NOVEL APPROACH TO BIOMASS DELIGNIFICATION

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; taurine; a taurine derivative; a taurine-related compound; alkylsulfonic acid; aryl sulfonic acid; triethanolamine; and combinations thereof; a metal salt; and a peroxide; for a period of time sufficient to remove substantially all (at least 80%) of the lignin present on said plant material.

Claims

1. 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 salt; and a peroxide.

2. The composition according to claim 1, wherein the alkysulfonic acid is selected from the group consisting of: methanesulfonic acid; ethanesulfonic acid; propanesulfonic acid and combinations thereof.

3. The composition according to claim 1, wherein the arylsulfonic acid is selected from the group consisting of: orthanilic acid; metanilic acid; sulfanilic acid; benzenesulfonic acid; and toluenesulfonic acid; and combinations thereof.

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

5. The composition according to claim 1, wherein the acid and the metal salt are present in a molar ratio ranging from 1:1 to 100:1.

6. The composition according to claim 1, wherein the acid and the metal salt are present in a molar ratio ranging from 20:1 to 100:1.

7. The composition according to claim 1, wherein the metal salt is selected from the group consisting of: a metal sulfate; a metal chloride; and combinations thereof.

8. The composition according to claim 1, wherein the metal salt is a metal sulfate selected from the group consisting of: ferrous sulfate; copper sulfate; and combinations thereof.

9. The composition according to claim 1, wherein the metal chloride is selected from the group consisting of: iron (II) chloride; copper (II) chloride; and combinations thereof.

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

11. The composition according to claim 1, wherein the acid and the modifying agent are present in a molar ratio ranging from 1:1 to 5:1.

12. The composition according to claim 1, wherein the acid and the modifying agent are present in a molar ratio ranging from 1:1 to 3:1.

13. The composition according to claim 1, wherein the acid is sulfuric acid.

14. A one-pot process to separate lignin from a lignocellulosic feedstock, said process comprising the steps of: providing a vessel; providing said lignocellulosic feedstock; providing 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; alkyl sulfonic acid; aryl sulfonic acid; triethanolamine; and combinations thereof; a metal salt; and a peroxide; 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, removing a liquid phase comprising dissolved lignin fragments from a solid phase comprising cellulose fibres.

15. The process according to claim 14, wherein the period of time is sufficient to remove at least 90% of the lignin present on said plant material.

16. The process according to claim 14, wherein said acid is sulfuric acid.

17. The process according to claim 14, wherein the alkysulfonic acid is selected from the group consisting of: methanesulfonic acid; ethanesulfonic acid; sulfamic acid and combinations thereof.

18. The process according to claim 14, wherein the arylsulfonic acid is selected from the group consisting of: toluenesulfonic acid; benzenesulfonic acid; and combinations thereof.

19. The process according to claim 14, wherein said peroxide is hydrogen peroxide.

20. The process according to claim 14 where the taurine derivative or taurine-related compound is selected from the group consisting of: sulfamic acid; taurolidine; taurocholic acid; tauroselcholic acid; tauromustine; 5-taurinomethyluridine and 5-taurinomethyl-2-thiouridine; homotaurine (tramiprosate); acamprosate; and taurates.

21. The process according to claim 14, wherein the initial temperature of the composition prior to the step of exposing it to the lignocellulosic feedstock is below 50° C.

22. The process according to claim 14, wherein the metal salt is selected from the group consisting of: a metal sulfate; a metal chloride; and combinations thereof.

23. A one-pot process to separate lignin from a lignocellulosic feedstock, said process comprising the steps of: providing a vessel; providing said lignocellulosic feedstock; providing a composition comprising; an acid; a modifying agent comprises a compound containing an amine group and a compound comprising a sulfonic acid moiety. a metal salt; and a peroxide; 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, removing a liquid phase comprising dissolved lignin fragments from a solid phase comprising cellulose fibres.

Description

DESCRIPTION OF THE INVENTION

[0100] The experiments carried out using an aqueous acidic composition according to a preferred embodiment of the present invention has shown that wood chips can undergo delignification under controlled reaction conditions and eliminate, or at least minimize, the degradation of cellulose as well as provide lignin depolymerization products which are soluble (i.e. separated from cellulose). Degradation of cellulose is understood to mean a darkening of cellulose, which is symbolic of an uncontrolled acid attack on the cellulose and oxidization thereof.

[0101] It is desirable to do so for many reasons. First, the lignin oligomers and/or monomers, because of their multiple aromatic structures, are desirable compounds to extract from the lignocellulosic biomass with as little degradation as possible. Second, the removal of lignin from the wood structure and away from the cellulose is the goal of any pulping process. Excess depolymerization of the lignin is quite unnecessary at this stage, so long as it has been separated from the cellulose. Third, the separation of lignin oligomers and/or monomers from the biomass is preferably carried out under atmospheric pressure and room temperature or close thereto. Most of the current wide scale commercialized delignification processes require high temperatures and pressurized conditions and/or utilize very hazardous and potentially polluting processes and are not feasible for economic, large industrial scale production. These types of conditions require energy inputs to reach the high temperatures as well as specialized equipment to contain the high pressures, both of which are sources of considerable expenditures and costly maintenance along with the other negatives.

[0102] According to a preferred embodiment of the present invention, there is a composition comprising an acid; a source of peroxide (includes all forms of peroxide, i.e. hydrogen peroxide, peroxide salts (organic and inorganic), peroxoacids etc.); and a metal salt which when used during a process to delignify biomass can achieve results of complete removal of lignin with loss of only 20% of the cellulose fibre mass under conditions of atmospheric pressure and room temperature conditions. Preferably, the process can yield cellulose with only a 15% loss in the fibre mass. More preferably, the process can yield cellulose with only a 10% loss in the fibre mass. Even more preferably, the process can yield cellulose with only a 5% loss in the fibre mass.

Examples

[0103] The composition according to a preferred embodiment of the present invention used in the delignification test was prepared by dissolving 1 molar equivalent of taurine into 10 moles of sulfuric acid. After this step was completed, a metal salt was added in the required amount to the composition. Subsequently, hydrogen peroxide was added to obtain a modified Caro's acid composition with a Fenton type metal salt. Incorporating a Fenton's reagent in this type of composition will allow one to reduce the sulfuric acid load while maintaining the reactivity of said composition to a level sufficient to obtain proper lignin removal.

[0104] In one of the preferred compositions, the final composition comprised sulfuric acid: hydrogen peroxide:taurine:CuSO.sub.4 in a 20:20:2:1 molar ratio. The resulting pH of the composition is less than 1. Preferably, the resulting pH of the composition was less than 0.5. A range of compositions with the same components were prepared and the delignification testing carried out on those compositions are reported in Table 2.

[0105] The compositions were clear and odorless with densities between 1.1 and 1.8 g/cm.sup.3. One of the advantages of the composition used in the process according to the present invention was the decreased reactivity of the composition as it is being prepared and upon exposure to the lignocellulosic feedstock.

[0106] 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, whereas a preferred embodiment of the process according to the present invention can delignify wood at far lower temperatures, even as low as 15° 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/scalability/lower technical support requirements/fewer permitting challenges or requirements vs large kraft process facilities/small footprint—land requirements/less pollution (chlorine or sulfite containing compounds are not used in the process according to the present invention)/recycling of chemicals; also, there are HSE advantages compared to conventional kraft pulping compositions.

[0107] 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 which correlates to increased commercial viability, lower pollution, less investment and infrastructure requirements etc.

[0108] 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.

[0109] 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.

[0110] 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 high temperature and high-pressure pulp digestors.

[0111] According to an aspect of the present invention, various degrees of cellulose crystallinity, depending on the intended use of the cellulose, can be achieved. For example, it may be advantageous to produce mostly amorphous cellulose fibres (intended for ethanol production, for example) or highly crystalline cellulose (intended for pharmaceutical industry application, as example).

Experiment #1

[0112] A preferred embodiment of the composition according to the present invention was tested to determine its ability to delignify a wood chip.

[0113] Commercially available lignin (Sigma-Aldrich; Lignin, kraft; Prod #471003) was also used as a control in the testing.

[0114] Commercially available cellulose (Sigma-Aldrich; Cellulose, fibres (medium); Prod #C6288) was also used as a control in the testing.

[0115] The ability of a composition to remove lignin from a wood sample was evaluated by performing a number of experiments with varying molar ratios of several components. A desirable result is one which dissolves all of the lignin in the wood and leaves behind only high-quality cellulose. The ability of the tested composition to remove lignin was evaluated against a sample of lignin as well as a sample of cellulose fibres. Ideally, a composition must not dissolve/destroy more than 20% of the cellulose present in the sample. Preferably, a composition must not dissolve more than 15% of the cellulose present in the sample. More preferably, a composition must not dissolve more than 10% of the cellulose present in the sample.

[0116] Ideally, as well, a treated sample of wood should not contain more than 20% by mass of residual lignin. Preferably, a treated sample of wood should not contain more than 10% by mass of residual lignin. More preferably, a treated sample of wood should not contain more than 5% by mass of residual lignin.

[0117] Wood pellets were utilized as the feedstock that were processed through a mill to yield product that were predominantly smaller than 2 mm. Also incorporated as a feedstock were walnut shells (typically consumed for sandblasting (12-20 grit) or burned) as well as pure pine shavings, hemp straw, alfalfa straw, wheat straw, peanut shells and mill feed. All of these items are common, widely available feedstocks and are typically not converted to a commercially viable product in scale.

[0118] The compositions are odorless solutions of pH<0; densities are between 1.1 and 1.8 g/cm.sup.3; the blends decompose when heating, so boiling points have not been established.

[0119] Delignification Testing

[0120] Compositions according to preferred embodiment of the present invention were tested to determine their ability to separate the lignin from a sample of a lignocellulosic material, in this case, wood. The experiments were carried out using two controls, lignin and cellulose, in order to assess the impact of each composition on each of those components separately and independently. The results from a first series of experiments where the molar ratios of each component of the composition are reported in Table 1 below.

TABLE-US-00001 TABLE 1 Results of the delignification reactions carried out at room temperature under atmospheric pressure using sulfuric acid and hydrogen peroxide in the presence of a metal salt Appearance of H.sub.2SO.sub.4:H.sub.2O.sub.2:metal recovery [mass %] wood after Metal Salt salt (mol ratio) wood lignin cellulose reaction FeSO.sub.4 20:20:1 N/A N/A N/A runaway reaction FeCl.sub.2 20:20:1 N/A N/A N/A runaway reaction CuSO.sub.4 20:20:1 42 31 100

[0121] The data obtained from a series of control experiments using sulfuric acid without modifier, a source of peroxide and various metal salts as reported in Table 1 above, clearly establish that a composition comprising sulfuric acid, peroxide and a metal salt is very difficult to use in a controlled delignification reaction of a lignocellulosic material even when such operation is carried out at room temperature under atmospheric pressure.

[0122] The results from a second series of experiments with a modifier where the molar ratios of each component of the composition are reported in Table 2 below.

TABLE-US-00002 TABLE 2 Results of the delignification reactions carried out at room temperature under atmospheric pressure using sulfuric acid, a modifier and hydrogen peroxide in the presence of a metal salt Appearance of H.sub.2SO.sub.4:H.sub.2O.sub.2:mod:metal recovery [mass %] wood after Metal Salt salt (mol ratio) wood lignin cellulose reaction FeSO.sub.4 20:20:2:1 N/A N/A N/A runaway reaction FeSO.sub.4 100:100:10:1 44 25 99 Not recorded FeCl.sub.2 20:20:2:1 76 56 88 Not recorded CuSO.sub.4 20:20:2:1 50 20 96 Not recorded PS.: mod. is an abbreviation for modifier and the modifier in this example is taurine

[0123] The data obtained from a second series of experiments and reported in Table 2 above, clearly establish that a composition comprising sulfuric acid with a modifier (in this case, taurine), a source of peroxide (H.sub.2O.sub.2) and a metal salt can provide for substantial delignification of a lignocellulosic material when such operation is carried out at room temperature under atmospheric pressure. At an optimal ratio of chemicals the reaction can yield a usable product as replacement to Kraft pulp or other conventionally prepared pulp.

[0124] Preferably, the composition comprising a copper salt seemed to be more selective when a modifier (such as taurine) was present. The composition comprising the iron (II) chloride resulted in a runaway reaction when the modifier is absent, but is stable when the modifier is present. The composition comprising the iron (II) sulfate resulted in a runaway reaction when the molar ratio concentration of the metal salt compared to the sulfuric acid and peroxide was too high in both cases where a modifier was present and in the absence of the modifier. However, when the metal salt concentration was lowered the composition comprising the modifier allowed for more control of the reaction.

[0125] Given that reactions involving Fenton's reagent usually result in the destruction of anything organic present in the reaction medium, the ability to control the reactivity of such a reagent when in the presence of a modifier (such as taurine) is substantial and provides an opportunity to apply such compositions to a number of applications where it could not previously be useful for.

[0126] On the basis of the results from the testing which was carried out, it is expected that such compositions could be used on a wide variety of lignocellulosic plants and waste material in the removal of lignin and separation thereof from cellulosic material in such a way as to utilize equipment and processes which do not require high pressures and/or high temperatures. This allows for considerable amount of flexibility for the implementation of large-scale operations employing such processes as well as substantially smaller investments as the engineering complexities are greatly reduced because of the parameters under which the processes can be carried out. In addition to the greatly minimized capital expenditures, reduced technical complexities, pollution by-products reduction (or elimination), scalability utilizing existing infrastructure is viable resulting in further reductions of capital requirements.

[0127] The above experiment is a clear indication that the composition according to the present invention not only provides an adequate technology to delignify plant material and/or woody biomass waste, but is also valuable in controlling the delignification reaction to prevent/avoid/minimize the ultimate degradation of cellulosic material into carbon black residue common in the Kraft process resulting in higher yields and qualities for industry thus increasing profitability while reducing emissions and the risk to the environment, employees, contractors and public.

[0128] A method to yield glucose from wood pulp would represent a significant advancement to the current process where the conversion of such is chemical and energy intensive, costly, emissions intensive and dangerous, all while not resulting in highly efficient results, especially in large-scale operations. It is desirable to employ a composition which can delignify lignocellulosic biomass but also allows industry a level of control in order to preserve the commercially valuable cellulose rather than degrading it to a non-commercial carbon black product, resulting in higher efficiencies, increased profitability and yields along with increased safety and reduced overall costs. Preferably, said composition used under appropriate conditions can also generate highly crystalline cellulose. The crystallinity of cellulose can be assessed by methods such as X-ray diffraction. Preferably, a composition according to the present invention can generate cellulose which has a crystallinity level above 60%.

Analysis of the Cellulose Extracted

[0129] The cellulose recovered from the series of experiments was analyzed under X-ray diffraction in order to assess the crystallinity of the product. The results of the analysis are reported below in Table 3.

TABLE-US-00003 TABLE 3 Results of the XRD of various samples of cellulose recovered from the process according to a preferred embodiment of the present invention Sample # Crystallinity in % Sample 1 64.6 Sample 2 62.9 Sample 3 66.3 Sample 4 64.2 Sample 5 63.2 Sample #2 is a commercially available microcrystalline cellulose.

[0130] 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.

[0131] 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.