CN114749031B - Positively charged nanofiltration membrane and preparation method and application thereof - Google Patents
Positively charged nanofiltration membrane and preparation method and application thereof Download PDFInfo
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0095—Drying
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- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/027—Nanofiltration
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0081—After-treatment of organic or inorganic membranes
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- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/10—Supported membranes; Membrane supports
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/10—Supported membranes; Membrane supports
- B01D69/105—Support pretreatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/66—Polymers having sulfur in the main chain, with or without nitrogen, oxygen or carbon only
- B01D71/68—Polysulfones; Polyethersulfones
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/50—Control of the membrane preparation process
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/24—Mechanical properties, e.g. strength
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
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Abstract
The invention relates to a positively charged nanofiltration membrane and a preparation method and application thereof. The preparation method of the positively charged nanofiltration membrane comprises the following steps of providing a support membrane; placing a pretreatment solution on the first surface of the support membrane, wherein the pretreatment solution comprises a cationic surfactant and takes fatty acid as a solvent, and the solubility of the fatty acid in water at 20 ℃ is less than or equal to 0.01g/100g of water; and sequentially placing the water-phase solution and the oil-phase solution on the first surface of the support membrane, and performing heat treatment to form a compact layer to obtain the positively-charged nanofiltration membrane, wherein the water-phase solution comprises a positively-charged water-soluble polymer and polyamine, and the oil-phase solution comprises polyacyl chloride. The preparation method enables positively charged groups to be firmly fixed on the surface of the dense layer, so that the prepared positively charged nanofiltration membrane has high surface potential, and can effectively separate Mg in water when being applied to a lithium extraction device 2+ And Li + And has a high water flux.
Description
Technical Field
The invention relates to the technical field of water treatment, in particular to a positively charged nanofiltration membrane as well as a preparation method and application thereof.
Background
The salt lake brine contains Li + 、Na + 、K + 、Ca 2+ 、Mg 2+ Isocation and SO4 2- 、Cl - 、CO 3 2- Anion due to Mg 2+ And Li + Has similar chemical properties, therefore, the effect of extracting lithium by using a precipitation method is poor for the salt lake brine with high magnesium-lithium ratio, and compared with the positive charge nanofiltration membrane, the positive charge nanofiltration membrane can intercept Mg 2+ Reacting Li + Therefore, the lithium resource can be separated from the salt lake brine with high magnesium-lithium ratio.
However, the traditional preparation methods of the positively charged nanofiltration membrane mainly comprise two methods, one method is to form a positively charged substance on the surface of the nanofiltration membrane by a coating method or a grafting method, however, the positively charged substance formed by the coating method is easy to fall off, and the grafting method has the problems of complex manufacturing process, small water flux and difficulty in large-scale production; the other method is to use positively charged monomers to prepare the positively charged nanofiltration membrane by an interfacial polymerization method, however, the positively charged nanofiltration membrane prepared by the preparation method has small water flux and unstable long-term operation performance.
Disclosure of Invention
In view of the above, it is necessary to provide a positively charged nanofiltration membrane, a preparation method and applications thereof; the preparation method enables positively charged groups to be firmly fixed on the surface of the dense layer, so that the prepared positively charged nanofiltration membrane has high surface potential, and can effectively separate Mg in water when being applied to a lithium extraction device 2+ And Li + And has a high water flux.
The invention provides a preparation method of a positively charged nanofiltration membrane, which comprises the following steps:
providing a support film;
placing a pretreatment solution on the first surface of the support membrane, wherein the pretreatment solution comprises a cationic surfactant and takes fatty acid as a solvent, and the solubility of the fatty acid in water at 20 ℃ is less than or equal to 0.01g/100g of water;
and sequentially placing the water phase solution and the oil phase solution on the first surface of the support membrane, and performing heat treatment to form a compact layer to obtain the positively charged nanofiltration membrane, wherein the water phase solution comprises a positively charged water-soluble polymer and polyamine, and the oil phase solution comprises polyacyl chloride.
In one embodiment, the cationic surfactant has a carbon chain length greater than or equal to 4.
In one embodiment, the cationic surfactant is selected from at least one of dodecylammonium bromide, hexadecylammonium bromide, or octadecylammonium bromide.
In one embodiment, the cationic surfactant is present in the pretreatment solution in an amount of 0.05% to 0.3% by mass.
In one embodiment, the fatty acid has a carbon chain length of 6 to 9.
In one embodiment, the fatty acid is selected from at least one of n-hexanoic acid, n-heptanoic acid, n-octanoic acid, or n-nonanoic acid.
In one embodiment, the positively charged water-soluble polymer is at least one selected from cationic polyacrylamide and chitosan quaternary ammonium salt.
In one embodiment, the mass fraction of the positively charged water-soluble polymer in the aqueous solution is 0.1% to 0.3%.
The positively charged nanofiltration membrane is prepared by the preparation method of the positively charged nanofiltration membrane.
An application of the positively charged nanofiltration membrane in a lithium extraction device.
In the preparation method of the positively charged nanofiltration membrane, the solvent fatty acid of the pretreatment solution is difficult to dissolve in water, when the aqueous phase solution is placed on the first surface of the support membrane, a phase interface is formed between the pretreatment solution and the aqueous phase solution, and the cationic surfactant can stably exist in the phase interface and repel the positively charged groups of the positively charged water-soluble polymer in the aqueous phase solution through electrostatic interaction due to the difference of the solubilities of the cationic surfactant in the fatty acid and the water; therefore, when the oil phase solution is placed on the first surface of the support membrane to form a water-oil interface surface, the positively charged group of the positively charged water-soluble polymer moves towards the water-oil interface surface due to electrostatic repulsion of the cationic surfactant, so that the molecular arrangement of the positively charged water-soluble polymer has high orientation, and the positively charged group of the positively charged water-soluble polymer is stably and firmly fixed on the surface of the dense layer as the interfacial polymerization reaction progresses, thereby enabling the positively charged nanofiltration membrane to have high surface potential.
The positively charged nanofiltration membrane obtained by the preparation method has high surface potential, so when the positively charged nanofiltration membrane is applied to a lithium extraction device, mg can be better intercepted 2+ From efficient separation of Mg 2+ And Li + Meanwhile, the positively charged water-soluble polymer can also be used as a water channel to improve the water flux of the positively charged nanofiltration membrane.
Detailed Description
In order that the invention may be more fully understood, reference will now be made to the accompanying examples. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
It should be noted that the terms "first" and "second" used in the embodiments of the present invention are only used for distinguishing similar objects, and do not represent a specific ordering for the objects, and the terms "first" and "second" may be interchanged with a specific order or sequence, where the terms "first" and "second" are allowed. It will be understood that the terms "first," "second," and similar terms are used interchangeably, where appropriate, to enable embodiments of the invention described herein to be practiced in sequences other than those described herein.
The positively charged nanofiltration membrane provided by the invention, and the preparation method and application thereof are further explained below.
The preparation method of the positively charged nanofiltration membrane provided by the invention comprises the following steps:
s10, providing a support film;
s20, placing a pretreatment solution on the first surface of the support membrane, wherein the pretreatment solution comprises a cationic surfactant and takes fatty acid as a solvent; and
and S30, sequentially placing the water phase solution and the oil phase solution on the first surface of the support membrane, and performing heat treatment to form a compact layer to obtain the positively charged nanofiltration membrane, wherein the water phase solution comprises a positively charged water-soluble polymer and polyamine, and the oil phase solution comprises polyacyl chloride.
In step S10, the material of the support membrane may include at least one of polysulfone, polypropylene, or polyacrylonitrile, wherein polysulfone is cheap and easily available, the membrane is simple to manufacture, the mechanical strength is good, the compression resistance is good, the chemical properties are stable, and the support membrane is non-toxic and can resist biological degradation, so the material of the support membrane is preferably polysulfone.
It is understood that the support film has a first surface and a second surface opposite to each other, and in order to increase the strength of the support film, in an embodiment, the second surface of the support film is stacked with a non-woven fabric layer.
In step S20, the solubility of the solvent fatty acid of the pretreatment solution in water is less than or equal to 0.01g/100g of water, that is, the solvent fatty acid of the pretreatment solution is insoluble in water, so that a phase interface is formed between the pretreatment solution and the aqueous phase solution when the aqueous phase solution is placed on the first surface of the support membrane, and the cationic surfactant can stably exist in the phase interface due to the difference in the solubilities of the cationic surfactant in the fatty acid and the water, and repel the positively charged groups of the positively charged water-soluble polymer in the aqueous phase solution through electrostatic interaction; when the oil phase solution is placed on the first surface of the support membrane to form a water-oil interface surface, the positively charged group of the positively charged water-soluble polymer moves towards the direction of the water-oil interface surface due to electrostatic repulsion of the cationic surfactant, so that the molecular arrangement of the positively charged water-soluble polymer has high orientation, and the positively charged water-soluble polymer is stably fixed on the surface of the dense layer along with the progress of the interfacial polymerization reaction, thereby enabling the positively charged nanofiltration membrane to have high surface potential.
In one embodiment, the fatty acid has a carbon chain length of 6 to 9, specifically 6, 7, 8, 9, and in one embodiment, the fatty acid is selected from at least one of n-hexanoic acid, n-heptanoic acid, n-octanoic acid, or n-nonanoic acid.
In order to better dissolve the cationic surfactant in the fatty acid and stay in the phase interface between the pretreatment solution and the aqueous phase solution, in one embodiment, the carbon chain length of the cationic surfactant is greater than or equal to 4, preferably, the carbon chain length of the cationic surfactant is 4 to 20, specifically, the carbon chain length of the cationic surfactant is 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20; in one embodiment, the cationic surfactant is selected from at least one of dodecylammonium bromide, hexadecylammonium bromide, or octadecylammonium bromide.
In order to make the cationic surfactant better repel the positively charged water-soluble polymer and stay more in the phase interface between the pretreatment solution and the aqueous phase solution, in one embodiment, the mass fraction of the cationic surfactant in the pretreatment solution is 0.05% to 0.3%, more preferably 0.05% to 0.25%, and still more preferably 0.15% to 0.25%.
In one embodiment, the step of placing the pretreatment solution on the first surface of the support membrane includes coating the pretreatment solution on the first surface of the support membrane, standing for a period of time to allow the pretreatment solution to fill the pores on the surface layer of the support membrane, pouring off the excess pretreatment solution, and drying the first surface of the support membrane, wherein the pores on the surface layer of the support membrane are still filled with the pretreatment solution.
In step S30, to make the positively charged nanofiltration membrane have a higher surface charge, mg can be trapped better 2+ Reacting Li + By doing so, the aqueous solution has a more suitable viscosity, and in one embodiment, the mass fraction of the positively charged water-soluble polymer in the aqueous solution is 0.1% to 0.3%, more preferably 0.1% to 0.25%, and still more preferably 0.15% to 0.25%.
In one embodiment, the positively charged water-soluble polymer is at least one selected from cationic polyacrylamide and chitosan quaternary ammonium salt.
In one embodiment, the polyamine in the aqueous solution is selected from at least one of aromatic polyamine, aliphatic polyamine or alicyclic polyamine, and in one embodiment, the polyamine is selected from at least one of m-phenylenediamine, piperazine or polyethyleneimine, and the mass fraction of the polyamine is 0.1% to 1.5%, more preferably 0.1% to 1%, and still more preferably 0.3% to 0.7%, based on the total weight of the aqueous solution.
In one embodiment, the polybasic acid chloride is selected from at least one of trimesoyl chloride or adipoyl chloride, and the mass fraction of the polybasic acid chloride is 0.05% to 0.35%, and more preferably 0.10% to 0.20%, based on the total weight of the oil phase solution.
The solvent of the oil phase solution comprises an isoparaffin solvent, which in one embodiment comprises at least one of isododecane or tetradecane.
It can be understood that polyamine and polyacyl chloride in the aqueous phase solution can be crosslinked to generate polyamide molecular chains, and in order to absorb hydrochloric acid generated as a byproduct in the crosslinking reaction of polyamine and polyacyl chloride, the aqueous phase solution further includes an acid scavenger, in an embodiment, the acid scavenger includes triethylamine, and the mass fraction of the acid scavenger is 0.5% -1.5% based on the total weight of the aqueous phase solution.
In one embodiment, the step of sequentially placing the aqueous phase solution and the oil phase solution on the first surface of the support membrane comprises coating the aqueous phase solution on the first surface of the support membrane, standing for a period of time to make the aqueous phase solution fill the pores on the surface layer of the support membrane, then pouring off the excess aqueous phase solution and drying the first surface of the support membrane; and finally, coating the oil phase solution on the first surface of the support membrane, standing for a period of time, and pouring out the redundant oil phase solution.
In the step of heat treatment, the temperature is 50-100 ℃ and the time is 2-10 min, so that molecular chains in the compact layer are more compact.
The invention provides a positively charged nanofiltration membrane, which is prepared by the preparation method of the positively charged nanofiltration membrane and comprises a support membrane and a dense layer which is stacked on the first surface of the support membrane.
In one embodiment, the surface potential of the positively charged nanofiltration membrane is greater than or equal to 80mV volts, more preferably 80mV to 120mV at pH 2.
The positively charged nanofiltration membrane obtained by the preparation method has high surface potential, so when the positively charged nanofiltration membrane is applied to a lithium extraction device, mg can be better intercepted 2+ From efficient separation of Mg 2+ And Li + Meanwhile, the positively charged water-soluble polymer can also be used as a water channel to improve the water flux of the positively charged nanofiltration membrane.
The invention also provides an application of the positively charged nanofiltration membrane in a lithium extraction device.
Specifically, salt lake brine enters from a dense layer of the positively charged nanofiltration membrane, the salt lake brine penetrates through the positively charged nanofiltration membrane under the action of pressure, and Li in the salt lake brine + Can pass through positively charged nanofiltration membrane, mg 2+ Is trapped to realize Mg 2+ And Li + Separation of (4).
The following specific examples further illustrate the positively charged nanofiltration membrane and the preparation method and application thereof.
Example 1
A polysulfone support membrane is provided.
Mixing dodecyl ammonium bromide and n-hexanoic acid to obtain a pretreatment solution, wherein the mass fraction of the dodecyl ammonium bromide in the pretreatment solution is 0.1%; and coating the pretreatment solution on the first surface of the polysulfone support membrane, standing for 60s, pouring out the redundant pretreatment solution, and drying the membrane surface by cold air.
Mixing cationic polyacrylamide (with the molecular weight of 800 ten thousand), piperazine, triethylamine and water to obtain an aqueous phase solution, wherein the mass fraction of the cationic polyacrylamide is 0.2%, the mass fraction of the piperazine is 0.5%, and the mass fraction of the triethylamine is 1%.
And mixing trimesoyl chloride and an isoalkane solvent Isopar L to obtain an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 0.15%.
Coating the water phase solution on a blow-dried polysulfone support membrane, standing for 60 seconds, pouring out the redundant water phase solution, and drying with cold air; and finally, coating the oil phase solution on the first surface of the blow-dried polysulfone support membrane, standing for 30 seconds, pouring out the redundant oil phase solution, and putting the obtained membrane into a forced air drying oven for heat treatment at 80 ℃ for 2 minutes to obtain the positively charged nanofiltration membrane.
Testing water flux of positively charged nanofiltration membrane and Mg 2+ The retention rate of (a) is as follows: the concentrate was a 2000ppm aqueous solution of magnesium chloride at a test pressure of 0.5MPa, a concentrate flow of 1.0GPM, a concentrated water pH of 7.0, and an ambient temperature of 25 deg.C, the results are described in Table 1.
Testing water flux of positively charged nanofiltration membranes and the corresponding Li + The retention rate of (a) is as follows: the concentrate was a 2000ppm aqueous solution of lithium chloride, the test pressure was 0.5MPa, the concentrate flow was 1.0GPM, the pH of the concentrate was 7.0, and the ambient temperatures were all 25 deg.C, the results are described in Table 1.
The surface potential of the positively charged nanofiltration membrane was measured at pH 2 using a Zeta potential tester, and the results are described in table 1.
Example 2
A polysulfone support membrane is provided.
Mixing dodecyl ammonium bromide and n-hexanoic acid to obtain a pretreatment solution, wherein the mass fraction of the dodecyl ammonium bromide in the pretreatment solution is 0.1%; and coating the pretreatment solution on the first surface of the polysulfone support membrane, standing for 60s, pouring out the redundant pretreatment solution, and drying the membrane surface by cold air.
Mixing chitosan quaternary ammonium salt (with the molecular weight of 314), piperazine, triethylamine and water to obtain an aqueous phase solution, wherein the mass fraction of the chitosan quaternary ammonium salt is 0.2%, the mass fraction of the piperazine is 0.5%, and the mass fraction of the triethylamine is 1%.
And mixing trimesoyl chloride and an isoalkane solvent Isopar L to obtain an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 0.15%.
The procedure for testing the positively charged nanofiltration membranes was as in example 1 and the results are described in table 1.
Example 3
Example 3 was carried out with reference to example 1, except that the cationic polyacrylamide mass fraction was 0.1%, the procedure for testing the positively charged nanofiltration membranes was carried out as in example 1, and the results are described in table 1.
Example 4
Example 3 was carried out with reference to example 2, except that the mass fraction of chitosan quaternary ammonium salt was 0.1%, the procedure for testing the positively charged nanofiltration membrane was carried out as in example 2, and the results are described in table 1.
Example 5
Example 5 was carried out with reference to example 1, except that the mass fraction of dodecylammonium bromide was 0.2%, the procedure for testing the positively charged nanofiltration membranes was carried out as in example 1, and the results are described in table 1.
Example 6
Example 6 was carried out with reference to example 2, except that the mass fraction of dodecylammonium bromide was 0.2%, the procedure for testing positively charged nanofiltration membranes was carried out as in example 2, and the results are described in table 1.
Example 7
Example 7 was carried out with reference to example 1, except that the mass fraction of piperazine was 0.1%, the test procedure for positively charged nanofiltration membranes was carried out as in example 1, and the results are described in table 1.
Example 8
Example 8 was carried out with reference to example 2, except that the mass fraction of piperazine was 0.1%, the procedure for testing the positively charged nanofiltration membranes was carried out as in example 2, and the results are described in table 1.
Comparative example 1
Mixing piperazine, triethylamine and water to obtain an aqueous phase solution, wherein the mass fraction of the piperazine is 0.5%, and the mass fraction of the triethylamine is 1%.
Mixing trimesoyl chloride and an isoparaffin solvent Isopar L to obtain an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 0.15%.
Coating the pretreatment solution on the first surface of the polysulfone support membrane, standing for 60s, pouring off the redundant pretreatment solution, and drying the membrane surface by cold air; coating the water phase solution on a blow-dried polysulfone support membrane, standing for 60 seconds, pouring out the redundant water phase solution, and drying with cold air; and finally, coating the oil phase solution on the first surface of the blow-dried polysulfone support membrane, standing for 30 seconds, pouring out the redundant oil phase solution, putting the obtained membrane into a forced air drying oven, and carrying out heat treatment at 80 ℃ for 2 minutes to obtain a nanofiltration membrane, wherein the testing steps of the nanofiltration membrane are carried out according to example 1, and the results are described in table 1.
Comparative example 2
Mixing cationic polyacrylamide (with the molecular weight of 800 ten thousand), piperazine, triethylamine and water to obtain an aqueous phase solution, wherein the mass fraction of the cationic polyacrylamide is 0.2%, the mass fraction of the piperazine is 0.5%, and the mass fraction of the triethylamine is 1%.
Mixing trimesoyl chloride and an isoparaffin solvent Isopar L to obtain an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 0.15%.
Coating the pretreatment solution on the first surface of the polysulfone support membrane, standing for 60s, pouring out the redundant pretreatment solution, and drying the membrane surface by cold air; coating the water phase solution on a blow-dried polysulfone support membrane, standing for 60 seconds, pouring out the redundant water phase solution, and drying with cold air; and finally, coating the oil phase solution on the first surface of the blow-dried polysulfone support membrane, standing for 30 seconds, pouring out the redundant oil phase solution, putting the obtained membrane into a forced air drying oven, and carrying out heat treatment at 80 ℃ for 2 minutes to obtain a nanofiltration membrane, wherein the testing steps of the nanofiltration membrane are carried out according to example 1, and the results are described in table 1.
Comparative example 3
Mixing dodecyl ammonium bromide and n-hexanoic acid to obtain a pretreatment solution, wherein the mass fraction of the dodecyl ammonium bromide in the pretreatment solution is 0.1%.
Mixing piperazine, triethylamine and water to obtain an aqueous phase solution, wherein the mass fraction of the piperazine in the aqueous phase solution is 0.5%, and the mass fraction of the triethylamine in the aqueous phase solution is 1%.
And mixing trimesoyl chloride and an isoalkane solvent Isopar L to obtain an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 0.15%.
Coating the pretreatment solution on the first surface of the polysulfone support membrane, standing for 60s, pouring out the redundant pretreatment solution, and drying the membrane surface by cold air; coating the water phase solution on a blow-dried polysulfone support membrane, standing for 60 seconds, pouring out the redundant water phase solution, and drying with cold air; and finally, coating the oil phase solution on the first surface of the blow-dried polysulfone support membrane, standing for 30 seconds, pouring out the redundant oil phase solution, putting the obtained membrane into a forced air drying oven for heat treatment at 80 ℃ for 2 minutes to obtain the nanofiltration membrane, wherein the testing steps of the nanofiltration membrane are carried out according to example 1, and the results are described in table 1.
Comparative example 4
And mixing the dodecyl ammonium bromide with water to obtain an aqueous solution of the dodecyl ammonium bromide, wherein the mass fraction of the dodecyl ammonium bromide in the aqueous solution of the dodecyl ammonium bromide is 0.1%.
Mixing cationic polyacrylamide (with the molecular weight of 800 ten thousand), piperazine, triethylamine and water to obtain an aqueous phase solution, wherein the mass fraction of the cationic polyacrylamide is 0.2%, the mass fraction of the piperazine is 0.5%, and the mass fraction of the triethylamine is 1%.
And mixing trimesoyl chloride and an isoalkane solvent Isopar L to obtain an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 0.15%.
Coating the pretreatment solution on the first surface of the polysulfone support membrane, standing for 60s, pouring out the redundant pretreatment solution, and drying the membrane surface by cold air; coating the water phase solution on a blow-dried polysulfone support membrane, standing for 60 seconds, pouring out the redundant water phase solution, and drying with cold air; and finally, coating the oil phase solution on the first surface of the blow-dried polysulfone support membrane, standing for 30 seconds, pouring out the redundant oil phase solution, putting the obtained membrane into a forced air drying oven for heat treatment at 80 ℃ for 2 minutes to obtain the nanofiltration membrane, wherein the testing steps of the nanofiltration membrane are carried out according to example 1, and the results are described in table 1.
TABLE 1
In table 1, the membrane flux (F) is calculated from the volume of water passing through the positively charged nanofiltration membrane over a certain time period, and the formula is: f = V/(a × T), where V is the volume of water passing through the positively charged nanofiltration membrane per unit time, a is the effective membrane area, and T is the time.
The retention rate (R) is calculated by the concentration of the concentrated water and the concentration of the permeate, and the calculation formula is as follows: r = (1-C) 1 /C 0 ) X 100%, wherein C 1 Is the concentration of concentrated water, C 0 The concentration of the permeate was used.
In the preparation method of the nanofiltration membrane provided by the comparative example 2, the pretreatment solution is not coated on the first surface of the polysulfone support membrane, so that the positively charged water-soluble polymer cation polyacrylamide in the aqueous phase solution cannot move towards the water-oil interface, i.e. the molecular arrangement does not have orientation, and the prepared nanofiltration membrane has low surface potential and is Mg-resistant 2+ The trapping capacity is weak.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only show several embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (7)
1. A preparation method of a positively charged nanofiltration membrane is characterized by comprising the following steps:
providing a support film;
placing a pretreatment solution on the first surface of the support membrane, wherein the pretreatment solution comprises a cationic surfactant and takes fatty acid as a solvent, the solubility of the fatty acid in water at 20 ℃ is less than or equal to 0.01g/100g of water, and the mass fraction of the cationic surfactant in the pretreatment solution is 0.05-0.3%;
sequentially placing a water phase solution and an oil phase solution on the first surface of the support membrane, and performing heat treatment to form a compact layer to obtain the positively charged nanofiltration membrane, wherein the water phase solution comprises a positively charged water-soluble polymer and polyamine, the positively charged water-soluble polymer is selected from at least one of cationic polyacrylamide or chitosan quaternary ammonium salt, the mass fraction of the positively charged water-soluble polymer in the water phase solution is 0.1-0.3%, and the oil phase solution comprises polyacyl chloride.
2. The method of claim 1, wherein the cationic surfactant has a carbon chain length of 4 or more.
3. The method of claim 2, wherein the cationic surfactant is at least one selected from the group consisting of dodecylammonium bromide, hexadecylammonium bromide and octadecylammonium bromide.
4. The method of any one of claims 1-3, wherein the fatty acid has a carbon chain length of 6-9.
5. The method for preparing a positively-charged nanofiltration membrane according to claim 4, wherein the fatty acid is at least one selected from n-hexanoic acid, n-heptanoic acid, n-octanoic acid and n-nonanoic acid.
6. A positively-charged nanofiltration membrane, wherein the positively-charged nanofiltration membrane is prepared by the preparation method of the positively-charged nanofiltration membrane according to any one of claims 1 to 5.
7. Use of a positively charged nanofiltration membrane according to claim 6 in a lithium extraction apparatus.
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