WO2016199042A1

WO2016199042A1 - Methods for treating lignocellulosic materials

Info

Publication number: WO2016199042A1
Application number: PCT/IB2016/053378
Authority: WO
Inventors: Jari KAVAKKA; Mari GRANSTRÖM
Original assignee: Stora Enso Oyj
Priority date: 2015-06-10
Filing date: 2016-06-09
Publication date: 2016-12-15
Also published as: US20180162958A1; EP3307791A4; EP3307791B1; US10899850B2; CA2987869C; BR112017026578A2; BR112017026578B1; EP3307791A1; CN107614536A; CN107614536B; CA2987869A1

Abstract

Methods for producing refined xylan from a biomass solution, including: (i) providing a biomass solution, which comprises xylan; (ii) concentrating or separating said biomass solution to obtain a xylan concentrate comprising xylan and impurities; (iii) washing and/or extracting the xylan concentrate with a solvent to obtain refined xylan and a solvent stream comprising the solvent and impurities; and (iv) collecting the refined xylan.

Description

METHODS FOR TREATING LIGNOCELLULOSIC MATERIALS

FIELD OF THE INVENTION

Aspects of the disclosure provide methods for producing refined xylan from a biomass solution. Such methods are practiced by providing a biomass solution, which comprises xylan; concentrating or separating said biomass solution to obtain a xylan concentrate comprising xylan and impurities; washing and/or extracting the xylan concentrate with a solvent to obtain refined xylan and a solvent stream comprising the solvent and impurities; and collecting the refined xylan.

BACKGROUND OF THE INVENTION

Xylan is a group of hemicelluloses made from units of xylose. It is found in the cell walls of plants, and next to cellulose it is the most abundant renewable polysaccharide in nature. Xylan is a P-l,4-linked D-xylose polymer with arabinofuranose, glucuronic acid, methylglucuronic acid, and acetyl side groups. Typically the content of xylans in hardwoods is 10 - 35 % of the hemicelluloses and in softwoods they are 10 - 15 % of the hemicelluloses. Xylans can be refined {see e.g., WO 2013144446, herein expressly incorporated by reference in its entirety) and refined xylan is useful as an auxiliary agent, thickening agent, an emulsifier, and as an additive in the manufacture of cellulose based fibre, papermaking, food products, cosmetic products, and coating agents. Xylan can also be used to obtain xylose. There remains a need for additional approaches to refine xylan.

SUMMARY OF THE INVENTION

Several methods of generating refined xylan from a biomass solution are disclosed. In some alternatives, these methods are practiced by: (i) providing a biomass solution, which comprises xylan; (ii) concentrating or separating said biomass solution to obtain a xylan concentrate comprising xylan and impurities; (iii) washing the xylan concentrate with a solvent to obtain refined xylan and a solvent stream comprising the solvent and impurities; and (iv) collecting the refined xylan.

In some alternatives, these methods further comprise adding a buffer to said biomass solution prior to step (i), wherein said buffer comprises a salt of an acid and has a pK_a value of 3-7. In more alternatives, the salt of said acid is an aromatic or aliphatic carboxylic acid salt. In one alternative, the salt of said acid is a salt of an inorganic acid. In still more alternatives, the salt of said acid is sodium acetate.

In some alternatives, the biomass solution is concentrated by evaporation at step ii).

In some alternatives, the solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, cis-2,3-butylene carbonate, trans- 2,3-butylene carbonate, diethyl carbonate, dimethyl carbonate, acetic acid, acetone, methyl ethyl ketone, isopropanol, 2-butanol, 1-propanol, ethanol, methanol, propanoic acid, butanoic acid, and methyl isobutyl ketone, or the solvent is any combination of the foregoing solvents. In one preferred alternative, the solvent includes acetic acid. In another preferred alternative, the solvent includes acetone. In another preferred alternative, the solvent is acetone, methyl ethyl ketone or methyl isobutyl ketone. In another preferred alternative, the solvent is methyl ethyl ketone or methyl isobutyl ketone. In another alternative, the solvent is selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, cis-2,3-butylene carbonate, trans-2,3 -butyl ene carbonate, diethyl carbonate, dimethyl carbonate. In some approaches, the xylan concentrate is washed with one or more solvents at step iii) under heating at a temperature of 30-180°C.

Some alternatives concern methods, wherein the refined xylan is separated by filtration. Some alternatives concern methods, wherein the refined xylan is collected by centrifugation. Some alternatives concern methods, wherein the refined xylan is collected by sedimentation.

In some alternatives, the method further includes recycling the solvent for use in a subsequent step (iii).

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a scheme for the isolation and/or purification of xylan from a biomass solution. DETAILED DESCRIPTION OF THE PREFERRED EMB ODEVIENT

The alternatives described herein relate to lignocellulosic biomass processing and refining conducted to produce xylan, lignin, cellulose and other high-value products. In some alternatives, methods of generating xylan from a biomass hydrolysis solution are disclosed. These methods include: i) providing a biomass solution, which comprises xylan; (ii) concentrating or separating said biomass solution to obtain a xylan concentrate comprising xylan and impurities; (iii) washing the xylan concentrate with a solvent to obtain a refined xylan and a solvent stream comprising the solvent and impurities; and (iv) collecting the refined xylan.

Desirably, aspects of the invention described herein allow for the isolation of a sugar stream that is enriched in hemicelluloses, such as xylan, after a single extraction of a biomass hydrolysis solution, e.g., a solvent extraction accomplished for instance by the addition of heat, such as 30°C -100°C, in the absence of chromatographic procedures, which can be required to enrich a sugar stream for monomeric and/or oligomeric sugars, such as a xylan. It has been surprisingly discovered that a class of solvents that has not been previously recognized for sugar extraction, quite efficiently separates xylan from impurities. These solvents are antisolvents for xylan at room temperature, and reach solubility by heating. Upon cooling, only xylan precipitates out, leaving all of the remaining impurities behind in a given solvent. Additionally, the solvent can be efficiently recycled and reused, which contributes to a significant cost savings on an industrial scale.

By some methods, the lignocellulosic biomass processing and refining processes described herein comprises: (1) preconditioning of the lignocellulosic biomass; (2) concentrating or separating said biomass solution to obtain a xylan concentrate comprising xylan and impurities, e.g., removing the water from the preconditioned lignocellulosic biomass solution; and (3) solvent extraction (for instance, in the presence of acetic acid, acetone, methyl ethyl ketone, isopropanol, 2-butanol, 1-propanol, ethanol, methanol, propanoic acid, butanoic acid, and/or methyl isobutyl ketone, herein also referred to as "antisolvents for xylane"). The section below describes in greater detail the preconditioning of the lignocellulosic biomass.

Preconditioning of the Lignocellulosic Biomass

While xylan can be refined from a variety of plant materials, e.g., soft woods such as, spruce or pine; plants such as, bagasse; preferably, hardwoods, such as birch, are used as the lignocellulosic starting material. Birch is an excellent source of xylan. In birch, xylan is particularly pure, because 98% of the hemicelluloses in birch consist of xylan. Furthermore, birch has an exceptionally high content of xylan, and therefore the yield of xylan obtained from birch is high, up to about 10% of the dry content of the wood.

Accordingly, hardwood pulp comprising of unrefined or slightly refined chemically defibrated wood fibres can be used in some of the methods described herein.

Lignocellulosic biomass processing and refining begins with a preconditioning of the lignocellulosic biomass, whereby the biomass is debarked, chipped, shred, dried, bleached, and/or ground to particles so as to generate a conditioned lignocellulose preparation. Preconditioning in this context refers to the reduction in biomass size and structure (e.g., mechanical breakdown with or without evaporation), which does not substantially affect the lignin, cellulose and hemicellulose compositions of the biomass. Preconditioning in this manner facilitates more efficient and economical processing of a downstream process (e.g., xylan refinement). In some alternatives, preconditioning of the lignocellulosic biomass can also utilize, for example, ultrasonic energy or hydrothermal treatments including water, heat, steam and/or pressurized steam. Preconditioning can occur or be deployed in various types of containers, reactors, pipes, flow through cells and the like. In some methods, it is preferred to have the lignocellulosic biomass

preconditioned before hemicellulose refinement. In some methods, depending on the biomass starting materials, no preconditioning is required.

In some alternatives, the lignocellulosic biomass (e.g., birch or bagasse) is milled or ground to reduce particle size. In some embodiments, the lignocellulosic biomass (e.g., birch or bagasse) is ground such that the average size of the particles is in the range of 100-10,000 micron, preferably 400-5,000, e.g., 100-400, 400-1,000, 1,000-3,000, 3,000- 5,000, or 5,000-10,000 microns or to a size within a range defined by any two of the aforementioned sizes. In some alternatives, the lignocellulosic biomass is ground such that the average size of the particles is less than 10,000, 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 1,000, or 400 microns or within a range defined by any two of the aforementioned sizes. Ground particles from different lignocellulosic biomass materials can be processed by the same set of equipment using similar or same operating parameters.

Once the lignocellulosic biomass (e.g., birch or bagasse) has been preconditioned or in some alternatives, in the absence of preconditioning, a liquid, such as water

(preferably hot water or steam), is added to the lignocellulosic biomass (e.g., birch or bagasse) so as to obtain a biomass solution that comprises xylan. In one embodiment, spent liquor from NSSC (neutral sulfite semi-chemical) pulping process may be the biomass solution from which xylan is refined according to the present invention. In some alternatives, a buffer is added to the biomass solution (e.g., the liquid added to the lignocellulosic biomass (e.g., birch or bagasse) can be a buffered liquid or a liquid can be added to a buffer and the lignocellulosic biomass (e.g., birch or bagasse)) so as to obtain a buffered biomass solution. In some alternatives, the buffer comprises a salt of an acid and has a pK_a value of 3, 4, 5, 6, or 7 or a pK_a value within a range defined by any two of the aforementioned pK_a values. In some alternatives, the buffer comprises a salt of an acid that is an aromatic or aliphatic carboxylic acid salt. In some alternatives, the buffer comprises a salt of an acid that is an inorganic acid salt. In some alternatives, the buffer comprises sodium acetate.

Concentration

With reference to Fig. 1, in some alternatives, the method comprises concentrating or separating the biomass solution to obtain a xylan concentrate, which comprises xylan and impurities. In one alternative, the biomass solution is concentrated by evaporation so as to obtain the xylan concentrate. More generally, the biomass solution is concentrated by the removal of water, which can be done by many approaches. In one embodiment, most but not all of the water is removed during the concentration step. In one

embodiment, the biomass solution is concentrated to be essentially dry.

Washing/Extraction

With reference to Fig. 1, in some alternatives, the xylan concentrate is washed and/or extracted with a solvent, such as ethylene carbonate, propylene carbonate, 1,2- butylene carbonate, cis-2,3-butylene carbonate, trans-2,3-butylene carbonate, diethyl carbonate, dimethyl carbonate, acetic acid, acetone, methyl ethyl ketone, isopropanol, 2- butanol, 1-propanol, ethanol, methanol, propanoic acid, butanoic acid, or methyl isobutyl ketone, or any combination thereof so as to obtain refined xylan having a reduced amount of impurities and a solvent stream comprising the solvent and impurities. In some alternatives, the solvent used comprises acetic acid and in some alternatives the solvent used comprises acetone. In another preferred alternative, the solvent is methyl ethyl ketone or methyl isobutyl ketone. In another alternative, the solvent is selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, cis-2,3-butylene carbonate, trans-2,3-butylene carbonate, diethyl carbonate, dimethyl carbonate. In some alternatives, the washing and/or extraction is performed in the presence of heat, such as 30°C - 180°C. That is, the washing and/or extraction can be performed at 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, or 180°C or at a temperature that is within a range defined by any two of the aforementioned temperatures. In some alternatives, the washing and/or extraction is carried out without addition of organic acid to the xylan concentrate. It has been found that the present invention efficiently refines xylan and avoids the deterioration of xylan that may otherwise be caused by organic acids, particularly at elevated temperatures.

After washing and/or extraction, in some alternatives, the refined xylan is collected by filtration, centrifugation, sedimentation, or any combination thereof, optionally during cooling. After the separation of xylan, the solvent can be recycled for subsequent rounds of extraction, so as to improve the yield of xylan from the biomass solution.

Products

The refined xylan obtained by any one or more of the methods described herein can be used as a raw material for bacterial and chemical production of xylose, xylonic acid, xylaric acid, 2-methylfuran, 2-methyltetrahydrofuran, furan, furfuryl alcohol, tetrahydrofurfuryl alcohol, furfuryl amine, furoic acid, furfural and tetrahydrofuran. Xylan can also be used as the starting material for preparing xylitol, a low calorie alternative sweetener that has beneficial properties for dental care and diabetes management, and has been shown to contribute to clearing ear and upper respiratory tract infections. Given these beneficial properties, xylitol is incorporated in food and beverages, toothpastes and mouth wash products, chewing gums and confectionary products. World xylitol market is limited due to its high price compared to other non-reducing polyol sugars (e.g., sorbitol, mannitol).

The xylan obtained by one or more of the processes described herein can also be reacted with chlorambucil to obtain benzenebutanoic acid, 4-[bis(2-chloroethyl)amino]-, 2-P-D-xylopyranosylhydrazide, a glycosylated chlorambucil analog which is useful as antitumor and/or anti-metastatic agent. Xylan may be reacted with phenethyl bromide and l-bromo-3,3-dimethoxypropane to obtain (2S,3S,4S)-2H-Pyrrole, 3,4-dihydro-3,4- bis(phenyl-methoxy)-2-[(phenylmethoxy)methyl]-, 1 -oxide, used as a-glucosidase inhibitor for preventing and/or treating diabetes mellitus, hyperlipidemia, neoplasm, and viral infection.

Although the invention has been described with reference to embodiments and examples, it should be understood that various modifications can be made without departing from the spirit of the invention. Accordingly, the invention is limited only by the following claims. All references cited herein are hereby expressly incorporated by reference in their entireties.

Claims

1. A method of producing refined xylan from a biomass solution, comprising: i) providing a biomass solution, which comprises xylan; ii) concentrating or separating said biomass solution to obtain a xylan concentrate comprising xylan and impurities;

iii) washing and/or extracting the xylan concentrate with a solvent which is selected from isopropanol, 2-butanol, 1-propanol, ethanol, methanol, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, cis-2,3-butylene carbonate, trans-2,3-butylene carbonate, diethyl carbonate, dimethyl carbonate, acetone, methyl ethyl ketone and methyl isobutyl ketone to obtain refined xylan and a solvent stream comprising the solvent and impurities; and

iv) collecting the refined xylan.

2. A method according to claim 1, wherein step iii) is carried out without addition of organic acid to the xylan concentrate.

3. A method according to claim 1 or 2, wherein the solvent in step iii) is selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, cis-2,3-butylene carbonate, trans-2,3-butylene carbonate, diethyl carbonate, dimethyl carbonate, acetone methyl ethyl ketone and methyl isobutyl ketone.

4. A method according to claim 3, wherein the solvent in step iii) is selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, cis-2,3-butylene carbonate, trans-2,3-butylene carbonate, diethyl carbonate and dimethyl carbonate.

5. A method according to claim 1, wherein the solvent in step iii) is selected from acetone, methyl ethyl ketone and methyl isobutyl ketone.

6. A method according to claim 5, wherein the solvent in step iii) is selected from methyl ethyl ketone and methyl isobutyl ketone.

7. The method of any one of Claims 1-6, further comprising adding a buffer to said biomass solution prior to step (i), wherein said buffer comprises a salt of an acid and has a pK_a value of 3-7.

8. The method of Claim 7, wherein the salt of said acid is an aromatic or aliphatic carboxylic acid salt.

9. The method of Claim 7, wherein the salt of said acid is an inorganic acid salt.

10. The method of Claim 7 or 8, wherein the salt of said acid is sodium acetate.

11. The method of anyone of Claims 1-10, wherein the biomass solution is evaporated at step ii).

12. The method of anyone of Claims 1-11, wherein the xylan concentrate is washed and/or extracted with solvent at step iii) under heating at a temperature of 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, or 180°C or at a temperature that is within a range defined by any two of the aforementioned temperatures.

13. The method of any one of Claims 1-12, wherein the refined xylan is separated by filtration.

14. The method of any one of Claims 1-12, wherein the refined xylan is collected by centrifugation.

15. The method of any one of Claims 1-12, wherein the refined xylan is collected by sedimentation.

16. The method of any one of Claims 1-15, further comprising recycling the solvent for use in a subsequent step (iii).