Method for producing L-lactic acid through lignocellulose fermentation

Abstract

The invention discloses a method for producing L-lactic acid through lignocellulose fermentation, and belongs to the technical field of L-lactic acid production. The method comprises the following steps: washing and cutting off a lignocellulose raw material, and soaking with clear water; adding the cut lignocellulose raw material and calcium hydroxide for kneading treatment, then carrying out heat preservation treatment, and finally carrying out twin-screw washing to obtain a fiber material; mixing the compound enzyme and the fiber material for enzymolysis, maintaining the pH stable by using a citric acid buffer solution, and then filtering and concentrating to obtain a mixed sugar solution; collecting black liquor generated by double-screw kneading and double-screw washing, and adding calcium hydroxide to obtain a neutralizer; the method comprises the following steps: preparing a seed culture medium and a fermentation culture medium by using a mixed sugar solution, inoculating a strain into a solid culture medium for culturing, inoculating into the seed culture medium, putting into a fermentation tank, adding the fermentation culture medium, feeding a neutralizing agent, and culturing and fermenting to obtain the L-lactic acid. The black liquor can be used as a lactic acid fermentation neutralizer, the black liquor recovery problem is solved, and the raw material utilization rate is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of L-lactic acid production, and specifically relates to a method for producing L-lactic acid by fermenting lignocellulose. Background Art

[0002] Polylactic acid is the bio-based degradable plastic with the highest market share in recent years. With the increasing market demand for polylactic acid, the market demand for lactic acid is also increasing. At present, the main method of producing lactic acid is through microbial fermentation using calcium salt method with starch as the carbon source. In order to solve the problem of competing with people for food and respond to the national "dual carbon" policy, the fermentation production of lactic acid using widely available, cheap and renewable wood cellulose as raw material has also become the most noteworthy production method in the lactic acid market in recent years.

[0003] Lignocellulose is a supramolecular complex structure. Effectively separating cellulose, hemicellulose and lignin through pretreatment is a prerequisite for biochemical processing of lignocellulose. Alkali pretreatment is the most commonly used chemical pretreatment method. Due to its high lignin removal rate and high enzymatic hydrolysis rate, it is one of the most commercially used pretreatment methods in large factories. However, alkaline pretreatment will produce a large amount of black liquor, which is difficult to recover and its discharge will cause environmental pollution. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for producing L-lactic acid by fermenting lignocellulose, which solves the problems in the prior art.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for producing L-lactic acid by fermenting lignocellulose, comprising the following steps:

[0007] Wash and cut the lignocellulose raw materials and soak them in clean water;

[0008] The cut wood cellulose raw material and calcium hydroxide are added for kneading treatment, followed by heat preservation treatment, and finally a twin-screw washing to obtain a fiber material;

[0009] The composite enzyme and the fiber material are mixed and hydrolyzed, and a citric acid buffer is used to maintain a stable pH value. After the hydrolysis is completed, the mixed sugar solution is filtered and concentrated to obtain a mixed sugar solution;

[0010] The black liquor produced by twin-screw kneading and twin-screw washing is collected and calcium hydroxide is added to obtain a neutralizing agent;

[0011] The mixed sugar solution is used as a carbon source to prepare a seed culture medium and a fermentation culture medium. After the bacterial strain is inoculated into a solid culture medium for cultivation, it is inoculated into a seed culture medium to complete seed preparation. The seed is then placed in a fermentation tank, a fermentation culture medium is added, and a neutralizer is added to perform cultivation and fermentation to obtain L-lactic acid.

[0012] Furthermore, when preparing the fiber material, the mass ratio of calcium hydroxide to lignocellulose raw material is (1-2):10.

[0013] Furthermore, the twin-screw kneading speed is 180 rpm, the insulation temperature is 80-90° C., the insulation time is 3-4 hours, and the twin-screw washing speed is 160 rpm.

[0014] Further, the composite enzyme includes: hemicellulase and cellulase, and the addition amount is 10-30FPU / g;

[0015] Furthermore, the enzymolysis temperature is 45-50°C, the enzymolysis speed is 150-200rpm, the enzymolysis time is 36-48h, the pH is 4.8-5.0; and the concentration of the mixed sugar solution is 80-140g / L.

[0016] Furthermore, when preparing the neutralizing agent, calcium hydroxide is added to adjust the pH to 8-10.

[0017] Furthermore, the culture and fermentation temperature is 45-55°C, a neutralizing agent is added to control the pH to 6.5-7.5, and the stirring speed is 100-200 r / min.

[0018] Furthermore, the seed culture medium configuration includes: 50g / L mixed sugar solution, 10g / L yeast extract powder, 0.01g / L sodium chloride, 0.5g / L sodium acetate, 0.2g / L ammonium citrate, 0.2g / L potassium dihydrogen phosphate, 0.2g / L magnesium sulfate heptahydrate, 0.05g / L manganese sulfate heptahydrate and 30g / L calcium carbonate.

[0019] Furthermore, the fermentation medium configuration includes: 80-140 g / L mixed sugar solution, 20 g / L yeast extract, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate and 0.15 g / L manganese sulfate heptahydrate.

[0020] Furthermore, the lignocellulose raw material is corn straw, wheat straw or rice straw.

[0021] Beneficial effects of the present invention:

[0022] By using calcium hydroxide for lignocellulose pretreatment, the lignocellulose structure can be effectively dissociated. Black liquor can be used as a neutralizer for lactic acid fermentation, reducing the use of calcium hydroxide, indirectly reducing fermentation costs, and solving the problem of black liquor recovery. At the same time, microorganisms can use the residual sugar in the black liquor to improve the utilization rate of raw materials. This provides a new idea for the green production of lactic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 It is a flow chart of the L-lactic acid production method of the present invention. DETAILED DESCRIPTION

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

[0026] A method for producing L-lactic acid by fermenting lignocellulose, comprising the following steps:

[0027] S1, wash and cut the lignocellulose raw material into 3-3.5 cm pieces and soak them in water for 1 hour;

[0028] S2, pretreatment: adding the cut lignocellulose raw materials and calcium hydroxide into a twin-screw kneading and separating machine for kneading treatment, then entering a heat preservation bin for heat preservation treatment, and finally performing twin-screw washing in the twin-screw kneading and separating machine to obtain a fiber material;

[0029] The mass ratio of calcium hydroxide to lignocellulose raw material is (1-2):10, the twin-screw kneading speed is 180rpm, the insulation temperature is 80-90℃, the insulation time is 3-4h, the twin-screw washing speed is 160rpm, and the feed humidity during washing is 30%-50%.

[0030] S3, putting the complex enzyme and the fiber material into an enzymatic saccharification tank for mixed enzymatic hydrolysis, and using citric acid buffer to maintain pH stability, and after the enzymatic hydrolysis is completed, filtering and concentrating to obtain a mixed sugar solution;

[0031] The complex enzyme includes hemicellulase and cellulase, with an addition amount of 10-30 FPU / g; the enzymatic hydrolysis temperature is 45-50°C, the enzymatic hydrolysis speed is 150-200rpm, the enzymatic hydrolysis time is 36-48h, the citric acid buffer solution maintains a pH of 4.8-5.0; and the concentration of the mixed sugar solution is 80-140g / L.

[0032] S4, collecting the black liquor produced by the twin-screw kneading and the twin-screw washing, and adding calcium hydroxide to adjust the pH to 8-10 to obtain a neutralizing agent.

[0033] S5, using the mixed sugar solution as a carbon source to prepare a seed culture medium and a fermentation culture medium, inoculating the strain into a solid culture medium and culturing for 24 hours, inoculating the strain into a seed culture medium to complete seed preparation, and then placing the strain into a 5L fermentation tank, adding a fermentation culture medium and feeding a neutralizer, culturing and fermenting to obtain L-lactic acid;

[0034] In the 5L fermentation tank, the liquid volume is 60-70%, the culture temperature is controlled at 45-55°C, the neutralizing agent is added to control the pH to 6.5-7.5, and the stirring speed is controlled between 100-200 r / min.

[0035] The seed culture medium configuration includes: 50g / L mixed sugar solution, 10g / L yeast extract powder, 0.01g / L sodium chloride, 0.5g / L sodium acetate, 0.2g / L ammonium citrate, 0.2g / L potassium dihydrogen phosphate, 0.2g / L magnesium sulfate heptahydrate, 0.05g / L manganese sulfate heptahydrate, 30g / L calcium carbonate (the usage amount is 0.6 times the concentration of the mixed sugar solution)

[0036] The fermentation medium is configured as follows: 80-140 g / L mixed sugar solution, 20 g / L yeast extract powder, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate, and 0.15 g / L manganese sulfate heptahydrate.

[0037] Among them, the lignocellulosic raw materials are: corn straw, wheat straw, rice straw and the like.

[0038] The production method of L-lactic acid of the present invention is described below by the following examples;

[0039] Example 1

[0040] A method for producing L-lactic acid by fermenting lignocellulose, comprising the following steps:

[0041] S1, wash and cut the wheat straw into 3-3.5 cm pieces and soak them in water for 1 hour;

[0042] S2, adding the cut lignocellulose raw material and calcium hydroxide for kneading treatment, then entering the heat preservation bin for heat preservation treatment, and finally performing twin-screw washing to obtain fiber material; wherein, the mass ratio of calcium hydroxide to straw is 1:10, the twin-screw kneading speed is 180rpm, the heat preservation temperature is 90℃, the heat preservation time is 4h, and the twin-screw washing speed is 160rpm.

[0043] S3, the composite enzyme (hemicellulase and cellulase) and the fiber material are mixed for enzymolysis, and the pH is maintained stable using citric acid buffer. After the enzymolysis is completed, the straw sugar is obtained by filtration and concentration; wherein, the addition amount of the composite enzyme is 30FPU / g; the enzymolysis temperature is 50°C, the enzymolysis speed is 180rpm, the enzymolysis time is 48h, and the pH is 5.0; the concentration of the straw sugar is 80g / L.

[0044] S4, collecting the black liquor produced by the twin-screw kneading and the twin-screw washing, and adding calcium hydroxide to adjust the pH to 9 to obtain a neutralizing agent.

[0045] S5, using straw sugar as a carbon source to prepare a seed culture medium and a fermentation culture medium, inoculating Bacillus coagulans into a solid culture medium and culturing it for 24 hours, inoculating it into a seed culture medium to complete seed preparation, and then placing it in a 5L fermentation tank, adding a fermentation medium and a neutralizer, culturing and fermenting to obtain L-lactic acid;

[0046] In the 5L fermentation tank, the liquid volume is 60%, the culture temperature is controlled at 45°C, the neutralizing agent is added to control the pH to 6.5, and the stirring speed is controlled at 120 r / min.

[0047] The seed culture medium configuration includes: 50g / L straw sugar, 10g / L yeast extract powder, 0.01g / L sodium chloride, 0.5g / L sodium acetate, 0.2g / L ammonium citrate, 0.2g / L potassium dihydrogen phosphate, 0.2g / L magnesium sulfate heptahydrate, 0.05g / L manganese sulfate heptahydrate, 30g / L calcium carbonate (the usage amount is 0.6 times the concentration of the mixed sugar solution)

[0048] The fermentation medium is configured as follows: 80 g / L straw sugar, 20 g / L yeast extract powder, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate, and 0.15 g / L manganese sulfate heptahydrate.

[0049] Example 2

[0050] A method for producing L-lactic acid by fermenting lignocellulose, comprising the following steps:

[0051] S1, wash and cut the wheat straw into 3-3.5 cm pieces and soak them in water for 1 hour;

[0052] S2, adding the cut lignocellulose raw material and calcium hydroxide for kneading treatment, then entering the heat preservation bin for heat preservation treatment, and finally performing twin-screw washing to obtain fiber material; wherein, the mass ratio of calcium hydroxide to straw is 1.5:10, the twin-screw kneading speed is 180rpm, the heat preservation temperature is 90℃, the heat preservation time is 4h, and the twin-screw washing speed is 160rpm.

[0053] S3, the composite enzyme (hemicellulase and cellulase) and the fiber material are mixed for enzymolysis, and the pH is maintained stable using citric acid buffer. After the enzymolysis is completed, the straw sugar is obtained by filtration and concentration; wherein, the addition amount of the composite enzyme is 30FPU / g; the enzymolysis temperature is 50°C, the enzymolysis speed is 180rpm, the enzymolysis time is 48h, and the pH is 5.0; the concentration of the straw sugar is 80g / L.

[0054] S4, collecting the black liquor produced by the twin-screw kneading and the twin-screw washing, and adding calcium hydroxide to adjust the pH to 9 to obtain a neutralizing agent.

[0055] S5, using straw sugar as a carbon source to prepare a seed culture medium and a fermentation culture medium, inoculating Bacillus coagulans into a solid culture medium and culturing it for 24 hours, inoculating it into a seed culture medium to complete seed preparation, and then placing it in a 5L fermentation tank, adding a fermentation medium and a neutralizer, culturing and fermenting to obtain L-lactic acid;

[0056] In the 5L fermentation tank, the liquid volume is 60%, the culture temperature is controlled at 45°C, the neutralizing agent is added to control the pH to 6.5, and the stirring speed is controlled at 120 r / min.

[0057] The seed culture medium configuration includes: 50g / L straw sugar, 10g / L yeast extract powder, 0.01g / L sodium chloride, 0.5g / L sodium acetate, 0.2g / L ammonium citrate, 0.2g / L potassium dihydrogen phosphate, 0.2g / L magnesium sulfate heptahydrate, 0.05g / L manganese sulfate heptahydrate, 30g / L calcium carbonate (the usage amount is 0.6 times the concentration of the mixed sugar solution)

[0058] The fermentation medium is configured as follows: 80 g / L straw sugar, 20 g / L yeast extract powder, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate, and 0.15 g / L manganese sulfate heptahydrate.

[0059] Example 3

[0060] A method for producing L-lactic acid by fermenting lignocellulose, comprising the following steps:

[0061] S1, wash and cut the wheat straw into 3-3.5 cm pieces and soak them in water for 1 hour;

[0062] S2, adding the cut lignocellulose raw material and calcium hydroxide for kneading treatment, then entering the heat preservation bin for heat preservation treatment, and finally performing twin-screw washing to obtain fiber material; wherein, the mass ratio of calcium hydroxide to straw is 2:10, the twin-screw kneading speed is 180rpm, the heat preservation temperature is 90℃, the heat preservation time is 4h, and the twin-screw washing speed is 160rpm.

[0063] S3, the composite enzyme (hemicellulase and cellulase) and the fiber material are mixed for enzymolysis, and the pH is maintained stable using citric acid buffer. After the enzymolysis is completed, the straw sugar is obtained by filtration and concentration; wherein, the addition amount of the composite enzyme is 30FPU / g; the enzymolysis temperature is 50°C, the enzymolysis speed is 180rpm, the enzymolysis time is 48h, and the pH is 5.0; the concentration of the straw sugar is 80g / L.

[0064] S4, collecting the black liquor produced by the twin-screw kneading and the twin-screw washing, and adding calcium hydroxide to adjust the pH to 9 to obtain a neutralizing agent.

[0065] S5, using straw sugar as a carbon source to prepare a seed culture medium and a fermentation culture medium, inoculating Bacillus coagulans into a solid culture medium and culturing it for 24 hours, inoculating it into a seed culture medium to complete seed preparation, and then placing it in a 5L fermentation tank, adding a fermentation medium and a neutralizer, culturing and fermenting to obtain L-lactic acid;

[0066] In the 5L fermentation tank, the liquid volume is 60%, the culture temperature is controlled at 45°C, the neutralizing agent is added to control the pH to 6.5, and the stirring speed is controlled at 120 r / min.

[0067] The seed culture medium configuration includes: 50g / L straw sugar, 10g / L yeast extract powder, 0.01g / L sodium chloride, 0.5g / L sodium acetate, 0.2g / L ammonium citrate, 0.2g / L potassium dihydrogen phosphate, 0.2g / L magnesium sulfate heptahydrate, 0.05g / L manganese sulfate heptahydrate, 30g / L calcium carbonate (the usage amount is 0.6 times the concentration of the mixed sugar solution)

[0068] The fermentation medium is configured as follows: 80 g / L straw sugar, 20 g / L yeast extract powder, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate, and 0.15 g / L manganese sulfate heptahydrate.

[0069] Example 4

[0070] A method for producing L-lactic acid by fermenting lignocellulose, comprising the following steps:

[0071] S1, wash and cut the wheat straw into 3-3.5 cm pieces and soak them in water for 1 hour;

[0072] S2, adding the cut lignocellulose raw material and calcium hydroxide for kneading treatment, then entering the heat preservation bin for heat preservation treatment, and finally performing twin-screw washing to obtain fiber material; wherein, the mass ratio of calcium hydroxide to straw is 1.5:10, the twin-screw kneading speed is 180rpm, the heat preservation temperature is 90℃, the heat preservation time is 4h, and the twin-screw washing speed is 160rpm.

[0073] S3, the composite enzyme (hemicellulase and cellulase) and the fiber material are mixed for enzymolysis, and the pH is maintained stable using citric acid buffer. After the enzymolysis is completed, the straw sugar is obtained by filtration and concentration; wherein, the addition amount of the composite enzyme is 30FPU / g; the enzymolysis temperature is 50°C, the enzymolysis speed is 180rpm, the enzymolysis time is 48h, and the pH is 5.0; the concentration of the straw sugar is 80g / L.

[0074] S4, collecting the black liquor produced by the twin-screw kneading and the twin-screw washing, and adding calcium hydroxide to adjust the pH to 8 to obtain a neutralizing agent.

[0075] S5, using straw sugar as a carbon source to prepare a seed culture medium and a fermentation culture medium, inoculating Bacillus coagulans into a solid culture medium and culturing it for 24 hours, inoculating it into a seed culture medium to complete seed preparation, and then placing it in a 5L fermentation tank, adding a fermentation medium and a neutralizer, culturing and fermenting to obtain L-lactic acid;

[0076] In the 5L fermentation tank, the liquid volume is 60%, the culture temperature is controlled at 45°C, the neutralizing agent is added to control the pH to 6.5, and the stirring speed is controlled at 120 r / min.

[0077] The seed culture medium configuration includes: 50g / L straw sugar, 10g / L yeast extract powder, 0.01g / L sodium chloride, 0.5g / L sodium acetate, 0.2g / L ammonium citrate, 0.2g / L potassium dihydrogen phosphate, 0.2g / L magnesium sulfate heptahydrate, 0.05g / L manganese sulfate heptahydrate, 30g / L calcium carbonate (the usage amount is 0.6 times the concentration of the mixed sugar solution)

[0078] The fermentation medium is configured as follows: 140 g / L straw sugar, 20 g / L yeast extract powder, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate, and 0.15 g / L manganese sulfate heptahydrate.

[0079] Example 5

[0080] A method for producing L-lactic acid by fermenting lignocellulose, comprising the following steps:

[0081] S1, wash and cut the wheat straw into 3-3.5 cm pieces and soak them in water for 1 hour;

[0082] S2, adding the cut lignocellulose raw material and calcium hydroxide for kneading treatment, then entering the heat preservation bin for heat preservation treatment, and finally performing twin-screw washing to obtain fiber material; wherein, the mass ratio of calcium hydroxide to straw is 1.5:10, the twin-screw kneading speed is 180rpm, the heat preservation temperature is 90℃, the heat preservation time is 4h, and the twin-screw washing speed is 160rpm.

[0083] S3, the composite enzyme (hemicellulase and cellulase) and the fiber material are mixed for enzymolysis, and the pH is maintained stable using citric acid buffer. After the enzymolysis is completed, the straw sugar is obtained by filtration and concentration; wherein, the addition amount of the composite enzyme is 30FPU / g; the enzymolysis temperature is 50°C, the enzymolysis speed is 180rpm, the enzymolysis time is 48h, and the pH is 5.0; the concentration of the straw sugar is 80g / L.

[0084] S4, collecting the black liquor produced by the twin-screw kneading and the twin-screw washing, and adding calcium hydroxide to adjust the pH to 10 to obtain a neutralizing agent.

[0085] S5, using straw sugar as a carbon source to prepare a seed culture medium and a fermentation culture medium, inoculating Bacillus coagulans into a solid culture medium and culturing it for 24 hours, inoculating it into a seed culture medium to complete seed preparation, and then placing it in a 5L fermentation tank, adding a fermentation medium and a neutralizer, culturing and fermenting to obtain L-lactic acid;

[0086] In the 5L fermentation tank, the liquid volume is 60%, the culture temperature is controlled at 45°C, the neutralizing agent is added to control the pH to 6.5, and the stirring speed is controlled at 120 r / min.

[0087] The seed culture medium configuration includes: 50g / L straw sugar, 10g / L yeast extract powder, 0.01g / L sodium chloride, 0.5g / L sodium acetate, 0.2g / L ammonium citrate, 0.2g / L potassium dihydrogen phosphate, 0.2g / L magnesium sulfate heptahydrate, 0.05g / L manganese sulfate heptahydrate, 30g / L calcium carbonate (the usage amount is 0.6 times the concentration of the mixed sugar solution)

[0088] The fermentation medium is configured as follows: 140 g / L straw sugar, 20 g / L yeast extract powder, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate, and 0.15 g / L manganese sulfate heptahydrate.

[0089] Results test;

[0090] The fermentation results in Examples 1-5 are shown in Table 1 below;

[0091] Table 1 Fermentation results statistics of Examples 1-5

[0092]

[0093]

[0094] It can be seen from the above examples that the black liquor recovery rate in Example 4 is high and has a good sugar-acid conversion rate.

[0095] The use of calcium hydroxide to pre-treat sugar production has achieved the recycling of alkaline wastewater, reduced wastewater discharge, and reduced pollution. It provides a reference for the industrial production of lactic acid

[0096] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0097] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for producing L-lactic acid by fermentation of lignocellulose, characterized in that: The following steps are involved: Wash and cut the lignocellulose raw materials and soak them in clean water; The cut wood cellulose raw material and calcium hydroxide are added for kneading treatment, followed by heat preservation treatment, and finally a twin-screw washing to obtain a fiber material; The composite enzyme and the fiber material are mixed and hydrolyzed, and a citric acid buffer is used to maintain a stable pH value. After the hydrolysis is completed, the mixed sugar solution is filtered and concentrated to obtain a mixed sugar solution; The black liquor produced by twin-screw kneading and twin-screw washing is collected and calcium hydroxide is added to obtain a neutralizing agent; The mixed sugar solution is used as a carbon source to prepare a seed culture medium and a fermentation culture medium. After the bacterial strain is inoculated into a solid culture medium for cultivation, it is inoculated into a seed culture medium to complete seed preparation. The seed is then placed in a fermentation tank, a fermentation culture medium is added, and a neutralizer is added to perform cultivation and fermentation to obtain L-lactic acid.

2. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1, characterized in that: When preparing the fiber material, the mass ratio of calcium hydroxide to lignocellulose raw material is (1-2):

10.

3. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1 or 2, characterized in that: The twin-screw kneading speed is 180 rpm, the insulation temperature is 80-90° C., the insulation time is 3-4 hours, and the twin-screw washing speed is 160 rpm.

4. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1, characterized in that: The compound enzyme comprises hemicellulase and cellulase, and the added amount is 10-30 FPU / g.

5. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1 or 4, characterized in that: The enzymatic hydrolysis temperature is 45-50°C, the enzymatic hydrolysis speed is 150-200rpm, the enzymatic hydrolysis time is 36-48h, the pH is 4.8-5.0; and the concentration of the mixed sugar solution is 80-140g / L.

6. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1, characterized in that: When preparing the neutralizer, add calcium hydroxide to adjust the pH to 8-10.

7. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1, characterized in that: The culture and fermentation temperature is 45-55° C., a neutralizer is added to control the pH to 6.5-7.5, and the stirring speed is 100-200 r / min.

8. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1, characterized in that: The seed culture medium configuration includes: 50 g / L mixed sugar solution, 10 g / L yeast extract powder, 0.01 g / L sodium chloride, 0.5 g / L sodium acetate, 0.2 g / L ammonium citrate, 0.2 g / L potassium dihydrogen phosphate, 0.2 g / L magnesium sulfate heptahydrate, 0.05 g / L manganese sulfate heptahydrate and 30 g / L calcium carbonate.

9. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1, characterized in that: The fermentation medium comprises: 80-140 g / L mixed sugar solution, 20 g / L yeast extract, 0.03 g / L sodium chloride, 1.5 g / L sodium acetate, 0.6 g / L ammonium citrate, 0.6 g / L potassium dihydrogen phosphate, 0.6 g / L magnesium sulfate heptahydrate and 0.15 g / L manganese sulfate heptahydrate.

10. The method for producing L-lactic acid by fermentation of lignocellulose according to claim 1, characterized in that: The lignocellulose raw material is corn straw, wheat straw or rice straw.

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