Preparation method of a high-concentration ratio anti-pollution composite distillation membrane with an armor structure

Abstract

The application discloses a preparation method of a high-concentration anti-pollution composite distillation membrane with an armoured structure, and the method comprises the following steps: step one, dissolving a polymer capable of forming a hydrogel into water to obtain a polymer solution; step two, adding a crosslinking agent into the polymer solution to obtain a hydrogel precursor solution; step three, adding an acid catalyst into the hydrogel precursor solution to obtain a gelling membrane solution; step four, rapidly coating the gelling membrane solution onto a hydrophobic substrate to obtain a composite distillation membrane; step five, keeping the composite distillation membrane in a hydrophilic layer to be in contact with water surface immersion, then cleaning the composite distillation membrane with deionized water, and then precooling the composite distillation membrane in a refrigerator; and step six, freeze-drying the pre-cooled composite distillation membrane to obtain a composite distillation membrane with an armoured structure. The composite distillation membrane with the armoured structure prepared by the method has the advantages of good stability, high water flux and wide anti-pollution range in a membrane distillation process, and has a wide application prospect in the field of industrial high-salinity wastewater treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane water treatment, and relates to a preparation method of a membrane for membrane distillation, in particular to a preparation method of a high-concentration-ratio anti-pollution composite distillation membrane with an armor structure. BACKGROUND

[0002] Membrane distillation technology has attracted extensive attention in the field of high-salinity wastewater treatment due to its low sensitivity to salinity, utilization of low-grade energy, and modular device. However, membrane pollution caused by oil, membrane wetting caused by surfactants, and membrane fouling caused by ultra-high concentration of inorganic salts have been the bottlenecks for the development of the technology. Oil pollutants can interact with hydrophobic membranes through hydrophobic-hydrophobic interaction, block the membrane pores, and further cause the failure of membrane distillation process. Surfactants can reduce the surface tension of the feed liquid, resulting in a decrease in the liquid access pressure of the membrane, and the membrane is prone to wetting. The increasing salt concentration during the membrane distillation concentration process can increase the risk of inorganic salt crystallization, deposition and growth, block the membrane pores, and damage the membrane structure. Many high-salinity water treatment occasions will simultaneously exist surfactants and oil pollutants, such as oil and gas exploration and processing, metal processing, textile and other industries, and the membrane distillation technology has the problems of low concentration ratio and poor stability in the treatment of high-salinity wastewater containing surfactants and oil pollutants at the same time.

[0003] How to improve the concentration ratio of the distillation membrane and the performance of simultaneously resisting oil and surfactants in a high-salinity environment is of great significance to the development of membrane distillation technology in the field of industrial high-salinity wastewater treatment. The traditional method for simultaneously dealing with high-concentration inorganic salts, oil and surfactants is to modify the interface of the hydrophobic membrane, construct a micro-nano multi-level structure and reduce the surface free energy to obtain a membrane with multi-lyophobic properties. Although the multi-lyophobic membrane can resist inorganic salts, oil and surfactants at the same time, the process is complex and the stability is general. The composite membrane combined with a hydrophilic layer on the hydrophobic membrane has outstanding advantages in resisting oil pollutants, but the traditional porous composite membrane does not have the function of intercepting surfactants. SUMMARY

[0004] In order to solve the problem of poor stability of the traditional distillation membrane in the membrane distillation technology when treating high-salinity wastewater containing oil and surfactant pollutants at the same time, the application provides a preparation method of a high-concentration-ratio anti-pollution composite distillation membrane with an armor structure. The method can prepare a composite distillation membrane with an armor structure, the armor surface with a gradient pore structure faces the feed liquid and is open, and faces the hydrophobic substrate and is closed, which not only reduces the mass transfer resistance of the hydrophilic layer, but also retains the interception performance of the hydrophilic layer to oil and salt crystallization. In addition, under the synergistic action of the armor layer and the hydrophobic substrate, the wetting front containing surfactants is difficult to diffuse in the substrate membrane pores, realizing strong surfactant resistance. The composite distillation membrane with an armor structure prepared by the application is helpful to the popularization and application of membrane distillation technology in complex water quality treatment.

[0005] The object of the present application is achieved by the following technical solutions:

[0006] A preparation method of a high-concentration anti-pollution composite distillation membrane with an armor structure, comprising the following steps:

[0007] Step one, dissolving a water gel-forming polymer into water to obtain a polymer solution, wherein the mass concentration of the polymer is controlled to be 10-20%, and the water gel-forming polymer is one or more of chitosan, hyaluronic acid, fibrin, alginic acid, cellulose, agarose, polyethylene glycol, polyacrylic acid and its derivatives, polyvinyl alcohol, polyacrylamide, polyacrylic acid and polymethacrylic acid;

[0008] Step two, adding a crosslinking agent to the polymer solution prepared in step one to obtain a water gel precursor solution, wherein the mass ratio of the crosslinking agent to the polymer is controlled to be 1:5-100, and the crosslinking agent is one or more of glutamine transaminase, genipin, glutaraldehyde and N,N'-methylene bisacrylamide;

[0009] Step three, adding an acid catalyst to the water gel precursor solution prepared in step two to obtain a gelling membrane solution, wherein the volume ratio of the acid catalyst to the water gel precursor solution is controlled to be 1:20-50, and the acid catalyst is one or more of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid; the acid is a catalyst for the crosslinking reaction of the polymer and the crosslinking agent, and after the acid catalyst is added, the crosslinking reaction will start rapidly, and with the continuous reaction, the viscosity of the solution gradually increases;

[0010] Step four, rapidly coating the gelling membrane solution prepared in step three on a hydrophobic substrate to obtain a composite distillation membrane, wherein the coating thickness is controlled to be 5-50 μm, and the hydrophobic substrate is a microporous membrane prepared by compounding one or more of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene and polyether sulfone;

[0011] Step five, immersing the composite distillation membrane prepared in step four in water for 0.5-3 h with the hydrophilic layer in contact with the water surface, then washing the composite distillation membrane with deionized water for 2-4 times to make the gel fully absorb water and remove residual impurities, and then placing the composite distillation membrane in a refrigerator at-10--20℃ for precooling for 24-72 h to control that no liquid water exists in the gel layer, which is beneficial to the pore formation of the gel layer and the protection of the freeze dryer;

[0012] Step six, freeze-drying the pre-cooled composite distillation membrane in step five to obtain a composite distillation membrane with an armor structure, wherein the freeze-drying time is 24-48 h, the vacuum degree is 10-30 Pa, and the temperature is-10--40℃.

[0013] Compared with the prior art, the present application has the following advantages:

[0014] 1. The composite distillation membrane with the armor structure prepared by the application has stable structure, low mass transfer resistance, can realize high concentration ratio in the membrane distillation desalination process, and can stably intercept surfactants and oil pollutants in a high salt environment.

[0015] 2. The composite distillation membrane with the armor structure prepared by the application is prepared by means of the wiped film technology and the freeze-drying technology, has simple preparation process and low cost, and can realize scale-up production.

[0016] 3. The composite distillation membrane with the armor structure prepared by the application has good stability in the membrane distillation process, high water flux, and wide pollution resistance range, and has wide application prospect in the field of industrial high-salt wastewater treatment. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a viscosity-time curve of the wiped film liquid in step S3 of Example 1;

[0018] Figure 2 is a scanning electron microscope image of the gel layer formed in step S5 of Example 1;

[0019] Figure 3 is a photo of the composite distillation membrane with the armor structure prepared in step S6 of Example 1;

[0020] Figure 4 is a scanning electron microscope image of the gel layer of the composite distillation membrane with the armor structure prepared in step S6 of Example 1;

[0021] Figure 5 is a cross-sectional scanning electron microscope image of the composite distillation membrane with the armor structure prepared in step S6 of Example 1;

[0022] Figure 6 is a photo of the water contact angle of the front and back surfaces of the armor structure high-concentration ratio anti-pollution composite distillation membrane prepared in Example 1;

[0023] Figure 7 is a photo of the underwater oil contact angle of the front and back surfaces of the armor structure high-concentration ratio anti-pollution composite distillation membrane prepared in Example 1;

[0024] Figure 8 is a stress-strain curve of the armor structure high-concentration ratio anti-pollution composite distillation membrane prepared in Example 1;

[0025] Figure 9 is an oil resistance test diagram of the armor structure high-concentration ratio anti-pollution composite distillation membrane prepared in Example 1;

[0026] Figure 10 is a surfactant resistance test diagram of the armor structure high-concentration ratio anti-pollution composite distillation membrane prepared in Example 1;

[0027] Figure 11 is a salt resistance test chart of the high-concentration ratio anti-pollution composite distillation membrane with an armoring structure prepared in Example 1, and the initial salt concentration is set to be a supersaturated concentration. DETAILED DESCRIPTION

[0028] The technical solutions of the present application are further described below in conjunction with examples, but are not limited thereto, and any modification or equivalent replacement to the technical solutions of the present application without departing from the spirit and scope of the technical solutions shall be covered in the protection scope of the present application.

[0029] Example 1

[0030] The present example provides a preparation method of a high-concentration ratio anti-pollution composite distillation membrane with an armoring structure, which is specifically performed according to the following steps:

[0031] Step S1: 5 g of polyvinyl alcohol (PVA) is first added to 50 mL of deionized water, which is stirred in a water bath at 80°C for 3 h, and then the completely dissolved PVA solution is placed at room temperature for stirring for 1 h to obtain a PVA solution.

[0032] Step S2: 1 mL of glutaraldehyde is added to the PVA solution prepared in step S1, and stirred for 1 h to obtain a pre-gelatinized solution.

[0033] Step S3: A polyvinylidene fluoride membrane is first fixed flat on a glass plate, and then 2.5 mL of 2 mol / L HCl solution is added to the pre-gelatinized solution prepared in step S2, and stirred for 3 min to obtain a gelatinizing blade coating solution.

[0034] Step S4: The blade coating solution prepared in step S3 is quickly coated on the surface of the polyvinylidene fluoride membrane, and the coating thickness is set to be 20 μm. After the gelatinization reaction is completed, an ultra-thin dense composite membrane with a PVA hydrogel layer on the surface is obtained.

[0035] Step S5: The composite membrane hydrogel layer prepared in step S4 is floated on water for 1 h with the hydrogel layer facing down, and then washed with deionized water for 3 times, and then placed in a refrigerator at -18°C for freezing for 48 h.

[0036] Step S6: The composite membrane prepared in step S5 is placed in a freeze dryer for freeze drying treatment for 24 h, and the temperature of the freeze dryer is set to be -30°C and the vacuum degree is set to be 15 Pa, to obtain a composite distillation membrane with an armoring structure.

[0037] In the composite distillation membrane with an armoring structure prepared in the present example, the mass ratio of PVA to water is 1:10, the water contact angle of the hydrophilic layer is 31°, the underwater oleophobic angle is 154°, and the liquid admission pressure is 250 kPa. The oil resistance test results of the composite distillation membrane with an armoring structure prepared in the present example are as follows:Figure 9 As shown, specifically, the salt concentration of the feed liquid in the oil resistance test was 7 wt%, and the oil concentration was 0.05 wt%. The results of the surfactant resistance test of the composite distillation membrane with the armoring structure prepared in this example are shown in Table 2. Figure 10 As shown, specifically, the salt concentration of the feed liquid in the surfactant resistance test was 7 wt%, and the surfactant concentration was 0.1 mM. The results of the salt resistance test of the composite distillation membrane with the armoring structure prepared in this example are shown in Table 3. Figure 11 As shown, specifically, the salt concentration of the feed liquid in the salt resistance test was a supersaturated concentration.

[0038] Example 2:

[0039] This example provides a method for preparing a high-concentration anti-pollution composite distillation membrane with an armoring structure, which is specifically performed according to the following steps:

[0040] Step S1: First, 1 g of chitosan and 4 g of polyvinyl alcohol (PVA) were added to 50 mL of deionized water, which was stirred in a water bath at 80°C for 3 h, and then the solution was placed at room temperature for 1 h of stirring to obtain a chitosan / PVA solution.

[0041] Step S2: 1 mL of glutaraldehyde was added to the chitosan / PVA solution prepared in step S1 and stirred for 1 h to obtain a pre-gel solution.

[0042] Step S3: First, the polyvinylidene fluoride membrane was fixed flat on a glass plate, and then 2.5 mL of 2 mol / L HCl solution was added to the pre-gel solution prepared in step S2 and stirred for 3 min to obtain a gelatinizing blade coating solution.

[0043] Step S4: The blade coating solution prepared in step S3 was quickly coated on the surface of the polyvinylidene fluoride membrane, and the coating thickness was set to 20 μm. After the gelatinization reaction was completed, an ultra-thin dense composite membrane with a chitosan / PVA hydrogel layer on the surface was obtained.

[0044] Step S5: The hydrogel layer of the composite membrane prepared in step S4 was floated on water for 1 h with the bottom up, and then washed with deionized water for 3 times and frozen in a refrigerator at -18°C for 48 h.

[0045] Step S6: The composite membrane prepared in step S5 was placed in a freeze dryer for freeze-drying treatment for 24 h, and the temperature of the freeze dryer was set to -30°C and the vacuum degree was set to 15 Pa to obtain a composite distillation membrane with an armoring structure.

[0046] Example 3:

[0047] This example provides a method for preparing a high-concentration anti-pollution composite distillation membrane with an armoring structure, which is specifically performed according to the following steps:

[0048] Step S1: First, 5 g of polyvinyl alcohol (PVA) was added to 60 mL of deionized water, which was stirred in a water bath at 80°C for 3 h, and then the completely dissolved PVA solution was placed at room temperature for 1 h of stirring to obtain a PVA solution.

[0049] Step S2: 1 mL of glutaraldehyde was added to the PVA solution prepared in step S1, and stirred for 1 h to obtain a pre-gel solution.

[0050] Step S3: First, the polypropylene film was fixed flat on a glass plate, and then 2.5 mL of 2 mol / L HCl solution was added to the pre-gel solution prepared in step S2, and stirred for 3 min to obtain a gelatinizing blade coating solution.

[0051] Step S4: The blade coating solution prepared in step S3 was quickly coated on the surface of the polyvinylidene fluoride film, and the coating thickness was set to 20 μm. After the gelatinization reaction was completed, an ultra-thin dense composite film with a PVA hydrogel layer on the surface was obtained.

[0052] Step S5: The composite film hydrogel layer prepared in step S4 was floated on water for 1 h with the bottom up, and then washed with deionized water for 3 times, and then placed in a refrigerator at -18°C for 48 h of freezing.

[0053] Step S6: The composite film prepared in step S5 was placed in a freeze dryer for freeze drying treatment for 24 h, and the temperature of the freeze dryer was set to -30°C and the vacuum degree was set to 15 Pa, to obtain a composite distillation film with an armor structure.

[0054] Example 4:

[0055] The present embodiment provides a preparation method of an armor structure high concentration ratio anti-pollution composite distillation film, which is specifically performed according to the following steps:

[0056] Step S1: First, 5 g of polyvinyl alcohol (PVA) was added to 60 mL of deionized water, which was stirred in a water bath at 80°C for 3 h, and then the completely dissolved PVA solution was placed at room temperature for 1 h of stirring to obtain a PVA solution.

[0057] Step S2: 1 mL of glutaraldehyde was added to the PVA solution prepared in step S1, and stirred for 1 h to obtain a pre-gel solution.

[0058] Step S3: First, the polyvinylidene fluoride film was fixed flat on a glass plate, and then 2.5 mL of 1 mol / L H2SO4 solution was added to the pre-gel solution prepared in step S2, and stirred for 3 min to obtain a gelatinizing blade coating solution.

[0059] Step S4: The prepared liquid in step S3 was quickly coated on the surface of the polyvinylidene fluoride membrane by blade coating, and the thickness of the coating was set to 20 μm. After the gelation reaction was completed, an ultra-thin dense composite membrane with a PVA hydrogel layer on the surface was obtained.

[0060] Step S5: The composite membrane hydrogel layer prepared in step S4 was floated on water for 1 h, then washed with deionized water for 3 times, and then frozen in a refrigerator at-18 ℃ for 48 h.

[0061] Step S6: The composite membrane prepared in step S5 was placed in a freeze dryer for freeze drying treatment for 24 h, and the temperature of the freeze dryer was set to-30 ℃ and the vacuum degree was set to 15 Pa. Finally, a composite distillation membrane with an armor structure was obtained.

Claims

1. A method for preparing a high-concentration, fouling-resistant composite distillation membrane with an armor structure, characterized in that... The method includes the following steps: Step 1: Dissolve the hydrogel-forming polymer in water, controlling the polymer mass concentration to be 10-20%, to obtain a polymer solution. The hydrogel-forming polymer is polyvinyl alcohol or a mixture of polyvinyl alcohol and chitosan. Step 2: Add a crosslinking agent to the polymer solution prepared in Step 1, and control the mass ratio of crosslinking agent to polymer to be 1:5~100 to obtain a hydrogel precursor solution. Step 3: Add an acid catalyst to the hydrogel precursor solution prepared in Step 2, and control the volume ratio of the acid catalyst to the hydrogel precursor solution to be 1:20~50 to obtain a scraping film solution that is gelling. Step 4: Quickly coat the membrane solution prepared in Step 3 onto the hydrophobic substrate to obtain a composite distillation membrane; Step 5: Immerse the composite distillation membrane prepared in Step 4 in water while keeping the hydrophilic layer in contact with the water surface, then wash it with deionized water to allow the gel to fully absorb water and remove residual impurities, and then place it in a refrigerator for pre-cooling. Step 6: Freeze-dry the pre-cooled composite distillation membrane from Step 5 to obtain a composite distillation membrane with an armor structure.

2. The method for preparing the armor-structured high-concentration-ratio anti-fouling composite distillation membrane according to claim 1, characterized in that... The crosslinking agent is one or more of the following: transglutaminase, genipin, glutaraldehyde, and N,N′-methylenebisacrylamide.

3. The method for preparing the armor-structured high-concentration-ratio, anti-fouling composite distillation membrane according to claim 1, characterized in that... The acid catalyst is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

4. The method for preparing the armor-structured high-concentration-ratio anti-fouling composite distillation membrane according to claim 1, characterized in that... The thickness of the coating solution applied to the hydrophobic substrate is 5~50 μm.

5. The method for preparing the armor-structured high-concentration-ratio anti-fouling composite distillation membrane according to claim 1, characterized in that... The hydrophobic substrate is a microporous membrane prepared by combining one or more of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethersulfone, and polyester.

6. The method for preparing the armor-structured high-concentration-ratio anti-fouling composite distillation membrane according to claim 1, characterized in that... The soaking time is 0.5 to 3 hours.

7. The method for preparing the armor-structured high-concentration-ratio anti-fouling composite distillation membrane according to claim 1, characterized in that... The deionized water rinsing is performed 2 to 4 times.

8. The method for preparing the armor-structured high-concentration-ratio anti-fouling composite distillation membrane according to claim 1, characterized in that... The pre-cooling temperature is -10 to -20°C, and the time is 24 to 72 hours.

9. The method for preparing the armor-structured high-concentration-ratio anti-fouling composite distillation membrane according to claim 1, characterized in that... The freeze-drying process takes 24 to 48 hours, with a vacuum level of 10 to 30 Pa and a temperature of -10 to -40°C.

Images