CN115845640A - Positively charged composite nanofiltration membrane as well as preparation method and application thereof - Google Patents
Positively charged composite nanofiltration membrane as well as preparation method and application thereof Download PDFInfo
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- 239000012528 membrane Substances 0.000 title claims abstract description 135
- 238000001728 nano-filtration Methods 0.000 title claims abstract description 84
- 239000002131 composite material Substances 0.000 title claims abstract description 58
- 238000002360 preparation method Methods 0.000 title claims abstract description 24
- 229920001661 Chitosan Polymers 0.000 claims abstract description 41
- 150000003242 quaternary ammonium salts Chemical class 0.000 claims abstract description 41
- 239000004952 Polyamide Substances 0.000 claims abstract description 39
- 229920002647 polyamide Polymers 0.000 claims abstract description 39
- 150000001768 cations Chemical class 0.000 claims abstract description 37
- 239000002346 layers by function Substances 0.000 claims abstract description 37
- GCICAPWZNUIIDV-UHFFFAOYSA-N lithium magnesium Chemical compound [Li].[Mg] GCICAPWZNUIIDV-UHFFFAOYSA-N 0.000 claims abstract description 29
- 238000000926 separation method Methods 0.000 claims abstract description 29
- 229920000768 polyamine Polymers 0.000 claims abstract description 28
- 238000006243 chemical reaction Methods 0.000 claims abstract description 22
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- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims abstract description 15
- 238000013329 compounding Methods 0.000 claims abstract description 14
- 239000000463 material Substances 0.000 claims abstract description 8
- 239000000243 solution Substances 0.000 claims description 59
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- 239000007864 aqueous solution Substances 0.000 claims description 32
- 239000010410 layer Substances 0.000 claims description 31
- 229920002873 Polyethylenimine Polymers 0.000 claims description 28
- 238000000034 method Methods 0.000 claims description 22
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 22
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 claims description 16
- 230000004048 modification Effects 0.000 claims description 14
- 238000012986 modification Methods 0.000 claims description 14
- 238000002791 soaking Methods 0.000 claims description 13
- NGNBDVOYPDDBFK-UHFFFAOYSA-N 2-[2,4-di(pentan-2-yl)phenoxy]acetyl chloride Chemical compound CCCC(C)C1=CC=C(OCC(Cl)=O)C(C(C)CCC)=C1 NGNBDVOYPDDBFK-UHFFFAOYSA-N 0.000 claims description 10
- 239000003960 organic solvent Substances 0.000 claims description 10
- 150000007519 polyprotic acids Polymers 0.000 claims description 10
- UWCPYKQBIPYOLX-UHFFFAOYSA-N benzene-1,3,5-tricarbonyl chloride Chemical compound ClC(=O)C1=CC(C(Cl)=O)=CC(C(Cl)=O)=C1 UWCPYKQBIPYOLX-UHFFFAOYSA-N 0.000 claims description 8
- 238000007598 dipping method Methods 0.000 claims description 7
- SNRUBQQJIBEYMU-UHFFFAOYSA-N dodecane Chemical compound CCCCCCCCCCCC SNRUBQQJIBEYMU-UHFFFAOYSA-N 0.000 claims description 6
- 229920002492 poly(sulfone) Polymers 0.000 claims description 4
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 claims description 3
- FDQSRULYDNDXQB-UHFFFAOYSA-N benzene-1,3-dicarbonyl chloride Chemical compound ClC(=O)C1=CC=CC(C(Cl)=O)=C1 FDQSRULYDNDXQB-UHFFFAOYSA-N 0.000 claims description 3
- LXEJRKJRKIFVNY-UHFFFAOYSA-N terephthaloyl chloride Chemical compound ClC(=O)C1=CC=C(C(Cl)=O)C=C1 LXEJRKJRKIFVNY-UHFFFAOYSA-N 0.000 claims description 3
- 239000004695 Polyether sulfone Substances 0.000 claims description 2
- 229920006393 polyether sulfone Polymers 0.000 claims description 2
- 229910052744 lithium Inorganic materials 0.000 abstract description 24
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 21
- 239000012267 brine Substances 0.000 abstract description 18
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 abstract description 18
- 239000008346 aqueous phase Substances 0.000 abstract description 14
- 238000000605 extraction Methods 0.000 abstract description 9
- 238000010889 donnan-equilibrium Methods 0.000 abstract description 6
- 239000012074 organic phase Substances 0.000 abstract description 6
- 230000007613 environmental effect Effects 0.000 abstract description 3
- 150000003839 salts Chemical class 0.000 abstract description 2
- 210000004379 membrane Anatomy 0.000 description 54
- 239000012071 phase Substances 0.000 description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 23
- 230000000052 comparative effect Effects 0.000 description 17
- 239000011777 magnesium Substances 0.000 description 15
- 229910052749 magnesium Inorganic materials 0.000 description 11
- 230000000694 effects Effects 0.000 description 9
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 8
- 238000005096 rolling process Methods 0.000 description 6
- 238000002474 experimental method Methods 0.000 description 5
- 230000014759 maintenance of location Effects 0.000 description 5
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- 238000003756 stirring Methods 0.000 description 4
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 3
- ZMANZCXQSJIPKH-UHFFFAOYSA-N Triethylamine Chemical compound CCN(CC)CC ZMANZCXQSJIPKH-UHFFFAOYSA-N 0.000 description 3
- 150000001263 acyl chlorides Chemical class 0.000 description 3
- 210000002469 basement membrane Anatomy 0.000 description 3
- 239000003093 cationic surfactant Substances 0.000 description 3
- 230000004907 flux Effects 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 229910001425 magnesium ion Inorganic materials 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 2
- DBMJMQXJHONAFJ-UHFFFAOYSA-M Sodium laurylsulphate Chemical compound [Na+].CCCCCCCCCCCCOS([O-])(=O)=O DBMJMQXJHONAFJ-UHFFFAOYSA-M 0.000 description 2
- 150000001412 amines Chemical class 0.000 description 2
- 238000007664 blowing Methods 0.000 description 2
- 150000001793 charged compounds Chemical class 0.000 description 2
- 230000005611 electricity Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910001416 lithium ion Inorganic materials 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- 229940083575 sodium dodecyl sulfate Drugs 0.000 description 2
- 235000019333 sodium laurylsulphate Nutrition 0.000 description 2
- 229920012266 Poly(ether sulfone) PES Polymers 0.000 description 1
- 125000003368 amide group Chemical group 0.000 description 1
- 125000003277 amino group Chemical group 0.000 description 1
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- GVGUFUZHNYFZLC-UHFFFAOYSA-N dodecyl benzenesulfonate;sodium Chemical compound [Na].CCCCCCCCCCCCOS(=O)(=O)C1=CC=CC=C1 GVGUFUZHNYFZLC-UHFFFAOYSA-N 0.000 description 1
- 238000000909 electrodialysis Methods 0.000 description 1
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- 238000006703 hydration reaction Methods 0.000 description 1
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- 230000007935 neutral effect Effects 0.000 description 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
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- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
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- 229940086542 triethylamine Drugs 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
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Abstract
The invention belongs to the technical field of membrane material preparation and membrane separation, and particularly relates to a positively charged composite nanofiltration membrane as well as a preparation method and application thereof. The invention provides a preparation method of a positively charged composite nanofiltration membrane, which comprises the steps of firstly carrying out interfacial polymerization reaction on polyamine aqueous phase and polyacyl chloride organic phase to generate a polyamide functional layer, then adjusting the charge property of the polyamide functional layer by using chitosan quaternary ammonium salt, and carrying out thermal compounding to obtain the positively charged composite nanofiltration membrane. The invention improves the positive charge intensity of the nanofiltration membrane, strengthens the Donnan effect of the composite nanofiltration membrane, and improves the rejection rate of the nanofiltration membrane on multivalent cations. The positively charged composite nanofiltration membrane prepared by the invention can effectively improve the magnesium-lithium separation performance of a high magnesium-lithium ratio system in brine, has the advantages of simple operation and environmental protection, and has good industrial application prospect in the aspect of lithium extraction in salt lakes.
Description
Technical Field
The invention belongs to the technical field of membrane material preparation and membrane separation, and particularly relates to a positively charged composite nanofiltration membrane as well as a preparation method and application thereof.
Background
Lithium and compounds thereof are important strategic resources for national economy and national defense construction, and the development of the salt lake lithium extraction technology has important significance for national economy and national development.
The technology for extracting lithium from salt lake mainly comprises solvent extraction method, adsorption method, electrochemical de-intercalation method, selective electrodialysis method, membrane separation method and the like. Compared with other methods, the membrane separation method has the advantages of low cost, simple process, easy operation, environmental protection and wide attention. The nanofiltration membrane is one of the most important methods in the membrane separation technology, is a separation membrane with a nano-scale aperture and charges on the surface, has higher rejection rate on bivalent and higher high-valence ions and higher transmittance on monovalent ions based on the synergistic action of multiple mechanisms such as Donnan effect, aperture sieving, dielectric effect and the like, and further realizes the separation of ions with different valence states. However, because magnesium and lithium in salt lake brine have very similar chemical properties and hydration radius, the higher the magnesium-lithium ratio in the brine is, the greater the difficulty in extracting lithium is.
At present, a common nanofiltration membrane is synthesized by an amine monomer and an acyl chloride monomer by adopting an interfacial polymerization method, the surface charge of the prepared membrane material is generally electronegative, the magnesium-lithium separation performance is low, and the membrane material cannot have both high permeability and high selectivity. Based on the separation principle of the nanofiltration membrane, the charge property on the surface of the nanofiltration membrane is considered to seriously influence the Donnan effect and the dielectric effect of the nanofiltration membrane, and the improvement of the positive charge property on the surface of the membrane can improve the separation effect of magnesium and lithium, and is also one of effective ways for realizing the separation of magnesium and lithium. In recent years, researchers at home and abroad adjust the surface charge property of the nanofiltration membrane by introducing a cationic surfactant into a traditional negatively charged nanofiltration membrane, and improve the rejection performance of the nanofiltration membrane on multivalent cations by utilizing the Donnan effect, wherein the cationic surfactant is mainly a nitrogenous organic amine derivative. For example, chinese patent CN113230888A discloses a method for preparing a positively charged nanofiltration membrane, which uses polyethyleneimine as a cationic surfactant, and amine groups in the polyethyleneimine have weak charge in a neutral solution, and have poor separation effect on multivalent cations and small cationic molecules. Therefore, it is required to develop a positively charged composite nanofiltration membrane having a good separation effect on multivalent cations and monovalent cations.
Disclosure of Invention
In view of the above, the present invention aims to provide a positively charged composite nanofiltration membrane, and a preparation method and an application thereof. According to the invention, the charge property of the polyamide functional layer is adjusted by adopting the chitosan quaternary ammonium salt, the chitosan quaternary ammonium salt can improve the positive charge strength, strengthen the Donnan effect of the composite nanofiltration membrane, improve the interception performance of the positive charge composite nanofiltration membrane on cations, and further improve the separation efficiency of multivalent cations and monovalent cations.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of a positively charged composite nanofiltration membrane, which comprises the following steps:
sequentially dipping a base membrane into polyamine aqueous solution and polyacyl chloride organic solution, and carrying out interfacial polymerization reaction to obtain a base membrane containing a polyamide functional layer;
soaking the base film containing the polyamide functional layer into a chitosan quaternary ammonium salt aqueous solution for charge modification to obtain a base film containing a polyamide functional layer and a cation modified layer;
and thermally compounding the base membrane containing the polyamide functional layer and the cation modified layer to obtain the positively charged composite nanofiltration membrane.
Preferably, the polyamine aqueous solution comprises polyethyleneimine and piperazine, and the mass ratio of the polyethyleneimine to the piperazine is 1-5.
Preferably, the polybasic acid chloride in the polybasic acid chloride organic solution comprises one or more of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride.
Preferably, the organic solvent in the organic solution of polyacyl chloride comprises one or more of n-hexane, dodecane and cyclohexane.
Preferably, the material of the base film comprises one or more of polyacrylonitrile, polyethersulfone and polysulfone.
Preferably, the concentration of the chitosan quaternary ammonium salt in the chitosan quaternary ammonium salt water solution is 0.1-0.7 wt%.
Preferably, the temperature of the thermal recombination is 50-100 ℃, and the time is 300-1500 s.
Preferably, the base film is immersed in the aqueous polyamine solution for 5 to 25min.
The invention also provides the positive charge composite nanofiltration membrane obtained by the preparation method in the technical scheme, which comprises a base membrane, a polyamide functional layer and a cation modified layer which are sequentially stacked, wherein the polyamide functional layer is prepared by performing interfacial polymerization reaction on polyamine aqueous solution and polyacyl chloride organic solution, and the cation modified layer is provided with positive charge groups by chitosan quaternary ammonium salt.
The invention also provides application of the positively charged composite nanofiltration membrane in magnesium-lithium separation.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a preparation method of a positively charged composite nanofiltration membrane, which comprises the following steps: sequentially dipping a base membrane into polyamine aqueous solution and polyacyl chloride organic solution, and carrying out interfacial polymerization reaction to obtain a base membrane containing a polyamide functional layer; dipping the base film containing the polyamide functional layer into a chitosan quaternary ammonium salt aqueous solution for charge modification to obtain a base film containing the polyamide functional layer and a cation modified layer; and thermally compounding the base membrane containing the polyamide functional layer and the cation modified layer to obtain the positively charged composite nanofiltration membrane.
According to the invention, the charge property of the polyamide functional layer is adjusted by adopting the chitosan quaternary ammonium salt, the chitosan quaternary ammonium salt has high charge density and good film forming property, the positive charge strength of the composite nanofiltration membrane can be improved, the Donnan effect of the composite nanofiltration membrane is enhanced, the interception performance of the positive charge composite nanofiltration membrane on multivalent cations is improved, and the separation efficiency of the multivalent cations and monovalent cations is further improved.
Furthermore, the polyamide functional layer is prepared by carrying out interfacial polymerization reaction on polyamine aqueous solution and polybasic acyl chloride organic solution, wherein the polyamine aqueous solution contains polyethyleneimine and piperazine, and the mixture of the polyethyleneimine and the piperazine is used as an interfacial polymerization aqueous phase reactant, so that the interception capability of the positively-charged composite nanofiltration membrane on monovalent cations can be reduced, the separation efficiency of the polyvalent cations and the monovalent cations is further improved, and the separation rate of magnesium and lithium is improved.
The positively charged composite nanofiltration membrane provided by the technical scheme can effectively improve the magnesium-lithium separation performance of a high magnesium-lithium ratio system in brine, has the advantages of simplicity in operation, greenness and environmental friendliness, and has a good industrial application prospect in the aspect of lithium extraction in salt lakes.
The invention also provides application of the positively charged composite nanofiltration membrane, wherein the positively charged composite nanofiltration membrane is used for magnesium-lithium separation of salt lake brine, and the water flux is 6.41Lm -2 h -1 bar -1 To Mg 2+ The rejection rate of the catalyst is up to 90 percent, and Li + Has a retention rate as low as 10%, namely has moderate water flux and excellent Mg 2+ Rejection and lower Li + The retention rate. The data of the examples and the comparative examples show that the positively charged composite nanofiltration membrane has higher multivalent cation rejection rate and better magnesium-lithium separation effect in the process of extracting lithium from a salt lake.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a graph of the results of magnesium lithium rejection for example 1;
FIG. 2 is a graph of the results of magnesium lithium rejection for example 2;
FIG. 3 is a graph of the results of magnesium lithium rejection for example 3;
FIG. 4 is a graph showing the results of the magnesium-lithium rejection rate of comparative example 1;
fig. 5 is a graph showing the results of magnesium lithium rejection of comparative example 2.
Detailed Description
The invention provides a preparation method of a positively charged composite nanofiltration membrane, which comprises the following steps:
sequentially dipping a base membrane into polyamine aqueous solution and polyacyl chloride organic solution, and carrying out interfacial polymerization reaction to obtain a base membrane containing a polyamide functional layer;
dipping the base film containing the polyamide functional layer into a chitosan quaternary ammonium salt aqueous solution for charge modification to obtain a base film containing the polyamide functional layer and a cation modified layer;
and thermally compounding the base membrane containing the polyamide functional layer and the cation modified layer to obtain the positively charged composite nanofiltration membrane.
In the present invention, materials and equipment used are commercially available in the art unless otherwise specified.
The invention sequentially immerses the basement membrane in polyamine aqueous solution and polyacyl chloride organic solution, and then carries out interfacial polymerization reaction to obtain the basement membrane containing the polyamide functional layer.
In the present invention, the material of the base film preferably includes one or more of Polyacrylonitrile (PAN), polyethersulfone (PES), and Polysulfone (PSF).
In the present invention, the polyamine aqueous solution preferably includes Polyethyleneimine (PEI) and piperazine (PIP) in a mass ratio of 1 to 5, more preferably 1.
In the present invention, the mass concentration of Polyethyleneimine (PEI) in the polyamine aqueous solution is preferably 0.2 to 1.0wt%, more preferably 0.6 to 0.8wt%; the mass concentration of piperazine (PIP) in the polyamine aqueous solution is preferably 0.1 to 0.5wt%, more preferably 0.2wt%.
In the present invention, the weight average molecular weight of the Polyethyleneimine (PEI) is preferably 600 to 10000.
In the present invention, the polyamine aqueous solution preferably further comprises an aqueous phase additive, the aqueous phase additive preferably comprises one or more of triethylamine, sodium dodecylbenzenesulfonate, sodium carbonate and sodium dodecylsulfate, the concentration of the aqueous phase additive in the polyamine aqueous solution is preferably 0.1 to 1.5wt%, and more preferably 0.3wt%, and the aqueous phase additive can promote an aqueous phase solvent to wet membrane pores, and shorten the aqueous phase soaking time.
In the present invention, the base film is immersed in the aqueous polyamine solution for a period of time preferably 300 to 1500 seconds (5 to 25 min), more preferably 5, 10, 15, 20 or 25min, in order to wet the surface of the base film with the aqueous polyamine solution. The invention has no special requirement on the volume of the polyamine aqueous solution during the impregnation, and the base film can be immersed.
In the invention, after the base film is immersed in the polyamine aqueous solution, the method preferably further comprises removing the excessive polyamine aqueous solution, and the method has no special requirement on the removing mode, such as pouring out or rolling the base film by using a rubber roller.
In the present invention, the polybasic acid chloride in the organic solution of polybasic acid chloride preferably comprises one or more of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride.
In the present invention, the mass concentration of the polybasic acid chloride in the polybasic acid chloride organic solution is preferably 0.05 to 0.25wt%, more preferably 0.15wt%.
In the present invention, the organic solvent in the organic solution of polyacyl chloride preferably comprises one or more of n-hexane, dodecane and cyclohexane, and the organic solvent is preferably an organic solvent immiscible with water.
In the present invention, the time for immersing in the organic solution of polybasic acid chloride is preferably 10 to 300s, and more preferably 120s, and the volume of the organic solution of polybasic acid chloride at the time of the immersion is preferably the same as the volume of the aqueous solution of polyamine.
In the invention, in the process of the interfacial polymerization reaction, the polyacyl chloride in the polyacyl chloride organic solution and the polyamine in the polyamine water solution are subjected to the interfacial polymerization reaction to form a polyamide layer on the surface of the basement membrane; the interfacial polymerization reaction preferably further comprises removing excess polyacyl chloride organic solution.
After the base film containing the polyamide functional layer is obtained, the base film containing the polyamide functional layer is soaked in a chitosan quaternary ammonium salt water solution for charge modification, and the base film containing the polyamide functional layer and a cation modified layer is obtained.
In the present invention, the concentration of the quaternary ammonium salt of chitosan in the aqueous solution of the quaternary ammonium salt of chitosan is preferably 0.1 to 0.7wt%, more preferably 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7wt%.
The time for soaking the base film containing the polyamide functional layer in the chitosan quaternary ammonium salt water solution is preferably 10-600 s, and more preferably 120-300 s; after the dipping, the method preferably also comprises the step of removing redundant chitosan quaternary ammonium salt aqueous solution; in the charge modification process, the amido of the chitosan quaternary ammonium salt reacts with the unreacted acyl chloride group of the interfacial polymerization.
After the base membrane containing the polyamide functional layer and the cation modified layer is obtained, the base membrane containing the polyamide functional layer and the cation modified layer is subjected to thermal compounding to obtain the positively charged composite nanofiltration membrane.
In the present invention, the temperature of the thermal compounding is preferably 50 to 100 ℃, more preferably 50, 60, 70, 80 or 90 ℃; the time is preferably 300-1500 s, more preferably 1200s, the shrinkage degrees of the base film supporting layer and the polyamide functional layer in the thermal compounding process are different, the roughness degree of the film surface can be increased, and the film flux is improved; the shrinkage of the support layer and the polyamide functional layer reduces the membrane pores and increases the rejection rate.
According to the invention, the blended water-phase interfacial polymerization is adopted to cooperate with the surface charge modification of the chitosan quaternary ammonium salt to prepare the positive charge composite nanofiltration membrane, so that the magnesium-lithium separation performance of the positive charge composite nanofiltration membrane on a high magnesium-lithium ratio system in brine can be effectively improved.
The invention also provides the positively charged composite nanofiltration membrane obtained by the preparation method in the technical scheme, which comprises a base membrane, a polyamide functional layer and a cation modified layer which are sequentially stacked, wherein the polyamide functional layer is prepared by carrying out interfacial polymerization reaction on polyamine aqueous solution and polyacyl chloride organic solution, and the cation modified layer is provided with positive charge groups by chitosan quaternary ammonium salt.
In the invention, the positive electricity group of the cation modification layer is provided by the chitosan quaternary ammonium salt, and the chitosan quaternary ammonium salt can show good charge and positive electricity performance in a solution with a full pH range.
The invention also provides application of the positively charged composite nanofiltration membrane in magnesium-lithium separation.
In the present invention, the solution for separating magnesium and lithium is preferably a high magnesium-lithium ratio (10-70).
In the present invention, the parameters for magnesium-lithium separation preferably include: the operation pressure is 5bar, the nanofiltration time is 60min, and the flow is 2.5L/min.
For further illustration of the present invention, the following detailed description of the positively charged composite nanofiltration membrane and the preparation method and application thereof are provided with reference to the drawings and examples, but they should not be construed as limiting the scope of the present invention.
Example 1
The present embodiment is a preparation method of a positively charged composite nanofiltration membrane sample 1, wherein a positively charged nanofiltration selection layer (cation modification layer) in the positively charged composite nanofiltration membrane sample 1 is provided with a positive charged group by chitosan quaternary ammonium salt.
Preparing a PEI/PIP mixed aqueous phase solution, wherein the mass concentration of PEI is 0.8wt%, the mass concentration of PIP is 0.2wt%, the mass concentration ratio of PEI to PIP is 4;
preparing 0.15wt% of trimesoyl chloride organic phase solution, wherein the organic solvent is n-hexane and is used as a second phase;
respectively preparing 0.1 wt% chitosan quaternary ammonium salt water solution, 0.2wt% chitosan quaternary ammonium salt water solution, 0.3wt% chitosan quaternary ammonium salt water solution, 0.4 wt% chitosan quaternary ammonium salt water solution, 0.5wt% chitosan quaternary ammonium salt water solution, stirring until the chitosan quaternary ammonium salt water solution is completely dissolved to be used as a third phase;
immersing a polyacrylonitrile base membrane into the first phase, immersing the surface of the base membrane for 600 seconds, taking out, rolling the polyacrylonitrile base membrane by using a rubber roller, removing redundant solution, pouring an isometric second phase for soaking for 120 seconds, pouring an isometric third phase for soaking for 120 seconds after the interfacial polymerization reaction is finished, putting the polyacrylonitrile base membrane into a 50 ℃ blast oven for thermal compounding for 1200 seconds after the reaction is finished, taking out to obtain a positively charged composite nanofiltration membrane sample 1, and storing the positively charged composite nanofiltration membrane sample in pure water for later use.
A simulated brine lithium extraction experiment is carried out under the operating conditions of 5bar of operating pressure, 60min of nanofiltration time and 2.5L/min of flow, the table 1 is a simulated brine composition table, and the magnesium-lithium retention rate result of the example 1 is shown in the figure 1.
TABLE 1 simulated brine ingredient table
| Composition (I) | Li + | Na + | Mg 2+ | Ca 2+ | Cl - | SO 4 2- | K + |
| Content g/L | 0.21 | 102.3 | 13.5 | 0.3 | 188.1 | 24 | 8.45 |
Example 2
The present embodiment is a preparation method of a positive charge composite nanofiltration membrane sample 2, wherein a positive charge nanofiltration selection layer (cation modification layer) in the positive charge composite nanofiltration membrane sample 2 is provided with positive charge groups by chitosan quaternary ammonium salt.
Preparing a PEI/PIP mixed aqueous phase solution, wherein the mass concentration of PEI is 0.8wt%, the mass concentration of PIP is 0.2wt%, the mass concentration ratio of PEI to PIP is 4;
preparing 0.15wt% of trimesoyl chloride organic phase solution, wherein the organic solvent is n-hexane and is used as a second phase;
preparing 0.3wt% of chitosan quaternary ammonium salt water solution, and stirring until the chitosan quaternary ammonium salt water solution is completely dissolved to be used as a third phase;
immersing a polyacrylonitrile base membrane into the first phase, immersing the surface of the base membrane for 600 seconds, taking out, rolling a polyacrylonitrile support membrane by using a rubber roller, removing redundant solution, pouring an isometric second phase for soaking for 120 seconds, pouring an isometric third phase for soaking for 120 seconds after the reaction is finished, putting the polyacrylonitrile base membrane into a blowing oven at 50 ℃, 60 ℃, 70 ℃, 80 ℃ and 90 ℃ respectively for thermal compounding for 1200 seconds after the reaction is finished, taking out, obtaining a positively charged composite nanofiltration membrane sample 2, and storing the positively charged composite nanofiltration membrane sample in pure water for later use.
A simulated brine lithium extraction experiment is carried out under the operating conditions of 5bar of operating pressure, 60min of nanofiltration time and 2.5L/min of flow, the simulated brine composition table is shown in Table 1, and the magnesium-lithium rejection rate of example 2 is shown in FIG. 2.
Example 3
The embodiment is a preparation method of a positively charged composite nanofiltration membrane sample 3, wherein a positively charged nanofiltration selection layer (cation modification layer) in the positively charged composite nanofiltration membrane sample 3 is provided with a positive electric group by chitosan quaternary ammonium salt.
Preparing a PEI/PIP mixed aqueous phase solution, wherein the mass concentration of PEI is 0.8wt%, the mass concentration of PIP is 0.2wt%, the mass concentration ratio of PEI to PIP is 4;
preparing 0.15wt% of trimesoyl chloride organic phase solution, wherein the organic solvent is n-hexane and is used as a second phase;
preparing 0.3wt% of chitosan quaternary ammonium salt water solution, and stirring until the chitosan quaternary ammonium salt water solution is completely dissolved to be used as a third phase;
immersing a polyacrylonitrile base membrane into the first phase, immersing the surface of the base membrane, respectively contacting the polyacrylonitrile base membrane with the surface for 5min, 10min, 15 min, 20 min and 25min (300-1500 sec), taking out, rolling the polyacrylonitrile base membrane by using a rubber roller, removing redundant solution, pouring an isovolumetric second phase for soaking for 120 sec, pouring an isovolumetric third phase solution on the surface of the base membrane for soaking for 600 sec after the reaction is finished, putting the base membrane into a 80 ℃ blast oven for thermal compounding for 1200 sec after the reaction is finished, taking out to obtain a positively charged composite nanofiltration membrane sample 3, and storing the positively charged composite nanofiltration membrane sample in pure water for later use.
The simulated brine lithium extraction experiment is carried out under the operation conditions of 5bar of operation pressure, 60min of nanofiltration time and 2.5L/min of flow, the component table of the simulated brine is shown in table 1, and the magnesium-lithium rejection rate of example 3 is shown in fig. 3.
Comparative example 1
The comparative example is the preparation of a negative charge composite nanofiltration membrane comparative sample 1, wherein a negative charge nanofiltration selection layer in the negative charge composite nanofiltration membrane comparative sample 1 uses piperazine (PIP) as a raw material to provide negative charge groups.
Respectively preparing 0.1 wt% PIP aqueous solution, 0.2wt% PIP aqueous solution, 0.3wt% PIP aqueous solution, 0.4 wt% PIP aqueous solution, adding 0.3wt% sodium dodecyl sulfate, and stirring until completely dissolving to obtain a first phase;
preparing 0.15wt% of trimesoyl chloride organic phase solution, wherein the organic solvent is n-hexane and is used as a second phase;
immersing the polyacrylonitrile-based membrane into the first phase to immerse the surface of the base membrane, allowing the polyacrylonitrile-based membrane to contact the surface for 600 seconds, taking out, then rolling the polyacrylonitrile-based membrane by using a rubber roller, removing redundant solution, pouring the polyacrylonitrile-based membrane into a second phase with the same volume for soaking for 120 seconds, after the reaction is finished, putting the polyacrylonitrile-based membrane into a forced air oven with the temperature of 80 ℃, performing thermal compounding for 10 minutes, taking out to obtain a negatively charged compound nanofiltration membrane sample 1, and storing the negatively charged compound nanofiltration membrane sample in pure water for later use.
The simulated brine lithium extraction experiment is carried out under the operation conditions of 5bar of operation pressure, 60min of nanofiltration time and 2.5L/min of flow, the component table of the simulated brine is shown in table 1, and the magnesium-lithium rejection rate of comparative example 1 is shown in fig. 4.
Comparative example 2
The comparative example is the preparation of a positively charged composite nanofiltration membrane comparative sample 2, wherein a positively charged nanofiltration selection layer in the positively charged composite nanofiltration membrane comparative sample 2 is provided with a positive charged group by a PEI/PIP mixed water phase.
Preparing a PEI/PIP mixed aqueous phase solution, wherein the mass concentration of PEI is 0.2, 0.4, 0.6, 0.8 and 1.0wt%, the mass concentration of PIP is 0.2wt%, and the mass concentration ratio of PEI to PIP is 1;
preparing 0.15wt% of trimesoyl chloride organic phase solution, wherein the organic solvent is n-hexane and is used as a second phase;
immersing the polyacrylonitrile base membrane into the first phase, immersing the surface of the base membrane for 600 seconds, taking out, rolling the polyacrylonitrile base membrane by using a rubber roller, removing redundant solution, pouring the polyacrylonitrile base membrane into a second phase with the same volume, immersing for 120 seconds, placing the polyacrylonitrile base membrane into a blowing oven with the temperature of 80 ℃ after the reaction is finished, thermally compounding for 10 minutes, taking out to obtain a positively charged composite nanofiltration membrane comparison sample 2, and storing the positively charged composite nanofiltration membrane comparison sample in pure water for later use.
The simulated brine lithium extraction experiment is carried out under the operation conditions of 5bar of operation pressure, 60min of nanofiltration time and 2.5L/min of flow, the simulated brine composition table is shown in table 1, and the magnesium-lithium rejection rate result of the comparative example 2 is shown in fig. 5.
FIG. 4 is a relationship between the nanofiltration membrane with negative charge and the magnesium-lithium rejection rate of comparative example 1, and it can be seen from FIG. 4 that the magnesium-lithium rejection rate has a consistent trend, and the highest magnesium rejection rate is only 40%, the lithium rejection rate is higher, and the magnesium-lithium separation effect is not good; fig. 5 is a relationship between the positively charged composite nanofiltration membrane of comparative example 2 and the rejection of magnesium and lithium, and it can be seen from fig. 5 that the rejection of magnesium ions increases with the increase of PEI concentration, and the rejection of lithium ions shows a decreasing trend, indicating that the positively charged nanofiltration membrane shows excellent magnesium and lithium separation performance.
FIG. 1 shows the influence of mass concentration of chitosan quaternary ammonium salt on magnesium-lithium rejection rate in example 1, with the increase of chitosan quaternary ammonium salt, the positive charge performance of the membrane surface is improved, the rejection rate of magnesium ions is further improved compared with comparative example 2, and the rejection rate of lithium ions is basically kept unchanged, which indicates that the improvement of the positive charge performance of the membrane surface by chitosan quaternary ammonium salt can improve the rejection rate of magnesium ions; FIG. 2 is a graph showing the effect of heat treatment temperature on the rejection rate of Mg and Li in example 2, wherein the temperature higher than 80 ℃ causes the collapse of the membrane pore channel to be unfavorable for Mg and Li separation; FIG. 3 is a graph showing the effect of soaking time of the aqueous phase (first phase) on the retention rate of Mg and Li in example 3, wherein the longer the soaking time, the better the wettability of the aqueous phase solution to the membrane, and the wetting of the membrane facilitates the interfacial polymerization reaction, resulting in a polyamide layer with defects on the surface.
According to the embodiment and the comparative example data, the positively charged composite nanofiltration membrane has high selectivity and high Mg content 2+ The retention rate is high, the preparation method is simple to operate, and the method can be applied to the field of lithium extraction from salt lake brine.
Although the present invention has been described in detail with reference to the above embodiments, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive work according to the embodiments of the present invention, and the embodiments are within the scope of the present invention.
Claims (10)
1. A preparation method of a positively charged composite nanofiltration membrane is characterized by comprising the following steps:
sequentially dipping a base membrane into polyamine aqueous solution and polyacyl chloride organic solution, and carrying out interfacial polymerization reaction to obtain a base membrane containing a polyamide functional layer;
soaking the base film containing the polyamide functional layer into a chitosan quaternary ammonium salt aqueous solution for charge modification to obtain a base film containing a polyamide functional layer and a cation modified layer;
and thermally compounding the base membrane containing the polyamide functional layer and the cation modified layer to obtain the positively charged composite nanofiltration membrane.
2. The preparation method according to claim 1, wherein the polyamine aqueous solution comprises polyethyleneimine and piperazine, and the mass ratio of the polyethyleneimine to the piperazine is 1-5.
3. The method according to claim 1, wherein the polybasic acid chloride in the organic solution of polybasic acid chloride comprises one or more of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride.
4. The method according to claim 1 or 3, wherein the organic solvent in the organic solution of polyacyl chloride comprises one or more of n-hexane, dodecane and cyclohexane.
5. The preparation method according to claim 1, wherein the material of the base membrane comprises one or more of polyacrylonitrile, polyethersulfone and polysulfone.
6. The method according to claim 1, wherein the concentration of the quaternary ammonium salt of chitosan in the aqueous solution of quaternary ammonium salt of chitosan is 0.1 to 0.7wt%.
7. The method of claim 1, wherein the temperature of the thermal compounding is 50 to 100 ℃ and the time is 300 to 1500 seconds.
8. The method according to claim 1 or 2, wherein the base film is immersed in the aqueous polyamine solution for a period of 5 to 25min.
9. The positively charged composite nanofiltration membrane obtained by the preparation method of any one of claims 1 to 8, which comprises a base membrane, a polyamide functional layer and a cation modification layer, wherein the base membrane, the polyamide functional layer and the cation modification layer are sequentially stacked, the polyamide functional layer is prepared by performing interfacial polymerization reaction on polyamine aqueous solution and polyacyl chloride organic solution, and the cation modification layer is provided with positive charge groups by chitosan quaternary ammonium salt.
10. The use of a positively charged composite nanofiltration membrane according to claim 9 in magnesium-lithium separation.
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