Patent Application
20250043507
The present invention is directed to a method and composition for the delignification of lignocellulosic material and post-treatment extraction of constituents.
Fossil fuel-based organic products include a vast array of end use and precursor products such as surfactants, pharmaceuticals, plastics, fuels, polymers, aromatics and elastomers which are abundant in all aspects of manufacturing consumer products and fuels which are used in all aspects of the global economy. Climate change, environmental and political pressures are forcing industry to find alternatives to fossil fuels and petroleum-based products that are carbon-neutral, renewable and economic. A well-known source of many commercialized non-fossil-fuel based products is lignocellulosic biomass but there is yet a scalable, economical process to extract these valuable constituents. Lignin is the second most abundant biopolymer of lignocellulosic biomass after cellulose. This is the single most abundant source of carbon-neutral organic materials on the planet and contains most of the required compounds to sustain multiple industries including, but not limited to, energy production, chemicals, polymers, food, pharmaceuticals, high strength concrete, various manufacturing and agriculture applications.
There are billions of tons of lignocellulosic biomass being produced by biosynthesis every year. However, economical and scalable processes to efficiently separate the three components of lignocellulosic biomass proves to be a challenge. In order for lignocellulosic biomass to be a strong and legitimate competitor or potentially a complete alternative to fossil fuel petroleum-based products new processes and chemical treatments need to be developed. To benefit from lignocellulosic biomass and to be able to further utilize it in industry, one must be able to separate the lignin from the hemicellulose and the cellulose in an economical, commercially viable process. Cellulose is an abundant, high molecular weight natural polymer that possesses great strength, has high biodegradability and is sustainable. Depending on the feedstock, cellulose can make up from 40 to 60 percent by weight, or in some cases more of the plant material and is found in trees, forestry residue, algae, crops, various plants, municipal and industrial waste.
Furthermore, due to cellulose encasement between lignin and hemicellulose, the efficient and commercially viable extraction of cellulose will depend greatly on the method and biomass source being utilized during the extraction process. Many current and proposed processing methods may limit the use or alter the structural integrity of the cellulose resulting in a marginal yield and excessive processing costs. Most commercial processes begin with already processed pulp, generally from the Kraft process which degrades the biomass in some aspects and requires massive inputs of energy in the form of heat and pressure. A process that requires little to no input of energy and minimal capital expenditure for processing facilities or is able to utilize existing infrastructure is highly desirable. In addition, processes that can utilize feedstock that does not require it to be pre-treated, other than general cleaning/milling, is highly desirable.
It is widely agreed that the technical difficulties in the known current processes are currently inefficient, expensive and difficult to scale. The separation of lignin and hemicellulose from the cellulose in the biomass is what prevents such known technology from being a viable alternative for petroleum-based or fossil fuel products on a global scale or even a localized viable scale. In addition, the desire for these materials in an economical manner from other industries is very large. These include, but are not limited to, pharmaceuticals, food production, cosmetics, manufacturing, chemicals, polymers, and fuels production. Many of the liquid hydrocarbon molecules yielded from biomass can be utilized or processed using much of the current oil & gas global infrastructure such as pipelines, processing facilities, upgraders, along with downstream assets such as gas stations, once the biomass has been converted to fuels. This makes lignocellulosic biomass like wood or straw the only real alternative to hydrocarbons as the next source of energy and sustainable raw materials for the human race that is arguably carbon-neutral or close to carbon-neutral, and that would likely keep much of the current global mid-stream and down-stream energy assets in use and commercially viable while retaining many millions of jobs with minimal economic disruption. Much of these multi-trillion-dollar assets and many millions of jobs globally would be lost with other alternative energy sources such as solar or wind. A viable source of energy from woody biomass would also make the internal combustion engine carbon-neutral thus retaining other global trillion-dollar industries with minimal interruption such as the airline industry, the automotive industry and the many hundreds of ancillary support industries.
The first step in paper production, and most energy-intensive step, is the production of pulp. This is one of the current few large and mature sources of cellulosic material, although it is very inefficient. polluting and energy intensive. Notwithstanding water, wood and other plant materials used to make pulp contain three main components: cellulose; lignin; and hemicellulose. Pulping has a primary goal to separate the fibres from the lignin. In general, cellulose extracted from plant materials contains both amorphous regions and a crystalline regions. Lignin is a three-dimensional crosslinked polymer which figuratively acts as a mortar or binding agent to hold all the fibres together within the plant. Its presence in finished pulp is undesirable and adds no industrial value to the finished product. Pulping wood refers to breaking down the bulk structure of the fibre source, be it chips, stems or other plant parts, into the constituent fibres. The cellulose fibres are the most desired component with regards to paper manufacturing. Hemicelluloses are shorter branched carbohydrate polymers consisting of various monosaccharides which form a random amorphous polymeric structure. The presence of hemicellulose in finished pulp is also regarded as bringing no value to a paper product. This is also true for biomass conversion. The challenges are similar. Only the desired outcome and constituents are different. Optimal biomass conversion would have the further breakdown to monosaccharides as a desired outcome, while the common pulp & paper processes normally stop right after lignin dissolution. With the process taught in this patent, there would be many additional valuable constituents including, but not limited to, microcrystalline cellulose (MCC), nanocrystalline cellulose (NCC) and cellulose nanofibres (CNF) along with other valuable commercial products yielded from the process effluent such as aromatic monomers.
There are two main approaches to processing wood pulp or woody biomass: mechanical treatment and chemical treatment. Mechanical treatment, or pulping, generally consists of mechanically tearing the biomass feedstock apart and, thus, tearing cellulose fibres in an effort to distinctly separate them from each other for further processing. The shortcomings of this approach include: damaged or broken cellulose fibres, thus shorter fibres and lignin being left on the cellulose fibres thus being inefficient or non-optimal for most commercial applications without further, expensive processing. The current process also consumes large amounts of energy, is polluting and is capital intensive. There are several approaches included in chemical pulping. These are generally aimed at the depolymerization of the lignin and hemicellulose into small, water-soluble molecules. These now degraded or processed components can be separated from the cellulose fibres by washing the latter without depolymerizing the cellulose fibres. The current, globally commercialized chemical process is energy intensive requiring high amounts of heat and/or high pressures; in many cases, agitation or mechanical intervention are also required, further adding inefficiencies and costs to the process. With this process, much of the effluent is waste product.
There exist pulping or treatment methods which combine, to a various extent, the chemical aspects of pulping with the mechanical aspects of pulping. To name a few, one must consider thermomechanical pulping (also commonly referred to as TMP), and chemi-thermomechanical pulping (CTMP). Through a selection of the advantages provided by each general pulping method, the treatments are designed to reduce the amount of energy required by the mechanical aspect of the pulping treatment. This can also directly impact the strength or tensile strength degradation of the fibres subjected to these combination pulping approaches and thus the commercial viability. Generally, these approaches involve a shortened chemical treatment times (compared to conventional exclusive chemical pulping) which is then typically followed by mechanical treatment to separate the fibres.
The most common process to make pulp for paper production is the kraft process. In the kraft process, wood chips are converted to wood pulp which is almost entirely pure cellulose fibres. The multi-step kraft process consists of a first step where wood chips are impregnated/treated with a chemical solution. This is done by soaking the wood chips and then pre-heating the wood chips with steam. This step swells the wood chips and expels the air present in the wood chips and replaces the air with the treatment liquid. This produces black liquor, a resultant by-product from the kraft process. It contains water, lignin residues, hemicellulose and inorganic chemicals. White liquor is a strong alkaline solution comprising sodium hydroxide and sodium sulfide. Once the wood chips have been soaked in the various chemical solutions, they undergo cooking. To achieve delignification in the wood chips, the cooking is carried out for several hours at temperatures reaching up to 176° C. At these temperatures, the lignin degrades to yield water soluble fragments. The remaining cellulosic fibres are collected and washed after the cooking step.
U.S. Pat. No. 5,080,756 teaches an improved kraft pulping process and is characterized by the addition of a spent concentrated sulfuric acid composition containing organic matter to a kraft recovery system to provide a mixture enriched in its total sulfur content that is subjected to dehydration, pyrolysis and reduction in a recovery furnace. The organic matter of the sulfuric acid composition is particularly beneficial as a source of thermal energy that enables high heat levels to be easily maintained to facilitate the oxidation and reduction reactions that take place in the furnace, thus resulting in the formation of sulfide used for the preparation of cooking liquor suitable for pulping.
Caro's acid, also known as peroxymonosulfuric acid (H2SO5), is one of the strongest oxidants known and can be explosive in its pure form. There are several known reactions for the preparation of Caro's acid, but one of the most straightforward involves the reaction between sulfuric acid (H2SO4) and hydrogen peroxide (H2O2). Preparing Caro's acid in this method allows one yield in a further reaction of potassium monopersulfate (PMPS) which is a valuable bleaching agent and oxidizer. While Caro's acid has several known useful applications, one noteworthy is its use in the delignification of wood. But because of its reactivity and dangers associated therewith, it is not a preferred approach to treat large volumes of material such as lignocellulosic biomass or feedstock.
Other methods have been developed for pretreating lignocellulosic feedstocks. These pretreatment methods include dilute acid pretreatment, steam explosion (CO2 explosion), pH-controlled water pretreatment, ammonia fibre expansion, ammonia recycle percolation (ARP), and lime pretreatment (Mosier et al. 2005; Wyman et al. 2005; Yang and Wyman 2008). One approach involves the concept of organosolv. Organosolv pulping is the process to extract lignin from lignocellulosic feedstocks with organic solvents or their aqueous solutions. Organosolv pulping has attracted interest since the 1970's because the conventional pulping processes, kraft and sulfite processes, have some serious shortcomings such as air and water pollution. Organosolv pretreatment is similar to organosolv pulping, but the degree of delignification for pretreatment is not expected/required to be as high as that of pulping. However, a drawback of organosolv pre-treatment is the high temperatures at which the processes are known to be carried out at, upwards of 100-250° C., often times in the range of 185-210° C. Such temperatures require high energy inputs.
Improved processes for delignification need to take into account environmental aspects as well as end-product generation. Ambient temperature processes (20-30° C.) are highly desirable as they do not require energy intensive inputs. However, to carry out delignification operations at low temperatures and atmospheric pressure, strong acids are typically required. The strength of the acids used while sufficient to remove lignin present on the lignocellulosic feedstock, can be deleterious to the lignin as it decomposes it beyond any lignin monomers which would be useable in other industries or applications, but can also damage the cellulose being yielded and therefore fail in delivering useable products from said feedstock.
One approach is to modify the acid by incorporating a modifying agent which tempers its reactivity and allows for more controlled/controllable reaction with the lignocellulosic feedstock. According to a preferred embodiment of the present invention, this step will allow for far more control in preventing cellulosic degradation from exposure to the acid systems. However, the presence of a modifying agent will not necessarily prevent the extensive depolymerization of lignin as it is being separated from the cellulose and hemicellulose.
Biofuel production is another potential application for the kraft process. One of the current drawbacks of biofuel production is that it typically requires the use of food grade plant parts (such as seeds) in order to transform the easily accessible carbohydrates into fuel in a reasonably efficient process. The carbohydrates could be obtained from cellulosic fibres, by using non-food grade biomass in the kraft process; however, the energy intensive and destructive nature of the kraft process for delignification makes this a less commercially viable option. In order to build a plant based chemical resource cycle there is a great need for energy efficient processes which can utilize plant-based feedstocks that do not compete with human food sources and which are generally inexpensive to produce.
Research (see HUNTLEY, C. “Influence of Strong Acid Hydrolysis Processing on the Thermal Stability and Crystallinity of Cellulose Isolated from Wheat Straw”, 2014) has shown that extraction of cellulose from an agricultural waste product such as wheat straw using strong acid hydrolysis such as sulfuric and nitric acids will yield similar crystalline and thermal properties as currently reported in the literature. However, the effect of various strong acids on the polymeric, structural, and thermal properties of cellulose extracted from wheat straw impacted the crystallinity of the end product cellulose and it was found to be desirable to use weaker acids where the crystallinity of the final cellulose product is of importance.
In addition to the recovery of cellulose, the recovery of lignin is increasingly important. Most conversion technologies relating to dissolved lignin use heat and metal catalysts to effectively break down lignin into low molecular weight aromatics which hold value for other uses/applications across industry. Some of the considerations to take into account when exploring various processes include: efficiency of the catalysts used; the stability of the catalysts; control of the condensation and repolymerization reactions of lignin. The condensation and repolymerization of lignin often yield products which cannot be broken down easily using the conventional approaches and therefore lose a tremendous amount of value in terms of future uses/applications in industry. The condensation and repolymerization of lignin have a direct impact on the recovery of target lignin products (such as low molecular weight phenolic compounds). Thus, avoiding the condensation and repolymerization reactions is critical in order to maximize the yields of the target products.
The lignin repolymerization has been a substantial concern during many stages of the process of the delignification of lignocellulosic biomass. Conventional fractionation process, namely biomass pretreatment, focuses on its effectiveness to remove lignin from biomass structure, generally employing acid or base catalysts. The resulting residual solid, mainly lignin, significantly undergoes irreversible repolymerization depending on the pretreatment conditions. This is an outcome which must be avoided in order to extract maximum value from a treatment which is geared at recovering both cellulose and lignin for future uses.
While the kraft pulping process is the most widely used chemical pulping process in the world, it is extremely energy intensive and has other drawbacks, for example, substantial odours emitted around pulp producing plants or general emissions that are now being highly regulated in many pulp and paper producing jurisdictions as well as being destructive to many of the commercially important constituents of the plant matter. In light of the current environmental challenges, economic challenges and climatic changes, along with emission fees being implemented by governments, it is highly desirable to optimize the current pulping processes in order to provide at least linear quality fibres without the current substantial detriment to the environment during the production thereof.
Accordingly, there still exists a need for a composition capable of performing delignification on lignocellulosic biomass under reduced temperatures and pressures versus what is currently in use without requiring any major additional capital expenditures and adapted to preserve the lignocellulosic biomass constituents as much as possible for further applications. In addition, when heat and pressure are removed from the process the capital expenditures are greatly reduced as plastics, such as high-density polyethylene (HDPE) can be utilized versus glass lined metals for piping, reactors and associated equipment.
There are two common processes used in the pulp and paper industry to produce pulp out of plant biomass which are the kraft and the sulfite process. Both processes are very energy intensive and produce a large amount of harmful contaminated waste water. There are high temperatures and pressures applied to separate lignin from cellulose. A by-product of these processes is the so-called liquor which contains organic substances that result from partial depolymerization of lignin, hemicellulose and cellulose. These depolymerization products need to be separated from the liquor by distillation or extraction. Another method of separation is the change in solubility by adding another solvent to the liquor in a way that the substances become insoluble and can be filtered out as solids.
European patent EP 2257669 B1 teaches a liquid fractionation composition, comprising: biomass, an ionic liquid, and a fractionation polymer, wherein the composition is bi-phasic and comprises a fractionation polymer rich liquid phase and an ionic liquid rich liquid phase, and wherein the composition is substantially free of water, preferably less than 1 percent by weight water, said composition optionally further comprising a processing aid, catalyst, surfactant, preservative, anti-microbial, or combination thereof. The method of fractioning biomass, is stated to comprise the following steps: a) providing a liquid fractionation composition comprising the biomass, an ionic liquid, and a fractionation polymer, wherein the liquid fractionation composition is substantially free of water and wherein the liquid fractionation composition is mono-phasic at a temperature; and b) adjusting the temperature of said mono-phasic liquid fractionation composition to provide a biphasic composition as claimed in any of claims 1-10, preferably by cooling, e.g. to less than 60° C. wherein a portion of the biomass is fractioned between each phase of the biphasic composition; and optionally c) separating the two phases of the biphasic composition. The reaction step is carried out at temperatures above 80° C. for a duration of 20 hours or more.
U.S. Pat. No. 7,763,715B2 teaches methods for using ionic liquids to extract and separate a biopolymer from a biomass containing the biopolymer are disclosed. Methods for dissolving a biopolymer in an ionic liquid are also disclosed. A recovery solvent is used to reduce the solubility of the biopolymer in the ionic liquid and conventional separation techniques are used to recover the biopolymer. Biopolymers encompassed by the teachings include chitin, chitosan, elastin, collagen, keratin and polyhydroxyalkanoate.
Organosolv is a biomass pretreatment method intended to extract lignin from lignocellulosic biomass in as close to its native state as possible. Whereas the Kraft process yields lignin which can be isolated if desired, its main purpose is to produce pulped cellulose from the biomass. The harsh reaction conditions of kraft pulping cause various side reactions of the lignin, altering its chemical composition compared to native lignin. The more gentle reaction conditions employed in an organosolv process aim to avoid these side reactions as much as possible. In general, the method involves heating the biomass in an aqueous solution of an organic solvent, most commonly an alcohol but others such as tetrahydrofuran (THF) can be used. Optionally, the solution can be made mildly alkaline by the addition of a hydroxide base at a few wt % of the composition. This composition selectively dissolves the lignin, leaving the cellulose and hemicellulose intact. The solution is then separated from the remaining biomass and then the solvent is evaporated to yield the lignin.
Because of its process conditions, Organosolv processes are not meant to depolymerize lignin, rather the conditions are such that the opposite is intended. Organosolv reactions are aimed at isolating lignin in a state which is as close as possible to native lignin. The process according to a preferred embodiment of the present invention is directed to the depolymerization of lignin into smaller molecules. Therefore by its shear intent, the present invention should be considered the diametrical opposite of the common Organosolv process.
One of the drawbacks of the lignin obtained through a kraft delignification or through the sulfite process is largely still polymerized and thus will not be useful in generating small molecules. Pyrolysis, on the other hand, is a method to produce lignin-derived molecules from lignocellulosic biomass. Conventional pyrolysis oil generates aldehydes which can polymerize over time and thus render such bio-oil unstable over time. Most bio-oils generated from pyrolysis have the same drawbacks. Their delignification process yields bio-oil which contains aldehydes, their aldehyde content makes them unstable for long-term storage. Pyrolysis oil also has other drawbacks which include: having a high oxygen content (making them less desirable for combustion in engines); they are largely non-volatile; and they may be corrosive.
In light of the current environmental challenges, economic challenges and climactic changes, along with emission fees being implemented, it is highly desirable to develop pulping processes which take into account those environmental challenges without impacting the price of the end products. Accordingly, there still exists a need for a composition capable of converting biomass (lignin, raw lignocellulosic biomass, or esterified LHDO) into high-value monomeric lignin esters in an efficient and cost effective manner.
According to an aspect of the present invention, there is provided a combined lignin depolymerization and esterification reaction which can treat lignocellulosic biomass to enhance the rate of conversion of lignin to small chemicals derived therefrom. Preferably, the delignification creates a number of lignin fragments which are esterified. This esterification prevents the subsequent condensation of lignin fragments together. This has been noted in the past when biomass is delignified and lignin fragments are obtained, there is a tendency for such lignin fragments to re-join into a condensation reaction and become very difficult to remove and practically unusable for further chemical reactions to obtain useful and valuable chemical derivatives.
According to an aspect of the present invention, there is provided a method which employs an combined lignin depolymerization and esterification reaction-approach as an alternative biomass treatment method with two main objectives: 1) accomplish lignin depolymerization and then esterification of those depolymerized lignin fragments in a single step, and 2) produce new fine chemicals which are otherwise not accessible through a conventional two-step process which includes a modified Caro's acid delignification followed by an esterification reaction.
According to a preferred embodiment of the present invention, highly desirable target molecules of the process include, but are not limited to, vanillate esters (variable types depending on choice of alcohol for reaction (e.g. ethyl or butyl vanillate). Under specific reaction conditions, phthalate esters have also formed. These compounds are in addition to paraben, malonate, succinate and maleate esters which are accessible through either a delignification-esterification pathway and combined delignification-esterification reaction. While the origins of the phthalate esters are unclear, the vanillate esters are derived from coniferyl alcohol, one of the key building blocks of lignin (coumaryl and synapyl alcohols being the other two).
The inventors have surprisingly and unexpectedly found is that vanillate esters are consistently accessible through a combined delignification-esterification reaction-type process according to a preferred embodiment of the present invention. This stands in contrast with the two-step processes disclosed in prior patent applications by the Applicant where such processes employ, in the first step, a modified Caro's acid. One of the main differences between such delignification processes and those proposed as preferred embodiments of the present invention and is that the combined delignification-esterification reaction blend is less aggressively oxidizing the lignin depolymerization products.
Electron-rich aromatic rings are prone to oxidative fragmentation, and under the harsher conditions of delignification using a modified Caro's acid, almost all of the coniferyl alcohol rings and all of the synapyl alcohol rings are fragmented (these fragmentations lead to products such as malonate and maleate). Under the milder reaction conditions of a combined delignification-esterification reaction (hereinafter referred to as CDE reaction) used in the process according to a preferred embodiment of the present invention, a portion of the coniferyl alcohol compounds survive and get converted into vanillate.
Moreover, it is to be noted that a modifier such as those found in the prior filed patent applications by the Applicant regarding modified Caro's acid, are not used in the CDE reaction as it is not required to control the reactivity of the blend and to prevent runaway reactions. Furthermore, it has been found that taurine, one of the preferred modifier for such delignification reactions, is not soluble in alcoholic solutions and would therefore be inert in a CDE reaction blend.
Compared to delignification using a modified Caro's acid delignification, the conditions in CDE reactions need to be milder, especially with respect to peroxide concentration. Higher acid:peroxide ratios gave higher yields of cleaner product, and fewer compounds resulting from degraded aromatic rings.
According to an aspect of the present invention, there is provided a method to perform a controlled delignification of lignocellulosic feedstock and conversion of lignin depolymerization products into at least one ester compound, said method comprising the steps of:
According to another aspect of the present invention, there is provided a method for depolymerizing a lignin-containing material into a mixture comprising: diesters and lignin monomers, where said method comprises the steps of:
According to yet another aspect of the present invention, there is provided a method for depolymerizing a lignin oligomeric material into a mixture comprising: diesters and lignin monomers, where said method comprises the steps of:
According to a preferred embodiment of the present invention, the alcohol is selected from the group consisting of: methanol; ethanol; n-propanol; isopropanol; n-butanol; isobutanol; n-pentanol; neo-pentanol; isopentanol; isoamyl alcohol and mixtures thereof. Preferably, the alcohol is n-butanol.
According to a preferred embodiment of the present invention, the alcohol and the sulfuric acid are present in a molar ratio ranging from 1.8:1 (alcohol:sulfuric acid) to 10:1 (alcohol:sulfuric acid).
According to a preferred embodiment of the present invention, the alcohol and the sulfuric acid are present in a molar ratio ranging from 3:1 (alcohol:sulfuric acid) to 5:1 (alcohol:sulfuric acid).
According to yet another aspect of the present invention, there is provided a one-pot process to delignify and convert lignin into diesters using a lignocellulosic feedstock, said process comprising the steps of:
Preferably, the lignin-derived material forms part of the solubilized lignin and hemicellulose depolymerized organics (LHDO) stream resulting from a delignification of a lignocellulosic biomass through the use of a modified Caro's acid. Preferably, said lignin-hemicellulose depolymerized organics (LHDO) is a composition comprising: a strong acid and said lignin-derived material; said lignin-derived material comprises: lignin monomers (20 to 50 wt. %); lignin depolymerization products (50 to 80 wt. %).
According to a preferred embodiment of the present invention, the alcohol is selected from the group consisting of: methanol; ethanol; n-propanol; isopropanol; n-butanol; isobutanol and mixtures thereof.
According to a preferred embodiment of the present invention, the alcohol and the sulfuric acid are present in a molar ratio ranging from 1.8:1 (alcohol:sulfuric acid) to 10:1 (alcohol:sulfuric acid). Preferably, the alcohol and the sulfuric acid are present in a molar ratio ranging from 3:1 (alcohol:sulfuric acid) to 5:1 (alcohol:sulfuric acid).
According to a preferred embodiment of the present invention, the acid:peroxide ratios can range from 7:1 to 1:3. It has been noted that the higher acid ratio blends favour the production of high value aromatics such as vanillate while the higher peroxide blends have a higher degree of nonspecific degradation. Higher peroxide content is understood to be more likely to breakdown aromatics compounds.
Specific molecules which can be obtained from a combined delignification-esterification reaction according to a preferred embodiment of the present invention include, but are not limited to vanillate esters.
Vanillate esters are highly sought after molecules which can be obtained by combined delignification-esterification reaction process. These esters are not obtained through the Applicant's two-step delignification-esterification method when the delignification step employs a modified Caro's acid. However, vanillate esters are consistently produced from alkali lignin in the combined delignification-esterification reaction blends, and they are very high-value compounds. According to a preferred embodiment of the present invention, the vanillate esters obtained depend on the alcohol used and, as such, they include: methylvanillate; ethylvanillate; propylvanillate; isopropylvanillate; butylvanillate; isobutylvanillate and so on, as well as combinations thereof.
Oxalate diesters are also consistently produced and are unique to the combined delignification-esterification reaction method, and while less valuable, they are still noteworthy.
Other molecules which are consistently produced the combined delignification-esterification reaction according to a preferred embodiment of the present invention include, but are not limited to, malonate, succinate and maleate diesters and parabens. These four compounds are produced in both combined delignification-esterification reaction as well as the two-step delignification-esterification method using a modified Caro's acid, but the former process offers a method for production of these compounds in a single step. There is also evidence indicating that treatment of the condensed aromatic fraction of LHDO with a combined delignification-esterification reaction blend further breaks down the material into additional malonate and paraben, increasing the total recovered yield of these valuable chemicals.
According to a preferred embodiment of the present invention, the acid:alcohol ranges from 1:1.8 to 1:7, with the variability attributable to the acid:peroxide ratio and the importance of maintaining an alcohol concentration of 50-60 wt % of the blend.
According to a preferred embodiment of the present invention, the peroxide and the sulfuric acid are present in a molar ratio ranging from 3:1 (peroxide:sulfuric acid) to 1:10 (peroxide:sulfuric acid). According to a preferred embodiment of the present invention, the peroxide and the sulfuric acid are present in a molar ratio ranging from 1.5:1 (peroxide:sulfuric acid) to 1:10 (peroxide:sulfuric acid). Preferably, the peroxide and the sulfuric acid are present in a molar ratio ranging from 1:3 (peroxide:sulfuric acid) to 1:7 (peroxide:sulfuric acid). More preferably, the peroxide and the sulfuric acid are present in a molar ratio of approximately 1:5 (peroxide:sulfuric acid).
According to a preferred embodiment of the present invention, the peroxide and the alcohol are present in a molar ratio ranging from 1:2.3 (peroxide:alcohol) to 1:20 (peroxide:alcohol). Preferably, the peroxide and the alcohol are present in a molar ratio ranging from 1:5 (peroxide:alcohol) to 1:15 (peroxide:alcohol). More preferably, the peroxide and the alcohol are present in a molar ratio ranging from 1:7 (peroxide:alcohol) to 1:10 (peroxide:alcohol).
According to another aspect of the present invention, there is provided a one-pot process to delignify and convert lignin into diesters using a lignocellulosic feedstock, said process comprising the steps of:
Preferably, the alkylsulfonic acid is selected from the group consisting of: methanesulfonic acid; ethanesulfonic acid; propanesulfonic acid and combinations thereof. Preferably, the arylsulfonic acid is selected from the group consisting of: toluenesulfonic acid; benzenesulfonic acid; and combinations thereof.
According to another preferred embodiment of the present invention, the temperature of the composition prior to the step of exposing it to the lignocellulosic feedstock is below 50° C. Preferably, the temperature of the composition prior to the step of exposing it to the lignocellulosic feedstock is below 40° C. More preferably, the temperature of the composition prior to the step of exposing it to the lignocellulosic feedstock is below 30° C. Most preferably, the temperature of the composition prior to the step of exposing it to the lignocellulosic feedstock is below 25° C.
According to a preferred embodiment of the present invention, the period of time is sufficient to remove at least 90% of the lignin present on said plant material. More preferably, the period of time is sufficient to remove at least 95% of the lignin present on said plant material.
According to a preferred embodiment of the present invention, the method is carried out at ambient temperature. According to a preferred embodiment of the present invention, the method is carried out at atmospheric pressure.
The experiments carried out using an aqueous acidic composition according to a preferred embodiment of the present invention have shown that various lignocellulosic biomass components (such as wood chips, straw, alfalfa, etc.) can undergo delignification under controlled reaction conditions and eliminate or at least minimize the degradation and/or depolymerization of the cellulose as well as provide lignin depolymerization products which are soluble (i.e. separated from cellulose). Degradation is understood to mean a darkening of cellulose, which is symbolic of an uncontrolled acid attack on the cellulose and staining thereof.
In the disclosed methods and compositions, biomass is used and/or fractioned. The term “biomass,” or “lignocellulosic biomass” as used herein, refers to living or dead biological material that can be used in one or more of the disclosed processes. Biomass can comprise any cellulosic or lignocellulosic material and includes materials comprising cellulose, and optionally further comprising hemicellulose, lignin, starch, oligosaccharides and/or monosaccharides, biopolymers, natural derivatives of biopolymers, their mixtures, and breakdown products (e.g., metabolites). Biomass can also comprise additional components, such as protein and/or lipids. Biomass can be derived from a single source, or biomass can comprise a mixture derived from more than one source. Some specific examples of biomass include, but are not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, sludge from paper manufacture, yard waste, wood and forestry waste. Additional examples of biomass include, but are not limited to, corn grain, corn cobs, crop residues such as corn husks, alfalfa, corn stover, grasses, wheat, wheat straw, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees (e.g., pine), branches, roots, leaves, wood chips, wood pulp, sawdust, shrubs and bushes, vegetables, fruits, flowers, animal manure, multi-component feed, and crustacean biomass (i.e., chitinous biomass).
According to a preferred embodiment of the present invention, the lignin breakdown products obtained through the delignification of lignocellulosic feedstock (or biomass) by the methods and process disclosed herein include but are not limited to: lignin monomers; lignin oligomers; lignin breakdown products such as esters derived from: vanillic acid; malonic acid; oxalic acid; succinic acid; maleic acid; and 4-hydroxybenzoic acid.
Carrying out delignification of lignocellulosic biomass using a method according to a preferred embodiment of the present invention provides for several advantages, including but not limited to: increase in the rates of reaction by shifting the equilibrium chemical reaction towards the product side; reducing the overall process time; and allow more facile separation of potential products which are not water-soluble but which are soluble in an organic solvent. Additional advantages of the present invention will be set forth in part in the description that follows, and in part will be obvious from the description, or can be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.
The composition according to a preferred embodiment of the present invention used in the delignification test was prepared by preparing a modified acid comprising: an acid selected from the group consisting of: sulfuric acid; an alkylsulfonic acid; and an arylsulfonic acid; a source of peroxide; and an alcohol selected from the group consisting of C1-C6 linear alcohol and C3-C6 branched alcohol.
The compositions were clear with densities ranging between 0.9 and 1.8 g/cm3.
When performing delignification of wood using a composition according to a preferred embodiment of the present invention, the process can be carried out at substantially lower temperatures than temperatures used in the conventional kraft pulping process. The advantages are substantial, here are a few: the kraft pulping process requires temperatures in the vicinity of 176-180° C. in order to perform the delignification process, a preferred embodiment of the process according to the present invention can delignify wood at far lower temperatures, even as low as 20° C. According to a preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 30° C. According to another preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 40° C. According to yet another preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 50° C. According to yet another preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 60° C. Other advantages include: a lower input of energy; reduction of emissions and reduced capital expenditures; reduced maintenance; lower shut down/turn around costs; also, there are HSE advantages compared to conventional kraft pulping compositions.
In each one of preferred embodiments disclosed herein, the temperature at which the processes are carried out are substantially lower than the current energy-intensive kraft process.
Moreover, the kraft process uses high pressures to perform the delignification of wood which is initially capital intensive, dangerous, expensive to maintain and has high associated turn-around costs. According to a preferred embodiment of the present invention, the delignification of wood can be performed at atmospheric pressure. This, in turn, circumvents the need for highly specialized and expensive industrial equipment such as pressure vessels/digestors. It also allows the implementation of delignification units in many of parts of the world where the implementation of a kraft plant would previously be impracticable due to a variety of reasons.
Some of the advantages of a process according to a preferred embodiment of the present invention, over a conventional kraft process are substantial as the heat/energy requirement for the latter is not only a great source of pollution but is, in large part, the reason the resulting pulp product is so expensive and has high initial capital requirements. The energy savings in the implementation of a process according to a preferred embodiment of the present invention would be reflected in a lower priced pulp and environmental benefits which would have both an immediate impact and a long-lasting multi-generational benefit for all.
Further cost savings in the full or partial implementation of a process according to a preferred embodiment of the present invention, can be found in the absence or minimization of restrictive regulations for the operation of a high temperature and high-pressure pulp digestors.
According to a preferred embodiment of the present invention, the acidic composition is selected from the group consisting of:
According to a preferred embodiment of the present invention, the use of an acidic composition on lignocellulosic feedstock achieves two goals: it delignifies the feedstock yielding solid cellulose fibers separated from dissolved lignin breakdown products and it allows for easier separation of contaminants found in the liquid phase prior to treatment for biofuel production. Preferably, the reaction of lignocellulosic feedstock with an acidic composition according to a preferred embodiment of the present invention allows for the conversion of several lignin breakdown products into valuable ester or diester compounds such as, but not limited to, diethyl malonate; diethyl maleate; diethyl succinate; and diethyl oxalate.
Preferably, the reaction using an acidic composition on lignocellulosic feedstock allows for easier separation of contaminants found in the liquid phase prior to treatment for biofuel production. The treated effluent from the delignification reaction according to a preferred embodiment of the present invention, will contain very little sulfur compounds and very little nitrogen containing compounds which are both contaminants when upgrading lignin to a biofuel. Also largely removed are acidic compounds which are detrimental to biofuel.
All yields of combined delignification-esterification reaction reactions are reported as weight percentages of the original lignin (or LHDO) starting mass, following workup and purification using column chromatography. The yields are further divided into three categories: diesters, aromatics, and total yield.
The diester yield is the weight percentage of initial lignin that was converted into aliphatic diester compounds (malonate, maleate, succinate, oxalate, and others) and isolated as such from the column. The aromatics yield is the weight percentage of initial lignin that was converted into monomeric aromatic compounds (vanillate and paraben) and isolated as such from the column. The total yield is the combination of these two plus the remaining uncharacterized material recovered during the flush stage of column purification. This material from the flush stage is equivalent to what is referred to as the heavy phase or high molecular weight phase of LHDO.
H2SO4 (0.67-7 molar equivalents) was added to a round bottom flask containing a magnetic stir bar, and then the flask was placed in an ice bath on a heating stir plate. Ethanol (EtOH) (5-20 molar equivalents) was added slowly with stirring, after which the mixture was left stirring in the ice bath for five minutes to cool, and then a source of peroxide (H2O2) (1 molar equivalent) was slowly added. The ice bath was removed, and then the biomass (1-5 wt %) was added. The mixture was placed in an oil bath on the heating stir plate and an air condenser was attached to the flask. The mixture was heated to 60° C. and then stirred for 16 hours.
Part 2a—Workup for Lignin Reactions
After the reaction was complete, the flask was removed from the oil bath and left to cool for 15 minutes. Ethanol was then removed using a rotavap, and then the residue was transferred to a separatory funnel. Water and ethyl acetate were added, and the product was extracted into the ethyl acetate phase. The ethyl acetate was collected, and then the aqueous phase was extracted two additional times with fresh ethyl acetate. The organic extracts were combined and then transferred back into the separatory funnel, where they were washed with a pH in the range of 5.5 to 6.5 (preferably pH 6) bicarbonate buffer solution. The ethyl acetate layer was collected, and the buffer solution was extracted an additional time with fresh ethyl acetate. The organic layers were combined, dried over MgSO4, filtered, and then the solvent was removed on the rotavap. The residue was then purified using silica gel chromatography using hexanes and ethyl acetate in a gradient from 95/5 to 75/25 hexanes/ethyl acetate, followed by flushes with ethyl acetate and methanol. According to another preferred method, the buffer is a pH 2 bisulfate buffer solution. Preferably, the bisulfate buffer can range between pH 1.5 and 2.5.
Desired fractions were then collected, the solvent was removed on the rotavap, and then yields were measured.
Part 2b—Workup for Wood Fiber Reactions
After the reaction was complete, the flask was removed from the oil bath and left to cool for 15 minutes. The mixture was then filtered through a P8 filter paper to collect the cellulose. The cellulose was rinsed with additional ethanol, collected, and dried in a 45° C. oven overnight. The filtrate was transferred to a roundbottom flask, and then ethanol was then removed using a rotavap. The residue was then transferred to a separatory funnel, and water and ethyl acetate were added. The product was extracted into the ethyl acetate phase, after which the ethyl acetate was collected, and then the aqueous phase was extracted two additional times with fresh ethyl acetate. The organic extracts were combined and then transferred back into the separatory funnel, where they were washed with a pH 6 bicarbonate buffer solution. The ethyl acetate layer was collected, and the buffer solution was extracted an additional time with fresh ethyl acetate. The organic layers were combined, dried over MgSO4, filtered, and then the solvent was removed on the rotavap. The residue was then purified using silica gel chromatography using hexanes and ethyl acetate in a gradient from 95/5 to 75/25 hexanes/ethyl acetate, followed by flushes with ethyl acetate and methanol. Desired fractions were then collected, solvent was removed on the rotavap, and then yields were measured. According to another preferred method, the buffer is a pH 2 bisulfate buffer solution. Preferably, the bisulfate buffer can range between pH 1.5 and 2.5.
The data summarized in table 1 indicates that upon exposure to a composition according to a preferred embodiment of the present invention, the lignin treated at 60° C. for 16 hours yielded over 2% diester compounds in every reaction. These reactions also yielded in all cases less than 2% of aromatics while the sum total of lignin monomers (diesters and aromatic esters) and partially degraded lignin oligomers yield ranged from 23% to over 57%.
The data summarized in table 2 indicates that upon exposure to a composition according to a preferred embodiment of the present invention, the lignin treated at either 60° C. or 90° C. for 16 hours yielded over 4.5% diester compounds in over half of the reactions carried out. These reactions also yielded in all cases less than 3% of aromatics while sum total of lignin monomers (diesters and aromatic esters) and partially degraded lignin oligomers yield ranged from close to 44% to over 60%. The total yield further comprises partially depolymerized lignin present as condensed rings of 2 to 5 or 6 units.
The data summarized in table 3 indicates that upon exposure to a composition according to a preferred embodiment of the present invention, the alkali lignin treated at 60° C. for 48 hours yielded over 4.8% diester compounds in the reactions carried out. These reactions also yielded in all cases less than 2% of aromatics while the sum total of lignin monomers (diesters and aromatic esters) and partially degraded lignin oligomers yield ranged from over 44% to over 62%.
The data summarized in table 4 indicates that upon exposure to a composition according to a preferred embodiment of the present invention, the hardwood fibers treated at 60° C. for 16 hours yielded over 2% diester compounds in the reactions carried out. These reactions also yielded, in all cases, less than 1.5% of aromatics while the sum total of lignin monomers (diesters and aromatic esters) and partially degraded lignin oligomers yield was more than 11% of the initial mass of fibers. As lignin forms only a fraction of the initial mass of the fiber which was treated, this roughly corresponds to between 30 and 45% of the total lignin initially present in the fibers which were treated. It is worth noting that the cellulose yield was quite high and is believed to provide over 90% recovery of the cellulose originally present in the hardwood tested. This would confirm that the method according to a preferred embodiment of the present invention provides both conversion of lignin depolymerization products, esterified compounds and cellulose in a one-step process.
The data summarized in tables 5 and 6 indicates that upon exposure to a composition according to a preferred embodiment of the present invention, the alkali lignin provided very good yields in terms of diester, aromatics and overall total yield where, in most cases, the total yield was above 60% and also quite often, above 70%.
It is to be noted that some of the loss of product can occur as follows: polar compounds which are water soluble, thus unrecovered in the organic phase; product loss during the workup, purification and in the column.
According to a preferred embodiment of the present invention, after the removal of the various esterified compounds (such as, but not limited to, diester compounds) present after the delignification reaction, the lignin breakdown compound stream will have a higher carbon:oxygen ratio which is highly desirable when carrying out hydrodeoxygenation reactions to yield usable biofuel.
According to a preferred embodiment of the method of the present invention, the method yielded bio-oil with a relatively low viscosity of 100 to 150 cP at RT which differentiates it from pyrolysis oil. The viscosity is an indication of the lower molecular weight or the lower number of condensed rings up to e.g. 6, which is highly desirable for upgrading as well.
The embodiments described herein are to be understood to be exemplary and numerous modification and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the claims appended hereto, the invention may be practiced otherwise than as specifically disclosed herein.
All publications, patents, patent applications and other documents cited in this application, including priority document CA3208516, are hereby incorporated by reference in their entireties for all purposes to the same extent as if each individual publication, patent, patent application or other document were individually indicated to be incorporated by reference for all purposes.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3208516 | Aug 2023 | CA | national |
