Preparation method of high-stability multi-effect anti-pollution double-network gel composite distillation membrane

Abstract

The invention discloses a preparation method of a high-stability multi-effect anti-pollution double-network gel composite distillation membrane, and belongs to the field of high-salt organic wastewater treatment. The method comprises the following steps: preparing a Tris-HCl buffer solution with the pH value of 8.8, adding dopamine powder, uniformly shaking, pouring on the surface of a hydrophobic microporous membrane, and polymerizing at normal temperature for 6-12 hours; washing with pure water, and repeating the process for one time; and preparing methyl cellulose / polyvinyl alcohol / cross-linking agent coating liquid, coating the surface of the membrane modified by the polydopamine with the coating liquid, drying at room temperature, carrying out thermal cross-linking at 100 DEG C for 10-15 minutes, and washing for 3-5 times to obtain the composite distillation membrane. According to the prepared composite membrane, the compact double-gel network on the surface layer can greatly improve the mechanical stability of the membrane, a regular flexible protruding structure is formed, the surface cleaning effect on various pollutants can be achieved, the responsiveness of methyl cellulose to the temperature can further remarkably improve the membrane pollution reversibility, surface deformation can be generated through low-temperature flushing, and the surface cleaning effect is good. Therefore, the structure of a polluted layer is loosened, the flushing effect is improved, and the reusability and long-acting stability of the membrane are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of high-salt organic wastewater treatment, and specifically 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 hydrophobic membrane as separation medium and the steam pressure difference on both sides of the membrane as driving force. It has the advantages of being able to utilize low-grade energy, simple equipment, and good water quality. In theory, it can achieve deep concentration of wastewater and near-zero discharge. However, membrane distillation has not yet been applied to engineering practice. One of the main limiting factors is that conventional hydrophobic membranes are prone to pollution and wetting problems. For high-salt organic wastewater, problems such as membrane scaling and membrane pore wetting caused by high-concentration inorganic salts are particularly serious and have not yet been effectively solved. Membrane scaling originates from the precipitation or deposition of inorganic salts in wastewater on the membrane surface. The growth of scale crystals into the membrane pores will cause irreversible damage to the membrane pore structure, eventually causing the membrane pores to be wetted and the membrane distillation process to fail. Organic pollutants in wastewater will adhere to the membrane surface or inside the membrane pores through hydrophobic action, thereby blocking or wetting the membrane pores and deteriorating the water quality of the produced water. Due to the hydrophobicity of the membrane, pollutants deposited in the membrane pores are difficult to clean and the 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 hydrophilicity of the membrane surface is mainly improved to promote the formation of a hydration layer on the membrane surface, or the adhesion of hydrophobic organic matter on the membrane surface is alleviated 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 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 that the existing distillation membrane is easily contaminated or wetted, and to provide a method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane.

[0005] To achieve the above purpose, 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, the method 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 concentration of dopamine to 2-5 g / L, shake well and pour it on the surface of the hydrophobic microporous membrane, the thickness of the liquid layer is not less than 3 mm, and 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, rinse with pure water 3 times, repeat the loading process of the polydopamine intermediate bonding layer in step 1 on the membrane surface, and perform polymerization reaction at room temperature in a shaker for 6 to 12 hours;

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

[0010] Step 4: Apply the solution prepared in step 3 to the surface of the polydopamine-modified membrane, control the thickness of the liquid layer to be greater than 10 μm, dry at room temperature for 24 to 48 hours, and then cross-link 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 one, 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 solution, 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 most of the inorganic and organic pollutants in the wastewater from penetrating, 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 the rigid crystal particles precipitated in the highly concentrated state of the 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 methylcellulose-polyvinyl alcohol double-network responsive gel composite membrane prepared by the present invention can significantly improve the recovery of membrane surface contamination due to the responsiveness change of the methylcellulose loaded on the surface to temperature. 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 in conjunction with 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 protection scope 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 of the 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 interlaced 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 the rigid crystal particles precipitated under the highly concentrated state of the wastewater; the methylcellulose loaded on the membrane surface will form a regular flexible convex structure in the swollen state, which will play a cilia-like cleaning role for the 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, and 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 for high-salt organic wastewater in a long-term and stable manner.

[0024] Embodiment 1:

[0025] A method for preparing a highly stable, multi-effect, anti-pollution double-network gel composite distillation membrane, the method 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, the concentration of dopamine is controlled to be 2 g / L, the prepared solution is poured on the surface of the hydrophobic microporous membrane, and placed on a shaker at room temperature for polymerization reaction for 12 hours;

[0027] Step S2: pour out the polydopamine solution on the membrane surface and rinse with pure water for 3 times, repeat the loading process of the polydopamine intermediate bonding 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 concentration of polyvinyl alcohol to 3wt%, the mass ratio of methylcellulose to polyvinyl alcohol and glutaraldehyde to 1:3:3, adjusting the pH to 1 with sulfuric acid, and ultrasonically mixing for 30s;

[0029] Step S4: coating the solution prepared in step S3 on the surface of the polydopamine-modified membrane, controlling the thickness of the liquid layer to be 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 for 3 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 responsiveness of methyl cellulose to temperature 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 rinse. 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 dodecylbenzene sulfonate, 500mg / L crude oil), the wastewater and condensate water temperatures were set to 60°C and 20°C, respectively, and the flow rates were both 0.1m / s. During 90 hours of continuous operation, the water flux of the prepared methyl cellulose-polyvinyl alcohol double network responsive gel composite membrane only decreased by 19.5%, 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°C), demonstrating the multi-effect anti-pollution, flushing recovery and long-term stability of the composite membrane for the treatment of high-salt organic wastewater.

[0032] Embodiment 2:

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

[0034] Step S1: firstly, 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, the concentration of dopamine is controlled to be 5 g / L, the prepared solution is poured on the surface of the hydrophobic microporous membrane, and placed on a shaker at room temperature for polymerization reaction for 8 hours;

[0035] Step S2: pour out the polydopamine solution on the membrane surface and rinse with pure water for 3 times, repeat the loading process of the polydopamine intermediate bonding 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 concentration of polyvinyl alcohol to 4wt%, the mass ratio of methylcellulose to polyvinyl alcohol and glyoxal to 1:4:4, adjusting the pH to 2 with hydrochloric acid, and ultrasonically mixing for 30s;

[0037] Step S4: coating the solution prepared in step 3 on the surface of the polydopamine-modified membrane, controlling the thickness of the liquid layer to be 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. In the process of concentration and water reuse of membrane distillation 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, 1g / L crude oil), the wastewater and condensed water temperatures were set to 50℃ and 20℃, respectively, and the flow rate was 0.1m / s. The prepared methylcellulose-polyvinyl alcohol double network responsive gel composite membrane had a water recovery rate of 90% and a water flux decrease of about 30% during 120 hours of continuous operation. At the same time, the conductivity of the produced water was always less than 5μS / cm. After operation, 92% of the water flux can be restored by washing with normal temperature water (about 20℃), showing the multi-effect anti-pollution, washing 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 in that: 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 concentration of dopamine to 2-5 g / L, shake well and pour it on the surface of the hydrophobic microporous membrane, the thickness of the liquid layer is not less than 3 mm, and 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, rinse with pure water 3 times, repeat the loading process of the polydopamine intermediate bonding layer in step 1 on the membrane surface, and perform polymerization reaction at room temperature in a shaker for 6 to 12 hours; Step 3: prepare methylcellulose / polyvinyl alcohol / crosslinking agent coating solution, adjust pH to ≤ 2 with sulfuric acid or hydrochloric acid, and mix by ultrasonic for 30 seconds; Step 4: Apply the solution prepared in step 3 to the surface of the polydopamine-modified membrane, control the thickness of the liquid layer to be greater than 10 μm, dry at room temperature for 24 to 48 hours, and then cross-link 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 solution, 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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