Method for extracting cellulose from biomass raw material

Abstract

The invention relates to the field of biomass refining, and discloses a method for extracting cellulose from a biomass raw material. The invention relates to a method for extracting cellulose from a biomass raw material, which comprises the following steps: (1) reacting the biomass raw material with an aqueous solution containing an ionic liquid at 60-95 DEG C to obtain a solid product; (2) freeze-drying the solid product to obtain a cellulose-rich component; wherein the ionic liquid is selected from at least one of quaternary ammonium salt compounds and choline compounds. By adopting the method, high-purity cellulose can be efficiently obtained.

Description

Technical Field

[0001] The invention relates to the field of biomass refining, and in particular to a method for extracting cellulose from biomass raw materials. Background Art

[0002] As an important source and component of biomass energy, lignocellulose has huge reserves, wide distribution, and is renewable. It has become a hot topic of extensive research in the scientific community. The sources of lignocellulose cover almost all plant areas, including forest vegetation, weeds, crop straw, and various annual plant straws or fruit shells. In addition to forest vegetation, crop straw and various annual plant straws play an important role in the material and energy cycle of nature. Lignocellulose is mainly composed of cellulose (35-55%), lignin (15-30%) and hemicellulose (20-35%) and a small amount of protein and inorganic salts. Cellulose and hemicellulose are essentially polysaccharides, which can be converted into monosaccharides, ethanol, 5-HMF and other high-value-added chemicals through hydrolysis or other chemical methods. However, lignocellulose that has not been pretreated cannot be used directly.

[0003] It is generally believed that the conversion of cellulose in lignocellulose into glucose requires two stages: pretreatment and enzymatic hydrolysis. Since lignin and hemicellulose are intertwined and attached to the surface of cellulose, and lignin will bind to cellulase, resulting in reduced activity, cellulase has a high requirement for lignin removal rate, and it is generally believed that the optimal removal rate is greater than 95%. The solvents used in the traditional pretreatment process are mostly acid, alkaline solutions or organic solvents, but these solvent systems generally have serious environmental pollution, cannot be recycled, have strict equipment requirements and high costs. CN105568729B discloses a method of first pretreating giant fungus grass with benzene-alcohol and hot water extraction and then separating cellulose, hemicellulose and lignin from giant fungus grass by microwave-alkali-alcohol method. The method is complicated, greatly prolongs the reaction process, and is not conducive to industrial production; the introduction of H2O2, a strong oxidant, and the use of microwave method may cause danger during the reaction; and the maximum purity of the extracted cellulose is only 88%, which is not conducive to the enzymatic hydrolysis process.

[0004] As a new type of green solvent for pre-treatment of lignocellulose, ionic liquids have become a research hotspot in the field of biomass refining in recent years. Ionic liquids have strong hydrogen bonds and electrostatic interactions, which enable them to destroy the complex structure of lignocellulose. The ability of some specific ionic liquids to dissolve biomass is not limited to the dissolution of individual components. On this basis, they can achieve the ability to completely dissolve biomass, or selectively dissolve components that conventional reagents cannot dissolve, and can achieve the integrity of biomass polymer components without destroying them.

[0005] CN106702800A discloses a method for pretreating straw by polyhydroxy proton ionic liquid, which obtains 70-90% pure cellulose by pretreating straw at 80-160°C using polyhydroxy ionic liquid. In the method of CN112064392A, proton ionic liquid is combined with high boiling alcohol to pretreat lignocellulose. In the method, the mass ratio of ionic liquid to high boiling alcohol is 1:(0.01-0.1), and the temperature range is 100-250°C. In the method disclosed in CN113605124A, imidazole ionic liquid is used and L-proline is added as an auxiliary agent, the addition amount is 2.5-7.5%, and lignocellulose is pretreated under high temperature conditions of 150-190°C to obtain a cellulose component with a purity of 70%.

[0006] According to the above method, in the prior art, ionic liquids are generally used in the case of adding pure solvents or adding a small amount of additives, and the pretreatment temperature is mostly concentrated at high temperature conditions exceeding 100°C. Ionic liquids are expensive, and the same high treatment temperature also faces the pressure of high energy consumption, which is contrary to the sustainable concept of green environmental protection. Therefore, it is of great significance to develop a green, efficient and gentle cellulose pretreatment process. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems existing in the prior art and provide a method for extracting cellulose from biomass raw materials. The method can efficiently obtain high-purity cellulose.

[0008] In order to achieve the above object, the present invention provides a method for extracting cellulose from biomass raw materials, the method comprising the following steps:

[0009] (1) reacting a biomass raw material with an aqueous solution containing an ionic liquid at 60-95° C. to obtain a solid product;

[0010] (2) freeze-drying the solid product to obtain a cellulose-rich fraction;

[0011] Wherein, the ionic liquid is selected from at least one of quaternary ammonium salt compounds and choline compounds.

[0012] Preferably, the aqueous solution containing the ionic liquid further contains an auxiliary agent, and the auxiliary agent is selected from at least one of 1-alkyl-3-methylimidazolium tetrafluoroborate, 1-alkyl-3-methylimidazolium ammonium hexafluorophosphate and 1-alkyl-3-methylimidazolium bistrifluoromethanesulfonyl imide salt.

[0013] Preferably, the mass ratio of the ionic liquid to the auxiliary agent is 1:0.3-3, preferably 1:0.5-1.5.

[0014] Through the above technical solution, the beneficial effects of the present invention include:

[0015] The method provided by the present invention uses a specific type of ionic liquid to treat biomass raw materials at a specific temperature, so that high-purity cellulose can be efficiently obtained; and the ionic liquid is provided in the form of an aqueous solution, which can reduce the processing cost; the reaction temperature is lower than the boiling point of water, the reaction temperature is mild, more energy-saving and environmentally friendly, and conforms to the concept of green engineering.

[0016] The method of the present invention is simple to operate, has low requirements on reactor devices, and is suitable for wide application. DETAILED DESCRIPTION

[0017] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0018] In one aspect, the present invention provides a method for extracting cellulose from a biomass raw material, the method comprising the following steps:

[0019] (1) reacting a biomass raw material with an aqueous solution containing an ionic liquid at 60-95° C. to obtain a solid product;

[0020] (2) freeze-drying the solid product to obtain a cellulose-rich fraction;

[0021] Wherein, the ionic liquid is selected from at least one of quaternary ammonium salt compounds and choline compounds.

[0022] The present invention has a wide range of selection for the type of the ionic liquid, which can be various quaternary ammonium salt compounds and choline compounds commonly used in the art. Preferably, the ionic liquid is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, choline hydroxide, choline acetate, choline propionate and choline butyrate.

[0023] According to the present invention, preferably, in the aqueous solution containing the ionic liquid, the concentration of the ionic liquid is not less than 25wt%, preferably 30-45wt%, for example, it can be 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt% and any value in the range formed by any two of these point values. This preferred embodiment is conducive to improving the purity of cellulose.

[0024] In the present invention, the ionic liquids are all soluble in water and stably exist in the prepared solution without changing their concentration.

[0025] According to the present invention, preferably, the aqueous solution containing the ionic liquid further contains an auxiliary agent, and the auxiliary agent is selected from at least one of 1-alkyl-3-methylimidazolium tetrafluoroborate, 1-alkyl-3-methylimidazolium ammonium hexafluorophosphate and 1-alkyl-3-methylimidazolium bistrifluoromethanesulfonyl imide salt.

[0026] According to the present invention, preferably, the alkyl group is a C2-C6 alkyl group, such as ethyl, propyl, butyl, pentyl, hexyl.

[0027] The present inventors have found that the use of a specific type of additives in synergistic effect with the ionic liquid is further beneficial to improving the cellulose purity and the lignin removal rate.

[0028] According to the present invention, preferably, the mass ratio of the ionic liquid to the auxiliary agent is 1:0.3-3, preferably 1:0.5-1.5. This preferred embodiment is further beneficial to improving the cellulose purity and lignin removal rate.

[0029] In the present invention, the reaction temperature in step (1) is 60-95°C, preferably 65-90°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C and any value in the range formed by any two of these point values. By adopting this preferred embodiment, the reaction efficiency can be greatly improved.

[0030] According to the present invention, preferably, the reaction time of step (1) is 1-8 hours, preferably 1-5 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours and any value in the range formed by any two of these point values. By adopting this preferred embodiment, the pretreatment time is greatly shortened to reduce the hydrolysis and dissolution loss of cellulose during the pretreatment process, and a higher cellulose yield can be obtained.

[0031] It should be noted that when the reaction time exceeds 8 h, more cellulose will be hydrolyzed and dissolved during the pretreatment process, which is not conducive to the extraction of cellulose.

[0032] According to the present invention, preferably, the reaction in step (1) is carried out under stirring.

[0033] The present invention has no particular limitation on the stirring rate, and can be appropriately selected according to the specific situation, as long as the purpose of accelerating the reaction process can be achieved. Preferably, the stirring rate is 200-500 rpm.

[0034] According to the present invention, preferably, in the reaction solution of step (1), the mass fraction of the biomass raw material is 5-15%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% and any value in the range formed by any two of these point values. This preferred embodiment is conducive to improving the cellulose purity and lignin removal rate.

[0035] Preferably, the method further comprises: separating the reaction product of step (1) to obtain a solid product.

[0036] The present invention has no particular limitation on the separation method, and the separation can be carried out by conventional technical means in the art. The present invention preferably adopts the method of centrifugation and washing.

[0037] According to a specific embodiment of the present invention, the reaction product of step (1) is diluted, centrifuged, and then washed.

[0038] The present invention has no particular limitation on the specific conditions of the washing, and the washing can be carried out according to conventional methods in the art, with the pH of the washing liquid being neutral.

[0039] The method of the present invention can also obtain lignin. Preferably, the liquid material produced after separation is adjusted to a pH of 1-2, and then the precipitate is recovered and dried. The precipitate here is the lignin-rich component.

[0040] In the present invention, the liquid material produced after separation includes the first liquid material obtained by centrifugation and the second liquid material obtained by the first washing.

[0041] Preferably, the pH is adjusted by acid. The acid described in the present invention can be various inorganic acids commonly used in the art, such as sulfuric acid, hydrochloric acid, nitric acid, etc.

[0042] The present invention has a wide range of freeze-drying conditions. Preferably, the freeze-drying conditions in step (2) include: a temperature of -100 to -80°C and a time of 12-24 hours.

[0043] According to the present invention, preferably, the method further comprises: before the biomass raw material reacts with the aqueous solution containing the ionic liquid, it is first pretreated, and the pretreatment makes the water content in the biomass raw material less than 10wt%, for example, it can be 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% and any value in the range formed by any two of these point values.

[0044] The present invention has no particular limitation on the pretreatment method, and the pretreatment can be performed according to conventional methods in the art. Preferably, the pretreatment includes powdering and drying.

[0045] Preferably, the method further comprises: screening the pretreated biomass raw material so that its average size is no greater than 0.25 mm.

[0046] The present invention has no particular limitation on the specific method of screening, and the screening can be performed according to conventional methods in the art.

[0047] The present invention has no particular limitation on the type of the biomass raw material, and it can be various cellulose-containing biomass raw materials. Preferably, the biomass raw material is selected from at least one of corn stalks, corn cobs, wheat stalks, wheat grass and cotton stalks, and more preferably corn stalks.

[0048] The method of the present invention can be used to extract cellulose of different concentrations. Preferably, the cellulose content in the biomass raw material is 20-40wt%.

[0049] According to the present invention, preferably, the method does not include adding an inorganic base. With this preferred embodiment, cellulose with higher purity can be obtained at a lower temperature, and it is more environmentally friendly.

[0050] The present invention will be described in detail below through examples.

[0051] In the following embodiments,

[0052] Lignin removal rate = (lignin mass in biomass - lignin mass in cellulose-rich fraction) / lignin mass in biomass × 100%.

[0053] Example 1

[0054] (1) Corn stalks (cellulose content: 33 wt%) were pulverized and dried to a water content of 8 wt%, and then sieved to obtain stalk powder with an average size of 0.25 mm.

[0055] (2) Add straw powder to a 40wt% tetrabutylammonium hydroxide aqueous solution (the straw powder accounts for about 5wt% of the reaction solution), heat to 65°C, stir at 350rpm, and react for 3 hours. Add 35mL of deionized water to the reaction system for dilution and centrifugation. Wash the solid obtained by centrifugation 5 times and then freeze-dry at -80°C for 24h to obtain a cellulose-rich component with a purity of 95%. The cellulose-rich component was analyzed for composition, and the lignin removal rate reached 97%.

[0056] Example 2

[0057] (1) Corn stalks (cellulose content: 33 wt%) were pulverized and dried to a water content of 8 wt%, and then sieved to obtain stalk powder with an average size of 0.25 mm.

[0058] (2) Add straw powder to a 37 wt% tetrabutylammonium hydroxide aqueous solution (the straw powder accounts for about 5 wt% of the reaction solution), heat to 85°C, stir at 350 rpm, and react for 3 hours. Add 35 mL of deionized water to the reaction system for dilution and centrifugation. Wash the solid obtained by centrifugation 5 times and then freeze-dry at -80°C for 24 hours to obtain a cellulose-rich component with a purity of 95%. The cellulose-rich component was analyzed for composition, and the lignin removal rate reached 98%.

[0059] Example 3

[0060] (1) Corn stalks (cellulose content: 33 wt%) were pulverized and dried to a water content of 8 wt%, and then sieved to obtain stalk powder with an average size of 0.25 mm.

[0061] (2) Add straw powder to a 35wt% choline hydroxide aqueous solution (the straw powder accounts for about 5wt% of the reaction solution), heat to 90°C, stir at 350rpm, and react for 3 hours. Add 35mL of deionized water to the reaction system for dilution and centrifugation. The solid obtained by centrifugation is washed with water 5 times and then freeze-dried at -80°C for 24h to obtain a cellulose-rich component with a purity of 94%. The cellulose-rich component was analyzed for composition, and the lignin removal rate reached 96%.

[0062] Example 4

[0063] (1) Corn stalks (cellulose content: 33 wt%) were pulverized and dried to a water content of 8 wt%, and then sieved to obtain stalk powder with an average size of 0.25 mm.

[0064] (2) Add straw powder to a 25wt% tetramethylammonium hydroxide aqueous solution (the straw powder accounts for about 10wt% of the reaction solution), heat to 85°C, stir at 350rpm, and react for 3 hours. Add 35mL of deionized water to the reaction system for dilution and centrifugation. Wash the solid obtained by centrifugation 5 times and then freeze-dry at -80°C for 24h to obtain a cellulose-rich component with a purity of 90%. The cellulose-rich component was analyzed for composition, and the lignin removal rate reached 93%.

[0065] Example 5

[0066] The method of Example 1 is followed, except that 1-ethyl-3-methylimidazolium tetrafluoroborate additive is also added to the reaction solution, and the mass ratio of the ionic liquid to the additive is 1:1. Specifically, straw powder is added to an aqueous solution containing tetrabutylammonium hydroxide and 1-ethyl-3-methylimidazolium tetrafluoroborate additives with a total concentration of 40wt% (the straw powder accounts for about 5wt% of the reaction solution).

[0067] A cellulose-rich component with a purity of 97% was obtained. The composition of the cellulose-rich component was analyzed, and the lignin removal rate reached 99%.

[0068] Example 6

[0069] The method of Example 1 is followed, except that 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt auxiliary is also added to the reaction solution, and the mass ratio of the ionic liquid to the auxiliary is 1:0.5. Specifically, straw powder is added to an aqueous solution containing tetrabutylammonium hydroxide and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt auxiliary with a total concentration of 40wt% (the straw powder accounts for about 5wt% in the reaction solution).

[0070] A cellulose-rich component with a purity of 97% was obtained. The composition of the cellulose-rich component was analyzed, and the lignin removal rate reached 98%.

[0071] Example 7

[0072] The method of Example 1 was followed, except that a 25 wt % tetrabutylammonium hydroxide aqueous solution was used.

[0073] A high purity 94% cellulose-rich component was obtained. The composition of the cellulose-rich component was analyzed, and the lignin removal rate reached 96%.

[0074] Comparative Example 1

[0075] The method of Example 1 was followed, except that the reaction temperature was 45°C instead of 65°C.

[0076] A cellulose-rich fraction with a purity of 84% was obtained. The composition of the cellulose-rich fraction was analyzed, and the lignin removal rate reached 68%.

[0077] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for extracting cellulose from biomass raw materials, characterized in that: The method comprises the following steps: (1) reacting a biomass raw material with an aqueous solution containing an ionic liquid at 60-95° C. to obtain a solid product; (2) freeze-drying the solid product to obtain a cellulose-rich fraction; Wherein, the ionic liquid is selected from at least one of quaternary ammonium salt compounds and choline compounds.

2. The method according to claim 1, wherein: The ionic liquid is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, choline hydroxide, choline acetate, choline propionate and choline butyrate.

3. The method according to claim 1, wherein: In the aqueous solution containing the ionic liquid, the concentration of the ionic liquid is not less than 25 wt %, preferably 30-45 wt %.

4. The method according to any one of claims 1 to 3, wherein: The aqueous solution containing the ionic liquid further contains an auxiliary agent, and the auxiliary agent is selected from at least one of 1-alkyl-3-methylimidazolium tetrafluoroborate, 1-alkyl-3-methylimidazolium ammonium hexafluorophosphate and 1-alkyl-3-methylimidazolium bistrifluoromethanesulfonyl imide salt; Preferably, the alkyl group is a C2-C6 alkyl group.

5. The method according to claim 4, wherein: The mass ratio of the ionic liquid to the auxiliary agent is 1:0.3-3, preferably 1:0.5-1.

5.

6. The method according to any one of claims 1 to 5, wherein: The reaction temperature of step (1) is 60-95°C, preferably 65-90°C; the reaction time is 1-8h, preferably 1-5h; Preferably, the reaction in step (1) is carried out under stirring at a rate of 200-500 rpm; Preferably, in the reaction solution of step (1), the mass fraction of the biomass raw material is 5-15%.

7. The method according to any one of claims 1 to 6, wherein: The freeze-drying conditions of step (2) include: temperature of -100 to -80°C and time of 12 to 24 hours.

8. The method according to any one of claims 1 to 7, wherein: The method further comprises: before the biomass raw material reacts with the aqueous solution containing the ionic liquid, pretreatment is first performed, and the pretreatment makes the water content in the biomass raw material less than 10wt%.

9. The method according to any one of claims 1 to 8, wherein: The biomass raw material is selected from at least one of corn stalks, corn cobs, wheat stalks, wheat grass and cotton stalks; Preferably, the cellulose content in the biomass raw material is 20-40wt%.

10. The method according to any one of claims 1 to 9, wherein: The process does not involve the addition of an inorganic base.