Method for preparing polyamide nanofiltration membrane based on non-reactive ionic liquid

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a method for preparing a polyamide nanofiltration membrane based on non-reactive ionic liquid, which comprises the following steps: preparation of a substrate PES membrane: weighing 16wt% of polyether sulfone PES, 16wt% of polyethylene glycol PEG and 68wt% of N-N dimethylformamide DMF, putting into a round-bottom flask, stirring in a water bath kettle, standing at the same temperature to remove bubbles, and then, adding the substrate PES membrane into the round-bottom flask to obtain the substrate PES membrane; casting the casting solution on a glass plate by using a steel knife, and immersing the glass plate in ultrapure water to remove the residual solvent; and preparation of a polyamide (PA) membrane: carrying out interfacial polymerization on a water phase solution containing piperazine (PIP) and chlorinated 1-butyl-3-methylimidazole and an oil phase solution containing TMC, and synthesizing a polyamide active layer on the PES membrane. The invention provides a new view angle for regulation and control of monomer diffusion and reaction in the interfacial polymerization process, and particularly has important application potential in the aspect of preparation of high-performance polyamide composite membranes.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a method for preparing a polyamide nanofiltration membrane based on ionic liquid. Background Art

[0002] As an important technical means to solve the global shortage of fresh water resources, seawater desalination has been widely used around the world. At present, seawater desalination technology is mainly divided into two categories: thermal method and membrane method. Thermal method includes multi-stage flash evaporation (MSF) and multi-effect distillation (MED), while membrane method mainly includes reverse osmosis (RO) and nanofiltration (NF). In recent years, membrane desalination has gradually become a mainstream technology due to its advantages such as low energy consumption and simple operation. In membrane desalination, nanofiltration membranes are often used in the pretreatment stage due to their unique selectivity and high flux to remove large molecular organic matter, colloids and some salts in seawater, thereby reducing the burden on subsequent reverse osmosis membranes and improving the overall efficiency and stability of the system.

[0003] Polyamide, a high-performance membrane material, is widely used in the preparation of nanofiltration membranes due to its excellent mechanical strength, chemical stability, and heat resistance. Currently, polyamide nanofiltration membranes mostly adopt a thin film composite structure, that is, an ultra-thin polyamide separation layer covered on a porous support layer. This structural design achieves an excellent balance between flux and selectivity, making it suitable for seawater desalination water treatment. Therefore, finding a superior method to prepare polyamide nanofiltration membranes is particularly critical. Summary of the Invention

[0004] In order to solve the above technical problems existing in the prior art, the present invention aims to provide a method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid. The specific technical solution is as follows:

[0005] The method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid comprises the following steps:

[0006] Preparation of the PES membrane substrate: 16 wt% polyethersulfone (PES), 16 wt% polyethylene glycol (PEG), and 68 wt% NN-dimethylformamide (DMF) were weighed and placed in a round-bottom flask, stirred in a water bath, and allowed to stand at the same temperature to remove bubbles. Subsequently, the casting solution was cast on a glass plate using a steel knife and immersed in ultrapure water to remove residual solvent.

[0007] Preparation of polyamide PA membrane: The polyamide active layer was synthesized on the PES membrane by interfacial polymerization of an aqueous solution containing piperazine PIP and 1-butyl-3-methylimidazole chloride with an oil solution containing TMC.

[0008] Furthermore, the preparation of the polyamide PA film includes the following steps:

[0009] An aqueous solution and an n-heptane solution of PIP and 1-butyl-3-methylimidazole chloride were prepared, respectively. First, a PES membrane was immersed in the aqueous solution to allow PIP and 1-butyl-3-methylimidazole chloride to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas. The PES membrane was then immersed in the n-heptane solution to complete the interfacial polymerization reaction, and then placed in an oven for post-treatment at 60°C for 10 minutes. Finally, the membrane was stored in deionized water.

[0010] Furthermore, the content of piperazine PIP in the aqueous solution is 0.2 wt %.

[0011] Furthermore, the content of 1-butyl-3-methylimidazole chloride in the aqueous solution is 0.02 wt%-0.08 wt%.

[0012] Furthermore, the TMC content in the oil phase solution is 0.1 wt%.

[0013] The present invention uses an in-situ interfacial polymerization method to prepare a polyamide membrane, utilizing the electrostatic and hydrogen bonding between an ionic liquid and piperazine in the aqueous phase. During the reaction process, the interaction between the ionic liquid and piperazine enhances the solvation of piperazine in the aqueous phase, slowing its diffusion into the oil phase. This increases the number of unreacted acyl chloride groups on TMC, ultimately generating more carboxylic acid groups through hydrolysis. This results in a thinner selective layer of the membrane and a stronger negative charge on the membrane surface in water, affecting membrane properties such as permeability, selectivity, and anti-fouling properties. The present invention provides a new perspective for regulating monomer diffusion and reaction during interfacial polymerization, and has significant application potential in the preparation of high-performance polyamide composite membranes (such as reverse osmosis membranes or nanofiltration membranes). By regulating these interactions, the thickness of the membrane's selective layer and separation performance can be optimized. DETAILED DESCRIPTION

[0014] The present invention will be further described below with reference to the embodiments.

[0015] The method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid of the present invention comprises the following steps:

[0016] Preparation of substrate PES membrane: 16 wt% polyethersulfone (PES), 16 wt% polyethylene glycol (PEG), and 68 wt% NN dimethylformamide (DMF) were weighed into a round-bottom flask, stirred in a 60 °C water bath for 6 h, and allowed to stand at the same temperature for 6 h to remove bubbles. Subsequently, the casting solution was cast on a glass plate with a steel knife and immersed in ultrapure water to remove residual solvent.

[0017] Preparation of polyamide (PA) membrane: A PA active layer was synthesized on a PES membrane by interfacial polymerization of an aqueous solution containing piperazine (PIP) and 1-butyl-3-methylimidazole chloride with an oily solution containing TMC.

[0018] Aqueous solutions of PIP (0.2 wt%) and 1-butyl-3-methylimidazole chloride (0.02 wt%-0.08 wt%) at varying concentrations, and a TMC (0.1 wt%) n-heptane solution were prepared. First, a PES membrane was immersed in the aqueous solution for 3 minutes to allow the PIP and 1-butyl-3-methylimidazole chloride to adsorb on the membrane surface. Excess solution was then blown away with nitrogen. The PES membrane was then immersed in the n-heptane solution for 1 minute to complete the interfacial polymerization reaction. The membrane was then post-treated in an oven at 60°C for 10 minutes and stored in deionized water.

[0019] The polyamide nanofiltration membrane prepared by the present invention is used for water purification, with Na2SO4 and NaCl aqueous solutions as simulated brine at a concentration of 1 g / L, and is mainly used to separate and recover Na2SO4 and NaCl.

[0020] Example 1

[0021] The PES membrane was immersed in an aqueous solution containing PIP (0.2 wt%) and 1-butyl-3-methylimidazole chloride (0.02 wt%) for 3 min to allow PIP to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas, and the PES membrane was immersed in an n-heptane solution for 1 min to complete the interfacial polymerization reaction. It was then placed in an oven for post-treatment at 60°C for 10 min and finally stored in deionized water.

[0022] The PA-10% membrane of Example 1 was used to separate anions in a water system, and the pure water flux of the membrane was 20.8 L m -2 h - 1 bar -1 , the Na2SO4 retention rate is 99.7%, and the NaCl retention rate is 34.1%.

[0023] Example 2

[0024] The PES membrane was immersed in an aqueous solution containing PIP (0.2 wt%) and 1-butyl-3-methylimidazole chloride (0.04 wt%) for 3 min to allow PIP to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas, and the PES membrane was immersed in an n-heptane solution for 1 min to complete the interfacial polymerization reaction. It was then placed in an oven for post-treatment at 60°C for 10 min and finally stored in deionized water.

[0025] The PA-20% membrane of Example 2 was used to separate anions in a water system, and the pure water flux of the membrane was 21.6 L m -2 h -1 bar -1 , the Na2SO4 retention rate is 100%, and the NaCl retention rate is 30.8%.

[0026] Example 3

[0027] The PES membrane was immersed in an aqueous solution containing PIP (0.2 wt %) and 1-butyl-3-methylimidazole chloride (0.05 wt %) for 3 min to allow PIP to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas, and the PES membrane was immersed in an n-heptane solution for 1 min to complete the interfacial polymerization reaction. It was then placed in an oven for post-treatment at 60°C for 10 min and finally stored in deionized water.

[0028] The PA-25% membrane of Example 3 was used to separate anions in a water system, and the pure water flux of the membrane was 21.9 L m -2 h -1 bar -1 ,Na2SO4 retention rate is 100%, NaCl retention rate is 29.8%

[0029] Example 4

[0030] The PES membrane was immersed in an aqueous solution containing PIP (0.2 wt %) and 1-butyl-3-methylimidazole chloride (0.06 wt %) for 3 min to allow PIP to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas, and the PES membrane was immersed in an n-heptane solution for 1 min to complete the interfacial polymerization reaction. It was then placed in an oven for post-treatment at 60°C for 10 min and finally stored in deionized water.

[0031] The PA-30% membrane of Example 4 was used to separate anions in a water system, and the pure water flux of the membrane was 25.6 L m -2 h -1 bar -1 , the Na2SO4 retention rate is 100%, and the NaCl retention rate is 27.8%.

[0032] Example 5

[0033] The PES membrane was immersed in an aqueous solution containing PIP (0.2 wt%) and 1-butyl-3-methylimidazole chloride (0.07 wt%) for 3 min to allow PIP to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas, and the PES membrane was immersed in an n-heptane solution for 1 min to complete the interfacial polymerization reaction. It was then placed in an oven for post-treatment at 60°C for 10 min and finally stored in deionized water.

[0034] The PA-35% membrane of Example 5 was used to separate anions in a water system, and the pure water flux of the membrane was 23.1 L m -2 h -1 bar -1,Na2SO4 retention rate is 100%, NaCl retention rate is 32.1%

[0035] Example 6

[0036] The PES membrane was immersed in an aqueous solution containing PIP (0.2 wt%) and 1-butyl-3-methylimidazole chloride (0.08 wt%) for 3 min to allow PIP to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas, and the PES membrane was immersed in an n-heptane solution for 1 min to complete the interfacial polymerization reaction. It was then placed in an oven for post-treatment at 60°C for 10 min and finally stored in deionized water.

[0037] The PA-40% membrane of Example 6 was used to separate anions in a water system, and the pure water flux of the membrane was 22.2 L m -2 h -1 bar -1 ,Na2SO4 retention rate is 100%, NaCl retention rate is 29.6%

[0038] Comparative Example 1

[0039] The PES membrane was immersed in an aqueous solution containing PIP (0.2 wt%) for 3 min to allow PIP to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas. The PES membrane was then immersed in an n-heptane solution for 1 min to complete the interfacial polymerization reaction. The membrane was then placed in an oven for post-treatment at 60°C for 10 min and finally stored in deionized water.

[0040] The PA membrane of Comparative Example 1 was used to separate anions in a water system, and the pure water flux of the membrane was 15.8 L m -2 h -1 bar -1 , the Na2SO4 rejection rate is 98.6%, the NaCl rejection rate is 41.4%, and the separation factor is 41.8.

[0041]

[0042]

[0043] Table 1 PA film performance table of various embodiments and comparative examples.

Claims

1. A method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid, characterized in that The following steps are involved: Preparation of the PES membrane substrate: 16 wt% polyethersulfone (PES), 16 wt% polyethylene glycol (PEG), and 68 wt% NN-dimethylformamide (DMF) were weighed and placed in a round-bottom flask, stirred in a water bath, and allowed to stand at the same temperature to remove bubbles. Subsequently, the casting solution was cast on a glass plate using a steel knife and immersed in ultrapure water to remove residual solvent. Preparation of polyamide PA membrane: The polyamide active layer was synthesized on the PES membrane by interfacial polymerization of an aqueous solution containing piperazine PIP and 1-butyl-3-methylimidazole chloride with an oil solution containing TMC.

2. The method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid according to claim 1, wherein: The preparation of the polyamide PA film comprises the following steps: An aqueous solution and an n-heptane solution of PIP and 1-butyl-3-methylimidazole chloride were prepared, respectively. First, a PES membrane was immersed in the aqueous solution to allow PIP and 1-butyl-3-methylimidazole chloride to adsorb on the surface of the PES membrane. Then, the excess solution was blown dry with nitrogen gas. The PES membrane was then immersed in the n-heptane solution to complete the interfacial polymerization reaction, and then placed in an oven for post-treatment at 60°C for 10 minutes. Finally, the membrane was stored in deionized water.

3. The method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid according to claim 1, wherein: The content of piperazine PIP in the aqueous phase solution is 0.2 wt %.

4. The method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid according to claim 1, wherein: The content of 1-butyl-3-methylimidazole chloride in the aqueous phase solution is 0.02 wt %-0.08 wt %.

5. The method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid according to claim 1, wherein: The TMC content in the oil phase solution is 0.1 wt %.

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