Oil-water separation membrane for biodiesel wastewater and preparation method thereof

Abstract

The application relates to the technical field of wastewater treatment, and particularly discloses an oil-water separation membrane for biodiesel wastewater and a preparation method thereof. The preparation method of the oil-water separation membrane for biodiesel wastewater comprises the following preparation steps: S1: uniformly mixing expanded graphite and carbon nanotubes, and heating at a constant temperature for 3-6 min to obtain a composite material; S2: in the composite material, dropwise adding methyl methacrylate and N,N'-methylene bisacrylamide to obtain a modified composite material; S3: stirring and dissolving hydroxyethyl cellulose and polyvinyl alcohol in water, then uniformly stirring methyl methacrylate and methacrylic acid butyl ester, and then adding an initiator, the modified composite material, ethyl acetate and water to react to obtain a separation membrane material; and S4: preparing a coating solution containing a certain concentration of the separation membrane material, coating the coating solution on a substrate, and drying to obtain the oil-water separation membrane. The oil-water separation membrane prepared by the application has the advantages of high-efficiency separation of biodiesel wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to an oil-water separation membrane for biodiesel wastewater and a preparation method thereof. BACKGROUND

[0002] Biodiesel is a renewable diesel fuel that can replace petrochemical diesel fuel, which is made of oil crops, wild oil plants, and engineering microalgae, etc. aquatic plant oils and animal oils, and restaurant waste oil, etc. as raw oil through ester exchange process. Biodiesel production is accompanied by pollution problems of production wastewater. Biodiesel wastewater is mainly produced in the water washing stage, and is a multi-phase system integrating suspended oil, emulsified oil, dissolved organic matter and salt. It has high oil content in free and emulsified state, high concentration of suspended solids, COD and BOD, so it is difficult to treat.

[0003] At present, there are mainly the following types of oil-water separation technologies: suspended gravity treatment method, centrifugal deposition method, biological treatment and electrodeposition, etc. These technologies have the problems of low separation efficiency, high separation cost, easy secondary pollution, etc., which limit the application of these technologies. Membrane separation is one of the effective means for treating domestic wastewater, which has simple equipment, low cost and easy to scale up, so it is necessary to develop an oil-water separation membrane for biodiesel wastewater with high treatment efficiency and economic practicability to alleviate the pollution of biodiesel wastewater to the environment. SUMMARY

[0004] In order to efficiently separate biodiesel wastewater, the present application provides an oil-water separation membrane for biodiesel wastewater and a preparation method thereof.

[0005] The oil-water separation membrane for biodiesel wastewater and the preparation method thereof provided by the present application adopt the following technical scheme:

[0006] A preparation method of an oil-water separation membrane for biodiesel wastewater, comprising the following preparation steps:

[0007] S1: uniformly mixing expanded graphite and carbon nanotubes, heating at a temperature of 800-930 DEG C for 3-6 min, to obtain a composite material;

[0008] S2: uniformly adding methyl methacrylate and N,N'-methylene bisacrylamide drop by drop in the composite material prepared in step S1, the weight ratio of methyl methacrylate and N,N'-methylene bisacrylamide being (1-3):1, vacuumizing, and reacting at a temperature of 50-70 DEG C for 6-10 h, to obtain a modified composite material;

[0009] S3: hydroxyethyl cellulose and polyvinyl alcohol are dissolved in distilled water, stirred uniformly, methyl methacrylate is added, the weight ratio of methyl methacrylate to hydroxyethyl cellulose is (20-35):1, stirring at a temperature of 65-85℃ for 1-2h, then adding methacrylate, initiator, modified composite, ethyl acetate and distilled water, stirring uniformly, after the reaction is completed, washing, drying, grinding, to obtain an oil-water separation membrane material;

[0010] S4: preparing a coating solution containing a certain mass concentration of oil-water separation membrane material, coating on a substrate, drying, to obtain an oil-water separation membrane.

[0011] By adopting the above technical scheme, since the composite material of expanded graphite and carbon nanotubes is adopted, the expanded graphite is a good adsorbent, especially it has a loose porous structure and has strong adsorption capacity for organic compounds, and has good adsorption performance for free and emulsified oil in biodiesel wastewater, the carbon nanotubes can improve the flux of oil-water separation and play a demulsification performance, and further improve the oil-water separation effect of the oil-water separation membrane.

[0012] By adopting in-situ polymerization of methyl methacrylate on the surface of the composite material, the polymer of polymethyl methacrylate is attached to the surface of the composite material, and the compatibility of the composite material in the oil-water separation membrane is improved.

[0013] By adopting grafting copolymerization of hydroxyethyl cellulose and methyl methacrylate, the hydroxyethyl cellulose is grafted onto the molecular chain of methyl methacrylate, the wettability of the oil-water separation membrane material is improved, the contact area between the biodiesel wastewater and the membrane material is increased, methyl methacrylate is used as a crosslinking agent, methyl methacrylate and methacrylate are crosslinked to form a three-dimensional space structure, and ethyl acetate is used as a pore-forming agent, so that the prepared oil-water separation membrane material has high oil absorption performance, the loose pore structure can intercept micron-sized suspended solids in sewage, and the modified composite material has good separation effect on the treatment of some macromolecular organic pollutants.

[0014] Optionally, the weight ratio of the carbon nanotubes to the expanded graphite is (1-4):5.

[0015] By adopting the above technical scheme, during the mixing and heat treatment of the carbon nanotubes and the expandable graphite at high temperature, the interlayer compound of the expandable graphite decomposes when heated, so that the carbon nanotubes enter the interlayer pores of the expandable graphite, and at high temperature, the carbon nanotubes are distributed between the layers of the expandable graphite. Since the carbon nanotubes and the expandable graphite layer structure are interlaced and intertwined, the adsorption capacity of the composite material is increased, and the strength and thermal stability of the oil-water separation membrane are improved.

[0016] Optionally, the weight ratio of the methyl methacrylate to the methacrylate is (15-25):1.

[0017] By adopting the technical scheme, with the increase of the amount of the crosslinking agent, the resin is crosslinked to form a three-dimensional network structure, and the oil absorption rate of the resin is improved; when the amount of the crosslinking agent is too much, the strength of the resin is increased, but the crosslinking density is too large, which is not conducive to the stretching of the polymer chain, and thus the separation performance of the oil-water separation membrane is reduced.

[0018] Optionally, the modified composite accounts for 0.5-2 wt% of the total weight of the hydroxyethyl cellulose, the polyvinyl alcohol, the methyl methacrylate, the methacrylic acid alkyl ester and the ethyl acetate in the step S3.

[0019] By adopting the technical scheme, with the increase of the amount of the modified composite, the adsorption amount of the polluting organic molecules and the oil molecules in the biodiesel wastewater is increased, and the separation efficiency is reduced when the content of the modified composite is continuously increased and the agglomeration occurs in the oil-water separation membrane.

[0020] Optionally, the mass concentration of the oil-water separation membrane material in the coating solution in the step S4 is 2-5 wt%.

[0021] By adopting the technical scheme, the coating solution reaches the appropriate viscosity and film-forming conditions, so that the oil-water separation membrane with excellent performance is prepared.

[0022] Optionally, the methacrylic acid alkyl ester, the initiator, the modified composite, the ethyl acetate and the distilled water are added in the step S3, and the reaction is carried out at a temperature of 55-85℃ for 4-6h; after the reaction is completed, the anhydrous ethanol and the distilled water are used for washing 3-5 times.

[0023] By adopting the technical scheme, the hydroxyethyl cellulose is dissolved in the distilled water under the stirring at a temperature of 65-85℃ for 1-2h with the polyvinyl alcohol as a dispersant, and then the reaction is carried out at a temperature of 55-85℃ for 4-6h, so that the hydroxyethyl cellulose is grafted on the molecular chain of the methyl methacrylate; the methacrylic acid propyl ester is used as a crosslinking agent to crosslink the methyl methacrylate to form a high oil absorption film material; the added modified composite has good adsorption performance on the organic pollutants in the biodiesel wastewater, and the strength and the thermal stability of the oil-water separation membrane material are increased.

[0024] Optionally, the solvent of the coating solution in the step S4 is N,N-dimethylformamide.

[0025] By adopting the technical scheme, the prepared oil-water separation membrane material is dissolved in N,N-dimethylformamide solvent to prepare a coating liquid, and N,N-dimethylformamide is used as a solvent to maintain a good volatilization rate and ensure the separation performance of the oil-water separation membrane.

[0026] In a second aspect, the application provides an oil-water separation membrane for biodiesel wastewater, which is prepared by the preparation method of the oil-water separation membrane for biodiesel wastewater.

[0027] By adopting the technical scheme, the addition of the composite material of carbon nanotubes and expanded graphite improves the strength of the oil-water separation membrane and has good adsorption performance on free and emulsified oil in the biodiesel wastewater, and the acrylic polymer grafted with hydroxyethyl cellulose is used as the membrane material to achieve high oil absorption performance.

[0028] In summary, the application has the following beneficial effects:

[0029] 1. The application uses a composite material of expanded graphite and carbon nanotubes, the expanded graphite has good adsorption capacity and good adsorption performance on free and emulsified oil in the biodiesel wastewater, and the carbon nanotubes can improve the flux of oil-water separation, play a demulsification performance, and further improve the oil-water separation effect of the oil-water separation membrane.

[0030] 2. In the application, methyl methacrylate is preferably used for in-situ polymerization on the surface of the composite material, and a polymer of polymethyl methacrylate is attached to the surface of the composite material, thereby improving the compatibility of the composite material in the oil-water separation membrane.

[0031] 3. The application grafts hydroxyethyl cellulose into the molecular chain of methyl methacrylate by graft copolymerization of hydroxyethyl cellulose and methyl methacrylate, thereby improving the wettability of the oil-water separation membrane material, increasing the contact area of the biodiesel wastewater and the separation membrane material, using methacrylate as a crosslinking agent to form a three-dimensional spatial structure, and the prepared oil-water separation membrane material has high oil absorption performance. DETAILED DESCRIPTION

[0032] The application will be further described in detail below in combination with examples and comparative examples.

[0033] The sources of raw materials for the following examples and comparative examples are as follows: The raw materials for the examples and comparative examples can be commercially purchased.

[0034] Examples

[0035] Example 1

[0036] A preparation method of an oil-water separation membrane for biodiesel wastewater includes the following preparation steps:

[0037] S1: 15 g of expanded graphite and 25 g of carbon nanotubes were uniformly mixed, the weight ratio of expanded graphite to carbon nanotubes was 3:5, constant temperature heating was performed in a muffle furnace at 890°C for 5 min, and a composite material was obtained;

[0038] S2: The composite material prepared in step S1 was placed in a vacuum drying box, dried at 90°C for 48 h, 10 g of the composite material was placed in a stirrer, vacuumized, and 0.2 g of methyl methacrylate and 0.1 g of N,N'-methylenebisacrylamide were added dropwise and uniformly at a rotation speed of 400 r / min, reaction was performed at 60°C for 8 h, and a modified composite material was obtained;

[0039] S3: 0.67 g of hydroxyethyl cellulose and 0.3 g of polyvinyl alcohol were dissolved in 50 ml of distilled water in a three-necked flask, stirring was performed for 1 h, 20 g of methyl methacrylate was added, the weight ratio of methyl methacrylate to hydroxyethyl cellulose was (20-35):1, stirring was performed at 70°C at a rotation speed of 400 r / min for 1.5 h, then 1 g of butyl methacrylate, 0.09 g of initiator benzoyl peroxide, 0.23 g of modified composite material, 1.2 g of ethyl acetate and 110 g of distilled water were added, reaction was performed at 70°C for 5 h, after the reaction was completed, washing was performed with anhydrous ethanol and distilled water 4 times respectively, drying was performed at 100°C for 5 h, grinding was performed, and an oil-water separation membrane material was obtained, wherein the weight ratio of methyl methacrylate to butyl methacrylate was 20:1, the weight ratio of methyl methacrylate to hydroxyethyl cellulose was 30:1, and the modified composite material accounted for 1 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, butyl methacrylate and ethyl acetate;

[0040] S4: A coating liquid containing 2.5 wt% of the oil-water separation membrane material was prepared, N,N-dimethylformamide was used as a solvent, coating was performed on a polytetrafluoroethylene plate, and drying was performed at 110°C for 10 h, and an oil-water separation membrane was obtained.

[0041] Example 2

[0042] A preparation method of an oil-water separation membrane for biodiesel wastewater, comprising the following preparation steps:

[0043] S1: 5 g of expanded graphite and 25 g of carbon nanotubes were uniformly mixed, the weight ratio of expanded graphite to carbon nanotubes was 1:5, constant temperature heating was performed in a muffle furnace at 800°C for 3 min, and a composite material was obtained;

[0044] S2: The composite material prepared in step S1 is placed in a vacuum drying oven and dried at 90°C for 48h. 10g of the composite material is placed in a stirrer, vacuumized, and 0.1g of methyl methacrylate and 0.1g of N,N'-methylenebisacrylamide are added dropwise and uniformly at a rotation speed of 400r / min. The reaction is carried out at 50°C for 6h to obtain a modified composite material;

[0045] S3: 0.75g of hydroxyethyl cellulose and 0.35g of polyvinyl alcohol are dissolved in 50ml of distilled water in a three-necked flask, stirred for 1h, and 15g of methyl methacrylate is added. The mixture is stirred at 65°C at a rotation speed of 400r / min for 1h, and then 1g of methacrylate, 0.09g of initiator benzoyl peroxide, 0.09g of modified composite material, 1.2g of ethyl acetate and 110g of distilled water are added. The reaction is carried out at 55°C for 4h. After the reaction is completed, the mixture is washed with anhydrous ethanol and distilled water for 3 times, and dried at 100°C for 5h. The mixture is ground to obtain an oil-water separation membrane material. The weight ratio of methyl methacrylate to methacrylate is 15:1, the weight ratio of methyl methacrylate to hydroxyethyl cellulose is 20:1, and the modified composite material accounts for 0.5wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylate and ethyl acetate;

[0046] S4: A coating solution containing 2wt% of oil-water separation membrane material is prepared, the solvent is N,N-dimethylformamide, and the coating solution is coated on a polytetrafluoroethylene plate and dried at 110°C for 10h to obtain an oil-water separation membrane.

[0047] Example 3

[0048] A method for preparing an oil-water separation membrane for biodiesel wastewater, comprising the following preparation steps:

[0049] S1: 20g of expanded graphite and 25g of carbon nanotubes are uniformly mixed, the weight ratio of expanded graphite to carbon nanotubes is 4:5, and the mixture is heated at 930°C in a muffle furnace for 6min to obtain a composite material;

[0050] S2: The composite material prepared in step S1 is placed in a vacuum drying oven and dried at 90°C for 48h. 10g of the composite material is placed in a stirrer, vacuumized, and 0.1g of methyl methacrylate and 0.1g of N,N'-methylenebisacrylamide are added dropwise and uniformly at a rotation speed of 400r / min. The reaction is carried out at 70°C for 10h to obtain a modified composite material;

[0051] S3: In a three-neck flask, 0.71 g of hydroxyethyl cellulose, 0.29 g of polyvinyl alcohol was dissolved in 50 ml of distilled water, stirred for 1 h, 25 g of methyl methacrylate was added, stirred at 85°C and 400 r / min for 2 h, then 1 g of methacrylic acid butyl ester, 0.09 g of initiator benzoyl peroxide, 0.56 g of modified composite material, 1.2 g of ethyl acetate and 110 g of distilled water were added, and the reaction was carried out at 85°C for 6 h. After the reaction was completed, it was washed with anhydrous ethanol and distilled water for 5 times respectively, and dried at 100°C for 5 h, ground to obtain an oil-water separation membrane material, wherein the weight ratio of methyl methacrylate to methacrylic acid butyl ester is 25:1, the weight ratio of methyl methacrylate to hydroxyethyl cellulose is 35:1, and the modified composite material accounts for 2wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylic acid butyl ester and ethyl acetate;

[0052] S4: A coating solution containing 5wt% of oil-water separation membrane material was prepared, the solvent was N,N-dimethylformamide, and the coating was coated on a polytetrafluoroethylene plate and dried at 110°C for 10 h to obtain an oil-water separation membrane.

[0053] Example 4

[0054] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from example 2 in that the carbon nanotube in step S1 is 2.5 g, the expanded graphite is 25 g, and the weight ratio of carbon nanotube to expanded graphite is 0.5:5.

[0055] Example 5

[0056] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from example 3 in that the carbon nanotube in step S1 is 5 g, the expanded graphite is 5 g, and the weight ratio of carbon nanotube to expanded graphite is 1:1.

[0057] Example 6

[0058] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from example 2 in that the weight ratio of methyl methacrylate to methacrylic acid butyl ester is 13:1, and the specific preparation steps of step S3 are as follows:

[0059] S3: 0.65 g of hydroxyethyl cellulose, 0.35 g of polyvinyl alcohol were dissolved in 50 ml of distilled water in a three-necked flask, stirred for 1 h, 13 g of methyl methacrylate was added, stirred at 65 °C and 400 r / min for 1 h, then 1 g of methacrylic acid butyl ester, 0.09 g of initiator benzoyl peroxide, 0.16 g of modified composite material, 1.2 g of ethyl acetate and 110 g of distilled water were added, reacted at 55 °C for 4 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 3 times respectively, dried at 100 °C for 5 h, ground, and the oil-water separation membrane material was obtained, wherein the weight ratio of methyl methacrylate to hydroxyethyl cellulose was 20:1, and the modified composite material accounted for 1 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylic acid butyl ester and ethyl acetate.

[0060] Example 7

[0061] A preparation method of an oil-water separation membrane for biodiesel wastewater, different from example 3, the weight ratio of methyl methacrylate to methacrylic acid butyl ester was 27:1, and the specific preparation steps of step S3 were as follows:

[0062] S3: 0.65 g of hydroxyethyl cellulose, 0.35 g of polyvinyl alcohol were dissolved in 50 ml of distilled water in a three-necked flask, stirred for 1 h, 13 g of methyl methacrylate was added, stirred at 65 °C and 400 r / min for 1 h, then 1 g of methacrylic acid butyl ester, 0.09 g of initiator benzoyl peroxide, 0.16 g of modified composite material, 1.2 g of ethyl acetate and 110 g of distilled water were added, reacted at 55 °C for 4 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 3 times respectively, dried at 100 °C for 5 h, ground, and the oil-water separation membrane material was obtained, wherein the weight ratio of methyl methacrylate to hydroxyethyl cellulose was 20:1, and the modified composite material accounted for 1 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylic acid butyl ester and ethyl acetate.

[0063] Example 8

[0064] A preparation method of an oil-water separation membrane for biodiesel wastewater, different from example 2, the weight ratio of methyl methacrylate to hydroxyethyl cellulose was 18:1, and the specific preparation steps of step S3 were as follows:

[0065] S3: 1.38 g of hydroxyethyl cellulose, 0.29 g of polyvinyl alcohol were dissolved in 50 ml of distilled water in a three-necked flask, stirred for 1 h, 25 g of methyl methacrylate was added, stirred at 85°C and 400 r / min for 2 h, then 1 g of methacrylate, 0.09 g of initiator benzoyl peroxide, 0.58 g of modified composite, 1.2 g of ethyl acetate and 110 g of distilled water were added, reacted at 85°C for 6 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 5 times respectively, dried at 100°C for 5 h, ground, and the oil-water separation membrane material was obtained, wherein the weight ratio of methyl methacrylate to methacrylate was 25:1, and the modified composite accounted for 2 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylate and ethyl acetate.

[0066] Example 9

[0067] A preparation method of an oil-water separation membrane for biodiesel wastewater, different from example 3, the weight ratio of methyl methacrylate to hydroxyethyl cellulose was 37:1, and the specific preparation steps of step S3 were as follows:

[0068] S3: 1.38 g of hydroxyethyl cellulose, 0.29 g of polyvinyl alcohol were dissolved in 50 ml of distilled water in a three-necked flask, stirred for 1 h, 25 g of methyl methacrylate was added, stirred at 85°C and 400 r / min for 2 h, then 1 g of methacrylate, 0.09 g of initiator benzoyl peroxide, 0.58 g of modified composite, 1.2 g of ethyl acetate and 110 g of distilled water were added, reacted at 85°C for 6 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 5 times respectively, dried at 100°C for 5 h, ground, and the oil-water separation membrane material was obtained, wherein the weight ratio of methyl methacrylate to methacrylate was 25:1, and the modified composite accounted for 2 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylate and ethyl acetate.

[0069] Example 10

[0070] A preparation method of an oil-water separation membrane for biodiesel wastewater, different from example 2, the modified composite accounted for 0.4 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylate and ethyl acetate, and the specific preparation steps of step S3 were as follows:

[0071] S3: 0.75 g hydroxyethyl cellulose, 0.35 g polyvinyl alcohol were dissolved in 50 ml distilled water in a three-necked flask, stirred for 1 h, 15 g methyl methacrylate was added, stirred at 65 °C and 400 r / min for 1 h, then 1 g methacrylate, 0.09 g initiator benzoyl peroxide, 0.074 g modified composite, 1.2 g ethyl acetate and 110 g distilled water were added, reacted at 55 °C for 4 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 3 times respectively, dried at 100 °C for 5 h, ground, to obtain an oil-water separation membrane material, wherein the weight ratio of methyl methacrylate to methacrylate is 15:1, and the weight ratio of methyl methacrylate to hydroxyethyl cellulose is 20:1.

[0072] Example 11

[0073] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from example 3 in that the modified composite accounts for 2.2 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylate and ethyl acetate, and the specific preparation steps of step S3 are as follows:

[0074] S3: 0.75 g hydroxyethyl cellulose, 0.35 g polyvinyl alcohol were dissolved in 50 ml distilled water in a three-necked flask, stirred for 1 h, 15 g methyl methacrylate was added, stirred at 65 °C and 400 r / min for 1 h, then 1 g methacrylate, 0.09 g initiator benzoyl peroxide, 0.074 g modified composite, 1.2 g ethyl acetate and 110 g distilled water were added, reacted at 55 °C for 4 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 3 times respectively, dried at 100 °C for 5 h, ground, to obtain an oil-water separation membrane material, wherein the weight ratio of methyl methacrylate to methacrylate is 15:1, and the weight ratio of methyl methacrylate to hydroxyethyl cellulose is 20:1.

[0075] Comparative example

[0076] Comparative example 1

[0077] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from example 1 in that the raw material does not include expanded graphite, comprising the following preparation steps:

[0078] S1: carbon nanotubes were placed in a vacuum drying oven and dried at 90 °C for 48 h, 10 g of carbon nanotubes were placed in a stirrer, vacuumized, and 0.2 g of methyl methacrylate and 0.1 g of N, N'-methylenebisacrylamide were added dropwise and uniformly, reacted at 60 °C for 8 h to obtain modified carbon nanotubes;

[0079] S3: 0.67 g of hydroxyethyl cellulose, 0.3 g of polyvinyl alcohol were dissolved in 50 ml of distilled water in a three-neck flask, stirred for 1 h, 20 g of methyl methacrylate was added, stirred at 70°C at a speed of 400 r / min for 1.5 h, then 1 g of methacrylate, 0.09 g of initiator benzoyl peroxide, 0.23 g of modified carbon nanotubes, 1.2 g of ethyl acetate and 110 g of distilled water were added, and the reaction was carried out at 70°C for 5 h. After the reaction was completed, it was washed with anhydrous ethanol and distilled water for 4 times respectively, and dried at 100°C for 5 h, ground, to obtain an oil-water separation membrane material, wherein the weight ratio of methyl methacrylate to methacrylate is 20:1, the weight ratio of methyl methacrylate to hydroxyethyl cellulose is 30:1, and the modified carbon nanotubes account for 1 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylate and ethyl acetate;

[0080] S4: A coating solution containing 2.5 wt% of oil-water separation membrane material was prepared, the solvent was N,N-dimethylformamide, and was coated on a polytetrafluoroethylene plate and dried at 110°C for 10 h to obtain an oil-water separation membrane.

[0081] Comparative Example 2

[0082] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from Example 1 in that the raw material does not include carbon nanotubes, comprising the following preparation steps:

[0083] S1: The expanded graphite was placed in a vacuum drying oven and dried at 90°C for 48 h. 10 g of expanded graphite was placed in a stirrer, vacuumized, and 0.2 g of methyl methacrylate and 0.1 g of N,N'-methylenebisacrylamide were added dropwise and uniformly at a speed of 400 r / min. The reaction was carried out at 60°C for 8 h to obtain modified expanded graphite;

[0084] S3: In a three-necked flask, 0.67 g of hydroxyethyl cellulose and 0.3 g of polyvinyl alcohol were dissolved in 50 ml of distilled water, stirred for 1 h, 20 g of methyl methacrylate was added, stirred at 70°C and 400 r / min for 1.5 h, then 1 g of methacrylic acid butyl ester, 0.09 g of initiator benzoyl peroxide, 0.23 g of modified expanded graphite, 1.2 g of ethyl acetate and 110 g of distilled water were added, reacted at 70°C for 5 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 4 times respectively, dried at 100°C for 5 h, ground, and an oil-water separation membrane material was obtained, wherein the weight ratio of methyl methacrylate to methacrylic acid butyl ester was 20:1, the weight ratio of methyl methacrylate to hydroxyethyl cellulose was 30:1, and the modified expanded graphite accounted for 1 wt% of the total weight of hydroxyethyl cellulose, polyvinyl alcohol, methyl methacrylate, methacrylic acid butyl ester and ethyl acetate;

[0085] S4: A coating solution containing 2.5 wt% of oil-water separation membrane material was prepared, the solvent was N,N-dimethylformamide, coated on a polytetrafluoroethylene plate, and dried at 110°C for 10 h to obtain an oil-water separation membrane.

[0086] Comparative Example 3

[0087] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from Example 1 in that the raw materials do not include carbon nanotubes and expanded graphite, comprising the following preparation steps:

[0088] S1: In a three-necked flask, 0.67 g of hydroxyethyl cellulose and 0.3 g of polyvinyl alcohol were dissolved in 50 ml of distilled water, stirred for 1 h, 20 g of methyl methacrylate was added, stirred at 70°C and 400 r / min for 1.5 h, then 1 g of methacrylic acid butyl ester, 0.09 g of initiator benzoyl peroxide, 1.2 g of ethyl acetate and 110 g of distilled water were added, reacted at 70°C for 5 h, after the reaction was completed, washed with anhydrous ethanol and distilled water for 4 times respectively, dried at 100°C for 5 h, ground, and an oil-water separation membrane material was obtained;

[0089] S2: A coating solution containing 2.5 wt% of oil-water separation membrane material was prepared, the solvent was N,N-dimethylformamide, coated on a polytetrafluoroethylene plate, and dried at 110°C for 10 h to obtain an oil-water separation membrane.

[0090] Comparative Example 4

[0091] A method for preparing an oil-water separation membrane for biodiesel wastewater, which is different from Example 1 in that the composite material is not subjected to modification treatment, comprising the following preparation steps:

[0092] S1: 15 g of expanded graphite and 25 g of carbon nanotubes were mixed uniformly, the weight ratio of expanded graphite to carbon nanotubes was 3:5, constant temperature heating was performed in a muffle furnace at 890°C for 5 min, and a composite material was obtained;

[0093] S2: 0.67 g of hydroxyethyl cellulose, 0.3 g of polyvinyl alcohol were dissolved in 50 ml of distilled water in a three-necked flask, stirring was performed for 1 h, 20 g of methyl methacrylate was added, stirring was performed at 70°C and a rotation speed of 400 r / min for 1.5 h, then 1 g of methacrylic acid butyl ester, 0.09 g of initiator benzoyl peroxide, 0.23 g of the composite material, 1.2 g of ethyl acetate and 110 g of distilled water were added, reaction was performed at 70°C for 5 h, after the reaction was completed, washing was performed with anhydrous ethanol and distilled water respectively for 4 times, drying was performed at 100°C for 5 h, grinding was performed, and an oil-water separation membrane material was obtained;

[0094] S4: a coating solution containing 2.5 wt% of the oil-water separation membrane material was prepared, N,N'-methylenebisacrylamide was used as a solvent, coating was performed on a polytetrafluoroethylene plate, drying was performed at 110°C for 10 h, and an oil-water separation membrane was obtained.

[0095] Comparative Example 5

[0096] A preparation method of an oil-water separation membrane for biodiesel wastewater, different from Example 1, the raw material does not include hydroxyethyl cellulose, and the preparation steps include the following:

[0097] S1: 15 g of expanded graphite and 25 g of carbon nanotubes were mixed uniformly, the weight ratio of expanded graphite to carbon nanotubes was 3:5, constant temperature heating was performed in a muffle furnace at 890°C for 5 min, and a composite material was obtained;

[0098] S2: the composite material prepared in step S1 was placed in a vacuum drying box, drying was performed at 90°C for 48 h, 10 g of the composite material was placed in a stirrer, vacuumizing was performed, 0.2 g of methyl methacrylate and 0.1 g of N,N'-methylenebisacrylamide were added drop by drop in sequence at a rotation speed of 400 r / min, reaction was performed at 60°C for 8 h, and a modified composite material was obtained;

[0099] S3: 20 g of methyl methacrylate and 1 g of methacrylic acid butyl ester were added to a three-necked flask and stirred uniformly, then 0.09 g of initiator benzoyl peroxide, 0.22 g of the modified composite material, 1.2 g of ethyl acetate and 110 g of distilled water were added, reaction was performed at 70°C for 5 h, after the reaction was completed, washing was performed with anhydrous ethanol and distilled water respectively for 4 times, drying was performed at 100°C for 5 h, grinding was performed, and an oil-water separation membrane material was obtained;

[0100] S4: A coating solution containing 2.5 wt% of the oil-water separation membrane material was prepared, with N,N-dimethylformamide as the solvent, coated on a polytetrafluoroethylene plate, and dried at 110°C for 10h to obtain the oil-water separation membrane.

[0101] Performance test

[0102] Test method

[0103] The oil-water separation membranes prepared in Examples 1-11 and Comparative Examples 1-5 were applied to separate biodiesel wastewater by membrane method. The oil-water separation membranes were fixed on a membrane separation device, and then biodiesel wastewater was poured into the device to separate the biodiesel wastewater by membrane filtration under the action of gravity.

[0104] 1. The membrane flux of the oil-water separation membrane was the volume of the filtrate (L) passing through the membrane per unit area (m2) per unit time (h), and the separation efficiency R (%) of the oil-water separation membrane was calculated by using an organic carbon analyzer to analyze the organic carbon, according to the following formula: R = (1-Cf / C0) x 100%, wherein Cf represents the organic carbon content in the filtrate, mg / L, and C0 represents the organic carbon content in the biodiesel wastewater, mg / L, and the oil-water separation efficiency was the average value of multiple measurements (at least three times). 2 f f

[0105] 2. Oil removal rate: n-hexane was used as an extractant to extract oil from the biodiesel wastewater sample, and the absorbance of the extract was detected by ultraviolet spectrophotometry. The diesel concentration was obtained according to the standard curve of the absorbance corresponding to different concentrations of diesel in n-hexane. The oil content of the biodiesel wastewater before and after passing through the oil-water separation membrane was tested, and the oil removal rate was calculated as (initial oil content - oil content after separation by the oil-water separation membrane) / initial oil content x 100%.

[0106] Table 1: Results of performance test

[0107]

[0108]

[0109] As can be seen from Examples 4-5 and Examples 2-3 and Table 1, the performance of Examples 2-3 is better than that of Examples 4-5. Under high temperature heating, the carbon nanotubes are distributed between the layers of the expanded graphite, and reducing the amount of carbon nanotubes added, the carbon nanotubes and the layer structure of the expanded graphite cannot form mutual lapping to form interlaced winding, which reduces the adsorption capacity of the composite material. However, increasing the amount of carbon nanotubes may block the pore structure of the expanded graphite, resulting in a decrease in adsorption performance and membrane flux.

[0110] ​​​It can be seen from the combination of Examples 6-7 and Examples 2-3 and Table 1 that the performance of Examples 6-7 is better than that of Examples 2-3, the amount of crosslinking agent is reduced, the three-dimensional network structure of the membrane material cannot be formed, and the separation efficiency of the oil-water separation membrane is reduced; the amount of crosslinking agent is increased, the crosslinking density is too large, the network space is reduced, the movement of the molecular chain is not conducive, and the separation performance is reduced.

[0111] It can be seen from the combination of Examples 8-9 and Examples 2-3 and Table 1 that the performance of Examples 8-9 is better than that of Examples 2-3, which shows that the grafting of hydroxyethyl cellulose on methyl methacrylate improves the wettability of the oil-water separation membrane, the flux and separation efficiency of the oil-water separation membrane are improved, the amount of hydroxyethyl cellulose is too low, the amount of copolymerized and grafted hydroxyethyl cellulose is small, the separation efficiency is reduced, the amount is increased, the molecular chain is entangled, the steric hindrance of the crosslinking reaction is increased, the crosslinking reaction is affected, and the separation efficiency of the prepared oil-water separation membrane is reduced.

[0112] It can be seen from the combination of Examples 10-11 and Examples 2-3 and Table 1 that the performance of Examples 10-11 is better than that of Examples 2-3, and the addition amount of the modified composite material is too low, so that the separation performance of the oil-water separation membrane is improved to a limited extent, and the addition amount of the modified composite material is too high, which causes agglomeration in the oil-water separation membrane, and reduces the performance of the separation membrane.

[0113] It can be seen from the combination of Example 1 and Comparative Examples 1-3 and Table 1 that the performance of Example 1 is better than that of Comparative Examples 1-3, which shows that the combination of carbon nanotubes and expanded graphite greatly improves the separation efficiency of organic matter in biodiesel wastewater, and the oil removal efficiency of the oil-water separation membrane is improved.

[0114] It can be seen from the combination of Example 1 and Comparative Example 4 and Table 1 that the performance of Example 1 is better than that of Comparative Examples 1-3, in-situ polymerization of polymethyl methacrylate on the surface of the composite material, the polymethyl methacrylate has good compatibility with the oil-water separation membrane material, the composite material is uniformly dispersed in the oil-water separation membrane, and good separation performance is achieved.

[0115] It can be seen from the combination of Example 1 and Comparative Example 5 and Table 1 that the performance of Example 1 is better than that of Comparative Example 5, and the introduction of hydroxyethyl cellulose into methyl methacrylate can improve the wettability of the separation membrane, increase the contact area with the biodiesel wastewater, and improve the oil-water separation efficiency of the separation membrane.

[0116] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, and the modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing an oil-water separation membrane for biodiesel wastewater, characterized by: The preparation method comprises the following steps: S1: uniformly mixing the expanded graphite and the carbon nanotube, heating at a temperature of 800-930 DEG C for 3-6 min to obtain a composite material; S2: adding methyl methacrylate and N,N'-methylene bisacrylamide into the composite material prepared in step S1 drop by drop, the weight ratio of methyl methacrylate and N,N'-methylene bisacrylamide being (1-3):1, vacuumizing, and reacting at a temperature of 50-70 DEG C for 6-10 h to obtain a modified composite material; S3: dissolving hydroxyethyl cellulose and polyvinyl alcohol in distilled water, stirring uniformly, adding methyl methacrylate, the weight ratio of methyl methacrylate and hydroxyethyl cellulose being (20-35):1, stirring at a temperature of 65-85 DEG C for 1-2 h, and then adding methacrylate butyl methacrylate, an initiator, the modified composite material, ethyl acetate and distilled water, stirring uniformly, washing, drying, grinding after the reaction to obtain an oil-water separation membrane material; S4: preparing a coating liquid containing a certain mass concentration of the oil-water separation membrane material, coating on a substrate, and drying to obtain an oil-water separation membrane.

2. A method for preparing a membrane for oil-water separation of biodiesel wastewater according to claim 1, characterized by: The weight ratio of the carbon nanotube and the expanded graphite is (1-4):

5.

3. A method for preparing a membrane for oil-water separation of biodiesel wastewater according to claim 1, characterized by: The weight ratio of the methacrylate butyl methacrylate and the methyl methacrylate is (15-25):

1.

4. The method for preparing a membrane for oil-water separation of biodiesel wastewater according to claim 1, characterized in that: The modified composite material accounts for 0.5-2 wt% of the total weight of the hydroxyethyl cellulose, the polyvinyl alcohol, the methyl methacrylate, the methacrylate butyl methacrylate and the ethyl acetate in step S3.

5. The method for preparing a membrane for oil-water separation of biodiesel wastewater according to claim 1, characterized in that: The mass concentration of the oil-water separation membrane material in the coating liquid in step S4 is 2-5 wt%.

6. The method for preparing a membrane for oil-water separation of biodiesel wastewater according to claim 1, characterized in that: The methacrylate butyl methacrylate, the initiator, the modified composite material, the ethyl acetate and the distilled water are added in step S3, and the reaction is carried out at a temperature of 55-85 DEG C for 4-6 h, and the reaction is washed with anhydrous ethanol and distilled water for 3-5 times after the reaction.

7. The method for preparing a membrane for oil-water separation of biodiesel wastewater according to claim 1, characterized in that: The solvent of the coating liquid in step S4 is N,N-dimethylformamide.

8. An oil-water separation membrane prepared by the preparation method of the oil-water separation membrane for biodiesel wastewater according to any one of claims 1-7.

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