Preparation method of high-performance magnesium-lithium separation membrane

Abstract

The invention discloses a preparation method of a high-performance magnesium-lithium separation membrane. The preparation method comprises the following steps: forming a polyamide film; mixing small molecular quaternary ammonium salt and amine monomer to serve as a solution for secondary interfacial polymerization; performing secondary interfacial polymerization to form a positive charge separation layer; and finally, promoting the reaction through high-temperature curing to obtain the nanofiltration membrane. According to the invention, the quaternary ammonium group with strong positive charges is introduced into the membrane in an in-situ grafting manner, the positive electricity of the membrane is increased, meanwhile, a transmission pore channel with positive charges is constructed, the operation is simple, the effect is obvious, the separation capacity of the membrane is greatly improved, and the method has a wide large-scale application prospect.

Description

Technical Field

[0001] The present invention relates to the field of nanofiltration membrane technology and magnesium-lithium separation, and in particular to a method for preparing a high-performance magnesium-lithium separation membrane. Background Art

[0002] With the booming electric vehicle industry and the demand for smart devices, the demand for lithium has increased dramatically. It is expected that by 2030, the supply and demand of lithium will reach about 2 million tons. Therefore, efficient and high-purity lithium extraction and separation processes are essential to meet the growing demand for electric vehicles. Brines around the world account for about 59% of the world's lithium reserves. Most salt lake brines contain a large amount of magnesium ions in their composition, so separating magnesium from lithium is one of the most important steps before lithium extraction. Most of my country's salt lakes are distributed in Qinghai and Tibet. Due to the limitations of local conditions, it is particularly important to find energy-saving and efficient separation methods.

[0003] Membrane separation is a separation technology that uses membrane as a separation medium to achieve the purpose of purification, screening, concentration, etc. of a mixed system under the action of a driving force. Compared with traditional separation technologies, it has many advantages such as high selectivity, low energy consumption, simple operation, and low maintenance and operation costs. Since its industrial application in the 1960s, membrane separation technology has been widely used in seawater desalination, wastewater treatment, gas separation, material purification and other fields. Nanofiltration technology can have a relatively large flux under low operating pressure, greatly reducing energy consumption and processing costs. Because of its small pore size and rich functional groups on the surface, multivalent salts can be separated by pore size screening and electrostatic effects. Therefore, it is an economical and effective way to separate magnesium and lithium ions through nanofiltration membranes. However, in the face of high salt concentrations and high magnesium-lithium ratios in salt lakes, nanofiltration membranes still have insufficient magnesium-lithium separation capacity. Summary of the invention

[0004] The invention aims to solve the technical problem of how to improve the magnesium-lithium separation ability of nanofiltration membranes, focusing on polyamide nanofiltration membranes, and providing a method for preparing a high-performance magnesium-lithium separation membrane.

[0005] In order to solve the above technical problems, the present invention is implemented through the following technical solutions:

[0006] A method for preparing a high-performance magnesium-lithium separation membrane comprises the following steps:

[0007] 1) Piperazine and acyl chloride monomers form a polyamide film on the surface of the polysulfone membrane through interfacial polymerization;

[0008] 2) mixing a small molecule quaternary ammonium salt with a reactive (amine-reactive) group with an amine monomer as a solution for secondary interfacial polymerization;

[0009] 3) pouring the solution obtained in step 2) onto the polyamide film obtained in step 1) to form a positive charge separation layer through secondary interfacial polymerization;

[0010] 4) Promoting the reaction by high temperature curing to obtain a nanofiltration membrane.

[0011] Preferably, the amine monomer contains two or more reactive amino groups.

[0012] Preferably, the active group of the small molecule quaternary ammonium salt with a reactive group is one of an epoxy group, an aldehyde group, a carboxyl group, and an acyl chloride group.

[0013] Preferably, the acyl chloride monomer contains two or more reactive acyl chloride groups.

[0014] Preferably, the curing temperature is 50-100°C.

[0015] The beneficial effects of the present invention are:

[0016] The present invention provides a method for preparing a high-performance magnesium-lithium separation membrane, wherein a quaternary ammonium group with a strong positive charge is introduced into the interior of the membrane by in-situ grafting, thereby increasing the positive charge of the membrane and constructing a transmission channel with a positive charge. Since the grafting process and the polymerization process are carried out step by step, the small molecule quaternary ammonium salt is wrapped by the polyamide and in-situ grafted inside the polyamide during the subsequent high-temperature curing. This reduces the membrane pore size and narrows the pore size distribution, which is conducive to strengthening the electrostatic repulsion of the positive charge in the pores. The prepared nanofiltration membrane has a conductivity of 13 L·m -2 ·h -1 bar -1 The water flux is 2000ppm, and the magnesium-lithium separation factor reaches 135 (2000ppm). At the same time, it still maintains a good separation effect (separation factor 37) under high salt concentration (32000ppm).

[0017] This method is simple to operate, has obvious effects, greatly improves the separation capacity of the membrane, and has broad prospects for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings.

[0019] Figure 1 Schematic diagram of in-situ grafting reaction;

[0020] Figure 2 It shows that in-situ grafting leads to changes in the Zeta potential of the membrane surface;

[0021] Figure 3 It was shown that in situ grafting resulted in a change in pore size distribution;

[0022] Figure 4 This is the magnesium-lithium separation performance diagram of the nanofiltration membrane. DETAILED DESCRIPTION

[0023] The preparation environment of all the initial nanofiltration membranes in the present invention is: temperature of 25° C., humidity of 60%, and normal pressure.

[0024] Several specific embodiments are provided below to illustrate and help further understand the present invention. However, the specific details of the embodiments are only for illustrating the present invention and do not represent all technical solutions under the concept of the present invention. Therefore, they should not be understood as limiting the overall technical solution of the present invention. Some non-substantial changes that do not deviate from the concept of the invention in the eyes of technical personnel, such as simple changes or replacements of technical features with the same or similar technical effects, all fall within the scope of protection of the present invention.

[0025] Embodiment 1:

[0026] This embodiment provides a method for controllably adjusting the pore size of a nanofiltration membrane, which is performed according to the following steps:

[0027] (1) Preparation of polyamide nanofiltration membrane: polysulfone (PSF) ultrafiltration membrane is used as the base membrane, 0.2% (w / v) piperazine solution is used as the aqueous phase, 0.25% (w / v) TMC solution is used as the oil phase, 1% anhydrous sodium phosphate is added to the aqueous phase as a buffer, and the pH is adjusted to 10 with concentrated hydrochloric acid; the aqueous phase is poured on the base membrane and allowed to stand for 5 minutes before being poured out, and the oil phase is poured out after 1 minute.

[0028] (2) Prepare the secondary interfacial polymerization solution: Polyethyleneimine (PEI) with a molecular weight of 600 Da 600， 0.2% (w / v)) and 2,3-epoxypropyltrimethylammonium bromide (0.2% (w / v)) were dissolved in water and stirred evenly.

[0029] (3) Secondary interfacial polymerization: After the organic phase on the membrane surface after step (1) is dried, pour the solution prepared in step (2) into it, let it stand for 1 min, pour it out and put the membrane into a 90°C oven.

[0030] (4) The membrane obtained in (3) was tested for flux and separation performance in a nanofiltration device at a test temperature of 25°C and a test pressure of 5 bar, and the water flux and desalination performance were measured.

[0031] Embodiment 2:

[0032] The membrane was prepared by the method of Example 1, the only difference being that in step (2), the amount of 2,3-epoxypropyltrimethylammonium bromide was changed to 0.4% (w / v).

[0033] Embodiment 3:

[0034] The membrane was prepared by the method of Example 1, the only difference being that in step (2), the amount of 2,3-epoxypropyltrimethylammonium bromide was changed to 0.6% (w / v).

[0035] Embodiment 4:

[0036] The membrane was prepared by the method of Example 1, the only difference being that in step (2), the amount of 2,3-epoxypropyltrimethylammonium bromide was changed to 0.8% (w / v).

[0037] Embodiment 5:

[0038] The membrane was prepared by the method of Example 1, the only difference being that in step (2), PEI 600 Replaced by PEI 3000 .

[0039] Embodiment 6:

[0040] The membrane was prepared by the method of Example 1, the only difference being that in step (2), PEI 600 Replaced by PEI 10000 (w / v).

[0041] Embodiment 7:

[0042] The membrane was prepared by the method of Example 1, the only difference being that in step (2), PEI 600 Replaced by PEI 250000 .

[0043] Embodiment 8:

[0044] The membrane was prepared by the method of Example 1, the only difference being that in step (2), PEI 600 Replaced by PEI 70000 .

[0045] Embodiment 9:

[0046] The membrane was prepared by the method of Example 1, the only difference being that in step (2), PEI 600 Replaced by PEI 750000 .

[0047] Embodiment 10:

[0048] The membrane was prepared by the method of Example 9, the only difference being that in step (2), PEI 750000 The amount was changed to 0.4% (w / v).

[0049] Embodiment 11:

[0050] The membrane was prepared by the method of Example 9, the only difference being that in step (2), PEI 750000 The amount was changed to 0.6% (w / v).

[0051] Embodiment 12:

[0052] The membrane was prepared by the method of Example 9, the only difference being that in step (2), PEI750000 The amount was changed to 0.8% (w / v).

[0053] Embodiment 13:

[0054] The membrane was prepared by the method of Example 9, the only difference being that in step (2), PEI 750000 The amount was changed to 1.0% (w / v).

[0055] Embodiment 14:

[0056] The membrane was prepared by the method of Example 9, the only difference being that in step (2), the amount of 2,3-epoxypropyltrimethylammonium bromide was changed to 1.2% (w / v).

[0057] The nanofiltration membrane samples obtained by stripping in the above embodiment and the poly-nanofiltration membrane prepared in step (1) were tested for magnesium-lithium separation capacity and water flux to investigate the effects of different formulations on the performance of the nanofiltration membrane. The average value of three consecutive tests was taken as the final result at a test temperature of 25° C. in a cross-flow manner (the solution magnesium-lithium ratio was 100:1 during magnesium-lithium separation, the low salt concentration was 2000 ppm, and the high salt concentration was 32000 ppm).

[0058] The water flux calculation formula is as follows:

[0059]

[0060] Among them, F represents water flux, V represents the volume of collected produced water, A is the effective membrane area, and t is the produced water collection time.

[0061] The separation coefficient calculation formula is:

[0062]

[0063] in and Li in the permeate solution + and Mg 2+ The concentration of and Cf, is the Li in the feed solution + and Mg 2+ concentration.

[0064] (I) Effect of 2,3-epoxypropyltrimethylammonium bromide concentration on membrane

[0065]

[0066] From the above table, we can see that as the concentration increases, the membrane water flux increases and the separation performance increases.

[0067] (II) Effects of different molecular weight PEI on membrane

[0068]

[0069]

[0070] From the above table, it can be seen that as the molecular weight of PEI increases, the membrane water flux increases but the separation performance decreases.

[0071] (III) Effect of PEI concentration on membrane

[0072]

[0073] From the above table, we can see that as the PEI concentration increases, the membrane flux decreases, the separation performance increases at low salt concentrations, but the separation performance is not excellent at high salt concentrations.

[0074] In summary, the introduction of quaternary ammonium groups into the membrane by in-situ grafting can greatly improve the magnesium-lithium separation ability of the membrane. By adjusting the concentration of PEI and small molecule quaternary ammonium salts with reactive (amine-reactive) groups, the flux and separation performance of the membrane can be regulated to obtain a suitable nanofiltration membrane.

[0075] Although the preferred embodiments of the present invention are described above, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms of specific changes without departing from the scope of protection of the invention spirit and claims, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance magnesium-lithium separation membrane, comprising the following steps: 1) Piperazine and acyl chloride monomers form a polyamide film on the surface of the polysulfone membrane through interfacial polymerization; 2) mixing a small molecule quaternary ammonium salt with a reactive group with an amine monomer as a solution for secondary interfacial polymerization; 3) pouring the solution obtained in step 2) onto the polyamide film obtained in step 1) to form a positive charge separation layer through secondary interfacial polymerization; 4) Promoting the reaction by high temperature curing to obtain a nanofiltration membrane.

2. The preparation method according to claim 1, characterized in that: The amine monomer contains two or more reactive amino groups.

3. The preparation method according to claim 1, characterized in that: The active group of the small molecule quaternary ammonium salt with reactive groups is one of epoxy, aldehyde, carboxyl and acyl chloride.

4. The preparation method according to claim 1, characterized in that: The acyl chloride monomer contains two or more reactive acyl chloride groups.

5. The preparation method according to claim 1, characterized in that: The curing temperature is 50-100°C.

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