisms, or some other shape. In some embodiments, the activated carbon particles may be substantially spherical, meaning that the distance from the activated carbon particle centroid (center of mass) to anywhere on the activated carbon particle outer surface varies by less than 30%, preferably by less than 20%, more preferably by less than 10% of the average distance.
In some embodiments, the carbon nanomaterial is carbon black. Carbon black refers to having a semi-crystalline, semi-graphitic structure and a large surface area. Carbon black may be distinguished from activated carbon by a comparatively lower surface area, typically 15 to 500 m2/g for carbon black. Additionally, carbon black may lack the requisite micropores and mesopores of activated carbon. The carbon black particles may have a spherical shape, or may be shaped like sheets, blocks, flakes, ribbons, discs, granules, platelets, angular chunks, rectangular prisms, or some other shape.
In some embodiments, the particles of a carbon nanomaterial are a single type of particle as described above. In this context, “a single type of particle” may refer to particles of a single carbon nanomaterial, particles which have substantially the same shape, particles which have substantially the same size, or any combination of these. In alternative embodiments, mixtures of types of particles are used.
As used herein, the term “zeolitic,” “zeolite,” “zeolitic materials,” and similar terms generally refer to a material having the crystalline structure or three-dimensional framework of, but not necessarily the elemental composition of, a zeolite. Zeolites are porous silicate or aluminosilicate minerals that occur in nature. Elementary building units of zeolites are SiO4 (and if appropriate, AlO4) tetrahedra. Adjacent tetrahedra are linked at their corners via a common oxygen atom, which results in an inorganic macromolecule with a three-dimensional framework (frequently referred to as the zeolite framework). The three-dimensional framework of a zeolite also comprises channels, channel intersections, and/or cages having dimensions in the range of 0.1-10 nm, preferably 0.2-5 nm, more preferably 0.2-2 nm. Water molecules may be present inside these channels, channel intersections, and/or cages. Zeolites which are devoid of aluminum may be referred to as “all-silica zeolites” or “aluminum-free zeolites”. Some zeolites which are substantially free of, but not devoid of, aluminum are referred to as “high-silica zeolites”. Sometimes, the term “zeolite” is used to refer exclusively to aluminosilicate materials, excluding aluminum-free zeolites or all-silica zeolites.
In some embodiments, the zeolitic material has a three-dimensional framework that is at least one zeolite framework selected from the group consisting of a 4-membered ring zeolite framework, a 6-membered ring zeolite framework, a 10-membered ring zeolite framework, and a 12-membered ring zeolite framework. The zeolite may have a natrolite framework (e.g. gonnardite, natrolite, mesolite, paranatrolite, scolecite, and tetranatrolite), edingtonite framework (e.g. edingtonite and kalborsite), thomsonite framework, analcime framework (e.g. analcime, leucite, pollucite, and wairakite), phillipsite framework (e.g. harmotome), gismondine framework (e.g. amicite, gismondine, garronite, and gobbinsite), chabazite framework (e.g. chabazite-series, herschelite, willhendersonite, and SSZ-13), faujasite framework (e.g. faujasite-series, Linde type X, and Linde type Y), mordenite framework (e.g. maricopaite and mordenite), heulandite framework (e.g. clinoptilolite and heulandite-series), stilbite framework (e.g. barrerite, stellerite, and stilbite-series), brewsterite framework, or cowlesite framework. In some embodiments, the porous silicate and/or aluminosilicate matrix is a zeolitic material having a zeolite framework selected from the group consisting of ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-18, ZSM-23, ZSM-35 and ZSM-39.
The International Union of Pure and Applied Chemistry (IUPAC) states that a metal organic framework (MOF) is a coordination network with organic ligands containing potential voids. A coordination network is a coordination compound extending, through repeating coordination entities, in one dimension, but with cross-links between two or more individual chains, loops, or spiro-links, or a coordination compound extending through repeating coordination entities in two or three dimensions; and finally a coordination polymer is a coordination compound with repeating coordination entities extending in one, two, or three dimensions. A coordination entity is an ion or neutral molecule that is composed of a central atom, usually that of a metal, to which is attached a surrounding array of atoms or groups of atoms, each of which is called ligands. More succinctly, a metal organic framework is characterized by metal ions or clusters coordinated to organic ligands to form one-, two-, or three-dimensional structures. Typically, a MOF exhibits a regular void or pore structure. The nature of the void or pore structure, including properties or structural factors such as the geometry about the metal ions or clusters, the arrangement of the linkages between metal ions or clusters, and the number, identity, and spatial arrangement of voids or pores. These properties may be described as the structure of the repeat units and the nature of the arrangement of the repeat units. The specific structure of the MOF, which may include the void or pore structure is typically referred to as the MOF topology.
The metal-organic framework comprises a metal ion which is an ion of at least one metal selected from the group consisting of a transition metal (e.g. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, and Cn), a post-transition metal (e.g. Al, In, Ga, Sn, Bi, Pb, Tl, Zn, Cd, and Hg), and an alkaline earth metal (e.g. Be, Mg, Ca, Sr, Ba, and Ra). Further, these metal ions may be of any oxidation state M+1, M+2, M+3, etc. In one or more embodiments, the metal ion is an ion of at least one metal selected from the group consisting of Zn, Cu, Fe, Ni, Co, Mn, Cr, Cd, Mg, Ca, and Zr.
In the formation of a metal organic framework, the organic ligands must meet certain requirements to form coordination bonds, primarily being multi-dentate, having at least two donor atoms (i.e. N-, and/or O-) and being neutral or anionic. The structure of the metal organic framework is also affected by the shape, length, and functional groups present in the organic linker. In certain embodiments, the metal organic framework of the present disclosure comprises anionic ligands as organic ligands. In one or more embodiments, the organic ligands may have at least two nitrogen donor atoms. For example, the organic ligands may be imidazolate-based, imidazole-derived or ligands similar to an imidazole including, but not limited to, optionally substituted imidazoles, optionally substituted benzimidazoles, optionally substituted imidazolines, optionally substituted pyrazoles, optionally substituted thiazoles, and optionally substituted triazoles. In a preferred embodiment, the metal organic framework of the present disclosure in any of its embodiments comprises 2-methylimidazole and 5-methylbenzimidazole as the organic ligands. 2-Methylimidazole and 5-methylbenzimidazole organic ligands have free nitrogen atoms that may each form a coordinative bond to the metal ions (e.g. Zn(II)) to produce a coordination network.
Metal organic frameworks comprising such imidazole or benzimidazole ligands are typically referred to as zeolitic imidazolate frameworks (ZIFs). In some embodiments, the metal organic framework is a zeolitic imidazolate framework. Examples of suitable metal organic frameworks include, but are not limited to isoreticular metal organic framework-3 (IRMOF-3), MOF-69A, MOF-69B, MOF-69C, MOF-70, MOF-71, MOF-73, MOF-74, MOF-75, MOF-76, MOF-77, MOF-78, MOF-79, MOF-80, DMOF-1-NH2, UMCM-1-NH2, MOF-69-80, ZIF-1, ZIF-2, ZIF-3, ZIF-4, ZIF-5, ZIF-6, ZIF-7, ZIF-9, ZIF-10, ZIF-11, ZIF-12, ZIF-14, ZIF-20, ZIF-21, ZIF-22, ZIF-23, ZIF-25, ZIF-60, ZIF-61, ZIF-62, ZIF-63, ZIF-64, ZIF-65, ZIF-66, ZIF-67, ZIF-68, ZIF-69, ZIF-70, ZIF-71, ZIF-72, ZIF-73, ZIF-74, ZIF-75, ZIF-76, ZIF-77, ZIF-78, ZIF-79, ZIF-80, ZIF-81, ZIF-82, ZIF-90, ZIF-91, ZIF-92, ZIF-93, ZIF-94, ZIF-96, ZIF-97, ZIF-100, ZIF-108, ZIF-303, ZIF-360, ZIF-365, ZIF-376, ZIF-386, ZIF-408, ZIF-410, ZIF-412, ZIF-413, ZIF-414, ZIF-486, ZIF-516, ZIF-586, ZIF-615, and ZIF-725.
In some embodiments, the material is aluminum oxide. In some embodiments, the aluminum oxide is gamma (7) aluminum oxide. These can include substances serving as a granulating agent or a binder. Examples thereof include alumina, silica, titania, silica-alumina, alumina-titania, alumina-zirconia, alumina-boria, phosphorus-alumina, silica alumina-boria, phosphorus-alumina-boria, phosphorus-alumina-silica, silica-alumina-titania, and silica-alumina-zirconia.
In some embodiment, the red mud material is modified by directly impregnating with one metal or combinations of metals selected from the group consisting of a transition metal (e.g. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, and Cn), a post-transition metal (e.g. Al, In, Ga, Sn, Bi, Pb, Tl, Zn, Cd, and Hg), and an alkaline earth metal (e.g. Be, Mg, Ca, Sr, Ba, and Ra). Further, these metal ions may be of any oxidation state M+1, M+2, M+3, etc. In one or more embodiments, the metal ion is an ion of at least one metal selected from the group consisting of Zn, Cu, Fe, Ni, Co, Mn, Cr, Cd, Mg, Ca, and Zr.
In some embodiments, the material is present in the form of particles. In general, the particles can be any shape known to one of ordinary skill in the art. Examples of suitable shapes the metal organic framework particles may take include spheres, spheroids, lentoids, ovoids, solid polyhedra such as tetrahedra, cubes, octahedra, icosahedra, dodecahedra, rectangular prisms, triangular prisms (also known as nanotriangles), nanoplatelets, nanodisks, nanotubes, blocks, flakes, discs, granules, angular chunks, and mixtures thereof.
In some embodiments, the material particles have uniform shape. Alternatively, the shape may be non-uniform. As used herein, the term “uniform shape” refers to an average consistent shape that differs by no more than 10%, by no more than 5%, by no more than 4%, by no more than 3%, by no more than 2%, by no more than 1% of the distribution of material particles having a different shape. As used herein, the term “non-uniform shape” refers to an average consistent shape that differs by more than 10% of the distribution of material particles having a different shape. In one embodiment, the shape is uniform and at least 90% of the material particles are spherical or substantially circular, and less than 10% are polygonal. In another embodiment, the shape is non-uniform and less than 90% of the material particles are spherical or substantially circular, and greater than 10% are polygonal.
At step 104, the method 100 includes reacting at least a portion of the CO2 and the H2 in the gas stream in the presence of the red mud catalyst composition at a temperature of 200 to 800° C., and under a pressure of 5 to 100 bar to form a gaseous product comprising a chemical reduction product of CO2. During operation, the reactor was maintained at a temperature range of 200-800° C., preferably 250-750° C., preferably 280-500° C., preferably 300 to 450° C., and more preferably 300 to 450° C. during operation. Other ranges are also possible. Likewise, the pressure in the reactor was between 5 to 100 bars, preferably 10-50 bars, preferably 15-45 bars, preferably 20-44 bars, preferably 25-40 bars, and more preferably between 30-40 bars during operation. Other ranges are also possible.
In some embodiments, the reaction yields a gaseous product that includes methane, ethane, ethylene, propane, propylene, methanol, dimethyl ether (DME), carbon monoxide, a hydrocarbon containing C4-C9 such as butane, butene, pentane, and pentene; and aromatics such as benzene, naphthalene, anthracene, or their isomers, or mixtures of these substance. In some embodiments, the C4-C9 hydrocarbon contains butane, butene, butyne, pentane, pentene, pentyne, hexane, hexene, hexyne, cyclohexane, cyclohexene, heptane, heptene, heptyne, octane, octene, octyne, nonane, nonene, nonyne, or their isomers, or mixtures of these substance.
In some embodiments, the methane is present in the gaseous product at a concentration of 20 to 50 wt. %, more preferably 24 to 45 wt. %, preferably 25 to 43 wt. %, preferably 27 to 32 wt. %, based on total weight of the gaseous product. In some embodiments, the ethane is present in the gaseous product at a concentration of 1 to 20 wt. %, more preferably 3 to 18 wt. %, preferably 5 to 16 wt. %, preferably 7 to 14 wt. %, based on total weight of the gaseous product. In some embodiments, the methanol is present in the gaseous product at a concentration of 0.01 to 1 wt. %, more preferably 0.05 to 0.8 wt. %, preferably 0.1 to 0.6 wt. %, preferably 0.1 to 0.4 wt. %, based on total weight of the gaseous product. In some embodiments, the propane is present in the gaseous product at a concentration of 0.5 to 10 wt. %, more preferably 1 to 8 wt. %, preferably 2 to 6 wt. %, preferably 2 to 4 wt. %, based on total weight of the gaseous product. In some embodiments, the dimethyl ether (DME) is present in the gaseous product at a concentration of 1 to 70 wt. %, more preferably 2 to 60 wt. %, preferably 3 to 50 wt. %, preferably 4 to 40 wt. %, based on total weight of the gaseous product. In some embodiments, the carbon monoxide is present in the gaseous product at a concentration of 1 to 50 wt. %, more preferably 3 to 40 wt. %, and yet more preferably 6 to 30 wt. %, based on total weight of the gaseous product. The method 100 of the present disclosure chemically reduces 10 to 40%, more preferably 10 to 30%, and yet more preferably 15 to 25 wt. %, of the CO2 based on a total weight of the gaseous mixture. Other ranges are also possible.
In some embodiments, when the red mud catalyst composition comprises about 13.1 wt. % Al, about 14.7 wt. % Fe, about 0.18 wt. % Mg, about 9.7 wt. % Na, about 0.5 wt. % P, about 4.8 wt. % Ti, about 0.16 wt. % V, about 2.9 wt. % Ca, about 7.1 wt. % Si, and about 0.23 wt. % K, each wt. % based on the total weight of the red mud catalyst composition as determined by ED-XRF, the gaseous product comprises 20 to 25 wt. % methane, 4 to 9 wt. % ethane, 1 to 3 wt. % propane, 0.05 to 0.15 wt. % methanol, 45 to 55 wt. % dimethyl ether (DME), and 5 to 15 wt. % carbon monoxide, each wt. % based on the total weight of the gaseous product. Other ranges are also possible.
In some embodiments, when the red mud catalyst composition comprises about 18.77 wt. % Al, about 4.98 wt. % Fe, about 0.07 wt. % Mg, about 4.47 wt. % Na, about 0.19 wt. % P, about 0.49 wt. % Ti, about 0.05 wt. % V, about 2.4 wt. % Ca, about 6.4 wt. % Si, and about 0.15 wt. % K, each wt. % based on the total weight of the red mud catalyst composition as determined by ED-XRF, the gaseous product comprises 35 to 45 wt. % methane, 9 to 15 wt. % ethane, 3 to 9 wt. % propane, 0.1 to 0.25 wt. % methanol, 1 to 10 wt. % dimethyl ether (DME), and 25 to 35 wt. % carbon monoxide, each wt. % based on the total weight of the gaseous product. Other ranges are also possible.
In some embodiments, the gaseous product contains about 25.3 wt. % of methane, about 6.5 wt. % of ethane, about 0.1 wt. % of methanol, about 2.1 wt. % of propane, about 51.4 wt. % of DME, and about 9.63 wt. % of CO, each wt. % based on total weight of the gaseous product. Other ranges are also possible.
In some embodiments, the gaseous product contains about 41.3 wt. % of methane, about 11.91 wt. % of ethane, about 0.18 wt. % of methanol, about 5.4 wt. % of propane, about 6.24 wt. % of DME, and about 30.7 wt. % of CO, each wt. % based on total weight of the gaseous product. Other ranges are also possible.
At step 202, the method 200 includes drying a red mud material and pulverizing to form a pulverized red mud material. In some embodiments, the red mud material is obtained from different geographical locations including Saudi Arabia and Indonesia. In some embodiments, the red mud material obtained from Saudi Arabia and Indonesia areas has a higher alkalinity value compared to a red mud material obtained from other geographical locations, as determined by a titration technique. This titration technique is well-known in the art and the details thereof are, therefore, not provided here. The alkalinity value of red mud material described in the present invention may be in a range of from 4,000 to 20,000 mg/L of CaCO3 equivalent, preferably from 6,000 to 15,000, or even more preferably from 8,000 to 12,000 mg/L of CaCO3 equivalent. Other ranges are also possible. In some embodiments, the red mud material is in the form of slurry and is filtered before the drying. In some further embodiments, the red mud material obtained is dried at a temperature of from 80 to 120° C., or more preferably about 100° C. for at least 2 hours, at least 12 hours, at least 24 hours, at least 48 hours, or even more preferably at least 96 hours. In some preferred embodiments, the red mud material after the drying is in the form of granular and powder. In some more preferred embodiments, the granular and powder form red mud material is pulverized to achieve the pulverized red mud material having an average particle size in a range of 1 to 800 micrometers (+m), preferably 20 to 400 μm, preferably 30 to 200 μm, preferably 40 to 100 μm, or even more preferably about 80 μm. Other ranges are also possible.
At step 202, the method 200 includes calcining the pulverized red mud material at a temperature of at least 600° C. to form the red mud catalyst composition. As used herein, the term ‘pulverization’ refers to applying an external force to a solid material of a certain size to break up the solid material and reduce the solid material into pieces smaller than the original size. The pulverization may be carried out using any suitable means, for example, by grinding, ball milling, blending, etc., using manual methods (e.g., mortar) or machine-assisted methods such as using a mechanical blender, or any other apparatus known to those of ordinary skill in the art. In some embodiments, the pulverization is carried out till the particle size of the red mud particles is reduced to a micrometer level. Further to pulverization, the red mud material is calcined by subjecting the micrometer-sized red mud material by heating it to a high temperature, under a restricted supply of ambient oxygen. This was performed to remove impurities or volatile substances and to incur thermal decomposition. In some embodiments, the calcination is carried out in a furnace preferably equipped with a temperature control system, which may provide a heating rate of up to 50° C./min, or preferably up to 40° C./min, or preferably up to 30° C./min, preferably up to 20° C./min, preferably up to 10° C./min, preferably up to 5° C./min. Other ranges are also possible. In preferred embodiments, the pulverized red mud material is heated with a heating rate in the range of 1 to 15° C./min, preferably 3 to 10° C./min, preferably 5 to 6° C./min to a temperature range of 500 to 1,000° C., preferably 600 to 975° C., preferably 650 to 950° C., preferably 675 to 925° C., preferably 700° C. for 1 to 15 hours, preferably 2 to 10 hours, preferably 3 to 8 hours, preferably 4 to 6 hours, preferably 6 hours. Other ranges are also possible.
At step 302, the method 300 includes impregnating the red mud catalyst composition by soaking particles of the red mud catalyst composition in a potassium salt solution and mixing to form the modified red mud catalyst composition as a crude mixture. To bring about impregnation of the alkali metals on the red mud catalyst composition, the red mud catalyst composition is soaked in the salt solution. In some embodiments, the salt solution includes at least one salt selected from the group consisting of an alkali metal salt and an alkaline earth metal salt. In some further embodiments, the alkali metal salt may include sodium carbonate, sodium acetate, sodium sulfide, sodium bicarbonate, sodium hydroxide, potassium cyanide, and/or combinations thereof. In some preferred embodiments, the alkaline earth metal salt may include, but are not limited to, epsom salt, gypsum, beryllium aluminum silicate, beryllium silicate hydroxide, carnalite, dolomite, magnesite, magnesium hydroxide, strontium sulfate, strontium carbonate, barium sulfate, barium carbonate and mixtures thereof. In some more preferred embodiments, the salt solution includes at least one salt selected from the group consisting of potassium fluoride (KF), potassium chloride (KCl), potassium bromide (KBr), potassium nitrate (KNO3), potassium sulfate (K2SO4), potassium carbonate (K2CO3), potassium phosphate (K3PO4), and potassium hydroxide (KOH). In some further preferred embodiments, the salt is present in the salt solution at a concentration of 0.5 to 10 wt. %, more preferably 5 to 9%, and yet more preferably 6 to 8%, based on the total weight of the salt solution. Other ranges are also possible. In some further preferred embodiments, the red mud catalyst composition is soaked in the salt solution till such a time, about 10-60 minutes, preferably 20-40 minutes, and more preferably for about 30 minutes, till the alkali metal is adsorbed on the surface of the red mud catalyst composition. Other ranges are also possible. In some further preferred embodiments, other conventionally known methods of impregnation may be adopted as well, as may be obvious to a person skilled in the art.
At step 304, the method 300 includes separating the modified red mud catalyst composition from the crude mixture and then drying the crude mixture to obtain the modified red mud catalyst composition. In some embodiments, the modified red mud catalyst composition may be separated from the crude mixture via centrifugation, filtration, evaporation, or by a method used or known in the art. In some further embodiments, the separated modified red mud catalyst composition is further dried to a temperature range of 60-120° C., preferably 70-110° C., preferably 80-100° C., and more preferably to about 90° C. for a period of 12 to 16 hours to remove any water molecules/volatile components in the modified red mud catalyst composition. Other ranges are also possible. In addition, the modified red mud catalyst may be dried in a heating device such as ovens, hot plates, heating mantles and tapes, oil baths, salt baths, sand baths, air baths, hot-tube furnaces, hot-air guns, and microwave ovens.
The catalytic activity of two sets of catalysts was evaluated in CO2 reduction. The first set of catalyst is the red mud catalyst composition that are used without any modification, while the second set of catalysts are modified red mud catalysts including impregnated red mud catalysts with a salt, e.g., potassium, to form potassium promoted catalyst. The catalysts are characterized using inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), temperature program reduction using H2 (H2-TPR), and N2 adsorption/desorption method for calculating the structure, reducibility/H2 uptake of the first set catalysts and Brunauer-Emmett-Teller (BET) surface area, respectively, while the second set of catalysts is characterized using CO2-TPD and NH3-TPD. Basicity and acidity of the first set catalysts are analyzed using temperature program desorption using carbon dioxide (CO2-TPD) and ammonia (NH3-TPD), respectively, to determine the physicochemical properties. Both sets of catalysts are tested for their performance in CO2 hydrogenation application using a fixed-bed reactor at the desired temperature and pressure in down-flow mode using a feed containing CO2 and H2.
As used herein, the term “inductively coupled plasma optical emission spectroscopy,” or “ICP-OES” generally refers to a technique used to determine the elemental composition of a sample, such as a red mud catalyst. In some embodiments, the red mud catalyst is atomized and excited in an inductively coupled plasma (ICP), which is a high-temperature argon gas plasma generated by an electrical discharge. In some further embodiments, the excited atoms emit light at characteristic wavelengths that are specific to each element. In some preferred embodiments, the emitted light is then separated into its component wavelengths using a spectrometer, and the intensity of the emitted light is measured to determine the concentration of each element in the red mud catalyst.
As used herein, the term “N2 adsorption/desorption method” generally refers to a technique used to measure the specific surface area of a solid material, such as a catalyst or a porous material. In some embodiments, the red mud catalyst is exposed to a stream of nitrogen gas at low temperature and pressure. The nitrogen gas is adsorbed onto the surface of the red mud catalyst, filling the pores and creating a monolayer of adsorbed nitrogen. In some further embodiments, the amount of nitrogen adsorbed at a given pressure is measured using a gas adsorption instrument, such as a BET instrument. In some preferred embodiments, the BET analysis is performed on a BELSORP analyzer according to the software manual, pages 62 to 66, manufactured by Bell Japan. In some more preferred embodiments, the nitrogen gas is gradually removed from the red mud catalyst, causing the desorption of the adsorbed nitrogen. The amount of nitrogen desorbed at a given pressure is also measured using the gas adsorption instrument. By analyzing the amount of nitrogen adsorbed and desorbed, the specific surface area of the red mud catalyst can be calculated using the BET (Brunauer-Emmett-Teller) and Barrett, Joyner and Halenda (BJH) equation.
The red mud catalyst composition was characterized by various analytical techniques, one among which is hydrogen temperature-programmed reduction (H2-TPR). As used herein, the term “temperature program reduction using H2,” or “H2-TPR” generally refers to a technique used to study the reducibility of a solid material, such as a red mud catalyst, by measuring the consumption of a reducing gas, such as hydrogen, as a function of temperature. In some embodiments, the red mud catalyst is first heated in an oxidizing gas, such as air or oxygen, to remove any adsorbed species and to convert the red mud catalyst to an oxide. In some further embodiments, the oxidized red mud catalyst is then cooled down and exposed to a stream of hydrogen gas, while the temperature is gradually increased. As the temperature increases, the hydrogen reacts with the oxidized red mud catalyst, causing a reduction of the material. In some preferred embodiments, this reduction reaction may be exothermic, and the heat generated by the reaction is monitored as a function of temperature.
In some embodiments, the H2-TPR was conducted on a BellCat chemisorption analyzer. The red mud catalyst was placed in a quartz calcined at a temperature of 400 to 800° C., preferably 450 to 750° C., preferably 500 to 700° C., preferably 550 to 650° C., or even more preferably about 600° C. under an argon flow for at least 30 minutes, at least 60 minutes, at least 120 minutes. In some further embodiments, the red mud catalyst was cooled to a temperature of no more than 70° C., preferably no more than 60° C., or even more preferably no more than 50° C. In some preferred embodiments, a gas flow contains hydrogen (H2) and argon (Ar) in a volumetric ratio of H2 to Ar ranging from 1:20 to 1:1, preferably 1:15 to 1:5, or even more preferably about 1:10 was introduced to flow over the red mud catalyst at a flow rate of 10 to 60 cubic centimeters per minutes (cm3/min), preferably 20 to 50 cm3/min, or even more preferably about 30 cm3/min. In some preferred embodiments, the temperature of the analyzer containing the red mud catalyst was increased at ramping rate of 5 to 20° C. per minute (° C./min) until the temperature reaches about 700 to 1200° C., or even more preferably about 900° C. Other ranges are also possible. In some most preferred embodiments, the composition of the present disclosure has an H2-TPR in a range of 0.5 to 5 mmol/g, preferably 0.7 to 4.5 mmol/g, preferably 1 to 4 mmol/g, and more preferably 1.34 to 3.89 mmol/g. Other ranges are also possible.
As used herein, the term “temperature program desorption using carbon dioxide,” or “CO2-TPD” generally refers to a technique used to study the surface acidity of a solid material, such as a red mud catalyst. In some embodiments, the red mud catalyst is first heated in an inert gas, such as nitrogen, to remove any adsorbed species and to stabilize the surface. In some embodiments, the red mud catalyst is then cooled down and exposed to a stream of carbon dioxide gas, which is adsorbed onto the surface of the red mud catalyst. The amount of carbon dioxide adsorbed is proportional to the surface acidity of the red mud catalyst. The red mud catalyst is then heated at a constant rate while the amount of carbon dioxide desorbed is monitored as a function of temperature. In some further embodiments, as the temperature increases, the adsorbed carbon dioxide begins to desorb from the surface of the red mud catalyst. In some preferred embodiments, the desorption of carbon dioxide may be exothermic, and the heat generated by the desorption process is monitored using a thermal conductivity detector.
As used herein, the term “temperature program desorption using ammonia,” or “NH3-TPD” generally refers to a technique used to study the surface basicity of a solid material, such as a red mud catalyst. In some embodiments, the red mud catalyst is first heated in an inert gas, such as nitrogen, to remove any adsorbed species and to stabilize the surface. In some embodiments, the red mud catalyst is then cooled down and exposed to a stream of ammonia gas, which is adsorbed onto the surface of the red mud catalyst. The amount of ammonia adsorbed is proportional to the surface basicity of the red mud catalyst. In some embodiments, the red mud catalyst is then heated at a constant rate while the amount of ammonia desorbed is monitored as a function of temperature. In some further embodiments, as the temperature increases, the adsorbed ammonia begins to desorb from the surface of the red mud catalyst. In some preferred embodiments, the desorption of ammonia may be exothermic, and the heat generated by the desorption process is monitored using a thermal conductivity detector.
The modified red mud catalyst was characterized mainly using CO2-TPD and NH3-TPD. Temperature programmed desorption (TPD) is a technique used to monitor surface interactions between molecular species on a surface when the surface temperature has changed in a controlled setting. This technique determines the strength of interactions between the red mud catalyst composition and the alkali metal adsorbed on the red mud catalyst composition. This is done by placing the modified red mud catalyst composition inside a reactor and pushing an inert gas into the chamber. Alternatively, the sample can be located in an ultra-high vacuum (UHV) chamber with no carrier gas. The sample is dosed with a probe gas such as CO, NH3, H2, etc. The sample is then increased in temperature at a linear ramp rate, and the desorption products are analyzed by a mass spectrometer.
The NH3-TPD was conducted on a MicrotracBEL equipment. The red mud catalyst was heated at a temperature of 500 to 600° C., preferably about 550° C. under a helium gas flow for 30 to 90 min, preferably about 60 min at a flow rate of 30 to 70 milliliters per minute (mL/min), preferably 50 mL/min. Other ranges are also possible. In some further embodiments, the red mud catalyst was then cooled to less than 150° C., preferably less than 100° C. before contacting with a NH3-containing gas mixture. In some preferred embodiments, NH3 is present in the gas mixture at a concentration of 1 to 20%, preferably about 5 to 15%, or even more preferably about 10% by volume. In some more preferred embodiments, the MicrotracBEL equipment containing the red mud samples is heated to a temperature of 600 to 700° C., preferably about 650° C. at a heating rate of 5 to 30° C./min, preferably 5 to 20° C./min, or even more preferably about 10° C./min. Other ranges are also possible. In some most preferred embodiments, the red mud catalyst composition has a temperature-programmed desorption of ammonia (NH3-TPD) of 0.001 to 0.1 mmol/g, more preferably 0.002 to 0.06 mmol/g, and yet more preferably 0.004 to 0.02 mmol/g. Other ranges are also possible.
In some embodiments, the CO2-TPD is performed by saturating the red mud catalyst in a CO2 atmosphere at a temperature of 25 to 65° C., preferably about 45° C. In some further embodiments, the red mud catalyst after saturation was flushed with a carrier gas for 5 to 60 min, or even more preferably about 30 min to remove physically adsorbed CO2. In some more preferred embodiments, the red mud catalyst after saturation was heated to a temperature of 600 to 800° C., or even more preferably about 700° C. to desorb CO2. In some most preferred embodiments, the red mud catalyst composition has a temperature-programmed desorption of carbon dioxide (CO2-TPD) of 0.01 to 0.5 mmol/g, more preferably 0.03 to 0.3 mmol/g, and yet more preferably 0.1 to 0.25 mmol/g. Other ranges are also possible.
The following examples describe and demonstrate exemplary embodiments of the method 100 described herein. The examples are provided solely for the purpose of illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without departing from the spirit and scope of the present disclosure.
The red mud material collected from two different geographical locations, namely from Saudi Arabia and Indonesia are dried at 100° C. to get granular or powder sample. For one of the samples, the starting material was in slurry form and needed to filter and wash before use for composition analysis. Each red mud material was separately crushed and then calcined at 700° C. for 6 h at ramping rate of 5° C. per minute and are used directly as catalytic materials named as RM-1 and, RM-2. Elemental composition of the sample is determined by ED-XRF analysis. The important metals and their concentrations are presented in Table 1. Major metals present are Fe, Al and Na whereas metals like V, Mg and P were also detected at various levels in each sample.
Structural properties, reducibility/H2 consumption, acidity/basicity, and surface area/porosity are investigated by the respective techniques before the catalytic evaluation of the prepared catalysts. Surface morphologies of the red mud material were analyzed using a scanning electron microscope (SEM) JEOL JSM-6460. An X-ray diffractometer (XRD, Miniflex from Rigaku) equipped with Cu Kα radiation (λ=0.15406 nm) was used to get the diffraction patterns of the red mud samples, which are given in
The surface areas and pore volumes of the samples were analyzed using the N2 adsorption method and are calculated using the Brunauer-Emmett-Teller (BET) and Barrett, Joyner, and Halenda (BJH) equation. The samples were degassed at 300° C. for 12 hours, and the analysis was performed in a liquid N2 bath at −195.8° C. BET/BJH results are given in Table 2.
H2-TPR was conducted using a BelCat chemisorption analyzer. Around 50 milligrams (mg) of the samples were placed in quartz calcined at 600° C. under the flow of Ar for 1 hour. Then, the samples were cooled down to 50° C. Following this, a gas consisting of 10 vol. % H2 and 90 vol. % Ar was allowed to flow over the samples at a flow rate of 30 cm3/min, and the temperature was ramped at a ramping rate of 10° per minute up to 900° C. The H2 consumed with the temperature increase was measured using a thermal conductivity detector (TCD) detector. H2-TPR results show the presence of reducible metals and their ability to adsorb and consume H2 during a catalytic reaction.
The acidity of the samples is determined using MicrotracBEL equipment, by using about 50 mg of the sample, pre-treated at 550° C. in the presence of continuous flow of helium gas for 60 min at a flow rate of 50 milliliters per minute (mL/min). After that, the sample was cooled to 100° C. followed by the adsorption of the NH3 mixture for 30 min (10% NH3 in helium, 50 mL/min). The physiosorbed gases were flushed with helium gas for 45 min with a helium flow rate of 30 ml/min. Finally, the sample was heated to 650° C. at a constant heating rate of 10° C. min−1 to desorb the NH3 from the sample, and simultaneously, the TPD signal was monitored by a TCD. The results of this study are shown in Table 3.
The affinity of the samples for CO2 uptake was studied by adsorption and desorption of CO2 (CO2-TPD) with the increase in temperature. The samples were saturated with CO2 at 45° C. Thereafter, the samples were flashed with carrier gas for 30 min to remove the physically adsorbed CO2. Finally, the saturated samples were heated up to 700° C., and the desorbed CO2 was measured using a TCD. The overlaid desorption plots are given in Table 3.
The performance of the prepared catalysts was evaluated for CO2 hydrogenation using a fixed-bed laboratory-scale reactor. The temperature of the catalyst bed was in the range of 300-400° C. and the hydrogen pressure was between 30-40 bar. The feed includes CO2 and H2 in a volumetric ratio of 1:3. The products were analyzed using an online-gas chromatograph (GC) equipped with multiple detectors. Results are shown here in Table 4 and are graphically represented in
Table 4 shows that RM-1 catalyst showed 23.60% CO2 conversion whereas RM-2 showed conversion around 15.25%. DME and Methane are major products in the case of RM-1, whereas a large amount of CO is generated over RM-2 catalyst. Iron content and other physicochemical properties, e.g., surface area value and acidity, are important factors to enhance these properties and functionalities of the red mud catalysts. Formation of CO is a sign that catalyst is able to activate CO2 and further conversion of CO to hydrocarbons is not occurring in priority. Red mud catalysts may be modified to enhance the selectivity to desired products like methanol and DME. Promoters have vital role in deciding the selectivity and suitable promoters will be incorporated on to the red mud catalysts. Producing high-value commodities using a low-cost catalyst and CO2 has the potential to be an environmentally-friendly solution for sustainable industrial practices.
Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
