A method for making a surface antifouling coating for a separation membrane

Abstract

The present application relates to the technical field of composite separation membrane, and provides a method for manufacturing an anti-fouling coating on the surface of a separation membrane to solve the problem that the anti-fouling coating of the separation membrane in the prior art results in the loss of membrane flux and unstable performance of the separation membrane, comprising the following steps: (1) coating an excess of an anti-fouling coating solution on the surface of the separation membrane; (2) forming a negative pressure on the surface of the separation membrane to remove the excess anti-fouling coating solution and dry the film after applying ultrasonic waves to the surface of the separation membrane or after the application of ultrasonic waves. The method can coat an extremely thin and complete anti-fouling coating on the surface of the separation membrane, thereby obtaining a separation membrane with both anti-fouling and low permeation resistance.

Description

Technical Field

[0001] This invention relates to the field of composite separation membrane technology, and in particular to a method for manufacturing an anti-fouling coating on the surface of a separation membrane. Background Technology

[0002] Separation membranes are widely used in water treatment, pharmaceuticals, and chemical industries. However, in practical applications, separation membranes are highly susceptible to fouling by contaminants in the feed solution, and cleaning them is difficult. These contaminants adhering to the separation membrane can affect the quality of the produced water and the lifespan of the membrane material. Therefore, developing separation membranes with excellent antifouling properties is crucial.

[0003] Currently, there is considerable research on improving the antifouling performance of separation membranes, primarily focusing on the fabrication of antifouling coatings. Patent CN115430291A prepares an antifouling coating by coating an acidic solution of polyvinyl alcohol and aldehydes onto the separation layer of a polyamide membrane, improving the membrane's antifouling ability and lifespan. Patent CN108126530A uses zwitterionic polymers and polyvinyl alcohol as crosslinking coating liquids to prepare a reverse osmosis membrane with an antifouling coating. Patent CN108939923A uses crosslinked water-soluble polymers as the main component of the antifouling coating, connected with rivet materials, and after coating and curing, obtains a permanently hydrophilic ultrafiltration membrane. While these methods improve the antifouling performance and rejection rate of separation membranes to some extent, the direct coating method causes excess feed liquid to deposit on the membrane surface, resulting in a thick antifouling coating with defects, leading to problems such as membrane flux loss and performance instability. Summary of the Invention

[0004] In order to overcome the problems of membrane flux loss and unstable performance caused by the antifouling coating of separation membranes in the prior art, the present invention provides a method for manufacturing an antifouling coating on the surface of a separation membrane. This method can coat an extremely thin and complete antifouling coating on the surface of the separation membrane, thereby obtaining a separation membrane that is both antifouling and has low permeation resistance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for manufacturing an antifouling coating on the surface of a separation membrane includes the following steps: (1) Coating the surface of the separation membrane with an excessive amount of antifouling coating solution; (2) Apply ultrasonic waves to the surface of the separation membrane while or after applying ultrasonic waves to form a negative pressure on the surface of the separation membrane to remove excess anti-fouling coating liquid and dry it into a film.

[0006] This invention involves pre-coating an excess of coating liquid onto the surface of a membrane material with selective permeability, then applying ultrasonic waves to break up the excess coating liquid, and then rapidly forming a negative pressure area on the surface of the separation membrane to absorb the excess coating liquid, thereby achieving a very small amount of complete coating effect and ultimately obtaining an antifouling coating that is both antifouling and has low permeation resistance.

[0007] Preferably, the separation membrane includes an ultrafiltration membrane, a nanofiltration membrane, and a reverse osmosis membrane.

[0008] Preferably, the coating solution is a solution containing an organic polymer.

[0009] The coating liquid can be one or more of polyvinyl alcohol, polyethylene glycol, polyether polyol, polyester polyol, polyoxyethylene, polyoxypropylene, polyoxazoline, polyacrylamide, polyN-vinylcaprolactam, polyacrylic acid, polymaleic anhydride, polyepoxysuccinic acid, polyetherimide and polystyrene sulfonic acid.

[0010] Preferably, the viscosity of the coating solution is 1–500 mPa·s.

[0011] If the viscosity of the coating solution is too high, it is not easy to break it up by ultrasound, nor is it easy to remove it by negative pressure, resulting in an excessively thick film. At the same time, if the viscosity of the coating solution is too low, it is not easy to form a complete film.

[0012] Preferably, the viscosity of the coating solution is 1–50 mPa·s.

[0013] Preferably, the frequency of the ultrasonic wave is 20 to 100 kHz.

[0014] Ultrasonic waves within this frequency range can break up excess coating liquid without damaging the film surface.

[0015] Preferably, in step (2), an ultrasonic vacuum device is used to apply ultrasonic waves to the surface of the separation membrane and form a negative pressure. The ultrasonic vacuum device includes several ultrasonic generators and several vacuum devices with the vacuum chamber opening downwards. The ultrasonic generator includes a pressure chamber and an ultrasonic generator. The positive pressure in the pressure chamber and the negative pressure in the vacuum chamber are balanced with each other. The ultrasonic generators and vacuum devices in the ultrasonic vacuum device are arranged symmetrically.

[0016] The vacuum chamber of an ultrasonic vacuum device can create a vacuum. When the ultrasonic vacuum device is placed above the separation membrane, ultrasonic waves can be applied to the separation membrane through the ultrasonic generator, creating a negative pressure area on the membrane surface. The ultrasonic generator and vacuum devices are symmetrically arranged within the ultrasonic vacuum device, such as a combination of ultrasonic generator (U) - vacuum device (V) - ultrasonic generator, which is a UVU type, or a VUV type or UVUVU type. Excessive positive pressure in the pressure chamber will compress the separation membrane, while high negative pressure in the vacuum chamber will attract the separation membrane. Therefore, the symmetrical structure allows the positive and negative pressures applied to the membrane surface to be balanced, resulting in a stable, non-contact relationship between the ultrasonic vacuum device and the separation membrane.

[0017] Preferably, the vacuum degree of the vacuum chamber is 10-50 kPa.

[0018] Preferably, the vacuum degree of the vacuum chamber is 15-30 kPa.

[0019] Preferably, the distance from the bottom of the vacuum chamber to the surface of the separation membrane is 0.5 to 5.0 mm.

[0020] Preferably, the distance from the bottom of the vacuum chamber to the surface of the separation membrane is 1.0 to 2.0 mm.

[0021] The vacuum level of the vacuum chamber and its distance from the surface of the separation membrane both affect the removal effect of the coating liquid. Within the scope defined by this invention, liquid particles can be effectively removed without damaging the membrane surface.

[0022] Therefore, the present invention has the following beneficial effects: it solves the contradiction between coating integrity and permeation resistance, and can achieve a thin and complete coating, thus obtaining an anti-fouling coating that is both anti-fouling and has low permeation resistance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an ultrasonic generator, where 1-1 is a vacuum chamber, 2-1 is an ultrasonic generator, and 2-2 is a pressure chamber. Detailed Implementation

[0024] The present invention will be further described below with reference to specific implementation methods.

[0025] The ultrasonic vacuum device used in the following implementation method is a UVU device, and its structure is as follows: Figure 1 As shown, the ultrasonic generator is rectangular in shape. Two ultrasonic generators are symmetrically arranged on the lower left and lower right sides of the ultrasonic generator. The ultrasonic generator includes an ultrasonic generator 2-1 and a pressure chamber 2-2. The ultrasonic generator 2-1 generates ultrasonic waves downward. The ultrasonic generator also includes a vacuum chamber with an opening downward, which is connected to a vacuum pumping device.

[0026] The commercial reverse osmosis membrane used in the following implementation methods is the WaterCraft RBW type, and the commercial nanofiltration membrane used is the WaterCraft TNF type.

[0027] Example 1 A reverse osmosis membrane with an antifouling coating is prepared by the following steps: (1) A commercial reverse osmosis membrane was coated on one side with an acidic feed solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 20 mPa·s. The coating process involved leaving excess feed solution on the surface of the reverse osmosis membrane, and then tilting the reverse osmosis membrane to remove part of the feed solution by gravity. The wet weight increase of the reverse osmosis membrane after coating was 20 g / m³. 2 ; (2) Then pass through the UVU device at a speed of 12m / min, with an ultrasonic frequency of 75KHz, a gap of 2mm between the UVU device and the membrane, a vacuum degree of 20KPa in the vacuum chamber, a pressure of 20KPa in the pressure chamber, and then enter the 60℃ drying tunnel for 1 minute.

[0028] Comparative Example 1 A reverse osmosis membrane with an antifouling coating is prepared by the following steps: (1) A single-sided acidic feed solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 20 mPa·s was directly coated onto a commercial reverse osmosis membrane. The wet weight increase of the reverse osmosis membrane after coating was 20 g / m³. 2 Dry at 60℃ for 5 minutes.

[0029] Comparative Example 2 A reverse osmosis membrane with an antifouling coating is prepared by the following steps: (1) A single-sided acidic feed solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 0.5 mPa·s was directly coated onto a commercial reverse osmosis membrane. Due to the low viscosity of the feed solution, the wet weight increase of the reverse osmosis membrane after coating was 5 g / m. 2 ; (2) Then pass through the UVU device at a speed of 12m / min, with an ultrasonic frequency of 75KHz, a gap of 2mm between the UVU device and the membrane, a vacuum degree of 20KPa in the vacuum chamber, a pressure of 20KPa in the pressure chamber, and then enter the 60℃ drying tunnel for 1 minute.

[0030] Comparative Example 3 A reverse osmosis membrane with an antifouling coating is prepared by the following steps: (1) A single-sided acidic feed solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 100 mPa·s was directly coated onto a commercial reverse osmosis membrane. The wet weight increase of the reverse osmosis membrane after coating was 40 g / m³. 2 ; (2) Then pass through the UVU device at a speed of 12m / min, with an ultrasonic frequency of 75KHz, a gap of 2mm between the UVU device and the membrane, a vacuum degree of 20KPa in the vacuum chamber, a pressure of 20KPa in the pressure chamber, and then enter the 60℃ drying tunnel for 1 minute.

[0031] Comparative Example 4 A reverse osmosis membrane with an antifouling coating is prepared by the following steps: (1) A commercial reverse osmosis membrane was coated on one side with an acidic feed solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 20 mPa·s. The wet weight increase of the reverse osmosis membrane after coating was 20 g / m. 2 ; (2) Then pass through the UVU device at a speed of 12m / min, with an ultrasonic frequency of 75KHz, a gap of 2mm between the UVU device and the membrane, a vacuum degree of 30KPa in the vacuum chamber, a pressure of 10KPa in the pressure chamber, and then enter the 60℃ drying tunnel for 1 minute.

[0032] Comparative Example 5 A reverse osmosis membrane with an antifouling coating is prepared by the following steps: (1) A commercial reverse osmosis membrane was coated on one side with an acidic feed solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 20 mPa·s. The wet weight increase of the reverse osmosis membrane after coating was 20 g / m. 2 ; (2) Then pass through the UVU device at a speed of 12m / min, with an ultrasonic frequency of 75KHz, a gap of 2mm between the UVU device and the membrane, a vacuum degree of 10KPa in the vacuum chamber, a pressure of 30KPa in the pressure chamber, and then enter the 60℃ drying tunnel for 1 minute.

[0033] Example 2 Nanofiltration membranes with antifouling coatings are prepared by the following steps: (1) A commercial nanofiltration membrane was coated on one side with an acidic solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 20 mPa·s. The wet weight increase of the nanofiltration membrane after coating was 20 g / m³. 2 ; (2) Then pass through the UVU device at a speed of 12m / min, with an ultrasonic frequency of 45KHz, a gap of 2mm between the device and the membrane, a vacuum degree of 20KPa in the vacuum chamber, a pressure of 20KPa in the pressure chamber, and then enter the 60℃ drying tunnel for 1 minute.

[0034] Comparative Example 6 Nanofiltration membranes with antifouling coatings are prepared by the following steps: (1) A commercial nanofiltration membrane was directly coated on one side with an acidic solution (pH = 2.0) containing 0.5% polyvinyl alcohol and 0.1% glutaraldehyde with a viscosity of 20 mPa·s. The wet weight increase of the nanofiltration membrane after coating was 20 g / m³. 2 Dry at 60℃ for 5 minutes.

[0035] The antifouling performance of commercial reverse osmosis membranes, commercial nanofiltration membranes, and the reverse osmosis and nanofiltration membranes with antifouling coatings obtained in the above examples and comparative examples was tested. The test method was as follows: cross-flow filtration was used, and pure water was pre-pressurized at 1.0 MPa for 30 min. Then, under the conditions of 25℃ and constant 25 LMH operating flux, 2000 ppm sodium chloride and 100 ppm bovine serum albumin were added to the pure water and the operation was carried out for 48 hours. The fouling decay rate of the separation membrane after fouling was tested. The results are listed in Table 1.

[0036] Table 1 Compared to commercial separation membranes, Examples 1 and 2 exhibit stronger antifouling capabilities and lower flux loss, indicating that the present invention can provide separation membranes with an antifouling coating that combines antifouling properties with low permeation resistance. Furthermore, the method of the present invention is applicable to various types of separation membranes. Comparison of Example 1 with Comparative Example 1, and Example 2 with Comparative Example 6, shows that the antifouling coating manufacturing method of the present invention produces a superior antifouling effect compared to the direct coating process. Comparison of Example 1 with Comparative Examples 2 and 3 shows that coatings manufactured using low-viscosity coating solutions are easily dispersed, resulting in incomplete coverage of the separation membrane and thus poor antifouling performance. Coatings manufactured using excessively high-viscosity coating solutions are difficult to disperse, leaving a thick coating on the membrane surface after passing through the vacuum chamber. This results in a significant decrease in flux compared to Example 1, despite good antifouling capabilities. Comparison of Example 1 with Comparative Examples 4 and 5 shows that excessively high vacuum levels in the vacuum chamber or pressure in the pressure chamber cause an imbalance in the forces on the membrane surface, leading to excessive coating solution moving away from or adhering to the membrane surface, both of which negatively impact the antifouling performance of the separation membrane.

Claims

1. A method for manufacturing an antifouling coating on the surface of a separation membrane, characterized in that, Includes the following steps: (1) Apply an excessive amount of antifouling coating solution to the surface of the separation membrane; (2) Apply ultrasonic waves to the surface of the separation membrane while or after applying ultrasonic waves to form a negative pressure on the surface of the separation membrane to remove excess anti-fouling coating liquid and then dry to form a film; In step (2), an ultrasonic vacuum device is used to apply ultrasonic waves to the surface of the separation membrane and form a negative pressure. The ultrasonic vacuum device includes several ultrasonic generators and several vacuum devices with the vacuum chamber opening downwards. The ultrasonic generator includes a pressure chamber and an ultrasonic generator. The positive pressure in the pressure chamber and the negative pressure in the vacuum chamber are balanced with each other. The ultrasonic generators and vacuum devices in the ultrasonic vacuum device are arranged symmetrically.

2. The method for manufacturing an anti-fouling coating on the surface of a separation membrane according to claim 1, characterized in that, The coating solution is a solution containing an organic polymer.

3. A method for manufacturing an anti-fouling coating on the surface of a separation membrane according to claim 1 or 2, characterized in that, The viscosity of the coating solution is 1~500 mPa•s.

4. A method for manufacturing an anti-fouling coating on the surface of a separation membrane according to claim 3, characterized in that, The viscosity of the coating solution is 1~50 mPa•s.

5. A method for manufacturing an anti-fouling coating on the surface of a separation membrane according to claim 3, characterized in that, The frequency of the ultrasound is 20~100 kHz.

6. A method for manufacturing an anti-fouling coating on the surface of a separation membrane according to claim 1, characterized in that, The vacuum level of the vacuum chamber is 10-50 kPa.

7. A method for manufacturing an anti-fouling coating on a separation membrane surface according to claim 6, characterized in that, The vacuum level of the vacuum chamber is 15~30 kPa.

8. A method for manufacturing an anti-fouling coating on the surface of a separation membrane according to claim 1, characterized in that, The distance from the bottom of the vacuum chamber to the surface of the separation membrane is 0.5~5.0 mm.

9. A method for manufacturing an anti-fouling coating on the surface of a separation membrane according to claim 8, characterized in that, The distance from the bottom of the vacuum chamber to the surface of the separation membrane is 1.0~2.0 mm.

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