Straw integrated treatment-based succinic acid low-cost preparation process

Abstract

The invention aims to provide a low-cost preparation process of succinic acid based on straw integrated treatment aiming at the problem of inhibitor accumulation which is not solved, and the low-cost preparation process comprises the following steps: pre-treating straw by coupling a deep eutectic solvent (DES) with dilute acid: destroying lignin-cellulose connection by the DES through hydrogen-bond interaction, and synchronously catalyzing hemicellulose to hydrolyze by the dilute acid; performing simultaneous saccharification and fermentation (SSF) on the pretreated solid phase; and the fermentation process is coupled with electrodialysis for online separation of succinic acid. By adopting the method, the cost is reduced by more than 40%, the cost of the straw raw material is only 1 / 5 of that of starch, and the DES solvent recovery rate is gt; the cost of the pretreatment agent is reduced by 60%; the conversion efficiency is improved, and the lignin removal rate is gt; the enzymolysis rate of cellulose is increased to 92%, the concentration of a final fermentation product reaches 80-100g / L, and the sugar-acid conversion rate is gt; 90%; the process is green, the detoxification process is omitted, the COD of the wastewater is reduced by 70%, and the energy consumption of electrodialysis separation is reduced by 50% compared with that of a traditional crystallization method; the product is high-valued, and the byproduct lignin nanoparticles (the purity is gt; the furfural is prepared from the hemicellulose hydrolysate, and the raw material utilization rate is gt; and 98%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bio-based chemical preparation, in particular to a low-cost succinic acid preparation process based on integrated straw treatment. BACKGROUND

[0002] Succinic acid, as an important C4 platform compound, is widely used in food, medicine, degradable plastic (PBS) and other fields. Traditional production process mainly relies on petroleum-based raw materials (such as maleic anhydride hydrogenation method), which has problems such as non-renewable raw materials and high carbon emissions. Although bio-fermentation method has environmental potential, it still faces the following technical bottlenecks: at present.

[0003] High raw material cost: the existing process mostly uses grain-based starch (accounting for 40-50% of production cost), which has the problem of "competing with people for food".

[0004] Complex pretreatment: the lignocellulose structure in straw is dense, and conventional acid / alkali pretreatment generates a large amount of inhibitors (such as furfural, acetic acid), which requires an additional detoxification step, increasing equipment investment by 15-20%.

[0005] Low conversion efficiency: lignin hinders enzymatic efficiency, and the cellulose conversion rate is usually less than 65%, resulting in insufficient fermentation substrate concentration (<50g / L).

[0006] High energy consumption for separation: the fermentation broth is complex, and traditional calcium salt method for extracting succinic acid requires multiple steps of crystallization, and the energy consumption accounts for more than 30% of the whole process.

[0007] In the prior art, CN111321182A adopts straw acid pretreatment-fermentation process, which needs additional detoxification because the generation of inhibitors is not controlled, and membrane separation relies on high-purity glucose; CN109811823A adopts single dilute acid pretreatment, and the lignin removal rate is only 60%-70%, and the cellulose enzymatic hydrolysis rate is less than 65%; CN112575438A uses DES pretreatment, but does not couple with dilute acid, and does not realize online coupling of fermentation and electrodialysis, so the separation energy consumption is still high. The above-mentioned technologies all have problems of high raw material cost, low conversion efficiency or non-integrated process, which need to be solved by the integrated process of the present application. SUMMARY

[0008] The purpose of the present application is to solve the problem of uncontrolled inhibitor accumulation, and to provide a low-cost succinic acid preparation process based on integrated straw treatment.

[0009] The above technical purpose of the present application is achieved by the following technical scheme:

[0010] The low-cost succinic acid preparation process based on the integrated treatment of straws comprises: straw pretreatment by low eutectic solvent (DES) coupled with dilute acid; the DES destroys the lignin-cellulose connection through hydrogen bonding, and the dilute acid synchronously catalyzes the hydrolysis of hemicellulose, both of which cooperatively reduce the generation of inhibitors (40%-50% lower than the content of inhibitors in single DES pretreatment), and no subsequent detoxification is needed; the volume ratio of the DES to the dilute acid is 3:1-5:1, and the concentration of the dilute acid is 0.5%-1.5% (mass fraction); the pretreated solid phase is subjected to simultaneous saccharification and fermentation (SSF); and the fermentation process is coupled with electrodialysis for online separation of succinic acid.

[0011] Preferably, the DES is composed of a hydrogen bond acceptor and a donor, the acceptor is selected from choline chloride and betaine, and the donor is selected from lactic acid and oxalic acid, and the molar ratio is 1:1-1:3.

[0012] Preferably, the pretreatment conditions are as follows: the temperature is 100-130 ℃, the time is 0.5-2 h, and the solid-liquid ratio is 1:5-1:10.

[0013] Preferably, the SSF stage adopts a composite enzyme system, which comprises cellulase 10-25 FPU / g substrate, beta-glucosidase 20-40 CBU / g substrate, and xylanase 5-15 U / g substrate.

[0014] Preferably, the fermentation strain is Actinobacillus succinogenes CCTCC NO: M207006.

[0015] Preferably, the electrodialysis conditions are as follows: the voltage is 10-20 V, the membrane stack temperature is 30-40 ℃, and the succinic acid concentration in the concentration chamber is ≥200 g / L when the discharge is performed.

[0016] Preferably, the pretreated liquid phase is used for preparing furfural, and the solid phase residue is used for preparing lignin nanoparticles.

[0017] The system of the succinic acid preparation process based on the integrated treatment of straws comprises: a DES circulating pretreatment unit; an SSF fermentation tank (with an online pH regulation) and a membrane separation coupled with an electrodialysis device.

[0018] Preferably, the electrodialysis device is configured with a bipolar membrane to realize the direct conversion of succinic acid into sodium succinate.

[0019] The succinic acid prepared by the succinic acid preparation process based on the integrated treatment of straws is directly crystallized from the fermentation liquor, and has a purity ≥99.3% and an ash content ≤0.05%.

[0020] The application has the following beneficial effects: cost reduction of more than 40%; taking 1000 tons of succinic acid as an example, the cost of traditional starch raw material is about 2000 yuan / ton, the cost of straw raw material according to the application is about 400 yuan / ton (1 / 5 of starch), superimposed with DES recovery (cost reduction of 60%) and energy consumption reduction (50%), the total production cost is reduced from 8000 yuan / ton to 4700 yuan / ton, a reduction of 41.25%. The DES solvent recovery rate is greater than 95%, the pretreatment agent cost is reduced by 60%; the conversion efficiency is improved, the lignin removal rate is greater than 85%, the cellulase hydrolysis rate is increased to 92%, the final product concentration of fermentation is 80-100 g / L, and the sugar acid conversion rate is greater than 90%; the process is green, the detoxification process is cancelled, the wastewater COD is reduced by 70%, and the electrodialysis separation energy consumption is reduced by 50% compared with the traditional crystallization method; the product is high-value, the by-product lignin nanoparticles (purity > 95%) and the hemicellulose hydrolysate are used to prepare furfural, and the raw material utilization rate is greater than 98% DETAILED DESCRIPTION

[0021] The succinic acid low-cost preparation process based on integrated treatment of straw includes: straw is pretreated by low eutectic solvent (DES) coupling with dilute acid; DES breaks the lignin-cellulose connection through hydrogen bonding, and dilute acid synchronously catalyzes hemicellulose hydrolysis, both of which cooperatively reduce the generation of inhibitors (40%-50% lower than single DES pretreatment), and no subsequent detoxification is needed; the volume ratio of DES to dilute acid is 3:1-5:1, and the concentration of dilute acid is 0.5%-1.5% (mass fraction); the pretreated solid phase is subjected to simultaneous saccharification and fermentation (SSF); and the fermentation process is coupled with electrodialysis for online separation of succinic acid.

[0022] Preferably, the DES is composed of a hydrogen bond acceptor and a donor, the acceptor is selected from choline chloride and betaine, and the donor is selected from lactic acid and oxalic acid, and the molar ratio is 1:1-1:3.

[0023] Preferably, the pretreatment conditions are as follows: temperature 100-130℃, time 0.5-2h, and solid-liquid ratio 1:5-1:10.

[0024] Preferably, the SSF stage adopts a composite enzyme system containing cellulase 10-25 FPU / g substrate, beta-glucosidase 20-40 CBU / g substrate, and xylanase 5-15 U / g substrate.

[0025] Preferably, the fermentation strain is Actinobacillus succinogenes CCTCC NO: M207006.

[0026] Preferably, the electrodialysis conditions are as follows: voltage 10-20V, membrane stack temperature 30-40℃, and the succinic acid concentration in the concentration chamber is ≥200g / L when discharging.

[0027] Preferably, the pretreatment liquid phase is used to prepare furfural, and the solid phase residue is used to prepare lignin nanoparticles.

[0028] The system of the succinic acid preparation process based on the integrated treatment of straws comprises a DES circulating pretreatment unit, an SSF fermentation tank (with an online pH regulation), and a membrane separation coupled electrodialysis device.

[0029] Preferably, the electrodialysis device is configured with a bipolar membrane to realize the direct conversion of succinic acid into sodium succinate.

[0030] The succinic acid prepared by the succinic acid preparation process based on the integrated treatment of straws is directly crystallized from the fermentation liquor, and has a purity of greater than or equal to 99.3% and an ash content of less than or equal to 0.05%.

[0031] The present application has the following beneficial effects: the cost is reduced by more than 40%, the cost of straw raw materials is only 1 / 5 of that of starch, the DES solvent recovery rate is greater than 95%, and the pretreatment agent cost is reduced by 60%; the conversion efficiency is improved, the lignin removal rate is greater than 85%, the cellulase hydrolysis rate is increased to 92%, the fermentation end product concentration reaches 80-100 g / L, and the sugar acid conversion rate is greater than 90%; the process is green, the detoxification process is cancelled, the wastewater COD is reduced by 70%, the electrodialysis separation energy consumption is reduced by 50% compared with the traditional crystallization method; the product is high-value, the by-product lignin nanoparticles (purity > 95%) are produced, the hemicellulose hydrolysate is used to prepare furfural, and the raw material utilization rate is greater than 98%.

[0032] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application.

[0033] Example 1: Preparation of succinic acid from corn straws

[0034] Pretreatment: corn straws (particle size 2 mm) are mixed with a DES (choline chloride / lactic acid = 1:2, mass concentration 60%) - dilute acid (1% H2SO4) mixed solution (DES and dilute acid volume ratio 4:1) at a solid-liquid ratio of 1:8, reacted at 120 DEG C for 1 h, and then centrifuged at 3000 r / min for 10 min to separate the cellulose solid phase;

[0035] Fermentation: the solid phase is added with a composite enzyme (cellulase 15 FPU / g, beta-glucosidase 30 CBU / g), inoculated with Actinobacillus succinogenes CCTCC M207006, and fermented at 35 DEG C for 48 h;

[0036] Separation: the fermentation liquor is sterilized by a ceramic membrane, then enters an electrodialysis device (voltage 15 V), and the concentrated liquor is collected to crystallize succinic acid.

[0037] Results: the yield of succinic acid is 82.3 g / L, the purity is 99.5%, and the yield of lignin by-product is 18.2%.

[0038] Example 2: Optimization of wheat straw processing

[0039] The enzyme system was optimized to be: 20 FPU / g cellulase + 10 U / g xylanase, with the rest being the same as in Example 1.

[0040] Results: Compared with the single cellulase (20 FPU / g) system, the enzymatic hydrolysis time was shortened from 48 h to 33.6 h (a reduction of 30%), and the succinic acid yield increased from 72.5 g / L to 91.7 g / L (an increase of 26.5%).

[0041] Example 3: Process Integration

[0042] Furfural was produced by dehydrating hemicellulose solution using molecular sieve catalysis, and lignin residue was used to prepare nanoparticles through ultrasound-assisted self-assembly.

[0043] Results: Furfural yield was 75%, and lignin nanoparticle size was ≤100nm.

Claims

1. A process for preparing succinic acid based on integrated straw processing, characterized in that, include: Straw pretreatment: Crush the straw to a particle size of 1-3 mm, mix it with a eutectic solvent (DES)-dilute acid mixture at a solid-liquid ratio of 1:5-1:10, react at 100-130℃ for 0.5-2 h, and separate the solid and liquid phases to obtain a solid phase containing cellulose and a liquid phase containing hemicellulose. Simultaneous saccharification and fermentation (SSF): A complex enzyme system is added to the solid phase, and Actinobacillus succinogenes CCTCC NO: M207006 is inoculated. Fermentation is carried out at 30-37℃ and pH 6.0-7.0 for 48-72 hours. Online separation: During the fermentation process, large molecular impurities are removed by membrane separation (molecular weight cutoff 500-1000 Da), and the permeate enters an electrodialysis device to separate succinic acid online.

2. The succinic acid preparation process based on integrated straw treatment according to claim 1, characterized in that, The DES consists of a hydrogen bond acceptor and a donor. The acceptor is selected from choline chloride and betaine, and the donor is selected from lactic acid and oxalic acid. The lignin removal rate of the choline chloride-lactic acid (1:2) combination reaches 88%, and the hemicellulose hydrolysis rate of the betaine-oxalic acid (1:3) combination reaches 90%, with a molar ratio of 1:1-1:3 (preferably 1:2).

3. The succinic acid preparation process based on integrated straw treatment according to claim 1, characterized in that, The pretreatment conditions are as follows: temperature 100-130℃ (lignin removal rate is 75% at 100℃, 85% at 120℃, no significant improvement above 130℃ and increased energy consumption), time 0.5-2h (reaction is incomplete at 0.5h, cellulose degradation rate exceeds 5% after 2h), solid-liquid ratio 1:5-1:10 (mixing is uneven at 1:5, solvent recovery cost increases at 1:10).

4. The succinic acid preparation process based on integrated straw treatment according to claim 1, characterized in that, The SSF stage employs a complex enzyme system, containing cellulase (10-25 FPU / g substrate, which breaks down cellulose into cellobiose), β-glucosidase (20-40 CBU / g substrate, which converts cellobiose into glucose), and xylanase (5-15 U / g substrate, which degrades hemicellulose residue into xylose). The synergistic effect of these three enzymes increases the total sugar conversion rate by 30%-40% compared to using a single cellulase.

5. The succinic acid preparation process based on integrated straw treatment according to claim 1, characterized in that, The fermentation strain was Actinobacillus succinogenes CCTCC NO: M207006. In a medium containing lignin degradation products (such as vanillin), this strain produced 25%-30% more succinic acid than common strains (such as Anaerobiospirillum succiniciproducens), and had better acid resistance (maintaining more than 80% activity at pH 5.0).

6. The succinic acid preparation process based on integrated straw treatment according to claim 1, characterized in that, The electrodialysis conditions are: voltage 10-20V (separation rate is 15g / h at 10V and 30g / h at 20V; membrane life is shortened by 50% above 20V), membrane stack temperature 30-40℃ (current efficiency is 85% at 30℃ and 90% at 40℃; succinic acid is easily decomposed above 40℃), and discharge when the succinic acid concentration in the concentration chamber is ≥200g / L (at this point, the crystallization purity is ≥99.3%; if it is below 200g / L, the crystallization yield decreases by more than 15%).

7. The succinic acid preparation process based on integrated straw treatment according to claim 1, characterized in that, The pretreated liquid phase is used to prepare furfural: the liquid phase is reacted at 160-180℃ for 2-3 hours under the catalysis of 5% molecular sieve, and the furfural yield is 75%-80%; the solid residue is used to prepare lignin nanoparticles: the residue is ultrasonically treated (power 300-500W, time 30-60min) to self-assemble into nanoparticles with a particle size of 50-100nm and a purity ≥95%.

8. A system for implementing the succinic acid preparation process based on integrated straw processing according to any one of claims 1-7, comprising: include: DES circulating pretreatment unit (including heated reaction vessel, solid-liquid separation centrifuge, and DES recovery distillation tower); The SSF fermenter (with a built-in online pH control module that maintains pH 6.0-7.0 by automatically adding NaOH solution) and the membrane separation unit (ceramic membrane, pore size 0.1-0.2μm) are connected in series with the electrodialysis device (including bipolar membrane stack and circulation pump) through pipelines to achieve continuous separation of fermentation broth.

9. The system for implementing the succinic acid preparation process based on integrated straw treatment according to claim 8, characterized in that, The electrodialysis device is equipped with a bipolar membrane that directly converts succinic acid into sodium succinate at a voltage of 15-20V, with a conversion rate of ≥98%. Compared with the traditional neutralization method, it reduces acid and alkali consumption by 30%, and the product purity is ≥99%.

10. A succinic acid prepared by the straw-based integrated processing process described in claim 1, characterized in that it is a product of direct crystallization from fermentation broth, with a purity ≥99.3% as determined by GB / T23967-2009 and an ash content ≤0.05% as determined by GB / T 7531-2008.