COMBINATION APPROACH TO DELIGNIFICATION OF BIOMASS UNDER AMBIENT CONDITIONS

Abstract

Method of delignification of plant material, said method comprising: providing said plant material comprising cellulose fibres and lignin; exposing said plant material requiring to a composition comprising: an acid; a modifying agent selected from the group consisting of: sulfamic acid; imidazole; N-alkylimidazole derivative; taurine; a taurine derivative; a taurine-related compound; alkylsulfonic acid; arylsulfonic acid; triethanolamine; and combinations thereof; a metal oxide; and a peroxide; adding an organic solvent to the resulting mixture; allowing a delignification reaction to occur for a period of time sufficient to remove at least 80% of the lignin present on said plant material.

Claims

1. Method of delignification of plant material, said method comprising: providing said plant material comprising cellulose fibres and lignin; exposing said plant material requiring delignification to a composition comprising: an acid; a modifying agent selected from the group consisting of: sulfamic acid; imidazole; N-alkylimidazole; taurine; a taurine derivative; a taurine-related compound; alkylsulfonic acid; arylsulfonic acid; triethanolamine; and combinations thereof; a metal oxide; and a peroxide; adding an organic solvent to the resulting mixture; allowing a delignification reaction to occur for a period of time sufficient to remove at least 80% of the lignin present on said plant material.

2. The method according to claim 1, wherein the taurine derivative or taurine-related compound is selected from the group consisting of: taurolidine; taurocholic acid; tauroselcholic acid; tauromustine; 5-taurinomethyluridine and 5-taurinomethyl-2-thiouridine; homotaurine (tramiprosate); acamprosate; and taurates.

3. The method according to claim 1, where said alkylsulfonic acid is selected from the group consisting of: alkylsulfonic acids where the alkyl groups range from C1-C6 and are linear or branched; and combinations thereof.

4. The method according to claim 1, wherein the alkylsulfonic acid is selected from the group consisting of: methanesulfonic acid; ethanesulfonic acid; sulfamic acid and combinations thereof.

5. The method according to claim 1, wherein the arylsulfonic acid is selected from the group consisting of: orthanilic acid; metanilic acid; sulfanilic acid; toluenesulfonic acid; 2,5-diaminobenzene sulfonic acid; benzenesulfonic acid; and combinations thereof.

6. The method according to claim 1, wherein the metal oxide is selected from the group consisting of: SiO.sub.2; TiO.sub.2; Al.sub.2O.sub.3; and combinations thereof.

7. The method according to claim 1, wherein the organic solvent is selected from the group consisting of: toluene; iso-octane; hexanes; xylene; and combinations thereof.

8. The method according to claim 1, wherein the acid and the metal oxide are present in a molar ratio ranging from 1:1 to 100:1.

9. The method according to claim 1, wherein the acid and the modifying agent are present in a molar ratio ranging from 1:1 to 10:1.

10. The method according to claim 1, wherein the acid is sulfuric acid.

11. The method according to claim 1, wherein the acid and said modifying agent are present in a molar ratio ranging from 28:1: to 2:1.

12. The method according to claim 1, wherein the period of time is sufficient to remove at least 95% of the lignin present on said plant material.

13. A one-pot process to separate lignin from a lignocellulosic feedstock, said process comprising the steps of: providing a vessel; providing said lignocellulosic feedstock comprising cellulose fibres and lignin; exposing said plant material requiring delignification to a composition comprising: an acid; a modifying agent; a metal oxide; and a peroxide; adding an organic solvent to the resulting mixture; exposing said lignocellulosic feedstock to said composition in said vessel for a period of time sufficient to remove substantially all (at least 80%) of the lignin present said lignocellulosic feedstock; optionally, separating and removing a liquid phase from a solid phase comprising cellulose fibres, said liquid phase comprising said water immiscible solvent.

14. The process according to claim 13, wherein said modifying agent selected from the group consisting of: sulfamic acid; imidazole; N-alkylimidazole derivative; taurine; a taurine derivative; a taurine-related compound; alkylsulfonic acid; arylsulfonic acid; triethanolamine; and combinations thereof.

15. The process according to claim 13, wherein the temperature of the composition prior to the step of exposing it to the lignocellulosic feedstock is below 50° C.

16. The process according to claim 13, wherein the metal oxide is selected from the group consisting of: SiO.sub.2; TiO.sub.2; Al.sub.2O.sub.3; and combinations thereof.

17. The process according to claim 13, wherein the organic solvent is selected from the group consisting of: toluene; iso-octane; hexanes; xylene and combination.

18. The process according to claim 13, wherein the acid and the metal oxide are present in a molar ratio ranging from 1:1 to 100:1.

19. The process according to claim 13, wherein the acid and the modifying agent are present in a molar ratio ranging from 1:1 to 10:1.

20. The process according to claim 13, wherein the acid is sulfuric acid.

21. The process according to claim 13, wherein the acid and said compound containing an amine group are present in a molar ratio ranging from 28:1: to 2:1.

22. The process according to claim 13, wherein the period of time is sufficient to remove at least 90% of the lignin present on said plant material.

Description

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0092] 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.

[0093] 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).

EXAMPLES

[0094] The composition according to a preferred embodiment of the present invention used in the delignification test was prepared by preparing a modified acid comprising taurine and sulfuric acid. This modified acid was prepared by dissolving 1 molar equivalent of taurine into sulfuric acid and subsequently adding hydrogen peroxide.

[0095] 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 “on-the-fly” 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.

[0096] According to a preferred embodiment of the method of the present invention, a composition comprising sulfuric acid:taurine:hydrogen peroxide in a 5.0:1.0:5.0 molar ratio is used. The resulting pH of the composition is less than 1. Preferably, the resulting pH of the composition was less than 0.5. According to another preferred embodiment of the method of the present invention, a composition comprising sulfuric acid:taurine:hydrogen peroxide in a 10:1.0:10 molar ratio is used. The resulting pH of the composition is less than 1. Preferably, the resulting pH of the composition was less than 0.5.

[0097] The compositions were clear and odorless with densities ranging between 1.1 and 1.8 g/cm.sub.3.

[0098] 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.

[0099] In each one of the above preferred embodiments, the temperature at which the processes are carried out are substantially lower than the current energy-intensive kraft process.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] A 2 immiscible liquids phase system can increase reaction rates when compounds are exposed to two non-miscible solvents that retain the feed material and reaction products differentially. For these biomass reactions, an aqueous “reaction phase” is used to hold all of the initial components and the feedstock, which in this case pertains to the plant biomass and the acid/peroxide mixture. Once the degradation reaction has started, the products are transferred into the non-reactive “holding phase”. Preferably, vigorous agitation is used to increase contact between the two phases and so to maximize transfer of reaction products which are soluble in the holding phase. Removing reaction products “on the fly” during the reaction can reduce the overall processing time as potential equilibrium reactions are pushed towards the product side. The cellulose is not soluble in either of the liquid phases and solid residuals can be filtered off at the end of the reaction process.

Experiments

[0104] Experiments were carried out using various organic solvents to determine whether the delignification reaction could be improved by having a 2-phase system which would allow dissolved lignin fragments to migrate into an organic (holding) phase and allow to push the reaction in the aqueous phase towards increased delignification and/or faster delignification.

[0105] Several solvents were selected to provide a holding phase for dissolved lignin fragments. Among the solvents tested, there was toluene, ethyl acetate, octanoic acid; iso-octane, hexanoic acid and nitrobenzene. Experiments involving the latter two solvents could not be completed as there was reaction between the acidic composition and the organic solvent which contaminated the reaction medium.

[0106] The experiments with the remaining solvents were carried out at room temperature under atmospheric pressure. The duration of the experiments was scheduled to be around 3 hours. The goal of the experiments was to assess the viability of each solvent to be part of a 2-phase system with an aqueous acid medium.

[0107] Commercially available lignin (Sigma-Aldrich; Lignin, kraft; Prod #471003) was also used as a control in the testing.

[0108] Commercially available cellulose (Sigma-Aldrich; Cellulose, fibres (medium); Prod #C.sub.6288) was also used as a control in the testing.

[0109] The use of lignin and cellulose controls allow the determination of the extent of reaction of the composition when exposed to a lignocellulosic material, in this case, wood shavings. This allows one to assess whether the composition tested is too reactive against cellulose or not sufficiently reactive enough to dissolve all of the pure lignin control.

[0110] The first set of experiments carried out was a control where there was no organic phase present in the reaction vessel. Hence, this control would allow to determine the increase in efficiency (if any) by using an approach according to the present invention. Each composition is exposed to a wood sample, a lignin control and a cellulose control.

[0111] Table 1 displays the results of a series of 3 control experiments where there are varying ratios of sulfuric acid, hydrogen peroxide and modifying agent (taurine) but where there is no holding phase (organic phase).

TABLE-US-00001 TABLE 1 Control Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in various ratios at room temperature and atmospheric pressure Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) 1:3:0 78.07 48.12 89.47 2:6:1 84.12 51.17 94.87 3:9:1 83.76 53.75 92.82

Delignification Reaction Using a Two-Phase System

[0112] Tables 2, 3, 4, 5 and 6 displays the results of a series of control experiments where there are varying ratios of sulfuric acid, hydrogen peroxide and modifying agent (taurine) in the presence of a 2-phase system (organic phase and aqueous phase). Table 2 provides the results of experiments carried out using toluene as the organic phase. Table 3 provides the results of experiments carried out using iso-octane as the organic phase. Table 4 provides the results of experiments carried out using xylene as the organic phase. Table 5 provides the results of experiments carried out using hexane as the organic phase. Table 6 provides the results of experiments carried out using HT-40 as the organic phase.

TABLE-US-00002 TABLE 2 Control Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in various ratios at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of toluene in a 1:1 weight ratio) 1:1 wt:wt Aq:toluene Blend recovery [mass %] H2SO4 H2O2 Taurine (moles) wood lignin cellulose 1 3 0 1:3:0 78.06 52.31 90.41 2 6 1 2:6:1 87.16 57.5 90.65 3 9 1 3:9:1 76.32 50.83 91.4

TABLE-US-00003 TABLE 3 Control Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in various ratios at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of iso-octane in a 1:1 weight ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) 2:6:1 92 63 100 3:9:1 70 41 93 10:10:1 47.69 31.73 99.02

TABLE-US-00004 TABLE 4 Control Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in various ratios at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of xylene in a 1:1 weight ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) 2:6:1 85.0 57.7 99.2 3:9:1 65.2 59.7 99.9 10:10:1 52.17 10.79 93.6

TABLE-US-00005 TABLE 5 Control Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in various ratios at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of hexane in a 1:1 weight ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) 2:6:1 79.8 60.8 99.2 3:9:1 71.0 58.9 99.6 10:10:1 50.01 7.36 96.37

TABLE-US-00006 TABLE 6 Control Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in various ratios at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of HT-40 in a 1:1 ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) 10:10:1 63.1 51.3 97.4

[0113] The results obtained and tabulated in the above series of experiments using a 2-phase system indicate that even at a ratio of 10:10:1 of sulfuric acid:peroxide:modifying agent, none of the 2-phase systems were capable of dissolving all of the lignin in the control sample. This is an indication that the delignification reaction does not go to completion and would not yield lignin-free pulp. The pulp obtained could still be used in applications where the presence of lignin is not detrimental to the end product such as packaging, for example. However, for higher value products the presence of lignin is not desirable.

[0114] To perform a delignification process at ambient temperature and at atmospheric pressure, it is desirable to limit the amount of peroxide used in the process as it is the most expensive reagent. In the various ratios tested 2:6:1 and 3:9:1, while some of the results may be good (in some cases) in terms of delignification, it is desirable to aim for a lower peroxide content. The 10:10:1 ratio of H.sub.2SO.sub.4:peroxide:modifying agent seems to provide a good reaction all the while not using too much peroxide as to make the reactions too expensive.

Delignification Reaction Using a Metal Oxide

[0115] Further investigations were carried out to determine the impact of a metal oxide in a similar process as the one set out in the above section.

[0116] Preferably, the metal oxide is incorporated into the aqueous acid composition to activate the peroxide and increase the lignin depolymerization reactions. This allows one to use less peroxide than would typically have to be used and thus lowers the costs of operations. Preferably, said metal oxide is a chemical compound selected from the group consisting of: titanium oxide; iron oxide; zinc oxide; aluminum oxide; silicon dioxide; tin oxide; bismuth oxide; tungsten oxide; zirconium/yttrium oxide and combinations thereof. Preferably said metal oxide is capable of regenerating the source of peroxide when present in a molar ratio ranging from 1:1 to 1:100 of metal oxide to peroxide.

[0117] Table 7 displays the results of a series of control experiments where there are varying ratios of sulfuric acid, hydrogen peroxide and modifying agent (taurine) in the presence of various metal oxides.

TABLE-US-00007 TABLE 7 Control Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide, a modifying agent in the presence of a metal oxide in various ratios at room temperature and atmospheric pressure Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) SiO.sub.2 (10:10:3:1) 43 0 86 SiO.sub.2 (10:10:1:1) 48.89 0 84.5 TiO.sub.2 (10:10:3:1) 31 0 74 TiO.sub.2 (10:10:1:1) 28.17 0 72.03 Al.sub.2O.sub.3 (10:10:1:1) 48 0 84

[0118] The results obtained and tabulated in the above series of experiments indicate that, at a ratio of 10:10:3:1 and 10:10:1:1 of sulfuric acid:peroxide:modifying agent:metal oxide, despite dissolving all of the lignin (in the control sample), the process can still be optimized. The cellulose control indicates that the values of remaining cellulose after reaction vary between 72% and 86%. Minimizing the loss of cellulose in the control sample would indicate that the delignification reaction is more selective and that, ultimately, the yield from the wood samples would be greater.

Combination of Two-Phase and Metal Oxides

[0119] A series of experiments involving the combination of a 2-phase system in the presence of a metal oxide was conducted in order to assess whether it could overcome some of the drawbacks encountered when using a single one of those two approaches to enhance delignification using a sulfuric acid:peroxide; modifying agent composition. The results of the experiment is found in Tables 8 to 11 below.

TABLE-US-00008 TABLE 8 Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in the presence of a metal oxide (in a 10:10:1:1 ratio) at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of toluene in a 1:1 weight ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) SiO.sub.2 (10:10:1:1) 41.75 0 94.94 TiO.sub.2 (10:10:1:1) 34.84 0 84.31 Al.sub.2O.sub.3 (10:10:1:1) 41.18 0 98.06

TABLE-US-00009 TABLE 9 Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in the presence of a metal oxide (in a 10:10:1:1 ratio) at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of iso-octane in a 1:1 weight ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) SiO.sub.2 (10:10:1:1) 43.01 0 95.85 TiO.sub.2 (10:10:1:1) 41.23 0 94 Al.sub.2O.sub.3 (10:10:1:1) 42.05 0 90.8

TABLE-US-00010 TABLE 10 Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in the presence of a metal oxide (in a 10:10:1:1 ratio) at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of xylenes in a 1:1 weight ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) SiO.sub.2 (10:10:1:1) 63.7 19.2 99.3 TiO.sub.2 (10:10:1:1) 36.8 12.5 106.2 Al.sub.2O.sub.3 (10:10:1:1) 57.6 16.4 97.4

TABLE-US-00011 TABLE 11 Experiments of delignification of lignocellulosic feedstock using sulfuric acid, hydrogen peroxide and a modifying agent in the presence of a metal oxide (in a 10:10:1:1 ratio) at room temperature and atmospheric pressure with a two-phase system (aqueous phase and an organic phase made up of hexanes in a 1:1 weight ratio) Wood Lignin Cellulose Ratio (yield %) (yield %) (yield %) SiO.sub.2 (10:10:1:1) 47.7 15.9 100.6 TiO.sub.2 (10:10:1:1) 32.3 18.8 95.8 Al.sub.2O.sub.3 (10:10:1:1) 35.1 10.2 81.3

[0120] Based on the data collected above, a method according to a preferred embodiment of the present invention comprising a 2-phase system, preferably using iso-octane as hydrophobic solvent, and a metal oxide does provide a clear advantage over a similar delignification method using either only a 2-phase system or only a metal oxide.

[0121] According to a preferred embodiment of the method of the present invention, the separation of lignin can be realized and the resulting cellulose fibres can be further processed to yield glucose monomers. Glucose chemistry has a multitude of uses including as a starting block in the preparation of widely used chemicals, including but not limited to, diacetonide, dithioacetal, glucoside, glucal and hydroxyglucal to name but a few.

[0122] 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.