Nanofiltration composite membrane as well as preparation method and application thereof

Abstract

The invention discloses a nanofiltration composite membrane as well as a preparation method and application thereof. The nanofiltration composite membrane is composed of a separation function layer and a porous support layer, the thickness of the separation functional layer is 1-900 nm; the composite material is composed of a polyamide layer and a polysulfonamide layer, the polyamide layer is polymerized on the porous supporting layer in situ, and the polysulfonamide layer is polymerized on the polyamide layer in situ; the side, close to the porous supporting layer, of the polyamide layer and the polysulfonamide layer are negatively charged, the side, close to the polysulfonamide layer, of the polyamide layer is positively charged, the sandwich-shaped mixed charge layer structure is achieved, monovalent / multivalent anions and cations can be effectively separated, the preparation process is simple and easy to operate, and large-scale production and application are facilitated.

Description

Technical Field

[0001] The present application relates to a nanofiltration composite membrane and a preparation method and application thereof, belonging to the field of membrane separation. Background Art

[0002] Lithium has become a vital strategic resource, and its key role in renewable energy storage and electric vehicle batteries has driven its demand growth. Global lithium consumption in lithium carbonate equivalent is expected to reach 900,000 tons by 2025, 3.4 times that of 2015 (265,000 tons), which is expected to lead to a lithium supply shortage. Extracting lithium from salt lake brine is an effective solution to the shortage of lithium resources, but the high concentration of divalent Mg2+ ions and high Mg2+ / Li+ ratio pose great challenges to extraction. Mg2+ and Li+ have similar hydration radii and chemical properties, which makes the selective extraction of high-purity lithium more complicated, so new separation technologies are urgently needed.

[0003] Nanofiltration membranes have attracted attention as a promising solution for extracting lithium from salt lake brines. These membranes have charged surfaces and sub-nanoscale pores, and use the Donnan effect and pore sieving principles to achieve ion separation. Traditional nanofiltration membranes are polyamide (PA) membranes prepared by interfacial polymerization of trimesoyl chloride (TMC) and piperazine (PIP). However, nanofiltration membranes are usually negatively charged, resulting in poor retention of Mg2+, making the magnesium-lithium selectivity (Mg2+ / Li+) unsatisfactory. Researchers have developed positively charged nanofiltration membranes to improve magnesium-lithium selectivity through strategies such as introducing or grafting positively charged monomers during interfacial polymerization and constructing positively charged interlayers. It is worth noting that polyethyleneimine-based PA membranes prepared using polyethyleneimine (PEI) and TMC have received widespread attention in the field of separating Mg2+ / Li from salt lake brines due to their high separation efficiency and the presence of a large number of positively charged amine groups.

[0004] However, nanofiltration membranes, whether positively or negatively charged, are usually limited to separating monovalent / multivalent cations or anions. For example, polyethyleneimine-based PA membranes can effectively intercept multivalent cations, but have poor interception effects on multivalent anions. In addition to cationic Mg2+ and Li+, salt lake brine also contains high concentrations of anions, such as sulfate ions (SO42-) and chloride ions (Cl-), as well as negatively charged natural small molecules. To meet production requirements, traditional lithium extraction processes usually couple membrane methods with precipitation, adsorption or electrochemical techniques, which makes the process complicated and significantly increases costs. Therefore, there is an urgent need to develop nanofiltration membranes that can separate monovalent / multivalent anions and cations. Summary of the invention

[0005] In view of the problem that polyamide nanofiltration membrane cannot separate monovalent / multivalent anions and cations, the present application intends to design the functional layer of the nanofiltration membrane as a unique "negative-positive-negative" sandwich mixed charge layer. Its preparation process starts with the chemical crosslinking of polyamines and polyacyl chlorides to form a preliminary polyamide membrane substrate. Subsequently, by utilizing the inherent diffusion rate difference between polyamines, the rapidly diffusing amine component further reacts with the subsequently introduced polysulfonyl chlorides on the membrane surface to form a polysulfonamide surface layer. This surface layer is rich in incompletely reacted sulfonyl chloride functional groups, which are converted into negatively charged sulfonic acid groups by hydrolysis, giving the surface layer negative charge characteristics. At the same time, at the water phase contact interface of the membrane, some acyl chloride groups tend to hydrolyze to form negatively charged carboxyl groups, which are located at the bottom of the polyamide layer. It is worth noting that compared with the polyacyl chlorides and polysulfonyl chlorides in the reactants, the polyamines used contain excess positively charged amine groups, which accumulate inside the functional layer to form a positively charged layer in the middle, thereby cleverly constructing the required "negative-positive-negative" sandwich mixed charge layer. This type of nanofiltration membrane exhibits efficient separation capabilities for monovalent and polyvalent anions and cations. Its preparation process is not only simple and efficient, but also has good scalability, facilitating industrial large-scale production and application, meeting the technical requirements and market potential for the development of high-performance membrane materials.

[0006] According to one aspect of the present application, a nanofiltration composite membrane is provided, wherein the nanofiltration composite membrane is composed of a separation functional layer and a porous support layer;

[0007] The thickness of the separation functional layer is 1 to 900 nm;

[0008] Optionally, the separation functional thickness of the nanofiltration composite membrane is 10 to 300 nm.

[0009] Optionally, the separation functional thickness of the nanofiltration composite membrane is any value among 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm or any range value between two of them.

[0010] The separation function layer consists of a polyamide layer and a polysulfonamide layer;

[0011] The polyamide layer is in-situ polymerized on the porous support layer, and the polysulfonamide layer is in-situ polymerized on the polyamide layer;

[0012] The side of the polyamide layer close to the porous support layer and the polysulfonamide layer are negatively charged, and the side of the polyamide layer close to the polysulfonamide layer is positively charged.

[0013] The porous support layer is a non-woven fabric compounded with a polymer;

[0014] The polymer is selected from at least one of polysulfone, polyethersulfone, sulfonated polyethersulfone, polyimide, polyacrylonitrile, polypropylene and polyetheretherketone.

[0015] According to another aspect of the present application, a method for preparing the above-mentioned nanofiltration composite membrane is provided, comprising the following steps:

[0016] (1) immersing the porous support layer in an aqueous solution containing a polyvalent organic amine to obtain a wetted porous support layer;

[0017] (2) pouring an organic solvent solution containing polyacyl chloride onto the wetted porous support layer, polymerizing I, and obtaining an initial nanofiltration membrane composite membrane;

[0018] (3) pouring an organic solvent solution containing polysulfonyl chloride onto the initial nanofiltration membrane composite membrane, polymerizing II, and drying to obtain the nanofiltration composite membrane.

[0019] The polyvalent organic amine is selected from at least one of polyethyleneimine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, phenylbiguanide, phenformin, phenylguanidine, metformin, buformin, iminomethyldiamine, 2,2',2"-triaminotriethylamine, polyamide-amine, piperazine, m-phenylenediamine, p-phenylenediamine, 1,2-ethylenediamine, 1,6-hexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, spermine or melamine;

[0020] In the aqueous solution containing polybasic organic amines, the concentration of the polybasic organic amines is 0.01 to 5 wt %;

[0021] Optionally, in the aqueous solution containing polybasic organic amines, the concentration of the polybasic organic amines is 0.05 to 2 wt %;

[0022] Optionally, in the aqueous solution containing the polyvalent organic amine, the concentration of the polyvalent organic amine is any value of 0.05wt%, 0.2wt%, 0.5wt%, 0.75wt%, 1wt%, 1.5wt%, 2wt% or any range between two of them.

[0023] The immersion time is 1s to 10min;

[0024] Optionally, the immersion time is 30s to 6min.

[0025] Optionally, the immersion time is any value among 10s, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, or a range value between any two of them.

[0026] The polybasic acid chloride is selected from at least one of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, pyromellitoyl chloride and adipoyl chloride;

[0027] In the organic solvent solution containing polyacid chloride, the concentration of the polyacid chloride is 0.01 to 5.00 wt %;

[0028] Optionally, in the organic solvent solution containing polyacyl chloride, the concentration of the polyacyl chloride is selected from any value of 0.01wt%, 0.15wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 4wt%, 5wt% or any range between two of them.

[0029] The polymerization time of said polymerization I is 1s to 5min;

[0030] Optionally, the polymerization I lasts for 5 seconds to 1 minute.

[0031] Optionally, the polymerization time is any value among 1s, 5s, 30s, 45s, 1min, 2min, 3min, 4min, 5min, or a range between any two of them.

[0032] The polysulfonyl chloride is selected from at least one of trimesyl chloride, isophthalene dimesyl chloride, terephthalene dimesyl chloride, pyromellitic methanesulfonyl chloride and hexane disulfonyl chloride;

[0033] In the organic solvent solution containing polysulfonyl chloride, the concentration of polysulfonyl chloride is 0.01-5.00 wt %;

[0034] Optionally, in the organic solvent solution containing polysulfonyl chloride, the concentration of the polyacyl chloride is selected from any value among 0.01wt%, 0.15wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 4wt%, 5wt% or any range between two values.

[0035] The polymerization time of said polymerization II is 1s to 5min;

[0036] Optionally, the polymerization II takes place over a period of 5 seconds to 1 minute.

[0037] Optionally, the polymerization II time is any value among 1s, 5s, 30s, 45s, 1min, 2min, 3min, 4min, 5min, or a range between any two of them.

[0038] The drying temperature is 50-150°C;

[0039] Optionally, the drying temperature is any value of 50°C, 75°C, 100°C, 125°C, 150°C, or any range therebetween.

[0040] The drying time is 1 to 20 minutes.

[0041] Optionally, the drying time is selected from any value among 1 min, 5 min, 10 min, 15 min, 20 min, or any range between two values.

[0042] The organic solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, n-octane, isopentane, Isopar-G, Isopar-E, Isopar-L or acetone.

[0043] The aqueous solution containing polybasic organic amines also contains a buffer;

[0044] The buffer is selected from at least one of trisodium phosphate / hydrochloric acid, triethylamine / camphorsulfonic acid, and sodium hydroxide / hydrochloric acid;

[0045] The pH of the aqueous solution containing polyvalent organic amines is 7-12.

[0046] According to another aspect of the present application, there is provided an application of the above-mentioned nanofiltration composite membrane for use in mono / polyvalent ion separation, water treatment or lithium extraction from salt lakes (magnesium-lithium separation).

[0047] The beneficial effects of this application include:

[0048] 1. The preparation method of the nanofiltration composite membrane provided in the present application first generates a nascent polyamide membrane by reacting a polyamine and a polyacyl chloride, and then, based on the difference in diffusion rates between the polyamines, the polyamine with a fast diffusion rate reacts with the later added polysulfonyl chloride on the surface of the nascent nanofiltration membrane to generate a polysulfonamide layer.

[0049] 2. The surface of the polysulfonamide layer contains many unreacted sulfonyl chloride groups, which hydrolyze to generate negatively charged sulfonic acid groups. In addition, some acyl chloride groups close to the water phase are easily hydrolyzed, resulting in negatively charged carboxyl groups at the bottom of the polyamide layer. Compared with polyacyl chlorides and polysulfonyl chlorides, polyamines contain excessive positively charged amine groups, resulting in positive charges in the middle of the functional layer, thus constructing a "negative-positive-negative" sandwich-shaped mixed charge layer.

[0050] 3. The nanofiltration composite membrane provided in this application can effectively separate monovalent / polyvalent anions and cations, and the preparation process is simple and easy to operate, which is conducive to large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1This is the infrared spectrum of the composite membrane functional layer prepared in Example 3 of the present application;

[0052] Figure 2 The water flux, magnesium chloride and lithium chloride rejection rates of the composite membranes prepared in Comparative Example 1 and Examples 1 to 5 of the present application;

[0053] Figure 3 These are atomic force microscope images of the surfaces of the polyamide nanofiltration composite membranes prepared in Comparative Example 1 and Example 3 of the present application, wherein a is an AFM image of a TFC-0 membrane, and b is an AFM image of an IC-0.35 membrane.

[0054] Figure 4 Thickness measurement of the polyamide nanofiltration composite membranes prepared in Comparative Example 1 and Example 3 of the present application. a is an AFM image of a TFC-0 membrane, and b is a thickness measurement image of an IC-0.35 membrane.

[0055] Figure 5 This is the longitudinal time-of-flight-secondary ion mass spectrometry image of the functional layer of the IC-0.35 membrane. DETAILED DESCRIPTION

[0056] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0057] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0058] The analysis method in the examples of this application is as follows:

[0059] An infrared spectrum of the composite membrane functional layer prepared in Example 3 was obtained by using an infrared spectrometer at room temperature;

[0060] Atomic force microscope images of the surfaces of the polyamide nanofiltration composite membranes prepared in Comparative Example 1 and Example 3 were obtained using an atomic force microscope at room temperature.

[0061] The calculation of water flux and solute retention rate in the examples of this application is as follows:

[0062] The formula for calculating the flux is (1):

[0063]

[0064] Among them J w (L / (m 2 h)) is the water flux, V represents the volume of the permeate, S (m 2 ) is the test area of ​​the diaphragm, and Δt(h) is the test time.

[0065] The calculation formula of solute retention rate is as follows:

[0066]

[0067] Among them C p (g / L) and C f (g / L) represent the salt concentration of the permeate and feed solution, respectively. The salt concentration was measured by a DDSJ-308A conductivity meter (Shanghai, China).

[0068] Comparative Example 1

[0069] The prepared nanofiltration composite membrane consists of three parts: an ultrathin separation polyamide layer, a porous polysulfone ultrafiltration support layer and a non-woven fabric. First, an aqueous solution with a concentration of 0.2wt% polyethyleneimine, 0.4wt% phenyl biguanide, and 1%wt trisodium phosphate is prepared, and the pH is adjusted to 10 using hydrochloric acid; a n-hexane solution with a concentration of 0.15wt% trimesoyl chloride is prepared. During the interfacial polymerization membrane preparation process, the aqueous solution is first poured on the surface of the polysulfone ultrafiltration membrane, the residual solution is poured out after immersion for 5 minutes, and the membrane surface is blown dry with nitrogen or air knife; then the n-hexane solution is poured on the membrane surface, and the excess n-hexane solution is poured out after the polymerization reaction for 30s, and the pure n-hexane solution is poured on the membrane surface for 30s and then poured out. Dry in a blast oven at 50 degrees Celsius for 10 minutes, and finally store the prepared nanofiltration composite membrane in deionized water for standby use, marked as TFC-0 membrane.

[0070] Example 1

[0071] The prepared nanofiltration composite membrane consists of three parts: an ultrathin separation polyamide layer, a porous polysulfone ultrafiltration support layer and a non-woven fabric. First, an aqueous solution with a concentration of 0.2wt% polyethyleneimine, 0.4wt% phenyl biguanide, and 1%wt trisodium phosphate is prepared, and the pH is adjusted to 10 using hydrochloric acid; a n-hexane solution with a concentration of 0.15wt% trimesoyl chloride is prepared. During the interfacial polymerization membrane preparation process, the aqueous solution is first poured on the surface of the polysulfone ultrafiltration membrane, and the residual solution is poured out after immersion for 5 minutes, and the membrane surface is blown dry with nitrogen or air knife; then the n-hexane solution is poured on the membrane surface, and the excess n-hexane solution is poured out after the polymerization reaction for 30s; then the n-hexane solution of 0.25wt% isophenyl disulfonyl chloride is poured on the membrane surface for 30s, and the remaining solution is poured out. Dry in a blast oven at 50 degrees Celsius for 10 minutes, and finally the prepared nanofiltration composite membrane is stored in deionized water for standby use, marked as IC-0.25 membrane.

[0072] Example 2

[0073] The experimental operation steps and conditions are the same as those of Example 1, except that the concentration of the n-hexane solution of isophenylenedisulfonyl chloride is 0.30 wt %, and is labeled as IC-0.30 membrane.

[0074] Example 3

[0075] The experimental operation steps and conditions were the same as those in Example 1, except that the concentration of the n-hexane solution of isophenylenedisulfonyl chloride was 0.35 wt %, and the membrane was labeled as IC-0.35.

[0076] Example 4

[0077] The experimental operation steps and conditions are the same as those of Example 1, except that the concentration of the n-hexane solution of isophenylenedisulfonyl chloride is 0.40 wt %, and is labeled as IC-0.40 membrane.

[0078] Example 5

[0079] The experimental operation steps and conditions were the same as those in Example 1, except that the concentration of the n-hexane solution of isophenylenedisulfonyl chloride was 0.45 wt %, and the membrane was labeled as IC-0.45.

[0080] Test Case

[0081] according to Figure 1 It can be seen that the IC-0.35 film has a peak at 1636 cm -1 The amide I band of semiaromatic polyamide was found at 914 cm-1, proving that the polyamide layer was successfully formed on the polysulfone-based membrane. -1 The signal peak of polysulfonamide was found at , indicating that a mixed functional layer of polyamide / polysulfonamide was formed.

[0082] The performance of the nanofiltration composite membrane was evaluated by measuring water flux and solute retention rate. The test conditions were: 6 bar, 20 ° C, 3 L / min, and pure water, magnesium chloride solution and lithium chloride solution were tested respectively. The salt concentration was 1 g / L. The test results are as follows: Figure 2 .

[0083] pass Figure 2 It can be seen that in comparative example 1, no isophenyl disulfonyl chloride is introduced after interfacial polymerization, and the cation selectivity and anion selectivity of the composite membrane of the nanofiltration example are improved. As the concentration of isophenyl disulfonyl chloride increases from 0.25% to 0.45%, the cation selectivity of the new nanofiltration membrane for magnesium chloride and lithium chloride increases from 32.99 to 36.01, among which IC-0.35 is the highest at 57.22; the anion selectivity for sodium sulfate and sodium chloride increases from 16.41 to 33.82, both better than 2.91 and 1.46 of TFC-0 membrane.

[0084] Figure 3 These are the AFM images of TFC-0 and IC-0.35 membranes. Compared with the TFC-0 membrane prepared by traditional interfacial polymerization, it can be found that the surface morphology of the IC-0.35 membrane is smoother.

[0085] Figure 4is the thickness of the TFC-0 and IC-0.35 films, which increases from 34.6 nm for the TFC-0 film to 128.9 nm for the IC-0.35 film.

[0086] Figure 5 This is a longitudinal time-of-flight-secondary ion mass spectrometry image of the functional layer of the IC-0.35 membrane. According to the figure, the surface content of the negatively charged sulfonic acid group is the highest, and gradually decreases with the depth of the functional layer; the positively charged amine group increases first and then decreases with the depth of the functional layer, and the content in the middle is the highest; the negatively charged carboxylic acid group has the highest content at the bottom, and gradually increases with the depth of the functional layer. Therefore, a "negative-positive-negative" sandwich-shaped mixed charge functional layer was successfully prepared.

[0087] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A nanofiltration composite membrane, characterized in that: The nanofiltration composite membrane consists of a separation functional layer and a porous support layer; The thickness of the separation functional layer is 1 to 900 nm; The separation function layer consists of a polyamide layer and a polysulfonamide layer; The polyamide layer is in-situ polymerized on the porous support layer, and the polysulfonamide layer is in-situ polymerized on the polyamide layer; The side of the polyamide layer close to the porous support layer and the polysulfonamide layer are negatively charged, and the side of the polyamide layer close to the polysulfonamide layer is positively charged.

2. The nanofiltration composite membrane according to claim 1, characterized in that The porous support layer is a non-woven fabric compounded with a polymer; The polymer is selected from at least one of polysulfone, polyethersulfone, sulfonated polyethersulfone, polyimide, polyacrylonitrile, polypropylene and polyetheretherketone.

3. A method for preparing the nanofiltration composite membrane according to claim 1, characterized in that: The following steps are involved: (1) immersing the porous support layer in an aqueous solution containing a polyvalent organic amine to obtain a wetted porous support layer; (2) pouring an organic solvent solution containing polyacyl chloride onto the wetted porous support layer, polymerizing I, and obtaining an initial nanofiltration membrane composite membrane; (3) pouring an organic solvent solution containing polysulfonyl chloride onto the initial nanofiltration membrane composite membrane, polymerizing II, and drying to obtain the nanofiltration composite membrane.

4. The preparation method according to claim 3, characterized in that: The polyvalent organic amine is selected from at least one of polyethyleneimine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, phenylbiguanide, phenformin, phenylguanidine, metformin, buformin, iminomethyldiamine, 2,2',2"-triaminotriethylamine, polyamide-amine, piperazine, m-phenylenediamine, p-phenylenediamine, 1,2-ethylenediamine, 1,6-hexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, spermine or melamine; In the aqueous solution containing polybasic organic amines, the concentration of the polybasic organic amines is 0.01 to 5 wt %; Preferably, in the aqueous solution containing polyvalent organic amines, the concentration of the polyvalent organic amines is 0.05 to 2 wt %; The immersion time is 1s to 10min; Preferably, the immersion time is 30 seconds to 6 minutes.

5. The preparation method according to claim 3, characterized in that: The polybasic acid chloride is selected from at least one of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, pyromellitoyl chloride and adipoyl chloride; In the organic solvent solution containing polyacid chloride, the concentration of polyacid chloride is 0.01-5.00wt%; The polymerization time of said polymerization I is 1s to 5min; Preferably, the polymerization I lasts for 5 seconds to 1 minute.

6. The preparation method according to claim 3, characterized in that: The polysulfonyl chloride is selected from at least one of trimesyl chloride, isophthalene dimesyl chloride, terephthalene dimesyl chloride, pyromellitic methanesulfonyl chloride and hexane disulfonyl chloride; In the organic solvent solution containing polysulfonyl chloride, the concentration of polysulfonyl chloride is 0.01-5.00 wt %; The polymerization time of said polymerization II is 1s to 5min; Preferably, the polymerization II takes 5 seconds to 1 minute.

7. The preparation method according to claim 3, characterized in that: The drying temperature is 50-150°C; The drying time is 1 to 20 minutes.

8. The preparation method according to claim 3, characterized in that: The organic solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, n-octane, isopentane, Isopar-G, Isopar-E, Isopar-L or acetone.

9. The preparation method according to claim 3, characterized in that: The aqueous solution containing polybasic organic amines also contains a buffer; The buffer is selected from at least one of trisodium phosphate / hydrochloric acid, triethylamine / camphorsulfonic acid, and sodium hydroxide / hydrochloric acid; The pH of the aqueous solution containing polyvalent organic amines is 7-12.

10. Use of the nanofiltration composite membrane according to any one of claims 1 or 2, characterized in that: Used for mono / polyvalent ion separation, water treatment or lithium extraction from salt lakes.

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