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

Abstract

The invention relates to a preparation method of a membrane material, in particular to a preparation method of a nanofiltration membrane applied to magnesium-lithium separation. According to the preparation method of the polyamide nanofiltration membrane capable of avoiding the acyl chloride hydrolysis influence, provided by the invention, the acyl chloride hydrolysis is avoided by mainly utilizing interfacial polymerization of gas-phase amine and acyl chloride, and the application potential of the membrane can be well improved by adopting the hollow fiber as the support body.

Description

Technical Field

[0001] The present invention relates to a preparation method of a membrane material, and particularly to a preparation method of 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 materials used for the separation of magnesium and lithium.

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

[0004] To solve the above problems, the prior art has adopted the interfacial reaction of volatile amino monomers and acyl chloride, 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 has tried to load porous materials on the surface of the carrier to improve the adsorption of amines, but it is 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 disadvantages of the above flat membranes. Therefore, how to prepare a nanofiltration membrane with a hollow fiber as the carrier and that can 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 preparation method of a polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis. It mainly uses the interfacial polymerization of gaseous amine and acyl chloride, thereby avoiding the hydrolysis of acyl chloride. Moreover, using a hollow fiber as a support can well enhance the application potential of the membrane.

[0007] First, the present invention provides a preparation method of a polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis, characterized in that the preparation method includes the following steps: Prepare a hollow fiber carrier with porous materials 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 a period of time; Immerse the hollow fiber carrier that still has volatile ethylenediamine gas flowing in and out in an oil-phase solution containing polyacyl chloride, and react for a period of time 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.

[0008] Specifically, the hollow fiber carrier with porous material loaded on its outer surface is prepared through the following steps: Mix and degas the casting solution containing polymer, solvent and additive, then spin it through a spinneret, enter the coagulation bath after an air gap for semi-coagulation, and then transfer it to a secondary coagulation bath containing porous material to continue coagulation until completion. Finally, dry the hollow fiber 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 the coagulating liquid, ultrasonic treating 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, polyethylene, with a pore size of 0.03-0.3 μm and an inner diameter of 1.8-3.8 mm.

[0011] Specifically, the porous material is one of molecular sieve, silica, carbon nanotube, 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 polyacyl chloride is one or more of isophthaloyl chloride, m-phthaloyl chloride, terephthaloyl chloride, biphenyltetracarbonyl chloride, biphenylhexacarbonyl chloride, with a concentration of 0.02-2 wt%, and the oil-phase solvent is one of n-hexane, cyclohexane, n-heptane, octane.

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

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

[0016] Finally, the present invention provides an application of the polyamide nanofiltration membrane to avoid 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 a porous material loaded on the surface of a carrier to adsorb more gaseous amine, thereby enabling an 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 it encounters 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 a method of internal ventilation and external impregnation with the oil phase to achieve interfacial polymerization in the area where there is no coverage of the porous material on the surface of the carrier, so as to avoid membrane defects. Specific embodiments

[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 embodiments of the present invention, but the present invention is not limited to the following examples. Example 1

[0019] A casting solution is prepared by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide and 10 wt% of polyvinylpyrrolidone, stirred at 60 °C for 12 hours and then left to stand for 24 hours for degassing. The degassed casting solution is continuously extruded from the spinning head by a metering pump at an extrusion speed of 9 revolutions per minute and a temperature of 50 °C. The extruded casting solution is injected into a water bath at 30 °C through a 10-mm air section for coagulation. The hollow fiber membrane coming out of the coagulation bath is wound onto a winding wheel at a winding speed set at 1 m / min, and then continuously immersed in a coagulation bath containing a suspension of 3 wt% NaA molecular sieve (particle size 480 nm) for 12 h until complete coagulation. Finally, the hollow fiber is dried in an oven. A gas containing volatile ethylenediamine is continuously introduced and discharged at both ends inside the hollow fiber carrier and maintained 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] The hollow fiber carrier still introducing and discharging the gas containing volatile ethylenediamine is immersed in a n-hexane solution containing trimesoyl chloride (1 wt%) and reacted 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.

[0021] Comparative Example 1 Prepare a casting solution by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide, and 10 wt% of polyvinylpyrrolidone. Stir the solution at 60 °C for 12 hours, then let it stand for 24 hours to remove air bubbles. Continuously extrude the degassed casting solution from the spinneret using a metering pump at an extrusion speed of 9 revolutions per minute and a temperature of 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 at a winding speed of 1 m / min, and then continuously immersed in the water coagulation bath for 12 hours until complete coagulation. Finally, dry the hollow fiber in an oven; Continuously introduce and discharge a gas containing volatile ethylenediamine at both ends inside the hollow fiber carrier 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.

[0022] 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.

[0023] Comparative Example 2 Prepare a casting solution by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide, and 10 wt% of polyvinylpyrrolidone. Stir the solution at 60 °C for 12 hours, then let it stand for 24 hours to remove air bubbles. Continuously extrude the degassed casting solution from the spinneret using a metering pump at an extrusion speed of 9 revolutions per minute and a temperature of 50 °C. The extruded casting solution passes through a 10-mm air section and is injected into a 30 °C water bath containing a 3 wt% suspension of NaA zeolite (particle size 480 nm) for coagulation. The hollow fiber membrane emerging from the coagulation bath is wound onto a winding wheel at a winding speed of 1 m / min, and then continuously immersed in the coagulation bath for 12 hours until complete coagulation. Finally, dry the hollow fiber in an oven; Place the hollow fiber carrier in a gas containing volatile ethylenediamine and let it 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.

[0024] Immerse the hollow fiber carrier 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.

[0025] Comparative Example 3 A casting solution is prepared by mixing 35 wt% of polysulfone, 55 wt% of dimethylacetamide, and 10 wt% of polyvinylpyrrolidone. After stirring at 60 °C for 12 hours, it is left to stand for 24 hours to remove bubbles. Then, the degassed casting solution is continuously extruded from the spinneret using a metering pump at an extrusion speed of 9 revolutions per minute and a temperature of 50 °C. The extruded casting solution is injected into a 30 °C water bath for coagulation through a 10-mm air section. The hollow fiber membrane emerging from the coagulation bath is wound onto a winding wheel at a winding speed of 1 m / min. Then, it is further 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; A gas containing volatile ethylenediamine is continuously introduced and discharged at both ends inside the hollow fiber carrier. The temperature of the gas containing volatile ethylenediamine is 750 °C, the concentration of ethylenediamine in the gas is 20 g / m3, and the flow rate is 10 ml / min. It is immediately immersed in a n-hexane solution containing 1 wt% of trimesoyl chloride and reacted 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.

[0026] The membrane samples of the above examples and comparative examples are subjected to performance tests: An aqueous solution of 3000 mg / L magnesium chloride and 500 mg / L lithium chloride is used as the test solution. Using a membrane test bench, the flux of the membrane sheet is tested at a pressure of 150 psi. The concentrations of Mg 2+ and Li+ in the produced water are separately tested, and the separation coefficient of the membrane sheet is calculated. The results are shown in the following table: Table 1 Performance Tests of Different Membrane Samples

[0027] 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 within the protection scope of the present invention.

Claims

1. A method for preparing a polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis, characterized in that The preparation method comprises the following steps: Prepare a hollow fiber carrier with a porous material loaded on the outer surface; The gas containing volatile ethylenediamine is continuously introduced into and out of the two ends of the hollow fiber carrier and maintained for a period of time; The hollow fiber carrier through which the volatile ethylenediamine gas is still passed is immersed in an oil phase solution containing polyacid chloride and reacted for a period of time 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.

2. The method according to claim 1, characterized in that The hollow fiber carrier loaded with porous materials on the outer surface is prepared by the following steps: a casting solution containing a polymer, a solvent and an additive is mixed and degassed, and then spun through a spinning head. After a period of air spacing, it enters a coagulation bath for semi-coagulation, and then is transferred to a secondary coagulation bath containing a porous material for further coagulation. Finally, the hollow fiber is dried for use.

3. The method according to claim 2, characterized in that The concentration of the porous material in the secondary coagulation bath is 1-5 wt %, which is obtained by mixing the porous material with the coagulation liquid, ultrasonically treating for 0.5-10 min, and continuing magnetic stirring for 2-5 min.

4. The method according to claim 1, characterized in that The hollow fiber carrier is made of 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.

5. The method according to claim 1, characterized in that The porous material is one of molecular sieve, silicon dioxide, carbon nanotube and metal organic framework material.

6. The method according to claim 1, characterized in that The temperature of the gas containing volatile ethylenediamine is 60-120°C, and the concentration of ethylenediamine in the gas is 0.5-50g / m 3 , flow rate is 5-100ml / min.

7. The method according to claim 1, characterized in that The polyacid chloride is one or more of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, biphenyl tetrachloride, and biphenyl hexachloride, with a concentration of 0.02-2wt%, and the oil phase solvent is one of n-hexane, cyclohexane, n-heptane, and octane.

8. The method according to claim 1, characterized in that The step (2) is maintained for 20-200 seconds, and the step (3) is reacted for 5-200 seconds.

9. A polyamide nanofiltration membrane prepared according to the method of claim 1 and free from the influence of acid chloride hydrolysis.

10. Use of the polyamide nanofiltration membrane that avoids the influence of acyl chloride hydrolysis according to claim 9 in magnesium and lithium separation.

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