Preparation method of polysulfone ultrafiltration membrane based on density gradient improvement

Abstract

This application discloses a method for preparing polysulfone ultrafiltration membranes based on density gradient improvement, relating to the field of ultrafiltration membrane preparation technology. The preparation method provided by this application includes the following steps: Preparation of the base solution: a base solution is prepared using an organic solvent, polysulfone, a pore-forming agent, and additives; Membrane casting: a primary membrane is obtained by spraying the base solution and heating the nonwoven fabric. This application allows for rapid preparation of the base solution with the aid of an organic solvent, and the formation of the primary membrane by heating the nonwoven fabric. A perforation, extending through the membrane, is created on the primary membrane through a suction process. Compared to some existing preparation methods, this method can control the density of the permeable pores in the prepared polysulfone ultrafiltration membrane to be uniformly varied, and reduces the occurrence of dead-end pores and ineffective pores, thereby increasing the overall permeability of the membrane structure and enhancing its hydrophilicity, thus improving its overall application performance.

Description

Technical Field

[0001] This application relates to the field of ultrafiltration membrane preparation technology, specifically to a method for preparing polysulfone ultrafiltration membranes based on density gradient improvement. Background Technology

[0002] Ultrafiltration membrane separation technology is used for the separation, concentration, or purification of substances. It boasts advantages such as high separation efficiency, small footprint, simple operation, and convenient maintenance, and has been widely applied in water treatment, food, pharmaceutical, and chemical industries. Membrane material is the core of ultrafiltration membrane separation technology and is key to achieving efficient separation. Polysulfone currently dominates the market for separation membrane materials. Due to the presence of sulfone groups in its molecular backbone, this polymer exhibits excellent thermal stability, chemical stability, resistance to acid and alkali corrosion, superior mechanical properties, and outstanding creep resistance. With the continuous development of membrane separation technology, polysulfone ultrafiltration membranes, as a polymeric membrane material with advantages such as good chemical stability, high mechanical strength, and good acid and alkali resistance, are widely used in drinking water purification, wastewater treatment, and biotechnology. However, because polysulfone ultrafiltration membranes contain a certain number of dead-end pores and ineffective pores, water does not easily permeate, resulting in low hydrophobicity of the entire membrane structure. This leads to lower water flux, poor hydrophilicity, and susceptibility to fouling and difficulty in cleaning, thus affecting its application in water treatment. Summary of the Invention

[0003] The purpose of this application is to provide a method for preparing polysulfone ultrafiltration membranes based on density gradient improvement in order to solve the problems mentioned above in the background art.

[0004] To achieve the above objectives, this application specifically adopts the following technical solution: A method for preparing polysulfone ultrafiltration membranes based on density gradient improvement includes the following steps: Preparation of the base solution: Select organic solvent, polysulfone, pore-forming agent and additives, mix them evenly and dissolve them in water, and stir them to obtain the base solution; Casting: The base liquid is sprayed onto the nonwoven fabric, the nonwoven fabric is kept in a flat state, and the nonwoven fabric is heated. After the moisture in the nonwoven fabric evaporates, it is placed in clean water to moisturize and shape it to obtain the original film. Pore ​​formation: The original membrane is removed from the water and one side is sucked up using an air suction device so that the pore-forming agent is drawn out from one side of the original membrane, thereby obtaining a polysulfone ultrafiltration membrane.

[0005] By adopting the above technical solution, with the aid of organic solvent, the additives and polysulfone can form a primary membrane on the nonwoven fabric. Under the action of the pore-forming agent, when it is absorbed, water-permeable pores with a density gradient can be formed on the primary membrane, thereby forming a polysulfone ultrafiltration membrane.

[0006] Furthermore, the organic solvent includes one or more of ethylene glycol dimethyl ether, lauryl alcohol polyoxyethylene ether, perchloroethylene, trichloroethylene, ethylene glycol ether, and triethanolamine, with perchloroethylene being preferred.

[0007] By adopting the above technical solutions, solvents such as ethylene glycol dimethyl ether, lauryl alcohol polyoxyethylene ether, perchloroethylene, trichloroethylene, ethylene glycol ether, and triethanolamine have the characteristics of chemical stability and low reactivity, which are conducive to the rapid dissolution of polysulfone and additives.

[0008] Furthermore, the pore-forming agent is ammonium carbonate, ammonium bicarbonate, ammonium chloride, pulverized coal, or carbon powder, with pulverized coal being preferred.

[0009] By adopting the above technical solution, substances such as ammonium carbonate, ammonium bicarbonate, ammonium chloride, coal powder or carbon powder, with preference given to coal powder, have the property of being able to dissolve quickly and are chemically unstable and easily decomposed, thus making them suitable for manufacturing permeable pores and resulting in pores with a relatively uniform texture.

[0010] Furthermore, the additive comprises one or more of citric acid, fumaric acid, lactic acid, acetic acid, hydrochloric acid, phosphoric acid, and a compound acidifying agent, with hydrochloric acid being preferred.

[0011] By adopting the above technical solution, citric acid, fumaric acid, lactic acid, acetic acid, hydrochloric acid, phosphoric acid, and composite acidifier all have the property of rapid dissolution when heated, thus easily and quickly mixing with polysulfone, thereby accelerating the forming speed of the original film.

[0012] Furthermore, the composite acidifying agent comprises one or more of L-lactic acid, fumaric acid, formic acid, acetic acid, propionic acid, butyric acid, and sorbic acid mixed with phosphoric acid and / or hydrochloric acid, and also includes silicon dioxide.

[0013] By adopting the above technical solution, L-lactic acid, fumaric acid, formic acid, acetic acid, propionic acid, butyric acid, sorbic acid, etc. all have good water solubility and can promote the formation of unsaturated polyester resin. Phosphoric acid and hydrochloric acid are not easily volatile or decomposed, and both have certain oxidizing properties. They can react with L-lactic acid, fumaric acid, formic acid, acetic acid, propionic acid, butyric acid, sorbic acid, etc. to form complexes, thereby promoting the formation of the original film.

[0014] Furthermore, the mixing operation in the base liquid preparation step includes the following steps: The pore-forming agent is added to a grinding device and ground for a certain period of time to obtain particulate matter with a diameter not exceeding 0.1 nanometers; Add the organic solvent, polysulfone, particulate matter and additives to the mixer, start the mixer and keep the speed at no less than 3000 rpm for a certain period of time. After mixing is complete, centrifuge for a certain period of time.

[0015] By adopting the above technical solution, grinding can make the pore-forming agent fine and uniform in particle diameter, and it can be evenly dispersed in the bottom liquid under stirring. Centrifugation can quickly remove the air from the bottom liquid.

[0016] Furthermore, in the casting process, the spraying of the primer includes the following steps: Use a fixing device to secure the nonwoven fabric and fully extend it to keep it in a horizontal position; Add the base liquid to the spraying equipment and start the spraying equipment. Spray along the downward side of the non-woven fabric in sequence. When one coat is completed, let it stand for a certain period of time and then spray again.

[0017] By adopting the above technical solution, when the liquid is sprayed from bottom to top to integrate with the nonwoven fabric, it is not easily affected by its own gravity, which would cause uneven penetration. Furthermore, the segmented spraying allows the liquid to penetrate the nonwoven fabric more fully.

[0018] Furthermore, in the pore-forming step, when using an air suction device to suction one side of the original membrane, the following steps are included: The original membrane is then fixed in place again using a fixing device, and the original membrane is ultrasonically treated using an ultrasonic device. Keep the original film horizontal and use the suction device to suck up the upward-facing side of the original film.

[0019] By adopting the above technical solution, ultrasound can cause the original membrane to vibrate at a certain frequency, so that the pore-forming agent is decomposed or forms particles. The particles will also vibrate at the same frequency to promote the formation of pores. By suction, the particles are moved to one side to form water-permeable pores that penetrate the original membrane.

[0020] Furthermore, when using an ultrasonic device to sonicate the original membrane, the ultrasonic time shall not be less than 3 minutes and the frequency shall not be less than 30,000 Hz.

[0021] By adopting the above technical solution, the time and frequency of ultrasound are limited, thereby ensuring the degree of particle movement within the original membrane and thus ensuring the formation of air pores.

[0022] Furthermore, in the casting step, when heating the nonwoven fabric, the heating temperature is not lower than 60 degrees Celsius, and the time is not lower than 5 minutes.

[0023] By adopting the above technical solution, the minimum heating temperature is limited to 60 degrees Celsius, and the minimum heating time is limited to 5 minutes, so that the base liquid can be quickly solidified, thereby quickly forming unsaturated polyester resin and enabling the original film to be formed quickly.

[0024] The beneficial effects of this application are as follows: 1. This application utilizes an organic solvent to rapidly fuse polysulfone and additives together, forming a base solution. This base solution is then solidified on a nonwoven fabric by heating, forming a primary membrane, i.e., a polysulfone ultrafiltration membrane. A suction process allows the pore-forming agent embedded in the primary membrane to emerge towards one side, leaving a perforation through the membrane thickness. This results in a polysulfone ultrafiltration membrane with a gradient density. Compared to existing preparation methods, this method can control the density of the permeable pores in the produced polysulfone ultrafiltration membrane to be uniformly varied, and reduces the occurrence of dead-end pores and ineffective pores, thereby increasing the overall permeability and hydrophilicity of the membrane structure and enhancing its overall application performance.

[0025] 2. The organic solvents used in this application are limited to substances such as ethylene glycol dimethyl ether, lauryl alcohol polyoxyethylene ether, perchloroethylene, trichloroethylene, ethylene glycol ether, and triethanolamine. Since these substances generally have relatively stable chemical properties, they are not easily oxidized and can maintain their original composition, thereby promoting the rapid dissolution of polysulfone and additives and increasing the preparation speed of the base solution.

[0026] 3. The pore-forming agent used in this application is limited to substances such as ammonium carbonate, ammonium bicarbonate, ammonium chloride, coal powder, or carbon powder. Since these substances are all rapidly soluble, they can quickly penetrate into the bottom liquid, thereby promoting the preparation speed of the bottom liquid. At the same time, these substances also have relatively active chemical properties, that is, they are chemically unstable and are easily decomposed quickly, which is conducive to promoting the formation of permeable pores. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method provided in this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0029] like Figure 1 As shown in one embodiment of this application, a method for preparing polysulfone ultrafiltration membranes based on density gradient improvement is proposed. This method is used to prepare polysulfone ultrafiltration membranes so that the density of the permeable pores of different prepared polysulfone ultrafiltration membranes can be arranged in a gradient, thereby enabling better filtration of water quality. The entire preparation method includes the following steps: Preparation of the base solution: First, select an organic solvent, polysulfone, pore-forming agent, and additives. The additives promote the dissolution of polysulfone in the organic solvent. Mix these materials evenly and dissolve them in water to form a solution. The polysulfone will be incorporated into the organic solvent and bonded together with the additives to form a semi-solid dense layer. Then, stir all the mixed substances thoroughly to ensure that the components are completely and evenly integrated to obtain the base solution. Casting: The base liquid is sprayed onto the nonwoven fabric. During spraying, it is necessary to ensure uniform spraying so that the thickness of the base liquid is consistent in every part of the nonwoven fabric. Then, the nonwoven fabric is kept in a flat state. The flat state is to ensure the smoothness and flatness of the membrane structure surface during subsequent film formation. Then, the nonwoven fabric is heated. After heating, the internal water of the base liquid will evaporate, and the remaining components will solidify to a certain extent, thus forming a soft and waterproof dense layer, that is, the primary polysulfone membrane structure. The nonwoven fabric is equivalent to the entire membrane matrix, acting as a physical carrier, so that the entire membrane structure has a certain degree of firmness and prevents the membrane structure from cracking or stretching to a certain extent. After the water in the nonwoven fabric evaporates, the entire primary polysulfone membrane structure is placed in clean water. Since the materials have solidified and formed, water will not penetrate or merge, so that the structure can be moisturized and shaped in water, making the surface glossy, soft and not easy to wrinkle, thus obtaining the complete original membrane structure. Pore ​​formation: First, the original membrane is removed from the water. The water can be blown dry to maintain a complete membrane shape. Then, one side is sucked up using an air suction device. Since the pore-forming agent has been decomposed in the original membrane and formed into gas or possibly solid, there must be cavities inside the original membrane under a microscopic perspective, and they are of uniform size. Through air suction, the pore-forming agent is sucked out from one side of the original membrane. That is, both gas and solid will be sucked out from one side. During the suction, whether it is solid or liquid, it will leave perforations in the movement path and penetrate to the outside, thus forming water-permeable pores, thereby obtaining the polysulfone ultrafiltration membrane. Compared with some existing methods, this method effectively ensures the permeability of the pores by using air suction during pore formation, allowing the pore-forming material to pass through the mold as it moves. In addition, when manufacturing different polysulfone ultrafiltration membranes, the density of pores in each membrane structure can be controlled by controlling the spraying of the substrate and the amount of the pore-forming agent. This allows the density of pores in multiple membrane structures to be arranged in a gradient, thus enabling better filtration of different substances during use.

[0030] In some embodiments, the organic solvent includes one or more of ethylene glycol dimethyl ether, lauryl polyoxyethylene ether, perchloroethylene, trichloroethylene, ethylene glycol ether, and triethanolamine, but perchloroethylene is preferred. Among these substances, due to the general properties of organic matter, carbon-hydrogen bonds are not easily broken, so no chemical change occurs when dissolved in water, making the properties relatively stable and not easily decomposed, thus facilitating the rapid dissolution of polysulfone and additive components.

[0031] To ensure the quality of pore formation, in some embodiments, the pore-forming agent is ammonium carbonate, ammonium bicarbonate, ammonium chloride, coal powder, or carbon powder, with coal powder being preferred. These substances are all chemically reactive and easily decompose when the original film is heated, thereby accelerating the pore formation speed and making the pore size more uniform.

[0032] In some embodiments, the additive comprises one or more of citric acid, fumaric acid, lactic acid, acetic acid, hydrochloric acid, phosphoric acid, and a composite acidifier, but hydrochloric acid is preferred. These substances can dissolve rapidly when the original film is heated, thereby rapidly fusing with polysulfone.

[0033] In some embodiments, the composite acidifier comprises one or more of L-lactic acid, fumaric acid, formic acid, acetic acid, propionic acid, butyric acid, and sorbic acid, combined with phosphoric acid and / or hydrochloric acid. L-lactic acid, fumaric acid, formic acid, acetic acid, propionic acid, butyric acid, and sorbic acid have good water solubility and can readily combine with water molecules in a short time. Phosphoric acid and hydrochloric acid are both strong acids, not easily volatile, and not easily decomposed. The nature of strong acids gives them a certain degree of oxidizing power, allowing them to quickly combine with L-lactic acid, fumaric acid, formic acid, acetic acid, propionic acid, butyric acid, and sorbic acid to form complexes. The composite acidifier also includes silicon dioxide, which, when combined with the complexes, can quickly fuse with polysulfone. This ensures the effectiveness of the additives.

[0034] To ensure the quality of the base solution preparation, in some embodiments, the mixing operation in the base solution preparation step includes the following steps: The pore-forming agent is added to a grinding device and ground for a certain period of time. The grinding process crushes the pore-forming agent to obtain particulate matter, ensuring that the size of the particulate matter is uniform and that its diameter does not exceed 0.1 nanometers, thereby guaranteeing the pore size during subsequent pore formation. Add the organic solvent, polysulfone, particulate matter, and additives to the mixer, start the mixer, and set the speed to no less than 3000 rpm to ensure thorough mixing of the substances and uniformity. Maintain a certain mixing time during mixing. After stirring is complete, centrifuge for a certain period of time. Centrifugation is to ensure that the air in the mixture is completely removed, so as to prevent the presence of too much air, which is not easy to expel when dissolved in water, thus easily affecting the compactness of the membrane structure.

[0035] In some embodiments, the casting step, when spraying the primer, includes the following steps: Use fixing equipment to fix the non-woven fabric. Specifically, you can use some clamping equipment or negative pressure adsorption equipment to fix it. When fixing, fully extend the non-woven fabric and keep it in a horizontal state. Add the primer to the spraying equipment, which can be an airless sprayer. Start the spraying equipment and spray sequentially along the bottom side of the nonwoven fabric, i.e., spray from bottom to top, so that the primer does not spread on the fabric surface due to its own gravity. After one coat is completed, let it stand for a certain period of time, and then spray again in the same way. By controlling the spraying time period, the primer can be fully integrated into the nonwoven fabric within the interval after each coat.

[0036] In some embodiments, when the pore-forming step involves using an air suction device to suction one side of the original membrane, the following steps are included: The original membrane is then fixed again using a fixing device, namely, by using a clamping or negative pressure adsorption device to fix the original membrane, and by using an ultrasonic device to sonicate the original membrane, which can promote the decomposition of the pore-forming agent particles and reduce the adhesion between them and the formed pores, making it easier to remove them later. Keep the original membrane in a horizontal position and use an air suction device to suck up the upward side of the original membrane to form water-permeable holes.

[0037] In some embodiments, when the original membrane is ultrasonically treated with an ultrasonic device, the ultrasonic time is not less than 3 minutes and the frequency is not less than 30,000 Hz. The 3 minutes of time is sufficient to ensure that each pore-forming agent particle is completely decomposed, and the 30,000 Hz frequency can ensure the stability of the particle vibration, so that the pores are fully compressed and the phenomenon of dead end pores or ineffective pores in the later stage is reduced.

[0038] In some embodiments, during the casting process, when heating the nonwoven fabric, the heating temperature is not lower than 60 degrees Celsius. 60 degrees Celsius allows the various substances in the original film to fully solidify without damaging the structure of the combination of the various substances. The heating time is not less than 5 minutes to ensure sufficient heating.

[0039] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing polysulfone ultrafiltration membranes based on density gradient improvement, characterized in that, Includes the following steps: Preparation of the base solution: Select organic solvent, polysulfone, pore-forming agent and additives, mix them evenly and dissolve them in water, and stir them to obtain the base solution; Casting: The base liquid is sprayed onto the nonwoven fabric, the nonwoven fabric is kept in a flat state, and the nonwoven fabric is heated. After the moisture in the nonwoven fabric evaporates, it is placed in clean water to moisturize and shape it to obtain the original film. Pore ​​formation: The original membrane is removed from the water and one side is sucked up using an air suction device so that the pore-forming agent is drawn out from one side of the original membrane, thereby obtaining a polysulfone ultrafiltration membrane; In the casting process, the spraying of the primer includes the following steps: Use a fixing device to secure the nonwoven fabric and fully extend it to keep it in a horizontal position; Add the base liquid to the spraying equipment and start the spraying equipment. Spray along the downward side of the non-woven fabric in sequence. When one coat is completed, let it stand for a certain period of time and then spray again. In the pore-forming step, when using an air suction device to suction one side of the original membrane, the following steps are included: The original membrane is then fixed in place again using a fixing device, and the original membrane is ultrasonically treated using an ultrasonic device. Keep the original film horizontal and use the suction device to suck up the upward-facing side of the original film; The organic solvent includes one or more of ethylene glycol dimethyl ether, lauryl alcohol polyoxyethylene ether, perchloroethylene, trichloroethylene, ethylene glycol ether, and triethanolamine; The pore-forming agent is ammonium carbonate, ammonium bicarbonate, ammonium chloride, coal powder, or carbon powder; The additives include one or more of the following: citric acid, fumaric acid, lactic acid, acetic acid, hydrochloric acid, phosphoric acid, and compound acidifiers. The composite acidifying agent comprises one or more of L-lactic acid, fumaric acid, formic acid, acetic acid, propionic acid, butyric acid, and sorbic acid mixed with phosphoric acid and / or hydrochloric acid, and also includes silicon dioxide.

2. The method for preparing polysulfone ultrafiltration membrane based on density gradient improvement according to claim 1, characterized in that, The mixing process in the preparation of the base liquid includes the following steps: The pore-forming agent is added to a grinding device and ground for a certain period of time to obtain particulate matter with a diameter not exceeding 0.1 nanometers; Add the organic solvent, polysulfone, particulate matter and additives to the mixer, start the mixer and keep the speed at no less than 3000 rpm for a certain period of time. After mixing is complete, centrifuge for a certain period of time.

3. The method for preparing polysulfone ultrafiltration membrane based on density gradient improvement according to claim 1, characterized in that, When using an ultrasonic device to sonicate the original membrane, the sonication time shall not be less than 3 minutes and the frequency shall not be less than 30,000 Hz.

4. The method for preparing polysulfone ultrafiltration membrane based on density gradient improvement according to claim 1, characterized in that, In the casting process, when heating the nonwoven fabric, the heating temperature is not lower than 60 degrees Celsius and the heating time is not lower than 5 minutes.

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