Lignin-based polymer pervaporation membrane, preparation method thereof and method for separating and purifying cyclohexane-KA oil

Abstract

The invention relates to a lignin-based polymer pervaporation membrane, a preparation method thereof and a method for separating and purifying cyclohexane-KA oil. The invention aims to provide a pervaporation membrane which is high in permselectivity, high in stability and good in mechanical property. The pervaporation membrane is used for cyclohexane-KA oil separation and has the advantages of high separation efficiency, low energy consumption and simple process. The preparation method comprises the following steps: adding the surfactant, the polymer and the solvent into a reactor, and stirring at 50-70 DEG C for 4-6 hours to obtain a mixed solution; the method comprises the following steps: adding lignin and a solvent into a reactor, and stirring at room temperature for 4-6 hours to obtain a lignin solution; dropwise adding the lignin solution into the mixed solution, and continuously stirring at constant temperature for 12-24 hours to obtain a membrane casting solution; transferring the membrane casting solution to a centrifugal tube, performing centrifugal separation, and uniformly coating the membrane casting solution on an ultrafiltration membrane material with the membrane thickness of 100-200mm to form a uniform liquid membrane; and drying the liquid membrane to obtain the lignin-based polymer pervaporation membrane. Belongs to the technical field of membrane separation.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane separation, and particularly relates to a method for preparing a lignin-based polymer pervaporation membrane and a method for separating and purifying cyclohexane-KA oil. Background Art

[0002] KA oil, a mixture of cyclohexanone and cyclohexanol, is a key intermediate in the production of caprolactam, which is further used in the manufacture of nylon 6 and is widely used in textiles, engineering plastics, and other fields. KA oil is produced through the cyclohexane oxidation reaction. In this reaction, cyclohexane is reacted with a catalyst to produce KA oil, along with unreacted cyclohexane and byproducts. Therefore, in industrial production, the unreacted cyclohexane must be efficiently separated from the KA oil after the cyclohexane oxidation reaction to achieve cyclohexane recovery and KA oil purification.

[0003] At present, the traditional separation methods in industry are distillation, liquid-liquid extraction, and adsorption separation. The distillation method uses the difference in boiling points between cyclohexane (boiling point 80.7°C) and KA oil (cyclohexanone 155.6°C, cyclohexanol 161°C) for fractionation, but the distillation method requires multiple distillations, resulting in high energy consumption and low efficiency during separation, and the equipment is complex and there is a risk of thermal sensitivity. Liquid-liquid extraction uses polarity differences to select solvents (such as water and ethylene glycol) to extract polar components in KA oil, but it also has obvious disadvantages. The cost of solvent recovery is high, new pollutants will be introduced, and environmental pressure will be increased. The adsorption separation method uses molecular sieves or activated carbon to selectively adsorb KA oil. Its limitations are that the adsorbent is difficult to regenerate, the processing volume is small, and it is difficult to industrialize. Summary of the Invention

[0004] To overcome the deficiencies of the prior art, the first object of the present invention is to provide a lignin-based polymer pervaporation membrane having good mechanical properties.

[0005] The second object of the present invention is to provide a method for preparing a lignin-based polymer pervaporation membrane, which is simple to operate.

[0006] Another object of the present invention is to provide a method for separating and purifying cyclohexane-KA oil using a lignin-based polymer pervaporation membrane; the method can have high separation performance for a cyclohexane-KA oil mixture system.

[0007] To this end, the first technical solution provided by the present invention is as follows:

[0008] A method for preparing a lignin-based polymer pervaporation membrane comprises the following steps in sequence:

[0009] 1) adding a surfactant, a polymer, and a solvent into a reactor and stirring at 50-70° C. for 4-6 hours to obtain a mixed solution;

[0010] 2) lignin and solvent are added into the reactor, and stirred at room temperature for 4-6 hours to obtain a lignin solution;

[0011] 3) the lignin solution of step 2) is added dropwise into the mixed solution of step 1), and constant temperature stirring is continued for 12-24 hours to obtain a casting solution;

[0012] 4) the casting solution of step 3) is transferred into a centrifugal tube, and after centrifugal separation, the casting solution is uniformly coated on the ultrafiltration membrane material at a film thickness of 100-200 mm to form a uniform liquid film;

[0013] 5) the liquid film of step 4) is dried, and after the solvent is completely volatilized, a lignin-based polymer pervaporation membrane is obtained;

[0014] The mass ratio of the lignin, the polymer, the surfactant, and the solvent is 1.5-7.5: 5-15: 0.125-0.750: 75-95.

[0015] Further, in the above lignin-based polymer pervaporation membrane preparation method, the lignin is one of alkali lignin, delignified lignin, enzymatic hydrolysis lignin, sodium lignosulfonate, calcium lignosulfonate, and sodium lignosulfate.

[0016] Further, in the above lignin-based polymer pervaporation membrane preparation method, the polymer is one of polyethylene glycol, polyvinylidene fluoride, cellulose diacetate, polyvinyl chloride, polyurethane, polyimide, polyvinylpyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyurethane, and polysulfone.

[0017] Further, in the above lignin-based polymer pervaporation membrane preparation method, the surfactant is one of sodium dodecyl sulfate, sodium alkyl benzene sulfonate, alpha-alkenyl sulfonate, Tween-80, cetyltrimethylammonium bromide, and cocamide propyl betaine.

[0018] Further, in the above lignin-based polymer pervaporation membrane preparation method, the solvent is one of chloroform, tetrahydrofuran, N, N-dimethylformamide, dioctyl phthalate, dichloromethane, and dimethyl sulfoxide.

[0019] The ultrafiltration membrane material is one of cellulose acetate, cellulose acetate ester, polyethylene, polysulfone, polyamide, and polyvinylidene fluoride.

[0020] Furthermore, in the above-mentioned method for preparing a lignin-based polymer pervaporation membrane, the centrifugation in step 3) is performed at a speed of 3000-5000 r / min for 1-5 minutes; and the liquid film drying in step 4) is performed by placing the liquid film in an oven and drying it at 50-70°C for 20-24 hours.

[0021] The second technical solution provided by the present invention is a lignin-based polymer pervaporation membrane, which is prepared by the preparation method described in the first technical solution.

[0022] Another technical solution of the present invention is to use the above-mentioned lignin-based polymer pervaporation membrane for separating and purifying cyclohexane-KA oil.

[0023] Another technical solution of the present invention is a method for separating and purifying cyclohexane-KA oil, which uses the aforementioned lignin-based polymer pervaporation membrane for separation.

[0024] Furthermore, in the above-mentioned method for separating and purifying cyclohexane-KA oil, the cyclohexane-KA oil mixture is added to a feed tank; the feed tank is then placed in a water bath at 50 to 80°C and heated to a constant temperature, and the lignin-based polymer pervaporation membrane obtained in claim 7 is driven by a pressure difference of 0.1 to -0.1 MPa to achieve pervaporation separation, and the filtrate is condensed and collected, and the condensation temperature is -180 to 200°C.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The technical solution provided by this invention utilizes a solvent evaporation phase inversion method to prepare a lignin-based polymer pervaporation membrane. Using lignin and polymer as raw materials, heating during the phase inversion membrane formation process promotes cross-linking of the lignin and polymer, resulting in a stable presence within the polymer separation membrane matrix. This results in a pervaporation membrane with high selectivity, high stability, and excellent mechanical properties. The membrane retains most of the lignin's active groups, such as hydroxyl groups and aromatic ring structures, and the resulting microporous structure of the composite membrane preferentially adsorbs and permeates KA oil, facilitating the separation of cyclohexane and KA oil. Furthermore, the rigid lignin network inhibits swelling of the polymer matrix in organic solvents, maintaining membrane stability and long-term separation efficiency.

[0027] 2. The technical solution provided by the present invention offers simple equipment, convenient operation, low energy consumption, high efficiency, ease of scalability, low cost, and safety during the separation process. The separation process is physical, without chemical reactions, thus reducing environmental impact. Compared to traditional extractive distillation processes, the separation device of the present invention occupies a small footprint, offers safe and simple process operation, and offers high separation performance. It solves the complexities of cyclohexane-KA oil separation, enables continuous separation, is eco-friendly, and is beneficial for industrial production. Furthermore, no new substances are introduced, and subsequent secondary separation is unnecessary. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a gas chromatographic detection diagram of the feed tank liquid in Example 4.

[0029] Figure 2 This is a gas chromatographic detection diagram of the storage tank liquid in Example 4.

[0030] Figure 3 This is a gas chromatographic detection diagram of the storage tank liquid in Example 5. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0032] Unless otherwise specified, all reagents and raw materials used in the present invention can be obtained from commercial sources.

[0033] The polyvinylidene fluoride membrane was purchased from Beijing Sepuret Equipment Co., Ltd. PVDF100000.

[0034] Example 1

[0035] 1) Weigh 0.1 g of sodium lauryl sulfate, 3 g of polyvinylidene fluoride, and 32.67 g of N,N-dimethylformamide into a three-necked flask and place in an oil bath at 50°C with constant temperature mechanical stirring for 4 h;

[0036] 2) Weigh 0.6 g of sodium lignin sulfonate and 3.63 g of N,N-dimethylformamide into a sample bottle, add a stirrer, and stir with a magnetic stirrer at room temperature for 4 h.

[0037] 3) All the lignin dissolved in step 2) was slowly added dropwise to the three-necked flask in step 1), and the mixture was stirred at a constant temperature for 14 h to obtain a casting solution.

[0038] 4) The three-necked flask was removed from the oil pan, and the casting solution in the flask was transferred to a 50 ml centrifuge tube while it was still hot. The tube was centrifuged at 3500 r / min for 4 min. After the centrifugation, the casting solution was evenly coated onto a polyvinylidene fluoride membrane with a thickness of 200 mm using a scraper. The polyvinylidene fluoride membrane coated with the casting solution was placed in an oven at 55°C and dried for 23 h. After the solvent was completely evaporated, a lignin-based polymer pervaporation membrane was obtained.

[0039] Example 2

[0040] 1) Weigh 0.15 g of sodium lauryl sulfate, 3 g of cellulose diacetate, and 32.09 g of N,N-dimethylformamide into a three-necked flask and place in an oil bath at 60°C with constant temperature mechanical stirring for 5 h;

[0041] 2) Weigh 1.2 g of calcium lignosulfonate and 3.57 g of N, N-dimethylformamide into the sample bottle, put in the stirring rod, and stir for 5 h at room temperature on a magnetic stirrer.

[0042] 3) Slowly drop the dissolved lignin of step 2) into the three-necked flask of step 1), continue constant temperature stirring for 16 h to obtain a casting solution.

[0043] 4) Take the three-necked flask out of the oil bath, while hot, transfer the casting solution in it to a 50 ml centrifuge tube, centrifuge at 400 r / min for 3 min, after centrifugation, use a film scraper to uniformly coat the casting solution on the polyvinylidene fluoride membrane at a thickness of 150 mm; put the polyvinylidene fluoride membrane coated with the casting solution into an oven at 60°C to dry into a film for 22 h, after the solvent is completely volatilized, obtain a lignin-based polymer pervaporation membrane.

[0044] Example 3

[0045] 1) Weigh 0.2 g of sodium dodecyl sulfate, 4 g of polyurethane, and 30.60 g of N, N-dimethylformamide into the three-necked flask, constant temperature mechanical stirring for 5 h in the oil bath at 65°C;

[0046] 2) Weigh 1.8 g of sodium lignosulfonate and 3.40 g of N, N-dimethylformamide into the sample bottle, put in the stirring rod, and stir for 5 h at room temperature on a magnetic stirrer.

[0047] 3) Slowly drop the dissolved lignin of step 2) into the three-necked flask of step 1), continue constant temperature stirring for 21 h to obtain a casting solution.

[0048] 4) Take the three-necked flask out of the oil bath, while hot, transfer the casting solution in it to a 50 ml centrifuge tube, centrifuge at 4500 r / min for 2 min, after centrifugation, use a film scraper to uniformly coat the casting solution on the polyvinylidene fluoride membrane at a thickness of 150 mm. Put the polyvinylidene fluoride membrane coated with the casting solution into an oven at 65°C to dry into a film for 21 h, after the solvent is completely volatilized, obtain a lignin-based polymer pervaporation membrane.

[0049] Example 4

[0050] 1) Weigh 0.25 g of sodium dodecyl sulfate, 5 g of polyethylene glycol, and 29.12 g of N, N-dimethylformamide into the three-necked flask, constant temperature mechanical stirring for 6 h in the oil bath at 70°C;

[0051] 2) Weigh 2.4 g of alkali lignin and 3.24 g of N, N-dimethylformamide into the sample bottle, put in the stirring rod, and stir for 6 h at room temperature on a magnetic stirrer.

[0052] 3) The dissolved lignin was slowly added dropwise to the three-necked flask in step 1), and the mixture was stirred at a constant temperature for 20 h to obtain a casting solution.

[0053] 4) Remove the three-necked flask from the oil pan and transfer the hot casting solution to a 50ml centrifuge tube. Centrifuge at 5000 rpm for 1 minute. After centrifugation, use a scraper to evenly coat the casting solution onto the polyvinylidene fluoride membrane to a thickness of 100 mm. Place the polyvinylidene fluoride membrane coated with the casting solution in an oven at 70°C for 20 hours to dry. After complete solvent evaporation, the lignin-based polymer pervaporation membrane is obtained.

[0054] Example 5

[0055] 1) Weigh 0.3 g of sodium lauryl sulfate, 6 g of polyvinylpyrrolidone, and 27.63 g of N,N-dimethylformamide into a three-necked flask and place in an oil bath at 70°C with constant temperature mechanical stirring for 6 h;

[0056] 2) Weigh 3 g of dealkalized lignin and 3.07 g of N,N-dimethylformamide, add them to a sample bottle, put in a stirrer, and stir with a magnetic stirrer at room temperature for 6 h.

[0057] 3) The dissolved lignin was slowly added dropwise to the three-necked flask in step 1), and the mixture was stirred at a constant temperature for 24 hours to obtain a casting solution.

[0058] 4) Remove the three-necked flask from the oil pan and transfer the hot casting solution to a 50ml centrifuge tube. Centrifuge at 5000 rpm for 1 minute. After centrifugation, use a scraper to evenly coat the casting solution onto the polyvinylidene fluoride membrane to a thickness of 100 mm. Place the polyvinylidene fluoride membrane coated with the casting solution in an oven at 70°C for 20 hours to dry. After complete solvent evaporation, the lignin-based polymer pervaporation membrane is obtained.

[0059] Comparative Example 1

[0060] 0.05g of sodium dodecyl sulfate, 2g of polyethylene glycol, and 37.95g of N,N-dimethylformamide were weighed and added to a three-necked flask. The mixture was mechanically stirred in a 50°C oil bath for 16 hours to obtain a casting solution. The three-necked flask was removed from the oil bath and, while still hot, the casting solution was transferred to a 50ml centrifuge tube. The tube was centrifuged at 3000 rpm for 5 minutes. After centrifugation, the casting solution was evenly coated onto a polyvinylidene fluoride membrane with a film scraper to a thickness of 200mm. The polyvinylidene fluoride membrane coated with the casting solution was placed in an oven at 50°C to dry for 24 hours. After complete solvent evaporation, a lignin-based polymer pervaporation membrane was obtained.

[0061] Performance comparison: The tensile properties of the unsupported lignin-based polymer films prepared in Examples 1 to 5 and Comparative Example 1 were compared using an electronic universal testing machine.

[0062] The lignin-based polymer pervaporation membranes prepared in Examples 1-5 and Comparative Example 1 were cut into standard dumbbell shapes of uniform size. A test protocol was created in the software, with the test type set to tensile. The test parameters were entered, and the sample was mounted in the fixture, ensuring a secure grip. The sensor was reset to zero, and the "Start Test" button in the software was clicked. The test was terminated immediately when the sample broke. After the test, the test data was saved and analyzed using Origin. The resulting data is shown in Table 1.

[0063] Table 1 Tensile test results

[0064]

[0065]

[0066] The tensile test results of Examples 1 to 5 and Comparative Example 1 show that with the increase of lignin, both stress and Young's modulus increase, indicating that the addition of lignin can enhance the stability of the polymer film structure, significantly improve the ability of the polymer film to resist deformation within the elastic range, and enhance the mechanical properties of the film.

[0067] Application Example 1

[0068] 0.000314m 2 The lignin-based polymer pervaporation membrane prepared in Example 1 was placed in a membrane assembly device, and a cyclohexane-KA oil mixed solution with a KA oil mass fraction of 10 wt% was passed into a feed tank. The feed tank was placed in a water bath at 60°C and heated to a constant temperature. The cyclohexane-KA oil to be separated in the feed tank entered the separation membrane pool equipped with the lignin-based polymer pervaporation membrane from the lower end of the full filter under the push of a peristaltic pump; through the adsorption and dissolution effect of the lignin-based polymer pervaporation membrane, the KA oil passed through the pervaporation membrane and entered the upper end of the full filter, and under the action of the vacuum pump, flowed into the KA oil storage tank. After 3 hours, the filtration was stopped, the filtrate was collected, the mass of the filtrate was weighed and the mass was recorded as 0.1518 g.

[0069] The pervaporation performance of the membrane is expressed in terms of permeation flux J (g·m -2 ·h -1 ), separation factor α and separation index PSI (g·m -2 ·h -1 ), as shown in formulas (1), (2) and (3), respectively.

[0070]

[0071] PSI=J×α (3)

[0072] Where m (g) represents the total weight of the permeate collected in t hours, A (m 2 ) is the effective area of ​​the membrane, a represents cyclohexane, b represents KA oil, X a and Y a are the cyclohexane concentrations (wt%) on the feed side and the permeate side, X b and Y b are the KA oil concentrations (wt %) on the feed side and the permeate side, respectively.

[0073] The filtrate product was tested by gas chromatography. According to the gas chromatography results, the mass fraction of KA oil was calculated to be 35.45%, and the permeation flux of the membrane was J = m / (A×t) = 0.1518 / (0.000314×3) = 161.13 g·m -2 ·h -1 The separation factor of the membrane is 13.01, and the separation index of the membrane is 2096.03 g·m -2 ·h -1 .

[0074] Application Example 2

[0075] 0.000314m 2 The lignin-based polymer pervaporation membrane prepared in Example 2 was placed in a membrane assembly device, and a cyclohexane-KA oil mixed solution with a KA oil mass fraction of 8 wt% was passed into a feed tank. The feed tank was placed in a 70°C water bath and heated to a constant temperature. The cyclohexane-KA oil to be separated in the feed tank entered the separation membrane pool equipped with the lignin-based polymer pervaporation membrane from the lower end of the full filter under the push of a peristaltic pump; through the adsorption and dissolution effect of the lignin-based polymer pervaporation membrane, the KA oil passed through the pervaporation membrane and entered the upper end of the full filter, and under the action of the vacuum pump, flowed into the KA oil storage tank. After 3 hours, the filtration was stopped, the filtrate was collected, the mass of the filtrate was weighed and the mass was recorded as 0.1144 g.

[0076] The pervaporation performance of the membrane is expressed in terms of permeation flux J (g·m -2 ·h -1 ), separation factor α and separation index PSI (g·m -2 ·h -1 ), as shown in formulas (1), (2) and (3), respectively.

[0077]

[0078] PSI=J×α (3)

[0079] Where m (g) represents the total weight of the permeate collected in t hours, A (m2 ) is the effective area of ​​the membrane, a represents cyclohexane, b represents KA oil, X a and Y a are the cyclohexane concentrations (wt%) on the feed side and the permeate side, X b and Y b are the KA oil concentrations (wt %) on the feed side and the permeate side, respectively.

[0080] The filtrate product was tested by gas chromatography. According to the gas chromatography results, the mass fraction of KA oil was 57.68%, and the permeation flux of the membrane was 121.42 g·m -2 ·h -1 The separation factor of the membrane is 17.87, and the separation index of the membrane is 2169.43 g·m -2 ·h -1 .

[0081] Application Example 3

[0082] 0.000314m 2 The lignin-based polymer pervaporation membrane prepared in Example 3 was placed in a membrane assembly device, and a cyclohexane-KA oil mixed solution with a KA oil mass fraction of 8 wt% was passed into a feed tank. The feed tank was placed in a 70°C water bath and heated to a constant temperature. The cyclohexane-KA oil to be separated in the feed tank entered the separation membrane pool equipped with the lignin-based polymer pervaporation membrane from the lower end of the full filter under the push of a peristaltic pump; through the adsorption and dissolution effect of the lignin-based polymer pervaporation membrane, the KA oil passed through the pervaporation membrane and entered the upper end of the full filter, and under the action of the vacuum pump, flowed into the KA oil storage tank. After 3 hours, the filtration was stopped, the filtrate was collected, the mass of the filtrate was weighed and the mass was recorded as 0.0396 g.

[0083] The pervaporation performance of the membrane is expressed in terms of permeation flux J (g·m -2 ·h -1 ), separation factor α and separation index PSI (g·m -2 ·h -1 ), as shown in formulas (1), (2) and (3), respectively.

[0084]

[0085] PSI=J×α (3)

[0086] Where m (g) represents the total weight of the permeate collected in t hours, A (m 2 ) is the effective area of ​​the membrane, a represents cyclohexane, b represents KA oil, X a and Y a are the cyclohexane concentrations (wt%) on the feed side and the permeate side, X b and Yb are the KA oil concentrations (wt %) on the feed side and the permeate side, respectively.

[0087] The obtained filtrate product was detected by gas chromatography, and the chromatogram is shown in Figure 1 、 Figure 2 According to the gas chromatography results, the mass fraction of KA oil was 98.62% and the permeation flux of the membrane was 42.01 g·m -2 ·h -1 The separation factor of the membrane is 961.27, and the separation index of the membrane is 40378.32 g·m -2 ·h -1 .

[0088] Application Example 4

[0089] 0.000314m 2 The lignin-based polymer pervaporation membrane prepared in Example 4 was placed in a membrane assembly device, and a cyclohexane-KA oil mixed solution with a KA oil mass fraction of 6 wt% was passed into a feed tank. The feed tank was placed in a water bath at 80°C and heated to a constant temperature. The cyclohexane-KA oil to be separated in the feed tank entered the separation membrane pool equipped with the lignin-based polymer pervaporation membrane from the lower end of the full filter under the push of a peristaltic pump; through the adsorption and dissolution effect of the lignin-based polymer pervaporation membrane, the KA oil passed through the pervaporation membrane and entered the upper end of the full filter, and under the action of the vacuum pump, flowed into the KA oil storage tank. After 3 hours, the filtration was stopped, the filtrate was collected, the mass of the filtrate was weighed and the mass was recorded as 0.0342 g.

[0090] The pervaporation performance of the membrane is expressed in terms of permeation flux J (g·m -2 ·h -1 ), separation factor α and separation index PSI (g·m -2 ·h -1 ), as shown in formulas (1), (2) and (3), respectively.

[0091]

[0092] PSI=J×α (3)

[0093] Where m (g) represents the total weight of the permeate collected in t hours, A (m 2 ) is the effective area of ​​the membrane, a represents cyclohexane, b represents KA oil, X a and Y a are the cyclohexane concentrations (wt%) on the feed side and the permeate side, X b and Y b are the KA oil concentrations (wt %) on the feed side and the permeate side, respectively.

[0094] The filtrate product was tested by gas chromatography, and the chromatogram is shown in Figure 3 According to the gas chromatography results, the mass fraction of KA oil was 98.91%, and the permeation flux of the membrane was 36.34 g·m -2 ·h -1 The separation factor of the membrane is 1054.32, and the separation index of the membrane is 38313.97 g·m -2 ·h -1 .

[0095] Application Example 5

[0096] 0.000314m 2 The lignin-based polymer pervaporation membrane prepared in Example 5 was placed in a membrane assembly device, and a cyclohexane-KA oil mixed solution with a KA oil mass fraction of 6 wt% was passed into a feed tank. The feed tank was placed in a water bath at 80°C and heated to a constant temperature. The cyclohexane-KA oil to be separated in the feed tank entered the separation membrane pool equipped with the lignin-based polymer pervaporation membrane from the lower end of the full filter under the push of a peristaltic pump; through the adsorption and dissolution effect of the lignin-based polymer pervaporation membrane, the KA oil passed through the pervaporation membrane and entered the upper end of the full filter, and under the action of the vacuum pump, flowed into the KA oil storage tank. After 3 hours, the filtration was stopped, the filtrate was collected, the mass of the filtrate was weighed and the mass was recorded as 0.0116 g.

[0097] The pervaporation performance of the membrane is expressed in terms of permeation flux J (g·m -2 ·h -1 ), separation factor α and separation index PSI (g·m -2 ·h -1 ), as shown in formulas (1), (2) and (3), respectively.

[0098]

[0099] PSI=J×α (3)

[0100] Where m (g) represents the total weight of the permeate collected in t hours, A (m 2 ) is the effective area of ​​the membrane, a represents cyclohexane, b represents KA oil, X a and Y a are the cyclohexane concentrations (wt%) on the feed side and the permeate side, X b and Y b are the KA oil concentrations (wt %) on the feed side and the permeate side, respectively.

[0101] The filtrate product was tested by gas chromatography. According to the gas chromatography results, the mass fraction of KA oil was 84.62%, and the permeation flux of the membrane was 12.31 g·m -2 ·h-1 The separation factor of the membrane was 70.58, and the separation index of the membrane was 868.80 g·m -2 ·h -1 .

[0102] Comparative Example 1

[0103] 0.000314 m 2 Comparative Example 1 The lignin-based polymeric pervaporation membrane was placed in a membrane module device, a cyclohexane-KA oil mixed solution with a KA oil mass fraction of 10 wt% was introduced into the feed tank, the feed tank was placed in a water bath at 50℃ for heating to constant temperature, the cyclohexane-KA oil to be separated in the feed tank was pushed by the peristaltic pump, entered the separation membrane pool containing the lignin-based polymeric pervaporation membrane from the lower end of the full volume filter; through the adsorption and dissolution of the lignin-based polymeric pervaporation membrane, KA oil permeated through the pervaporation membrane into the upper end of the full volume filter, under the action of the vacuum pump, flowed into the KA oil storage tank, after 3 h, the filtration was stopped, the filtrate was collected, the mass of the filtrate was weighed and recorded as 1.2392 g.

[0104] The pervaporation performance of the membrane was represented by permeation flux J (g·m -2 ·h -1 ), separation factor a and separation index PSI (g·m -2 ·h -1 ), respectively represented by formula (1), (2) and (3).

[0105]

[0106] PSI = J x a (3)

[0107] Wherein m (g) represents the total weight of the permeate collected in t hours, A (m 2 ) is the effective area of the membrane, a represents cyclohexane, b represents KA oil, X a and Y a are the cyclohexane concentrations (wt%) on the feed side and the permeation side, respectively, X b and Y b are the KA oil concentrations (wt%) on the feed side and the permeation side, respectively.

[0108] The filtrate product obtained by gas chromatography was detected, and according to the gas chromatography results, the mass fraction of KA oil was calculated as 2.51%, the permeation flux of the membrane was 1315.46 g·m -2 ·h -1 , the separation factor of the membrane was 0.44, and the separation index of the membrane was 578.87 g·m -2 ·h -1 .

[0109] Through Application Examples 1-5, compared with Application Example 1, it can be seen that with the increase of lignin, the pure polymer pervaporation membrane is modified, which effectively improves the problems of low selectivity and low separation performance of the pure polymer pervaporation membrane, and overcomes the problems of poor separation effect and high energy consumption of cyclohexane-KA oil in the classical separation method.

Claims

1. A method for preparing a lignin-based polymer pervaporation membrane, characterized in that: The method includes the following steps in sequence: 1) adding a surfactant, a polymer, and a solvent into a reactor and stirring at 50-70° C. for 4-6 hours to obtain a mixed solution; 2) adding lignin and solvent into a reactor and stirring at room temperature for 4 to 6 hours to obtain a lignin solution; 3) adding the lignin solution from step 2) dropwise to the mixed solution from step 1), and continuing to stir at a constant temperature for 12 to 24 hours to obtain a casting solution; 4) transferring the casting solution in step 3) to a centrifuge tube, and after centrifugation, evenly coating the casting solution on the ultrafiltration membrane material with a film thickness of 100 to 200 mm to form a uniform liquid film; 5) drying the liquid film in step 4) to obtain a lignin-based polymer pervaporation membrane; The mass ratio of the lignin, polymer, surfactant and solvent is 1.5-7.5:5-15:0.125-0.750:75-95.

2. The method for preparing a lignin-based polymer pervaporation membrane according to claim 1, characterized in that: The lignin is one of alkali lignin, dealkalized lignin, enzymatic lignin, sodium lignin sulfonate, calcium lignin sulfonate and sodium lignin sulfate.

3. The method for preparing a lignin-based polymer pervaporation membrane according to claim 1, characterized in that: The polymer is one of polyethylene glycol, polyvinylidene fluoride, cellulose diacetate, polyvinyl chloride, polyurethane, polyimide, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyurethane, and polysulfone.

4. The method for preparing a lignin-based polymer pervaporation membrane according to claim 1, characterized in that: The surfactant is one of sodium lauryl sulfate, sodium alkylbenzene sulfonate, α-olefin sulfonate, Tween-80, cetyltrimethylammonium bromide, and cocamidopropyl betaine.

5. The method for preparing a lignin-based polymer pervaporation membrane according to claim 1, characterized in that: The solvent is one of chloroform, tetrahydrofuran, N,N-dimethylformamide, dioctyl phthalate, dichloromethane and dimethyl sulfoxide; The ultrafiltration membrane material is one of cellulose acetate, cellulose acetate ester, polyethylene, polysulfone, polyamide and polyvinylidene fluoride.

6. The method for preparing a lignin-based polymer pervaporation membrane according to claim 1, characterized in that: The centrifugation in step 3) is performed at a speed of 3000-5000 r / min for 1-5 minutes; and the liquid film drying in step 4) is performed by placing the liquid film in an oven and drying it at 50-70° C. for 20-24 hours.

7. A lignin-based polymer pervaporation membrane, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 8.

8. The lignin-based polymer pervaporation membrane according to claim 7 is used for separating and purifying cyclohexane-KA oil.

9. A method for separating and purifying cyclohexane-KA oil, characterized in that: The separation is performed using the lignin-based polymer pervaporation membrane according to claim 6.

10. The method for separating and purifying cyclohexane-KA oil according to claim 9, characterized in that: A cyclohexane-KA oil mixture is added to a feed tank; the feed tank is then placed in a water bath at 50 to 80°C and heated to a constant temperature, and the lignin-based polymer pervaporation membrane obtained according to claim 7 is driven by a pressure difference of 0.1 to -0.1 MPa to achieve pervaporation separation, and the filtrate is condensed and collected at a condensation temperature of -180 to 200°C.

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