A method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane

Abstract

A method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane belongs to the field of high-salt organic wastewater treatment. The method is as follows: a Tris-HCl buffer solution with a pH of 8.8 is prepared, dopamine powder is added, and the mixture is poured onto the surface of a hydrophobic microporous membrane after shaking and polymerizing at room temperature for 6 to 12 hours; the mixture is rinsed with pure water and the aforementioned process is repeated once; a methylcellulose / polyvinyl alcohol / cross-linking agent coating liquid is prepared and applied to the surface of the polydopamine-modified membrane. After drying at room temperature, the membrane is thermally cross-linked at 100°C for 10 to 15 minutes and rinsed 3 to 5 times to obtain a composite distillation membrane. The composite membrane prepared by the present invention has a dense double gel network on the surface layer, which can greatly improve the mechanical stability of the membrane and form a regular, flexible protruding structure, which can clean the surface of various types of pollutants. The responsiveness of methylcellulose to temperature can also significantly improve the reversibility of membrane pollution. Low-temperature rinsing can produce surface deformation, thereby loosening the structure of the pollution layer, improving the rinsing effect, and significantly improving the reusability and long-term stability of the membrane.

Description

Technical Field

[0001] The invention belongs to the field of high-salt organic wastewater treatment, and particularly relates to a method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane. Background Art

[0002] Membrane distillation uses a hydrophobic membrane as the separation medium and the vapor pressure difference across the membrane as the driving force. It has the advantages of utilizing low-grade energy, simple equipment, and high-quality produced water. Theoretically, it can achieve deep concentration of wastewater and near-zero emissions. However, membrane distillation has not yet been applied in practical engineering. One of the main limiting factors is that conventional hydrophobic membranes are prone to fouling and wetting problems. For high-salt organic wastewater, membrane scaling and pore wetting caused by high concentrations of inorganic salts are particularly serious and remain unresolved. Membrane scaling results from the precipitation or deposition of inorganic salts in the wastewater on the membrane surface. The growth of scale crystals into the membrane pores irreversibly damages the membrane pore structure, ultimately causing pore wetting and rendering the membrane distillation process ineffective. Organic pollutants in the wastewater adhere to the membrane surface or within the pores through hydrophobicity, thereby clogging or wetting the pores and deteriorating the produced water quality. Due to the hydrophobic nature of the membrane, pollutants deposited in the pores are difficult to remove, and membrane performance is difficult to restore. Therefore, controlling membrane fouling / wetting and improving membrane fouling recovery are crucial to achieving long-term stability in membrane distillation treatment of high-salt organic wastewater.

[0003] Existing distillation membrane materials are mostly used to control individual pollutants (such as salt scale or organic matter). For example, increasing the hydrophobicity of the membrane surface can reduce the contact and interaction between the solution and the membrane, thereby reducing the heterogeneous crystallization tendency of inorganic ions on the membrane surface and alleviating inorganic pollution on the membrane surface. For organic pollutants in wastewater, the main method is to increase the hydrophilicity of the membrane surface to promote the formation of a hydration layer on the membrane surface, or to alleviate the adhesion of hydrophobic organic matter on the membrane surface through the hydrophilic-hydrophobic repulsion effect, thereby alleviating the problem of organic pollution on the membrane surface. In addition, studies have shown that when organic matter coexists, it will strengthen the adhesion of the inorganic salt scale layer on the membrane surface through bridging, making the formed composite pollution layer denser and more difficult to rinse. In actual high-salt organic wastewater, multiple types of pollutants usually coexist, affecting membrane efficiency. However, in response to the multiple types of pollutants and composite pollution problems in the water treatment process, there is currently no distillation membrane material that can be highly efficient, multi-anti-pollution, and long-term recycled, which limits the industrial application of membrane distillation. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of existing distillation membranes being easily contaminated or wetted, and to provide a method for preparing a highly stable, multi-effect, and pollution-resistant double-network gel composite distillation membrane.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane, comprising:

[0007] Step 1: Loading the polydopamine intermediate bonding layer on the surface of the hydrophobic microporous membrane: First, prepare a Tris-HCl buffer solution with a pH of 8.8, add dopamine powder to the buffer solution, control the dopamine concentration to 2-5 g / L, shake well, and pour it onto the surface of the hydrophobic microporous membrane. The liquid layer thickness should not be less than 3 mm. Place it in a shaker at room temperature for polymerization reaction for 6-12 hours;

[0008] Step 2: Pour out the polydopamine solution on the surface of the hydrophobic microporous membrane and rinse with pure water three times. Repeat the loading process of the polydopamine intermediate adhesive layer in step 1 on the membrane surface and carry out the polymerization reaction at room temperature in a shaker for 6 to 12 hours.

[0009] Step 3: Prepare methylcellulose / polyvinyl alcohol / crosslinker coating solution, adjust pH to ≤ 2 with sulfuric acid or hydrochloric acid, and mix by ultrasonic mixing for 30 seconds;

[0010] Step 4: Apply the solution prepared in step 3 to the surface of the polydopamine-modified membrane, controlling the thickness of the liquid layer to be greater than 10 μm, drying at room temperature for 24 to 48 hours, and then crosslinking in an oven at 100° C. for 10 to 15 minutes;

[0011] Step 5: Rinse the surface layer of the membrane prepared in step 4 with pure water for 3 to 5 times to remove the unreacted substances remaining in the preparation process, thereby obtaining a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane.

[0012] Furthermore, in step 1, the hydrophobic microporous membrane is made of polyvinylidene fluoride, polytetrafluoroethylene, or polypropylene.

[0013] Furthermore, in step 1, the average pore size of the hydrophobic microporous membrane is not greater than 0.45 μm.

[0014] Furthermore, in step three, the cross-linking agent is one of glutaraldehyde, glyoxal or borax.

[0015] Furthermore, in step three, in the coating liquid, the concentration of polyvinyl alcohol is controlled to be 2-4 wt %, and the mass ratio of methyl cellulose to polyvinyl alcohol and cross-linking agent is controlled to be 1:2:2-1:5:5.

[0016] The beneficial effects of the present invention compared to the prior art are:

[0017] 1. The methylcellulose-polyvinyl alcohol double-network responsive gel composite membrane prepared by the present invention can not only prevent the infiltration of most inorganic and organic pollutants in wastewater and avoid the pollution and wetting problems of the hydrophobic separation layer, but the double-network structure of the surface anti-fouling layer can also greatly improve the mechanical strength and toughness of the membrane, and has high-efficiency wear-resistant stability for rigid crystal particles precipitated in the highly concentrated state of wastewater; the surface-loaded methylcellulose will also form a regular flexible protrusion structure in the swollen state, which will play a cilia-like cleaning role on the organic pollutants in the wastewater, thereby alleviating the deposition and adhesion of organic pollutants on the membrane surface, and can perform deep desalination and water recovery of high-salt organic wastewater in a long-term and stable manner.

[0018] 2. The methyl cellulose-polyvinyl alcohol double-network responsive gel composite membrane prepared by the present invention has a surface-loaded methyl cellulose that responds to temperature and can significantly improve the recovery of membrane surface contamination. The membrane, after high-temperature operation, will undergo surface deformation when flushed at low temperature, thereby loosening the structure of the contamination layer, improving the flushing effect, and significantly improving the reusability and long-term stability of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron microscope image of the surface of the methyl cellulose / polyvinyl alcohol double network gel composite distillation membrane prepared in Example 1 of the present invention.

[0020] Figure 2 This is a graph showing the water flux and produced water conductivity results of the methyl cellulose / polyvinyl alcohol double-network gel composite distillation membrane prepared in Example 1 of the present invention during long-term treatment of high-salt organic wastewater.

[0021] Figure 3 This is a graph showing the water flux flushing recovery rate of the methyl cellulose / polyvinyl alcohol double-network gel composite distillation membrane prepared in Example 1 of the present invention after a long-term high-salt organic wastewater treatment experiment. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0023] The present invention constructs a methylcellulose-polyvinyl alcohol double-network responsive dense gel layer on the surface of the hydrophobic separation membrane. The density of the gel layer can prevent most inorganic and organic pollutants in the wastewater from penetrating, thereby avoiding the pollution and wetting problems of the hydrophobic separation membrane; the methylcellulose and polyvinyl alcohol polymer chains in the surface gel layer are intertwined to form a double network structure, which can greatly improve the mechanical strength and toughness of the surface anti-fouling layer, and has high efficiency and wear resistance stability for rigid crystal particles precipitated in the highly concentrated state of wastewater; the methylcellulose loaded on the membrane surface will form a regular flexible protrusion structure in the swollen state, which will play a cilia-like cleaning role for organic pollutants in the wastewater, thereby alleviating the deposition and adhesion of organic pollutants on the membrane surface; in addition, the responsiveness of methylcellulose to temperature can also significantly improve the recovery of membrane surface pollution. The membrane after high-temperature operation will undergo surface deformation when washed at low temperature, thereby loosening the pollution layer structure and improving the washing effect. The membrane prepared by the present invention can perform deep desalination and water recovery of high-salt organic wastewater in a long-term and stable manner.

[0024] Example 1:

[0025] A method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane, comprising:

[0026] Step S1: First, a polydopamine intermediate bonding layer is loaded on the surface of a hydrophobic PVDF microporous membrane with an average pore size of 0.22 μm. A Tris-HCl buffer solution with a pH of 8.8 is prepared, dopamine powder is added to the buffer solution, and the dopamine concentration is controlled to be 2 g / L. The prepared solution is poured onto the surface of the hydrophobic microporous membrane and placed on a shaker for polymerization reaction at room temperature for 12 hours.

[0027] Step S2: Pour out the polydopamine solution on the membrane surface and rinse with pure water three times. Repeat the loading process of the polydopamine intermediate adhesive layer in step S1 on the membrane surface, and perform polymerization reaction at room temperature in a shaker for 12 hours.

[0028] Step S3: preparing a methylcellulose / polyvinyl alcohol / glutaraldehyde coating solution, controlling the polyvinyl alcohol concentration to 3 wt %, the mass ratio of methylcellulose to polyvinyl alcohol to glutaraldehyde to 1:3:3, adjusting the pH to 1 with sulfuric acid, and ultrasonically mixing for 30 seconds;

[0029] Step S4: coating the solution prepared in step S3 on the surface of the polydopamine-modified membrane to a thickness of 20 μm, drying at room temperature for 24 h, and further cross-linking in an oven at 100° C. for 10 min;

[0030] Step S5: Rinse the membrane surface layer prepared in step S4 with pure water three times to remove the unreacted substances remaining in the preparation process, thereby obtaining a highly stable, multi-effect, anti-pollution methylcellulose / polyvinyl alcohol double-network gel composite distillation membrane.

[0031] The membrane surface was observed by scanning electron microscopy ( Figure 1 ) It can be found that the membrane surface is loaded with needle-shaped methyl cellulose, and the dense and smooth part is polyvinyl alcohol gel. The embedding of methyl cellulose in polyvinyl alcohol can form a double network interlocking structure, which significantly improves the mechanical strength and toughness of the membrane. Compared with the original hydrophobic microporous membrane, the loading of the surface gel layer can significantly increase the tensile strength of the membrane by 3 to 5 times. During the water treatment process, polyvinyl alcohol and methyl cellulose will swell unevenly, thereby forming a flexible fibrous protrusion structure, which can clean pollutants in the water and alleviate the organic and inorganic pollution problems on the membrane surface. For the surface pollution layer formed during long-term high-temperature membrane distillation treatment, the temperature responsiveness of methyl cellulose is utilized. When rinsed with cold water, the membrane surface will further produce uneven deformation, which can loosen the structure of the pollution layer, thereby improving the recovery of the membrane after rinsing. In the concentration and water reuse process of membrane distillation using simulated high-salt organic wastewater (600mM sodium chloride, 20mM sodium sulfate, 20mM calcium chloride, 20mM sodium bicarbonate, 50mg / L humic acid, 17.4mg / L sodium dodecylbenzenesulfonate, 500mg / L crude oil), the wastewater and condensate temperatures were set to 60℃ and 20℃, respectively, and the flow rates were both 0.1m / s. The prepared methyl cellulose-polyvinyl alcohol double-network responsive gel composite membrane had a water flux decrease of only 19.5% during 90 hours of continuous operation, and the concentration multiple of the wastewater could reach 10 times. At the same time, the conductivity of the produced water was always less than 2.5μS / cm. After operation, 96% of the water flux could be restored by flushing with room temperature water (about 20℃), demonstrating the multi-effect anti-pollution, flushing recovery and long-term stability of the composite membrane in treating high-salt organic wastewater.

[0032] Example 2:

[0033] A method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane, comprising:

[0034] Step S1: First, a polydopamine intermediate bonding layer is loaded on the surface of a hydrophobic polypropylene microporous membrane with an average pore size of 0.45 μm. A Tris-HCl buffer solution with a pH of 8.8 is prepared, dopamine powder is added to the buffer solution, and the dopamine concentration is controlled to be 5 g / L. The prepared solution is poured onto the surface of the hydrophobic microporous membrane and placed on a shaker at room temperature for a polymerization reaction for 8 hours;

[0035] Step S2: Pour out the polydopamine solution on the membrane surface and rinse with pure water three times. Repeat the loading process of the polydopamine intermediate adhesive layer in step S1 on the membrane surface, and perform polymerization reaction at room temperature in a shaker for 8 hours.

[0036] Step S3: preparing a methylcellulose / polyvinyl alcohol / glyoxal coating solution, controlling the polyvinyl alcohol concentration to 4 wt %, the mass ratio of methylcellulose to polyvinyl alcohol to glyoxal to 1:4:4, adjusting the pH to 2 with hydrochloric acid, and ultrasonically mixing for 30 seconds;

[0037] Step S4: coating the solution prepared in step 3 on the surface of the polydopamine-modified membrane to a thickness of 15 μm, drying at room temperature for 36 h, and further cross-linking in an oven at 100° C. for 10 min;

[0038] Step S5: Rinse the membrane surface layer prepared in step 4 with pure water for 5 times to remove the unreacted substances remaining in the preparation process, thereby obtaining a highly stable, multi-effect, anti-pollution methylcellulose / polyvinyl alcohol double-network gel composite distillation membrane.

[0039] Compared with the original hydrophobic polypropylene microporous membrane, the loading of the surface gel layer can significantly increase the tensile strength of the membrane by 2 to 3 times. Using simulated high-salinity organic wastewater (600mM sodium chloride, 25mM sodium sulfate, 25mM calcium chloride, 25mM sodium bicarbonate, 100mg / L humic acid, 50mg / L sodium dodecylbenzene sulfonate, and 1g / L crude oil) for membrane distillation concentration and water reuse, the wastewater and condensate temperatures were set at 50°C and 20°C, respectively, and the flow rate was 0.1m / s. The prepared methylcellulose-polyvinyl alcohol double-network responsive gel composite membrane achieved a water recovery rate of 90% during 120 hours of continuous operation, with a water flux decrease of about 30%. At the same time, the conductivity of the produced water was always less than 5μS / cm. After operation, 92% of the water flux was restored by rinsing with room temperature water (about 20°C), demonstrating the multi-effect anti-fouling, rinse recovery, and long-term stability of the methylcellulose / polyvinyl alcohol double-network gel composite distillation membrane for the treatment of high-salinity organic wastewater.

Claims

1. A method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane, characterized by: The method is: Step 1: Loading the polydopamine intermediate bonding layer on the surface of the hydrophobic microporous membrane: First, prepare a Tris-HCl buffer solution with a pH of 8.8, add dopamine powder to the buffer solution, control the dopamine concentration to 2-5 g / L, shake well, and pour it onto the surface of the hydrophobic microporous membrane. The liquid layer thickness should not be less than 3 mm. Place it in a shaker at room temperature for polymerization reaction for 6-12 hours; Step 2: Pour out the polydopamine solution on the surface of the hydrophobic microporous membrane and rinse with pure water three times. Repeat the loading process of the polydopamine intermediate adhesive layer in step 1 on the membrane surface and carry out the polymerization reaction at room temperature in a shaker for 6 to 12 hours. Step 3: Prepare methylcellulose / polyvinyl alcohol / crosslinker coating solution, adjust pH to ≤ 2 with sulfuric acid or hydrochloric acid, and mix by ultrasonic mixing for 30 seconds; Step 4: Apply the solution prepared in step 3 to the surface of the polydopamine-modified membrane, controlling the thickness of the liquid layer to be greater than 10 μm, drying at room temperature for 24 to 48 hours, and then crosslinking in an oven at 100° C. for 10 to 15 minutes; Step 5: Rinse the surface layer of the membrane prepared in step 4 with pure water for 3 to 5 times to remove the unreacted substances remaining in the preparation process, thereby obtaining a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane.

2. The method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane according to claim 1, characterized in that: In step 1, the hydrophobic microporous membrane is made of polyvinylidene fluoride, polytetrafluoroethylene, or polypropylene.

3. The method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane according to claim 1 or 2, characterized in that: In step 1, the average pore size of the hydrophobic microporous membrane is no more than 0.45 μm.

4. The method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane according to claim 1, characterized in that: In step three, the cross-linking agent is one of glutaraldehyde, glyoxal or borax.

5. The method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane according to claim 1, characterized in that: In step three, in the coating liquid, the concentration of polyvinyl alcohol is controlled to be 2-4 wt %, and the mass ratio of methyl cellulose to polyvinyl alcohol and cross-linking agent is controlled to be 1:2:2-1:5:5.

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