Preparation method of oil removal micro-filtration membrane

Abstract

The invention belongs to the field of micro-filtration membrane preparation, and particularly relates to a preparation method of an oil removal micro-filtration membrane. The invention discloses a preparation method of an oil-removing microfiltration membrane, which is characterized in that two segmented copolymer membrane layers are prepared on the basis of the existing microfiltration membrane, and the membrane performance is regulated and controlled by regulating and controlling the block ratio, swelling time and the like in the two segmented copolymers. According to the prepared membrane, the flux performance of the membrane is remarkably improved while the interception performance is kept unchanged or increased, and meanwhile, the membrane has very good regeneration performance.

Description

Technical Field

[0001] The invention belongs to the field of microfiltration membrane preparation, and particularly relates to a method for preparing an oil-removing microfiltration membrane. Background Art

[0002] At present, the treatment of oily wastewater in industrial waste gas is an important water treatment task. Oil pollutants are extremely harmful to the environment and ecosystem. In order to solve the problem of wastewater discharge, the main oil-water separation technologies currently include gravity sedimentation, flocculation sedimentation, centrifugal separation, biological decomposition or oxidation treatment, etc. Membrane separation technology is also a common oily wastewater treatment technology, which has certain advantages for emulsified oil wastewater in oily wastewater. At present, microfiltration membranes are usually used for screening and purification when treating emulsified oil wastewater.

[0003] However, the current application of microfiltration membranes in the treatment of emulsified oil wastewater faces problems such as microfiltration membrane contamination caused by oil droplet aggregation, short membrane life, and significant overall decline in membrane performance after repeated use. Currently, there are methods such as modifying the membrane and preparing a network structure coating to make the microfiltration membrane have properties such as low oil adhesion. However, in actual operation, the above methods are too complicated and the process is difficult to control.

[0004] The present invention provides a method for preparing an oil-removing microfiltration membrane to solve the above technical problems. Summary of the invention

[0005] The purpose of the present invention is to solve the pollution of conventional microfiltration membranes in the treatment of emulsified oil wastewater and to maintain the performance of the membranes at a high level after repeated use.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0007] A method for preparing an oil removal microfiltration membrane, the method comprising the following steps:

[0008] Step 1, soaking the microfiltration membrane in deionized water for 10 minutes to 24 hours; the microfiltration membrane is a PVDF microfiltration membrane or a PTFE microfiltration membrane;

[0009] Step 2, preparing a solution of the first block copolymer, wherein the solute is the first amphiphilic block copolymer, the solvent is chloroform, the mass concentration is 0.5-3wt%, the hydrophilic segment in the first amphiphilic block copolymer is one of PEG, P2VP, P4VP or PDMAEMA, and the hydrophobic segment is one of PSf or PS;

[0010] Step 3, preparing a solution of the second block copolymer, wherein the solute is the second amphiphilic block copolymer, the solvent is chloroform, the mass concentration is 0.5-3wt%, the hydrophilic segment in the second amphiphilic block copolymer is one of PEG, P2VP, P4VP or PDMAEMA, and the hydrophobic segment is one of PSf or PS;

[0011] The molecular weight of the hydrophilic segment in the first amphiphilic block copolymer accounts for 60%-70% of the total molecular weight, and the molecular weight of the hydrophilic segment in the second amphiphilic block copolymer accounts for 20%-30% of the total molecular weight;

[0012] Step 4: After taking out the microfiltration membrane, a dense first block copolymer layer is prepared on the first surface of the microfiltration membrane by spin coating or doctor blade coating using a solution of the first block copolymer to obtain a double-layer microfiltration membrane;

[0013] Step 5, drying the double-layer microfiltration membrane prepared in step 4 under a vacuum environment at 250-300° C. for 1-10 hours, taking it out and naturally cooling it to room temperature, and then soaking it in deionized water for 10 minutes to 24 hours, then taking out the double-layer microfiltration membrane, and using the solution of the second block copolymer to prepare a dense second block copolymer layer on the second surface of the microfiltration membrane by spin coating or blade coating, to obtain a three-layer microfiltration membrane;

[0014] Step 6: Dry the three-layer microfiltration membrane prepared in step 5 at room temperature and normal pressure for 8-24 hours, where normal pressure is one standard atmospheric pressure and room temperature is 20°C-25°C; place the dried three-layer microfiltration membrane in ethanol at 65°C-70°C, soak for 10h-15h and then take it out to obtain an oil-removing microfiltration membrane.

[0015] The second side of the oil removal microfiltration membrane contacts the solution to be filtered, and the first side contacts the filtered clean liquid.

[0016] Preferably, the total molecular weight of the block copolymer is 125 kDa-200 kDa;

[0017] Preferably, the hydrophilic segments and hydrophobic segments of the first block copolymer and the second block copolymer are the same, and the only difference between the two is the proportion of the hydrophilic segments.

[0018] The oil removal microfiltration membrane prepared by the invention is applied in the field of emulsified oil wastewater treatment.

[0019] Compared with the prior art, the advantages of the present invention are:

[0020] 1. The oil removal microfiltration membrane prepared by the present invention can significantly improve the flux while maintaining the original retention rate.

[0021] 2. The obtained double-layer microfiltration membrane, due to the high proportion of hydrophilic segments in the first block copolymer, is prone to peeling due to swelling of the hydrophilic segments after immersion in ethanol. To avoid peeling during the subsequent ethanol immersion process, it is subjected to high-temperature vacuum drying before preparing a three-layer microfiltration membrane, and then dried at room temperature. After two dryings, the first block copolymer layer and the microfiltration membrane have sufficient connection strength to cope with the subsequent swelling process.

[0022] 3. Using deionized water for back flushing, the membrane performance of the oil removal microfiltration membrane can still be maintained at a high level, with less attenuation and significantly improved service life. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with specific embodiments.

[0024] Example 1

[0025] A method for preparing an oil removal microfiltration membrane, the method comprising the following steps:

[0026] 1. Soak the PVDF microfiltration membrane in deionized water for 1 hour;

[0027] 2. Prepare a solution of the first block copolymer, wherein the first amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, the mass concentration is 1 wt%, the molecular weight of the PS segment is 60 kDa, and the molecular weight of the P2VP segment is 90 kDa;

[0028] 3. Prepare a solution of the second block copolymer, wherein the second amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, and the mass concentration is 1 wt %; the molecular weight of the PS segment is 105 kDa, and the molecular weight of the P2VP segment is 45 kDa;

[0029] 4. After taking out the microfiltration membrane, take 300 mL of the first block copolymer solution, and prepare a dense first block copolymer layer on the first surface of the microfiltration membrane by spin coating to obtain a double-layer microfiltration membrane;

[0030] 5. The prepared double-layer microfiltration membrane was dried at 300°C in a vacuum environment for 2 hours, then taken out and naturally cooled to 25°C, and then immersed in deionized water for 1 hour. The double-layer microfiltration membrane was taken out, and 300 mL of the second block copolymer solution was taken to prepare a dense second block copolymer layer on the second surface of the microfiltration membrane by spin coating to obtain a three-layer microfiltration membrane;

[0031] 6. Dry the prepared three-layer microfiltration membrane at 25°C for 15 h;

[0032] 7. Place the dried three-layer microfiltration membrane in ethanol at 70°C, soak for 10 hours and then take it out to obtain an oil removal microfiltration membrane;

[0033] 8. Use 5g / L emulsion to measure the emulsified oil retention rate. The emulsifier is common sodium dodecyl sulfate. The second side of the oil removal microfiltration membrane contacts the solution to be filtered, and the first side contacts the filtered clean liquid. The measured pressure is 0.1Mpa.

[0034] Example 2

[0035] The difference between Example 2 and Example 1 is that the dried three-layer microfiltration membrane is placed in ethanol at 70° C., soaked for 12 hours and then taken out to obtain an oil-removing microfiltration membrane;

[0036] Example 3

[0037] The difference between Example 3 and Example 1 is that the dried three-layer microfiltration membrane is placed in ethanol at 70° C., soaked for 15 hours and then taken out to obtain an oil-removing microfiltration membrane;

[0038] Example 4

[0039] The difference between Example 4 and Example 1 is that the first amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, the mass concentration is 1wt%, the molecular weight of the PS segment is 53kDa, and the molecular weight of the P2VP segment is 97kDa;

[0040] Example 5

[0041] The difference between Example 5 and Example 1 is that the first amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, the mass concentration is 1wt%, the molecular weight of the PS segment is 45kDa, and the molecular weight of the P2VP segment is 105kDa;

[0042] Example 6

[0043] The difference between Example 6 and Example 1 is that: a solution of a second block copolymer is prepared, the second amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, and the mass concentration is 1wt%; the molecular weight of the PS segment is 113kDa, and the molecular weight of the P2VP segment is 37kDa;

[0044] Example 7

[0045] The difference between Example 7 and Example 1 is that: a solution of a second block copolymer is prepared, the second amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, and the mass concentration is 1wt%; the molecular weight of the PS segment is 120kDa, and the molecular weight of the P2VP segment is 30kDa;

[0046] Comparative Example 1

[0047] The PVDF microfiltration membrane was immersed in deionized water for 1 hour; the emulsified oil retention rate was measured using a 5 g / L emulsion, the emulsifier was common sodium dodecyl sulfate, and the measurement pressure was 0.1 MPa.

[0048] Comparative Example 2

[0049] Compared with Example 1, the difference is that: the dried three-layer microfiltration membrane is placed in ethanol at 70°C, soaked for 5 hours and then taken out to obtain an oil-removing microfiltration membrane;

[0050] Comparative Example 3

[0051] Compared with Example 1, only the first block copolymer layer is prepared in Comparative Example 3, and the specific difference is: a method for preparing an oil removal microfiltration membrane, the preparation method comprising the following steps:

[0052] 1. Soak the PVDF microfiltration membrane in deionized water for 1 hour;

[0053] 2. Prepare a solution of the first block copolymer, wherein the first amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, the mass concentration is 1 wt%, the molecular weight of the PS segment is 60 kDa, and the molecular weight of the P2VP segment is 90 kDa;

[0054] 3. After taking out the microfiltration membrane, take 300 mL of the first block copolymer solution, and prepare a dense first block copolymer layer on the first surface of the microfiltration membrane by spin coating to obtain a double-layer microfiltration membrane;

[0055] 4. The prepared double-layer microfiltration membrane was dried at 300°C in a vacuum environment for 2 hours, then taken out and naturally cooled to 25°C, then immersed in deionized water for 1 hour, and dried at 25°C at normal pressure for 15 hours;

[0056] 5. Dry the obtained microfiltration membrane at normal pressure and 25°C for 15h;

[0057] 6. Place the dried microfiltration membrane in 70°C ethanol, soak for 10 hours and then take it out to obtain an oil-removing microfiltration membrane;

[0058] 7. Use 5g / L emulsion to measure the emulsified oil retention rate. The emulsifier is common sodium dodecyl sulfate. The second side of the oil removal microfiltration membrane contacts the solution to be filtered, and the first side contacts the filtered clean liquid. The measuring pressure is 0.1Mpa.

[0059] Comparative Example 4

[0060] Compared with Example 1, only the second block copolymer layer was prepared in Comparative Example 4. The specific difference lies in a method for preparing an oil removal microfiltration membrane, which comprises the following steps:

[0061] 1. Soak the PVDF microfiltration membrane in deionized water for 1 hour;

[0062] 2. Prepare a solution of the second block copolymer, wherein the second amphiphilic block copolymer is PS-b-P2VP, the solvent is chloroform, and the mass concentration is 1 wt %; the molecular weight of the PS segment is 105 kDa, and the molecular weight of the P2VP segment is 45 kDa;

[0063] 3. After taking out the microfiltration membrane, take 300 mL of the second block copolymer solution, and prepare a dense second block copolymer layer on the second side of the microfiltration membrane (only textual description, in fact, one side coated with the solution can be used as the second side, and the other side is used as the first side) by spin coating to obtain a double-layer microfiltration membrane;

[0064] 4. Dry the double-layer microfiltration membrane prepared in step 3 at 25°C for 15 hours;

[0065] 5. Place the dried double-layer microfiltration membrane in 70°C ethanol, soak for 10 hours and then take it out to obtain an oil removal microfiltration membrane;

[0066] 6. Use 5g / L emulsion to measure the emulsified oil retention rate. The emulsifier is common sodium dodecyl sulfate. The second side of the oil removal microfiltration membrane contacts the solution to be filtered, and the first side contacts the filtered clean liquid. The measuring pressure is 0.1Mpa.

[0067] Comparative Example 5

[0068] Compared with Example 5, the difference is that: 5 g / L emulsion is used to measure the emulsified oil retention rate, the emulsifier is common sodium dodecyl sulfate, the first side of the oil removal microfiltration membrane is in contact with the solution to be filtered, and the second side is in contact with the filtered clean liquid, and the measuring pressure is 0.1 MPa.

[0069] The interception rate, interception flux (retention flux refers to the flux when the emulsion is filtered, not the pure water flux) of Examples 1-7 and Comparative Documents 1-5, and the interception flux after 5 filtrations (each microfiltration membrane filters 1000L of emulsion, and then rinses with deionized water, and repeats five times to measure the interception flux of the emulsion) and cleaning are as follows:

[0070]

[0071]

[0072] It can be seen from the above data that the microfiltration oil removal film obtained in this application can improve the retention rate and significantly improve the flux. The reason may be that the block copolymer attached to the filtration side (the second side of the microfiltration oil removal film) has a PS segment (and is a continuous phase), which has an affinity for the organic molecules in the emulsifier to achieve capture, and the block copolymer attached to the clean liquid side (the first side of the microfiltration oil removal film) has a large number of P2VP segments, which will form a similar water absorption driving force on the back side of the microfiltration membrane and greatly increase the flux. In addition, since the swelling process of the block copolymer is excessive swelling or supersaturated swelling, the block copolymer will basically not form a smaller pore or even locally form a damaged membrane structure, and it is the above structure that avoids the reduction of flux (such as the mild swelling conditions in Comparative Example 2).

[0073] In addition, the second side is mainly composed of PS segments and is a continuous phase. During the deionized water rinsing process, the P2VP segments may swell slightly due to their hydrophilicity, forcing the PS segments to undergo temporary deformation. After multiple rinsings, the oily components adhered to the second side (or more precisely, the block copolymer layer adhered to the second side) can be easily peeled off to achieve the regeneration of the microfiltration membrane (Comparative Examples 1 and 3 can serve as evidence for the above speculation, and both have obvious flux attenuation).

[0074] Comparison of Comparative Example 5 with Example 5 shows that the microfiltration membrane has better stability and retention flux when the second side is used as the filtration side. The reason may be that the higher content of PS on the filtration side can provide more attraction to adsorb and retain oily components; when the P2VP content on the filtration side is too high, the microfiltration membrane is slightly inferior in retention performance. At the same time, due to the high P2VP content, during the deionized water flushing process, a large amount / large volume of P2VP segments will slightly swell and lock the oily components adsorbed by the PS segments inside the first side of the membrane, and excellent regeneration performance cannot be obtained.

[0075] From the above data and analysis, it can be seen that the microfiltration oil removal membrane prepared in the present application has excellent flux performance and regeneration performance in the treatment of emulsified wastewater.

Claims

1. A method for preparing an oil removal microfiltration membrane, characterized in that: The preparation method comprises the following steps: Step 1, soaking the microfiltration membrane in deionized water; Step 2, preparing a first block copolymer solution, wherein the hydrophilic segment in the first block copolymer is one of PEG, P2VP, P4VP or PDMAEMA, and the hydrophobic segment is one of PSf or PS; Step 3, preparing a second block copolymer solution, wherein the hydrophilic segment in the second block copolymer is one of PEG, P2VP, P4VP or PDMAEMA, and the hydrophobic segment is one of PSf or PS; Step 4: after taking out the microfiltration membrane, using the first block copolymer solution to prepare a dense first block copolymer layer on the first surface of the microfiltration membrane to obtain a double-layer microfiltration membrane; Step 5, vacuum drying the double-layer microfiltration membrane prepared in step 4, and then using the second block copolymer solution to prepare a dense second block copolymer layer on the second surface of the microfiltration membrane to obtain a three-layer microfiltration membrane; Step 6: Dry the three-layer microfiltration membrane prepared in step 5, soak the dried three-layer microfiltration membrane in ethanol and then take it out to obtain an oil-removing microfiltration membrane.

2. The preparation method according to claim 1, wherein the total molecular weight of the block copolymer is 125 kDa-200 kDa; and the hydrophilic segment and the hydrophobic segment of the first block copolymer and the second block copolymer are of the same type.

3. The preparation method according to claim 1, wherein the vacuum drying post-treatment in step 5 is drying under a vacuum environment at 250-300°C for 1-10h, then taking out and naturally cooling to room temperature, and then soaking in deionized water for 10 minutes to 24 hours, and then taking out the double-layer microfiltration membrane; the drying condition in step 6 is drying at normal pressure and room temperature for 8-24 hours.

4. The preparation method as claimed in claim 3, wherein the room temperature is 20-25 degrees Celsius and the normal pressure is a standard atmospheric pressure.

5. The preparation method as claimed in claim 1, wherein the microfiltration membrane is a PVDF microfiltration membrane or a PTFE microfiltration membrane.

6. The preparation method according to claim 1, wherein the molecular weight of the hydrophilic segment in the first block copolymer accounts for 60%-70% of the total molecular weight, and the molecular weight of the hydrophilic segment in the second block copolymer accounts for 20%-30% of the total molecular weight.

7. The preparation method according to claim 1, wherein the mass concentration of the first block copolymer solution and the second block copolymer solution is 0.5-3wt%, and the solvent is chloroform.

8. The preparation method according to claim 1, wherein the soaking time in step 1 is 10 minutes to 24 hours.

9. preparation method as claimed in claim 1, soaking in ethanol in step 6 is 65 ℃-70 ℃ ethanol, and taking out after soaking for 10h-15h.

10. Application of the oil removal microfiltration membrane prepared by the preparation method according to any one of claims 1 to 9 in the field of emulsified oil wastewater treatment, characterized in that: The second side of the oil removal microfiltration membrane contacts the solution to be filtered, and the first side contacts the filtered clean liquid.

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