Method for preparing lactic acid by pretreating biomass with lactic acid fermentation waste liquid

Abstract

The invention discloses a method for preparing lactic acid by recycling lactic acid fermentation waste liquid. The method comprises the following steps: firstly, collecting organic acid waste liquid in a lactic acid fermentation liquid separation process in sections and concentrating, and simultaneously removing polymer impurities and suspended particles contained in the lactic acid waste liquid at the bottom of a kettle after the lactic acid fermentation liquid is rectified by using a flocculating agent; the method comprises the following steps: mixing concentrated organic acid waste liquid and lactic acid waste liquid filtrate by taking the concentrations of formic acid, acetic acid, succinic acid and lactic acid and the total acid concentration as indexes, pretreating lignocellulose, and performing detoxification, filtration, cellulase enzymolysis and lactobacillus fermentation on the pretreated lignocellulose solution to prepare lactic acid. The method provided by the invention solves the problem of recycling organic acid and waste liquid at the bottom of a distillation kettle in the production process of lignocellulose-based lactic acid, and greatly improves the lactic acid fermentation efficiency through the combination of mixed acid synergistic pretreatment of lignocellulose raw materials, flocculation and detoxification processes and selective ventilation operation of facultative anaerobic bacteria.

Description

Technical Field

[0001] The invention belongs to the field of biochemical engineering, and specifically relates to a method for preparing lactic acid by efficiently recycling lactic acid fermentation waste liquid. Background Art

[0002] Lactic acid has been widely used as a bio-based bulk chemical. At present, the main production method of lactic acid is bio-fermentation using corn, wheat and other starch as raw materials. However, my country's food security issues are prominent, and the demand for environmental protection is increasing. Exploring the production of lactic acid by fermentation of non-grain raw materials represented by lignocellulose has become one of the important ways to maintain the level of national strategic grain reserves and implement environmental protection policies.

[0003] The utilization rate of lignocellulose in my country is extremely low. The fundamental reason is that the dry basis of lignocellulose has a low crude protein content, a high crude fiber content, poor palatability, and a rough texture, making it difficult to be directly utilized by microorganisms. Due to the strong interactions of lignocellulosic biomass (i.e., hydrogen bonds and hydrophobic interactions), the biopolymer structure has a strong resistance to hydrolysis, which requires a series of efficient pretreatment methods to improve the hydrolysis effect. The pretreatment of lignocellulosic biomass is the process of converting complex lignocellulose into simple components such as cellulose, hemicellulose, and lignin, ultimately removing lignin, retaining hemicellulose, reducing cellulose crystallinity, and increasing the porosity of the material. Currently, a variety of pretreatment technologies have been developed to increase the yield of biomass chemicals and fuels, including physical, chemical, biological, and physicochemical methods. However, in the traditional biorefining process, a single physical or biological pretreatment method is often difficult to achieve the expected treatment effect under limited investment costs due to its high energy consumption and time consumption, and there is a lack of cases of scaled-up production; physical and chemical methods such as steam explosion and ammonia fiber explosion are not only energy-intensive but also have highly toxic by-products; and chemical methods, such as alkaline pretreatment processes represented by sodium hydroxide, potassium hydroxide, triethylamine, and ethylenediamine, are difficult to treat the black liquor wastewater produced during the pretreatment process; acid pretreatment processes such as sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, and phthalic anhydride all require the purchase of pretreatment catalysts from external sources, and a process for removing these acidic impurities needs to be added during the subsequent product separation process. In addition, in addition to the above-mentioned raw material pretreatment problems, the current fermentation production of cellulose-based lactic acid still has many areas that need to be improved. For example, the toxicity of lignocellulose pretreatment liquid is relatively high, which affects the fermentation production of lactic acid bacteria and leads to low lactic acid production; when ion exchange resin is used to remove other impurities for separation and extraction of lactic acid, the acid solution is often neutralized with alkali and discarded; the lactic acid solution is concentrated and distilled to obtain the product, and the bottom liquid is either discarded or simply merged into the fermentation liquid of the next batch of lactic acid production. However, the impurities enriched by concentration and the high molecular colloids produced during the distillation process will not only affect the fermentation production of the next batch of lactic acid bacteria, but also increase the difficulty of lactic acid separation and purification. Therefore, in response to these problems, it is necessary to develop a new technical method to improve the efficiency of lignocellulose pretreatment, lactic acid production, and reduce waste liquid discharge in the lactic acid production process. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing lactic acid by efficiently recycling lactic acid fermentation waste liquid in view of the deficiencies in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solution: A method for preparing lactic acid by recycling lactic acid fermentation waste liquid, comprising the following steps: 1) Collect and concentrate the organic acid waste liquid generated during the separation of lactic acid fermentation broth in sections, and then determine the organic acid concentration therein; 2) Dilute the lactic acid waste liquid at the bottom of the kettle after the lactic acid fermentation liquid is distilled, add a flocculant, stir and mix, and then filter to determine the concentration of lactic acid in the filtrate; 3) the organic acid waste liquid obtained in step 1) and the filtrate obtained in step 2) are mixed in a certain proportion, and then lignocellulose is added to the mixed waste liquid, and the mixture is heated to a certain temperature and then kept warm for pretreatment, and a detoxifying agent is added after the mixture is cooled, and the mixture is stirred and filtered to obtain a pretreated lignocellulose residue; 4) Deionized water is added to the obtained pretreated lignocellulose residue, and after adjusting the pH to 4-7, cellulase is added for enzymatic hydrolysis; then a nitrogen source is added, and lactic acid bacteria are inoculated, compressed air is passed for a period of time, nitrogen is passed, and calcium hydroxide suspension is continuously added for fermentation until the lactic acid concentration no longer increases.

[0006] Furthermore, the lactic acid fermentation liquid is obtained by fermenting lignocellulose raw materials such as corn stalks, sugarcane bagasse, rice stalks, tobacco stalks, bamboo shoot shells, etc. using traditional biological fermentation technology.

[0007] Furthermore, in step 1), the organic acid waste liquid collected in sections is concentrated to 20% to 90% of the original volume.

[0008] Furthermore, in step 2), water is used as a diluent to dilute the lactic acid waste liquid, and the amount used is 1.0 to 5.0 times the weight of the lactic acid waste liquid.

[0009] Furthermore, in step 2), the flocculant is polyacrylamide (PHIII), the molecular weight of which is 5 to 10 million, and the dosage is 0.5 to 3 g / L.

[0010] Furthermore, in step 3), the ratio of the organic acid waste liquid to the filtrate is converted according to the lactic acid concentration of 1-10 g / L, the formic acid concentration of 0.1-5 g / L, the acetic acid concentration of 0.1-5 g / L, the succinic acid concentration of 1-8 g / L, and the total acid concentration of 5-20 g / L in the obtained mixed waste liquid.

[0011] Furthermore, the wood cellulose used in step 3) is corn straw, bagasse, rice straw, tobacco straw, bamboo shoot shells, etc., and its amount is 1-25% of the mass of the mixed waste liquid.

[0012] Furthermore, the pretreatment temperature in step 3) is 100-130°C and the time is 0.5-3 h.

[0013] Furthermore, the detoxifying agent in step 3) is ethylenediaminetetraacetic acid or its sodium salt, and its usage is calculated by adding 0.01-0.5 g per liter of mixed waste liquid.

[0014] Furthermore, the stirring time in steps 2) and 3) is 1 to 3 h.

[0015] Furthermore, in step 4), phosphoric acid or its acid salt is used to adjust the pH.

[0016] Furthermore, the amount of cellulase added in step 4) is converted based on 5-30 FPU per gram of lignocellulose.

[0017] Furthermore, in step 4), the system temperature for adding cellulase for enzymatic hydrolysis is 47-55°C and the time is 2-5h.

[0018] Furthermore, the nitrogen source used in step 4) is an organic nitrogen source such as yeast powder, corn steep liquor or corn gluten powder, and the amount thereof is converted to 5-30 g per liter of enzymatic hydrolyzate.

[0019] Furthermore, in step 4), the amount of lactic acid bacteria introduced is 1% to 20% of the volume of the enzymatic hydrolysate.

[0020] Furthermore, in step 4), the time for introducing compressed air is 2 to 6 hours.

[0021] Furthermore, in step 4), the time for introducing nitrogen is 1 to 3 h.

[0022] Furthermore, the concentration of the calcium hydroxide suspension used in step 4) is 50-300 g / L, and the amount used is based on maintaining the pH of the fermentation system at 4.5-6.5.

[0023] Furthermore, the fermentation temperature in step 4) is 50-55°C.

[0024] The present invention has the following technical advantages: 1. The present invention recovers the organic acid produced in the lactic acid separation process and the lactic acid waste liquid at the bottom of the kettle, and uses them for lignocellulose pretreatment; 2. In the present invention, the organic acid waste liquid is collected in sections, which is beneficial to regulating the content of formic acid, acetic acid, succinic acid and lactic acid and the total acid concentration in the mixed acid solution; 3. In the distillation step of lactic acid separation, as the bottom liquid continues to concentrate, metal ions continue to accumulate and produce a series of polymer impurities. The present invention uses polyacrylamide as a flocculant that can cross-link with high-valent metal ions to form an insoluble gel; and the polar groups of its molecular chain can bridge the particles by adsorbing the solid particles suspended in the solution, and agglomerate the particles to form large floccules through charge neutralization, which is convenient for removing most of the heavy metal ions and polymer impurities.

[0025] 4. The present invention uses mixed organic acids to pretreat lignocellulose raw materials, the reaction conditions are mild, and under the joint action of multiple organic acids, the pretreatment effect is good; 5. Ethylenediaminetetraacetic acid or its sodium salt is a strong metal chelating agent that can form a stable water-soluble complex with metal ions. It can also separate heavy metal ions from pretreated lignocellulose residues through filtration operations, thus avoiding the inhibitory effect of heavy metal ions on cellulase in the subsequent saccharification step and increasing the efficiency of enzymatic saccharification.

[0026] 6. The use of phosphoric acid or its acid salt in the present invention can not only adjust the pH value of the solution, but also be used as a phosphorus source required for the growth of microorganisms.

[0027] 7. The semi-synchronous saccharification and fermentation method of enzymatic saccharification for a period of time before inoculation of lactic acid bacteria is adopted in the present invention, which is conducive to accumulating more carbon sources in the early stage of fermentation to maintain the rapid growth of microorganisms after inoculation.

[0028] 8. After the facultative anaerobic lactic acid bacteria are inoculated, the present invention first introduces compressed air for a period of time to facilitate their rapid reproduction and increase the OD value; then nitrogen is introduced to replace the oxygen in the solution, which is beneficial to anaerobic fermentation and improves the lactic acid production efficiency.

[0029] In summary, the present invention solves the problem of recycling and reusing formic acid, acetic acid, succinic acid and lactic acid in organic acid waste liquid and distillation bottom waste liquid in the production process of lignocellulose-based lactic acid. Polyacrylamide is used to remove polymer impurities and suspended particles in the bottom liquid, and the recovered organic acid is formulated into a mixed acid solution in an appropriate ratio for the pretreatment of lignocellulose, and the treatment effect is outstanding. After the pretreated lignocellulose solution is detoxified by ethylenediaminetetraacetic acid or its sodium salt, the lignocellulose residue obtained by filtration is hydrolyzed by cellulase, and the lactic acid bacteria are semi-synchronously saccharified and fermented, and the lactic acid yield is high. Compressed air is first passed to increase the OD value of the production strain, and then the oxygen in the solution is replaced by nitrogen, which greatly improves the efficiency of anaerobic fermentation. DETAILED DESCRIPTION

[0030] A method for preparing lactic acid by recycling lactic acid fermentation waste liquid, comprising the following steps: 1) Collect the organic acid waste liquid generated during the separation of lactic acid fermentation broth in sections and concentrate it to 20%~90% of the original volume, and then measure the organic acid concentration in it; 2) Dilute the waste lactic acid liquid at the bottom of the kettle after distillation of the lactic acid fermentation liquid with 1.0-5.0 times its weight of water, add 0.5-3 g / L of flocculant polyacrylamide (molecular weight 5-10 million), stir for 1-3 hours to mix well, filter, and determine the concentration of lactic acid in the filtrate; 3) the organic acid waste liquid obtained in step 1) and the filtrate obtained in step 2) are mixed, so that the lactic acid concentration in the mixed waste liquid is 1-10 g / L, the formic acid concentration is 0.1-5 g / L, the acetic acid concentration is 0.1-5 g / L, the succinic acid concentration is 1-8 g / L, and the total acid concentration is 5-20 g / L, and then 1-25% of the mass of the mixed waste liquid is added with lignocellulose, and the mixture is heated to 100-130°C and pretreated for 0.5-3 hours by heat preservation, and after cooling, 0.01-0.5 g / L of ethylenediaminetetraacetic acid or its sodium salt is added as a detoxification agent, and the mixture is stirred for 1-3 hours and filtered to obtain a pretreated lignocellulose residue; 4) Deionized water is added to the obtained pretreated lignocellulose residue, and after adjusting the pH to 4-7 with phosphoric acid or its acid salt, cellulase is added in an amount of 5-30 FPU per gram of lignocellulose, heated to 47-55°C, stirred for 2-5 hours, and then a nitrogen source is added in an amount of 5-30 g per liter of enzymatic hydrolysate, and lactic acid bacteria are added in an amount of 1%-20% of the volume of the enzymatic hydrolysate. After compressed air is introduced for 2-6 hours, nitrogen is introduced for 1-3 hours, and a calcium hydroxide suspension with a concentration of 50-300 g / L is continuously added to maintain the pH of the fermentation system at 4.5-6.5, and ferment at 50-55°C until the lactic acid concentration no longer increases.

[0031] Wherein, the wood cellulose used in step 3) is corn straw, sugarcane bagasse, rice straw, tobacco straw, bamboo shoot shells, etc.

[0032] The nitrogen source used in step 4) is an organic nitrogen source such as yeast powder, corn syrup or corn gluten powder.

[0033] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0034] The organic acid waste liquid and the bottom lactic acid waste liquid used in the embodiment are obtained by fermenting lignocellulosic raw materials such as corn stalks, bagasse, rice straw, tobacco straw, bamboo shoot shells, etc. using traditional biological fermentation technology, and then collecting them. Specifically, after the fermentation is completed, the pH is adjusted to 1~2 with dilute sulfuric acid, and solids such as calcium sulfate and bacteria are removed by centrifugation. After decolorization with activated carbon, impurities such as miscellaneous acids are removed by ion exchange resin. During the process, lactic acid fermentation liquid and waste liquid containing formic acid, waste liquid containing acetic acid, and mixed waste liquid containing lactic acid and succinic acid are collected in stages; the collected lactic acid fermentation liquid is concentrated and sent to a distillation kettle for purification to obtain lactic acid, and the lactic acid waste liquid at the bottom of the kettle is collected.

[0035] The molecular weight of the polyacrylamide (PHIII) used in the examples is 5 to 10 million.

[0036] Example 1 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 3.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 4.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 7.3 g / L and 4.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide (PHIII) was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 37.5 g / L. Then, 1.54 L of formic acid waste liquid, 1.30 L of acetic acid waste liquid, 1.64 L of mixed waste liquid of lactic acid and succinic acid, 0.75 L of bottom filtrate, and 0.77 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 1 g / L, 1 g / L, 2 g / L and 6 g / L respectively, and the total acid concentration was 10 g / L.

[0037] Add 6 L of the above mixed acid solution and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then lower to room temperature, add 1.8 g of sodium ethylenediaminetetraacetate, stir for 2 hours and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 hours, then pass nitrogen for 2 hours, during which the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 hours of fermentation, the lactic acid content in the fermentation broth is 136 g / L.

[0038] Example 2 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 3.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 4.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 7.3 g / L and 4.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide (PHIII) was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 37.5 g / L. Then, 1.54 L of formic acid waste liquid, 1.30 L of acetic acid waste liquid, 1.64 L of mixed waste liquid of lactic acid and succinic acid, 0.75 L of bottom filtrate, and 0.77 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 1 g / L, 1 g / L, 2 g / L and 6 g / L respectively, and the total acid concentration was 10 g / L.

[0039] Add 6 L of the above mixed acid solution and 1 kg of bagasse to the reactor, heat to 120 ℃, and keep warm for 2 h; then lower to room temperature, add 1.8 g of sodium ethylenediaminetetraacetate, stir for 2 h, and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g bagasse, stir for 3 h, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 h, then pass nitrogen for 2 h, during which the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 h of fermentation, the lactic acid content in the fermentation broth is 141 g / L.

[0040] Example 3 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 3.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 4.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 7.3 g / L and 4.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide (PHIII) was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 37.5 g / L. Then, 1.54 L of formic acid waste liquid, 1.30 L of acetic acid waste liquid, 1.64 L of mixed waste liquid of lactic acid and succinic acid, 0.75 L of bottom filtrate, and 0.77 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 1 g / L, 1 g / L, 2 g / L and 6 g / L respectively, and the total acid concentration was 10 g / L.

[0041] Add 6 L of the above mixed acid solution and 1 kg of rice straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then lower to room temperature, add 1.8 g of sodium ethylenediaminetetraacetate, stir for 2 hours and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g rice straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 hours, then pass nitrogen for 2 hours, during which the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 hours of fermentation, the lactic acid content in the fermentation broth is 128 g / L.

[0042] Example 4 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 1.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 1.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 3.3 g / L and 2.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide (PHIII) was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 68.3 g / L. Then, 1.58 L of formic acid waste liquid, 1.88 L of acetic acid waste liquid, 1.82 L of mixed waste liquid of lactic acid and succinic acid, 0.63 L of bottom filtrate, and 0.09 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 0.5 g / L, 0.5 g / L, 1 g / L and 8 g / L respectively, and the total acid concentration was 10 g / L.

[0043] Add 6 L of the above mixed acid solution and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then lower to room temperature, add 1.8 g of sodium ethylenediaminetetraacetate, stir for 2 hours and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 hours, then pass nitrogen for 2 hours, during which the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 hours of fermentation, the lactic acid content in the fermentation broth is 130 g / L.

[0044] Example 5 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 1.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 1.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 3.3 g / L and 2.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide (PHIII) was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 68.3 g / L. Then, 1.58 L of formic acid waste liquid, 1.88 L of acetic acid waste liquid, 1.82 L of mixed waste liquid of lactic acid and succinic acid, 0.63 L of bottom filtrate, and 0.09 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 0.5 g / L, 0.5 g / L, 1.0 g / L and 8 g / L respectively, and the total acid concentration was 10 g / L.

[0045] Add 6 L of the above mixed acid solution and 1 kg of tobacco straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then lower to room temperature, add 2.0 g of sodium ethylenediaminetetraacetate, stir for 2 hours and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g tobacco straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 hours, then pass nitrogen for 2 hours, during which the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 hours of fermentation, the lactic acid content in the fermentation broth is 126 g / L.

[0046] Comparative Example 1 Add 6 L of 10% hydrochloric acid solution and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 h; then lower to room temperature, filter to obtain lignocellulose residue; transfer it to a fermenter, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 h, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass nitrogen for 2 h, control the system temperature at 50 ℃, and continuously pump in 300 g / L calcium hydroxide suspension to maintain the system pH 4.5-6.5. After 36 h of fermentation, the lactic acid content in the fermentation broth was 95 g / L.

[0047] Comparative Example 2 Add 6 L of 10 g / L dilute sulfuric acid aqueous solution and 1 kg of corn straw to the reactor, heat to 120℃, and keep warm for 2 h; then lower the temperature to room temperature, add 1.8 g of sodium ethylenediaminetetraacetate, stir for 2 h, and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust the pH to 5.0 with phosphoric acid, heat to 50℃, add cellulase at 20 FPU / g corn straw, stir for 3 h, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 h, then pass nitrogen for 2 h, during which the system temperature is controlled at 50℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 h of fermentation, the lactic acid content in the fermentation broth is 92 g / L.

[0048] Comparative Example 3 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 3.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 4.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 7.3 g / L and 4.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then activated carbon was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 37.5 g / L. Then, 1.54 L of formic acid waste liquid, 1.30 L of acetic acid waste liquid, 1.64 L of mixed waste liquid of lactic acid and succinic acid, 0.75 L of bottom filtrate, and 0.77 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 1 g / L, 1 g / L, 2 g / L and 6 g / L respectively, and the total acid concentration was 10 g / L.

[0049] Add 6 L of the above mixed acid solution and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then lower to room temperature, add 1.8 g of sodium ethylenediaminetetraacetate, stir for 2 hours and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 hours, then pass nitrogen for 2 hours, during which the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 hours of fermentation, the lactic acid content in the fermentation broth is 76 g / L.

[0050] Comparative Example 4 The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide (PHIII) was added at an amount of 1.5 g / L, stirred for 2 h, filtered to remove solids, and then the lactic acid concentration was adjusted to 10 g / L.

[0051] Add 6 L of the above lactic acid filtrate and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 h; then lower the temperature to room temperature, add 1.8 g of sodium ethylenediaminetetraacetate, stir for 2 h, and filter to obtain lignocellulose residue; transfer it to a fermenter, add 3 kg of deionized water, adjust the pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 h, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 h, and then pass nitrogen for 2 h. During the process, the system temperature was controlled at 50 ℃, and a calcium hydroxide suspension with a concentration of 300 g / L was continuously pumped in to maintain the system pH 4.5-6.5. After 36 h of fermentation, the lactic acid content in the fermentation broth was 85 g / L.

[0052] Comparative Example 5 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 3.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 4.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 7.3 g / L and 4.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 68.3 g / L. Then, 2.54 L of formic acid waste liquid, 2.30 L of acetic acid waste liquid, 0.6 L of mixed waste liquid of lactic acid and succinic acid, 0.35 L of bottom filtrate, and 0.21 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid, and lactic acid were 1.65 g / L, 1.76 g / L, 0.48 g / L, and 6.11 g / L, respectively, and the total acid concentration was 10 g / L.

[0053] Add 6 L of the above mixed acid solution and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then lower to room temperature, add 2.0 g of sodium ethylenediaminetetraacetate, stir for 2 hours and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 hours, then pass nitrogen for 2 hours, during which the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 hours of fermentation, the lactic acid content in the fermentation broth is 79 g / L.

[0054] Comparative Example 6 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 1.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 1.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 3.3 g / L and 2.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 68.3 g / L. Then, 1.58 L of formic acid waste liquid, 1.88 L of acetic acid waste liquid, 1.82 L of mixed waste liquid of lactic acid and succinic acid, 0.63 L of bottom filtrate, and 0.09 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 0.5 g / L, 0.5 g / L, 1.0 g / L and 8 g / L respectively, and the total acid concentration was 10 g / L.

[0055] Add 6 L of the above mixed acid solution and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then reduce to room temperature, filter, and obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust pH 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass compressed air for 4 hours, and then pass nitrogen for 2 hours. During the process, the system temperature is controlled at 50 ℃, and the system pH is maintained at 4.5-6.5 by continuously pumping in a calcium hydroxide suspension with a concentration of 300 g / L. After 36 hours of fermentation, the lactic acid content in the fermentation broth is 96 g / L.

[0056] Comparative Example 7 The formic acid-containing waste liquid, acetic acid-containing waste liquid and mixed waste liquid containing lactic acid and succinic acid collected in stages during the ion exchange process of the lactic acid fermentation broth were concentrated to 50% of the original volume. The concentration of formic acid in the formic acid waste liquid was 1.9 g / L, the concentration of acetic acid in the acetic acid waste liquid was 1.6 g / L, and the concentrations of lactic acid and succinic acid in the mixed waste liquid of lactic acid and succinic acid were 3.3 g / L and 2.8 g / L, respectively. The lactic acid waste liquid at the bottom of the distillation kettle was diluted with deionized water twice its weight, and then polyacrylamide (PHIII) was added at an amount of 1.5 g / L, stirred for 2 hours, filtered to remove solids, and the concentration of lactic acid in the filtrate was measured by HPLC to be 37.5 g / L. Then, 1.54 L of acid waste liquid, 1.30 L of acetic acid waste liquid, 1.64 L of lactic acid and succinic acid mixed waste liquid, 0.75 L of kettle bottom waste liquid, and 0.77 L of deionized water were taken to prepare 6 L of mixed acid solution, in which the concentrations of formic acid, acetic acid, succinic acid and lactic acid were 0.5 g / L, 0.5 g / L, 1.0 g / L and 8 g / L respectively, and the total acid concentration was 10 g / L.

[0057] Add 6 L of the above mixed acid solution and 1 kg of corn straw to the reactor, heat to 120 ℃, and keep warm for 2 hours; then lower the temperature to room temperature, add 2.0 g of sodium ethylenediaminetetraacetate, stir for 2 hours and filter to obtain lignocellulose residue; transfer it to a fermentation tank, add 3 kg of deionized water, adjust the pH to 5.0 with phosphoric acid, heat to 50 ℃, add cellulase at 20 FPU / g corn straw, stir for 3 hours, then add 60 g of yeast powder, and inoculate Bacillus coagulans at 5% (v / v), pass nitrogen for 2 hours, control the system temperature at 50 ℃ during the process, and continuously pump in a calcium hydroxide suspension with a concentration of 300 g / L to maintain the system pH 4.5-6.5. After 36 hours of fermentation, the lactic acid content in the fermentation broth was 98 g / L.

[0058] As can be seen from the above, compared with the comparative example, the present invention uses the organic acid waste liquid and the waste liquid at the bottom of the distillation kettle generated in the production process of lignocellulose-based lactic acid, removes polymer impurities and suspended particles through polyacrylamide, and adjusts the concentrations of formic acid, acetic acid, succinic acid and lactic acid in the mixed acid solution for the pretreatment of corn straw, bagasse, rice straw and tobacco straw, and detoxifies the pretreated lignocellulose solution through sodium ethylenediaminetetraacetic acid, semi-synchronous saccharification and fermentation by Bacillus coagulans, combines the introduction of compressed air to increase the OD value of the production strain, and introduces nitrogen to replace the oxygen in the solution, which greatly improves the anaerobic fermentation efficiency. After 36 hours of fermentation, the lactic acid concentration in the fermentation broth can reach more than 126 g / L, which is more than 32% higher than the yield of the traditional lactic acid fermentation process (Comparative Example 1).

[0059] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing lactic acid by recycling lactic acid fermentation waste liquid, characterized in that: The following steps are involved: 1) Collect and concentrate the organic acid waste liquid generated during the separation of lactic acid fermentation broth in sections, and then determine the organic acid concentration therein; 2) Dilute the lactic acid waste liquid at the bottom of the kettle after the lactic acid fermentation liquid is distilled, add a flocculant, stir and mix, and then filter to determine the concentration of lactic acid in the filtrate; 3) the organic acid waste liquid obtained in step 1) and the filtrate obtained in step 2) are mixed in a certain proportion, and then lignocellulose is added to the mixed waste liquid, and the mixture is heated to a certain temperature and then kept warm for pretreatment, and a detoxifying agent is added after the mixture is cooled, and the mixture is stirred and filtered to obtain a pretreated lignocellulose residue; 4) Deionized water is added to the obtained pretreated lignocellulose residue, and after adjusting the pH to 4-7, cellulase is added for enzymatic hydrolysis; then a nitrogen source is added, and lactic acid bacteria are inoculated, compressed air is passed for a period of time, nitrogen is passed, and calcium hydroxide suspension is continuously added for fermentation until the lactic acid concentration no longer increases.

2. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: In step 1), the organic acid waste liquid collected in sections is concentrated to 20% to 90% of the original volume.

3. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: In step 2), water is used as a diluent to dilute the lactic acid waste liquid, and the amount used is 1.0 to 5.0 times the weight of the lactic acid waste liquid.

4. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: The flocculant in step 2) is polyacrylamide, with a molecular weight of 5 to 10 million and a dosage of 0.5 to 3 g / L.

5. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: The ratio of the organic acid waste liquid to the filtrate in step 3) is calculated based on the lactic acid concentration of 1-10 g / L, the formic acid concentration of 0.1-5 g / L, the acetic acid concentration of 0.1-5 g / L, the succinic acid concentration of 1-8 g / L, and the total acid concentration of 5-20 g / L in the obtained mixed waste liquid.

6. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: The wood cellulose used in step 3) is corn straw, bagasse, rice straw, tobacco straw, and bamboo shoot shells, and its usage is 1-25% of the mass of the mixed waste liquid; the detoxification agent is ethylenediaminetetraacetic acid or its sodium salt, and its usage is converted by adding 0.01-0.5 g per liter of mixed waste liquid.

7. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: The pretreatment temperature in step 3) is 100-130°C and the time is 0.5-3 h.

8. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: In step 4), phosphoric acid or its acid salt is used to adjust the pH.

9. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: In step 4), the amount of cellulase added is calculated based on 5-30 FPU per gram of lignocellulose; the system temperature for enzymolysis with cellulase is 47-55°C, and the time is 2-5 h; the nitrogen source used is yeast powder, corn slurry or corn protein powder, and the amount is calculated based on 5-30 g per liter of enzymolysis solution; the accession amount of lactic acid bacteria is 1%-20% of the volume of the enzymolysis solution.

10. The method for preparing lactic acid by recycling lactic acid fermentation waste liquid according to claim 1, characterized in that: In step 4), the time for introducing compressed air is 2 to 6 hours; the time for introducing nitrogen is 1 to 3 hours; the concentration of the calcium hydroxide suspension used is 50 to 300 g / L, and the amount used is based on maintaining the pH of the fermentation system at 4.5 to 6.5; the fermentation temperature is 50 to 55°C.