Method for preparing positively charged composite nanofiltration membrane based on nitrated aniline monomer

Abstract

The novel positively-charged composite nanofiltration membrane is prepared on the basis of a nitrated aniline monomer. The preparation method of the composite membrane comprises the following steps: on a base membrane, performing interfacial polymerization reaction on water-phase monomers (nitrated aniline and piperazine) and acyl chloride monomers to form a separation layer; further, the Fe powder is used for converting nitryl into amido, so that the positively charged composite nanofiltration membrane is obtained. The preparation method of the positively charged composite nanofiltration membrane has the advantages of simplicity and convenience in operation, easiness in popularization and the like, has great application potential in the field of lithium extraction from salt lakes in China due to excellent ion separation performance, and is expected to realize high-efficiency low-carbon lithium enrichment.

Description

Technical Field

[0001] The present invention relates to a method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer, which is applicable to water treatment fields such as magnesium and lithium separation. Background Art

[0002] Lithium and its compounds are widely used in various industries, including electronics, alloys, glass, ceramics, oils and fats, and metallurgy. With the rapid development of the lithium-ion battery industry, global demand for lithium is growing rapidly. my country has abundant lithium reserves, over 80.0% of which is contained in salt lake brines. However, these salt lake brines have a high magnesium-to-lithium ratio and low lithium ion concentration, making traditional salt lake lithium extraction processes difficult to efficiently extract lithium from them. As a result, my country relies on imports for 80.0% of its lithium needs. Developing technologies that can efficiently extract lithium from my country's salt lake brines will help promote the development of the new energy industry and enhance the international competitiveness of my country's lithium battery and downstream supply chains.

[0003] Traditional large-scale lithium production methods, such as evaporation, are slow, pose a high risk of contamination, and introduce impurities that reduce product quality. Membrane separation, as an emerging separation technology, offers advantages such as simple operation, low resource consumption, and high separation purity. Nanofiltration membrane separation technology, with its high flux, low operating pressure, and excellent ion selectivity, can effectively improve the extraction efficiency of lithium ions from salt lake brine.

[0004] The separation performance of nanofiltration membranes for magnesium and lithium is controlled by the combined effects of size screening and dielectric repulsion. Since ions in aqueous solution are hydrated by dipolar water molecules, the pore size screening effect of nanofiltration membranes mainly depends on the hydration radius of the ions. 2+ He Li + The hydration radius of Mg and Li is 0.428 and 0.382 nm respectively. Theoretically, efficient separation of Mg and Li can be achieved by precisely controlling the pore radius of the nanofiltration membrane to about 0.40 nm. In fact, when ions enter the membrane pores, they can remove part of the hydration layer to reduce their own size, thereby passing through nanopores smaller than their hydration radius. Therefore, by controlling the membrane pore size to achieve effective separation of Mg and Li, the ions can be separated from the ions by the nanopores. 2+ He Li + The goal is difficult to achieve. On the other hand, the charge on the nanofiltration membrane surface also has a significant impact on the magnesium-lithium separation effect. Based on the dielectric repulsion effect, it can be seen that positively charged nanofiltration membranes show better magnesium-lithium separation than negatively charged nanofiltration membranes. Summary of the Invention

[0005] The present invention utilizes nitroaniline and piperazine as aqueous phase comonomers, and prepares a nanofiltration membrane through interfacial polymerization with organic phase monomers. Furthermore, Fe powder is used to convert the nitro groups on the surface of the nanofiltration membrane into amino groups, thereby obtaining a positively charged composite nanofiltration membrane. The specific method is as follows:

[0006] A method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer comprises the following steps:

[0007] (1) Fixing the base membrane in the plate frame, coating the aqueous solution containing nitroaniline and piperazine comonomers on the surface of the base membrane for a certain period of time, and then completely removing the solution on the membrane surface; (2) Soaking the membrane surface in an organic phase solution containing acyl chloride monomers for a certain period of time, and then rinsing the membrane surface with an organic phase solvent; (3) Placing the prepared composite nanofiltration membrane in an oven for heat treatment for a certain period of time and then taking it out; (4) Dispersing Fe powder in an aqueous solution with a certain pH value, and using the solution to soak the membrane surface for a certain period of time to convert nitro groups into amino groups, thereby obtaining a positively charged nanofiltration composite membrane.

[0008] The nitroaniline monomers in step (1) include 1-nitroaniline, 2-nitroaniline, 3-nitroaniline, 2-nitro-p-phenylenediamine, 4-nitro-m-phenylenediamine, and 5-nitro-m-phenylenediamine; the mass fraction of the nitroaniline in the aqueous solution is 0.1-5wt%, and the mass fraction of piperazine is 0.1-5wt%; and the time for soaking the base film in the aqueous solution is 1-10 minutes.

[0009] The acyl chloride monomer in step (2) includes one or more of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, cyclohexanetrichloride, 1,2,3,4-cyclobutanetetracarboxylic acid chloride, oxalyl chloride, malonyl chloride, and succinyl chloride; the organic phase solvent is one or more of n-hexane, cyclohexane, cyclopentane, n-heptane, n-octane, and Isopar; the mass fraction of the acyl chloride monomer in the organic phase solution is 0.01-5wt%; the organic phase solution soaks the membrane surface for 5s-5min; and the organic phase solvent washes the membrane surface for 5-30s.

[0010] The heat treatment temperature in step (3) is 50-80° C., and the heat treatment time is 30 s-10 min.

[0011] The amount of Fe powder used in step (4) is 1-10 g per 100 mL of solution, and the pH of the solution is adjusted to 0-3 using hydrochloric acid.

[0012] Advantages of the present invention:

[0013] 1. This invention solves the problem of poor selectivity of monovalent / divalent cations in common nanofiltration membranes and greatly improves the Mg 2+ / Li + Ion selectivity can be applied to my country's salt lake lithium extraction industry.

[0014] 2. The present invention has the advantages of low energy consumption and small footprint.

[0015] 3. The present invention has simple operation process, low cost and industrial scale-up advantage. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0017] Example 1:

[0018] A method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer comprises the following steps:

[0019] (1) An aqueous solution containing o-nitroaniline monomer and piperazine monomer is allowed to enter the pores of polysulfone by immersion, wherein the mass fraction of piperazine is 1.0 wt%, the mass fraction of o-nitroaniline is 1.0 wt%, and the mass fraction of water is 98.0 wt%.

[0020] (2) coating the organic phase solution on the polysulfone base membrane obtained in step (1) to carry out interfacial polymerization reaction for 30 seconds, wherein the organic phase solution is composed of trimesoyl chloride and oil phase solvent n-hexane, wherein the mass fraction of trimesoyl chloride is 0.15wt%, and the mass fraction of n-hexane is 99.85wt%.

[0021] (3) After washing the membrane obtained in step (2) with an organic phase solvent, n-hexane, for 10 seconds, the membrane was placed in an oven at 60° C. for heat treatment for 2 minutes to obtain a nanofiltration membrane product.

[0022] (4) Soak the nanofiltration membrane obtained in step (3) in an aqueous solution containing Fe powder for 2 minutes to obtain a positively charged composite nanofiltration membrane product. Each 100 mL of Fe powder solution contains 5 g of Fe powder, and the pH of the Fe powder solution is adjusted to 1 with hydrochloric acid.

[0023] (5) Mixing salt (Mg 2+ / Li + Mass ratio 20) performance test, the permeation flux is 5.5L·m -2 ·h -1 bar -1 , Mg 2+ / Li + The separation factor is 55.1.

[0024] Example 2:

[0025] A method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer comprises the following steps:

[0026] (1) An aqueous solution containing 4-nitro-m-phenylenediamine monomer and piperazine monomer is allowed to enter the pores of polysulfone by immersion, wherein the mass fraction of piperazine is 1.5 wt%, the mass fraction of o-nitroaniline is 1.0 wt%, and the mass fraction of water is 97.5 wt%.

[0027] (2) coating the organic phase solution on the polysulfone base membrane obtained in step (1) to carry out interfacial polymerization reaction for 30 seconds, wherein the organic phase solution is composed of trimesoyl chloride and oil phase solvent n-hexane, wherein the mass fraction of trimesoyl chloride is 0.15wt%, and the mass fraction of n-hexane is 99.85wt%.

[0028] (3) After washing the membrane obtained in step (2) with an organic phase solvent, n-hexane, for 10 seconds, the membrane was placed in an oven at 60° C. for heat treatment for 2 minutes to obtain a nanofiltration membrane product.

[0029] (4) Soak the nanofiltration membrane obtained in step (3) in an aqueous solution containing Fe powder for 2 minutes to obtain a positively charged composite nanofiltration membrane product. Each 100 mL of Fe powder solution contains 5 g of Fe powder, and the pH of the Fe powder solution is adjusted to 1 with hydrochloric acid.

[0030] (5) Mixing salt (Mg 2+ / Li + Mass ratio 20) performance test, the permeation flux is 2.8L·m -2 ·h -1 bar -1 , Mg 2+ / Li + The separation factor is 98.8.

Claims

1. A method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer, the specific operations are as follows: (1) fixing a base membrane in a plate frame, coating an aqueous phase solution containing nitroaniline and piperazine comonomers on the surface of the base membrane for a certain period of time, and then completely removing the solution on the membrane surface; (2) soaking the membrane surface in an organic phase solution containing acyl chloride monomer for a certain period of time, and then washing the membrane surface with an organic phase solvent; (3) placing the prepared composite nanofiltration membrane in an oven for heat treatment for a certain period of time and then taking it out; (4) dispersing Fe powder in an aqueous solution with a certain pH value, and using the solution to soak the membrane surface for a certain period of time to convert nitro groups into amino groups, thereby obtaining a positively charged nanofiltration composite membrane.

2. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: The nitroaniline monomers in step (1) include 1-nitroaniline, 2-nitroaniline, 3-nitroaniline, 2-nitro-p-phenylenediamine, 4-nitro-m-phenylenediamine, and 5-nitro-m-phenylenediamine.

3. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: In the aqueous solution in step (1), the mass fraction of nitroaniline is 0.1-5wt%, the mass fraction of piperazine is 0.1-5wt%, and the mass fraction of the aqueous solvent is 90-99.8wt%.

4. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: The time for soaking the basement membrane in the aqueous solution in step (1) is 1-10 minutes.

5. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: The acyl chloride monomer in step (2) includes one or a mixture of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, cyclohexanetrichloride, 1,2,3,4-cyclobutanetetracarboxylic acid chloride, oxalyl chloride, malonyl chloride, and succinyl chloride; the organic phase solvent in step (2) is one or a mixture of n-hexane, cyclohexane, cyclopentane, n-heptane, n-octane, and Isopar.

6. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: The mass fraction of the acyl chloride monomer in the organic phase solution in step (2) is 0.01-5wt%, and the mass fraction of the organic phase solvent is 95-99.99wt%.

7. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: In step (2), the organic phase solution soaks the membrane surface for 5 seconds to 5 minutes, and the organic phase solvent washes the membrane surface for 5 to 30 seconds.

8. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: The heat treatment temperature in step (3) is 50-80° C., and the heat treatment time is 30 s-10 min.

9. The method for preparing a positively charged composite nanofiltration membrane based on nitroaniline monomer according to claim 1, characterized in that: The amount of Fe powder used in step (4) is 1-10 g per 100 mL of solution, and the pH of the solution is adjusted to 0-3 using hydrochloric acid.