A method for preparing a durable hydrophilic ultrafiltration membrane

Abstract

The application belongs to the field of filtration membranes, and relates to a preparation method of a persistent hydrophilic ultrafiltration membrane. Firstly, functional hydrophilic molecules are simultaneously synthesized in a conventional dissolving process of a polymer membrane material; then, after the polymer solution (nascent membrane) enters a coagulation bath, a cross-linking reaction between the functional hydrophilic molecules is initiated by the coagulation bath to form a hydrophilic cross-linking network. By in-situ forming a hydrophilic cross-linking interpenetrating network in the polymer phase separation process, the movement of polymer chains and the formation and growth of micelles are limited, a relatively uniform polymer interpenetrating network structure is formed, and a persistent hydrophilic ultrafiltration membrane with a relatively uniform membrane pore structure is obtained. The method has mild reaction conditions, a simple preparation method, and universality.

Description

Technical Field

[0001] This invention belongs to the field of filtration membranes, and relates to ultrafiltration membranes, particularly a method for preparing a durable hydrophilic ultrafiltration membrane. Background Technology

[0002] With the increasing severity of global water scarcity, water purification and reuse are playing an increasingly important role in human and industrial activities. Membrane technology has become the mainstream water purification technology due to its low cost and high efficiency. Ultrafiltration technology has advantages such as strong membrane structure adaptability, low operating pressure, high water flux, and low operating cost, and can achieve highly efficient removal of colloidal particles, macromolecular organic matter, proteins, and microorganisms from water. Ultrafiltration technology has become the preferred technology for next-generation urban and industrial wastewater recycling.

[0003] Ultrafiltration membranes primarily remove impurities from water through pore size sieving. However, in the dry-wet phase separation process for ultrafiltration membrane preparation, the randomness of the phase separation process results in a relatively wide pore size distribution in most ultrafiltration membranes, limiting their separation efficiency. Analyzing the phase separation principle, the pore structure of ultrafiltration membranes is mainly influenced by the migration and solidification processes of polymer molecular chains in the casting solution during phase separation, i.e., the formation, growth, and solidification of polymer micelles.

[0004] Therefore, achieving the controllable development of relatively random polymer micelle nucleation and growth processes is the key to realizing the homogenization of ultrafiltration membrane pore structure. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a durable hydrophilic ultrafiltration membrane. The method involves constructing a cross-linked network in situ to assist phase separation. By constructing a hydrophilic cross-linked interpenetrating network in situ, the pore size of the durable hydrophilic ultrafiltration membrane is simultaneously made uniform during the membrane preparation process, thereby promoting the simultaneous improvement of ultrafiltration membrane permeation flux, separation performance and antifouling ability.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] This invention achieves in-situ synthesis of functional hydrophilic molecules during the conventional dissolution of polymer membrane materials using a one-pot method. Then, after the polymer solution (nascent membrane) enters a coagulation bath, the coagulation bath initiates a cross-linking reaction between the functional hydrophilic molecules, forming an in-situ cross-linked interpenetrating network with the polymer membrane material molecular chains. This in-situ formed hydrophilic cross-linked interpenetrating network synergistically regulates the phase separation process, restricts polymer chain movement and micelle formation and growth, resulting in a more uniform polymer network structure and ultimately obtaining a durable hydrophilic ultrafiltration membrane with a more uniform pore structure. This method simultaneously achieves hydrophilization and pore size uniformity of the membrane material during membrane fabrication, promoting a simultaneous improvement in ultrafiltration membrane permeate flux, separation performance, and antifouling ability.

[0008] The method of the present invention includes the following steps:

[0009] The polymer membrane material, active molecule A, active molecule B, and solvent are stirred at a constant temperature to achieve in-situ synthesis of functional hydrophilic polymers during the conventional dissolution process of the polymer membrane material, and a polymer solution is obtained. Then, the obtained polymer solution is used to prepare an ultrafiltration membrane using a dry-wet phase separation method. The cross-linking reaction between functional hydrophilic molecules is initiated by a coagulation bath and solidified into a membrane, which is the finished ultrafiltration membrane.

[0010] The proportions of each component in the casting solution are as follows: the polymer membrane material accounts for 13wt% to 20wt% of the weight of the casting solution, the solvent accounts for 55wt% to 86wt% of the weight of the casting solution, active molecule A accounts for 1wt% to 10wt% of the weight of the casting solution, and active molecule B accounts for 1wt% to 15wt% of the weight of the casting solution, with a total of 100%.

[0011] The polymer membrane material is one or a mixture of two or more of the most common polymer membrane materials, such as polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene fluoride, polyvinylidene fluoride-trifluorochloroethylene copolymer, polysulfone, polyethersulfone, polyacrylonitrile, etc.

[0012] The solvent is one or a mixture of dimethylformamide, dimethyl sulfoxide, and dimethylacetamide.

[0013] The constant temperature stirring temperature is 30-90℃, and the constant temperature mixing time is 2h-48h.

[0014] The active molecule A is a molecule that simultaneously contains amino and siloxane groups, specifically one or a mixture of two or more of the following: (3-aminopropyl)trimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropyldiethoxymethylsilane, diethylenetriaminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and 3-piperazinylpropylmethyldimethoxysilane.

[0015] The active molecule B is one or a mixture of two or more of the following: diglycidyl ether, glycerol diglycidyl ether, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether.

[0016] Among them, active molecule A can react with active molecule B, endowing active molecule B with self-crosslinking characteristics. Active molecule B is rich in hydrophilic groups. Active molecules A and B combine in the casting solution and crosslink with polymer molecular chains in the coagulation bath to form a crosslinked interpenetrating structure. The synergistic effect of active molecules A and B is beneficial to pore size uniformity, promoting a simultaneous improvement in ultrafiltration membrane permeation flux, separation performance, and antifouling ability.

[0017] A coagulation bath is an aqueous solution of sodium hydroxide or hydrochloric acid, with a concentration maintained between 0.1 wt% and 30 wt%, and a temperature controlled between 25°C and 80°C.

[0018] Ultrafiltration membranes refer to either flat sheet membranes or hollow fiber membranes.

[0019] Advantages and beneficial effects of the present invention:

[0020] 1. This invention utilizes a coagulation bath to initiate a cross-linking reaction between functional hydrophilic molecules, enabling them to form a hydrophilic cross-linked interpenetrating network in situ with the molecular chains of the polymer membrane material, thereby giving the ultrafiltration membrane durable hydrophilicity.

[0021] 2. This invention regulates the phase separation process by forming an in-situ hydrophilic cross-linked interpenetrating network, interfering with polymer chain movement and micelle formation and growth, forming a more uniform polymer network structure, and obtaining a durable hydrophilic ultrafiltration membrane with a more uniform membrane pore structure.

[0022] 3. This invention achieves simultaneous improvement in ultrafiltration membrane permeation flux, separation performance, and antifouling ability by constructing a hydrophilic cross-linked interpenetrating network in situ. Attached Figure Description

[0023] Figure 1 Comparison of the solubility of ultrafiltration membranes with different amounts of added active molecules in solvents;

[0024] Figure 2 A comparison of the pore size and pore size distribution of ultrafiltration membranes with different amounts of added hydrophilic molecules. Detailed Implementation

[0025] To better understand the purpose, structure, and function of this invention, the following provides a more detailed description of a method for preparing ultrafiltration membranes based on in-situ construction of cross-linked networks to assist phase separation.

[0026] Examples 1 to 10 and Comparative Example 1:

[0027] Weigh out 13 wt% of membrane material polymer, 5 wt% of active molecule A, 75 wt% of dimethylformamide (solvent), and add 7 wt% of active molecule B. Stir at 40℃ for 48 h until completely dissolved to form a homogeneous solution. After coating, place the solution in a coagulation bath containing crosslinking agents to prepare a flat sheet ultrafiltration membrane using a phase inversion method. The types of active molecules A and B, as well as the composition of the coagulation bath, are shown in Table 1. The coagulation bath temperature was 25℃.

[0028] Table 1. Effects of adding different reactive molecules on the performance of flat sheet membranes

[0029]

[0030]

[0031] Table 1 shows the effects of adding different active molecules A and B to the casting solution on the hydrophilicity / hydrophobicity and antifouling performance of the ultrafiltration membrane. Comparative Example 1 served as the control group, and Examples 1 to 10 were the experimental groups. Different amounts of active molecule A were added to polymer membrane materials such as polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene fluoride, polyvinylidene fluoride-trifluorochloroethylene copolymer, polysulfone, polyethersulfone, and polyacrylonitrile. Examples of active molecules A included (3-aminopropyl)trimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropyldiethoxymethylsilane, diethylenetriaminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. Methoxysilanes, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilanes, 3-piperazinylpropylmethyldimethoxysilanes, and various active molecules B, such as diglycidyl ether, glycerol diglycidyl ether, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether, can all impart excellent long-lasting hydrophilicity and antifouling properties, and also demonstrate the universality of this method.

[0032] In Example 1, a flat-sheet ultrafiltration membrane was prepared using polyethersulfone resin as the polymer membrane material and 3-aminopropyltriethoxysilane as active molecule A and polyethylene glycol diglycidyl ether as active molecule B. Compared with control group 1 of Comparative Example 1, which only added active molecule A, or control group 2 of Comparative Example 1, which only added active molecule B, the resulting ultrafiltration membrane had a lower water contact angle, which remained stable after 300 hours of operation in pure water. Furthermore, the flux recovery rate of the ultrafiltration membrane was significantly improved compared to the control group. This demonstrates that by simultaneously introducing a certain amount of active molecules A and B into the casting solution, the hydrophilicity of the ultrafiltration membrane is enhanced, resulting in durable hydrophilicity and improved antifouling performance.

[0033] Examples 11 to 16

[0034] Weigh 20 wt% of polyethersulfone resin (polymer membrane material), a certain amount of 3-aminopropyltriethoxysilane and ethylene glycol diglycidyl ether, with the remainder as solvent, maintaining the total amount of casting solution at 100%. Stir at 80℃ for 24 h until completely dissolved to form a homogeneous solution. After coating, place the membrane in a coagulation bath containing crosslinking agents to prepare a flat-sheet ultrafiltration membrane using a phase inversion method. The amounts of 3-aminopropyltriethoxysilane and ethylene glycol diglycidyl ether added are shown in Table 2. The coagulation bath is deionized water with pH = 8.5, and the coagulation bath temperature is 80℃.

[0035] Table 2. Effect of the amount of reactive active molecules added on the performance of polyethersulfone hollow fiber membranes.

[0036]

[0037] Table 2 shows the effect of the addition amount of reactive molecule A and reactive molecule B on the performance of polyethersulfone hollow fiber ultrafiltration membranes. Examples 11 to 16 were prepared by adding different amounts of reactive molecule A and reactive molecule B to the casting solution. As shown in Examples 11, 12, 13, 14, and 15, 16, with the increase of the amount of reactive molecule added, the proportion of cross-linked structures in the ultrafiltration membrane increases, the ultrafiltration membrane flux shows an increasing trend, and the BSA molecule rejection rate remains stable, while the water contact angle decreases significantly and the flux recovery rate increases. This demonstrates that increasing the amount of reactive molecule added helps to improve the hydrophilicity, antifouling performance, and filtration performance of the ultrafiltration membrane.

[0038] The solubility of the ultrafiltration membranes obtained in Examples 11 to 16 in the solvent dimethylacetamide is as follows: Figure 1 As shown, M0 is control group 1, i.e., the ultrafiltration membrane without added active molecule A. M1, M2, M3, M4, M5, and M6 correspond to Examples 11, 12, 13, 14, 15, and 16, respectively. Compared with control group M0, as the amount of active molecule A and active molecule B increases, the ultrafiltration membrane gradually becomes insoluble, and the amount of insoluble residue shows an increasing trend. The morphology of the residue also changes from flocculent to a complete film, thus proving the successful construction of the hydrophilic crosslinking network. The pore size and pore size distribution of the ultrafiltration membranes obtained in Examples 11 to 16 are shown in the figure. Figure 2 As shown, M0 is the control group 1 of Comparative Example 1, and M1, M2, M3, M4, M5, and M6 correspond to Examples 11, 12, 13, 14, 15, and 16, respectively. Compared with the control group 1 M0, after adding active molecules A and B, the pore size of the ultrafiltration membrane became more uniform, unlike the wider distribution of M0. Furthermore, with the increase in the amount of active molecules A and B, the average pore size of the ultrafiltration membrane increased while maintaining the same maximum pore size, which helps to improve the separation efficiency of the ultrafiltration membrane. This proves that the pore size of the ultrafiltration membrane is made uniform after adding active molecules A and B.

[0039] This invention achieves in-situ synthesis of functional hydrophilic polymers during the conventional dissolution process of polymer membrane materials, and obtains a polymer solution; then, the obtained polymer solution is used to prepare an ultrafiltration membrane using a dry-wet phase separation method, and a coagulation bath is used to initiate a cross-linking reaction between functional hydrophilic molecules and solidify the membrane, which is the finished ultrafiltration membrane.

[0040] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for preparing a durable hydrophilic ultrafiltration membrane, characterized in that: Includes the following steps: First, polymer membrane material, active molecule A, active molecule B, and solvent are stirred at a constant temperature to simultaneously synthesize functional hydrophilic molecules during the dissolution of the polymer membrane material, resulting in a homogeneous polymer solution. Then, the obtained polymer solution is used to prepare an ultrafiltration membrane via a dry-wet phase separation method. A coagulation bath is used to initiate a cross-linking reaction between active molecules A and B, forming a cross-linked network in situ. During phase separation, this network, along with the polymer membrane material molecular chains, forms a cross-linked interpenetrating network. The in-situ cross-linking process regulates the phase separation process, restricting polymer chain movement and micelle formation and growth, resulting in a more uniform polymer interpenetrating network structure and a durable hydrophilic ultrafiltration membrane with a more uniform pore structure. The active molecule A is a molecule that simultaneously contains amino and siloxane groups, and the active molecule B is a diglycidyl ether functional hydrophilic molecule. The active molecule A is one or a mixture of two or more of the following: (3-aminopropyl)trimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropyldiethoxymethylsilane, diethylenetriaminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and 3-piperazinylpropylmethyldimethoxysilane. The active molecule B is one or a mixture of two or more of the following: diglycidyl ether, glycerol diglycidyl ether, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and polyethylene glycol diglycidyl ether.

2. The method according to claim 1, characterized in that: The polymer membrane material accounts for 13wt%~20wt% of the casting solution by weight, the solvent accounts for 60wt%~86wt% of the casting solution by weight, active molecule A accounts for 1wt%~10wt% of the casting solution by weight, and active molecule B accounts for 1wt%~15wt% of the casting solution by weight, with a total amount of 100%.

3. The method according to claim 1, characterized in that: The polymer membrane material is one or a mixture of two or more of the following: polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene fluoride, polyvinylidene fluoride-trifluorochloroethylene copolymer, polysulfone, polyethersulfone, and polyacrylonitrile.

4. The method according to claim 1, characterized in that: The solvent is one or a mixture of two or more of dimethylformamide, dimethyl sulfoxide, and dimethylacetamide.

5. The method according to claim 1, characterized in that: The temperature of the constant temperature stirring is 30~90℃, and the stirring time is 2h~48h.

6. The method according to claim 1, characterized in that: The coagulation bath is an aqueous solution of sodium hydroxide or hydrochloric acid with a concentration of 0.1wt% to 30wt%, and the temperature of the coagulation bath is controlled at 25℃ to 80℃.

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