A highly selectively permeable polyamide composite nanofiltration membrane, its preparation method, and its application.

Abstract

This invention discloses a highly selective permeable polyamide composite nanofiltration membrane, its preparation method, and its application. The preparation method includes the following steps: Step 1, contacting the surface of a porous ultrafiltration support layer with an aqueous solution and removing excess liquid from the surface, wherein the aqueous solution includes an aqueous monomer and an aqueous additive; Step 2, contacting the surface of the porous ultrafiltration membrane support layer treated in Step 1 with an organic phase solution to obtain a membrane to be heat-treated; Step 3, subjecting the membrane to be heat-treated obtained in Step 2 to heat treatment to obtain the polyamide composite nanofiltration membrane. The preparation method of this invention uses a multi-ether additive in an aqueous solution to prepare a highly selective permeable nanofiltration membrane for separating monovalent and divalent ions, and is characterized by simple operation, environmental friendliness, and low cost and availability.

Description

Technical Field

[0001] This invention relates to the field of water treatment membrane technology, and in particular to a highly selectively permeable polyamide composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] The separation of monovalent and divalent inorganic ions has significant application value in fields such as lithium extraction from salt lakes, denitrification of chlor-alkali brine, treatment of high-salinity wastewater, and drinking water preparation. Nanofiltration is an effective method for separating monovalent and divalent inorganic salt solutions, possessing important economic and environmental significance. As the core component of nanofiltration technology, the performance of the nanofiltration membrane determines the separation efficiency, profoundly impacting operating costs and product quality. Currently, polyamide composite nanofiltration membranes are commonly used, with a desalination rate of approximately 98% for divalent ions and relatively low selectivity for monovalent / divalent ions. Nanofiltration membranes consist of a support layer and a separation layer. The support layer provides mechanical strength, while the separation layer determines ion permeation and retention. To improve the performance of nanofiltration membranes, the separation layer needs to be controlled to allow as much water and monovalent ions as possible to pass through while retaining divalent ions.

[0003] Using novel reactive monomers is a common method to improve the performance of nanofiltration membranes. Chinese patent "An Ion-Selective Nanofiltration Membrane and Its Preparation Method and Application" (Publication No. CN115228300A) uses glucosamine salt as the aqueous phase monomer and trimesoyl chloride as the organic phase monomer to prepare a nanofiltration membrane via interfacial polymerization. This membrane is used for the separation of salt solutions with different valence states, and its separation factor for sodium sulfate / magnesium chloride is no greater than 15. Chinese patent "A Composite Nanofiltration Membrane and Its Preparation Method and Application" (Publication No. CN110394065A) prepares a nanofiltration membrane using interfacial polymerization of an amino polymer and glycidyl ether, achieving a salt removal rate of no more than 97.5%. However, these existing technologies cannot simultaneously guarantee both water flux and salt selectivity. Summary of the Invention

[0004] The purpose of this invention is to provide a polyamide composite nanofiltration membrane with high selective permeability, addressing the limitation of existing nanofiltration membranes in simultaneously ensuring water flux and salt selectivity.

[0005] Another object of the present invention is to provide a method for preparing the polyamide composite nanofiltration membrane.

[0006] Another object of the present invention is to provide an application of the polyamide composite nanofiltration membrane.

[0007] The technical solution adopted to achieve the purpose of this invention is:

[0008] A method for preparing a highly selective permeable polyamide composite nanofiltration membrane, the polyamide composite nanofiltration membrane comprising a porous ultrafiltration membrane support layer and a polyamide layer; the preparation method includes the following steps:

[0009] Step 1: Contact the surface of the porous ultrafiltration membrane support layer with an aqueous solution and remove excess liquid from the surface. The aqueous solution includes aqueous monomers and aqueous additives.

[0010] Step 2: The surface of the porous ultrafiltration membrane support layer after step 1 is brought into contact with the organic phase solution, so that the aqueous monomers on the surface of the porous ultrafiltration membrane support layer and the organic monomers in the organic phase solution are polymerized on the surface of the porous ultrafiltration membrane support layer through an interfacial polymerization reaction, to obtain the membrane to be heat-treated.

[0011] Step 3: Heat-treat the membrane to be heat-treated obtained in Step 2 to obtain the polyamide composite nanofiltration membrane.

[0012] In the above technical solution, the aqueous monomer accounts for 1wt%-3wt% of the mass percentage of the aqueous solution; the aqueous monomer is a polyamine.

[0013] Preferably, the polyamine is one or more selected from piperazine, m-phenylenediamine, polyethyleneimine, o-phenylenediamine, p-phenylenediamine, and hexamethylenediamine; more preferably, the polyamine is piperazine.

[0014] The aqueous phase additive accounts for 0.05wt%-1.0wt% of the aqueous phase solution by mass; the aqueous phase additive is a polyether; preferably, the polyether is one or more of diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether; more preferably, the polyether is diethylene glycol dimethyl ether.

[0015] In the above technical solution, the aqueous phase solution further includes a pH adjuster, and the pH adjuster accounts for 0.1wt%-1.0wt% of the aqueous phase solution by mass; the pH adjuster is one or more of sodium hydroxide, potassium hydroxide, and sodium carbonate; preferably, the pH adjuster is sodium hydroxide.

[0016] In the above technical solution, the organic phase solution is an alkane solution; preferably, the alkane solution is one or more of n-hexane, cyclohexane, n-heptane, and Isopar G; more preferably, the organic phase solution is Isopar G; the organic phase monomer accounts for 0.06wt%-0.15wt% of the organic phase solution by mass; the organic phase monomer is a polyacryl chloride; the polyacryl chloride is one or more of trimesoyl chloride, isophthaloyl chloride, glutaryl chloride, adipicoyl chloride, and octanoyl chloride; preferably, the polyacryl chloride is trimesoyl chloride.

[0017] In the above technical solution, before the porous ultrafiltration support layer in step 1 comes into contact with the aqueous solution, it is soaked and rinsed with deionized water and blown until there are no droplets on the surface of the porous ultrafiltration support layer; the contact time between the porous ultrafiltration support layer and the aqueous solution in step 2 is 45s-120s.

[0018] In the above technical solution, the time for the interfacial polymerization reaction in step 2 is 45s-90s; the temperature for the heat treatment in step 3 is 50℃-90℃, and the time for the heat treatment is 3min-10min.

[0019] In the above technical solution, the porous ultrafiltration support layer is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, and sulfonated polyethersulfone ultrafiltration membrane; preferably, the porous ultrafiltration support layer is a polysulfone ultrafiltration membrane; the pore size distribution of the porous ultrafiltration support layer is concentrated in the range of 10nm-100nm.

[0020] In another aspect, the present invention provides a polyamide composite nanofiltration membrane prepared by the preparation method described above, wherein the polyamide composite nanofiltration membrane allows monovalent ions to pass through while retaining divalent ions.

[0021] In another aspect, the present invention provides a polyamide composite nanofiltration membrane prepared by the aforementioned method, wherein the flux of the polyamide composite nanofiltration membrane is greater than 55 L / m³. 2 •h; The LiCl desalination rate of the polyamide composite nanofiltration membrane is not greater than 29%, and the MgCl2 desalination rate of the polyamide composite nanofiltration membrane is not less than 97%.

[0022] In another aspect, the present invention provides an application of the polyamide composite nanofiltration membrane prepared by the preparation method described above, wherein the polyamide composite nanofiltration membrane is used for material separation, seawater desalination, hard water softening or wastewater treatment, preferably lithium extraction from salt lakes.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. The preparation method of this invention uses a polyether additive in an aqueous solution to prepare a highly selective nanofiltration membrane for separating monovalent and divalent ions. It is characterized by its simple operation, environmental friendliness, and low cost. Furthermore, because the polyether promotes the diffusion of the aqueous monomer into the organic phase solution and increases the interfacial polymerization rate, the resulting polyamide separation layer exhibits high selective permeation performance.

[0025] 2. The polyamide composite nanofiltration membrane prepared using piperazine as the aqueous phase monomer of this invention is robust and durable, and has certain performance advantages. By adding trace amounts of additives to the reaction phase and controlling the structure of the separation layer polypiperazine, the retention performance of the separation layer for monovalent or divalent ions can be adjusted, thus preparing a nanofiltration membrane with selective retention for different salt ions or solutes, achieving the separation of ions or solutes in the solution. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0027] Example 1

[0028] A polyamide composite nanofiltration membrane is prepared by the following method:

[0029] Step 1: Soak the polysulfone ultrafiltration membrane in deionized water, purge the membrane surface with nitrogen until no droplets remain, prepare an aqueous solution with 1.5 wt% piperazine, 0.6 wt% sodium hydroxide, and 0.1 wt% diethylene glycol dimethyl ether, contact the surface of the polysulfone ultrafiltration membrane with the aqueous solution for 60 seconds, and purge the membrane surface with nitrogen until no droplets remain.

[0030] Step 2: Prepare an Isopar G organic phase solution with a pyromellitic methyl chloride content of 0.1 wt%. Contact the surface of the polysulfone ultrafiltration membrane treated in Step 1 with the organic phase solution for 60 s to obtain the membrane to be heat-treated.

[0031] Step 3: Place the membrane to be treated in a 60°C oven for 5 minutes for heat treatment, and then rinse with pure water to obtain the polyamide composite nanofiltration membrane.

[0032] Example 2

[0033] A polyamide composite nanofiltration membrane is prepared by the following method:

[0034] Step 1: Soak the polysulfone ultrafiltration membrane in deionized water, purge the membrane surface with nitrogen until no droplets remain, prepare an aqueous solution with 1.5 wt% piperazine, 0.6 wt% sodium hydroxide, and 0.2 wt% diethylene glycol dimethyl ether, contact the surface of the polysulfone ultrafiltration membrane with the aqueous solution for 60 seconds, and purge the membrane surface with nitrogen until no droplets remain.

[0035] Step 2: Prepare an Isopar G organic phase solution with a pyromellitic methyl chloride content of 0.1 wt%. Contact the surface of the polysulfone ultrafiltration membrane treated in Step 1 with the organic phase solution for 60 s to obtain the membrane to be heat-treated.

[0036] Step 3: Place the membrane to be treated in a 60°C oven for 5 minutes for heat treatment, and then rinse with pure water to obtain the polyamide composite nanofiltration membrane.

[0037] Example 3

[0038] A polyamide composite nanofiltration membrane is prepared by the following method:

[0039] Step 1: Soak the polysulfone ultrafiltration membrane in deionized water and purge the membrane surface with nitrogen until no droplets remain. Prepare an aqueous solution with 1.5 wt% piperazine, 0.6 wt% sodium hydroxide, and 0.3 wt% diethylene glycol dimethyl ether. After contacting the surface of the polysulfone ultrafiltration membrane with the aqueous solution for 60 seconds, purge the membrane surface with nitrogen until no droplets remain.

[0040] Step 2: Prepare an Isopar G organic phase solution with a pyromellitic methyl chloride content of 0.1 wt%. Contact the surface of the polysulfone ultrafiltration membrane treated in Step 1 with the organic phase solution for 60 s to obtain the membrane to be heat-treated.

[0041] Step 3: Place the membrane to be treated in a 60°C oven for 5 minutes for heat treatment, and then rinse with pure water to obtain the polyamide composite nanofiltration membrane.

[0042] Example 4

[0043] A polyamide composite nanofiltration membrane is prepared by the following method:

[0044] Step 1: Soak the polysulfone ultrafiltration membrane in deionized water and purge the membrane surface with nitrogen until no droplets remain. Prepare an aqueous solution with 1.5 wt% piperazine, 0.6 wt% sodium hydroxide, and 0.4 wt% diethylene glycol dimethyl ether. After contacting the surface of the polysulfone ultrafiltration membrane with the aqueous solution for 60 seconds, purge the membrane surface with nitrogen until no droplets remain.

[0045] Step 2: Prepare an Isopar G organic phase solution with a pyromellitic methyl chloride content of 0.1 wt%. Contact the surface of the polysulfone ultrafiltration membrane treated in Step 1 with the organic phase solution for 60 s to obtain the membrane to be heat-treated.

[0046] Step 3: Place the membrane to be treated in a 60°C oven for 5 minutes for heat treatment, and then rinse with pure water to obtain the polyamide composite nanofiltration membrane.

[0047] Comparative Example 1

[0048] A polyamide composite nanofiltration membrane without added diethylene glycol dimethyl ether in the aqueous phase was selected as a comparative example. Its preparation method was as follows: a polysulfone ultrafiltration membrane was soaked in deionized water, and the membrane surface was purged with nitrogen until no droplets remained. An aqueous solution containing 1.5 wt% piperazine and 0.6 wt% sodium hydroxide was prepared. The surface of the polysulfone ultrafiltration membrane was contacted with the aqueous solution for 60 s, and the membrane surface was purged with nitrogen until no droplets remained. An organic solution containing 0.1 wt% trimesoyl chloride (Isopar G) was prepared. The surface of the aforementioned membrane was contacted with the organic solution for 60 s, and then heat-treated in a 60°C oven for 5 min. The surface was then washed with deionized water to obtain the polyamide composite nanofiltration membrane without added diethylene glycol dimethyl ether in the aqueous phase.

[0049] Example 5

[0050] The present invention tests the separation performance (water flux, desalination rate) of the polyamide composite nanofiltration membranes obtained in Examples 1-4, and compares the results with those of the comparative polyamide composite nanofiltration membranes.

[0051] Detection method:

[0052] The water flux and desalination rate were tested as follows: A cross-flow membrane detection device was used. The influent was a mixed aqueous solution of LiCl and MgCl2 at 2000 ppm (Mg / Li = 20). The operating pressure was 0.69 MPa, the temperature was 25℃, the influent pH was 7.0, and the membrane was pre-pressurized for 0.5 h before testing the water flux and desalination rate.

[0053] Test results:

[0054] The measured water flux and desalination rate data are shown in Table 1.

[0055] Table 1. Results of water flux and desalination rate

[0056] membrane <![CDATA[Flux (L / m 2 ·h)]]> LiCl desalination rate (%) <![CDATA[Desalination rate of MgCl2(%)]]> Comparative Example 1 51.5 39.6 99.0 Example 1 56.8 28.9 99.0 Example 2 63.0 25.2 99.0 Example 3 65.7 25.0 98.1 Example 4 65.9 23.7 97.2

[0057] The water flux and desalination rate of the polyamide composite nanofiltration membranes obtained in Examples 1-4 were compared with those of the comparative nanofiltration membranes, and the results are shown in Table 1. Table 1 shows that the water flux of the polyamide composite nanofiltration membranes in Examples 1-4 was increased compared to the comparative nanofiltration membranes, and the increase in water flux increased with the increase in the amount of diethylene glycol dimethyl ether added. Compared to the comparative nanofiltration membranes, the desalination rate of LiCl by the polyamide composite nanofiltration membranes in Examples 1-4 was decreased, and the decrease in LiCl desalination rate increased with the increase in the amount of diethylene glycol dimethyl ether added. The MgCl2 desalination rates of Examples 1 and 2 were the same as those of the comparative nanofiltration membranes. The above results indicate that when the amount of diethylene glycol dimethyl ether added is 0.1%-0.2%, as in Examples 1 and 2, the water flux of the nanofiltration membrane increases, the desalination rate for divalent ions remains unchanged, the desalination rate for monovalent ions decreases, more monovalent ions are allowed to pass through, the selective separation of monovalent and divalent ions is improved, and the separation efficiency of monovalent and divalent ions is significantly enhanced. When the amount of diethylene glycol dimethyl ether added is 0.3%-0.4%, as in Examples 3 and 4, the water flux of the nanofiltration membrane increases, the desalination rate for monovalent ions decreases, more monovalent ions are allowed to pass through, although the desalination rate for divalent ions decreases slightly, more monovalent ions can be enriched in the permeate.

[0058] The polysulfone ultrafiltration membrane in this invention is prepared by immersion precipitation phase inversion method, or it can be a commercially available polysulfone ultrafiltration membrane.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly selective permeable polyamide composite nanofiltration membrane, which is applied to lithium extraction from salt lakes, characterized in that... The polyamide composite nanofiltration membrane comprises a porous ultrafiltration membrane support layer and a polyamide layer; the preparation method includes the following steps: Step 1: Contact the surface of the porous ultrafiltration membrane support layer with an aqueous solution and remove excess liquid from the surface. The aqueous solution includes an aqueous monomer and an aqueous additive, wherein the aqueous monomer is piperazine and the aqueous additive is one or more of diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether. Step 2: Contact the surface of the porous ultrafiltration membrane support layer treated in Step 1 with an organic solution, so that the aqueous monomer on the surface of the porous ultrafiltration membrane support layer and the organic monomer in the organic solution are polymerized on the surface of the porous ultrafiltration membrane support layer through an interfacial polymerization reaction, thereby obtaining a membrane to be heat-treated. Step 3, subjecting the film to be heat treated obtained in step 2 to heat treatment to obtain the polyamide composite nanofiltration membrane, wherein the temperature of the heat treatment is 50-90℃, the time of the heat treatment is 3-10min; the flux of the polyamide composite nanofiltration membrane is greater than 55L / m 2 h; the LiCl desalination rate of the polyamide composite nanofiltration membrane is not greater than 29%, and the MgCl2 desalination rate of the polyamide composite nanofiltration membrane is not less than 97%.

2. The preparation method according to claim 1, characterized in that, The aqueous monomer accounts for 1wt%-3wt% of the aqueous solution by mass; the aqueous additive accounts for 0.05wt%-1.0wt% of the aqueous solution by mass; and the aqueous additive is diethylene glycol dimethyl ether.

3. The preparation method according to claim 1, characterized in that, The aqueous solution further includes a pH adjuster, wherein the pH adjuster accounts for 0.1wt%-1.0wt% of the aqueous solution by mass; the pH adjuster is one or more of sodium hydroxide, potassium hydroxide, and sodium carbonate.

4. The preparation method according to claim 3, characterized in that, The pH adjuster is sodium hydroxide.

5. The preparation method according to claim 1, characterized in that, The organic phase solution is an alkane solution; the alkane solution is one or more of n-hexane, cyclohexane, n-heptane, and IsoparG; the organic phase monomer is a polyacryl chloride; the polyacryl chloride is one or more of trimesoyl chloride, isophthaloyl chloride, glutaryl chloride, adipicoyl chloride, and octanoyl chloride.

6. The preparation method according to claim 5, characterized in that, The organic phase solution is IsoparG; the organic phase monomer accounts for 0.06wt%-0.15wt% of the organic phase solution by mass; the polyacrylamide chloride is pyromellitic trimethylolpropionate chloride.

7. The preparation method according to claim 1, characterized in that, Before the porous ultrafiltration membrane support layer in step 1 comes into contact with the aqueous solution, it is soaked and rinsed with deionized water and then blown until there are no droplets on the surface of the porous ultrafiltration membrane support layer; the contact time between the porous ultrafiltration membrane support layer and the aqueous solution in step 2 is 45s-120s.

8. The preparation method according to claim 1, characterized in that, The time for the interfacial polymerization reaction in step 2 is 45s-90s.

9. The preparation method according to claim 1, characterized in that, The porous ultrafiltration membrane support layer is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, and sulfonated polyethersulfone ultrafiltration membrane; the pore size distribution of the porous ultrafiltration membrane support layer is concentrated in the range of 10 nm to 100 nm.

10. The preparation method according to claim 1, characterized in that, The porous ultrafiltration membrane support layer is a polysulfone ultrafiltration membrane.

11. A polyamide composite nanofiltration membrane prepared by the preparation method according to any one of claims 1-10, characterized in that, The polyamide composite nanofiltration membrane allows monovalent ions to pass through while retaining divalent ions.

12. The application of a polyamide composite nanofiltration membrane prepared by the preparation method according to any one of claims 1-10 in the lithium extraction process of salt lakes.