Method for continuously synthesizing medium-chain fatty acid

Abstract

The invention provides a method for continuously synthesizing medium-chain fatty acid, and belongs to the technical field of biochemistry and resource recycling. The invention provides a method for continuously synthesizing medium-chain fatty acid, which comprises the following steps: mixing pretreated distillers' grains with a polyvinyl alcohol-sodium alginate composite matrix to obtain a fermentation matrix; adding the fermentation substrate into a fermentation system for pre-acidification; after pre-acidification is completed, adjusting feeding and discharging of the fermentation system every day, adjusting the retention time of the materials to be 9-15 days through the discharging amount, controlling the pH value of the top area of the fermentation system to be 4.0-5.5 and / or ORP to be-350-150 mV, and constructing an axial coupling system of a top hydrolytic acidification lactic acid production area and a bottom partition medium-chain fatty acid synthesis area of the fermentation system. According to the method, exogenous inoculums do not need to be added, and continuous synthesis of the medium-chain fatty acid can be achieved through partition regulation and control.

Description

Technical Field

[0001] The invention belongs to the technical field of biochemistry and resource recycling, and particularly relates to a method for continuously synthesizing medium-chain fatty acids. Background Art

[0002] With the surge in global demand for biomass waste resource utilization, distiller's grains, a major byproduct of the brewing industry, account for over 120 million tons of annual global production. Distiller's grains contain not only a rich source of crude fiber, crude starch, crude protein, organic acids, ethanol, amino acids, and polysaccharides, but also microorganisms such as lactic acid bacteria, acetic acid bacteria, and Bacillus. Ethanol content ranges from 299.64 to 11,667.45 mg / kg·DM (DM = dry matter), acetic acid content ranges from 1.80 to 7.11 g / kg·DM, and lactic acid content ranges from 25.41 to 92.90 g / kg·DM.

[0003] Wine lees are rich in carbon sources and nutrients. Traditional ways of utilizing wine lees are mainly as feed or fertilizer, and there are deficiencies in improving functional substances. With the development of science and technology, people have begun to explore new ways to utilize wine lees in order to maximize the utilization of resources. Based on carbon chain extension technology, short-chain carbon sources such as ethanol and lactic acid in wine lees can be converted into medium-chain fatty acids, which can be used as biofuels, antibacterial agents, spices, etc. Using wine lees as a carbon source for carbon chain extension can not only realize the resource utilization of wine lees, but also produce high value-added products. At present, the carbon chain extension process is dependent on inoculum, and most of them require exogenous addition of acetic acid-producing bacteria (such as Clostridium kluyverii ) and acid-producing bacteria, resulting in competition between lactic acid-producing bacteria and medium-chain fatty acid-producing bacteria, conflict in metabolic pathways, and loss of energy efficiency of the dual-bacteria system. Summary of the Invention

[0004] In view of the defects in the prior art, the purpose of the present invention is to provide a method for continuously synthesizing medium-chain fatty acids using vinasse, which does not require the addition of exogenous inoculum and can achieve continuous synthesis of medium-chain fatty acids through zoning regulation.

[0005] The purpose of the present invention is achieved through the following technical solutions: The present invention provides a method for continuously synthesizing medium-chain fatty acids, comprising the following steps: The pretreated vinasse is mixed with a polyvinyl alcohol-sodium alginate composite matrix to obtain a fermentation matrix; the pretreated vinasse has a solid content of 8% to 10%, a carbon-nitrogen ratio of (25-30):1, 90% of the particle diameter is ≤2 mm, and the pH value is 4.4-4.6; the mass ratio of the polyvinyl alcohol-sodium alginate composite matrix to the pretreated vinasse is 1:(10-20); Adding the fermentation substrate to the fermentation system for pre-acidification; the pre-acidification temperature is 37.5-38.5° C.; the dissolved oxygen in the pre-acidification is ≤0.5 ppm; and the pre-acidification pH is 4.0-5.0; After pre-acidification is completed, the daily feed and discharge of the fermentation system are adjusted, and the material residence time in the fermentation system is adjusted to 9-15 days by the discharge rate. The pH in the top area of ​​the fermentation system is controlled to 4.0-5.5 and / or the ORP is controlled to -350-150 mV, and an axial coupling system is established between the hydrolysis and acidification lactic acid production zone at the top of the fermentation system and the medium-chain fatty acid synthesis zone at the bottom. The top area of ​​the fermentation system is the upper 1 / 3 to 1 / 4 area of ​​the fermentation system; The discharge is the discharge from the bottom of the fermentation system; the feed is the feed from the top of the fermentation system; and the feed is the addition of the fermentation substrate to the fermentation system.

[0006] Preferably, the method for controlling the pH of the top region of the fermentation system to 4.0-5.5 and / or the ORP to -350-150 mV comprises: when the pH is <4.0 and the ORP is lower than -350 mV, the feeding and discharging frequency is adjusted to 48-72 h / time; when the pH is >5.5 and the ORP is higher than -150 mV, the feeding and discharging frequency is adjusted to 6-12 h / time.

[0007] Preferably, the pre-acidification time is 3 to 7 days.

[0008] Preferably, during the first 7 days of adjusting the daily feeding and discharging of the fermentation system, 30% to 50% of the daily discharge is refluxed to the lower 1 / 3 to 1 / 4 area of ​​the fermentation system before feeding.

[0009] Preferably, when feeding and discharging materials every day, the feeding amount is less than or equal to the discharging amount.

[0010] Preferably, the polyvinyl alcohol-sodium alginate composite matrix comprises polyvinyl alcohol-sodium alginate hydrogel.

[0011] Preferably, the material for adjusting the carbon-nitrogen ratio of the pretreated distiller's grains includes any one or more of corn straw, wheat straw, urea and pig manure; and the distiller's grains include any one or more of white wine distiller's grains, beer distiller's grains and aged distiller's grains.

[0012] Preferably, the method for separating the medium chain fatty acids in the effluent comprises heat treatment.

[0013] Preferably, the temperature of the heat treatment is 80-100° C., and the time of the heat treatment is 10 minutes.

[0014] Preferably, the medium-chain fatty acid includes any one or two or more of hexanoic acid, heptanoic acid and octanoic acid.

[0015] Beneficial effects of the present invention: The invention provides a method for continuous synthesis of medium-chain fatty acids, comprising the following steps: mixing pretreated vinasse with a polyvinyl alcohol-sodium alginate composite matrix to obtain a fermentation matrix; the pretreated vinasse has a solid content of 8% to 10%, a carbon-nitrogen ratio of (25-30):1, 90% of the particle diameters are ≤2 mm, and the pH value is 4.4-4.6; the mass ratio of the polyvinyl alcohol-sodium alginate composite matrix to the pretreated vinasse is 1:(10-20); adding the fermentation matrix to a fermentation system for pre-acidification; the pre-acidification temperature is 37.5-38.5°C; the dissolved oxygen in the pre-acidification is ≤0.5 ppm; the pre-acidification pH value is 4.0-5.0; after the pre-acidification is completed, adjusting the daily feed and discharge of the fermentation system, adjusting the material residence time in the fermentation system to 9-15 days according to the discharge rate; and controlling the pH of a top region of the fermentation system to 4.0-5.5 and / or the ORP to -350--150. mV, construct an axial coupling system of the hydrolysis and acidification lactic acid production zone at the top of the fermentation system and the medium-chain fatty acid synthesis zone at the bottom; the top area of ​​the fermentation system is the 1 / 3~1 / 4 area above the fermentation system; the discharge is the discharge from the bottom of the fermentation system; the feed is the feed from the top of the fermentation system; the feed is the addition of the fermentation matrix to the fermentation system. The method provided by the present invention establishes a system without exogenous inoculum, and the lees itself carries a rich microbial flora, including lactic acid bacteria, acetic acid-producing bacteria, butyrate-producing bacteria, etc. By regulating the conditions in the fermentation system, the dominant flora in the endogenous microbial community of the lees is regulated, and the organic matter in the lees is converted into medium-chain fatty acids. The method introduces a polyvinyl alcohol-sodium alginate composite matrix into the extraction system of medium-chain fatty acids to construct a "carrier-catalyst" dual-modal synergistic mechanism. The polyvinyl alcohol-sodium alginate composite matrix has both microbial immobilization and selective adsorption-catalytic effects. In the process of carbon chain extension, the polyvinyl alcohol-sodium alginate composite matrix can be used to immobilize acid-producing functional bacteria (such as Clostridium kluyverii) are fixed in the three-dimensional network structure, which increases the density of the bacterial population and enhances the stability of the biofilm, thereby promoting the production of medium-chain fatty acids; the polyvinyl alcohol-sodium alginate composite matrix adsorbs the target product in real time in the carbon chain extension zone, and the medium-chain fatty acids can be obtained by treating the polyvinyl alcohol-sodium alginate composite matrix and the fermentation product complex in the output of the system. In the continuous separation and purification process of medium-chain fatty acids, making full use of the polyvinyl alcohol-sodium alginate composite matrix can reduce the subsequent purification steps and reduce the separation energy consumption. The method utilizes a vertical axial partitioned fermentation tank partitioned controlled release system. First, the pH of anaerobic fermentation of distiller's grains is regulated to achieve continuous hydrolysis and acidification of the distiller's grains to produce short-chain fatty acids in the top 1 / 4 to 1 / 3 of the fermentation tank. Second, the porosity and material transfer efficiency are optimized by regulating the feeding and discharging frequency to ensure that the short-chain fatty acids form a stable mass transfer gradient and permeate downward, thereby making the middle 1 / 4 to 1 / 3 a transition zone. The fermentation system in the bottom 1 / 4 to 1 / 3 of the fermentation tank maintains its pH at 5.5 to 6.0 due to acetic acid / lactic acid metabolic buffering, which is conducive to the synthesis of medium-chain fatty acids. This forms a carbon chain extension synthesis zone for medium-chain fatty acids, and more efficiently produces medium-chain fatty acids under the catalytic action of a polyvinyl alcohol-sodium alginate composite matrix. In the present invention, after the polyvinyl alcohol-sodium alginate composite matrix carrier completes the adsorption of medium-chain fatty acids, it is heat-treated to weaken the physical binding force between the hydrophobic modification layer and the product, releasing the adsorbed target products such as octanoic acid and hexanoic acid, while maintaining the mechanical strength of the hydrogel (swelling rate <10%) and adsorption capacity (maintaining more than 90% of the initial value after 10 cycles). The regenerated polyvinyl alcohol-sodium alginate composite matrix is ​​further returned to the fermentation tank, achieving in-situ recycling of the carrier material, reducing the amount of hydrogel added per batch by 50% (i.e., the regenerated polyvinyl alcohol-sodium alginate hydrogel is returned to the fermentation tank. After adopting this recycling method, the amount of fresh polyvinyl alcohol-sodium alginate hydrogel required is 50% of the hydrogel used in the first addition, and the recycled polyvinyl alcohol-sodium alginate hydrogel accounts for 50%), significantly reducing operating costs. In addition, through the closed-loop design of the hydrogel "adsorption-regeneration-re-adsorption", this method minimizes material consumption and waste emissions, conforming to the concept of a circular economy and achieving sustainable resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 The process flow chart of the method for continuous synthesis of medium-chain fatty acids; Figure 2Schematic diagram of the apparatus for the continuous synthesis of medium-chain fatty acids. DETAILED DESCRIPTION

[0018] The present invention provides a method for continuously synthesizing medium-chain fatty acids, comprising the following steps: The pretreated vinasse is mixed with a polyvinyl alcohol-sodium alginate composite matrix to obtain a fermentation matrix; the pretreated vinasse has a solid content of 8% to 10%, a carbon-nitrogen ratio of (25-30):1, 90% of the particle diameter is ≤2 mm, and the pH value is 4.4-4.6; the mass ratio of the polyvinyl alcohol-sodium alginate composite matrix to the pretreated vinasse is 1:(10-20); Adding the fermentation substrate to the fermentation system for pre-acidification; the pre-acidification temperature is 37.5-38.5° C.; the dissolved oxygen in the pre-acidification is ≤0.5 ppm; and the pre-acidification pH is 4.0-5.0; After pre-acidification is completed, the fermentation system's daily feed and discharge are adjusted, and the material residence time is adjusted to 9-15 days based on the discharge rate. The pH in the top region of the fermentation system is controlled to 4.0-5.5 and / or the ORP is -350--150 mV, establishing an axial coupling system between the top hydrolysis and acidification lactic acid production zone and the bottom subzone medium-chain fatty acid synthesis zone in the fermentation system. The top area of ​​the fermentation system is the upper 1 / 3 to 1 / 4 area of ​​the fermentation system; The discharge is the discharge from the bottom of the fermentation system; the feed is the feed from the top of the fermentation system; and the feed is the addition of the fermentation substrate to the fermentation system.

[0019] The present invention mixes pretreated distiller's grains with a polyvinyl alcohol-sodium alginate composite matrix to obtain a fermentation matrix. In the present invention, the pretreated distiller's grains processing method includes: adjusting the carbon-nitrogen ratio and solids content of the distiller's grains to obtain a fermentation feedstock; pulverizing the fermentation feedstock and controlling the pH to 4.4-4.6. As an optional embodiment of the present invention, the carbon-nitrogen ratio can be adjusted to (25-30):1, or 25:1, 26:1, 27:1, 28:1, 29:1, or 30:1. In the present invention, the raw material for adjusting the carbon-nitrogen ratio of the distiller's grains can be any one or more of corn straw, wheat straw, urea, and pig manure; the corn straw can be corn silage. The solids content can be adjusted to 8%-10% (w / w), or 8%, 9%, or 10% (w / w). After adjusting the solids content, the present invention obtains the fermentation feedstock. After obtaining the fermentation feedstock, the present invention pulverizes the fermentation feedstock. The present invention does not specifically limit the pulverization method; conventional pulverization methods in the art can be used. As an optional embodiment of the present invention, the crushed particle size can be ≤2 mm, 90% of the particles can be ≤2 mm, or 1.2 mm. After the crushing is completed, the present invention preferably adjusts the system pH to 4.4-4.6, and can also be 4.4, 4.5, or 4.6. After adjusting the system pH, the present invention obtains pretreated vinasse.

[0020] After obtaining the pretreated vinasse, the present invention mixes the pretreated vinasse with a polyvinyl alcohol-sodium alginate composite matrix to produce a fermentation matrix. As an optional embodiment of the present invention, the polyvinyl alcohol-sodium alginate composite matrix comprises a polyvinyl alcohol-sodium alginate hydrogel. The mass ratio of the polyvinyl alcohol-sodium alginate composite matrix to the pretreated vinasse can be 1:(10-20), or 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, or 1:20. The present invention does not specifically limit the mixing method; conventional mixing methods in the art can be used.

[0021] After obtaining the fermentation substrate, the present invention adds the fermentation substrate to the fermentation system for pre-acidification. As an optional embodiment of the present invention, the pre-acidification temperature can be 37.5-38.5°C, or 38°C; the dissolved oxygen in the pre-acidification is ≤0.5ppm; the pre-acidification pH is 4.0-5.0, or 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5.0; and the pre-acidification time can be 3-7 days, or 3, 4, 5, 6, or 7 days.

[0022] During the pre-acidification process, acid-producing bacteria such as lactic acid bacteria and acetic acid bacteria in the raw distiller's grains primarily undergo hydrolysis and acidification reactions, converting complex organic matter into products primarily consisting of short-chain fatty acids and alcohols, such as lactic acid, ethanol, acetic acid, propionic acid, and butyric acid. The low pH inhibits methanogenesis and carbon chain extension reactions, ensuring the accumulation of acids and alcohols. In the subsequent carbon chain extension reaction, acetic acid acts as an electron acceptor, while ethanol and lactic acid act as electron donors.

[0023] After pre-acidification is completed, the present invention adjusts the fermentation system to have daily feed and discharge, adjusting the material residence time in the fermentation system to 9 to 15 days based on the discharge rate. The pH in the top region of the fermentation system is controlled to 4.0 to 5.5 and / or the ORP to -350 to -150 mV, establishing an axially coupled system between the top hydrolysis and acidification lactic acid production zone and the bottom subzone medium-chain fatty acid synthesis zone in the fermentation system; the top region of the fermentation system refers to the upper 1 / 3 to 1 / 4 of the fermentation system. In the present invention, discharge refers to discharge from the bottom of the fermentation system; feed refers to feed from the top of the fermentation system; and feed refers to the addition of the fermentation substrate to the fermentation system.

[0024] As an optional embodiment of the present invention, when loading and unloading materials every day, it is preferred to discharge the materials first and then feed the materials. As an optional embodiment of the present invention, the daily feed amount is less than or equal to the discharge amount. The present invention adjusts the material residence time to 9 to 15 days by the discharge amount, and can also be 9, 10, 11, 12, 13, 14 or 15 days. In the present invention, the material residence time refers to the residence time of the same batch of materials in the fermentation system calculated from the start of loading and unloading. For example, when the feed amount is the total volume of the fermentation system, the material residence time in the fermentor = fermentor volume / daily discharge amount; or it can be the material residence time in the fermentor = fermentation system volume / daily discharge amount.

[0025] According to the present invention, during the first 7 days of continuous feeding and discharging, the discharge is refluxed to the lower 1 / 3 to 1 / 4 area of ​​the fermentation system after discharging every day; the refluxed discharge amount can be 30% to 50% of the total discharge amount, or can be 40% for reflux; the reflux is to directly reflux 30% to 50% of the discharge from the feed inlet to the lower 1 / 3 to 1 / 4 area of ​​the fermentation system through a peristaltic pump.

[0026] The first discharge of the present invention is an intermediate fermentation broth that has completed 3-7 days of pre-acidification but has not undergone carbon chain extension. For the first seven days of this initial continuous feed-in / feed-out mode, the discharge liquid is refluxed to allow the system to reach a stable state. During these first seven days, 30%-50% of the discharge liquid is refluxed daily to the medium-chain fatty acid synthesis zone at the bottom of the fermentation system, while new fermentation substrate is continuously added from the top until the fermentation system is full. During this reflux period, the system's net discharge decreases until reflux ceases on the eighth day and full discharge mode is entered. During this reflux period, the feed still needs to be fed with fermentation substrate in a prescribed manner until the fermentation system is full. Specifically, a fermentation substrate prepared by mixing pretreated vinasse and a polyvinyl alcohol-sodium alginate composite substrate is added to the top of the fermentation system. This is because the refluxed discharge liquid primarily regulates the internal ecological environment of the system, while the addition of fermentation substrate to the feed continuously provides raw materials for the fermentation process, maintaining the fermentation reaction. These two functions complement each other to ensure the stable operation of the fermentation system and product production.

[0027] This invention constructs an axially coupled system consisting of a top hydrolysis and acidification lactic acid production zone and a bottom sub-zone medium-chain fatty acid synthesis zone, using daily feed and discharge, based on the daily leachate collection volume and material porosity. In this invention, the daily leachate collection volume (unit: L / (L·d)) refers to the volume of liquid leachate produced and collected per unit volume of the fermentation system within 24 hours. The porosity of the material reflects the ratio of the void volume within the entire mixed material (including solid components such as pretreated lees, PVA-SA hydrogel, and microbial metabolites) to the total volume of the fermentation system, and is a key parameter reflecting the material porosity and liquid flow space within the entire fermentation device. As an optional embodiment of the present invention, the daily leachate collection volume can be 0.08 L / (L·d); the material porosity is the porosity of the collected material, which is 30% to 40%. The material porosity described in this invention can be obtained by configuring the relevant parameters of the fermentation system described in the above technical solution. The porosity of the material in the fermentation system is stable at 30%~40%, which not only ensures that the hydrolysis products are transferred from top to bottom, but also provides a continuous and stable substrate supply for the carbon chain extension bacteria at the bottom, ultimately realizing the synergistic function of "hydrolysis and acidification at the top to produce lactic acid, and carbon chain extension at the bottom to produce medium-chain fatty acids", and completing the construction of the axial coupling system.

[0028] After the feeding and unloading are completed every day, the present invention preferably monitors the pH and ORP of the top area of ​​the fermentation system in real time, so that the pH of the top area of ​​the fermentation system is maintained at 4.0~5.5 and / or the ORP is -150~-350 mV, and constructs an axial coupling system of the top hydrolysis and acidification lactic acid production zone and the bottom partition medium-chain fatty acid synthesis zone in the fermentation system. The present invention preferably starts with changing the feeding method and monitors the pH and ORP of the top area of ​​the fermentation tank in real time every day. The top area of ​​the fermentation tank is the top 1 / 3~1 / 4 area of ​​the fermentation tank. The present invention monitors the pH and ORP of the top area of ​​the fermentation system in real time. If the pH deviates from 4.0~5.5 and the ORP deviates from -350~-150 mV, the feeding and unloading frequency of the fermentation system in the fermentation system is regulated, and the pH and ORP of the top area are regulated.

[0029] As an optional embodiment of the present invention, the method of controlling the pH of the top area of ​​the fermentation system to 4.0~5.5 and the ORP to -350~-150 mV includes: when the pH is <4.0 and the ORP is lower than -350 mV, the feeding and discharging frequency is adjusted to 48~72 h / time, which can be 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71 or 72 h / time; when the pH is >5.5 and the ORP is higher than -150 mV, the feeding and discharging frequency is adjusted to 6~12 h / time, which can be 6, 7, 8, 9, 10, 11 or 12 h / time.

[0030] Starting with daily feed and discharge, the present invention regulates the pH and ORP of the top region of the fermentation system, causing the top region of the fermentation system to primarily undergo a pre-acidification phase. The primary microorganisms in this pre-acidification phase are acid-producing bacteria (e.g., lactic acid bacteria and acetic acid bacteria), whose metabolites primarily consist of organic acids such as lactic acid and acetic acid, resulting in a decrease in pH. If the pH in the top region of the fermentation system is <4.0 and the ORP is below -350 mV, extending the material residence time allows methanogens (e.g., Methanobacterium) more time to convert organic acids (e.g., acetic acid) into methane (CH4) and carbon dioxide (CO2). This process consumes organic acids, thereby raising the pH. In the present invention, a high pH, ​​i.e., pH >5.5, is caused by excessive consumption of organic acids or accumulation of ammonia nitrogen. If the pH in the top region of the fermentation system is >5.5 and the ORP is above -150 mV, shortening the residence time reduces organic acid degradation by methanogens. Furthermore, frequent feed introduction introduces new fermentable substrates, stimulating the metabolism of acid-producing bacteria (e.g., butyric acid bacteria and propionic acid bacteria), leading to the reaccumulation of organic acids (e.g., butyric acid and propionic acid), resulting in a decrease in pH. Oxidation-reduction potential (ORP) is a key parameter that characterizes the redox state of the system. The higher its value, the more oxidizing the environment. Methanogens, as strict anaerobic microorganisms, rely on a low ORP environment to maintain their metabolic activity. Control strategies for abnormal ORP: When ORP is higher than -150 mV, it indicates that the anaerobic environment may be damaged, usually caused by oxygen input. At this time, the feeding and discharging intervals should be extended or the feeding should be suspended. The main purpose is to reduce the oxygen that may be introduced from the new material. During the stagnant stage, the facultative anaerobic bacteria in the system can quickly consume the residual oxygen and consume electron acceptors (such as O2, NO3 - ), while also generating reducing substances (such as H2 and reduced ferredoxin), effectively lowering the ORP. However, when the ORP falls below –350 mV, it indicates that the system is too reducing, often accompanied by excessive proliferation of methanogens. In this case, the feed and discharge intervals should be shortened to accelerate the feed turnover rate, thereby removing over-reduced metabolites and enriched methanogens from the system. The addition of fresh feed can introduce trace oxidizing components or alter the substrate composition, thereby gently increasing the ORP value within a controllable range.

[0031] After the feeding and unloading are completed, the pH and ORP of the top area of ​​the fermentation tank are regulated to regulate the metabolism of acid-producing bacteria (such as lactic acid bacteria and acetic acid bacteria), producing organic acids such as lactic acid and acetic acid, while inhibiting the activity of methanogens and carbon chain extension bacteria. Due to the buffering of acetic acid / lactic acid metabolism, the original remaining fermentation system gradually maintains the pH at 5.5-6.0. Carbon chain extension bacteria, as the dominant bacteria in the fermentation system, carry out carbon chain extension reaction. Clostridium kluyverii ) and other carbon chain extension microorganisms to elongate the carbon chain, synthesizing medium-chain fatty acids such as caproic acid and octanoic acid using ethanol and lactic acid as electron donors.

[0032] The method utilizes a vertical axial partitioned fermenter partitioned control system, first, by regulating the pH of the upper 1 / 3~1 / 4 of the fermentation system to 4.0~5.5 and the ORP to -350~-150 mV, to realize the continuous production of short-chain fatty acids in the top 1 / 4~1 / 3 of the fermenter, forming a lactic acid-rich zone.

[0033] Secondly, by regulating the feeding and discharging frequency to optimize the porosity and material transfer efficiency, the stable mass transfer gradient of short-chain fatty acids is ensured to penetrate downward, and then the middle 1 / 4~1 / 3 of the fermentation system serves as a phase transition zone.

[0034] The bottom 1 / 4~1 / 3 of the fermentation system maintains a pH of 5.5~6.0 due to the acetic acid and / or lactic acid metabolic buffer system and microbial metabolic feedback mechanism, which is beneficial to the synthesis of medium-chain fatty acids, forming a carbon chain extension medium-chain fatty acid synthesis region, and more efficient production of medium-chain fatty acids under the catalysis of polyvinyl alcohol-sodium alginate composite matrix, forming a carbon chain extension zone.

[0035] In the phase transition zone and the carbon chain extension zone, no real-time monitoring and adjustment of pH and ORP is performed. In the carbon chain extension zone, as the reaction proceeds, metabolic changes occur in organic acids such as acetic acid and lactic acid. On the one hand, acetic acid and lactic acid will participate in subsequent reactions as substrates, for example, in carbon chain extension reactions, they are consumed as electron donors, reducing the concentration of acidic substances in the system. On the other hand, the metabolism of these organic acids by microorganisms may produce some basic byproducts or change the ratio of acidic and basic substances in the system, thereby increasing the pH. The carbon chain extension zone has strong buffering capacity based on the acetic acid and / or lactic acid metabolic buffer system, and through the balance adjustment mechanism of its own weak acid and its conjugate base, under the synergistic action of microbial metabolic feedback, it resists pH changes, thereby maintaining the pH at 5.5~6.0. Under this condition, acid-producing bacteria such as Clostridium kluyveri (Clostridium kluyveri) can be directed to enrich. Clostridium kluyverii The acid-producing bacteria convert C2~C4 precursors to C6~C10 medium-chain fatty acids through the reverse beta-oxidation pathway.

[0036] In the present invention, when short-chain fatty acids penetrate downward from the phase transition zone to the lower region of the fermenter (i.e. the bottom 1 / 4~1 / 3 of the fermenter), they will synthesize medium-chain fatty acids such as caproic acid and caprylic acid in the lower region, i.e. the carbon chain extension zone.

[0037] In the present invention, the carbon chain extension reaction is mainly carried out by Clostridium (Clostridium) and Megasphaera (Megasphaera). Clostridium Megasphere ​) is driven by the reverse β-oxidation pathway, extending short-chain fatty acids to C6-C12 and converting them into medium-chain fatty acids. For example, using ethanol or lactic acid as electron donors, short-chain fatty acids are first oxidized to form acetyl-CoA, which then enters the RBO cycle. After undergoing four steps of condensation, dehydrogenation, dehydration, and reduction, two carbon atoms are added each cycle. For example, two molecules of acetyl-CoA condense to form acetoacetyl-CoA, which then reacts in sequence to form butyryl-CoA. Butyryl-CoA continues to combine with acetyl-CoA in a cyclic reaction to form hexanoyl-CoA, ultimately releasing medium-chain fatty acids such as hexanoic acid and octanoic acid. Furthermore, during lees fermentation, PVA-SA hydrogels adsorb acid-producing bacteria to form a biofilm structure, accelerating substrate transfer and providing precursors for carbon chain extension.

[0038] The present invention discharges materials every day, separates the fermentation products in the axial coupling system, and obtains medium-chain fatty acids. As an optional embodiment of the present invention, the method for separating medium-chain fatty acids in the discharge includes heat treatment; the temperature of the heat treatment can be 80~100°C, or 80, 90 or 100°C; the time of the heat treatment is 10 minutes. After the medium-chain fatty acids are separated and obtained by the present invention, the polyvinyl alcohol-sodium alginate composite matrix can also be recovered. The polyvinyl alcohol-sodium alginate composite matrix can continue to be mixed with pretreated wine lees as a hydrogel for the synthesis of medium-chain fatty acids. In the present invention, in order to better make the fermentation system more efficient, the recycled polyvinyl alcohol-sodium alginate composite matrix can be used to replace 50% of the polyvinyl alcohol-sodium alginate composite matrix when the fermentation matrix is ​​configured for recycling.

[0039] In the carbon chain extension fermentation process, the separation and purification of the product is a key link. Traditional separation and purification methods usually require the fermentation broth to be taken out of the fermentation tank and go through a series of complex separation and purification steps to achieve the purpose of separating and purifying the fermentation product. It has the characteristics of complex operation and low separation and purification efficiency. The method described in the present invention is through the introduction of a polyvinyl alcohol-sodium alginate composite matrix, for example, polyvinyl alcohol-sodium alginate hydrogel. The polyvinyl alcohol-sodium alginate hydrogel is a polymer material with a three-dimensional network structure, which has a high specific surface area, adjustable pore size and chemical modification flexibility. Polyvinyl alcohol-sodium alginate hydrogel can not only fix functional bacteria through physical adsorption or chemical cross-linking to improve the operating stability of the reactor, but also selectively enrich medium-chain fatty acids through hydrogen bonds, hydrophobic interactions, etc. The application of polyvinyl alcohol-sodium alginate hydrogel in the lees carbon chain extension system can achieve the purpose of in situ purification, improve the efficiency of the fermentation process and the purity of the product. The present invention further returns the regenerated polyvinyl alcohol-sodium alginate composite matrix to the fermentation tank, thereby realizing in-situ recycling of the carrier material. The dosage of each batch of fresh polyvinyl alcohol-sodium alginate hydrogel can be reduced by 50%, which can significantly reduce the operating cost.

[0040] In order to further illustrate the present invention, the technical solution provided by the present invention is described in detail below with reference to the accompanying drawings and embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0041] Polyvinyl alcohol-sodium alginate hydrogel was purchased from Delta Biotechnology.

[0042] The material residence time refers to the time from the start of feeding and discharging of the pretreated vinasse and PVA-SA hydrogel mixed system or from the time when it enters the fermentation system to the time when it leaves the fermentation system. Specifically, when calculating the material residence time, the pre-acidification time is not included.

[0043] The process flow chart of the method for continuous synthesis of medium-chain fatty acids is as follows: Figure 1 As shown, the schematic diagram of the device for the method of continuous synthesis of medium-chain fatty acids is as shown Figure 2 The technical solution of the present invention is described in detail below with reference to the embodiments.

[0044] Example 1 A method for continuous synthesis of medium-chain fatty acids, comprising the following steps: Step 1: Raw Material Pretreatment: Take baijiu lees and mix them with crushed corn silage. Adjust the C / N ratio of the mixture to 25:1 and the solids content to 10% (w / w) to obtain the fermentation feedstock. Grind the fermentation feedstock twice to a particle size D90 ≤ 2 mm, meaning 90% of the particles have a diameter ≤ 2 mm. Adjust the pH to 4.5 ± 0.1 to obtain the pretreated lees.

[0045] Polyvinyl alcohol-sodium alginate hydrogel (PVA-SA hydrogel) and pretreated lees were mixed in a mass ratio of 1:15 and added to the fermenter. The fermenter was started, with the initial feed volume equal to the fermenter's effective volume (2 L). Pre-acidification was performed within the fermenter for 5 days. No feed or discharge was performed during the pre-acidification process. The fermenter was maintained at 38°C ± 0.5°C, with dissolved oxygen ≤ 0.5 ppm and a pH of 4.0. After 5 days of pre-acidification, the feed system was changed to daily addition and removal.

[0046] During the pre-acidification process, acid-producing bacteria, such as lactic acid bacteria and acetic acid bacteria, in the raw distiller's grains primarily undergo hydrolysis and acidification reactions, converting complex organic matter into products primarily consisting of short-chain fatty acids and alcohols, such as lactic acid, ethanol, acetic acid, propionic acid, and butyric acid. The low pH inhibits methanogenesis and carbon chain extension reactions, ensuring the accumulation of acids and alcohols. In the subsequent carbon chain extension reaction, acetic acid acts as an electron acceptor, while ethanol and lactic acid act as electron donors, providing raw materials for carbon chain extension.

[0047] Step 2: After pre-acidification is completed, change the feeding method to daily feeding and discharging.

[0048] The specific method is: the frequency of feeding and discharging is 24h / time, specifically: First, discharge the material, and control the material residence time to 12 days by adjusting the daily discharge volume to 167 mL, so that the material residence time of the 2L mixed system in the fermenter is 12 days. The mixed system in the fermenter is not stirred during the fermentation process.

[0049] Based on the daily leachate collection volume and material porosity, the daily leachate collection volume was controlled at 0.08 L / (L·d) during the daily inlet and outlet processes, and the porosity of the collected material was 30%-40%. An axially coupled system was constructed, connecting the top hydrolysis and acidification lactic acid production zone and the bottom partitioned medium-chain fatty acid synthesis zone.

[0050] During the first 7 days of continuous feed-in / feed mode, the discharge liquid needs to be directly refluxed to the lower 1 / 3 area of ​​the fermentation system via a peristaltic pump every day. The daily reflux discharge volume should be 50% of the total discharge volume for that day. After the first 7 days of continuous feed-in / feed mode, feed should be added again. The total volume fed to the fermentation system is 2L.

[0051] Starting from the 8th day of the first continuous feeding and discharging mode, there is no need to reflux the discharge liquid. Thereafter, the feeding is stopped until the feeding amount is equal to the discharging amount.

[0052] Starting with the change in feed method, monitor the pH and ORP of the top area of ​​the fermenter daily in real time. The top area of ​​the fermenter is the top 1 / 3 of the fermenter. Monitor the pH and ORP of the top area of ​​the fermenter to maintain the pH value in the range of 4.0-5.5 and / or the ORP in the range of -350-150 mV in the top area of ​​the fermenter. Perform the pre-acidification treatment phase. If the pH deviates from 4.0-5.5 and the ORP exceeds -350-150 mV, adjust the feeding and discharging frequency.

[0053] The control strategies are as follows: When pH < 4.0 and ORP is lower than -350 mV, the feeding and discharging frequency is adjusted to 48~72 h / time.

[0054] When pH>5.5 and ORP is higher than -150 mV: the feeding and discharging frequency is increased to 6~12 h / time.

[0055] After the feeding and discharging are completed, the metabolism of acid-producing bacteria (such as lactic acid bacteria and acetic acid bacteria) is regulated by adjusting the pH and ORP in the top area of ​​the fermentation tank to produce organic acids such as lactic acid and acetic acid, while inhibiting the activity of methanogens.

[0056] The original remaining fermentation system maintains pH at 5.5-6.0 due to acetic acid / lactic acid metabolism buffering, and the carbon chain extension reaction proceeds. Clostridium kluyverii) and other carbon chain extension microorganisms to elongate the carbon chain, synthesizing medium-chain fatty acids such as caproic acid and octanoic acid using ethanol and lactic acid as electron donors.

[0057] As the material is fed in and out, the top of the fermenter (the top 1 / 3 area of ​​the fermenter) is regulated by pH and ORP, and mainly undergoes hydrolysis and acidification to produce acetic acid, lactic acid and other materials. This area is called the lactic acid enrichment area.

[0058] In the middle of the fermenter (the area one-third below the top of the fermenter), pH and ORP are not regulated. Instead, the porosity and material transfer efficiency are optimized by adjusting the feeding and discharging frequencies, allowing short-chain fatty acids to form a stable mass transfer gradient and diffuse downward. This area is called the phase transition zone.

[0059] The pH and ORP are not regulated in the lower part of the fermenter (the lower 1 / 3 of the fermenter). The fermentation system can maintain the pH at 5.5-6.0 by itself due to the acetic acid / lactic acid metabolic buffer system and the microbial metabolic feedback mechanism. Clostridium kluyverii ) etc. The acid-producing bacteria convert C2~C4 precursors into C6~C10 medium-chain fatty acids through the reverse β-oxidation pathway. This section of the fermentation tank is called the carbon chain extension zone.

[0060] In the actual fermentation process, there is no strict dividing line between the lactic acid enrichment zone, phase transition zone and carbon chain extension zone.

[0061] Step 3: Purification of the effluent and continuous product recovery. The fermentation broth (effluent) is heat-treated at 80-100°C for 10 minutes to achieve controlled release and high-purity recovery of the adsorbed products (medium-chain fatty acids), while simultaneously completing in-situ regeneration of the hydrogel carrier.

[0062] The material was processed as follows: centrifuged at 4°C and 8000 rpm for 10 minutes, the supernatant was filtered through a 0.22 μm filter to remove microorganisms and suspended impurities, and the test solution was obtained. The test solution was then heat-treated at 80-100°C for 10 minutes. This heat treatment separated the PVA-SA hydrogel from the aqueous solution, and the acid production in the aqueous solution was analyzed by GC-MS. The resulting hydrogel can be recycled, replacing 50% of fresh hydrogel.

[0063] The day when the feeding and unloading began was counted as Day 0, and 24 hours after the feeding and unloading began was counted as Day 1. The acid production was measured. After the feeding and unloading was completed every day, the concentrations of short-chain fatty acids and medium-chain fatty acids in the output were measured, and the daily production of short-chain fatty acids and medium-chain fatty acids was calculated.

[0064] The daily acid production rate was calculated from the first day of feeding and unloading, and the results are shown in Table 1.

[0065] Table 1 Acid production in Example 1 from 1 to 12 days from the start of continuous feeding and discharging

[0066] Note: The unit is mg / L.

[0067] As shown in Table 1, the acid production of medium-chain fatty acids (the sum of hexanoic acid, heptanoic acid and octanoic acid) on the second day was 3.93 g / L, and the hexanoic acid production was 3.93 g / L. On the third day, the acid production of medium-chain fatty acids was 7.21 g / L, and the hexanoic acid production was 5.53 g / L. On the fourth day, the acid production of medium-chain fatty acids was 6.64 g / L, and the hexanoic acid production was 5.19 g / L. On the fifth day, the acid production of medium-chain fatty acids was 2.65 g / L, and the hexanoic acid production was 2.58 g / L. On the sixth day, the acid production of medium-chain fatty acids was 2.74 g / L, and the hexanoic acid production was 2.66 g / L. On the seventh day, the acid production of medium-chain fatty acids was 1.09 g / L, and the hexanoic acid production was 2.10 g / L. On the 1st day, the acid production of medium-chain fatty acids was 3.15g / L, and the production of caproic acid was 3.06g / L. On the 8th day, the acid production of medium-chain fatty acids was 6.09g / L, and the production of caproic acid was 4.55g / L. On the 9th day, the acid production of medium-chain fatty acids was 6.51g / L. On the 10th day, the acid production of medium-chain fatty acids was 6.2g / L, and the production of caproic acid was 5.74g / L. On the 11th day, the acid production of medium-chain fatty acids was 7.67g / L, and the production of caproic acid was 7.01g / L. On the 12th day, the acid production of medium-chain fatty acids was 7.91g / L, and the production of caproic acid was 6.92g / L. Among them, on the 11th day, the acid production of medium-chain fatty acids was 7.67g / L, and the production of caproic acid was 7.01g / L.

[0068] After 72 hours (3 days) of continuous feeding and discharging, the medium-chain fatty acid adsorption capacity of polyvinyl alcohol-sodium alginate hydrogel remained at 92.4% (initial value 0.42 g / g) after 5 regeneration cycles.

[0069] The initial value was calculated through adsorption experiments: To eliminate complex interferences from the fermentation process, a simulated volume V (100 mL) of real fermentation broth with a concentration of C0 was prepared. Unused PVA-SA hydrogel, weighing 1 g, was placed in the simulated broth and allowed to stand until adsorption equilibrium (i.e., the hydrogel no longer adsorbed MCFAs). After the reaction, the mixture was centrifuged and filtered, and the supernatant was analyzed by GC-MS to determine the fatty acid concentration C1. The initial adsorption capacity Q0 (g / g) = [(C0 - C1) × V] / m, resulting in a calculated value of 0.42 g / g.

[0070] The discharge was heat treated (80–100°C for 10 minutes) to release the product and the polyvinyl alcohol-sodium alginate hydrogel. The polyvinyl alcohol-sodium alginate hydrogel became the regenerated hydrogel. The regenerated hydrogel replaced 50% of the polyvinyl alcohol-sodium alginate hydrogel and was reintroduced into the fermentation system to adsorb medium-chain fatty acids. This "adsorption-regeneration" cycle was repeated five times. The adsorption capacity of the hydrogel after the fifth regeneration (denoted as Q5, g / g) was measured using the same method for determining initial adsorption capacity as described above. The retention rate was calculated as (Q5 / Q1) × 100%. The initial adsorption capacity was 0.42 g / g, with Q1 showing little difference from the initial adsorption capacity (Q0). After five regenerations, the adsorption capacity was 0.388 g / g, resulting in a retention rate of 92.4%.

[0071] Example 2 A method for continuous synthesis of medium-chain fatty acids, comprising the following steps: Raw material pretreatment: Beer lees and aged lees were mixed in a mass ratio of 7:3 to obtain lees. The lees were then mixed with urea, adjusting the C / N ratio to 30:1. The solids content of the mixture was then adjusted to 8% (w / w) to obtain the fermentation feed. The fermentation feed was ball-milled to a particle size D50 ≤ 1.2 mm, and the pH was adjusted to 4.5 ± 0.1 to obtain pretreated lees.

[0072] PVA-SA hydrogel and pretreated lees were mixed in a mass ratio of 1:10 and added to the fermenter. The fermenter was started, with the initial feed volume equal to the fermenter's effective volume (2 L). Pre-acidification was performed within the fermenter for three days. No feed or discharge was performed during the pre-acidification process. The fermenter was maintained at 38°C ± 0.5°C, with dissolved oxygen ≤ 0.5 ppm and a pH of 4.0. After three days of pre-acidification, the feed system was changed to daily feed and discharge.

[0073] Step 2: After pre-acidification is completed, change the feeding method to daily feeding and discharging.

[0074] The specific method is: the frequency of feeding and discharging is 24h / time, specifically: First, discharge the material, and control the material residence time to 15 days by adjusting the daily discharge volume to 133 mL, so that the material residence time of the 2L mixed system in the fermenter is 15 days. The mixed system in the fermenter is not stirred during the fermentation process.

[0075] During the first seven days of continuous feed-in / feed mode, the discharge liquid should be directly refluxed to the lower third of the fermentation system via a peristaltic pump daily. The reflux volume should be 50% of the total daily discharge. After the first seven days of continuous feed-in / feed mode, feed should be resumed. The total volume fed to the fermentation system should be 2 L.

[0076] Starting from the 8th day of the first continuous feeding and discharging mode, there is no need to reflux the discharge liquid. Thereafter, the feeding is stopped until the feeding amount is equal to the discharging amount.

[0077] Starting from the change of the feeding method, the pH and ORP of the top area of ​​the fermenter were monitored in real time every day, using the same method as in Example 1.

[0078] The pH and ORP were not regulated in the middle part of the fermenter (the 1 / 3 area below the top of the fermenter) and the lower part of the fermenter (the lower 1 / 3 area of ​​the fermenter).

[0079] Step 3: Purification of the Discharge and Continuous Product Recovery. The fermentation broth (discharge) was heat-treated at 80-100°C for 10 minutes to achieve controlled release and high-purity recovery of the adsorbed product (medium-chain fatty acids), while simultaneously regenerating the hydrogel support in situ. The method was the same as in Example 1.

[0080] The daily acid production rate was calculated from the first day of material feeding and unloading. The results are shown in Table 2.

[0081] On the second day, the acid production of medium-chain fatty acids was 2.23 g / L, and the hexanoic acid production was 1.77 g / L. On the third day, the acid production of medium-chain fatty acids was 3.66 g / L, and the hexanoic acid production was 2.94 g / L. On the fourth day, the acid production of medium-chain fatty acids was 3.99 g / L, and the hexanoic acid production was 3.30 g / L. On the fifth day, the acid production of medium-chain fatty acids was 3.92 g / L, and the hexanoic acid production was 3.49 g / L. On the sixth day, the acid production of medium-chain fatty acids was 4.19 g / L, and the hexanoic acid production was 3.97 g / L. On the seventh day, the acid production of medium-chain fatty acids was 5.10 g / L, and the hexanoic acid production was 4.95 g / L. On the eighth day, the acid production of medium-chain fatty acids was 3.92 g / L, and the hexanoic acid production was 3.67 g / L. On the ninth day, the acid production of medium-chain fatty acids was 3.57 g / L. On the 10th day, the production of medium-chain fatty acids was 4.85 g / L, and the production of caproate was 4.35 g / L. On the 11th day, the production of medium-chain fatty acids was 4.15 g / L, and the production of caproate was 3.61 g / L. On the 12th day, the production of medium-chain fatty acids was 3.99 g / L, and the production of caproate was 3.94 g / L. On the 13th, 14th, and 15th days, the average production of caproate was about 3.48 g / L.

[0082] Comparative Example 1 A method for continuously synthesizing medium-chain fatty acids, comprising the same steps as in Example 1, except that polyvinyl alcohol-sodium alginate hydrogel is not added.

[0083] Specifically, baijiu (white liquor) lees were mixed with crushed corn silage, with the C / N ratio of the mixture adjusted to 25:1. The solid content of the mixture was then adjusted to 10% (w / w) to obtain a fermentation feedstock. The fermentation feedstock was then pulverized twice to a particle size D90 ≤ 2 mm, meaning that 90% of the particles had a diameter ≤ 2 mm. The pH was then adjusted to 4.5 ± 0.1 to obtain the pretreated lees.

[0084] Add pretreated stillage directly to the fermentation tank. Start the fermentation unit with an initial feed volume equal to the fermentation unit's effective volume, i.e., 2 L. Pre-acidification is performed within the fermentation unit for 5 days. No feed or discharge occurs during the pre-acidification process. Maintain the fermentation unit at 38°C ± 0.5°C, with dissolved oxygen ≤ 0.5 ppm and a pH of 4.0. After 5 days of pre-acidification, change the feed schedule to daily addition and removal.

[0085] After pre-acidification, the feed system was changed to daily feed and discharge. A daily discharge volume of 167 mL was first discharged, and 50% of this 167 mL was then refluxed from the top of the fermenter to the lower third of the fermentation system via a peristaltic pump. After reflux, the total volume fed to the fermentation system was 2 L. During the first seven days of continuous feed and discharge, 50% of the daily discharge was refluxed.

[0086] Starting from the 8th day of the first continuous feeding and discharging mode, there is no need to reflux the discharge liquid. Thereafter, the feeding is stopped until the feeding amount is equal to the discharging amount.

[0087] Starting from the change in the feeding method, the pH and ORP of the top area of ​​the fermentor were monitored in real time every day. The top area of ​​the fermentor, i.e., the top 1 / 3 area of ​​the fermentor, was monitored to maintain the pH value of the top area of ​​the fermentor within the range of 4.0 to 5.5 and / or the ORP within the range of -350 to -150 mV, using the same method as in Example 1.

[0088] The daily acid production rate is calculated from the first day of feeding and unloading, and the result is: The daily acid production rate was calculated from the first day of material feeding and unloading, and the production of caproic acid from day 1 to day 12 was measured. The results showed that the maximum caproic acid production was 4.5 g / L on day 9.

[0089] Comparative Example 2 A method for continuous synthesis of medium-chain fatty acids, comprising the same steps as in Example 1, except that no pre-acidification treatment is performed, specifically: Liquor lees were mixed with crushed corn silage, with the C / N ratio adjusted to 25:1. The solids content of the mixture was then adjusted to 10% (w / w) to obtain a fermentation feedstock. The fermentation feedstock was then pulverized twice to a particle size D90 ≤ 2 mm, meaning that 90% of the particles had a diameter ≤ 2 mm. The pH was then adjusted to 4.5 ± 0.1 to obtain pretreated lees.

[0090] Polyvinyl alcohol-sodium alginate hydrogel (PVA-SA hydrogel) and pretreated lees were mixed in a mass ratio of 1:15 and added to the fermenter. The fermenter was started, and the initial feed volume was equal to the fermenter's effective volume, i.e., 2 L. The day of feed was designated Day 0, and feed and discharge were performed daily starting on Day 1. Each day, 167 mL of feed was first discharged. Then, 50% of this 167 mL of discharge was refluxed from the top of the fermenter to the lower third of the fermentation system via a peristaltic pump. After reflux, the total volume fed to the fermentation system was 2 L. For the first seven days of continuous feed and discharge, 50% of the daily discharge was refluxed. Starting on Day 8 of the initial continuous feed and discharge operation, reflux of the discharge liquid was no longer required. Feed was then continued until the feed volume equaled the discharge volume, at which point feeding was stopped.

[0091] The pH and ORP of the top area of ​​the fermenter were monitored in real time every day. The top area of ​​the fermenter, i.e., the top 1 / 3 area of ​​the fermenter, was monitored to maintain the pH value of the top area of ​​the fermenter within the range of 4.0 to 5.5 and / or the ORP within the range of -350 to -150 mV, using the same method as in Example 1.

[0092] The daily acid production rate was calculated from the first day of material feeding and unloading, and the production of caproic acid from day 1 to day 12 was measured. The results showed that the maximum caproic acid production was 1.4 g / L on day 3.

[0093] Comparative Example 3 A method for continuously synthesizing medium-chain fatty acids, comprising the same steps as in Example 1, except that the pH of the pre-acidification process is maintained at 5.5.

[0094] The daily acid production rate was calculated from the first day of material feeding and unloading, and the production of caproic acid from day 1 to day 12 was measured. The results showed that the maximum caproic acid production was 3.06 g / L on day 7.

[0095] Comparative Example 4 A method for continuously synthesizing medium-chain fatty acids, comprising the same steps as in Example 1, except that the material is fed and discharged once every two days.

[0096] The pH and ORP of the top area of ​​the fermenter are monitored in real time every day. The top area of ​​the fermenter is the top 1 / 3 area of ​​the fermenter. The pH and ORP of the top area of ​​the fermenter are monitored to maintain the pH value of the top area of ​​the fermenter in the range of 4.0~5.5 and / or the ORP in the range of -350~-150 mV.

[0097] When pH < 4.0 and ORP is lower than -350 mV, the feeding and discharging frequency is adjusted to 72 h / time.

[0098] When pH>5.5 and ORP is higher than -150 mV: the feeding and discharging frequency is increased to 24 h / time.

[0099] The daily acid production rate was calculated from the first day of material feeding and unloading, and the production of caproic acid from day 1 to day 12 was measured. The results showed that the maximum caproic acid production was 3.58 g / L on day 7.

[0100] Comparative Example 5 A method for continuously synthesizing medium-chain fatty acids comprises the same steps as in Example 1, except that the mass ratio of the polyvinyl alcohol-sodium alginate hydrogel to the pretreated vinasse is 1:25.

[0101] The daily acid production rate was calculated from the first day of material feeding and unloading, and the production of caproic acid from day 1 to day 12 was measured. The results showed that the maximum caproic acid production was 4.2 g / L on day 8.

[0102] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for continuous synthesis of medium-chain fatty acids, characterized in that: The following steps are involved: The pretreated vinasse is mixed with a polyvinyl alcohol-sodium alginate composite matrix to obtain a fermentation matrix; the pretreated vinasse has a solid content of 8% to 10%, a carbon-nitrogen ratio of (25-30):1, 90% of the particle diameter is ≤2 mm, and the pH value is 4.4-4.6; the mass ratio of the polyvinyl alcohol-sodium alginate composite matrix to the pretreated vinasse is 1:(10-20); Adding the fermentation substrate to the fermentation system for pre-acidification; the pre-acidification temperature is 37.5-38.5° C.; the dissolved oxygen in the pre-acidification is ≤0.5 ppm; and the pre-acidification pH is 4.0-5.0; After pre-acidification is completed, the daily feed and discharge of the fermentation system are adjusted, and the material residence time in the fermentation system is adjusted to 9-15 days by the discharge rate. The pH in the top area of ​​the fermentation system is controlled to 4.0-5.5 and / or the ORP is controlled to -350-150 mV, and an axial coupling system is established between the hydrolysis and acidification lactic acid production zone at the top of the fermentation system and the medium-chain fatty acid synthesis zone at the bottom. The top area of ​​the fermentation system is the upper 1 / 3 to 1 / 4 area of ​​the fermentation system; The discharge is the discharge from the bottom of the fermentation system; the feed is the feed from the top of the fermentation system; and the feed is the addition of the fermentation substrate to the fermentation system.

2. The method according to claim 1, characterized in that The method for controlling the pH of the top area of ​​the fermentation system to 4.0~5.5 and / or the ORP to -350~-150 mV includes: when the pH is <4.0 and the ORP is lower than -350 mV, the feeding and discharging frequency is adjusted to 48~72 hours / time; when the pH is >5.5 and the ORP is higher than -150 mV, the feeding and discharging frequency is adjusted to 6~12 hours / time.

3. The method according to claim 1, characterized in that The pre-acidification time is 3 to 7 days.

4. The method according to claim 1, characterized in that During the first 7 days of adjusting the daily feed and discharge of the fermentation system, 30% to 50% of the daily discharge should be refluxed to the lower 1 / 3 to 1 / 4 area of ​​the fermentation system before feeding.

5. The method according to claim 1, characterized in that: During daily loading and unloading, the input volume is less than or equal to the output volume.

6. The method according to claim 1, characterized in that The polyvinyl alcohol-sodium alginate composite matrix includes polyvinyl alcohol-sodium alginate hydrogel.

7. The method according to claim 1, characterized in that The material for adjusting the carbon-nitrogen ratio of the pretreated vinasse includes any one or more of corn straw, wheat straw, urea and pig manure; and the vinasse includes any one or more of liquor vinasse, beer vinasse and aged vinasse.

8. The method according to claim 1, characterized in that: Methods for separating medium-chain fatty acids from the effluent include heat treatment.

9. The method according to claim 8, characterized in that The heat treatment temperature is 80-100° C., and the heat treatment time is 10 minutes.

10. The method according to claim 1, characterized in that: The medium-chain fatty acid includes any one or two or more of hexanoic acid, heptanoic acid and octanoic acid.

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