CN114752635B - Process for recycling caproic acid in anaerobic fermentation liquid based on forward osmosis technology - Google Patents
Process for recycling caproic acid in anaerobic fermentation liquid based on forward osmosis technology Download PDFInfo
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Abstract
The application discloses a process for recycling caproic acid in anaerobic fermentation liquid based on forward osmosis technology, which mainly comprises an anaerobic fermentation unit and a forward osmosis concentration unit. The inoculum of the anaerobic fermentation unit is anaerobic sludge after heat treatment, and ethanol and lactic acid are used as composite substrates for fermentation to produce caproic acid; the fermentation liquor is filtered by a microfiltration device and then concentrated by a forward osmosis technology. The forward osmosis concentration unit comprises a concentration tank, a forward osmosis membrane component and a liquid drawing tank, and fermentation liquor is filtered and then injected into the concentration tank. The forward osmosis membrane component comprises an inner cavity and an outer cavity, the inner cavity is connected with the concentration tank, and the outer cavity is connected with the liquid drawing tank. Under the drive of osmotic pressure, water continuously flows from one side of the concentration tank to one side of the liquid drawing tank in a transmembrane way, so that the concentration of the caproic acid fermentation liquid is realized. And further, the pH value of the concentrated solution is regulated to separate out the caproic acid in the form of oily matters, so that the high-efficiency and low-consumption separation of the caproic acid is realized, and a high-concentration crude product of the caproic acid is obtained.
Description
Technical Field
The application belongs to the field of efficient recycling of resources, and particularly relates to a process for recycling caproic acid in anaerobic fermentation liquid based on forward osmosis technology.
Background
As a means for recycling biomass, anaerobic biological treatment can convert organic waste into energy (methane, hydrogen, etc.) or chemicals. Among them, the production of organic acids by anaerobic mixed fermentation is one of the recent research hotspots. The waste biomass is used as a substrate, and liquid phase products (namely fermentation liquor) obtained by anaerobic fermentation of mixed flora for producing acid mainly comprise short chain fatty acid, ethanol and lactic acid, and the products have strong hydrophilicity, difficult separation and purification and low energy density.
Based on the reverse beta-oxidation pathway (reverse oxidation) of anaerobic microorganisms, short-chain organic acids/alcohols produced by anaerobic acidification of organic waste can be further converted into medium-chain fatty acids such as caproic acid. Compared with short-chain fatty acid, the caproic acid has higher energy density, low water solubility (slightly soluble in water) and is easy to separate from fermentation liquor; the catalyst can be further processed into fuel substances and other chemical materials, and has higher added value.
How to effectively recover caproic acid from fermentation liquor is important. It has been studied to extract caproic acid from fermentation broth by extraction technique, first by forming complex with carboxyl group by specific extractant, then recovering caproic acid from the extract by rectification or electrodialysis, and regenerating extractant. The main research direction is currently to improve the chemical interactions between solutes and extractants and to optimize the relevant process conditions. Trioctylphosphine oxide (TOPO) has found some application in caproic acid extraction due to its low toxicity to microorganisms and higher extraction yield. However, regardless of the extraction system or extraction solvent selected, conventional extraction processes are not free from some drawbacks. On the one hand, the organic acid needs to be fully contacted with the extractant in the process of transferring from one phase to the other, and a stable separation interface is difficult to form. On the other hand, the extractant regeneration process is complex, the energy consumption is high, and certain influence on the environment exists.
The forward osmosis is a membrane separation technology taking the osmotic pressure difference of the feed liquid and the drawing liquid as the driving force, does not need external pressure in operation, has the advantages of lower energy consumption, lower membrane pollution, higher material recovery rate and the like, and is suitable for the water treatment fields of sewage purification, sea water desalination and the like. In recent years, forward osmosis technology has shown better application potential in product concentration, but lacks related research in product separation and recovery of caproic acid fermentation.
Disclosure of Invention
The application aims to: in order to solve the defects in the prior art, the application provides a process for recycling caproic acid in anaerobic fermentation liquid based on forward osmosis technology. Firstly, ethanol and lactic acid are used as composite substrates to ferment and produce caproic acid, and then the forward osmosis technology is utilized to concentrate fermentation liquor; and further, by adjusting the pH value of the concentrated solution, the caproic acid is separated out in the form of oil, so that the separation and recovery of the target product are realized, and the high-concentration crude caproic acid product is obtained.
The technical scheme adopted by the application is as follows: provides a process for recycling caproic acid in anaerobic fermentation liquid based on forward osmosis technology. The heat-treated anaerobic sludge is used as an inoculum to ferment ethanol and lactic acid to produce caproic acid, and the obtained fermentation liquor is filtered by a microfiltration device and then concentrated by a forward osmosis technology. The forward osmosis technology adopts a forward osmosis device, and the forward osmosis device comprises a concentration tank, a forward osmosis membrane component and a liquid drawing tank. The filtered fermentation liquor is collected in a concentration tank, and then is continuously pumped into the inner cavity of the forward osmosis membrane component and returned to the concentration tank; the outer cavity of the forward osmosis membrane component is connected with a drawing liquid tank, and drawing liquid continuously circulates in the outer cavity of the forward osmosis membrane component. Under the drive of osmotic pressure, the caproic acid fermentation liquid is continuously concentrated, and then the high-concentration crude caproic acid product is obtained through acidification and oil extraction.
In one embodiment of the application, the method comprises the steps of:
s1, anaerobic caproic acid fermentation: the anaerobic fermentation device is inoculated with the anaerobic sludge after heat treatment, and the caproic acid batch fed-batch fermentation is carried out by taking ethanol and lactic acid as composite substrates.
S2, feeding by a forward osmosis membrane device: the fermentation liquor flows out from a discharge hole of the anaerobic device, is filtered by the microfiltration device and enters a concentration tank of the forward osmosis device.
S3, concentrating anaerobic fermentation liquid: the inner cavity of the forward osmosis membrane component is connected with the concentration tank, and anaerobic fermentation liquid is continuously pumped into the inner cavity of the forward osmosis membrane component and circularly flows to the concentration tank; the outer cavity of the forward osmosis membrane component is connected with a drawing liquid tank, and drawing liquid continuously circulates in the outer cavity of the forward osmosis membrane component. Under the drive of osmotic pressure, water continuously flows from one side of the concentration tank to one side of the liquid drawing tank in a transmembrane way, so that the concentration of the caproic acid fermentation liquid is realized.
S4, recovering concentrated solution: and discharging the concentrated fermentation liquor through a discharge pipe of the concentration tank to obtain concentrated liquor.
S5, acidizing the concentrated solution by adjusting the pH value to form acid oil to be separated out, and obtaining a coarse caproic acid product.
In one embodiment of the application, the anaerobic sludge is heat treated at 121 ℃ for 10 minutes before inoculation, with an inoculum size of 20g/L (VS).
In one embodiment of the application, the anaerobic fermentation temperature is maintained at 35+ -1deg.C, the stirring speed is 100rpm, and the fermentation pH is controlled at 6.5.
In one embodiment of the application, the fermentation broth is filtered by a microfiltration device before entering the forward osmosis concentration device, the microfiltration membrane having a pore size of 0.22 μm.
In one embodiment of the present application, the feed liquid is fed in from top to bottom, and the draw liquid is fed in from bottom to top.
In one embodiment of the present application, the flow rates of the feed liquid and the draw liquid are each 500.0 to 600.0mL/min.
In one embodiment of the application, the forward osmosis membrane module is a hollow fiber forward osmosis membrane having a tolerance pH of 3 to 10 and a maximum operating temperature of 45 ℃.
In one embodiment of the application, the draw solution is 1-3 mol/L NaCl.
In one embodiment of the application, the pH of the feed solution is from 6.5 to 8.5.
In one embodiment of the application, the total acid concentration is 9.5 to 38.0g/L.
In one embodiment of the application, the fermentation concentrated solution is subjected to pH adjustment to 2.5-6.5, shaking and standing, and the concentrated solution is layered to obtain a crude caproic acid product.
The application creatively provides a method for recycling caproic acid in anaerobic fermentation liquid based on forward osmosis technology. Firstly, ethanol and lactic acid are used as composite substrates to efficiently synthesize caproic acid; concentrating the fermentation liquor by adopting a forward osmosis device; and further, the pH value of the concentrated solution is regulated to separate out the caproic acid in the form of oily matters, so that the high-efficiency and low-consumption separation of the caproic acid is realized, and a high-concentration crude product of the caproic acid is obtained.
The beneficial effects are that: ethanol and lactic acid are used as composite substrates, so that the production intensity of anaerobic sludge caproic acid fermentation is effectively improved, and the fermentation period is obviously shortened. By fed-batch fermentation, the substrate was completely consumed for 18 days and the caproic acid yield reached 9.2g/L. The forward osmosis technology efficiently concentrates the caproic acid in the fermentation liquor, and the concentration of the caproic acid is improved to 9.0 times within 15 minutes under the condition that the NaCl concentration of the extracting solution is 3mol/L, and the concentration recovery rate of the caproic acid film is close to 100.0 percent. The concentrated solution can separate out the caproic acid in the form of oil, the extraction rate of the caproic acid reaches 76.2-92.0% under the acidification condition of pH 5.5-4.5, the concentration of the caproic acid in the acid oil reaches 486.2-578.2g/L, the purity is 73.5-66.4%, and the total concentration multiple reaches 52.8-62.8 times.
Drawings
FIG. 1 is a schematic diagram of the anaerobic fermentation device and the forward osmosis concentration device;
FIG. 2 shows the effect of positive osmosis concentration of NaCl concentration of different drawing solutions;
FIG. 3 shows the effect of pH forward osmosis concentration of different feed solutions;
FIG. 4 shows the effect of forward osmosis concentration at different total acid concentrations;
FIG. 5 shows the pH acidification oil extraction effect of different concentrates;
FIG. 6 shows the material composition of the resulting acid oil at different pH conditions;
in the figure, a 1-pH detector, a 2-dissolved oxygen detector, a 3-temperature detector, a 4-liquid level meter, a 5-discharge pump, a 6-feed pump, a 7-alkaline liquid pump, an 8-stirring slurry, a 9-temperature control cushion layer, a 10-exhaust port, a 11-alkaline liquid tank, a 12-substrate tank, a 13-microfiltration device, a 14-concentration tank, a 15-drawing liquid tank, a 16-forward osmosis feed pump, a 17-drawing liquid pump, a 18-forward osmosis membrane component, a 19-inner cavity liquid inlet and a 20-outer cavity liquid inlet are arranged.
Detailed Description
The application will be further described with reference to the drawings and examples. The application will be better understood from the following examples. However, it will be readily understood by those skilled in the art that the specific material ratios, process conditions and results thereof described in the examples are illustrative of the present application and should not be construed as limiting the application described in detail in the claims.
The design idea of the embodiment of the application is as follows:
(1) The fed-batch fermentation produced caproic acid, i.e., the anaerobic fermentation of ethanol and lactic acid as a composite substrate produced caproic acid, yielded a caproic acid broth, which was example 1.
(2) A simulated fermentation broth was prepared according to the organic acid component and concentration in the anaerobic fermentation broth obtained in example 1. The effect of the concentration of NaCl in the draw solution, the pH of the feed solution and the total acid concentration on the concentration effect of the forward osmosis unit was examined, examples 2 to 8.
(3) After the actual anaerobic fermentation liquid obtained in example 1 was filtered, efficient concentration of the fermentation liquid was achieved by a forward osmosis apparatus under optimal conditions, which is example 9.
(4) After the fermentation concentrate of example 9 was acidified by adjusting the pH, caproic acid was precipitated as an oil, thereby obtaining a crude high-concentration caproic acid product. Examples 10 to 14 are described.
Example 1: anaerobic fermentation production of caproic acid by using ethanol and lactic acid as composite substrates
The total reaction volume was 10L using a fully automatic stirred anaerobic fermentation tank as shown in FIG. 1. The inoculum was anaerobic granular sludge after heat treatment at 121 ℃ for 10 minutes, and the inoculum size was 20g/L (calculated as VS). The reaction mode is fed-batch fermentation, the fermentation substrate is a compound consisting of ethanol and lactic acid, and the initial concentration is 0.1mol/L. After complete consumption of the complex substrate, the substrate is again fed to the initial concentration. The temperature in the whole fermentation process is kept at 35+/-1 ℃, the stirring rotating speed is 100rpm, and the fermentation pH is controlled at 6.5. After nitrogen stripping for 5 minutes, the anaerobic reactor was started.
As shown in fig. 1, fermentation medium is fed from a substrate tank 12 to the reactor by a feed pump 6; the alkaline pump 7 is connected with the alkaline tank 11, and the automatic alkaline liquid feeding on-line controls the fermentation pH; after fermentation, the fermentation liquid is pumped into a micro-filtration device 13 by a discharge pump 5, and the filtrate is collected in a concentration tank 14. In the anaerobic fermentation tank, the pH detector 1 is used for feeding back the pH value in the fermentation process on line; the dissolved oxygen detector 2 monitors the anaerobic state of the fermentation system; the temperature detector 3 is used for feeding back and regulating the temperature on line; the liquid level meter 4 monitors the liquid level in the tank; the stirring paddle 8 is used for stirring materials and the rotating speed is controllable; the exhaust port 10 is used for introducing nitrogen and collecting gas.
Example 2: optimizing forward osmosis process conditions with simulated fermentation broth
According to the organic acid components and the concentration in the anaerobic fermentation liquid, preparing the simulated fermentation liquid into the forward osmosis feed liquid, and examining the influence of the NaCl concentration of the drawing liquid, the pH value of the feed liquid and the total acid concentration on the concentration effect of the forward osmosis device (examples 2-8). The application adopts a hollow fiber type forward osmosis membrane, the tolerance pH range is 3-10, and the maximum operating temperature is 45 ℃. The membrane assembly is composed of an inner cavity and an outer cavity, wherein the inner cavity is continuously circulated with the simulated fermentation liquid up and down, and the outer cavity is continuously circulated with the drawing liquid up and down (figure 1). In this example, the simulated broth feed was 1L, the initial pH was 6.5, and the total acid concentration was 21.0g/L (acetic acid 2.5g/L, propionic acid 1.0g/L, butyric acid 4.0g/L, valeric acid 4.0g/L, caproic acid 9.5 g/L). Example 2 was concentrated using 1mol/L NaCl draw. The volume ratio of the drawing liquid to the simulated fermentation liquid is controlled to be 1:1, and the circulation of the drawing liquid is in a circulating mode. As shown in fig. 1, a feed inlet and a discharge outlet are provided on the side of the concentrating tank 14, and anaerobic fermentation liquid is filtered as feed liquid by the microfiltration device 13 and introduced into the concentrating tank from the feed inlet. The forward osmosis feed pump 16 circulates the fermentation broth in the concentration tank into the inner cavity of the forward osmosis membrane module 18, the draw solution pump 17 circulates the draw solution into the outer cavity of the membrane module, the flow rates of the two are 500.0mL/min, and the running time is 3 minutes. Under the drive of osmotic pressure, water continuously flows from one side of the concentration tank to one side of the drawing liquid in a transmembrane way, so that the concentration of the caproic acid fermentation liquid is realized.
Example 3:
the difference is that the draw solution is 2mol/L NaCl as in example 2.
Example 4:
the difference is that the draw solution is 3mol/L NaCl as in example 2.
Example 5:
the difference from example 4 is that the concentration is carried out after the initial pH of the forward osmosis feed solution has been adjusted to 7.5.
Example 6:
the difference from example 4 is that the concentration is carried out after the initial pH of the forward osmosis feed solution has been adjusted to 8.5.
Examples 7 to 8:
as in example 4, the concentration of the organic acid was carried out at a pH of the feed solution of 3mol/L NaCl at an initial pH of 6.5. Except that the total acid concentrations corresponding to examples 7 and 8 were 9.5g/L and 38.0g/L, respectively. The forward osmosis feed components and concentrations of examples 4, 7 and 8 are shown in table 2.
TABLE 2 simulation of fermentation broths at different concentrations
Example 9: concentrating the actual acidogenic fermentation broth by forward osmosis
5L of the actual fermentation broth in example 1, with pH of 6.5, is fed into a forward osmosis device after microfiltration treatment, and the liquid extract is 3mol/L NaCl. Unlike examples 2-8, the draw solution was directly drained through the forward osmosis membrane outer chamber and no longer returned to the draw solution tank. In the concentration process, the flow rates of the feed liquid and the drawing liquid are set to be 500.0mL/min, and the running time is 15 minutes.
Example 10: extracting caproic acid by adjusting pH of concentrated solution
The pH of the fermentation broth increases after forward osmosis concentration, and the pH of the concentrate is adjusted to be acidic by adding hydrochloric acid, so that caproic acid is separated out in the form of oily matter (acidizing oil extraction). The concentrate in example 9 was acidified to extract oil, 30mL of the concentrate was taken, the pH was adjusted to 6.5 by adding hydrochloric acid, shaking was sufficient, and the mixture was allowed to stand for 12 hours to extract acid oil after the concentrate had been stratified.
Example 11:
the procedure is as in example 10, except that hydrochloric acid is added to adjust the pH of the concentrate to 5.5.
Example 12:
the procedure is as in example 10, except that hydrochloric acid is added to adjust the pH of the concentrate to 4.5.
Example 13:
the procedure is as in example 10, except that hydrochloric acid is added to adjust the pH of the concentrate to 3.5.
Example 14:
the procedure is as in example 11, except that hydrochloric acid is added to adjust the pH of the concentrate to 2.5.
Results and analysis of examples
(1) Fermenting ethanol and lactic acid as composite substrate to produce caproic acid
The inoculum was anaerobic granular sludge after heat treatment at 121 ℃ for 10 minutes, and the inoculum size was 20g/L (calculated as VS). The reaction mode is fed-batch fermentation, the fermentation substrate is a compound consisting of ethanol and lactic acid, and the initial concentration is 0.1mol/L. After complete consumption of the complex substrate, the substrate is again fed to the initial concentration. The two batches of substrates are completely consumed in 18 days, the caproic acid yield reaches 9.2g/L, and the main organic acid components and the concentrations in the obtained anaerobic fermentation liquid are shown in Table 1.
TABLE 1 organic acid concentration (g/L) in anaerobic fermentation broth
(2) Effect of draw solution NaCl concentration on concentration Effect of Forward osmosis System
The initial pH of the simulated fermentation broth is regulated to 6.5, the total acid concentration is 21.0g/L, examples 2-4 are respectively concentrated by using NaCl drawing liquid of 1mol/L, 2mol/L and 3mol/L, and the influence of the concentration of the drawing salt on the concentration effect of the forward osmosis system is examined.
Membrane concentrate recovery was calculated according to formulas (1) and (2):
the membrane water flux increased with increasing draw solution NaCl concentration from 175.3mL/min in example 2 to 266.3mL/min in example 4. The concentration effect of the organic acid film is shown in figure 2, and the concentration multiple of the feed liquid is improved from 2.1 times to 5.0 times. In terms of acid recovery effect, the overall acid recovery was reduced from 100.0% in example 2 to 97.1% in example 4. The recovery of caproic acid membrane concentration was reduced from 100.0% in example 2 to 97.8% in example 4. The higher osmotic pressure accelerates the water to flow through the membrane and enlarges the pore diameter of the membrane, so that a small part of organic acid is lost. Therefore, the concentration of NaCl in the drawing liquid is increased, the concentration effect is effectively improved, and the recovery rate of the product is not obviously affected. Thus, in the subsequent examples 5 to 10, the NaCl concentration of the drawing liquid was set to 3mol/L.
(3) Influence of feed liquid pH on concentration effect of forward osmosis system
In order to clearly determine the influence of the pH of the feed liquid on the forward osmosis concentration effect under the condition that the total acid concentration is 21.0g/L and the draw liquid is 3mol/L NaCl, examples 4, 5 and 6 are concentrated after respectively adjusting the initial pH of the feed liquid to 6.5, 7.5 and 8.5. As shown in fig. 3, the concentration factors were 5.0 (pH 6.5), 4.9 (pH 7.5), and 4.8 (pH 8.5) at different feed pH conditions, respectively; the total acid recovery rate is 97.1%,98.8% and 99.2% respectively; the recovery rate of caproic acid is 97.8%,100% and 100% respectively. Thus, the feed pH has no significant effect on the concentration effect of the forward osmosis system, without additional pH adjustment. The forward osmosis feed pH was 6.5 in each of the subsequent examples 7-10.
(4) Effect of feed organic acid concentration on the concentration Effect of Forward osmosis System
Under the condition that the drawing liquid is 3mol/L NaCl and the pH value of the feed liquid is 6.5, the influence of the concentration of the total organic acid on the forward osmosis concentration effect is further examined. An increase in the concentration of the organic acid reduces the osmotic pressure difference of the solution across the membrane, resulting in a decrease in the concentration driving force of the forward osmosis membrane. When the total acid concentration is increased from 9.5g/L to 38.0g/L, the concentration multiple is reduced from 9.7 times to 2.7 times. In all three examples, the total acid recovery was maintained above 96% with little loss of hexanoic acid and recovery approaching 100%. The concentration of caproic acid in the concentrated solution reached 24.5g/L (example 7), 47.3g/L (example 4) and 36.4g/L (example 8), respectively, and the difference was remarkable. The control of the total acid concentration during forward osmosis concentration of the fermentation broth is therefore critical.
(5) Concentrating the actual acidogenic fermentation broth by using forward osmosis system
And under the condition that the drawing liquid is 3mol/L NaCl and the pH value of the feed liquid is 6.5, the forward osmosis concentration is utilized to actually produce the acid fermentation liquid. After 15 minutes of continuous concentration, the concentration of total acid and caproic acid is improved by 9 times, and the average water flux of the forward osmosis membrane is 296.3mL/min. As shown in Table 3, the total acid film concentration recovery was 99.9%, the caproic acid film concentration recovery was 100.0%, and only very small amounts of acetic acid and butyric acid were eluted with the draw solution. In addition, in continuous repeated experiments, the forward osmosis system can always keep higher membrane flux and membrane concentration recovery rate, which shows that the actual fermentation liquid can effectively reduce the pollution of the forward osmosis membrane after macromolecular substances are removed by ultrafiltration.
TABLE 3 continuous concentration effect of actual fermentation broths
(6) Extraction of caproic acid by acidification of concentrate pH
In examples 10-14, the effect of concentrate pH on the extraction of hexanoic acid was examined by acidifying the concentrate to precipitate hexanoic acid as an oil. The acid oil extraction rate is calculated according to formula (3):
FIG. 5 is a graph showing the actual effect of acid oil extraction of the concentrate at pH 6.5, 5.5, 4.5, 3.5, 2.5. The initial pH of the concentrate was 7.3, and the solution became cloudy when the pH of the concentrate was adjusted to 6.5 in example 10, but no significant oil film was separated out; as the pH further decreases, the concentrate of examples 11-14 begins to appear as an oil layer and gradually increases in thickness, the more clear the oil layer and solution, the more pronounced the two-phase separation.
Table 4 shows the extraction rates of the organic acid components after acidification and oil extraction at different pH values. As the pH decreases, the extraction rate of each organic acid in the concentrate increases gradually, and the longer the carbon chain, the higher the extraction rate of the carboxylic acid. When the pH of the concentrate was adjusted to 4.5 (example 12), the caproic acid extraction rate reached 92.0%. As the pH further decreases, the caproic acid extraction rate does not change much, but the amount of other short chain carboxylic acids evolved continues to increase, thus decreasing the purity of the caproic acid in the acid oil.
TABLE 4 extraction yield of the components after acidification and oil extraction at different pH (%)
Table 5 shows the organic acid concentrations in the oil phase after acidification and oil extraction at different pH values. As the pH of the concentrate decreases, the concentration of organic acid in the precipitated acid oil gradually increases. When the pH was reduced from 5.5 (example 11) to 4.5 (example 12), the caproic acid concentration in the sour oil increased significantly from 486.2g/L to 578.2g/L. Further reductions in pH had reduced effects on the amount of caproic acid precipitated, with caproic acid concentrations in the acid oils of examples 13 (pH 3.5) and 14 (pH 2.5) being 583.2g/L and 600.4g/L, respectively.
TABLE 5 concentration of the components in acid oils at different pH conditions
The ratio of the substance components in the acid oil extracted under different pH conditions is shown in FIG. 6, for example, and the caproic acid content in the initial concentrated solution is 51.5%. The caproic acid purity after acidification and oil extraction at pH 5.5 (example 11) and pH 4.5 (example 12) can be increased to 73.5% and 66.4%, respectively. However, further lowering of the pH results in a decrease in hexanoic acid purity. The purities of caproic acid after acidification and oil extraction at pH 3.5 (example 13) and pH 2.5 (example 14) were 63.5% and 62.9%, respectively.
The results show that the caproic acid can be effectively extracted by acidifying the forward osmosis concentrated solution based on the physicochemical properties of the caproic acid. The pH of acidification can be controlled between 4.5 and 5.5, the extraction rate of the caproic acid reaches 76.2 to 92.0 percent, the concentration of the caproic acid in the acid oil reaches 486.2 to 578.2g/L, and the purity of the caproic acid reaches 73.5 to 66.4 percent.
The foregoing is only a preferred embodiment of the application, it being noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present application, and such modifications and adaptations are intended to be comprehended within the scope of the application.
Claims (1)
1. A process for recovering caproic acid in anaerobic fermentation liquid based on forward osmosis technology is characterized in that heat-treated anaerobic sludge is used as an inoculum, ethanol and lactic acid are used as composite substrates for caproic acid fermentation, and the obtained fermentation liquid is filtered by a microfiltration device and then concentrated by the forward osmosis technology;
the forward osmosis technology adopts a forward osmosis concentration device, the forward osmosis concentration device comprises a concentration tank, a forward osmosis membrane component and a liquid drawing tank, the fermentation filtrate is collected in the concentration tank, and then is continuously pumped into the inner cavity of the forward osmosis membrane component and returned to the concentration tank; the outer cavity of the forward osmosis membrane component is connected with a liquid drawing tank, liquid drawing continuously circulates in the outer cavity, fermentation liquid is efficiently concentrated under the drive of osmotic pressure, and then high-concentration crude caproic acid is obtained through acidification and oil extraction, and the method comprises the following steps:
s1, anaerobic caproic acid fermentation: inoculating the anaerobic sludge subjected to heat treatment in an anaerobic fermentation device, and carrying out caproic acid batch fed-batch fermentation by taking ethanol and lactic acid as composite substrates; the main organic acid components and the concentration of the anaerobic fermentation liquid are in accordance with the following relation, 20g/L of the anaerobic fermentation liquid is calculated by VS according to the inoculation amount, and the main organic acid components and the concentration of the anaerobic fermentation liquid are as follows: acetic acid 2.7+/-0.1 g/L, propionic acid 1.3+/-0.3 g/L, butyric acid 4.5+/-0.2 g/L, valeric acid 4.2+/-0.1 g/L and caproic acid 9.2+/-0.1 g/L;
s2, feeding by a forward osmosis membrane device: the fermentation liquor flows out from a discharge port of the anaerobic fermentation device, is filtered by the microfiltration device and enters a concentration tank of the forward osmosis device;
s3, concentrating anaerobic fermentation liquid: the inner cavity of the forward osmosis membrane component is connected with the concentration tank, and anaerobic fermentation liquid is continuously pumped into the inner cavity of the forward osmosis membrane component and circularly flows to the concentration tank; the outer cavity of the forward osmosis membrane component is connected with a drawing liquid tank, and drawing liquid continuously circulates in the outer cavity of the membrane component; concentrating the fermentation liquor under the action of osmotic pressure;
the feeding liquid is fed in from top to bottom, the extracting liquid is fed in from bottom to top, and the flow rates of the feeding liquid and the extracting liquid are 500.0-600.0mL/min;
the forward osmosis membrane component is a hollow fiber forward osmosis membrane, the tolerance pH is 3-10, and the maximum operating temperature is 45 ℃;
the NaCl concentration of the drawing liquid is 1-3 mol/L;
the pH value of the feed liquid of the forward osmosis membrane component is 6.5-8.5, and the total acid concentration is 9.5-38.0 g/L;
s4, recovering concentrated solution: discharging the concentrated fermentation liquor through a discharge pipe of the concentration tank to obtain concentrated liquor;
s5, acidizing the concentrated solution to form acid oil after adjusting the pH value to be 4.5-5.5, and separating out the acid oil to obtain a coarse caproic acid product;
heat treatment is carried out for 10 minutes at 121 ℃ before the anaerobic sludge inoculation, and the inoculation amount is 20g/L in terms of VS;
the temperature in the anaerobic fermentation process is kept at 35+/-1 ℃, the stirring speed is 100rpm, and the fermentation pH is controlled at 6.5.
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| CN107619090A (en) * | 2017-09-30 | 2018-01-23 | 浙江师范大学 | A kind of kitchen garbage anaerobic acid-production zymotic fluid concentrating recovery device and method |
| CN108251462A (en) * | 2018-04-04 | 2018-07-06 | 江南大学 | A kind of method that caproic acid is recycled in anaerobic fermented liquid |
| CN111394397A (en) * | 2020-03-17 | 2020-07-10 | 北京科技大学 | Method for producing caproic acid by fermenting kitchen waste |
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| CN107619090A (en) * | 2017-09-30 | 2018-01-23 | 浙江师范大学 | A kind of kitchen garbage anaerobic acid-production zymotic fluid concentrating recovery device and method |
| CN108251462A (en) * | 2018-04-04 | 2018-07-06 | 江南大学 | A kind of method that caproic acid is recycled in anaerobic fermented liquid |
| CN111394397A (en) * | 2020-03-17 | 2020-07-10 | 北京科技大学 | Method for producing caproic acid by fermenting kitchen waste |
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| 李威等.《十二五制药类生物技术类药学类专业规划教材 药剂学》.湖北科学技术出版社,2014,第28-29页. * |
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