METHOD FOR PREPARING HIGH-SELECTIVITY LITHIUM-MAGNESIUM SEPARATION MEMBRANE

Abstract

A method for preparing a high-selectivity lithium-magnesium separation membrane includes: (1) preparing an aqueous phase mixture containing aqueous phase monomer, crown ethers or aza-macrocycles, acid acceptor, surfactant and water; (2) preparing an organic phase mixture containing organic phase monomer, and organic solvent that is incompatible with water; (3) contacting the supporting membrane with the aqueous phase mixture to obtain an aqueous phase monomer-adsorbed supporting membrane; (4) contacting the aqueous phase monomer-adsorbed supporting membrane with an organic phase mixture for an interfacial polymerization reaction; and (5) placing a nascent membrane obtained into a drying oven and heat-treating the membrane to obtain a lithium-magnesium separation membrane. The present method is simple in preparation process, mild in preparation conditions, easy to scale up, and easy to realize industrial production. The prepared high-selectivity lithium-magnesium separation membrane is large in permeation flux, high in lithium-magnesium selectivity and good in long-term operation stability.

Claims

1. A method for preparing a high-selectivity lithium-magnesium separation membrane, comprising the following steps: (1) preparing an aqueous phase mixture containing an aqueous phase monomer, crown ethers or aza-macrocycles, an acid acceptor, a surfactant, and water; (2) preparing an organic phase mixture containing an organic phase monomer and an organic solvent, wherein the organic solvent is incompatible with the water; (3) contacting a supporting membrane with the aqueous phase mixture to adsorb for a preset time to obtain an aqueous phase monomer-adsorbed supporting membrane; (4) contacting the aqueous phase monomer-adsorbed supporting membrane with the organic phase mixture for an interfacial polymerization reaction to obtain a nascent membrane; (5) placing the nascent membrane obtained in the step (4) into a drying oven and heat-treating the nascent membrane to obtain the high-selectivity lithium-magnesium separation membrane; wherein the aqueous phase mixture in the step (1) comprises, by mass fraction, 0.1-1% of the aqueous phase monomer, 0.1-1% of the crown ethers or the aza-macrocycles, 0.1-2% of the acid acceptor, 0.1-2% of the surfactant, and a remaining amount of the water; the organic phase mixture in the step (2) comprises, by mass fraction, 0.05-2% of the organic phase monomer and a remaining amount of the organic solvent; the high-selectivity lithium-magnesium separation membrane comprises a structurally stable polyamide active layer taking the crown ethers or the aza-macrocycles as internal channels allowing a permeation of lithium-ion and water molecules.

2. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein the aqueous phase monomer in the step (1) is selected from molecules consisting of two or more primary amine groups and secondary amine groups, the organic phase monomer is selected from molecules consisting of two or more acyl chloride groups.

3. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 2, wherein the aqueous phase monomer in the step (1) is selected from one or more of polyethylene imine, ethylene imine polymer, polyether amine, piperazine, and m-phenylenediamine.

4. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein the crown ethers in the step (1) are selected from one or more of 15-crown-5-ether, cyclohexane-15-crown-5, benzo-15-crown ether-5, 4′-acetylbenzo-15-crown-5-ether, 4′-aminobenzo-15-crown-5-ether, 4, 13-diazo-18-crown-6-ether, 18-crown ether-6, 1-aza-18-crown-6-ether, and 2-(hydroxymethyl)-18-crown-6-ether.

5. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein the aza-macrocycles in the step (1) are selected from one or more of 1,4,7,10-tetraazacyclododecane, 1,4,7-tri-boc-1,4,7,10-tetraazacyclododecane, 1,4,7,10,13,16-hexaazacyclooctadecane, 1,4,7,10-tetraazacyclotridecane, 1,5,9-triazacyclododecane, 1,4,8,12-tetraazacyclopentadecane, 1,4,8,11-tetraazacyclotetradecane, Tetraethyl 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetate, and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane.

6. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein the acid acceptor in the step (1) is one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

7. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein the surfactant in the step (1) is one or more of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, Tween 20, and cetyl trimethyl ammonium bromide.

8. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein the organic phase monomer in the step (2) is selected from one or more of 1, 3, 5-benzenetricarbonyl trichloride, 2,4-mesitylenedisulfonyl dichloride, 5-amino-2,4,6-triiodoisophthaloyl dichloride, 1,2-benzenedisulfonyl dichloride, 1,3-benzenedisulfonyl chloride, 2,6-pyridinedicarbonyl chloride, p-phthaloyl chloride, and 2,4-mesitylenedisulfonyl dichloride.

9. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein the organic solvent in the step (2) is at leaast one selected from N-hexane, n-heptane, and cyclohexane.

10. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein a membrane material of the supporting membrane in the step (3) is polysulfone, polyethersulfone, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, or polytetrafluoroethylene with a molecular weight cut-off of 10 kDa-80 kDa.

11. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein in the step (3), a contacting operation between the supporting membrane and the aqueous phase mixture is wetting or dipping, a contacting time is 1-10 min, and a temperature of the aqueous phase mixture is 15-40° C.

12. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein in the step (4), a contacting operation is wetting or dipping, a contacting time is 1-10 min, and a temperature of the organic phase mixture is 15-40° C.

13. The method for preparing the high-selectivity lithium-magnesium separation membrane according to claim 1, wherein in the step (5), a temperature of the heat-treating is 60-100° C., and a time is 1-20 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is an SEM image of the surface of the supporting membrane in example 1 of the present invention.

[0032] FIG. 2 is an SEM image of the surface of the high-selectivity lithium-magnesium separation membrane in example 1 of the present invention.

[0033] FIG. 3 is an SEM image of the cross section of the high-selectivity lithium-magnesium separation membrane in example 1 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention will be further described below. It should be noted that the present embodiment is predicated on the present technical solution and gives the detailed implementation mode and specific operation process, but the present invention is not limited to the present embodiment.

[0035] Materials used in the present invention: there is no special limitation to the source of all raw materials in the present invention and the following embodiments, and the raw materials are commercially available.

[0036] Method for testing the membrane flux of the high-selectivity lithium-magnesium separation membrane: a cross-flow filtration equipment was used to test membrane permeance, salt rejection, and selectivity. The test system includes a pump, a membrane cell, a pipeline, a regulating valve, and a pressure and flow detector, wherein the tested effective membrane area was 9.61 cm.sup.2, the test pressure was 5 bar, and the test temperature was 25 ± 0.5° C. Concentrations of MgCl.sub.2 and LiCl are both 500 ppm during the single-salt retention rate. A mixed salt concentration and a magnesium-lithium ratio for the lithium-magnesium separation performance were tested with total concentration of MgCl.sub.2 and LiCl as 2,000 ppm and Mg.sup.2+/Li.sup.+=20.

[0037] The water permeance (L • m-.sup.2.h.sup.-1.bar.sup.-1) was determined from Equation (1).

[00001]$Permeance=\frac{V}{A\cdot \Delta t\cdot \Delta P}$

[0038] Where A (m.sup.2) refers to the valid membrane area, Δt (h) refers to the permeate time, ΔP (bar) refers to the trans-membrane pressure, V (L) refers to the permeate volume.

[0039] MgCl.sub.2 or LiCl concentration in both sides was examined by the conductivity meter (DDSJ-308A, INASE Scientific Instrument Co., Ltd), while the salt rejection (%) was evaluated at pH 6.4. The rejection of Li.sup.+ or Mg.sup.2+ was examined by Equation (2).

[00002]$Rejection=\left(1-\frac{C_{permeate}}{C_{feed}}\right)\times 100\%$

[0040] Where C.sub.permeate (mg.Math.L.sup.-1) and C.sub.feed (mg.Math.L.sup.-1) refer to the salt concentrations in permeate and feed solutions.

[0041] The separation factor (Li, Mg) was described the tendency of Li.sup.+ penetrating through the membrane relative to Mg.sup.2+, and calculated according to Equation (3). Inductively coupled plasma optical emission spectroscopy (ICP-OES; ICAP7000 Series, USA) was utilized to determine ion concentrations in mixed salt solutions.

[00003]$Separationfactor=\frac{C_{L{i}^{+},p}/C_{M{g}^{2+},p}}{C_{L{i}^{+},f}/C_{M{g}^{2+},f}}$

where C.sub.Li,p and C.sub.Mg,p are the concentrations of Li.sup.+ and Mg.sup.2+ in the permeate respectively (g/L); C.sub.Li,p and C.sub.Mg,p are the concentrations of Li.sup.+ and Mg.sup.2+ in the raw material solution respectively (g/L).

Example 1

[0042] An aqueous solution containing 0.3% of polyethyleneimine (a molecular weight of 70,000 Da), 0.2% of 15-crown-5-ether, 0.1% of sodium carbonate and 0.1% of sodium dodecyl sulfate was prepared as an aqueous phase mixture. An n-hexane solution containing 0.1% of 1,3,5-benzenetricarboxylic acid chloride was prepared as an organic phase mixture. The aqueous phase mixture was placed on the surface of a polysulfone supporting membrane and adsorbed for 10 min, and excess solution was removed. Then the organic phase mixture was placed on the surface of the membrane, and reaction was kept for 1 min. Excess solution was removed, and unreacted monomers were rinsed off with n-hexane. Then the membrane was dried in a blast air oven at 80° C. for 10 min, and the prepared lithium-magnesium separation membrane was stored in deionized water for further testing of the separation property.

[0043] The lithium-magnesium separation membrane was tested to have a retention rate of ~25% for Li.sup.+, a retention rate of ~95% for Mg.sup.2+, a lithium-magnesium selectivity of ~18, and a water permeation flux of ~15 L • m.sup.-2 • h.sup.-1 • bar.sup.-1.

Example 2

[0044] An aqueous solution containing 0.5% of polyethyleneimine (a molecular weight of 10,000 Da), 0.3% of 4′-aminobenzo-15-crown-5-ether, 0.1% of sodium bicarbonate and 0.1% of sodium dodecyl sulfate was prepared as an aqueous phase mixture. An n-hexane solution containing 0.1% of 1,3,5-benzenetricarboxylic acid chloride was prepared as an organic phase mixture. The aqueous phase mixture was placed on the surface of a polyacrylonitrile supporting membrane and adsorbed for 5 min, and excess solution was removed. Then the organic phase mixture was placed on the surface of the membrane, and reaction was kept for 5 min. Excess solution was removed, and unreacted monomers were rinsed off with n-hexane. Then the membrane was dried in a blast air oven at 80° C. for 10 min, and the prepared lithium-magnesium separation membrane was stored in deionized water for further testing of the separation property.

[0045] The lithium-magnesium separation membrane was tested to have a retention rate of ~35% for Li.sup.+, a retention rate of ~95% for Mg.sup.2+, a lithium-magnesium selectivity of ~12, and a water permeation flux of ~8 L • m.sup.-2 • h.sup.-1 • bar.sup.-1.

Example 3

[0046] An aqueous solution containing 0.3% of polyetheramine (a molecular weight of 1800 Da), 0.5% of 4,13-diazo-18-crown-6-ether, 0.1% of sodium hydroxide and 0.1% of cetyl trimethyl ammonium bromide was prepared as an aqueous phase mixture. An n-hexane solution containing 0.2% of 1,3,5-benzene tricarbonic acid was prepared as an organic phase mixture. The aqueous phase mixture was placed on the surface of a polyether sulfone supporting membrane and adsorbed for 5 min, and excess solution was removed. Then the organic phase mixture was placed on the surface of the membrane, and reaction was kept for 10 min. Excess solution was removed, and unreacted monomers were rinsed off with n-hexane. Then the membrane was dried in a blast air oven at 80° C. for 10 min, and the prepared lithium-magnesium separation membrane was stored in deionized water for further testing of the separation property.

[0047] The lithium-magnesium separation membrane was tested to have a retention rate of ~20% for Li.sup.+, a retention rate of -91% for Mg.sup.2+, a lithium-magnesium selectivity of ~9, and a water permeation flux of ~13 L • m.sup.-2 • h.sup.-1 • bar.sup.-1.

Example 4

[0048] An aqueous solution containing 0.5% of polyetheramine (a molecular weight of 20,000 Da), 0.06% of 1,4,7,10-tetraazacyclododecane, 0.1% of sodium hydroxide and 0.1% of sodium dodecyl sulfate was prepared as an aqueous phase mixture. An n-hexane solution containing 0.1% of 1,3,5-benzene tricarbonic acid was prepared as an organic phase mixture. The aqueous phase mixture was placed on the surface of a polysulfone supporting membrane and adsorbed for 5 min, and excess solution was removed. Then the organic phase mixture was placed on the surface of the membrane, and reaction was kept for 10 min. Excess solution was removed, and unreacted monomers were rinsed off with n-hexane. Then the membrane was dried in a blast air oven at 80° C. for 10 min, and the prepared lithium-magnesium separation membrane was stored in deionized water for further testing of the separation property.

[0049] The lithium-magnesium separation membrane was tested to have a retention rate of ~24% for Li.sup.+, a retention rate of -91% for Mg.sup.2+, a lithium-magnesium selectivity of ~8, and a water permeation flux of ~12 L • m.sup.-2 • h.sup.-1 • bar.sup.-1.

Example 5

[0050] An aqueous solution containing 0.3% of polyetheramine (a molecular weight of 600 Da), 0.1% of 1,4,8,12-Tetraazacyclopentadecane, 0.1% of sodium hydroxide and 0.1% of cetyl trimethyl ammonium bromide was prepared as an aqueous phase mixture. An n-hexane solution containing 0.2% of 1,3,5-benzene tricarbonic acid was prepared as an organic phase mixture. The aqueous phase mixture was placed on the surface of a polyacrylonitrile supporting membrane and adsorbed for 5 min, and excess solution was removed. Then the organic phase mixture was placed on the surface of the membrane, and reaction was kept for 10 min. Excess solution was removed, and unreacted monomers were rinsed off with n-hexane. Then the membrane was dried in a blast air oven at 80° C. for 10 min, and the prepared lithium-magnesium separation membrane was stored in deionized water for further testing of the separation property.

[0051] The lithium-magnesium separation membrane was tested to have a retention rate of ~20% for Li.sup.+, a retention rate of ~89% for Mg.sup.2+, a lithium-magnesium selectivity of ~8, and a water permeation flux of ~14 L • m.sup.-2 • h.sup.-1 • bar.sup.-1.

Comparative Example

[0052] This comparative example is the same as example 1 except that the aqueous phase mixture of this comparative example did not contain 15-crown-5-ether.

[0053] The lithium-magnesium separation membrane was tested to have a retention rate of ~40% for Li.sup.+, a retention rate of ~75% for Mg.sup.2+, a lithium-magnesium selectivity of ~5, and a water permeation flux of ~4 L • m.sup.-2 • h.sup.-1 • bar.sup.-1.

[0054] Comparing the test results of example 1 with those of the comparative example, it can be seen that the retention rates for Li.sup.+ and Mg.sup.2+ in example 1 were quite different, the lithium-magnesium selectivity in example 1 was higher, and the water permeation flux in example 1 was much larger than that in the comparative example. This indicated that no crown ether molecules were added in the process of reaction between the organic monomer and aqueous monomer in the comparative example, the organic monomer and aqueous monomer directly underwent a polymerization reaction, and a polyamide active layer taking the crown ether molecules as lithium-ion channels was not formed. Therefore, it was difficult to obtain a separation membrane with a high water permeation flux and a high lithium-magnesium selectivity.

[0055] The lithium-magnesium separation membrane obtained in example 1 was tested for long-term stability. After 12 hours of continuous separation test, the water permeation flux and lithium-magnesium selectivity of the membrane were basically unchanged, indicating that the prepared lithium-magnesium separation membrane had a good long-term stability. The high-selectivity lithium-magnesium separation membrane obtained in example 1 was characterized by a scanning electron microscopy. The surface morphology and cross-sectional morphology of the obtained membrane are shown in FIGS. 2 and 3. The high-selectivity lithium-magnesium separation membrane was analyzed to have a smooth and dense surface with no defects, and the thickness of the selective separation layer was about 100 nm.

[0056] Therefore, the method for preparing a high-selectivity lithium-magnesium separation membrane in the above structure is adopted in the present invention. The method is simple in preparation process, mild in preparation conditions, wide in application range, easy to scale up, and easy to realize industrial production. The prepared high-selectivity lithium-magnesium separation membrane is high in firmness of the separation layer, large in permeation flux, and good in long-term operation stability.

[0057] Finally, it should be noted that the examples described above are intended only to illustrate, rather than to limit, the technical solution of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those of ordinary skill in the art that modifications or equivalent replacements may be made to the technical solution of the present invention, and these modifications or equivalent replacements cannot make the modified technical solution depart from the spirit and scope of the technical solution of the present invention.