CN118286863A - High-heat-resistance loose nanofiltration membrane and preparation method and application thereof - Google Patents
High-heat-resistance loose nanofiltration membrane and preparation method and application thereof Download PDFInfo
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- LCZVSXRMYJUNFX-UHFFFAOYSA-N 2-[2-(2-hydroxypropoxy)propoxy]propan-1-ol Chemical compound CC(O)COC(C)COC(C)CO LCZVSXRMYJUNFX-UHFFFAOYSA-N 0.000 claims description 5
- 239000002202 Polyethylene glycol Substances 0.000 claims description 4
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Abstract
The invention relates to the technical field of membrane separation, in particular to a high-heat-resistance loose nanofiltration membrane and a preparation method and application thereof, wherein the preparation method comprises the following steps: uniformly mixing PMIA polymer stock solution and a pore-foaming agent in a polar solvent, and obtaining a casting film solution after defoaming; scraping a film on a glass plate by using a film casting solution; and (3) carrying out heat treatment on the glass plate with the membrane liquid, and immersing the membrane in a coagulating bath to obtain the high-heat-resistance loose nanofiltration membrane. The temperature of the heating treatment is 40-70 ℃, and the time of the heating treatment is 10-20min. The nanofiltration membrane can be applied to the separation and purification processes of high-temperature fluid in the industries of printing and dyeing, spinning and the like, can realize stable salt and dye separation at high temperature, and overcomes the use limit of the existing membrane separation technology in high-temperature materials. Compared with the existing separation membrane preparation technology, the preparation method provided by the invention greatly simplifies the membrane preparation process and is beneficial to large-scale production.
Description
Technical Field
The invention relates to a high heat resistance loose nanofiltration membrane, a preparation method and application thereof, and belongs to the technical field of membrane separation.
Background
The membrane separation technology is used as a novel separation technology for efficient separation, concentration and purification, has the advantages of simple operation, small occupied area, high separation efficiency, high integration degree and the like, and is widely applied to the fields of water treatment, solvent recovery and the like. However, most membrane modules have poor temperature resistance, and the use temperature is more than 50 ℃; in addition, membranes made from most polymeric materials often suffer from low water permeation flux and poor rejection and separation properties for high value added solutes. The performance defects limit the use of the membrane separation technology under the high-temperature condition and the high-efficiency membrane method treatment of the high-temperature printing and dyeing wastewater in the textile industry.
Poly (m-phenylene isophthalamide) (PMIA) is formed by mutually connecting amide groups with meta-phenyl groups, a molecular chain is in a linear zigzag shape, and a strong hydrogen bonding effect exists between molecules. The molecular structure imparts a relatively high glass transition temperature (270 ℃) and excellent thermal stability. Therefore, the PMIA material has good development and application prospect in the preparation of the high heat resistance separation membrane. In addition, a large number of amide bonds and hydrogen bond network structures in the PMIA main chain endow the membrane material with excellent hydrophilicity, and can greatly enhance the water permeation flux. At present, related patents report some methods for preparing PMIA porous membranes, but the pore structures are mostly ultrafiltration level. Chinese patent application CN112755816A discloses a preparation method of a PMIA film with high heat resistance, which endows a product with excellent heat resistance, but the preparation method is complex, and interfacial polymerization is needed to reduce the pore diameter of the film after phase inversion. The Chinese patent application CN105327625A discloses a preparation method of a polyamide nanofiltration membrane in a flat plate direction, but the preparation method is focused on the improvement of the membrane performance, and the research on a high-temperature material separation system is not in depth. The patent proposes a method for constructing a loose high temperature resistant nanofiltration membrane by one step by using a composite induced phase separation method. The PMIA porous membrane prepared by combining thermal induced phase separation and non-solvent induced phase separation is used for constructing a compact cortex and a supporting layer penetrating through a network structure, and can realize high-performance separation of salt/dye in a high-temperature material system.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides a high-heat-resistance loose nanofiltration membrane, a preparation method and application thereof, and overcomes the use limit of the existing membrane separation technology in high-temperature materials.
The technical scheme for solving the technical problems is as follows: a preparation method of a high heat resistance loose nanofiltration membrane comprises the following steps:
S1, preparing casting film liquid
Uniformly mixing PMIA polymer stock solution and a pore-foaming agent in a polar solvent, and obtaining a casting film solution after defoaming;
S2, film scraping
Scraping a film on a glass plate by using a film casting solution;
s3, heat treatment and coagulation bath treatment
And (3) carrying out heat treatment on the glass plate with the membrane liquid, and immersing the membrane in a coagulating bath to obtain the high-heat-resistance loose nanofiltration membrane.
Further, the PMIA polymer stock solution has a PMIA polymer stock solution solid content of 15% +/-1% and a viscosity of 550-650P, the molecular weight distribution of the aramid polymer in the PMIA polymer stock solution is Mw/Mn=1.1-1.3, and the solvent used for polymerization is N, N-dimethylacetamide.
Further, the pore-forming agent is one or more of polyvinylpyrrolidone, acetone, polyethylene glycol, tripropylene glycol, water and ethanol;
the polar solvent is one or two of N, N-dimethylacetamide and N-methylpyrrolidone.
Further, the content of the pore-forming agent in the casting solution is 3-8 g/L, and the content of PMIA in the casting solution is 10-20 g/L.
Further, the operation of step S1 is: adding PMIA polymer stock solution and pore-forming agent into polar solvent, stirring to form uniform solution at 55-65deg.C, and vacuum defoaming at constant temperature to obtain the final product.
Further, in step S2, the thickness of the doctor blade is 50-200 μm, and the temperature of the doctor blade is 10-50 ℃.
Further, in step S3, the temperature of the heating treatment is 40-70 ℃, and the time of the heating treatment is 10-20min.
In step S3, the coagulating bath is deionized water, the temperature of the coagulating bath is 15-50 ℃, and the coagulating time is 0.5-5min.
The invention also discloses a high heat resistance loose nanofiltration membrane, which is prepared by the preparation method.
The invention also discloses application of the high-heat-resistance loose nanofiltration membrane, which is applied to separation and purification of salt or dye in high-temperature fluid, wherein the temperature of the high-temperature fluid is 40-90 ℃. For example, the high heat resistance loose nanofiltration membrane can be applied to separation and purification of high-temperature fluid in the industries of printing and dyeing, spinning and the like.
The beneficial effects of the invention are as follows:
(1) The high heat resistance loose nanofiltration membrane prepared by the invention has stronger heat stability and is more stable in a long-term operation process. When the porous membrane is operated at the operating temperature of 40-90 ℃, the flux of the porous membrane is increased from 13L/m 2 ∙ h ∙ bar to 32L/m 2 ∙ h ∙ bar, the retention rate of dye in a salt/dye mixed feeding system is always higher than 90%, the retention rate of inorganic salt is lower than 10%, and the porous membrane has excellent salt/dye separation performance. In addition, the high heat resistance loose nanofiltration membrane can stably run in a high temperature salt/dye mixed solution at 90 ℃ for at least 20 days, and the membrane structure stability of the high heat resistance loose nanofiltration membrane avoids the cost problem caused by frequent replacement of a membrane component in actual high temperature fluid treatment. Therefore, the high heat resistance loose nanofiltration membrane has better applicability in the separation of a high-temperature material system.
(2) The high heat resistance loose nanofiltration membrane of the invention utilizes a polyamide structure with excellent high temperature resistance on the membrane surface to improve the heat stability of the membrane material. The membrane pore canal structure constructed by the composite induced phase separation method can realize the high-efficiency separation of small molecular substances, does not need to further reduce the membrane pore diameter by means of complex post-crosslinking and the like, avoids the problem of difficult large-scale preparation caused by complex membrane preparation steps, and is convenient for large-scale popularization.
(3) The existing porous membrane applied to high-temperature material separation often needs complex post-treatment processes such as modification, crosslinking, interfacial polymerization and the like, and complex preparation steps not only can increase instability in the large-scale preparation process, but also can cause membrane permeability reduction, and obviously reduce membrane separation efficiency. The porous nanofiltration membrane is prepared by a composite induced phase separation method in one step, and the preparation method of the porous nanofiltration membrane with high heat resistance is simple to operate, short in time consumption and low in requirements on external environment, and can obviously reduce the membrane preparation cost; in addition, the membrane technology is controlled simply and monotonously, so that the regulation and control of the membrane aperture from ultrafiltration to nanofiltration can be realized.
(4) The PMIA adopted by the high heat resistance loose nanofiltration membrane has higher glass transition temperature and excellent heat stability. The rich amide bond and hydrogen bond network in the main chain simultaneously endows the membrane material with good hydrophilicity, and effectively avoids the trade-off effect between the permeability and the selectivity of the traditional separation membrane.
Drawings
FIG. 1 is a scanning electron microscope image of the surface of PMIA-1 film prepared in example 1;
FIG. 2 is a sectional Scanning Electron Microscope (SEM) image of PMIA-1 film prepared in example 1.
Detailed Description
The following describes the present invention in detail. The present invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit of the invention, so that the invention is not limited to the specific embodiments disclosed.
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 is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
A preparation method of a high heat resistance loose nanofiltration membrane comprises the following steps:
S1, preparing casting film liquid
Uniformly mixing PMIA polymer stock solution and a pore-foaming agent in a polar solvent, and obtaining a casting film solution after defoaming;
S2, film scraping
Scraping a film on a glass plate by using a film casting solution;
s3, heat treatment and coagulation bath treatment
And (3) carrying out heat treatment on the glass plate with the membrane liquid, and immersing the membrane in a coagulating bath to obtain the high-heat-resistance loose nanofiltration membrane.
Specifically, the PMIA polymerization stock solution has a solid content of 15% +/-1%, a viscosity of 550-650P, a molecular weight distribution Mw/Mn=1.1-1.3, and a solvent used for polymerization is N, N-dimethylacetamide.
More specifically, the PMIA polymerization stock solution used in the embodiment of the invention is self-made, and the specific preparation method is as follows: performing polymerization reaction on m-phthaloyl chloride and m-phenylenediamine in a molar ratio of 1.02:1 in an organic solvent, namely dissolving 300 mol m-phenylenediamine in an organic solvent N, N-dimethylacetamide (DMAc) to prepare a m-phenylenediamine solution with a mass ratio of 7.8%, and then adding 306mol of m-phthaloyl chloride to perform polymerization reaction to obtain a polymerization solution mixture; wherein the polymerization reaction is divided into a first polymerization and a second polymerization, specifically: dividing 306mol of isophthaloyl dichloride into first isophthaloyl dichloride and second isophthaloyl dichloride with the mass ratio of 9:1 before the polymerization reaction, wherein the first isophthaloyl dichloride is used for first polymerization, and the second isophthaloyl dichloride is used for second polymerization; the first polymerization is to add first m-phthaloyl chloride into m-phenylenediamine solution, the first polymerization temperature is controlled to be 10+/-1 ℃, the stirring speed is 500r/min, and the reaction time of the first polymerization is 30min; then adding second isophthaloyl dichloride into the system, controlling the second polymerization temperature to be 55 ℃, stirring at the speed of 500r/min, and reacting for 15min; the total time of the polymerization reaction is 45min, and the polymerization reaction is polycondensation reaction; after the reaction is finished, adding a neutralizing agent calcium hydroxide to neutralize inorganic acid in the polymerization solution mixture, and filtering to obtain PMIA polymerization stock solution; the mass concentration of the aramid polymer in the PMIA polymerization raw liquid is 15%, the viscosity of the PMIA polymerization raw liquid is 600P, the molecular weight distribution Mw/Mn of the aramid polymer in the PMIA polymerization raw liquid is=1.2, and the pH value of the PMIA polymerization raw liquid is 7.5.
Specifically, the pore-forming agent is one or more of polyvinylpyrrolidone, acetone, polyethylene glycol, tripropylene glycol, water and ethanol. Wherein the pore-forming agent is purchased from one or more of microphone, polyvinylpyrrolidone with molecular weight of 2500-58000, and polyethylene glycol with molecular weight of 200-2000.
The polar solvent is one or two of N, N-dimethylacetamide and N-methylpyrrolidone.
Specifically, the content of the pore-forming agent in the film casting liquid is 3-8 g/L, and the content of PMIA in the film casting liquid is 10-20 g/L.
Specifically, the operation in step S1 is as follows: adding PMIA polymer stock solution and pore-forming agent into polar solvent, stirring to form uniform solution at 55-65deg.C, and vacuum defoaming at constant temperature to obtain the final product.
Specifically, in the step S2, the thickness of the scraping film is 50-200 mu m, and the temperature of the scraping film is 10-50 ℃.
Specifically, in step S3, the temperature of the heating treatment is 40-70 ℃, and the time of the heating treatment is 10-20min.
More specifically, in order to ensure the accuracy of controlling the pore diameter of the nanofiltration membrane surface, the temperature of the heating treatment is further preferably 60 ℃.
Specifically, in the step S3, the coagulating bath is deionized water, the temperature of the coagulating bath is 15-50 ℃, and the coagulating time is 0.5-5min.
More specifically, the coagulation bath temperature is t, in degrees celsius; the thickness of the nanofiltration membrane is D, the unit is mu m, t=T+ -4, and T=70.7e -0.008D. The control of the coagulation bath temperature and the thickness of the nanofiltration membrane are cooperatively matched, so that the control of the pore diameter on the nanofiltration membrane is more facilitated.
The high heat resistance loose nanofiltration membrane is applied to separation and purification of salt or dye in high-temperature fluid, and the temperature of the high-temperature fluid is 40-90 ℃.
Example 1
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 60 ℃ for 8h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone (K30 average molecular weight 40000) in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a baking oven at 40 ℃ for 20min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 30 ℃, and the coagulating time is 3min, so that the high heat resistance loose nanofiltration membrane PMIA-1 membrane is obtained.
The obtained PMIA-1 film was subjected to surface and section scanning electron microscope characterization, and the results are shown in FIG. 1 and FIG. 2. As can be seen from fig. 1 and 2, the surface of the membrane has a dense skin layer, and the cross section of the membrane shows a regular finger-shaped pore structure.
Example 2
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 55 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the casting solution is 3 g/L, and the content of PMIA in the casting solution is 10 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 10 ℃, and the film scraping thickness is 50 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a 60 ℃ oven for 16 min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 50 ℃, and the coagulating time is 4 min, so as to obtain the high heat resistance loose nanofiltration membrane PMIA-2 membrane.
Example 3
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 65 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the film casting liquid is 8 g/L, and the content of PMIA in the film casting liquid is 20 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 50 ℃, and the film scraping thickness is 200 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a 70 ℃ oven for 13 min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 15 ℃, and the coagulating time is 0.5 min, so as to obtain the high heat resistance loose nanofiltration membrane PMIA-3 membrane.
Example 4
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 60 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a 60 ℃ oven for 10 min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 35 ℃, and the coagulating time is 5min, so as to obtain the high heat resistance loose nanofiltration membrane PMIA-4 membrane.
Example 5
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 55 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the casting solution is 3 g/L, and the content of PMIA in the casting solution is 10 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a baking oven at 50 ℃ for 17 min hours, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 35 ℃, and the coagulating time is 2 min, so that the high heat resistance loose nanofiltration membrane PMIA-5 membrane is obtained.
Example 6
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and acetone in N, N-dimethylacetamide, stirring at 65 ℃ for 8 h to fully dissolve, and carrying out vacuum defoaming to obtain casting solution; wherein the content of acetone in the casting solution is 8 g/L, and the content of PMIA in the casting solution is 20 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a baking oven at 60 ℃ for 13.5min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 30 ℃, and the coagulating time is 5min, so that the high heat resistance loose nanofiltration membrane PMIA-6 membrane is obtained.
Example 7
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and tripropylene glycol in N, N-dimethylacetamide, stirring at 60 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of tripropylene glycol in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a baking oven at 60 ℃ for 20min minutes, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 30 ℃, and the coagulating time is 0.5 minutes, so as to obtain the high heat resistance loose nanofiltration membrane PMIA-7 membrane.
Example 8
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 60 ℃ for 8h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone (K30 average molecular weight 40000) in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a baking oven at 60 ℃ for 20min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 30 ℃, and the coagulating time is 3min, so that the high heat resistance loose nanofiltration membrane PMIA-8 membrane is obtained.
Example 9
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 65 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the film casting liquid is 8 g/L, and the content of PMIA in the film casting liquid is 20 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 50 ℃, and the film scraping thickness is 200 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a 70 ℃ oven for 13 min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 30 ℃, and the coagulating time is 0.5 min, so as to obtain the high heat resistance loose nanofiltration membrane PMIA-9 membrane.
Example 10
The preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 60 ℃ for 8h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone (K30 average molecular weight 40000) in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a baking oven at 40 ℃ for 20min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 15 ℃, and the coagulating time is 3min, so that the high heat resistance loose nanofiltration membrane PMIA-10 membrane is obtained.
Comparative example 1
Nanofiltration membranes were prepared by the same method as in example 1, except that no heat treatment was performed, and the specific preparation method was as follows:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 60 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Coagulation bath treatment
Immersing the glass plate with the membrane liquid into a coagulating bath of deionized water for solvent exchange to remove redundant solvent, wherein the temperature of the coagulating bath is 25 ℃, the coagulating time is 3min, and finally, placing the glass plate into clean deionized water for preservation to obtain the nanofiltration membrane PMIA-0 membrane.
Comparative example 2
Nanofiltration membranes were prepared by the same method as in example 1, except that the heat treatment temperature was reduced, and the specific preparation method was as follows:
the preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 60 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
And (3) placing the glass plate with the membrane liquid into a baking oven at 30 ℃ for 20 min, and immersing the membrane into a coagulating bath of deionized water, wherein the temperature of the coagulating bath is 25 ℃, and the coagulating time is 3min, so as to obtain the nanofiltration membrane PMIA-00 membrane.
Comparative example 3
Nanofiltration membranes were prepared by the same method as in example 1, except that the heat treatment temperature was increased, and the specific preparation method was as follows:
the preparation method of the high heat resistance loose nanofiltration membrane comprises the following steps:
(1) Preparing casting film liquid
Dissolving PMIA polymer stock solution and polyvinylpyrrolidone in N, N-dimethylacetamide, stirring at 60 ℃ for 8 h to fully dissolve, and vacuum defoaming to obtain casting solution; wherein the content of polyvinylpyrrolidone in the casting solution is 5 g/L, and the content of PMIA in the casting solution is 15 g/L.
(2) Scraping film
Spreading the casting film liquid on a smooth glass plate, wherein the film scraping temperature is 25 ℃, and the film scraping thickness is 100 mu m;
(3) Heat treatment and coagulation bath treatment
The glass plate with the membrane liquid is placed in an oven at 80 ℃ for 20min, then the membrane is immersed in a coagulating bath of deionized water, the temperature of the coagulating bath is 25 ℃, and the coagulating time is 3min, so as to obtain the nanofiltration membrane PMIA-000 membrane.
Comparative example 4
The nanofiltration membrane was prepared by the same method as in example 1, except that the PMIA polymer dope was replaced with an aramid polymer in the PMIA polymer dope, and lithium chloride as a cosolvent (the mass ratio of lithium chloride to aramid polymer is 1:10) was added when preparing the casting solution; other operating conditions were the same as in example 1 to obtain PMIA-0000 film.
The nanofiltration membranes obtained in examples 1 to 10 and comparative examples 1 to 4 above were subjected to pore size characterization, and the nanofiltration membranes were tested for water flux, dye/salt separation performance, and long-term heat stability, with specific results as shown in tables 1,2 and 3 below.
The specific test method of the water flux and dye/salt separation performance reference ：M.J. Tang#, M.L. Liu#, L. Li, G.J. Su, X.Y. Yan, C. Ye, S.P. Sun*, W. Xing, Solvation-amination-synergy that neutralizes interfacially polymerized membranes for ultrahigh selective nanofiltration. AIChE J. 68 (2022) e17602. comprises the following steps: the tests were performed using a laboratory self-made cross-flow apparatus. The effective area of the membrane pool in the measuring device is 12.56 cm
2 The feed solution was heated and maintained at a constant temperature using a water bath. The feed solution was a mixed solution of 500ppm Congo red dye and 1000ppm NaCl. Prior to testing, deionized water was used to precompacte 30min at 10bar pressure. The membrane was then tested for dye/salt separation performance at different feed temperatures under 6 bar pressure drive. Dye concentration was measured using an ultraviolet spectrophotometer and salt concentration was measured using ion chromatography. The water flux and retention rate were calculated as follows:
；
wherein Flux is the permeate Flux of the membrane, deltaV is the volume of permeate, A is the effective membrane area, deltat is the test time, and P is the test pressure.
；
Wherein R is the solute rejection rate, c p is the solute concentration in the permeate, and c f is the solute concentration in the feed liquid.
The long-term heat-resistant stability test method comprises the following steps: the membrane was tested for permeation flux and dye/salt rejection performance at 1h intervals at a certain feed temperature.
The membrane pore diameter test method comprises the following steps: the retention rates of nanofiltration membranes on PEG 400, PEG 800, PEG 600 and PEG 1000 were used to calculate the composite membrane retention molecular weight, average effective pore size and pore size distribution. The following formula was used to calculate PEG solute radii for different molecular weights
rs：
；
Where MW is the molecular weight of the different PEGs. The pore size distribution of the membrane was calculated as follows:
；
where R p is the effective pore size of the membrane, the geometric mean radius of the solute at r=55.0%; mu p is the average effective pore size; the geometric standard deviation σ p is the ratio of R s at R T =84.13% and 50%.
TABLE 1 nanofiltration membrane pore size, water flux and rejection of the corresponding salt/dye at Mixed salt feed
TABLE 2 rejection of Congo Red by nanofiltration membranes at different temperatures
TABLE 3 rejection of dye by continuous operation of nanofiltration membranes at 90℃
From the above data in tables 1 to 3, it can be seen that the nanofiltration membrane (PMIA-1 to PMIA-10) prepared by the preparation method of the present invention has smaller pore size, and simultaneously exhibits excellent salt/dye separation performance, and the retention rate of dye increases, because the higher ambient temperature and evaporation time (heat treatment process) cause the solvent volatilization amount to increase during the thermally induced phase separation process, resulting in a denser and thicker skin structure, thereby achieving higher dye separation performance. The comparison of PMIA-8 and PMIA-1 shows that the nano-filtration membrane with excellent performance is more favorable to be obtained at the heat treatment temperature of 60 ℃. As can be seen from the comparison of PMIA-9 and PMIA-3 and the comparison of PMIA-10 and PMIA-1, the aperture control of the nanofiltration membrane is more facilitated when the nanofiltration membrane thickness and the coagulation bath temperature condition are matched with each other in the preparation process, and finally, the nanofiltration membrane product with excellent performance is obtained.
From the comparison of experimental data of example 1 (PMIA-1) and comparative examples 1,2 (PMIA-0, PMIA-00), it can be seen that: if the heat treatment operation is not carried out or the heat treatment temperature is lower in the nanofiltration membrane preparation process, the nanofiltration membrane has larger pore diameter and lower separation precision of salt/dye. Thus, by adjusting the heat treatment operation process, the adjustment of the membrane pore diameter can be achieved.
From the comparison of experimental data of example 1 (PMIA-1) and comparative example 3 (PMIA-000), it can be seen that: if the heat treatment temperature is too high in the nanofiltration membrane preparation process, the aperture of the nanofiltration membrane is very small, and the membrane flux of the nanofiltration membrane is seriously affected. Therefore, the heat treatment conditions defined by the invention are more beneficial to obtaining the nanofiltration membrane with excellent application performance.
The invention adopts a method of combining thermally induced phase separation and non-solvent induced phase separation to realize the preparation of the high heat-resistant loose nanofiltration membrane. Before non-solvent phase separation, the membrane is heated, so that the pore diameter of the membrane can be effectively reduced, and the one-step preparation of the nanofiltration membrane is realized. This is mainly because a proper temperature treatment causes a part of the solvent on the surface of the primary film to evaporate, thereby forming a dense skin layer; and when the temperature is too high, the volatilization amount of the solvent is too fast, the thickness of the compact cortex can be increased, and the pore diameter of the membrane is smaller, so that the flux of the membrane is finally influenced.
From the comparison of experimental data of example 1 (PMIA-1) and comparative example 4 (PMIA-0000), it can be seen that: if PMIA polymer stock solution is replaced by aramid polymer, the solubility is relatively poor when preparing casting solution, and for better solubility, the cosolvent lithium chloride is needed to be added. However, the pore diameter of the membrane prepared by the method is large, lithium chloride plays a role of a pore-forming agent while playing a role of a cosolvent, and the existence of the lithium chloride can lead the whole process to be incapable of preparing qualified nanofiltration membrane products.
The technical features of the above-described embodiments may be arbitrarily combined, and in order to simplify the description, all possible combinations of the technical features in the above-described embodiments are not exhaustive, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims.
Claims (10)
1. The preparation method of the high heat resistance loose nanofiltration membrane is characterized by comprising the following steps of:
S1, preparing casting film liquid
Uniformly mixing PMIA polymer stock solution and a pore-foaming agent in a polar solvent, and obtaining a casting film solution after defoaming;
S2, film scraping
Scraping a film on a glass plate by using a film casting solution;
s3, heat treatment and coagulation bath treatment
And (3) carrying out heat treatment on the glass plate with the membrane liquid, and immersing the membrane in a coagulating bath to obtain the high-heat-resistance loose nanofiltration membrane.
2. The method for preparing the high heat resistance loose nanofiltration membrane according to claim 1, wherein the solid content of the PMIA polymerization raw liquid is 15% ± 1%, the viscosity is 550-650P, the molecular weight distribution of the aramid polymer in the PMIA polymerization raw liquid is Mw/Mn=1.1-1.3, and the solvent used for polymerization is N, N-dimethylacetamide.
3. The method for preparing the high heat resistance loose nanofiltration membrane according to claim 1, wherein the pore-forming agent is one or more of polyvinylpyrrolidone, acetone, polyethylene glycol, tripropylene glycol, water and ethanol;
the polar solvent is one or two of N, N-dimethylacetamide and N-methylpyrrolidone.
4. The method for preparing a porous nanofiltration membrane with high heat resistance according to claim 1, wherein the content of the pore-forming agent in the casting solution is 3-8 g/L, and the content of PMIA in the casting solution is 10-20 g/L.
5. The method for preparing a porous nanofiltration membrane with high heat resistance according to claim 1, wherein the operation of step S1 is as follows: adding PMIA polymer stock solution and pore-forming agent into polar solvent, stirring to form uniform solution at 55-65deg.C, and vacuum defoaming at constant temperature to obtain the final product.
6. The method for preparing a porous nanofiltration membrane with high heat resistance according to claim 1, wherein in the step S2, the thickness of the scraped membrane is 50-200 μm, and the temperature of the scraped membrane is 10-50 ℃.
7. The method for preparing a porous nanofiltration membrane with high heat resistance according to claim 1, wherein in the step S3, the heating treatment is performed at a temperature of 40-70 ℃ for 10-20min.
8. The method for preparing a porous nanofiltration membrane with high heat resistance according to claim 1, wherein in the step S3, the coagulation bath is deionized water, the temperature of the coagulation bath is 15-50 ℃, and the coagulation time is 0.5-5min.
9. A high heat resistant bulk nanofiltration membrane, characterized in that the high heat resistant bulk nanofiltration membrane is produced by the production process of any one of claims 1 to 8.
10. The application of the high heat resistance loose nanofiltration membrane is characterized in that the high heat resistance loose nanofiltration membrane prepared by the preparation method according to any one of claims 1-8 is applied to separation and purification of salt or dye in high temperature fluid, and the temperature of the high temperature fluid is 40-90 ℃.
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