Extraction process for efficiently extracting cellulose from cotton straws

Abstract

The invention discloses an extraction process for efficiently extracting cellulose from cotton straws. The extraction process comprises the following steps: crushing the cotton straws, carrying out microwave-ultrasonic synergistic pretreatment, recycling alkali liquor, carrying out immobilized enzymolysis, carrying out simultaneous saccharification and fermentation, purifying the cellulose and recycling wastes. According to the method, the cellulose yield is 78%-82%, the lignin removal rate is 92%-95%, and the comprehensive cost is reduced by 85.6% through a microwave-ultrasonic synergistic pretreatment, immobilized enzymolysis and recycling integrated system. The lignin adsorption material, the biomass fuel and the fuel ethanol are synchronously produced by the process, the COD (Chemical Oxygen Demand) of the waste liquid is less than or equal to 2000mg / L, the water consumption is reduced by 70 percent, the economical efficiency and the environmental protection property are obviously improved, and the process is suitable for large-scale resource utilization of agricultural wastes.

Description

Technical Field

[0001] The invention relates to the technical field of cellulose extraction from cotton straws, in particular to a process for efficiently extracting cellulose from cotton straws. Background Art

[0002] Cotton straw contains cellulose, which can be extracted from cotton straw. For the extraction process, existing technologies mostly use a single chemical method or enzymatic hydrolysis method, which has problems such as high energy consumption (≥1.2 kWh / kg), low lignin removal rate (≤75%), and insufficient cellulose purity (≤88%). The amount of chemical reagents used is large (such as NaOH concentration ≥4%), the COD of the waste liquid is high (≥8000 mg / L), and the processing cost accounts for more than 35% of the overall cost. The enzyme preparation in the enzymatic hydrolysis process is not recyclable and has a low reuse rate. The lignin and enzymatic hydrolysis residue in the pretreatment waste liquid are not effectively utilized, resulting in a waste of biomass resources.

[0003] Therefore, in order to correct the above-mentioned defects, we proposed an extraction process for efficiently extracting cellulose from cotton straw. Summary of the Invention

[0004] The technical problem solved by the present invention is a process for efficiently extracting cellulose from cotton straw. Through microwave and ultrasonic synergistic pretreatment, efficient lignin removal (≥92%) is achieved, the amount of chemical reagents used is reduced by more than 30%, and the immobilized enzymatic hydrolysis technology is used to increase the reuse rate of enzyme preparations to 5 times, reduce the enzymatic hydrolysis cost by 57%, build a waste cascade utilization system, and simultaneously produce lignin adsorption materials, biomass fuel particles and fuel ethanol, thereby improving comprehensive benefits.

[0005] To achieve the above object, the present invention provides the following technical solution: a process for efficiently extracting cellulose from cotton straw, comprising the following steps:

[0006] S1. First, crush the cotton straw;

[0007] S2, the crushed straw is subjected to microwave and ultrasound synergistic pretreatment;

[0008] S3, recycling the alkali solution produced in step S2;

[0009] S4, after the straw is pretreated by microwave and ultrasound, it is subjected to immobilized enzymatic hydrolysis;

[0010] S5. In step S4, saccharification and fermentation are carried out simultaneously;

[0011] S6. Then, cellulose is purified and a waste cascade utilization system is constructed.

[0012] Furthermore, in step S2, the microwave-ultrasound synergistic pretreatment includes: first preparing a composite alkali solution as a catalyst, then placing the crushed straw in the composite alkali solution, and then performing microwave-ultrasound synergistic treatment to enhance the reaction, and the total alkali concentration of the composite alkali solution is 1.5% to 2.5%.

[0013] Furthermore, in step S4, the immobilized enzymatic hydrolysis uses an immobilized complex enzyme, which includes an enzyme preparation and a synergist. The enzyme preparation is made of cellulase and xylanase, the synergist is tea saponin, the mass ratio of cellulase to xylanase is 2:1, and the mass ratio of the enzyme preparation to the synergist is 10:1.

[0014] Furthermore, in step S5, saccharification and fermentation is performed by adding yeast during immobilized enzymatic hydrolysis to produce ethanol through fermentation.

[0015] Furthermore, in step S3, ceramic membrane filtration is used.

[0016] Furthermore, in step S6, the waste cascade utilization system includes:

[0017] Pretreatment of wastewater: acid precipitation to extract lignin and prepare adsorption materials;

[0018] Enzyme hydrolysis residue: compressed and granulated into biomass fuel;

[0019] Water circulation: Washing water is reused after desalination through electrodialysis.

[0020] Furthermore, the composite alkali solution is prepared by mixing NaOH, Na2CO3 and H2O2, and the composite alkali solution is recovered by adding Fe3O4 nanoparticles.

[0021] Furthermore, the mass ratio of the composite alkali solution to the added straw is 8:1, and the mass ratio of NaOH, Na2CO3, and H2O2 in the composite alkali solution is 3:1:2.

[0022] Furthermore, during the immobilized enzymatic hydrolysis, pH=5.5.

[0023] Compared with existing technologies, the present invention achieves the following benefits: through microwave-ultrasound synergistic pretreatment, immobilized enzymatic hydrolysis, and an integrated resource utilization system, it achieves a cellulose yield of 78%-82%, a lignin removal rate of 92%-95%, and an overall cost reduction of 85.6%. The process also simultaneously produces lignin adsorption material, biomass fuel, and fuel ethanol, with a wastewater COD of ≤2000 mg / L and a 70% reduction in water consumption. This significantly improves economic and environmental performance, making it suitable for large-scale resource utilization of agricultural waste. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described 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 making creative efforts are within the scope of protection of the present invention.

[0025] The present invention provides a technical solution:

[0026] A process for efficiently extracting cellulose from cotton straw comprises the following steps: cotton straw crushing → microwave-ultrasound coordinated pretreatment → alkali solution recycling → immobilized enzymatic hydrolysis → simultaneous saccharification and fermentation → cellulose purification + waste resource utilization.

[0027] (1) Microwave and ultrasonic synergistic pretreatment

[0028] Composite alkali system: NaOH and Na2CO3 (mass ratio 3:1), total alkali concentration 1.5% to 2.5%, and H2O2 dosage reduced by 40%.

[0029] Intensification reaction: pulsed microwave (300W / kg, working 30s / rest 15s) coupled with ultrasound (40kHz, 100W / m 3 ), the reaction time was shortened to 1220min.

[0030] Catalyst recovery: Adding 0.05% Fe3O4 nanoparticles (magnetic recovery rate ≥ 98%), the reaction efficiency increased by 25%.

[0031] (2) Alkali circulation system

[0032] 90% of the alkali solution was recovered by ceramic membrane filtration (molecular weight cut-off 5000Da) and reused in the pretreatment process.

[0033] (3) Immobilized composite enzymatic hydrolysis

[0034] Enzyme preparation: Cellulase and xylanase were immobilized on a sodium alginate carrier (enzyme activity retention rate 85%) and reused 5 times.

[0035] Synergist: Adding 0.1% tea saponin, the enzymatic hydrolysis time is shortened to 1.5-2.5h.

[0036] Simultaneous saccharification and fermentation: The residual liquid from enzymatic hydrolysis was inoculated with yeast (Saccharomyces cerevisiae QD8) to produce fuel ethanol (yield 0.18g / g straw).

[0037] (4) Resource integration system

[0038] Pretreatment of wastewater: acid precipitation to extract lignin and prepare adsorption material (BET520m 2 / g).

[0039] Enzyme hydrolysis residue: compressed and pelletized into biomass fuel (calorific value 16MJ / kg).

[0040] Water circulation: Washing water is reused after desalination through electrodialysis, reducing water consumption by 70%.

[0041] Example

[0042] 1. Raw material processing

[0043] Take 100g of cotton straw (particle size ≤ 2mm).

[0044] 2. Preprocessing

[0045] Compound alkali solution (1.8% NaOH + 0.6% Na2CO3 + 1.2% H2O2 + 0.05% Fe3O4), material-liquid ratio 1:8.

[0046] Microwave and ultrasonic synergistic treatment (pulsed microwave 300W, ultrasonic 40kHz), reaction at 60℃ for 15min.

[0047] 3. Alkali recovery

[0048] Ceramic membrane filtration, alkali liquor recycling rate reaches 90%.

[0049] 4. Enzymatic hydrolysis

[0050] Immobilized complex enzyme (1500 U / g, cellulase:xylanase = 2:1), added with 0.1% tea saponin, pH 5.5, enzymatic hydrolysis at 50°C for 2 h.

[0051] Yeast is added simultaneously and fermented for 24 hours to produce ethanol.

[0052] 5. Results

[0053] The cellulose yield is 80.5%, the purity is 94.2%, and the lignin removal rate is 93.8%.

[0054] The ethanol produced was 17.3 g, and the calorific value of the residue pelletized was 15.8 MJ / kg.

[0055] Comparative Example

[0056] 100 g of cotton straw (particle size ≤ 2 mm) was taken and then extracted using the chemical method and enzymatic method in the prior art.

[0057] Performance comparison between the embodiment and the comparative example

[0058]

[0059]

[0060] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for efficiently extracting cellulose from cotton straw, characterized by: The steps include: S1. First, crush the cotton straw; S2, the crushed straw is subjected to microwave and ultrasound synergistic pretreatment; S3, recycling the alkali solution produced in step S2; S4, after the straw is pretreated by microwave and ultrasound, it is subjected to immobilized enzymatic hydrolysis; S5. In step S4, saccharification and fermentation are carried out simultaneously; S6. Then, cellulose is purified and a waste cascade utilization system is constructed.

2. The process for efficiently extracting cellulose from cotton straw according to claim 1, characterized in that: In step S2, the microwave-ultrasound synergistic pretreatment includes: first preparing a composite alkali solution as a catalyst, then placing the crushed straw in the composite alkali solution, and then performing microwave-ultrasound synergistic treatment to enhance the reaction, wherein the total alkali concentration of the composite alkali solution is 1.5% to 2.5%.

3. The process for efficiently extracting cellulose from cotton straw according to claim 1, characterized in that: In step S4, immobilized enzymatic hydrolysis uses immobilized complex enzyme, which includes an enzyme preparation and a synergist. The enzyme preparation is made of cellulase and xylanase, the synergist is tea saponin, the mass ratio of cellulase to xylanase is 2:1, and the mass ratio of enzyme preparation to synergist is 10:

1.

4. The process for efficiently extracting cellulose from cotton straw according to claim 1, characterized in that: In step S5, saccharification and fermentation is performed by adding yeast during immobilized enzymatic hydrolysis to produce ethanol through fermentation.

5. The process for efficiently extracting cellulose from cotton straw according to claim 1, characterized in that: In the step S3, ceramic membrane filtration is used.

6. The process for efficiently extracting cellulose from cotton straw according to claim 1, characterized in that: In step S6, the waste cascade utilization system includes: Pretreatment of wastewater: acid precipitation to extract lignin and prepare adsorption materials; Enzyme hydrolysis residue: compressed and granulated into biomass fuel; Water circulation: Washing water is reused after desalination through electrodialysis.

7. The process for efficiently extracting cellulose from cotton straw according to claim 2, characterized in that: The composite alkali solution is prepared by mixing NaOH, Na2CO3 and H2O2, and the composite alkali solution is recovered by adding Fe3O4 nanoparticles.

8. The process for efficiently extracting cellulose from cotton straw according to claim 7, characterized in that: The mass ratio of the composite alkali solution to the added straw is 8:1, and the mass ratio of NaOH, Na2CO3, and H2O2 in the composite alkali solution is 3:1:

2.

9. The process for efficiently extracting cellulose from cotton straw according to any one of claims 1 or 3, characterized in that: During the immobilized enzymatic hydrolysis, pH=5.5.

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