Method for separating and purifying butanol from ABE fermentation liquor

Abstract

The invention relates to the technical field of butanol separation and purification, in particular to a method for separating and purifying butanol from ABE fermentation liquor. Comprising the following steps: filtering ABE fermentation liquor through a micro-filtration membrane to obtain micro-filtration membrane filtrate; performing selective permeation on the micro-filtration membrane filtrate through a pervaporation membrane to obtain permeation steam; the permeation steam is sequentially introduced into a first condenser and a second condenser, and a first condensation product and a second condensation product are obtained; mixing the first condensation product with a salt to obtain a water phase and an organic phase; enabling the organic phase to pass through an ultra-infiltration membrane to obtain ultra-infiltration filtrate; mixing the ultra-infiltration membrane filtrate with anhydrous salt, and filtering through an ultra-infiltration membrane to obtain butanol. The green and efficient separation method is developed, butanol is efficiently separated and recycled from the ABE fermentation liquor, meanwhile, high-added-value products such as acetone and medium and long chain hydrocarbons are produced as byproducts, the separation cost is reduced, and the economical efficiency of the whole process is improved.

Description

Technical Field

[0001] The invention relates to the technical field of alcohol separation and purification, and in particular to a method for separating and purifying butanol from ABE fermentation broth. Background Art

[0002] Biobutanol is a high-quality renewable liquid biofuel with a higher calorific value, lower volatility, and less corrosiveness than bioethanol (which has been successfully commercialized). It is also more compatible with gasoline and diesel, making it a better candidate to replace gasoline fuel. Although biobutanol has great potential in utilizing biomass chemical energy and reducing environmental burden, its main preparation pathway is acetone-butanol-ethanol (ABE) fermentation of sugar substrates, which has constraints such as low solvent concentration and product azeotropy. The traditional biobutanol separation process has problems such as high separation energy consumption and high cost, which restricts its industrial preparation. A green and efficient separation and purification technology is urgently needed.

[0003] In order to solve the technical difficulties of bio-butanol separation, many technicians have explored and tested new separation technologies such as pervaporation, adsorption, and extraction in the laboratory or pilot scale in recent years. For example, patents CN103772144B, CN101851641A, CN109012222B, CN102994573B, CN102965399B, CN101898945B, CN102372595B, and CN101979615B. Compared with the traditional "fermentation-distillation" process, these separation technologies can reduce the energy consumption of ABE solvent product extraction, but the obtained products still need to be further concentrated and cascaded to the subsequent distillation system to achieve the separation and purification of the final product butanol. The economy of the overall process route is still poor, so there are still many challenges in applying these new separation technologies to actual production.

[0004] Therefore, how to efficiently extract ABE while achieving the simultaneous separation of the product butanol becomes the key to solving the problem. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for separating and purifying butanol from ABE fermentation broth. The present invention develops a green and efficient separation method, which can efficiently separate and recover butanol from ABE fermentation broth, and simultaneously produce high value-added products such as acetone and medium- and long-chain hydrocarbons, thereby reducing separation costs and improving the economy of the overall process.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for separating and purifying butanol from ABE fermentation broth, comprising the following steps:

[0008] 1) filtering the ABE fermentation broth through a microfiltration membrane to obtain a microfiltration membrane filtrate;

[0009] The ABE fermentation broth contains acetone, butanol and ethanol, and the total mass percentage of acetone, butanol and ethanol in the ABE fermentation broth is 1-2%;

[0010] 2) selectively permeating the microfiltration membrane filtrate obtained in step 1) through a pervaporation membrane to obtain permeate vapor under vacuum conditions; the total mass percentage of acetone, butanol and ethanol in the permeate vapor is 30wt% to 50wt%;

[0011] The permeation pressure of the vacuum condition is 100Pa to 5000Pa;

[0012] 3) introducing the permeate steam obtained in step 2) into a first condenser and a second condenser in sequence to obtain a first condensation product and a second condensation product; the first condenser and the second condenser are in a series relationship;

[0013] The condensation temperature of the first condenser is -10°C to -40°C, and the condensation temperature of the second condenser is -40 to -196°C;

[0014] 4) mixing the first condensation product obtained in step 3) with salt to obtain an aqueous phase and an organic phase;

[0015] 5) passing the organic phase obtained in step 4) through a superwetting membrane to obtain a superwetting membrane filtrate;

[0016] 6) The superwetting membrane filtrate obtained in step 5) is mixed with anhydrous salt, and then filtered through a superwetting membrane to obtain butanol.

[0017] Preferably, the pore size of the microfiltration membrane in step 1) is 0.1-1 μm.

[0018] Preferably, the flow rate of the microfiltration membrane filtrate in step 2) through the pervaporation membrane is 20 to 120 L / h;

[0019] The temperature of the microfiltration membrane filtrate passing through the pervaporation membrane is 30 to 70°C;

[0020] The pervaporation membrane is an organophilic pervaporation membrane;

[0021] The pressure on the permeation side of the pervaporation membrane is 100-5000 Pa.

[0022] Preferably, the salt in step 4) includes one or more of potassium carbonate, potassium phosphate, potassium dihydrogen phosphate, potassium pyrophosphate and dipotassium hydrogen phosphate.

[0023] Preferably, the concentration of the salt in the first condensation product of step 4) is 350-550 g / kg.

[0024] Preferably, the superwetting membranes in step 5) and step 6) both include a porous support and a functional coating, and the pore size of the superwetting membrane is 0.1-2 μm.

[0025] Preferably, the anhydrous salt in step 6) includes one or more of anhydrous potassium carbonate, anhydrous potassium phosphate, anhydrous potassium dihydrogen phosphate, anhydrous potassium pyrophosphate and anhydrous dipotassium hydrogen phosphate.

[0026] Preferably, the amount of the anhydrous salt added is 10-20 wt % of the mass of the super-wet membrane filtrate.

[0027] Preferably, the second condensation product in step 3) is mixed with anhydrous salt, and after passing through a superwetting membrane, the filtrate is catalytically alkylated to obtain long-chain alkanes and acetone.

[0028] Preferably, the amount of the anhydrous salt added is 10-20 wt% of the mass of the second condensate;

[0029] The anhydrous salt includes one or more of anhydrous potassium carbonate, anhydrous potassium phosphate, anhydrous potassium dihydrogen phosphate, anhydrous potassium pyrophosphate and anhydrous dipotassium hydrogen phosphate.

[0030] The present invention utilizes the difference in affinity and mass transfer resistance of ABE and water in the feed liquid by the pervaporation membrane to realize selective extraction and enrichment of ABE products. At the same time, considering that acetone, butanol and ethanol in the permeation product have different condensation potentials, the butanol in the permeation steam can be effectively separated from acetone and ethanol by the graded condensation technology. The first-stage condensation with a relatively high temperature obtains a butanol aqueous solution (a high-purity final product can be obtained by dehydration only), and the remaining uncondensed gas enters the second-stage condensation with a lower temperature. For the separation of butanol water, the present invention utilizes the low polarity and poor water solubility of butanol, adds salt as an enhanced phase separation agent, so that butanol and water form an immiscible phase, butanol quickly penetrates through the non-polar interaction with the super-wetting membrane, and the salt solution is retained, thereby realizing the separation of butanol and water with extremely low energy consumption. In addition, the high-purity ABE solution obtained by the second-stage condensation is subjected to a catalytic reaction to obtain medium- and long-chain hydrocarbons and acetone with higher added value after being absorbed and dehydrated by the salt.

[0031] The present invention gives full play to the advantages of several separation technologies, while avoiding inherent deficiencies, making the ABE extraction, separation and purification process green, efficient and energy-saving, greatly reducing the separation cost of the product, and improving the economy of the overall process of biological butanol production. In this process, the pervaporation membrane gives full play to the preferential dissolution and diffusion performance of ABE in the fermentation broth, and there is no need to worry about the problem of low butanol selectivity caused by competitive permeation of acetone and ethanol; salt is used as a phase-separating agent only for the permeate after product concentration, which is energy-saving and efficient and avoids the problem of large salt dosage and difficulty in reuse. In addition, the high-purity ABE solution obtained by the second-stage condensation is subjected to a catalytic reaction after salt dehydration to obtain a product with higher added value. In this way, all product separations are completely free from the high-energy-consuming and investment-intensive distillation process, which shows great application potential in actual bio-butanol production.

[0032] For the fermentation broth, pervaporation-graded condensation technology is used to efficiently extract ABE while simultaneously achieving effective separation of butanol from acetone and ethanol. Products mainly consisting of butanol and water are obtained in the first-stage condenser, and an ABE solution mainly consisting of acetone is obtained in the second-stage condenser.

[0033] Salts that are easily soluble in water but insoluble in ABE (potassium carbonate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium phosphate, potassium pyrophosphate) are added to the primary and secondary condensation products to promote liquid-liquid phase separation, and the super-wetting membrane selectively passes through the organic phase to obtain the product.

[0034] The first-stage condensate is subjected to salting out and dehydration to obtain butanol product; the second-stage condensate is subjected to salting out and dehydration to obtain ABE product, and the ABE product enters the catalytic alkylation unit to obtain acetone and medium- and long-chain alkanes.

[0035] The salts used in the process to enhance phase separation and water absorption can be recovered and recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0037] Figure 1 Flow chart for separating and purifying butanol from ABE fermentation broth, raw material tank 1, pump 2, pervaporation membrane assembly 3, condenser 4, condenser 5, vacuum regulating valve 6, vacuum pump 7, liquid storage tank 8, super-wet membrane assembly 9, liquid storage tank 10, super-wet membrane assembly 11, salt warehouse 12, liquid storage tank 13, super-wet membrane assembly 14, pump 15. DETAILED DESCRIPTION

[0038] The present invention provides a method for separating and purifying butanol from ABE fermentation broth, comprising the following steps:

[0039] 1) filtering the ABE fermentation broth through a microfiltration membrane to obtain a microfiltration membrane filtrate;

[0040] The ABE fermentation broth contains acetone, butanol and ethanol, and the total mass percentage of acetone, butanol and ethanol in the ABE fermentation broth is 1-2wt%;

[0041] 2) selectively permeating the microfiltration membrane filtrate obtained in step 1) through a pervaporation membrane to obtain permeate vapor under vacuum conditions; the total mass percentage of acetone, butanol and ethanol in the permeate vapor is 30wt% to 50wt%;

[0042] The permeation pressure of the vacuum condition is 100Pa to 5000Pa;

[0043] 3) introducing the permeate steam obtained in step 2) into a first condenser and a second condenser in sequence to obtain a first condensation product and a second condensation product; the first condenser and the second condenser are in a series relationship;

[0044] The condensation temperature of the first condenser is -10°C to -40°C, and the condensation temperature of the second condenser is -40 to -196°C;

[0045] 4) mixing the first condensation product obtained in step 3) with salt to obtain an aqueous phase and an organic phase;

[0046] 5) passing the organic phase obtained in step 4) through a superwetting membrane to obtain a superwetting membrane filtrate;

[0047] 6) The superwetting membrane filtrate obtained in step 5) is mixed with anhydrous salt, and then filtered through a superwetting membrane to obtain butanol.

[0048] The present invention filters the ABE fermentation broth through a microfiltration membrane to obtain a microfiltration membrane filtrate; the ABE fermentation broth contains acetone, butanol and ethanol, and the total mass percentage of acetone, butanol and ethanol in the ABE fermentation broth is 1-2wt%. The present invention does not specifically limit the preparation method of the ABE fermentation broth, and it can be prepared by a conventional fermentation method in the art. In the present invention, the total mass percentage of acetone, butanol and ethanol in the ABE fermentation broth is preferably 1.5%. In the present invention, the pore size of the microfiltration membrane is 0.1-1 μm. In the present invention, the microfiltration membrane intercepts the microbial cells and the solid suspended matter in the fermentation broth, thereby reducing the contamination of the pervaporation membrane and improving the separation efficiency. In the present invention, the microfiltration membrane is preferably a molecular sieve membrane, a stainless steel membrane, polystyrene, polyvinylidene fluoride, polytetrafluoroethylene, nylon, polyester, polycarbonate, polyethylene, polypropylene, polysulfone, polyacrylonitrile or a cellulose membrane.

[0049] The present invention permeates the obtained microfiltration membrane filtrate through a pervaporation membrane to obtain a permeate. In the present invention, the flow rate of the microfiltration membrane filtrate through the pervaporation membrane is preferably 20 to 120 L / h, more preferably 50 to 100 L / h. In the present invention, the temperature of the microfiltration membrane filtrate through the pervaporation membrane is preferably 30 to 70°C, more preferably 50 to 60°C. In the present invention, the pervaporation membrane is preferably a silicone rubber flat membrane. In the present invention, the osmotic pressure of the microfiltration membrane filtrate through the pervaporation membrane is preferably 100Pa to 5000Pa.

[0050] The present invention introduces the obtained permeate into the first condenser and the second condenser in sequence to obtain the first condensation product and the second condensation product; the first condenser and the second condenser are in a series relationship; the condensation temperature of the first condenser is -10°C to -40°C, and the condensation temperature of the second condenser is -40 to -196°C.

[0051] The present invention mixes the obtained first condensation product with a salt to obtain an aqueous phase and an organic phase. In the present invention, the salt preferably includes one or more of potassium carbonate, potassium phosphate, potassium dihydrogen phosphate, potassium pyrophosphate and dipotassium hydrogen phosphate. In the present invention, the concentration of the salt in the first condensation product is 350 to 550 g / kg.

[0052] The present invention passes the obtained organic phase through a superwetting membrane to obtain a superwetting membrane filtrate. In the present invention, the superwetting membrane includes a porous support and a functional coating, and the pore size of the superwetting membrane is 0.1 to 2 μm. The surface functional coating can be an organic small molecule, including but not limited to a silicone coupling agent, an alkylamine, an amine-containing aromatic compound, etc.; it can also be a polymer, including but not limited to polymethyl methacrylate, polybutyl methacrylate, polystyrene, polybenzyl methacrylate, polymethacrylate N, N-dimethylaminoethyl, polyacrylic acid, polyacrylamide, poly-N-isopropylacrylamide, poly-N, N-dimethylacrylamide, polymethacryloylethylsulfonic acid betaine, polymethacryloylethyl carbonate betaine, poly-2-acrylamide-2-methylpropanesulfonic acid, poly(2-methacryloyloxyethyl phosphorylcholine), etc. In the present invention, the porous support may be rigid, including but not limited to porous stainless steel, porous nickel, porous titanium, porous ceramics, porous glass, etc.; it may also be flexible, including but not limited to cellulose derivatives, polysulfones, polyimides, polyesters, polyolefins, fluorine-containing polymers, etc. The coating is coated on the porous support. In the present invention, the porous support may be a rigid inorganic material or a flexible organic material, and the functional coating may be an organic small molecule or a polymer. The present invention coats a suitable functional coating on the surface of the porous support to regulate the super-wetting behavior of each phase after liquid-liquid phase separation on the surface of the porous membrane, so that it selectively wets one of the phases and excludes the other phase, thereby achieving separation.

[0053] The present invention mixes the obtained super-wetting membrane filtrate with anhydrous salt, and then filters it through the super-wetting membrane to obtain butanol. In the present invention, the anhydrous salt preferably includes one or more of anhydrous potassium carbonate, anhydrous potassium phosphate, anhydrous potassium dihydrogen phosphate, anhydrous potassium pyrophosphate and anhydrous dipotassium hydrogen phosphate. In the present invention, the addition amount of the anhydrous salt is 10 to 20 wt% of the mass of the super-wetting membrane filtrate.

[0054] In the present invention, the obtained second condensate product is preferably mixed with anhydrous salt, and after passing through a super-wetting membrane, the obtained ABE product is transported to a catalytic alkylation unit for oligomerization and hydrogenation under the action of a catalyst. Since the main product acetone has carbon as a nucleophilic reaction site, it can form a CC bond with the carbon of electrophilic ethanol or n-butanol, and lose an equivalent amount of water at the same time, so the carbon chain can be extended. Then, medium- and long-chain alkanes and acetone products are finally obtained by separation. In the present invention, the addition amount of the anhydrous salt is 10 to 20 wt% of the mass of the second condensate. In the present invention, the anhydrous salt preferably includes one or more of anhydrous potassium carbonate, anhydrous potassium dihydrogen phosphate, anhydrous potassium pyrophosphate, anhydrous potassium phosphate and anhydrous dipotassium hydrogen phosphate.

[0055] In the present invention, when the mass concentration of the total solvent of acetone, butanol and ethanol in the fermentation broth in the fermentation unit reaches 1.0-2.0wt%, the fermentation broth is filtered through a microfiltration membrane and transported to a raw material tank 1 and heated to 30-70°C. The feed liquid is transported to the permeation vaporization membrane assembly 3 by a pump 2, and circulates between the upstream side of the membrane and the raw material tank 1, and the flow rate is controlled at 60L / h. The permeation steam is introduced into two condensers 4 and 5 in series by vacuuming on the downstream side of the membrane, and the permeation pressure is coordinated and controlled by a vacuum regulating valve 6 and a vacuum pump 7. The temperature of the condenser 4 is controlled at -10 to -40°C, which is used to condense as much butanol as possible in the permeation steam and condense as little acetone and ethanol as possible, and the obtained product enters the liquid storage tank 8. The temperature of the condenser 5 is between -50 and -196°C to completely capture the permeation steam that is not condensed in the condenser 4, and the obtained product enters the liquid storage tank 13. Add salt to the product in the liquid storage tank 8 to control the salt concentration in the tank to 400-500g / kg. Under the action of salt, the liquid-liquid phase separation of water and butanol in the product is strengthened, and the super-wetting membrane component 9 selectively enters the liquid storage tank 10 through the organic phase butanol. Add anhydrous salt from the salt warehouse 12 to the liquid storage tank 10 to absorb a small amount of water in the butanol, and obtain a high-purity butanol product after filtering through the super-wetting membrane component 11. Add anhydrous salt from the salt warehouse 12 to the liquid storage tank 13 to absorb a small amount of water in the product ABE of the condenser 5, and obtain a high-purity ABE product after filtering through the super-wetting membrane component 14. The ABE product is transported to the catalytic alkylation unit to finally obtain medium- and long-chain alkanes and acetone products. The anhydrous salt added to the liquid storage tanks 10 and 13 is transported to the liquid storage tank 8 for recycling by pump 15 when it gradually absorbs water to become a saturated salt solution and separates at the bottom. When the salt solution in the liquid storage tank 8 is excessive, it is discharged into the salt recovery unit after the phase separation in the tank is stable. When the total concentration of ABE in the raw material tank 1 drops below 0.3wt%, it exchanges heat with the liquid to be extracted and then returns to the fermentation unit.

[0056] In order to further illustrate the present invention, the present invention is described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] When the total mass concentration of acetone, butanol and ethanol in the fermentation broth in the fermentation unit reaches 2.0wt%, the fermentation broth is filtered through a 0.22μm polytetrafluoroethylene microfiltration membrane and transported to the raw material tank 1. The total mass of the microfiltrate is 10kg, of which the ABE mass ratio is about 3:6:1, and it is heated to 60°C. The feed liquid is transported to the pervaporation membrane assembly 3 by pump 2, and circulates between the upstream side of the membrane and the raw material tank 1, and the flow rate is controlled at 60L / h. The pervaporation membrane used in the pervaporation membrane assembly is a silicone rubber flat membrane. The downstream side of the membrane introduces the permeation steam into two condensers 4 and 5 in series by vacuuming, and the permeation pressure is controlled at 1000Pa. The temperature of condenser 4 is controlled at -25°C, and 95.9wt% of butanol in the pervaporation steam is condensed here, and the obtained product enters the liquid storage tank 8, in which butanol accounts for 31.5wt%, and acetone and ethanol account for 0.21wt%. The temperature of condenser 5 is -196°C, and the uncondensed gas in condenser 4 is condensed here. The obtained product enters liquid storage tank 13, in which butanol accounts for 7.2wt%, and acetone and ethanol account for 77.4wt%. Potassium carbonate is added to the product in liquid storage tank 8 to control the salt concentration in the tank to 450g / kg. The ABE dissolved in the aqueous phase in the product migrates to the organic phase under the action of salt, and the organic phase selectively passes through the super-wetting membrane component 9 and enters the liquid storage tank 10. The membrane used in the super-wetting membrane components 9, 11, and 14 is a polytetrafluoroethylene flat membrane with a pore size of 0.22μm. Anhydrous potassium carbonate from salt warehouse 12 is added to liquid storage tank 10, and the addition amount is 10% of the mass of the feed liquid entering liquid storage tank 10 to absorb and remove a small amount of water in the product. After filtering through the super-wetting membrane component 11, 106.34g of butanol product with a purity of 99.2wt% is obtained, and the overall recovery rate of butanol is about 87.9%. Anhydrous potassium carbonate from salt warehouse 12 is added to liquid storage tank 13, and the amount added is 15% of the mass of the feed liquid entering liquid storage tank 13 to absorb a small amount of water in the product ABE of condenser 5, and a high-purity ABE product is obtained by filtering through super-wetting membrane assembly 14. The ABE product is transported to the catalytic alkylation unit for oligomerization and hydrogenation, and then the medium- and long-chain alkanes and acetone products are finally obtained by separation. The anhydrous salt added to liquid storage tanks 10 and 13 is gradually absorbed by water to become a saturated salt solution and phase separated at the bottom. It is transported to liquid storage tank 8 for recycling through pump 15. When the salt solution inside liquid storage tank 8 is excessive, it is discharged into the salt recovery unit after the phase separation in the tank is stable. When the total concentration of ABE in raw material tank 1 drops below 0.3wt%, it is returned to the fermentation unit after heat exchange with the feed liquid to be extracted.

[0059] Example 2

[0060] When the mass concentration of the total solvent of acetone, butanol and ethanol in the fermentation broth in the fermentation unit reaches 1.5wt%, the fermentation broth is filtered through a 0.22μm polyvinylidene fluoride microfiltration membrane and transported to the raw material tank 1. The total mass of the microfiltrate is 15kg, of which the ABE mass ratio is about 3:6:1, and it is heated to 55°C. The feed liquid is transported to the pervaporation membrane assembly 3 by pump 2, and circulates between the upstream side of the membrane and the raw material tank 1, and the flow rate is controlled at 50L / h. The pervaporation membrane used in the pervaporation membrane assembly is a silicone rubber flat membrane. The downstream side of the membrane introduces the permeation steam into two condensers 4 and 5 in series by vacuuming, and the permeation pressure is controlled at 1500Pa. The temperature of condenser 4 is controlled at -30°C, and 96.8wt% of butanol in the pervaporation steam is condensed here, and the obtained product enters the liquid storage tank 8, in which butanol accounts for 31.1wt%, and acetone and ethanol account for 0.6wt%. The temperature of condenser 5 is -196°C, and the uncondensed gas in condenser 4 is condensed here. The obtained product enters liquid storage tank 13, in which butanol accounts for 7.2wt%, and acetone and ethanol account for 78.5wt%. Potassium phosphate is added to the product in liquid storage tank 8 to control the salt concentration in the tank at 500g / kg. The ABE dissolved in the aqueous phase in the product migrates to the organic phase under the action of salt, and the organic phase selectively passes through the super-wetting membrane component 9 and enters the liquid storage tank 10. The membrane used in the super-wetting membrane components 9, 11, and 14 is a polytetrafluoroethylene flat membrane with a pore size of 0.22μm. Anhydrous potassium phosphate from salt warehouse 12 is added to liquid storage tank 10, and the addition amount is 15% of the mass of the feed liquid entering liquid storage tank 10 to absorb and remove a small amount of water in the product. After filtering through the super-wetting membrane component 11, 117.15g of butanol product with a purity of 99.1wt% is obtained, and the overall recovery rate of butanol is about 86%. Anhydrous potassium phosphate from the salt warehouse 12 is added to the liquid storage tank 13, and the amount added is 20% of the mass of the feed liquid entering the liquid storage tank 13 to absorb a small amount of water in the product ABE of the condenser 5, and a high-purity ABE product is obtained by filtering through the super-wetting membrane component 14. The ABE product is transported to the catalytic alkylation unit to finally obtain medium- and long-chain alkanes and acetone products. The anhydrous salt added to the liquid storage tanks 10 and 13 is gradually absorbed by water to become a saturated salt solution and phase separated at the bottom. It is transported to the liquid storage tank 8 for recycling through the pump 15. When the salt solution inside the liquid storage tank 8 is excessive, it is discharged into the salt recovery unit after the phase separation in the tank is stable. When the total concentration of ABE in the raw material tank 1 drops below 0.3wt%, it is returned to the fermentation unit after heat exchange with the feed liquid to be extracted.

[0061] Example 3

[0062] When the mass concentration of the total solvent of acetone, butanol and ethanol in the fermentation broth in the fermentation unit reaches 1.0wt%, the fermentation broth is filtered through a 0.22μm polytetrafluoroethylene microfiltration membrane and transported to the raw material tank 1. The total mass of the microfiltrate is 20kg, of which the ABE mass ratio is about 3:6:1, and it is heated to 40°C. The feed liquid is transported to the pervaporation membrane assembly 3 by pump 2, and circulates between the upstream side of the membrane and the raw material tank 1, and the flow rate is controlled at 40L / h. The pervaporation membrane used in the pervaporation membrane assembly is a silicone rubber flat membrane. The downstream side of the membrane introduces the permeation steam into two condensers 4 and 5 in series by vacuuming, and the permeation pressure is controlled at 1000Pa. The temperature of condenser 4 is controlled at -30°C, and 95.1wt% of butanol in the pervaporation steam is condensed here, and the obtained product enters the liquid storage tank 8, in which butanol accounts for 26.6wt%, and acetone and ethanol account for 0.9wt%. The temperature of condenser 5 is -196°C, and the uncondensed gas in condenser 4 is condensed here. The obtained product enters liquid storage tank 13, in which butanol accounts for 6.6wt%, and acetone and ethanol account for 67.9wt%. Potassium hydrogen phosphate is added to the product in liquid storage tank 8 to control the salt concentration in the tank at 500g / kg. The ABE dissolved in the aqueous phase of the product migrates to the organic phase under the action of salt, and the organic phase selectively passes through the super-wetting membrane component 9 and enters liquid storage tank 10. Anhydrous potassium hydrogen phosphate from salt warehouse 12 is added to liquid storage tank 10, and the addition amount is 12% of the mass of the feed liquid entering liquid storage tank 10 to absorb and remove a small amount of water in the product. After filtration through super-wetting membrane component 11, 96.1g of butanol product with a purity of 99wt% is obtained, and the overall recovery rate of butanol is about 79.3%. Anhydrous potassium hydrogen phosphate from salt warehouse 12 is added to liquid storage tank 13, and the amount added is 20% of the mass of the feed liquid entering liquid storage tank 13 to absorb a small amount of water in the product ABE of condenser 5, and a high-purity ABE product is obtained by filtering through super-wetting membrane assembly 14. The ABE product is transported to the catalytic alkylation unit to finally obtain medium- and long-chain alkanes and acetone products. The anhydrous salt added to liquid storage tanks 10 and 13 is transported to liquid storage tank 8 for recycling by pump 15 when it gradually absorbs water to become a saturated salt solution and separates phases at the bottom. When there is an excess of salt solution in liquid storage tank 8, it is discharged into the salt recovery unit after the phase separation in the tank is stable. When the total concentration of ABE in raw material tank 1 drops below 0.3wt%, it is returned to the fermentation unit after heat exchange with the feed liquid to be extracted.

[0063] Although the above embodiment describes the present invention in detail, 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 protection scope of the present invention.

Claims

1. A method for separating and purifying butanol from ABE fermentation broth, characterized in that: The following steps are involved: 1) filtering the ABE fermentation broth through a microfiltration membrane to obtain a microfiltration membrane filtrate; The ABE fermentation broth contains acetone, butanol and ethanol, and the total mass percentage of acetone, butanol and ethanol in the ABE fermentation broth is 1-2wt%; 2) selectively permeating the microfiltration membrane filtrate obtained in step 1) through a pervaporation membrane to obtain permeate vapor under vacuum conditions; the total mass percentage of acetone, butanol and ethanol in the permeate vapor is 30wt% to 50wt%; The permeation pressure of the vacuum condition is 100Pa to 5000Pa; 3) introducing the permeate steam obtained in step 2) into a first condenser and a second condenser in sequence to obtain a first condensation product and a second condensation product; the first condenser and the second condenser are in a series relationship; The condensation temperature of the first condenser is -10°C to -40°C, and the condensation temperature of the second condenser is -40 to -196°C; 4) mixing the first condensation product obtained in step 3) with salt to obtain an aqueous phase and an organic phase; 5) passing the organic phase obtained in step 4) through a superwetting membrane to obtain a superwetting membrane filtrate; 6) The superwetting membrane filtrate obtained in step 5) is mixed with anhydrous salt, and then filtered through a superwetting membrane to obtain butanol.

2. The method according to claim 1, characterized in that The pore size of the microfiltration membrane in step 1) is 0.1-1 μm.

3. The method according to claim 1, characterized in that The flow rate of the microfiltration membrane filtrate in step 2) passing through the pervaporation membrane is 20 to 120 L / h; The temperature of the microfiltration membrane filtrate passing through the pervaporation membrane is 30 to 70°C; The pervaporation membrane is an organophilic pervaporation membrane; The pressure on the permeation side of the pervaporation membrane is 100-5000 Pa.

4. The method according to claim 1, characterized in that The salt in step 4) includes one or more of potassium carbonate, potassium phosphate, potassium dihydrogen phosphate, potassium pyrophosphate and dipotassium hydrogen phosphate.

5. The method according to claim 1 or 4, characterized in that: In step 4), the concentration of the salt in the first condensation product is 350-550 g / kg.

6. The method according to claim 1, characterized in that The superwetting membranes in step 5) and step 6) both include a porous support and a functional coating, and the pore size of the superwetting membrane is 0.1-2 μm.

7. The method according to claim 1, characterized in that The anhydrous salt in step 6) includes one or more of anhydrous potassium carbonate, anhydrous potassium phosphate, anhydrous potassium dihydrogen phosphate, anhydrous potassium pyrophosphate and anhydrous dipotassium hydrogen phosphate.

8. The method according to claim 1 or 7, characterized in that: The amount of the anhydrous salt added is 10-20 wt % of the mass of the super-wet membrane filtrate.

9. The method according to claim 1 or 7, characterized in that: In the step 3), the second condensed product is mixed with anhydrous salt, and after passing through a super-wetting membrane, the filtrate is catalytically alkylated to obtain long-chain alkanes and acetone.

10. The method according to claim 9, characterized in that The amount of the anhydrous salt added is 10-20 wt% of the mass of the second condensate; The anhydrous salt includes one or more of anhydrous potassium carbonate, anhydrous potassium dihydrogen phosphate, anhydrous potassium pyrophosphate, anhydrous potassium phosphate and anhydrous dipotassium hydrogen phosphate.

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