阅读说明：本技术 基于水热耦合低共熔溶剂预处理木质纤维素类生物质的转化方法 (Conversion method for pretreating lignocellulose biomass based on hydrothermal coupling eutectic solvent ) 是由 田东 沈飞跃 陈怡奕 蒋月菡 胥露 胡岑涵毅 魏颖 沈飞 于 2021-01-07 设计创作，主要内容包括：本发明公开了一种基于水热耦合低共熔溶剂预处理木质纤维素类生物质的转化方法,基于绿色高效的水热耦合低共熔溶剂两步法预处理手段选择性分离出半纤维素、纤维素和木质素。此分离所得的三大组分具有结构完整、生物兼容性好和可利用价值高等优点。其中将半纤维素、纤维素和木质素分别制备成高价值的生物基纳米材料：高比表面积(>2000)的碳纳米材料,高结晶度(>70％)、高纵横比(>140)的木质纤维素纳米纤维和粒径低至100nm具有核壳结构的木质素纳米球。实现了低值木质纤维废弃物到高价值纳米材料平台的全组分转化,并进一步探索了所制备纳米材料的优良性能,为其产业化应用开辟了新途径。(The invention discloses a conversion method for pretreating lignocellulose biomass based on a hydrothermal coupling eutectic solvent, which selectively separates hemicellulose, cellulose and lignin based on a green and efficient hydrothermal coupling eutectic solvent two-step pretreatment means. The three separated components have the advantages of complete structure, good biocompatibility, high utilization value and the like. Wherein, the hemicellulose, the cellulose and the lignin are respectively prepared into the high-value bio-based nano material: the composite material comprises carbon nano materials with high specific surface area (>2000), lignocellulose nano fibers with high crystallinity (> 70%), high aspect ratio (>140) and lignin nanospheres with core-shell structures and particle sizes as low as 100 nm. The full component conversion from low-value wood fiber waste to a high-value nano material platform is realized, the excellent performance of the prepared nano material is further explored, and a new way is opened up for the industrial application of the nano material.)

1. A conversion method for pretreating lignocellulose biomass based on a hydrothermal coupling eutectic solvent is characterized by comprising the following steps:

1) chopping, steaming and hydrothermal treating the air-dried lignocellulose biomass, adding dilute sulfuric acid as a catalyst for reaction, and dissolving to obtain hemicellulose filtrate;

2) mixing the separated solid component with an acidic eutectic solvent, heating for reaction, washing the filtered solid with deionized water to be neutral to obtain cellulose; adding acetone/water mixed solution into the filtrate, and flocculating and precipitating to obtain lignin;

3) performing hydrothermal carbonization on a hydrolysate of hemicellulose, mixing and grinding the obtained coke with KOH, and performing high-temperature activation to obtain a carbon nano material;

4) grinding and ultrasonically crushing the cellulose suspension to obtain lignocellulose nanocellulose;

5) dissolving lignin in gamma valerolactone solvent, adding glycerol, stirring to form lignin emulsion, and placing the lignin emulsion in a pressure tank of an SPG membrane emulsifier to prepare the lignin micro/nanospheres.

2. The conversion method for pretreating lignocellulose biomass based on the hydrothermal coupling eutectic solvent as claimed in claim 1, wherein the hydrothermal treatment conditions in the step 1) are as follows: and (3) steaming and boiling for 1-3 h at 140-180 ℃, wherein the dilute sulfuric acid is 0.7% sulfuric acid solution.

3. The conversion method for pretreating lignocellulose biomass based on the hydrothermal coupling eutectic solvent as claimed in claim 1, wherein the biomass and the acidic eutectic solvent in the step 2) are mixed according to a mass ratio of 1: 10-1: 20, and the heating condition is 130 ℃ for 3 hours.

4. The conversion method for pretreating lignocellulose biomass based on the hydrothermal coupling eutectic solvent as claimed in claim 3, wherein the acidic eutectic solvent is formed by mixing choline chloride and lactic acid according to a molar ratio of 1: 1-1: 4.

5. The method for converting the lignocellulosic biomass based on the hydrothermal coupling eutectic solvent pretreatment of the biomass as claimed in claim 4, wherein the ratio of the acetone/water mixture is 1:1 to 1:3.

6. The method for converting lignocellulosic biomass based on eutectic solvent pretreatment of the biomass in accordance with claim 1, wherein the carbonization conditions in step 3) are: carbonizing at 140-200 ℃ for 5-12 h; the mass ratio of the hydrothermal coke to KOH is 1: 2-1: 4, and the high-temperature activation conditions are as follows: 500-800 ℃ for 2 h.

7. The conversion method for pretreating lignocellulose biomass based on the hydrothermal coupling eutectic solvent as claimed in claim 1, wherein the mass concentration of the cellulose suspension in the step 4) is 0.5-1%.

8. The conversion method for pretreating lignocellulose biomass based on the hydrothermal coupling eutectic solvent as claimed in claim 1, wherein the volume of glycerol in the step 5) is 5-10 times that of gamma valerolactone solution, and the stirring conditions are as follows: magnetically stirring at 80 ℃ for 3 h.

9. The method of claim 8, wherein the lignin is dissolved in gamma valerolactone solvent at a ratio of 1:5 (m/v).

Technical Field

The invention belongs to the technical field of biomass material conversion and application, and relates to a conversion method for pretreating lignocellulose biomass based on a hydrothermal coupling eutectic solvent, in particular to a process for selectively separating lignocellulose full-component nano material conversion.

Background

China, as a traditional agricultural kingdom, inevitably produces a huge amount of agricultural and forestry wastes with abundant varieties in the agricultural and forestry production process. The main component of the agricultural and forestry wastes is lignocellulose which is the most abundant renewable resource, chemical and material on the earth, but most of the agricultural and forestry wastes are only treated by burning and landfill and are not reasonably developed and utilized. Lignocellulose mainly comprises cellulose, hemicellulose and lignin, and the main components of the lignocellulose are efficiently separated, so that the lignocellulose is the basis for realizing diversified and high-valued biorefinery. Therefore, a set of green and efficient pretreatment system is explored, three major components of lignocellulose are selectively separated, and the basis for realizing the conversion of the high-value nano materials of the three major components is provided. In recent years, deep eutectic solvent (deep eutectic solvent) pretreatment has been receiving attention from researchers as a green ion liquid with high efficiency and easy synthesis. The eutectic solvent is generally prepared by combining a hydrogen bond acceptor (such as quaternary ammonium salt) and a hydrogen bond donor (such as amide, carboxylic acid and polyalcohol) in a certain stoichiometric ratio and reacting at a certain temperature to generate a eutectic mixture. It has similar physicochemical properties with ionic liquid, such as low volatility, incombustibility and the like, and has good dissolution characteristics for biomass components, especially dissolution and separation of lignin.

The carbon nano material is a structural carbon material with at least one dimension less than 100nm in dispersion, and mainly comprises fullerene, a carbon nano-tube, graphene, nano mesoporous carbon and the like. The nano carbon material has the characteristics of good stability, high strength, high specific surface area, rich sources and the like, and is the nano material with the most development potential; the nano-cellulose has excellent degradability, biocompatibility, thermal stability, specific surface area, easy interweaving into a net, high strength, optical transparency, mechanical stability, thickening property and the like, is widely applied to various fields and has wide market prospect; the lignin nanosphere is micro-nano lignin with a regular structure, and is mainly applied to aspects of drug carriers, ultraviolet protection, nano fillers and the like. Although there are some reports on the preparation of lignocellulose-based nano materials at present, most of the preparation materials have single target products, generate secondary pollution of lignocellulose byproducts, and are difficult to realize full utilization of resource materials. At present, the hydrothermal DES synergistic pretreatment is adopted to selectively separate three major components of the lignocellulose, and no report is reported on the realization of the conversion of the full-component nano material of the lignocellulose.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a green high-efficiency lignocellulose pretreatment means for selectively separating three components of lignocellulose, the method is green and sustainable, the cost is low, the synchronous preparation of a carbon nano material, lignocellulose nano fiber and lignin nanospheres of the three components at the rear end can be realized, and the resource conversion of a waste biomass full-component nano material is realized.

In order to achieve the technical purpose, the invention is specifically realized by the following technical scheme:

a conversion method for pretreating lignocellulose biomass based on a hydrothermal coupling eutectic solvent comprises the following steps:

1) chopping, steaming and hydrothermal treating the air-dried lignocellulose biomass, adding dilute sulfuric acid as a catalyst for reaction, and separating to obtain hemicellulose filtrate;

2) mixing the separated solid with an acidic eutectic solvent, heating for reaction, washing the filtered solid with deionized water to be neutral to obtain a cellulose solid component; adding acetone/water mixed solution into the filtrate, and flocculating and precipitating to obtain lignin;

3) performing hydrothermal carbonization on a hydrolysate of hemicellulose, mixing and grinding the obtained coke with KOH, and performing high-temperature activation to obtain a carbon nano material;

4) grinding and ultrasonically crushing the cellulose suspension to obtain lignocellulose nanocellulose;

5) dissolving lignin in gamma valerolactone solvent, adding glycerol, stirring to form lignin emulsion, and placing the lignin emulsion in a pressure tank of an SPG membrane emulsifier to prepare the lignin micro/nanospheres.

Further, the lignocellulosic biomass is selected from waste biomass of untreated herbaceous plants (straw stalks, rice stalks), hardwoods (poplar), softwoods (pine), gramineous plants (moso bamboo chips) and the like.

Further, the hydrothermal treatment conditions in the step 1) are as follows: and (3) steaming and boiling for 1-3 h at 140-180 ℃, wherein the dilute sulfuric acid is 0.7% sulfuric acid solution. Preferably, the hydrothermal treatment temperature is 170 ℃, and the cooking time is 1.5 h.

The dilute sulfuric acid solution is used as a catalyst for hydrothermal treatment, so that the degradation of hemicellulose long chains can be catalyzed preferentially to form shorter oligomers and sugar monomers, and the hemicellulose is degraded and separated from the hydrolysate.

Further, the acidic eutectic solvent is formed by mixing choline chloride and lactic acid according to a molar ratio of 1: 1-1: 4. Preferably, the molar ratio of choline chloride to lactic acid is 1: 2. The acidic eutectic solvent has good lignin dissolving capacity and high thermal stability.

Further, in the step 2), the solid component and the acidic eutectic solvent are mixed according to the mass ratio of 1: 10-1: 20, and the heating condition is that the temperature is 130 ℃ for 3 hours. Preferably, the mass ratio of the solid to the acidic eutectic solvent is 1: 20.

According to the invention, the DES prepared from choline chloride and lactic acid is selected, under the pretreatment condition, lignin can be selectively extracted, and polysaccharide components can be better maintained.

The mechanism of separating and extracting lignin by adopting the acidic DES pretreatment is different from that of the traditional solvent or alkali solution. The DES solvent has mild reaction conditions, mainly depends on the strong ion characteristics of the DES solvent, high hydrogen bond destruction capability and high lignin solubility, and dissolves lignin wound on cellulose while swelling the cellulose fiber in a substrate.

Further, the ratio of the acetone/water mixed solution is 1: 1-1: 3.

Further, the carbonization conditions in the step 3) are as follows: hydrothermal carbonization is carried out for 5-12 h at 140-200 ℃. Preferably carbonizing at 200 ℃ for 12 h; the mass ratio of the coke to the KOH is 1: 2-1: 4, and the high-temperature activation conditions are as follows: 500-800 ℃ for 2 h. Preferably, the mass ratio of the coke to the KOH is 1:3.5, the activation temperature is 800 ℃, and the time is 2 hours.

The invention adopts KOH high-temperature activation to obtain the activated carbon nano material with uniform aperture and high specific surface area.

Further, the mass concentration of the cellulose suspension in the step 4) is 0.5-1%. Preferably, the mass concentration of the cellulose suspension is 0.5%.

The grinding of the invention adopts a mechanical millstone, and strong acting forces such as shearing, friction, impact and the like are generated by utilizing the relative motion of a pair of fixed millstones (stators) and a high-speed rotating grinding body (rotor), so that hydrogen bonds among and in cellulose molecules are destroyed, molecular chains of the cellulose are continuously reduced, and thus, nano-scale fibers are stripped from biomass fibers, and the micro-nano treatment of the cellulose is realized.

Further, the volume of the glycerol in the step 5) is 5-10 times of that of the gamma valerolactone solution, and the stirring conditions are as follows: magnetically stirring at 80 ℃ for 3 h. The ratio of lignin dissolved in gamma valerolactone solvent was 1:5 (m/v).

Wherein gamma valerolactone is an important platform compound which can be derived from lignocellulose and can be used as a substitute for a regenerated aprotic polar organic solvent for dissolving lignin.

Preferably, the pressure of the nitrogen in the SPG membrane emulsifier is 0.01MPa, and the pore diameter of the SPG membrane is 100 nm.

Wherein different emulsification pressures result in different droplet formation processes. The emulsification pressure is slightly higher than the critical pressure, and single liquid drop forms on the membrane surface, and when the liquid drop size reaches certain scale automatic the dropping, emulsification pressure is 2 ~ 5 times of critical pressure comparatively suitable. The proper emulsification pressure corresponds to the matched membrane aperture, and the smaller the membrane aperture particle size is, the smaller the prepared lignin micro-nano sphere is.

The specific surface area of the active carbon nano material obtained by the invention is up to 2000m² g^-1The crystallinity of the cellulose nano-fiber is more than 70 percent, and the particle size of the lignin nanosphere is as small as 100 nm.

The invention has the beneficial effects that:

(1) the hydrothermal pretreatment aims at the characteristic that hemicellulose is easier to degrade than cellulose, so that water with heat energy and organic acid separated from a hemicellulose side chain catalyze the decomposition of a hemicellulose long chain to form a short chain oligomer and a sugar monomer, thereby separating and recovering a hemicellulose component without loss to the cellulose component.

(2) The acidic DES pretreatment reaction condition of the invention is mild, mainly depends on self strong ion characteristic, high hydrogen bond destruction capability and high lignin solubility, dissolves lignin wound on cellulose while swelling cellulose fiber in a substrate, and has good reservation for polysaccharide component and lignin structure.

(3) The invention successfully applies the waste hemicellulose component in the traditional industry to the preparation of the activated carbon nano material, and obtains the specific surface area up to 2000m² g^-1The carbon nano material realizes the magnificent transformation from the traditional waste to the high-value nano material.

(4) The lignin nanosphere has an obvious core-shell structure, the particle size range is 100-500 nm, the Zeta potential value is less than-30 mV, and the lignin nanosphere has high stability and shows a huge industrial application value.

(5) According to the preparation method, three major components of the lignocellulose are obtained through two-step coupling pretreatment layering and selective separation, the structural integrity of the components is kept while the components are efficiently separated, and the high-value material application of low-value wastes is realized by the converted full-component nano material platform.

Drawings

FIG. 1 is an index of the hemicellulose dissolution rate of different raw materials under the temperature gradient of 140 ℃ and 180 ℃ in the hydrothermal pretreatment in example 6 of the present invention;

FIG. 2 shows the morphology of lignin micro-nanospheres prepared from lignin according to the invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

The embodiment specifically provides a novel process for selectively separating lignocellulose and converting full-component nano materials based on hydrothermal coupling acidic DES pretreatment, which comprises the following steps:

(1) separating the lignocellulosic components:

carrying out high-temperature hydrothermal treatment on poplar sawdust (hardwood): 1kg of poplar wood chips were placed in a plastic bag and impregnated with a 0.7 wt% (based on dry wood weight) solution of dilute sulfuric acid at a solid-to-liquid ratio of 1:15 and left overnight at room temperature. The impregnated poplar samples were then transferred to a 2L digester and, after hydrothermal digestion at 170 ℃ for 1.5h, the resulting slurry was collected and filtered, the liquid fraction was collected and the solid fraction was washed with 1L of water and stored at 4 ℃ for future use.

DES pretreatment: adding high-temperature hydrothermal pretreated poplar and DES into an erlenmeyer flask according to the mass ratio of 1:20, continuously stirring and heating at 130 ℃ for 3 hours, cooling the reaction mixture to about 80 ℃, then adding 30mL of acetone/water mixture (the volume ratio is 50/50) to reduce the viscosity, filtering, washing cellulose twice by using 30mL of acetone/water mixture in order to remove residual eutectic solvent and lignin in the cellulose component, then washing twice by using hot water until the pH is neutral, collecting filtrate and washing liquid, standing overnight, evaporating acetone, precipitating the lignin component, then filtering and washing by using a nylon membrane with the aperture of 0.45 mu m, and finally freeze-drying for later use.

(2) Preparing a carbon nano material:

placing the reaction kettle filled with 150mL of hemicellulose hydrolysate in a high-temperature oven, performing primary carbonization on hemicellulose hydrolysis oligomer and monosaccharide components at 200 ℃ for 12 hours, cooling to normal temperature, performing vacuum filtration by using a nylon filter membrane, washing to be neutral, drying in the oven at 105 ℃, and preserving coke materials. Grinding and uniformly mixing the obtained hydrothermal coke material and KOH according to the mass ratio of 1:3.5 in a grinding dish, placing the mixture in a tubular furnace at 800 ℃, and firing for 2 hours. After firing is completed, cooling to room temperature, and using 3mol L of the fired sample^-1Neutralizing excessive KOH with hydrochloric acid, vacuum filtering with nylon membrane, water washing to neutrality, stoving sample and storing carbon nanometer material.

(3) Preparing the lignocellulose nanofibers:

diluting 20g of cellulose component obtained by two-step coupling pretreatment with distilled water to the concentration of 0.5%, grinding ten times by using a mechanical grinder at the rotating speeds of-1, -5 and-10, respectively sampling 50mL, and observing the stripping degree of cellulose at different grinding rotating speeds. The method is characterized in that prepared fiber pulp with a certain concentration is poured into a grinding chamber, a arsenolite millstone is started to rub and rotate, the upper arsenolite and the lower arsenolite are repeatedly and continuously ground, so that cellulose in the fiber pulp is rolled, sheared, torn and ground when contacting with the arsenolite, tooth grooves of the arsenolite millstone are favorable for cracking the cellulose, and the upper and lower spacing and the rotating speed of the arsenolite millstone can be adjusted according to the final size requirement of the ground cellulose. The method has the advantages of relatively low energy consumption and convenient disassembly and washing of the equipment. And (3) placing the sample ground by the grinding disc in an ultrasonic cell crusher for 100W ultrasonic crushing and homogenizing and alternating treatment by a homogenizer, and storing the prepared nano-cellulose in a refrigerator at 4 ℃.

(4) Preparing lignin nanospheres:

in order to ensure as far as possible that the lignin structure is not affected by the extraction conditions, the extraction of lignin is carried out under very mild conditions. The method comprises the following specific steps: putting lignin obtained by the coupling pretreatment into a flask, and adding a proper amount of gamma valerolactone (the solid concentration is 4mg mL)^-1) And (5) performing ultrasonic treatment for 15min to completely dissolve and disperse the materials. And (2) uniformly pouring 5 times of glycerol as an oil phase into the dissolved lignin solution, magnetically stirring at 80 ℃ for 3 hours to form uniformly dispersed lignin emulsion, pouring the lignin emulsion into an SPG membrane emulsifier pressure tank, adjusting the magnetic stirring speed to 500rmp, and slowly increasing the nitrogen pressure to 0.01MPa to enable the lignin dispersed phase to pass through an SPG membrane with the pore diameter of 200nm to prepare the lignin micro-nanospheres with uniform particle sizes. It was transferred to a blue-top bottle and stored under sealed conditions at 4 ℃.

Example 2

The procedure was substantially the same as in example 1 except that: the hard wood poplar wood chips are replaced by soft wood pine wood chips.

Example 3

The procedure was substantially the same as in example 1 except that: the hardwood poplar wood chips are replaced by herbaceous plant wheat straws.

Example 4

The procedure was substantially the same as in example 1 except that: the hard wood poplar wood chips are replaced by herbaceous plant rice straws.

Example 5

The procedure was substantially the same as in example 1 except that: the hardwood poplar wood chips are replaced by grass family plant moso bamboo chips.

As shown in tables 1 and 2, the hydrothermal pretreatment of the present invention can significantly dissolve different types of hemicellulose components of biomass in examples 1 to 5, the dissolution efficiency is close to 100%, and except for the raw material of moso bamboo in example 5, a relatively high cellulose recovery rate (> 80%) is maintained. The acidic DES pretreatment results show that it has lignin removal rates as high as 70% for both examples 1 and 5, and retains cellulose recovery rates as high as 100%, whereas examples 2-4 do not exhibit a good lignin selective removal effect, which demonstrates the functional differences of acidic DES pretreatment on different types of biomass, making reasonable assumptions for back-end material selective derivatization.

TABLE 1 EXAMPLES 1 TO 5 measurement of index of dissolution rate of hemicellulose and recovery rate of cellulose in hydrothermal pretreatment

TABLE 2 determination of the respective indices of the acid DES pretreatment for the selective separation of lignin and retention of the cellulosic components of examples 1-5

Example 6

The hydrothermal digestion temperature in step (1) of examples 1 to 5 was changed to a gradient of 140 ℃, 150 ℃, 160 ℃ and 180 ℃, and other operation steps were the same as those of example 1.

As shown in fig. 1, the optimal temperature for 1.5h of hydrothermal pretreatment cooking of the present invention is 170 ℃. Under these conditions, the water with heat energy and the organic acid decomposed from the side chain of hemicellulose promote the decomposition of the long chain of hemicellulose into small molecular oligomers and monosaccharides without damaging the cellulose. Therefore, for different kinds of biomass, the high hemicellulose dissolution rate is obtained, the high cellulose recovery rate is kept, and the energy consumption is reduced to the minimum.

Example 7

The pore sizes of the SPG membranes used for preparing the lignin micro-nanospheres in the steps (4) of examples 1 to 5 were adjusted to 100nm, 200nm, 300nm, 400nm, and 500nm, respectively, and the other operation steps were the same as those of example 1.

As shown in table 3, nanospheres prepared from different lignin obtained by hydrothermal coupling acidic DES two-step coupling pretreatment all showed uniform spherical core-shell structures, wherein the dark black part in the middle was a core formed by lignin hydrophobic groups, and the light color part around was a shell formed by hydrophilic groups, and the specific morphology is shown in fig. 2. The lignin nanospheres derived from the softwood lignin have the smallest particle size of 100-200, and the lignin nanospheres derived from the gramineae moso bamboo have the largest particle size of 500nm, and the difference is derived from different lignocellulose authigenic physicochemical properties. The prepared lignin micro-nanospheres have good solution dispersion stability (zeta value is less than-30), the particle size of the micro-nanospheres has approximate linear relation with the membrane pore size, namely the smaller the membrane pore size is, the smaller the particle size of the prepared micro-nanospheres is, the smaller the shearing force required for preparing the micro-nanospheres with the same particle size is, and the possibility is provided for the application of the lignin nanospheres in different fields.

Table 3 examples 1-5 indexes of lignin micro-nanospheres prepared by membrane emulsification with membrane pore size of 100nm

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.