Method for removing lignin from meta-acidic butanediol

Abstract

The invention relates to the technical field of agricultural and forestry residue biomass resource treatment, and particularly discloses a method for removing lignin from meta-acidic butanediol, which is used for solving the problem of how to improve the removal rate of lignin in acid pretreatment. Comprising the following steps that 1, straw is smashed and sieved through a 20-60-mesh sieve, the smashed straw is subjected to extraction and dewaxing treatment through an organic solvent, and the organic solvent is absolute ethyl alcohol or a solvent obtained by mixing methylbenzene and ethyl alcohol according to the volume ratio of 2: 1; according to the method, the lignin removal effect of acid pretreatment can be enhanced, the removal rate of the lignin in the straw can be increased to 80.4% from 25.6% by adjusting the proportion of butanediol to dilute acid, and the removal rate of the lignin in the straw can be increased to 80.4% from 25.6% by adjusting the proportion of butanediol to dilute acid. The pretreated sample is subjected to enzyme hydrolysis for 48 hours, and when the enzyme dosage is 10 FPU cellulase + 500 U xylanase / g substrate, the yield of glucose can reach 90% or above.

Description

Technical Field

[0001] The invention relates to the technical field of agricultural and forestry residue biomass resource processing, in particular to a method for removing lignin by using slightly acidic butanediol. Background Art

[0002] Agricultural and forestry waste is a widely available and renewable biomass resource. In recent years, the conversion of biomass resources into fuels or high-value-added chemicals through biological or chemical methods has received widespread attention from the scientific community. Generally speaking, lignocellulosic biomass is mainly composed of three components: cellulose, hemicellulose, and lignin, of which cellulose accounts for 40%-50% of the total mass, hemicellulose accounts for about 15%-30%, and lignin accounts for about 15%-30%. In the preparation process of lignocellulosic raw materials to fuel bioethanol, it is usually necessary to pretreat the raw materials first, then enzymatically treat them to produce fermentable monosaccharides, and finally prepare bioethanol through microbial fermentation.

[0003] Lignin is the main barrier to the enzymatic saccharification of wood fiber. Generally speaking, solvent-based or alkaline pretreatment will dissolve lignin, while acidic or steam pretreatment will dissolve hemicellulose, leaving lignin in the raw material. Dilute acid pretreatment is one of the most commonly used pretreatment technologies, with the advantages of low cost and high efficiency. During the dilute acid pretreatment process, lignin will depolymerize and re-condense, and re-adsorb on the surface of the raw material. Lignin is highly hydrophobic and difficult to dissolve in the pretreatment reaction solution, resulting in a low lignin removal rate. Residual lignin in the raw material has an adverse effect on the subsequent enzymatic hydrolysis of lignocellulose to prepare fermentable monosaccharides, resulting in reduced enzyme hydrolysis efficiency and increased conversion costs.

[0004] How to improve the removal rate of lignin by acid pretreatment is a problem to be solved. Based on this, a method for removing lignin by using a partially acidic butanediol is now provided. Summary of the invention

[0005] The purpose of the present invention is to provide a method for removing lignin by using slightly acidic butanediol, which solves the problems in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for removing lignin by using slightly acidic butanediol comprises the following steps:

[0008] Step 1: crush the straw and pass it through a 20-60 mesh sieve, and then extract and dewax the crushed straw with an organic solvent, wherein the organic solvent is anhydrous ethanol or a solvent obtained by mixing toluene and ethanol in a volume ratio of 2:1;

[0009] Step 2: pretreating the straw treated in step 1, the pretreatment conditions are: 1% (w / w) dilute acid and butanediol, the volume ratio of dilute acid to butanediol is 5:1, 2:1, 1:1, the reaction temperature is 110, 120, 130 or 140 °C, and the reaction time is 30, 60, 90 min;

[0010] Step 3: After pretreatment, the solid residue and the supernatant are separated by centrifugation, and the solid residue is washed once with deionized water and then washed once with an organic solvent dioxane or anhydrous ethanol. After each washing, the solid and liquid are separated by vacuum filtration, and the organic solvent filtrate is concentrated and recovered by vacuum evaporation to separate the lignin dissolved in the organic solvent. After washing, the solid residue is washed with deionized water until neutral, and the residue is freeze-dried to obtain the pretreated sample;

[0011] Step 4: Mix the supernatant obtained by centrifugation in step 3 with 2-5 volumes of deionized water to obtain lignin precipitate and xylose-rich supernatant.

[0012] Step 5: The pretreated samples obtained in step 3 were hydrolyzed by cellulase (5, 10, 15 FPU / g dry matter) and xylanase (200, 500, 1000 U / g dry matter) for 48 h.

[0013] Step 6: Mix the filtrate obtained in step 3 after washing with deionized water and the supernatant rich in xylose obtained in step 4, and concentrate it by vacuum evaporation to make its volume 1 / 4-1 / 8 of the original volume. The concentrated solution is cooled to 20-25 °C, and 95% ethanol by volume is added to control the ethanol content to 75%-85% by volume. The solution is allowed to stand for 1-3 hours, and then centrifuged to obtain a solid part and a supernatant. The solid part is freeze-dried to obtain xylose. The centrifuged supernatant is concentrated by vacuum evaporation, and the ethanol and water therein are recovered to obtain a residual liquid. The acidic butanediol in the residual liquid is recovered for the next pretreatment.

[0014] On the basis of the above technical solution, the present invention also provides the following optional technical solution:

[0015] In an optional scheme: the dilute acid in step 2 is one or more of sulfuric acid, hydrochloric acid, and acetic acid.

[0016] In an optional embodiment, the butanediol in step 2 is 1,2-butanediol, 1,3-butanediol or 1,4-butanediol.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention can enhance the removal effect of lignin by acid pretreatment. By adjusting the ratio between butanediol and dilute acid, the removal rate of lignin in straw can be increased from 25.6% to 80.4%. After pretreatment, the sample is hydrolyzed by enzyme for 48 hours. When the enzyme dosage is 10 FPU cellulase + 500 U xylanase / g substrate, the glucose yield can reach more than 90%.

[0019] 2. The technical route designed in the present invention is simple and convenient to operate. The organic solvent used to wash the solid residue after pretreatment and the ethanol used for alcohol precipitation and separation of xylose can be recycled by vacuum evaporation.

[0020] 3. Since the butanediol added to the pretreatment liquid of the present invention has a high boiling point, the butanediol after pretreatment will be retained in the residual liquid after vacuum evaporation to recover ethanol and can be recycled for multiple times.

[0021] 4. The present invention increases the proportion of dilute acid used when treating straw, reduces the amount of butanediol used, and thus greatly reduces the treatment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the technical roadmap of the present invention.

[0023] Figure 2 The scanning electron microscope images of the straw of the present invention before and after pretreatment.

[0024] Figure 3 It is the glucose yield after enzymatic hydrolysis of the pretreated straw in one embodiment of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] See also Figure 1-Figure 3 The embodiment of the present invention provides a method for removing lignin by using slightly acidic butanediol, comprising the following steps:

[0027] Step 1: grind the corn stalks and pass them through a 60-mesh sieve, and then extract and dewax the crushed stalks with an organic solvent, wherein the volume ratio of toluene to ethanol is 2:1;

[0028] Step 2: Then pre-treat the straw treated in step 1, and the pre-treatment conditions are: the mass fraction of dilute sulfuric acid is 1%, the volume ratio of dilute sulfuric acid to 1,2-butanediol is 5:1, the treatment temperature is 120°C, and the treatment time is 1 hour;

[0029] Step 3: After pretreatment, the solid residue and the supernatant are separated by centrifugation, the solid residue is washed once with water, washed once with an organic solvent dioxane, filtered, the organic filtrate is vacuum evaporated to recover dioxane for reuse, the lignin dissolved in dioxane is recovered, the residue after washing is washed with deionized water to neutrality, and freeze-dried to obtain the pretreated raw material sample;

[0030] Step 4: Mix the supernatant obtained by centrifugation in step 3 with 3 volumes of deionized water to obtain lignin precipitate and xylose-rich supernatant.

[0031] Step 5: The treated raw material samples were hydrolyzed by cellulase (10 FPU / g dry matter) and xylanase (500 U / g dry matter) for 48 h.

[0032] Step 6: The filtrate obtained in step 3 after washing with deionized water and the supernatant rich in xylose obtained in step 4 are mixed, and vacuum evaporation is used to concentrate the volume to 1 / 6 of the original volume. The concentrated solution is cooled to 25°C, and 95% ethanol by volume is added to control the ethanol content to 75% by volume. The solution is allowed to stand for 3 hours, and then centrifuged to obtain a solid part and a supernatant. The solid part is freeze-dried to obtain xylose. The centrifuged supernatant is concentrated by vacuum evaporation, and the ethanol and water therein are recovered to obtain a residual liquid, and the acidic butanediol in the residual liquid is recovered for the next pretreatment.

[0033] Table 1 Determination results of chemical components of straw before and after pretreatment:

[0034] sample Dextran(%) Xylan (%) Arabinan (%) Acid insoluble lignin (%) Acid soluble lignin (%) Lignin removal rate (%) Straw raw materials 31.2 18.2 2.9 16.3 4.6 -- Control group 47.7 8.7 0.5 26.6 2.5 25.6 Experimental Group 50.1 20.5 1.3 5.2 2.1 80.4

[0035] Note: The pretreatment conditions of the control group were: 1% dilute acid was used to treat the straw material at 120 ℃ for 1 hour; the pretreatment conditions of the experimental group were: 1% dilute acid and butanediol were mixed in a certain proportion and then treated at 120 ℃ for 1 hour.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing lignin by using slightly acidic butanediol, characterized in that: The following steps are involved: Step 1: crush the straw and pass it through a 20-60 mesh sieve, and then extract and dewax the crushed straw with an organic solvent, wherein the organic solvent is anhydrous ethanol or a solvent obtained by mixing toluene and ethanol in a volume ratio of 2:1; Step 2: pretreating the straw treated in step 1, the pretreatment conditions are: 1% (w / w) dilute acid and butanediol, the volume ratio of dilute acid to butanediol is 5:1-1:1, the reaction temperature is 110-140°C, and the reaction time is 30-90 min; Step 3: After the pretreatment, the solid residue and the supernatant are separated by centrifugation, and the solid residue is washed once with deionized water and once with an organic solvent such as dioxane or anhydrous ethanol; After each washing, the solid and liquid are separated by vacuum filtration, the organic solvent filtrate is concentrated by vacuum evaporation to recover the organic solvent, and the lignin dissolved in the organic solvent is separated. The solid residue after washing is washed with deionized water to neutrality, and the residue is freeze-dried to obtain the pretreated sample; Step 4: Mix the supernatant obtained by centrifugation in step 3 with 2–5 times the volume of deionized water to obtain lignin precipitate and xylose-rich supernatant; Step 5: The pretreated sample obtained in step 3 is hydrolyzed by cellulase and xylanase for 48 hours; Step 6: The vacuum filtered filtrate obtained after washing with deionized water obtained in step 3 and the xylose-rich supernatant obtained in step 4 are mixed, and concentrated by vacuum evaporation to reduce its volume to 1 / 4-1 / 8 of the original volume. The concentrated solution is cooled to 20-25°C, and 95% by volume ethanol is added to control the ethanol content to 75%-85% by volume. The solution is allowed to stand for 1-3 hours, and is centrifuged to obtain a solid portion and a supernatant. The solid portion is freeze-dried to obtain xylose.

2. The method for removing lignin by using a partial acidic butanediol according to claim 1, characterized in that: The dilute acid in step 2 is one or more of sulfuric acid, hydrochloric acid and acetic acid.

3. The method for removing lignin by using slightly acidic butanediol according to claim 1, characterized in that: In the step 2, the butanediol is 1,2-butanediol, 1,3-butanediol or 1,4-butanediol.

4. The method for removing lignin by using slightly acidic butanediol according to claim 1, characterized in that: The pretreated sample obtained in step 3 was hydrolyzed by cellulase and xylanase for 48 hours, with the cellulase dosage being 5-15 FPU / g dry matter and the xylanase dosage being 200-1000 U / g dry matter.

5. The method for removing lignin by using slightly acidic butanediol according to claim 1, characterized in that: In step six: the centrifuged supernatant is concentrated by vacuum evaporation to recover ethanol and water therein to obtain a residual liquid, and the acidic butanediol in the residual liquid is recovered for use in the next pretreatment.

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