A method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid

Abstract

The application belongs to the technical field of polymer materials, and discloses a method for preparing a polyamide nanofiltration membrane based on a non-reactive ionic liquid, which comprises the following steps: preparation of a substrate PES membrane: 16wt% of polyethersulfone PES, 16wt% of polyethylene glycol PEG, and 68wt% of N-N dimethylformamide DMF are weighed and placed in a round-bottom flask, stirred in a water bath, and left to stand at the same temperature to remove air bubbles, then, the casting solution is cast on a glass plate with a steel knife and immersed in ultrapure water to remove residual solvent; preparation of a polyamide PA membrane: interfacial polymerization is performed on the PES membrane by using an aqueous phase solution containing piperazine PIP and 1-butyl-3-methylimidazole chloride and an oil phase solution containing TMC to synthesize a polyamide active layer. The application provides a new perspective for the regulation of monomer diffusion and reaction in the interfacial polymerization process, and has important application potential in the preparation of high-performance polyamide composite membranes.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a method for preparing polyamide nanofiltration membranes based on ionic liquids. Background Technology

[0002] Seawater desalination, as a crucial technological means to address global freshwater scarcity, has been widely applied worldwide. Currently, seawater desalination technologies are mainly divided into two categories: thermal methods and membrane methods. Thermal methods include multi-stage flash distillation (MSF) and multi-effect distillation (MED), while membrane methods primarily include reverse osmosis (RO) and nanofiltration (NF). In recent years, membrane-based seawater desalination has gradually become the mainstream technology due to its advantages such as lower energy consumption and ease of operation. In membrane-based seawater desalination, nanofiltration membranes, due to their unique selectivity and high flux, are often used in the pretreatment stage to remove large molecular organic matter, colloids, and some salt from seawater, thereby reducing the burden on the subsequent reverse osmosis membrane and improving the overall efficiency and stability of the system.

[0003] Polyamide, as a high-performance membrane material, has been widely used in the preparation of nanofiltration membranes due to its excellent mechanical strength, chemical stability, and heat resistance. Currently, most polyamide nanofiltration membranes employ a thin-film composite structure, where an ultrathin polyamide separation layer is coated onto a porous support layer. This structural design achieves a good balance between flux and selectivity, making it suitable for seawater desalination. Therefore, finding an excellent method for preparing polyamide nanofiltration membranes is particularly crucial. Summary of the Invention

[0004] To address the aforementioned technical problems in the existing technology, the present invention aims to provide a method for preparing polyamide nanofiltration membranes based on non-reactive ionic liquids. The specific technical solution is as follows:

[0005] A method for preparing polyamide nanofiltration membranes based on non-reactive ionic liquids includes the following steps:

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

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

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

[0009] Aqueous solutions of PIP and 1-butyl-3-methylimidazole chloride and n-heptane solutions were prepared separately. First, the PES membrane was immersed in the aqueous solution to allow PIP and 1-butyl-3-methylimidazole chloride to adsorb onto the surface of the PES membrane. Then, excess solution was dried with nitrogen gas. Next, the PES membrane was immersed in the n-heptane solution to complete the interfacial polymerization reaction. After post-treatment at 60°C for 10 min in an oven, it was finally stored in deionized water.

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

[0011] Furthermore, the aqueous solution contains 0.02 wt% to 0.08 wt% 1-butyl-3-methylimidazolium chloride.

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

[0013] This invention employs an in-situ interfacial polymerization method to prepare polyamide membranes. It utilizes the electrostatic and hydrogen bonding interactions between ionic liquids and piperazine in the aqueous phase. During the reaction, the interaction between the ionic liquid and piperazine enhances the solvation of piperazine in the aqueous phase and slows its diffusion into the oil phase. This results in an increase in unreacted acyl chloride groups on the TMC (transfer membrane matrix), ultimately leading to the formation of more carboxylic acid groups through hydrolysis. This results in a thinner selective layer and a stronger negative charge on the membrane surface in water, affecting membrane performance such as permeability, selectivity, and antifouling properties. This invention provides a new perspective for the regulation of monomer diffusion and reaction during interfacial polymerization, and has significant application potential, particularly in the preparation of high-performance polyamide composite membranes (such as reverse osmosis or nanofiltration membranes). By regulating these interactions, the selective layer thickness and separation performance of the membrane can be optimized. Detailed Implementation

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

[0015] The method for preparing polyamide nanofiltration membranes based on non-reactive ionic liquids of the present invention includes the following steps:

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

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

[0018] Aqueous solutions of PIP (0.2 wt%) and 1-butyl-3-methylimidazole chloride (0.02 wt%–0.08 wt%) at different concentrations, and a heptane solution of TMC (0.1 wt%) were prepared. First, the PES membrane was immersed in the aqueous solution for 3 min to allow PIP and 1-butyl-3-methylimidazole chloride to adsorb onto the surface of the PES membrane. Then, excess solution was dried with nitrogen gas. The PES membrane was then immersed in the heptane solution for 1 min to complete the interfacial polymerization reaction, post-treated in an oven at 60 °C for 10 min, and finally stored in deionized water.

[0019] The polyamide nanofiltration membrane prepared by this invention is used for water purification. It uses an aqueous solution of Na2SO4 and NaCl as a simulated saline solution with a concentration of 1 g / L, mainly for the separation and recovery of 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-methylimidazolium chloride (0.02 wt%) for 3 min to allow PIP to adsorb onto the surface of the PES membrane. Then, excess solution was dried with nitrogen gas. The PES membrane was then immersed in n-heptane solution for 1 min to complete the interfacial polymerization reaction. After post-treatment at 60°C for 10 min in an oven, it was finally stored in deionized water.

[0022] The PA-10% membrane from Example 1 was used for the separation of anions in an aqueous system. The membrane's pure water flux was 20.8 L / m³. -2 h - 1 bar -1 The rejection rate for Na₂SO₄ was 99.7%, and the rejection rate for NaCl was 34.1%.

[0023] Example 2

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

[0025] The PA-20% membrane from Example 2 was used for the separation of anions in an aqueous system, and the membrane's pure water flux was 21.6 L / m³. -2 h - 1 bar -1The rejection rate for Na₂SO₄ was 100%, and the rejection rate for NaCl was 30.8%.

[0026] Example 3

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

[0028] The PA-25% membrane from Example 3 was used for the separation of anions in an aqueous system, and the membrane's pure water flux was 21.9 L / m³. -2 h - 1 bar -1 The rejection rate for Na₂SO₄ was 100%, and the rejection rate for NaCl was 29.8%.

[0029] Example 4

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

[0031] The PA-30% membrane from Example 4 was used for the separation of anions in an aqueous system, and the membrane's pure water flux was 25.6 L / m³. -2 h - 1 bar -1 The rejection rate for Na₂SO₄ was 100%, and the rejection rate for NaCl was 27.8%.

[0032] Example 5

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

[0034] The PA-35% membrane from Example 5 was used for the separation of anions in an aqueous system, and the membrane's pure water flux was 23.1 L / m³. -2h - 1 bar -1 The rejection rate for Na₂SO₄ was 100%, and the rejection rate for NaCl was 32.1%.

[0035] Example 6

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

[0037] The PA-40% membrane from Example 6 was used for the separation of anions in an aqueous system, and the membrane's pure water flux was 22.2 L / m³. -2 h - 1 bar -1 The rejection rate for Na₂SO₄ was 100%, and the rejection rate for NaCl was 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 onto the surface of the PES membrane. Then, the excess solution was dried with nitrogen gas. The PES membrane was then immersed in n-heptane solution for 1 min to complete the interfacial polymerization reaction. After post-treatment at 60°C for 10 min in an oven, it was finally stored in deionized water.

[0040] The comparative example 1PA membrane was used for the separation of anions in an aqueous system, and the membrane's pure water flux was 15.8 L / m³. -2 h -1 bar -1 The Na2SO4 rejection rate was 98.6%, the NaCl rejection rate was 41.4%, and the separation factor was 41.8.

[0041]

[0042]

[0043] Table 1 shows the performance of the PA films in each embodiment and comparative example.

Claims

1. A method for preparing polyamide nanofiltration membranes based on non-reactive ionic liquids, characterized in that... Includes the following steps: Preparation of the substrate PES membrane: 16 wt% polyethersulfone PES, 16 wt% polyethylene glycol PEG, and 68 wt% N-dimethylformamide DMF were weighed and placed in a round-bottom flask. The mixture was stirred in a water bath and allowed to stand at the same temperature to remove air bubbles. Then, the casting solution was cast onto a glass plate with a steel knife and immersed in ultrapure water to remove residual solvent. Preparation of polyamide PA membrane: A polyamide active layer was synthesized on a PES membrane by interfacial polymerization of an aqueous solution containing piperazine (PIP) and 1-butyl-3-methylimidazolium chloride with an oil solution containing trimesoyl chloride (TMC). The preparation of the polyamide PA film includes the following steps: An aqueous solution of PIP and 1-butyl-3-methylimidazole chloride and a heptane solution of TMC were prepared separately. First, the PES membrane was immersed in the aqueous solution to adsorb PIP and 1-butyl-3-methylimidazole chloride onto the surface of the PES membrane. Then, the excess solution was dried with nitrogen gas. The PES membrane was then immersed in a heptane solution to complete the interfacial polymerization reaction, placed in an oven at 60°C for 10 minutes for post-treatment, and finally stored in deionized water. The aqueous solution contains 0.02 wt% to 0.08 wt% 1-butyl-3-methylimidazolium chloride.

2. The method for preparing polyamide nanofiltration membranes based on non-reactive ionic liquids as described in claim 1, characterized in that: The content of piperazine (PIP) in the aqueous solution is 0.2 wt%.

3. The method for preparing polyamide nanofiltration membranes based on non-reactive ionic liquids as described in claim 1, characterized in that: The TMC content in the oil phase solution is 0.1 wt%.

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