Method for co-production of organic acid and lignin from lignocellulose

Abstract

The invention provides a method for co-producing organic acid and lignin from lignocellulose, which comprises the following steps: step 1, pretreating a lignocellulose raw material to obtain a pretreated material; step 2, carrying out enzymolysis on the pretreated material to obtain enzymatic hydrolysate containing pentose, hexose and lignin; 3, carrying out solid-liquid separation on the enzymatic hydrolysate to obtain enzymatic hydrolysate containing pentose and hexose and a solid phase containing lignin; step 4, carrying out acidogenic fermentation on the enzymatic hydrolysate containing pentose and hexose to obtain fermentation liquor containing an organic acid mixture; and 5, carrying out lignin extraction on the lignin-containing solid phase to obtain the lignin. According to the method provided by the invention, lignin can be efficiently separated, and various organic acids can be obtained through a simple process.

Description

Technical Field

[0001] The invention relates to the technical field of biochemical production, and more particularly to a method for co-producing organic acid and lignin from lignocellulose. Background Art

[0002] Lignocellulose is mainly composed of lignin, hemicellulose and cellulose, among which lignin is a cross-linked phenolic polymer, hemicellulose is a short branched heteropolysaccharide, and cellulose is a polymer of monosaccharide glucose covalently linked by beta-1,4 bonds. In recent years, people have been constantly exploring and studying methods to separate lignin, hemicellulose and cellulose, and at the same time, they are also exploring methods to convert these polymers into other important intermediate raw materials.

[0003] Organic acids contain carboxyl (-COOH) in their chemical structure. They are acidic organic compounds and are important raw materials for organic synthesis, industrial and agricultural production, and the pharmaceutical industry. Organic acids include natural organic acids and synthetic organic acids. Natural organic acids are widely found in the fruits, roots, and leaves of plants and can be directly extracted and separated; synthetic organic acids are obtained by chemical synthesis, enzyme-catalyzed fermentation, microbial fermentation, and the like. Lignocellulose is abundant and renewable. In recent years, people have used lignocellulose as a raw material to prepare a variety of organic acids. For example, patent CN1934249A provides a method for degrading lignocellulose materials. In the presence of a surfactant, enzymatic saccharification of lignocellulose is promoted, and organic acids are obtained by fermentation of the saccharified lignocellulose. This method has a complex reaction system and is difficult to extract products, which is not conducive to industrial applications. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for co-producing organic acids and lignin from lignocellulose, which can efficiently separate lignin and obtain a variety of organic acids through a simple process.

[0005] The object of the present invention is to provide a method for co-producing organic acid and lignin from lignocellulose, comprising the following steps:

[0006] Step 1: pretreating the lignocellulosic raw material to obtain a pretreated material containing cellulose, xylose and lignin;

[0007] Step 2: performing enzymatic hydrolysis on the pretreated material obtained in step 1 to obtain an enzymatic hydrolyzate containing pentose, hexose and lignin;

[0008] Step 3, performing solid-liquid separation on the enzymatic hydrolyzate obtained in step 2 to obtain an enzymatic hydrolyzate containing pentose and hexose and a solid phase containing lignin;

[0009] Step 4: subjecting the enzymatic hydrolysate containing pentose and hexose obtained in step 3 to acid-producing fermentation to obtain a fermentation liquid containing an organic acid mixture;

[0010] Step 5: extracting lignin from the lignin-containing solid phase obtained in step 3 to obtain lignin.

[0011] Preferably, the lignocellulose raw material in the present invention can be selected from one or more of corn straw, rice straw, wheat straw, reed, corn cob and bean straw.

[0012] Preferably, in step 1, the method for pretreating the lignocellulosic raw material is: after the lignocellulosic raw material is crushed and impurities are removed, it is subjected to acid treatment, alkali treatment, and steam explosion treatment to obtain a pretreated material.

[0013] It is worth mentioning that the pulverization and impurity removal of the wood cellulose raw material of the present invention is achieved by using a complete set of pulverization and impurity removal equipment, which specifically includes coarse pulverization, impurity and iron removal, fine pulverization and dust removal processing stages.

[0014] Preferably, in step 2, the enzyme used for enzymatic hydrolysis of the pretreated material is cellulase, wherein the mass ratio of the added cellulase to the mass ratio of the lignocellulose raw material is 0.01-0.3:1.

[0015] It is worth mentioning that after the pretreatment material is enzymatically hydrolyzed, a solid-liquid mixed enzymatic hydrolyzate containing pentoses, hexoses and lignin is obtained. In step three, in order to separate the solid and liquid, plate and frame filtration or centrifugal separation can be used to separate the solid-liquid mixed enzymatic hydrolyzate into an enzymatic hydrolyzate containing pentoses and hexoses and a solid phase containing lignin.

[0016] Preferably, in step four, the conditions for acidogenic fermentation are: batch fermentation, semi-continuous fermentation or continuous fermentation under anaerobic conditions; the pH of the acidogenic fermentation is 5-10, preferably pH 5-7; the temperature of the acidogenic fermentation is 30-58°C, preferably 35-40°C; the C / N ratio is 20-60, preferably 30-40; the fermentation time is 2-50 days, preferably 7-14 days.

[0017] Preferably, the nitrogen source comes from one or a combination of NH4Cl, corn steep liquor, sludge, potassium nitrate and urea.

[0018] Preferably, the acid-producing fermentation of the present invention adopts an acid-producing microbial flora; preferably, the anaerobic fermentation acid-producing microbial flora enriched by the method provided in the patent application (application number 2023113103664) is adopted.

[0019] Specifically, the enrichment method of the anaerobic fermentation acid-producing microbial community includes the F1 stage to the F3 stage, that is, the reactor can be divided into the F1, F2 and F3 stages during the entire operation process, and the organic load of the straw is gradually increased in the three stages until it operates stably in the F3 stage. Among them, the F1 stage is the start-up stage of the reactor, and the solid content and load are low. The solid content and load are increased to enter the F2 stage. After the acid production in F2 is stabilized, the proportion of straw in the material is increased, the C / N ratio is increased, and the F3 stage is entered to adapt the bacterial community to the high C / N ratio straw material.

[0020] Specifically as follows:

[0021] F1 stage:

[0022] The operation time of the F1 stage is 80 to 120 days, preferably 100 to 110 days;

[0023] The inoculum source is added to the reactor, and nitrogen is introduced to exhaust the air and then the reactor is closed; after starting the reactor, no material is fed in or discharged for two days, and then the substrate is supplied under the condition of 0.4-0.6 g VTS / L / d organic load; wherein the TS value of the substrate is 4.8-5.4%; the VTS value is 4.0-4.4%; the C / N ratio is 18-22; the material can be fed in and discharged once every two days, and the hydraulic retention time of the reactor is 90-110 days; and the physical and chemical parameters of the reactor can be monitored once every four days.

[0024] Specifically, regarding the inoculation source:

[0025] The solid content of the inoculation source used in the present invention is ≤5%.

[0026] Furthermore, in order to inhibit the activity of methanogens, the inoculum source is preferably pretreated, and the pretreatment method is: heat-treating the inoculum source at 75-85°C for 0.5-1.2 hours, and adding a methane inhibitor with a final concentration of 4-6 mM. Preferably, the methane inhibitor is 2-bromoethanosulfophate (BES).

[0027] Furthermore, the inoculum source may include inocula from different sources; specifically, inocula from different sources may be selected from a mixture of anaerobic digestion sludge from grain sugar factories, anaerobic digestion sludge from restaurant waste, anaerobic digestion sludge from cellulose, anaerobic digestion sludge from glucose, and anaerobic fermentation acid production reactor sludge from fruit waste. Among them, the anaerobic digestion sludge from cellulose is preferably anaerobic digestion sludge from cellulose at high temperature or anaerobic digestion sludge from cellulose at medium temperature; the anaerobic digestion sludge from glucose is preferably anaerobic digestion sludge from glucose at high temperature or anaerobic digestion sludge from glucose at medium temperature. Specifically, the appropriate sludge type may be selected according to different reaction temperatures.

[0028] Furthermore, the inoculum source comprises inocula from different sources mixed according to the total solids concentration (TS), each type of sludge accounts for more than 10% of the total solids concentration (TS), and more preferably, the inoculum sludges from multiple different sources are mixed in equal proportions according to the total solids concentration (TS).

[0029] In specific operations, the inoculum source can be crushed with a blender and then filtered (for example, using 2-3 layers of gauze for filtration) to ensure that the solid content of the sludge at the start-up of the reactor is below 5%.

[0030] Specifically, regarding the substrate:

[0031] The substrate used in the present invention is a mixture of straw, kitchen waste and a nitrogen source substrate; in the F1 stage, the VTS ratio of the straw, kitchen waste and nitrogen source substrate in the substrate is preferably (0.8-1.2): (0.8-1.2): (0.8-1.2).

[0032] Furthermore, the source substrate can be a substrate conventionally used in the field, specifically, residual sludge from a sewage treatment plant can be used; currently, urban sewage treatment plants in my country use the activated sludge method to treat sewage, which produces a large amount of residual sludge, and the sludge treatment process is still immature. Using residual sludge from a sewage treatment plant as a nitrogen source substrate can reuse the sludge, which is environmentally friendly and cost-saving.

[0033] Furthermore, the straw may be selected from a combination of at least one or more of corn straw, rice straw, wheat straw, reed or bean straw.

[0034] Furthermore, the straw can be steam-exploded straw. The steam-exploded straw can be straw that has been conventionally treated with steam explosion in the art, or it can be prepared according to the following method: adding straw material and water into a sealed container, maintaining for a period of time (which can be several minutes), and then suddenly reducing the pressure to steam-explode the straw material, so that the connecting layer between hemicellulose and lignin is destroyed, so that more active groups of cellulose are exposed, which is more conducive to degradation.

[0035] Furthermore, the food waste may be common food waste, or homemade, such as a wet weight mixture of crushed fruits, vegetables, and grains.

[0036] Preferably, the substrate can be stored at low temperature (eg, 4° C.) and diluted to a target solid content when used.

[0037] Specifically, regarding the reactor:

[0038] The reactor used in the present invention can be a high temperature reactor or a medium temperature reactor. A conventional reactor in the art can be selected, such as a conventional mechanical stirring tank and the like. The stirring speed of the reactor can be 0 to 150 ppm to ensure uniform mixing of the materials.

[0039] Preferably, the pH value of the reactor is 5.5-6.0; the operating temperature of the high-temperature reactor is 50-55°C; and the operating temperature of the medium-temperature reactor is 35-40°C.

[0040] Furthermore, when the reactor is a high-temperature reactor, the cellulose anaerobic digestion sludge can be selected from cellulose high-temperature anaerobic digestion sludge, and the glucose anaerobic digestion sludge can be selected from glucose high-temperature anaerobic digestion sludge.

[0041] Furthermore, when the reactor is a mesophilic reactor, the cellulose anaerobic digestion sludge can be selected from cellulose mesophilic anaerobic digestion sludge, and the glucose anaerobic digestion sludge can be selected from glucose mesophilic anaerobic digestion sludge.

[0042] In specific practice, a semi-continuous fully mixed flow anaerobic fermentation acid production reactor system can be constructed, and a high-temperature reactor or a medium-temperature reactor can be used to enrich the high-temperature bacterial community and the medium-temperature bacterial community respectively.

[0043] F2 stage:

[0044] The operation time of the F2 stage is 50 to 100 days, preferably 75 to 90 days; the pH value of the reactor is 5.5 to 6.0; the feed solid content is adjusted to 8 to 12%, the organic load is increased to 0.8 to 1.2 g VTS / L / d, the substrate is supplied, the substrate TS is 9.8 to 10.5%, the substrate VTS is 8.0 to 8.5%, and the VTS ratio of straw, kitchen waste and sludge in the substrate is (0.8 to 1.2): (0.8 to 1.2): (0.8 to 1.2); the substrate C / N ratio is 18 to 22; the material can be loaded and unloaded once every two days; the hydraulic retention time of the reactor can be 90 to 110 days; and the operation is continued until it is stable.

[0045] F3 stage:

[0046] The operation time of the F3 stage is 120 to 200 days, preferably 165 to 185 days; the pH value of the reactor is 5.5 to 6.0; the feed solid content is kept unchanged in this stage (the feed solid content is kept at 8 to 12% in this stage), and the organic load is increased to 1.8 to 2.2 g The substrate is supplied at VTS / L / d, the hydraulic retention time is adjusted to 45-55 days, and the VTS ratio of straw, food waste and sludge in the feed is changed from (0.8-1.2):(0.8-1.2):(0.8-1.2) to (2.8-3.2):(1.8-2.2):(0.8-1.2), and the substrate C / N ratio is increased from 18-22 to 38-42; the substrate TS is 9.5-10%, and the substrate VTS is 8.0-8.6%; the material can be loaded and discharged once every two days; the operation is continued until it is stable; and the microbial flora in the reactor during the stable operation of the F3 stage is collected.

[0047] It is worth mentioning that the microbial flora of the reactor during the stable operation of the F3 stage was collected by taking the fermentation liquid, centrifuging it at 4°C for 10 minutes, removing the supernatant, and the precipitate was the flora. The enriched flora was used for the acid production fermentation of the enzymatic hydrolyzate of the present invention.

[0048] Preferably, the enzymatic hydrolyzate containing pentose and hexose is subjected to acidogenic fermentation by an enriched bacterial community to obtain a fermentation broth containing a mixture of organic acids, wherein the organic acids in the fermentation broth are a combination of lactic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, valeric acid, and isovaleric acid. The present invention can adjust the composition and content of the acid in the mixed organic acid by controlling the conditions of the acidogenic fermentation.

[0049] Preferably, in step five, lignin can be extracted by alkali dissolution, solid-liquid separation, acid precipitation, water washing, and airflow drying.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a method for co-producing mixed organic acids and lignin by using lignocellulose as a raw material to replace grain raw materials, and by controlling the acid production fermentation conditions, adjusting the composition and content of the acid in the mixed organic acid, a high organic acid concentration in the mixed organic acid fermentation liquid is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The present invention is a flow chart of the co-production of organic acid and lignin using lignocellulose as raw material. DETAILED DESCRIPTION

[0052] The present invention is described in detail below in conjunction with specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0053] The raw materials used in the examples, unless otherwise specified, are all disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0054] The sources of the sludge, kitchen waste and straw used in the embodiments of the present invention are as follows:

[0055] Anaerobic digestion sludge from grain and sugar factories: COFCO Biochemical (Chengdu) Co., Ltd.;

[0056] Anaerobic digestion sludge of restaurant kitchen waste: The anaerobic methanogenetic reactor stably operated by the Environmental Biotechnology Research Center of the School of Architecture and Environment of Sichuan University. The restaurant kitchen waste was taken from the student cafeteria of Sichuan University;

[0057] Cellulose high temperature anaerobic digestion sludge: The high temperature anaerobic methanogenic reactor stably operated by the Environmental Biotechnology Research Center of the School of Architecture and Environment of Sichuan University uses commercially available carboxymethyl cellulose as the carbon source;

[0058] Cellulose mesophilic anaerobic digestion sludge: The mesophilic anaerobic methanogenic reactor stably operated by the Environmental Biotechnology Research Center of the School of Architecture and Environment of Sichuan University uses commercially available carboxymethyl cellulose as the carbon source;

[0059] Glucose thermophilic anaerobic digestion sludge: The thermophilic anaerobic methanogenic reactor stably operated by the Environmental Biotechnology Research Center of the School of Architecture and Environment of Sichuan University uses commercially available glucose as the carbon source;

[0060] Glucose mesophilic anaerobic digestion sludge: The mesophilic anaerobic methanogenetic reactor stably operated by the Environmental Biotechnology Research Center of the School of Architecture and Environment of Sichuan University uses commercially available glucose as the carbon source;

[0061] Anaerobic fermentation acid production reactor sludge from fruit waste: The anaerobic fermentation acid production reactor stably operated by the Environmental Biotechnology Research Center of the School of Architecture and Environment of Sichuan University uses commercially available fruits (banana, watermelon, and orange mixed in a weight ratio of 1:1:1) as raw materials;

[0062] The wastewater plant residual sludge is the dewatered sludge from a municipal wastewater treatment plant in Chengdu;

[0063] Artificially prepared food waste is a mixture of bananas, oranges, cabbages and rice at equal wet weight after crushing;

[0064] Steam-exploded straw refers to steam-exploded straw, wherein the steam explosion treatment comprises: adding corn straw and water into a closed container, and maintaining the pressure at 1.7 MPa for 2 minutes, and then suddenly reducing the pressure to steam-explode the straw material.

[0065] Table 1 shows the TS and VTS data of inoculum and substrate from different sources.

[0066] Table 1

[0067]

[0068] In the embodiment, one high-temperature reactor (working volume 4 L) and one medium-temperature reactor (working volume 2.4 L) were prepared to enrich the bacterial flora suitable for high temperature and the bacterial flora suitable for medium temperature, respectively.

[0069] Example 1

[0070] This example is used to illustrate the enrichment method of microbial flora.

[0071] 1. Reactor construction

[0072] Preparation of inoculum source: In order to enrich the anaerobic fermentation and acid-producing microbial community, the anaerobic digestion sludge of grain sugar factory, the anaerobic digestion sludge of restaurant waste, the high-temperature anaerobic digestion sludge of cellulose, the high-temperature anaerobic digestion sludge of glucose and the anaerobic fermentation and acid-producing reactor sludge of fruit waste were mixed and used as the inoculum source; inocula from different sources were mixed in equal proportions (i.e., 1:1:1:1:1) according to the total solids (TS) concentration (TS and VTS of inocula from different sources are shown in Table 1).

[0073] Preparation of substrate: Steam-exploded straw, artificially prepared food waste (banana, orange, cabbage and rice were crushed and mixed with equal wet weight) and wastewater plant residual sludge were used as substrates. Different substrates were mixed in equal proportions according to the volatile total solids (VTS) concentration (TS and VTS of various substrates are shown in Table 1). The mixed substrates were stored at 4°C and diluted to the target solid content when used.

[0074] A high temperature reactor (working volume 4 L, named H) was prepared.

[0075] 2. Reactor startup and operation

[0076] The present invention starts up a high temperature reactor (H).

[0077] The whole operation process of the reactor is divided into F1, F2 and F3 stages. The organic load of straw is gradually increased in the three stages until it operates stably in the F3 stage. The operating conditions of the reactor in the three stages are shown in Table 2.

[0078] Days 0 to 105 are the F1 stage.

[0079] The startup and operation temperature of the high-temperature reactor is 53°C, the stirring speed is 100rpm, and the pH value is controlled at 5.5-6.0. According to TS, the inoculation source obtained by mixing inoculum sludge from various sources in equal proportions is crushed with a blender and filtered with 2-3 layers of gauze to ensure that the solid content of the reactor startup sludge is less than 5%. In order to inhibit the activity of methanogens, the startup sludge needs to be pretreated. The startup sludge is heat-treated at 80°C for 1 hour, and a methane inhibitor 2-bromoethane sulfonic acid (2-bromoethanosulfophate, BES) is added at a final concentration of 5mM. The pretreated mixed inoculum is injected into the working volume of the reactor, and the reactor is closed after nitrogen is introduced to exhaust the air to reach an anaerobic state. After starting the reactor, no material was added or removed for two days. After that, a substrate containing straw, food waste and sludge (TS: 5.2%; VTS: 4.1%; C / N ratio: 20) was supplied under an organic loading condition of 0.5 g VTS / L / d. The VTS ratio of straw, food waste and sludge in the substrate was 1:1:1. The material was added and removed every two days. The hydraulic retention time of the reactor was 100 days. The physical and chemical parameters of the reactor were monitored every four days.

[0080] Days 105 to 189 are the F2 stage.

[0081] During this stage, the hydraulic retention time was maintained at 100 days, the feed solid content was adjusted to 10%, the substrate TS was 10.3%, the substrate VTS was 8.2%, the VTS ratio of straw, food waste and sludge in the substrate was 1:1:1; the substrate C / N ratio was 20; the organic load was increased to 1g VTS / L / d; and the operation was continued until stability.

[0082] Days 189 to 368 are the F3 stage.

[0083] In this stage, the feed solid content was maintained at 10%, the organic load was increased to 2g VTS / L / d, the hydraulic retention time was adjusted to 50 days, the substrate TS was 9.7%, the substrate VTS was 8.3%, and the VTS ratio of straw, kitchen waste and sludge in the feed was changed from 1:1:1 to 3:2:1, which increased the proportion of straw, reduced the proportion of sludge, and increased the feed C / N ratio from 20 to 40. Continue to operate until stable.

[0084] The microbial flora of the reactor during the stable operation of the F3 stage was collected by taking the fermentation broth, centrifuging it at 4°C for 10 minutes, removing the supernatant, and the precipitated part was the flora.

[0085] Example 2

[0086] This example is used to illustrate the enrichment method of microbial flora.

[0087] 1. Reactor Construction

[0088] Preparation of inoculum source: In order to enrich the anaerobic fermentation acid-producing microbial community, the anaerobic digestion sludge of grain sugar factory, the anaerobic digestion sludge of restaurant waste, the mesophilic anaerobic digestion sludge of cellulose, the mesophilic anaerobic digestion sludge of glucose and the anaerobic fermentation acid-producing reactor sludge of fruit waste were mixed and used as the inoculum source; inocula from different sources were mixed in equal proportions according to the total solids (TS) concentration (TS and VTS of inocula from different sources are shown in Table 1).

[0089] Preparation of substrate: Steam-exploded straw, artificially prepared food waste (banana, orange, cabbage and rice were crushed and mixed with equal wet weight) and wastewater plant residual sludge were used as substrates. Different substrates were mixed in equal proportions according to the volatile total solids (VTS) concentration (TS and VTS of various substrates are shown in Table 1). The mixed substrates were stored at 4°C and diluted to the target solid content when used.

[0090] Prepare 1 mesophilic reactor (working volume 2.4 L).

[0091] 2. Reactor startup and operation

[0092] The present invention starts up a medium temperature reactor.

[0093] The whole operation process of the reactor is divided into F1, F2 and F3 stages. The organic load of straw is gradually increased in the three stages until it operates stably in the F3 stage. The operating conditions of the reactor in the three stages are shown in Table 2.

[0094] Days 0 to 105 are the F1 stage.

[0095] The startup and operation temperature of the mesophilic reactor is 37°C, the stirring speed is 100rpm, and the pH value is controlled at 5.5-6.0. According to TS, the inoculation source obtained by mixing inoculum sludge from various sources in equal proportions is crushed with a blender and filtered with 2-3 layers of gauze to ensure that the solid content of the reactor startup sludge is less than 5%. In order to inhibit the activity of methanogens, the startup sludge needs to be pretreated. The startup sludge is heat treated at 80°C for 1 hour, and a methane inhibitor 2-bromoethane sulfonic acid (2-bromoethanosulfophate, BES) is added at a final concentration of 5mM. The pretreated mixed inoculum is injected into the working volume of the reactor, and the reactor is closed after nitrogen is introduced to exhaust the air to reach an anaerobic state. After starting the reactor, no material was added or removed for two days. After that, a substrate containing straw, food waste and sludge (TS: 5.2%; VTS: 4.1%; C / N ratio: 20) was supplied under an organic loading condition of 0.5 g VTS / L / d. The VTS ratio of straw, food waste and sludge in the substrate was 1:1:1. The material was added and removed every two days. The hydraulic retention time of the reactor was 100 days. The physical and chemical parameters of the reactor were monitored every four days.

[0096] Days 105 to 189 are the F2 stage.

[0097] During this stage, the hydraulic retention time was maintained at 100 days, the feed solid content was adjusted to 10%, the substrate TS was 10.3%, the substrate VTS was 8.2%, the VTS ratio of straw, food waste and sludge in the substrate was 1:1:1; the substrate C / N ratio was 20; the organic load was increased to 1g VTS / L / d, and the operation was continued until stability.

[0098] Days 189 to 368 are the F3 stage.

[0099] In this stage, the feed solid content was maintained at 10%, the organic load was increased to 2g VTS / L / d, the hydraulic retention time was adjusted to 50 days, the substrate TS was 9.7%, the substrate VTS was 8.3%, and the VTS ratio of straw, kitchen waste and sludge in the feed was changed from 1:1:1 to 3:2:1, which increased the proportion of straw, reduced the proportion of sludge, and increased the feed C / N ratio from 20 to 40. Continue to operate until stable.

[0100] The microbial flora of the reactor during the stable operation of the F3 stage was collected. The specific collection method was as follows: the fermentation liquid was taken and centrifuged at 4°C for 10 minutes, the supernatant was removed, and the precipitated part was the flora.

[0101] Table 2 shows the operating conditions data of the reactor at different stages.

[0102] Table 2

[0103] F1 F2 F3 Substrate TS (%) 5.2 10.3 9.7 Substrate VTS (%) 4.1 8.2 8.3 VTS ratio of straw, kitchen waste and sludge in substrate 1:1:1 1:1:1 3:2:1 Substrate C / N ratio 20 20 40 Organic load (gVTS / L / d) 0.5 1 2 Residence time (d) 100 100 50

[0104] Example 3

[0105] This example is used to illustrate the method of obtaining an organic acid mixture and lignin using lignocellulose as raw material (see the specific process flow for details). Figure 1 ), comprising the following steps:

[0106] Step 1: crush and remove impurities from corn stalks, and soak the corn stalks with 2 wt % dilute sulfuric acid, the amount of dilute sulfuric acid used is 5 times that of the dry corn stalks, soak for 20 minutes at room temperature, and treat for 30 minutes at a pressure of 0.9 MPaG to obtain a pretreated material containing cellulose, xylose and lignin;

[0107] Step 2, enzymatic hydrolysis of the pretreated material containing cellulose, xylose and lignin, using a cellulase dosage of 0.18 g / g cellulose, an enzymatic hydrolysis dry matter concentration of 10 wt%, an enzymatic hydrolysis pH of 5, and an enzymatic hydrolysis time of 96 h to obtain a solid-liquid mixed enzymatic hydrolyzate containing pentose, hexose and lignin;

[0108] Step 3, subjecting the solid-liquid mixed enzymatic hydrolysate containing pentose, hexose and lignin to solid-liquid centrifugation separation to obtain an enzymatic hydrolysate containing pentose and hexose and a solid phase containing lignin;

[0109] Step 4: The enzymatic hydrolyzate containing pentose and hexose is subjected to acid fermentation, the bacterial flora used is the enriched bacterial flora in Example 2, the acid fermentation inoculation amount is 2%, the temperature is 37°C, pH=6, the nitrogen source is NH4Cl, and the C / N ratio is 40. The fermentation is carried out for 8 days to obtain 33.68 g / L of an organic acid mixture and a carbon conversion rate of 88%. Among them, 16.9 g / L of lactic acid, 5.43 g / L of acetic acid, 2.7 g / L of propionic acid, 8.34 g / L of isovaleric acid, and 0.31 g / L of other volatile fatty acids such as butyric acid, isobutyric acid, and valeric acid are obtained by high performance liquid chromatography analysis.

[0110] Step 5, extracting lignin from the solid phase containing lignin, the specific steps are as follows:

[0111] (1) Alkali dissolution: Sodium hydroxide is used to dissolve the lignin in the solid phase. The amount of sodium hydroxide used is 11% of the solid phase dry matter, and the mass of water added is 7 times the mass of the solid phase dry matter. The treatment time is 2 hours to obtain a lignin alkaline solution;

[0112] (2) solid-liquid separation: centrifuging the lignin alkaline solution to obtain a solution containing lignin;

[0113] (3) Acid precipitation: sulfuric acid is added to the lignin solution and treated at 80°C for 1 h to precipitate the lignin. The mass amount of sulfuric acid is 1.15 times the mass amount of sodium hydroxide. Then, wet lignin is obtained by centrifugation.

[0114] (4) Water washing: The wet lignin is washed with water, and the amount of water added is 8 times the dry weight of the wet lignin, and then centrifugal separation is performed to obtain the washed wet lignin;

[0115] (5) After air flow drying, lignin is obtained.

[0116] Example 4

[0117] This example is used to illustrate the method of obtaining an organic acid mixture and lignin using lignocellulose as raw material (see the specific process flow for details). Figure 1 ), comprising the following steps:

[0118] Step 1: crush and remove impurities from corn stalks, and soak the corn stalks with 2 wt% dilute sulfuric acid, the amount of dilute sulfuric acid used is 5 times that of the dry corn stalks, soak for 20 minutes at room temperature, and then treat for 30 minutes at a pressure of 0.9 MPaG to obtain a pretreated material containing cellulose, xylose and lignin;

[0119] Step 2, enzymatic hydrolysis of the pretreated material containing cellulose, xylose and lignin, using a cellulase dosage of 0.18 g / g cellulose, an enzymatic hydrolysis dry matter concentration of 10 wt%, an enzymatic hydrolysis pH of 5, and an enzymatic hydrolysis time of 96 h to obtain a solid-liquid mixed enzymatic hydrolyzate containing pentose, hexose and lignin;

[0120] Step 3, subjecting the solid-liquid mixed enzymatic hydrolysate containing pentose, hexose and lignin to solid-liquid centrifugation separation to obtain an enzymatic hydrolysate containing pentose and hexose and a solid phase containing lignin;

[0121] Step 4: The enzymatic hydrolyzate containing pentose and hexose is subjected to acid-producing fermentation, the bacterial flora used is the bacterial flora enriched in Example 1, the acid-producing fermentation inoculation amount is 2%, the temperature is 53°C, pH=5, the nitrogen source is NH4Cl, and the C / N ratio is 40. The fermentation is carried out for 14 days to obtain 21.72 g / L of an organic acid mixture and a carbon conversion rate of 46%. Among them, 13.18 g / L of lactic acid, 2.83 g / L of acetic acid, 2.69 g / L of propionic acid, 2.68 g / L of isovaleric acid, and 0.33 g / L of other volatile fatty acids such as butyric acid, isobutyric acid, and valeric acid are obtained by high performance liquid chromatography analysis.

[0122] Step 5, extracting lignin from the solid phase containing lignin, the specific steps are as follows:

[0123] (1) Alkali dissolution: Sodium hydroxide is used to dissolve the lignin in the solid phase. The amount of sodium hydroxide used is 11% of the solid phase dry matter, and the mass of water added is 7 times the mass of the solid phase dry matter. The treatment time is 2 hours to obtain a lignin alkaline solution;

[0124] (2) solid-liquid separation: centrifuging the lignin alkaline solution to obtain a solution containing lignin;

[0125] (3) Acid precipitation: sulfuric acid is added to the lignin solution and treated at 80°C for 1 h to precipitate the lignin. The mass amount of sulfuric acid is 1.15 times the mass amount of sodium hydroxide. Then, wet lignin is obtained by centrifugation.

[0126] (4) Water washing: The wet lignin is washed with water, and the amount of water added is 8 times the dry weight of the wet lignin, and then centrifugal separation is performed to obtain the washed wet lignin;

[0127] (5) After air flow drying, lignin is obtained.

Claims

1. A method for co-producing organic acid and lignin from lignocellulose, characterized in that: The method comprises the following steps: Step 1: pretreating the lignocellulosic raw material to obtain a pretreated material containing cellulose, xylose and lignin; Step 2: performing enzymatic hydrolysis on the pretreated material obtained in step 1 to obtain an enzymatic hydrolyzate containing pentose, hexose and lignin; Step 3, performing solid-liquid separation on the enzymatic hydrolyzate obtained in step 2 to obtain an enzymatic hydrolyzate containing pentose and hexose and a solid phase containing lignin; Step 4: subjecting the enzymatic hydrolysate containing pentose and hexose obtained in step 3 to acid-producing fermentation to obtain a fermentation liquid containing an organic acid mixture; Step 5: extracting lignin from the lignin-containing solid phase obtained in step 3 to obtain lignin.

2. The method for co-producing organic acids and lignin from lignocellulose according to claim 1, characterized in that: In the step 1, the lignocellulose raw material comes from one or more of corn straw, rice straw, wheat straw, reed, corn cob and bean straw.

3. The method for co-producing organic acid and lignin from lignocellulose according to claim 1, characterized in that: In the step 1, the method for pretreating the lignocellulose raw material is: after the lignocellulose raw material is crushed and impurities are removed, it is treated with acid, alkali or steam explosion to obtain a pretreated material.

4. The method for co-producing organic acid and lignin from lignocellulosic raw materials according to claim 1, characterized in that: In the step 2, the enzyme used for the enzymatic hydrolysis is cellulase.

5. The method for co-producing organic acid and lignin from lignocellulose according to claim 1, characterized in that: In step 4, the conditions of the acidogenic fermentation are: Batch fermentation, semi-continuous fermentation or continuous fermentation under anaerobic conditions; and / or, The pH of the acidogenic fermentation is 5 to 10; preferably, the pH is 5 to 7; The temperature of the acidogenic fermentation is 30-58°C; preferably 35-40°C; C / N ratio is 20 to 60; preferably 30 to 40; The fermentation time is 2 to 50 days, preferably 7 to 14 days.

6. The method for co-producing organic acid and lignin from lignocellulosic raw materials according to claim 5, characterized in that: The nitrogen source is one or a combination of NH4Cl, corn syrup, sludge, potassium nitrate and urea.

7. The method for co-producing organic acid and lignin from lignocellulose according to claim 1, characterized in that: In the step 4, the acid-producing fermentation adopts an acid-producing microbial flora, preferably an anaerobic fermentation acid-producing microbial flora.

8. The method for co-producing organic acid and lignin from lignocellulose according to claim 7, characterized in that: The anaerobic fermentation acid-producing microbial community is enriched by the following method, which includes the F1 stage to the F3 stage: F1 stage: The F1 phase runs for 80 to 120 days; The inoculum source is added to the reactor, and nitrogen is introduced to exhaust the air and then the reactor is closed; the solid content of the inoculum source is ≤5%; no material is fed or discharged for two days after the reactor is started, and then the substrate is supplied under the organic load condition of 0.4-0.6g VTS / L / d; the TS value of the substrate is 4.8-5.4%; the VTS value is 4.0-4.4%; the C / N ratio is 18-22; the substrate comprises a mixture of straw, food waste and a nitrogen source substrate; preferably, the VTS ratio of straw, food waste and nitrogen source substrate in the substrate is (0.8-1.2): (0.8-1.2): (0.8-1.2); the nitrogen source substrate is preferably residual sludge from a sewage treatment plant; the straw is preferably steam-exploded straw; the material is fed and discharged once every two days; the hydraulic retention time of the reactor is 90-110 days; F2 stage: The operation time of the F2 stage is 50 to 100 days; the feed solid content is adjusted to 8 to 12%, the organic load is increased to 0.8 to 1.2 g VTS / L / d, the substrate TS is 9.8 to 10.5%, the substrate VTS is 8.0 to 8.5%, and the substrate C / N ratio is 18 to 22; the VTS ratio of straw, kitchen waste and nitrogen source substrate in the substrate is preferably (0.8 to 1.2): (0.8 to 1.2): (0.8 to 1.2); the hydraulic retention time of the reactor is 90 to 110 days; F3 stage: The operation time of the F3 stage is 120 to 200 days; in this stage, the feed solid content is maintained at 8 to 12%, the organic load is increased to 1.8 to 2.2 g VTS / L / d, the hydraulic retention time of the reactor is adjusted to 45 to 55 days, and the VTS ratio of straw, kitchen waste and nitrogen source substrate in the substrate is preferably changed from (0.8 to 1.2): (0.8 to 1.2): (0.8 to 1.2) to (2.8 to 3.2): (1.8 to 2.2): (0.8 to 1.2), and the substrate C / N ratio is increased from 18 to 22 to 38 to 42; the substrate TS is 9.5 to 10%, and the substrate VTS is 8.0 to 8.6%; Collect the microbial flora in the F3 stage reactor.

9. The method for co-producing organic acid and lignin from lignocellulose according to claim 8, characterized in that: The inoculum source is pretreated, and the pretreatment method is: heat-treating the inoculum source at 75-85° C. for 0.5-1.2 hours, and adding a methane inhibitor with a final concentration of 4-6 mM; the methane inhibitor is preferably selected from 2-bromoethane sulfonic acid.

10. The method for co-producing organic acid and lignin from lignocellulose according to claim 8, characterized in that: The inoculum source comprises inocula from different sources; the inocula from different sources are selected from a mixture of anaerobic digestion sludge from grain sugar factories, anaerobic digestion sludge from restaurant waste, anaerobic digestion sludge from cellulose, anaerobic digestion sludge from glucose, and anaerobic fermentation acid production reactor sludge from fruit waste; Preferably, the cellulose anaerobic digestion sludge is selected from cellulose high-temperature anaerobic digestion sludge or cellulose medium-temperature anaerobic digestion sludge; and / or, Preferably, the glucose anaerobic digestion sludge is selected from glucose high-temperature anaerobic digestion sludge or glucose mesophilic anaerobic digestion sludge.

11. The method for co-producing organic acid and lignin from lignocellulose according to claim 10, characterized in that: The inoculation source comprises inocula from different sources mixed according to the total solid concentration, each type of sludge accounts for more than 10% of the total solid concentration, and more preferably is mixed in equal proportions according to the total solid concentration.

12. The method for co-producing organic acid and lignin from lignocellulose according to claim 10, characterized in that: The reactor is a high temperature reactor or a medium temperature reactor; Preferably, The pH value of the reactor is 5.5 to 6.0; and / or, The operating temperature of the high temperature reactor is 50-55°C; and / or, The working temperature of the medium temperature reactor is 35-40°C.

13. The method for co-producing organic acid and lignin from lignocellulose according to claim 12, characterized in that: When the reactor is a high-temperature reactor, the cellulose anaerobic digestion sludge is selected from cellulose high-temperature anaerobic digestion sludge, and the glucose anaerobic digestion sludge is selected from glucose high-temperature anaerobic digestion sludge; When the reactor is a mesophilic reactor, the cellulose anaerobic digestion sludge is selected from cellulose mesophilic anaerobic digestion sludge, and the glucose anaerobic digestion sludge is selected from glucose mesophilic anaerobic digestion sludge.

14. The method for co-producing organic acid and lignin from lignocellulose according to claim 1, characterized in that: The organic acid is a combination of lactic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, valeric acid and isovaleric acid.

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