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 modifiying 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;
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 modifiying 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;

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

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

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

7. 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.

8. 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.

9. 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.

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

11. The composition according to claim 1, wherein the metal oxide is selected from the group consisting of: TiO.sub.2; Fe.sub.2O.sub.3; ZnO; Al.sub.2O.sub.3; SiO.sub.2; ZrO.sub.2/Y.sub.2O.sub.3; WO.sub.3; SnO; Bi.sub.2O.sub.3; and combinations thereof.

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

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; providing a composition comprising; an acid; a modifiying agent; a metal oxide; and a peroxide; exposing said lignocellulosic feedstock to said composition in said vessel for a period of time sufficient to remove 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.

14. The process according to claim 13, wherein said acid is sulfuric acid.

15. The process according to claim 13, wherein said peroxide is hydrogen peroxide.

16. 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.

17. 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.

18. The process according to claim 13 where the modifying agent is 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.

19. The process according to claim 13 where the modifying agent is taurine derivative or taurine-related compound 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.

20. The process according to claim 13 where the modifying agent is an alkysulfonic acid is selected from the group consisting of: methanesulfonic acid; ethanesulfonic acid; sulfamic acid and combinations thereof.

21. The process according to claim 13 where the modifying agent is an arylsulfonic acid is selected from the group consisting of: toluenesulfonic acid; benzenesulfonic acid; and combinations thereof.

22. The process according to claim 13 where the modifying agent comprises a compound containing an amine group and a compound comprising a sulfonic acid moiety.

23. The process according to claim 13, wherein the metal oxide is selected from the group consisting of: TiO.sub.2; Fe.sub.2O.sub.3; ZnO; Al.sub.2O.sub.3; SiO.sub.2; ZrO.sub.2/Y.sub.2O.sub.3; WO.sub.3; SnO; Bi.sub.2O.sub.3; and combinations thereof.

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

Description

DESCRIPTION OF THE INVENTION

[0063] 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.

[0064] 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), peracids etc.) and a metal oxide 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. 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.

[0065] According to another preferred embodiment, the reaction phase comprises a modified mineral acid and a source of peroxide. Preferably, the modified acid is created by combining a mineral acid such as sulfuric acid with a compound comprising an amine moiety and a sulfonic acid moiety selected from the group consisting of: taurine and derivatives thereof such as taurine-related compounds; wherein the sulfuric acid and said amine-containing compound are present in a mole ratio ranging from 3:1 to 100:1. More preferably, the sulfuric acid and said compound comprising an amine moiety and a sulfonic acid moiety are present in a mole ratio ranging from 3:1 to 50:1. Even more preferably, the sulfuric acid and said compound comprising an amine moiety and a sulfonic acid moiety are present in a mole ratio ranging from 3:1 to 10:1.

[0066] Preferably, said 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. According to another preferred embodiment, the modifying agent is selected from the group consisting of: sulfamic acid; aminomethanesulfonic acid; aminopropanesulfonic acid; aminobutanesulfonic acid; aminopentanesulfonic acid; aminohexanesulfonic acid; and combinations thereof.

[0067] Preferably, said modifying agent is a compound comprising an amine moiety and a sulfonic acid moiety is selected from the group consisting of: taurine; taurine derivatives; and taurine-related compounds. Preferably also, said 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; arylsulfonic acids; as well as aminoalkylsulfonic acids where the alkyl is selected from the group consisting of C.sub.1-C.sub.5 linear alkyl and C.sub.1-C.sub.5 branched alkyl. Preferably, the alkyl moiety in said linear alkylaminosulfonic acid is selected form the group consisting of: methyl; ethyl (taurine); propyl; and butyl. Preferably, the alkyl moiety in said branched aminoalkylsulfonic is selected from the group consisting of: isopropyl; isobutyl; and isopentyl.

[0068] According to another preferred embodiment of the present invention, the modifying agent comprises a compound containing an amine group and a compound comprising a sulfonic acid moiety. Preferably, the compound containing an amine group has a molecular weight below 300 g/mol. Also preferably, said compound containing an amine group has a molecular weight below 150 g/mol. More preferably, said compound containing an amine group is a secondary amine. Even more preferably, said compound containing an amine group is triethanolamine.

[0069] Preferably, said compound comprising a sulfonic acid moiety is selected from the group consisting of: alkylsulfonic acid; and arylsulfonic acid. More preferably, the arylsulfonic acid is selected from the group consisting of: orthanilic acid; metanilic acid; sulfanilic acid; benzenesulfonic acid; and toluenesulfonic acid.

EXAMPLES

[0070] 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 sulfuric acid and subsequently adding hydrogen peroxide. Once this step was completed, a metal oxide was added to the composition to obtain a modified Caro's acid composition with a metal compound.

[0071] The compositions had 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.

[0072] Preferably, the metal compound is incorporated into the aqueous acid composition to function as a catalyst accelerating the lignin depolymerization.

[0073] 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 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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

[0079] A preferred embodiment of the composition according to the present invention was tested to determine its ability to delignify a wood chip.

[0080] Commercially available lignin (Sigma-Aldrich; Lignin, Kraft; Prod #471003) was also used as a control in the testing.

[0081] Commercially available cellulose (Sigma-Aldrich; Cellulose, fibres (medium); Prod #C6288) was also used as a control in the testing.

[0082] 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. 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.

[0083] 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 as well as 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.

[0084] Compositions were prepared by the sequential addition of a modifying agent, a peroxide source and a metal oxide compound to a mineral acid such as sulfuric acid.

[0085] The compositions are 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 yet been established.

Delignification Testing

[0086] 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 various metal oxides are tested with 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 and taurine (as a modifying agent) in the presence of various metal oxides Blend recovery [mass %] (H.sub.2SO.sub.4:PO:MOD:MO) wood lignin cellulose no MO 10:10:3:0  39  0  93 TiO.sub.2 Ti-10:10:3:1  31  0  74 Fe.sub.2O.sub.3 Fe-10:10:3:1  33  0  69 ZnO Zn-10:10:3:1  45  0  93 Al.sub.2O.sub.3 Al-10:10:3:1  48  0  84 SiO.sub.2 Si-10:10:3:1  43  0  86 ZrO.sub.2/Y.sub.2O.sub.3 Zr/Yt-10:10:3:1  34  0  57 WO.sub.3 W-10:10:3:1  30  0  81 SnO Sn-10:10:3:1 170 32  210* Bi.sub.2O.sub.3 Bi-10:10:3:1  65 15  112* *Indicates the presence of metal oxide in the cellulose PO indicates peroxide, MOD indicates modifying agent, MO indicates metal oxide.

[0087] Also tested were vanadium oxide, copper oxide and sodium silicate which did not have satisfactory results. Both the vanadium oxide and the copper oxide created an unstable blend when the metal oxide was added to the modified acid—peroxide composition. They reacted with H.sub.2O.sub.2 upon mixing, triggering runaway decomposition reaction. The reaction with sodium silicate was not successful.

[0088] The data obtained from a series of control experiments using a modified sulfuric acid with a peroxide but without a metal oxide where compared to a number of other compositions comprising various metal oxides to carry out the delignification of a lignocellulosic material at room temperature under atmospheric pressure.

[0089] The results from a second series of experiments with a modifier where the molar ratios of some of the previously tested metal oxide were reduced 100-fold 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 and hydrogen peroxide and taurine (as a modifying agent) in the presence of various metal oxide Blend Recovery (mass %) Comment/ (H.sub.2SO.sub.4:PO:MOD:MO) wood lignin cellulose observation Al-10:10:3:0.01 67 12 103 MO in Cellulose Zn-10:10:3:0.01 47 16  96 Ti-10:10:3:0.01 51  7 125 MO in Cellulose

[0090] 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 (taurine), a source of peroxide (H.sub.2O.sub.2) and a metal oxide (at very low concentration—0.01) can provide for substantial delignification of a lignocellulosic material when such operation is carried out at room temperature under atmospheric pressure.

[0091] The testing revealed that the reactions were conducted faster than the control experiment. The yield of wood is the best indication of rate of reaction (lower yield=faster reaction). Titanium, iron, tungsten, and zirconium/yttrium oxides had lower yields, therefore they were faster.

[0092] However, if one of these metal oxides (MO) showed specificity also for cellulose in any amount, then the colour of wood matters. Some MO's gave low yields but orange colored wood which can be undesirable in some applications. This obvious colour change (or delignification) as well as specificity (lignin over cellulose removal) was the metric when choosing millimolar-MO samples.

[0093] 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.

[0094] 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 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 employees, contractors, and public.

[0095] 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

[0096] The cellulose recovered from the series of experiments was analyzed under X-ray diffraction in order to assess the crystallinity of the product. The crystallinity is calculated by the peak deconvolution method. 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 micromystalline cellulose.

[0097] 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.

[0098] 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.