Preparation method of polyamide nanofiltration membrane for avoiding influence of acyl chloride hydrolysis

Abstract

The present invention relates to a method for preparing a membrane material, and particularly to a method for preparing a nanofiltration membrane applied to the separation of magnesium and lithium. The present invention provides a method for preparing a polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis. It mainly uses gas-phase amine and acyl chloride interfacial polymerization to avoid acyl chloride hydrolysis. Moreover, using hollow fibers as the support can well enhance the application potential of the membrane.

Description

Technical Field

[0001] The present invention relates to a method for preparing a membrane material, and particularly to a method for preparing a nanofiltration membrane applied to the separation of magnesium and lithium. Background Art

[0002] Nowadays, the development of lithium extraction technology from salt lakes is getting faster and faster. Among them, compared with other lithium extraction methods, using nanofiltration membranes for lithium extraction has the advantages of low cost, simple process, easy operation, and environmental friendliness. Among them, polyamide nanofiltration membranes are a common type of nanofiltration membrane material used for the separation of magnesium and lithium.

[0003] The most common method for preparing polyamide nanofiltration membranes is the interfacial polymerization method, which uses an aqueous monomer solution of polyamine and an oil-phase monomer solution of polyacyl chloride to diffuse to the interface respectively to undergo an interfacial polymerization reaction to form a network structure. However, during the interfacial polymerization reaction, acyl chloride will hydrolyze when it encounters water, thereby changing the charge amount on the membrane surface, which limits the separation performance of magnesium-lithium separation.

[0004] To solve the above problems, the prior art uses a volatile amino monomer to react with acyl chloride at the interface, which mainly utilizes the adsorption performance of the carrier for amines. However, the common organic membrane materials have poor adsorption ability for amines. To improve the above situation, the inventor tried to load porous materials on the surface of the carrier to improve the adsorption of amines, but found that the loading uniformity of the porous materials on the surface of the carrier membrane is poor.

[0005] Moreover, the existing nanofiltration membranes generally use flat membranes, and the problem is that the packing density of this kind of membrane is low and the flux is relatively small. And hollow fiber membranes are a common type of membrane in the art, which can well overcome the above disadvantages of flat membranes. Therefore, how to prepare a nanofiltration membrane with a hollow fiber as the carrier and avoid the influence of acyl chloride hydrolysis is an urgent problem to be solved. Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for preparing a polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis. It mainly uses gas-phase amine and acyl chloride for interfacial polymerization, thereby avoiding acyl chloride hydrolysis. Moreover, using hollow fibers as the support can well improve the application potential of the membrane.

[0007] First, the present invention provides a method for preparing a polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis, characterized in that the preparation method includes the following steps: preparing a hollow fiber carrier with a porous material loaded on the outer surface; continuously introducing and discharging a gas containing volatile ethylenediamine at both ends inside the hollow fiber carrier and maintaining it for a period of time; immersing the hollow fiber carrier still introducing and discharging the gas containing volatile ethylenediamine in an oil-phase solution containing polyacyl chloride and reacting for a period of time to form a polyamide nanofiltration membrane; removing the excess oil-phase solution on the surface of the nanofiltration membrane and drying to obtain the product.

[0008] Specifically, the hollow fiber carrier with a porous material loaded on its outer surface is prepared by the following steps: after mixing and degassing a casting solution containing a polymer, a solvent, and an additive, it is spun through a spinneret, enters a coagulation bath after passing through an air gap for semi-coagulation, and then is transferred to a secondary coagulation bath containing a porous material to continue coagulation until completion. Finally, the hollow fibers are dried for standby.

[0009] Specifically, the concentration of the porous material in the secondary coagulation bath is 1-5 wt%, which is obtained by mixing the porous material with a coagulating liquid, performing ultrasonic treatment for 0.5-10 min, and continuing magnetic stirring for 2-5 min.

[0010] Specifically, the material of the hollow fiber carrier is one or more of polyacrylonitrile, polyether, polyvinylidene fluoride, polysulfone, and polyethylene, the pore diameter is 0.03-0.3 μm, and the inner diameter is 1.8-3.8 mm.

[0011] Specifically, the porous material is one of molecular sieve, silica, carbon nanotube, and metal-organic framework material.

[0012] Specifically, the temperature of the gas containing volatile ethylenediamine is 60-120 °C, the concentration of ethylenediamine in the gas is 0.5-50 g / m3, and the flow rate is 5-100 ml / min.

[0013] Specifically, the polyfunctional acyl chloride is one or more of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, or biphenyltetracarbonyl chloride, biphenylhexacarbonyl chloride, the concentration is 0.02-2 wt%, and the oil-phase solvent is one of n-hexane, cyclohexane, n-heptane, and octane.

[0014] Specifically, it is maintained for 20-200 s in step (2) and the reaction is carried out for 5-200 s in step (3).

[0015] Secondly, the present invention also provides a polyamide nanofiltration membrane prepared by the above method to avoid the influence of acyl chloride hydrolysis.

[0016] Finally, the present invention provides an application of the polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis in the separation of magnesium and lithium.

[0017] Compared with the prior art, the present invention has the following beneficial effects: First, the present invention utilizes the porous material loaded on the surface of the carrier to adsorb more gaseous amine, thereby realizing the interfacial polymerization reaction between the gaseous amine and the oil-phase acyl chloride at the interface of the porous material, avoiding the hydrolysis of acyl chloride when encountering water; Secondly, aiming at the uneven coating situation when the porous material is loaded on the surface of the carrier, the present invention utilizes the characteristics of the hollow fiber membrane and selects the method of internal ventilation and external impregnation with the oil phase, realizing that interfacial polymerization can also be achieved in the area where the surface of the carrier is not covered by the porous material to avoid membrane defects. Detailed implementation mode

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will further describe in detail in combination with the implementation modes of the present invention. However, the present invention is not limited to the following embodiments. Embodiment

[0019] Prepare a casting solution by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide, and 10 wt% of polyvinylpyrrolidone. Stir at 60 °C for 12 hours and then stand for 24 hours to remove bubbles. Continuously extrude the degassed casting solution from the spinneret using a metering pump. The extrusion speed is 9 revolutions per minute, and the temperature is 50 °C. The extruded casting solution passes through a 10-mm air section and is injected into a 30 °C water bath for coagulation. The hollow fiber membrane emerging from the coagulation bath is wound onto a winding wheel, and the winding speed is set at 1 m / min. Then, it is continuously immersed in a coagulation bath containing a suspension of 3 wt% NaA zeolite (particle size 480 nm) for 12 h until complete coagulation. Finally, the hollow fiber is dried in an oven. Continuously introduce and discharge a gas containing volatile ethylenediamine at both ends inside the hollow fiber carrier and maintain it for 100 s. The temperature of the gas containing volatile ethylenediamine is 75 °C, the concentration of ethylenediamine in the gas is 20 g / m3, and the flow rate is 10 ml / min.

[0020] Immerse the hollow fiber carrier still introducing and discharging the gas containing volatile ethylenediamine in a n-hexane solution containing 1 wt% of trimesoyl chloride and react for 60 s to form a polyamide nanofiltration membrane. Remove the excess oil-phase solution on the surface of the nanofiltration membrane and dry to obtain the product.

[0021] Comparative Example 1

[0022] Prepare a casting solution by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide, and 10 wt% of polyvinylpyrrolidone. Stir at 60 °C for 12 hours and then stand for 24 hours to remove bubbles. Continuously extrude the degassed casting solution from the spinneret using a metering pump. The extrusion speed is 9 revolutions per minute, and the temperature is 50 °C. The extruded casting solution passes through a 10-mm air section and is injected into a 30 °C water bath for coagulation. The hollow fiber membrane emerging from the coagulation bath is wound onto a winding wheel, and the winding speed is set at 1 m / min. Then, it is continuously immersed in a water coagulation bath for 12 h until complete coagulation. Finally, the hollow fiber is dried in an oven. Continuously introduce and discharge a gas containing volatile ethylenediamine at both ends inside the hollow fiber carrier and maintain it for 100 s. The temperature of the gas containing volatile ethylenediamine is 75 °C, the concentration of ethylenediamine in the gas is 20 g / m3, and the flow rate is 10 ml / min.

[0023] The hollow fiber carrier through which the volatile ethylenediamine gas still flows in and out is immersed in a n - hexane solution containing trimesoyl chloride (1 wt%), and reacts for 60 s to form a polyamide nanofiltration membrane; the excess oil - phase solution on the surface of the nanofiltration membrane is removed, and dried to obtain the product.

[0024] Comparative Example 2

[0025] A casting solution is prepared by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide, and 10 wt% of polyvinylpyrrolidone. It is stirred at 60 °C for 12 hours and then left to stand for 24 hours for defoaming. Then, the defoamed casting solution is extruded from the spinneret using a metering pump. The extrusion speed is 9 revolutions per minute, and the temperature is 50 °C. The extruded casting solution passes through a 10 - mm air section and is injected into a 30 °C water - bath for coagulation. The hollow - fiber membrane coming out of the coagulation bath is wound onto a winding wheel, and the winding speed is set at 1 m / min. Then, it is continuously immersed in a coagulation bath containing a 3 wt% suspension of NaA zeolite (particle size 480 nm) for 12 h until complete coagulation. Finally, the hollow fiber is dried in an oven. The hollow - fiber carrier is placed in a gas containing volatile ethylenediamine and left to stand for 10 min. The temperature of the gas containing volatile ethylenediamine is 75 °C, and the concentration of ethylenediamine in the gas is 20 g / m3.

[0026] The hollow fiber carrier is immersed in a n - hexane solution containing trimesoyl chloride (1 wt%), and reacts for 60 s to form a polyamide nanofiltration membrane; the excess oil - phase solution on the surface of the nanofiltration membrane is removed, and dried to obtain the product.

[0027] Comparative Example 3

[0028] A casting solution is prepared by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide, and 10 wt% of polyvinylpyrrolidone. It is stirred at 60 °C for 12 hours and then left to stand for 24 hours for defoaming. Then, the defoamed casting solution is extruded from the spinneret using a metering pump. The extrusion speed is 9 revolutions per minute, and the temperature is 50 °C. The extruded casting solution passes through a 10 - mm air section and is injected into a 30 °C water - bath for coagulation. The hollow - fiber membrane coming out of the coagulation bath is wound onto a winding wheel, and the winding speed is set at 1 m / min. Then, it is continuously immersed in a coagulation bath containing a 3 wt% suspension of NaA zeolite (particle size 480 nm) for 12 h until complete coagulation. Finally, the hollow fiber is dried in an oven. Volatile ethylenediamine - containing gas is continuously passed in and out at both ends inside the hollow - fiber carrier. The temperature of the volatile ethylenediamine - containing gas is 75 °C, the concentration of ethylenediamine in the gas is 20 g / m3, and the flow rate is 10 ml / min. Immediately, it is immersed in a n - hexane solution containing trimesoyl chloride (1 wt%), and reacts for 60 s to form a polyamide nanofiltration membrane; the excess oil - phase solution on the surface of the nanofiltration membrane is removed, and dried to obtain the product.

[0029] Perform performance tests on the membrane samples of the above-mentioned examples and comparative examples: Use an aqueous solution of 3000 mg / L magnesium chloride and 500 mg / L lithium chloride as the test solution, and use a membrane test bench to test the flux of the membrane at a pressure of 150 psi. Measure the concentrations of Mg 2+ and Li+ in the produced water respectively, and calculate the separation coefficient of the membrane. The results are shown in the following table:

[0030] Table 1 Performance Tests of Different Membrane Samples

[0031]

[0032] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a polyamide nanofiltration membrane for avoiding the influence of acyl chloride hydrolysis, characterized in that The preparation method includes the following steps: Prepare a hollow fiber carrier with a porous material loaded on its outer surface; Continuously introduce and discharge a gas containing volatile ethylenediamine at both ends inside the hollow fiber carrier, and maintain for 20 - 200 s; Immerse the hollow fiber carrier still introducing and discharging the gas containing volatile ethylenediamine in an oil-phase solution containing polyvalent acyl chloride, and react for 5 - 200 s to form a polyamide nanofiltration membrane; Remove the excess oil-phase solution on the surface of the nanofiltration membrane and dry it to obtain the product; the hollow fiber carrier with porous material loaded on its outer surface is prepared by the following steps: after mixing and degassing the casting solution containing polymer, solvent and additive, spin it through a spinneret, enter the coagulation bath for semi-coagulation after passing through an air gap, then transfer it to a secondary coagulation bath containing porous material to continue coagulation until completion, and finally dry the hollow fiber for standby; the temperature of the gas containing volatile ethylenediamine is 60-120 °C, and the concentration of ethylenediamine in the gas is 0.5-50 g / m 3 , and the flow rate is 5-100 ml / min.

2. The method according to claim 1, wherein The concentration of the porous material in the secondary coagulation bath is 1 - 5 wt%, which is obtained by mixing the porous material with a coagulant solution, ultrasonically treating for 0.5 - 10 min, and then continuously magnetically stirring for 2 - 5 min.

3. The method according to claim 1, wherein The material of the hollow fiber carrier is one or more of polyacrylonitrile, polyether, polyvinylidene fluoride, polysulfone, and polyethylene, with a pore size of 0.03 - 0.3 μm and an inner diameter of 1.8 - 3.8 mm.

4. The method according to claim 1, wherein The porous material is one of molecular sieve, silica, carbon nanotube, and metal-organic framework material.

5. The method according to claim 1, characterized in that The polyvalent acyl chloride is one or more of trimellitic acid chloride, isophthaloyl chloride, terephthaloyl chloride, biphenyltetracarboxylic acid chloride, and biphenylhexacarboxylic acid chloride, with a concentration of 0.02 - 2 wt%, and the oil-phase solvent is one of n-hexane, cyclohexane, n-heptane, and octane.

6. A polyamide nanofiltration membrane prepared by the method according to claim 1, which avoids the influence of acyl chloride hydrolysis.

7. Application of the polyamide nanofiltration membrane according to claim 6, which avoids the influence of acyl chloride hydrolysis, in the separation of magnesium and lithium.

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