Biomass pulping method based on synergy of eutectic solvent and multiple enzymes

Abstract

The invention discloses a deep eutectic solvent and multienzyme synergistic biomass pulping method, and belongs to the technical field of biomass pulping. The method comprises the following steps: treating a wood raw material by using a choline chloride / lactic acid eutectic solvent, and carrying out enzymolysis treatment by using a compound enzyme preparation of cellulase, xylanase and laccase, the choline chloride / lactic acid eutectic solvent is prepared by mixing choline chloride and lactic acid according to a molar ratio of 1: 2-1: 5. According to the biomass pulping method, the lignin dissolution rate and the enzymolysis efficiency can be remarkably improved, and the energy consumption and the wastewater COD value are reduced. The fiber length of the obtained pulp is greater than or equal to 1.2 mm, and the tensile strength and the electric strength of finished paper are both improved to meet the performance requirements of industrial paper. The scheme is environment-friendly, the solvent can be recycled, and the method has remarkable economic and ecological benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass pulping, and particularly to a method for grinding biomass by synergistically using a deep eutectic solvent and multiple enzymes. Background Art

[0002] The biomass pulping process is the core link of the paper industry, and its efficiency and quality directly affect the performance and production cost of paper products. At present, there are mainly three pulping processes on the market: traditional chemical pulping method, single bio-enzyme method, and DES pretreatment technology. The traditional chemical pulping method (such as the sulfate method) relies on a strong acid / strong base system. Although it has a high pulping efficiency, it has serious environmental problems: the COD value of the wastewater is as high as 8000 - 12000 mg / L, and the water consumption per ton of pulp reaches 50 - 80 m 3 , and it produces toxic by-products such as dioxins, posing a threat to the ecological environment and human health. In addition, the lignin degradation in chemical pulping is not thorough, resulting in limited pulp properties. The single bio-enzyme method is environmentally friendly, but it has a long treatment cycle (laccase requires more than 72 h), a low yield (the bamboo pulp yield is only 58 - 62%), and insufficient lignin degradation ability, making it difficult to meet the requirements for high-quality pulp. The existing deep eutectic solvent (DES) pretreatment technology (such as the choline chloride / urea system) is a green solvent, but it has problems such as low hemicellulose retention rate, insufficient solvent recovery rate (<75%), and poor selectivity, which easily lead to fiber damage and cost increase. The existing methods are difficult to balance efficiency, environmental friendliness, and economy, seriously restricting the industrial application of green pulping technology.

[0003] In recent years, although existing patented technologies have tried to assist bio-enzyme pulping with ternary DES (such as choline chloride + ethylene glycol / 1,4-butanediol + p-hydroxybenzenesulfonic acid), its components are complex, the regulation is difficult, and the sulfonic acid components may cause equipment corrosion or wastewater treatment problems. For example, in patent CN117166276B, the ternary DES has limited ability to destroy the lignin-carbohydrate complex (LCC), the solvent recovery process is vague, and the recycling rate is not clear. In addition, existing technologies mostly use single enzymes or simple compounding (such as xylanase and lipase), lacking the synergistic effect of multiple enzymes, resulting in low enzymatic hydrolysis efficiency and high lignin residue. Technologically, traditional DES pretreatment uses a single high temperature (100 - 150°C) treatment, with high energy consumption, and the grinding process is not optimized in segments, and the properties of the formed paper (such as tensile strength and electrical strength) are limitedly improved. The above defects indicate that existing technologies urgently need to make breakthroughs in simplifying the solvent system, enzymatic hydrolysis synergistic effect, and process energy-saving optimization. Summary of the Invention

[0004] The object of the present invention is to provide a biomass pulping method synergistically using a deep eutectic solvent and multiple enzymes to solve the problems existing in the above-mentioned prior art. The present invention improves the catalytic efficiency and adaptability of the biological enzyme by compounding the DES prepared from choline chloride-lactic acid with the biological enzyme, optimizes the beating performance of the pulp and the electrical properties of the formed paper, and simultaneously realizes the production goals of energy conservation, environmental protection and lightweight.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] Technical solution one: A biomass pulping method synergistically using a deep eutectic solvent and multiple enzymes, including the step of treating wood raw materials with a choline chloride / lactic acid deep eutectic solvent and performing enzymatic hydrolysis treatment using a compound enzyme preparation of cellulase, xylanase and laccase; the choline chloride / lactic acid deep eutectic solvent is prepared by mixing the choline chloride and lactic acid in a molar ratio of 1:2-1:5.

[0007] Further, it specifically includes the following steps:

[0008] Mix the pretreated wood raw materials with the choline chloride / lactic acid deep eutectic solvent at a mass ratio of 1:7 for treatment; perform atmospheric pressure penetration and high temperature and high pressure treatment in sequence; use the compound enzyme preparation to carry out enzymatic hydrolysis at pH 4.5-6.0 and a temperature of 40-60 °C for 12-48 h; perform coarse grinding and fine grinding in sequence, and finally recover the solvent through multi-stage vacuum distillation and gradient crystallization.

[0009] Further, the pretreatment includes dehydrating the wood raw materials to a moisture content of 12% through gradient dehydration.

[0010] Further, the atmospheric pressure penetration is carried out at atmospheric pressure of 80-100 °C for 1 h; the high temperature and high pressure treatment is carried out at 120 °C and 0.3-0.5 MPa for 2 h.

[0011] Further, the addition ratios of the cellulase, xylanase and laccase are 0.5-2.0%, 0.3-1.0%, and 0.1-0.5% of the dry weight of the raw materials, respectively.

[0012] Further, the vacuum degree of the multi-stage vacuum distillation is 0.09 MPa.

[0013] Further, the cooling rate of the gradient crystallization is 1-2 °C / min.

[0014] Technical solution two: The application of the chemi-thermomechanical pulp prepared by the biomass pulping method described above in the production of electrical and industrial papers.

[0015] The present invention discloses the following technical effects:

[0016] Through the multi - enzyme synergistic action of choline chloride / lactic acid deep eutectic solvent (DES) with cellulase, xylanase and laccase, combined with the segmented pretreatment and high - consistency refining process, the comprehensive performance of bio - enzymatic pulping is significantly improved. In terms of pulping efficiency, the synergistic action of the composite enzymes increases the enzymatic hydrolysis efficiency by 30%, shortens the treatment cycle to 24 - 48 h. At the same time, the fiber separation degree is increased to 92%, the average fiber length increases from 0.8 mm of the untreated to 1.2 mm, the residual lignin content is reduced to ≤3.5%, and the Kappa number is reduced from 28.3 to 8.5, significantly optimizing the processability of the pulp. In terms of the properties of the formed paper, the tensile strength is increased by 20% to 4.8 kN / m, the tear index and burst index are increased by 18% and 40% respectively, and the electrical strength is increased by 41% to 12 kV / mm, meeting the high requirements of industrial paper for mechanical strength and insulation. In terms of environmental protection and economic benefits, the COD value of the wastewater is reduced to 120 mg / L (80% lower than the traditional process), the energy consumption is reduced by 33% to 1.2 tce / t pulp, and DES realizes a solvent recovery rate of ≥90% through multi - stage vacuum distillation and gradient crystallization technology, and the purity is still ≥95% after being recycled 3 times, significantly reducing the solvent cost. In addition, the method provided by the present invention is compatible with various raw materials such as pine and bamboo, and can be applied on a large scale in industrial fields such as electrical insulation paper and packaging paper, with the comprehensive advantages of environmental protection, energy - saving and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the following - described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 It is the process flow chart of the biomass pulping method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0020] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0021] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0022] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0023] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0024] The cellulase, xylanase, and laccase in the following examples of this invention are all purchased from Novozymes (China) Biotechnology Co., Ltd. Other reagents and drugs involved in the examples of this invention are all ordinary commercially available products without special instructions; the experimental operations and steps involved in the examples are all carried out according to the conventional operations in the art without special instructions.

[0025] Example 1 Treatment by Biomass Pulping Method

[0026] (1) Raw material pretreatment: The pine raw material is crushed to a particle size of 3 cm by a jaw crusher (power 5.5 kW), de-dusted by a drum washing machine (rotation speed 15 rpm), and after controlling the water content to 25%, it enters a hot air drying tower (temperature 80 °C, wind speed 2 m / s) to be dried to a water content of 12%, and then stored in a constant humidity warehouse (temperature 20 ± 2 °C, humidity 30%);

[0027] (2) DES preparation: Choline chloride (99% purity) and lactic acid (85% concentration) are fed and mixed at a molar ratio of 1:2 (

[0028] 139.62 g of choline chloride + 180.16 g of lactic acid), and reacted in a jacketed reaction kettle (stirring speed 300 rpm, temperature control 80 °C) for 2 h to generate a homogeneous DES; the water content is controlled to 10% by vacuum dehydration (vacuum degree -0.08 MPa, temperature 60 °C);

[0029] (3) Biological enzyme compounding: Cellulase (enzyme activity 120 FPU / g), xylanase (enzyme activity 800 U / g), and laccase (enzyme activity 50 U / g) were compounded at 1.0%, 0.5%, and 0.3% of the dry weight of the raw materials, and enzymolysis was carried out in a constant temperature shaker (50 °C, oscillation frequency 80 rpm, pH 5.0) for 24 h;

[0030] (4) DES pretreatment: The raw materials and DES in the pretreatment tank were mixed at a mass ratio of 1:7 (stirring speed 200 rpm), and processed in two stages: Atmospheric pressure penetration stage: 80 °C, atmospheric pressure for 1 h; High temperature and high pressure reaction stage: heated to 120 °C, pressure 0.3 MPa, maintained for 2 h;

[0031] (5) Composite enzyme pretreatment: After enzymolysis, the slurry was dewatered by a plate and frame filter press (pressure 0.5 MPa), and the enzymolysis solution was retained for recycling;

[0032] (6) Pulping and beating: Atmospheric pressure pulping: The double-disc refiner (rotation speed 3200 rpm, power 110 kW) was ground in two stages: The first stage: gap 0.15 mm, beating degree 25 °SR; The second stage: gap 0.05 mm, beating degree 40 °SR (ISO 5267-1); The pulping concentration in the first stage of rough grinding was 3%-5%, and the pulping concentration in the second stage of fine grinding was 8-12%. Post-treatment: De-inking tank (60 °C, 30 min) → Three-stage countercurrent washing (fresh water consumption 4 m 3 / t pulp) → Pressure screen (slot width 0.15 mm) → Desander (sand removal rate ≥ 95%);

[0033] (7) Papermaking: The pulp was formed by an inclined screen former (concentration 0.8%), the pressing pressure was 0.8 MPa, and the drying temperature was 105 °C;

[0034] (8) DES recovery: Multi-stage vacuum distillation (vacuum degree -0.09 MPa, temperature 70 °C); The cooling rate of gradient crystallization was 1-2 °C / min; The recovery rate was 90%; The solvent purity was still ≥ 95% after recycling 3 times.

[0035] The process flow chart of the biomass pulping method is shown in Figure 1 .

[0036] Effect evaluation

[0037] (1) Fiber properties: The average fiber length is 1.2 mm (0.8 mm before treatment), and the content of fines is ≤ 12% (25% before treatment);

[0038] (2) Slurry characteristics: Kappa number 8.5 (28.3 before treatment), and the residual lignin content is ≤ 3.5%;

[0039] (3) Paper properties: Tensile strength is 4.8 kN / m (compared with 4.0 kN / m for untreated paper, an increase of 20%); air permeability is 420 mL / min (compared with 365 mL / min for untreated paper, an increase of 15%); electrical strength is 12 kV / mm (compared with 8.5 kV / mm for untreated paper, an increase of 41%).

[0040] (4) Environmental protection indicators: Wastewater COD is 120 mg / L (600 mg / L for traditional process, a reduction of 80%); energy consumption is 1.2 tce / t pulp (1.8 tce / t pulp for traditional process, a reduction of 33%).

[0041] Example 2 Biomass pulping method treatment

[0042] (1) Raw material pretreatment: Pine raw materials are crushed to a particle size of 3 cm by a jaw crusher (power 5.5 kW), dust is removed by a drum washing machine (rotation speed 15 rpm), and after water control to a moisture content of 25%, they enter a hot air drying tower (temperature 80 °C, wind speed 2 m / s) for drying to a moisture content of 12%, and are stored in a constant humidity warehouse (temperature 20 ± 2 °C, humidity 30%).

[0043] (2) DES preparation: Choline chloride (99% purity) and lactic acid (85% concentration) are fed and mixed at a molar ratio of 1:5 (139.62 g choline chloride + 450.40 g lactic acid), and react in a jacketed reaction kettle (stirring speed 300 rpm, temperature control 80 °C) for 2 h to generate homogeneous DES; after vacuum dehydration (vacuum degree -0.08 MPa, temperature 60 °C), the moisture content is controlled to 10%.

[0044] (3) Enzyme complexing: Cellulase (enzyme activity 120 FPU / g), xylanase (enzyme activity 800 U / g), and laccase (enzyme activity 50 U / g) are complexed at 1.5%, 0.8%, and 0.4% of the dry weight of the raw materials, and enzymolysis is carried out in a constant temperature shaker (55 °C, oscillation frequency 80 rpm, pH 5.5) for 36 h.

[0045] (4) DES pretreatment: The raw materials and DES in the pretreatment tank are mixed at a mass ratio of 1:7 (stirring speed 200 rpm), and processed in two stages: Atmospheric pressure penetration stage: 90 °C, atmospheric pressure for 1 h; High temperature and high pressure reaction stage: Heat up to 120 °C, pressure 0.5 MPa, and maintain for 2 h.

[0046] (5) Composite enzyme pretreatment: The enzymolyzed pulp is dewatered by a plate and frame filter press (pressure 0.5 MPa), and the enzymolysis liquid is retained for recycling.

[0047] (6) Pulping and beating: Atmospheric pulping: The double-disc refiner (rotating speed 3200 rpm, power 110 kW) grinds in two stages: The first stage: the gap is 0.15 mm, and the beating degree is 25°SR; The second stage: the gap is 0.05 mm, and the beating degree is 40°SR (ISO 5267-1); The pulping concentration in the first-stage rough grinding is 3%-5%, and the pulping concentration in the second-stage fine grinding is 8-12%. Post-treatment: De-inking tank (60°C, 30 min) → three-stage countercurrent washing (fresh water consumption 4 m 3 / t pulp) → pressure screen (slot width 0.15 mm) → desander (sand removal rate ≥ 95%);

[0048] (7) Paper making: The pulp is formed by an inclined wire former (concentration 0.8%), the pressing pressure is 0.8 MPa, and the drying temperature is 105°C;

[0049] (8) DES recovery: Multi-stage vacuum distillation (vacuum degree -0.09 MPa, temperature 70°C); The cooling rate of gradient crystallization is 1-2°C / min; The recovery rate is 92%; The solvent purity is still ≥ 90% after recycling 2 times.

[0050] Effect evaluation

[0051] (1) Fiber properties: Fiber coarseness 18 mg / 100 m (22 mg / 100 m before treatment), fiber bonding index 85 (60 before treatment);

[0052] (2) Paper properties: Tear index 12.5 mN·m 2 / g (compared with 10.6 of the untreated, increased by 18%), burst index 4.5 kPa·m 2 / g (compared with 3.2 of the untreated, increased by 40%), electrical strength 15 kV / mm (compared with the untreated, increased by 47%).

[0053] Comparative Example 1 Single DES treatment

[0054] The same raw material preparation steps as in Example 1 are adopted, but only DES is used for pretreatment without using bio-enzyme. The preparation of DES, pretreatment conditions and subsequent pulping, beating, and paper-making steps are the same as in Example 1.

[0055] Effect evaluation

[0056] (1) Fiber properties: Fiber length 0.9 mm (lower than 1.2 mm in Example 1), lignin residue 12% (significantly higher than 3.5% in Example 1);

[0057] (2) Paper properties: Tensile strength 4.4 kN / m (increased by 10%), air permeability 383 mL / min (increased by 5%), electrical strength 9.2 kV / mm (increased by 8%);

[0058] (3) Environmental disadvantages: The COD of the wastewater is 300 mg / L (higher than 120 mg / L in Example 1), and the energy consumption is 1.5 tce / t pulp (higher than 1.2 tce / t pulp in Example 1).

[0059] Comparative Example 2: Single bio-enzyme method

[0060] The same raw material preparation steps as in Example 1 were adopted, but only the compound bio-enzyme was used for treatment without using DES. The selection and compounding of the bio-enzyme, the enzymolysis conditions, and the subsequent steps of pulping, beating, and papermaking were the same as in Example 1.

[0061] Effect evaluation

[0062] (1) Fiber properties: The fiber separation degree is 65% (92% in Example 1), and the cellulose crystallinity is 72% (58% in Example 1);

[0063] (2) Paper properties: The tensile strength is 4.2 kN / m (increased by 5%), the tear index is 11.0 mN·m 2 / g (increased by 4%), and the electrical strength is 10.5 kV / mm (increased by 24%);

[0064] (3) Process disadvantages: The enzyme dosage increases by 30% (to compensate for the undissolved lignin), and the COD of the wastewater is 450 mg / L (enzyme solution residue).

[0065] Comparative Example 3: Conventional vacuum distillation and crystallization

[0066] The same raw material preparation, DES preparation, bio-enzyme compounding, and pulping treatment steps as in Example 1 were adopted, but in the DES recovery stage, a method combining conventional vacuum distillation (vacuum degree -0.06 MPa, temperature 85 °C) and conventional crystallization (natural cooling) was used.

[0067] Effect evaluation

[0068] (1) Recovery efficiency: The DES recovery rate is 78% (lower than 90% in Example 1), and the purity drops to 88% after 3 cycles of use;

[0069] (2) Paper properties: The tensile strength is 4.5 kN / m (lower than 4.8 kN / m in Example 1), the electrical strength is 10.8 kV / mm (lower than 12 kV / mm in Example 1), and the air permeability is 395 mL / min (lower than 420 mL / min in Example 1);

[0070] (3) Energy consumption index: The energy consumption is 1.4 tce / t pulp (higher than 1.2 tce / t pulp in Example 1).

[0071] Comparative Example 4: DES + laccase / cellulase + laccase

[0072] 1. DES + Laccase Scheme

[0073] The same raw material preparation and DES preparation steps as in Example 1 were adopted. After pretreatment, only laccase (0.5%) was used for enzymatic hydrolysis (other conditions were the same as in Example 1).

[0074] Effect Evaluation

[0075] (1) Lignin Removal: The residual lignin content was 6.8% (between Example 1 and Comparative Example 1);

[0076] (2) Paper Properties: The electrical strength was 11.2 kV / mm (6.7% lower than that in Example 1);

[0077] (3) Process Defects: Incomplete fiber separation led to a 15% increase in beating energy consumption.

[0078] 2. DES + Cellulase + Laccase Scheme

[0079] The same raw material preparation and DES preparation steps as in Example 1 were adopted. After pretreatment, a compound enzymatic hydrolysis using cellulase (1.0%) + laccase (0.3%) was carried out (xylanase was cancelled).

[0080] Effect Evaluation

[0081] (1) Hemicellulose Retention: The hemicellulose content was 14.5% (lower than 18.2% in Example 1).

[0082] (2) Paper Properties: The tear index was 11.8 mN·m 2 / g (5.6% lower than that in Example 1).

[0083] (3) Environmental Protection Index: The COD of the wastewater was 180 mg / L (50% higher than that in Example 1).

[0084] In summary, by combining the DES system with bio - enzymes, the present invention significantly improves the efficiency and quality of biomass pulping, reduces energy consumption and environmental pollution, enhances the physical and electrical properties of paper products, and simultaneously achieves the production goal of energy conservation and environmental protection, having broad application prospects and market value.

[0085] The above - described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A biomass refining method using a deep eutectic solvent and multiple enzymes, characterized in that: The method comprises the steps of treating wood raw materials with a choline chloride / lactic acid low eutectic solvent and performing enzymolysis treatment with a composite enzyme preparation of cellulase, xylanase and laccase; the choline chloride / lactic acid low eutectic solvent is obtained by mixing choline chloride and lactic acid in a molar ratio of 1:2-1:

5.

2. The biomass pulping method according to claim 1, characterized in that: The specific steps include: The pretreated wood raw material is mixed with the choline chloride / lactic acid low eutectic solvent in a mass ratio of 1:7; normal pressure infiltration and high temperature and high pressure treatment are sequentially performed; the composite enzyme preparation is used for enzymolysis at pH 4.5-6.0 and temperature 40-60° C. for 12-48 hours; coarse grinding and fine grinding are sequentially performed, and finally the solvent is recovered by multi-stage vacuum distillation and gradient crystallization.

3. The biomass pulping method according to claim 2, characterized in that: The pretreatment includes dehydrating the wood raw material to a moisture content of 12% through gradient dehydration.

4. The biomass pulping method according to claim 2, characterized in that: The normal pressure infiltration is carried out at a normal pressure of 80-100° C. for 1 hour; the high temperature and high pressure treatment is carried out at a temperature of 120° C. and 0.3-0.5 MPa for 2 hours.

5. The biomass pulping method according to claim 2, characterized in that: The addition ratios of the cellulase, xylanase and laccase are 0.5-2.0%, 0.3-1.0% and 0.1-0.5% of the dry weight of the raw materials respectively.

6. The biomass pulping method according to claim 2, characterized in that: The vacuum degree of the multi-stage reduced pressure distillation is 0.09 MPa.

7. The biomass pulping method according to claim 2, characterized in that: The cooling rate of the gradient crystallization is 1-2°C / min.

8. Use of chemimechanical pulp prepared by the biomass pulping method according to any one of claims 1 to 7 in the production of electrical and industrial paper.

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