CN111871209A - Preparation method of heat-resistant condensation tetrafluoroethylene composite nanofiltration membrane - Google Patents
Preparation method of heat-resistant condensation tetrafluoroethylene composite nanofiltration membrane Download PDFInfo
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Abstract
The invention relates to the technical field of membrane separation, and discloses a preparation method of a heat-resistant condensation polymerization tetrafluoroethylene composite nanofiltration membrane. The method comprises the following steps: s1, preparing chitosan microspheres; s2, carrying out hydrophilic activation modification on the hydrophobic polytetrafluoroethylene microporous membrane by using sodium dodecyl benzene sulfonate; s3, filling and modifying micropores on the surface of the hydrophilic polytetrafluoroethylene microporous membrane by tetrabutyl titanate and chitosan microspheres; s4, putting the modified polytetrafluoroethylene microporous membrane into a triethylene tetramine aqueous monomer for dipping treatment; s5, placing the modified polytetrafluoroethylene microporous membrane into a trimesoyl chloride solution for an interfacial polymerization reaction to obtain a nascent state polytetrafluoroethylene microporous membrane; s6, carrying out thermosetting crosslinking treatment on the nascent state polytetrafluoroethylene microporous membrane. The composite nanofiltration membrane prepared by the invention has excellent heat shrinkage resistance, so that the functional layer of the composite nanofiltration membrane is protected from being damaged in the heat treatment process of the composite nanofiltration membrane, and the lasting stability of the performance of the composite nanofiltration membrane is maintained.
Description
Technical Field
The invention relates to the technical field of membrane separation, in particular to a preparation method of a heat-resistant condensation polymerization tetrafluoroethylene composite nanofiltration membrane.
Background
The nanofiltration technology is a novel membrane separation technology based on reverse osmosis, which is an effective method for treating drinking water and production wastewater, has good removal effect on multivalent ions and organic molecules with the molecular weight of 150-. Therefore, compared with reverse osmosis, the transmembrane pressure is generally 0.7MPa and is far less than the pressure required by a reverse osmosis membrane, so that the operating pressure is low, the high flux enables the characteristics of the nanofiltration membrane, and meanwhile, the nanofiltration membrane has certain charge property, and not only has a screening effect in the nanofiltration separation process, but also has the characteristics of a southward effect and an adsorption effect. The composite nanofiltration membrane prepared by the composite method has the following advantages: 1. the functional layer can optimize the thickness of the membrane by controlling the process conditions, so as to obtain a modified composite membrane, and the mechanical strength of the obtained membrane can be optimized by selecting the supporting layer; 2. the application range of the material can be further expanded through the composite nanofiltration membrane. The composite nanofiltration membrane mainly comprises a supporting layer and a separation functional layer positioned above the supporting membrane, wherein the supporting layer mainly provides a supporting function for the separation functional layer, and the separation functional layer is used for intercepting ions or organic molecules in a water body. The interface polymerization method is an advanced technology for the polymerization reaction between two immiscible phase interfaces. In the interfacial polymerization process, the properties of the solvent and the monomer, as well as the concentration and reaction time of the monomer determine the porosity, pore size and thickness of the selective layer, thereby affecting the separation performance of the nanofiltration membrane. The polytetrafluoroethylene material has the reputation of the king plastic, has excellent performances of acid and alkali resistance, solvent resistance, high mechanical strength and the like, so that the polytetrafluoroethylene membrane material adopted as the supporting layer of the composite nanofiltration membrane has natural advantages.
Chinese patent publication No. CN105854640 discloses a preparation method of a positively charged hollow polytetrafluoroethylene composite nanofiltration membrane, which comprises the steps of injecting a carboxylated chitosan aqueous solution into an active base membrane by using an injector to obtain a hydrophilic polytetrafluoroethylene tubular membrane, then respectively injecting a hyperbranched polyethyleneimine aqueous phase solution and a trimesoyl chloride organic phase solution into the polytetrafluoroethylene tubular membrane to carry out interfacial polymerization reaction to synthesize a polyamide separation functional layer on the polytetrafluoroethylene membrane, and finally carrying out heat treatment in an oven to obtain the composite nanofiltration membrane. Because the microstructure of the polytetrafluoroethylene microporous membrane presents a fiber-node structure, the fiber-node structure of the polytetrafluoroethylene microporous membrane shrinks after the polytetrafluoroethylene microporous membrane is heated in the subsequent heat treatment step, and the separation functional layer covered above the polytetrafluoroethylene microporous membrane is damaged in the shrinking process of the polytetrafluoroethylene microporous membrane, so that the mechanical strength of the separation functional layer is reduced, and the separation functional layer is easy to crack in the filtering operation process of the composite nanofiltration membrane, so that the interception performance of the composite nanofiltration membrane is reduced.
Disclosure of Invention
The invention aims to overcome the problems in the prior art and provides a preparation method of a heat-resistant condensation polymerization tetrafluoroethylene composite nanofiltration membrane. The composite nanofiltration membrane prepared by the invention has excellent heat shrinkage resistance, so that the functional layer of the composite nanofiltration membrane is protected from being damaged in the heat treatment process of the composite nanofiltration membrane, and the lasting stability of the performance of the composite nanofiltration membrane is maintained.
In order to achieve the purpose, the invention adopts the following technical scheme: a preparation method of a heat-resistant condensation polymerization tetrafluoroethylene composite nanofiltration membrane comprises the following steps:
s1, preparing chitosan microspheres:
adding chitosan into an acetic acid solution, and dissolving by magnetic stirring to obtain a chitosan solution; uniformly mixing and stirring liquid paraffin and span 80 to obtain an oil phase solution, dripping a chitosan solution into the oil phase solution, heating to 40-50 ℃, emulsifying for 20-40min by magnetic stirring, then adding a glutaraldehyde crosslinking agent for crosslinking reaction for 2-3h, and carrying out suction filtration, washing and drying to obtain chitosan microspheres;
s2, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 20-50min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s3, preparing a modified polytetrafluoroethylene microporous membrane:
adding butyl titanate into absolute ethyl alcohol, and uniformly stirring and mixing to obtain a butyl titanate solution; adding glacial acetic acid and distilled water into absolute ethyl alcohol, uniformly stirring, dropwise adding a hydrochloric acid solution to adjust the pH to 2-3, then adding chitosan microspheres, uniformly dispersing the chitosan microspheres in the solution by ultrasonic oscillation to obtain a suspension, immersing a hydrophilic polytetrafluoroethylene microporous membrane into the suspension, then dropwise adding a butyl titanate solution into the suspension, uniformly stirring, heating in a water bath to 45-55 ℃, carrying out heat preservation reaction for 2-5h, standing for 5-10h, taking out, and then placing in an oven for drying treatment to obtain a modified polytetrafluoroethylene microporous membrane;
s4, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving to prepare a triethylene tetramine solution, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution; immersing the modified polytetrafluoroethylene microporous membrane into the aqueous phase solution for 10-30min to obtain an intermediate membrane body;
s5, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction at room temperature to obtain a nascent-state polytetrafluoroethylene composite nanofiltration membrane;
s6, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction, taking out the nascent state polytetrafluoroethylene composite nanofiltration membrane, and cooling the nascent state polytetrafluoroethylene composite nanofiltration membrane at room temperature to obtain the nano-porous polytetrafluoroethylene composite nanofiltration membrane.
Preferably, the addition amount of the glutaraldehyde cross-linking agent in step S1 is 5.0wt% of the chitosan.
Preferably, the concentration of the sodium dodecylbenzenesulfonate solution in the step S2 is 0.1 to 0.5 wt%.
Preferably, the mass ratio of the butyl titanate to the chitosan microspheres in the step S3 is 1: 0.2-0.5.
Preferably, the mass concentration percentage of triethylene tetramine in the aqueous phase solution in the step S4 is 1.0-3.0%.
Preferably, the concentration of the trimesoyl chloride solution in step S5 is 0.2-0.8 wt%.
Preferably, the interfacial polymerization reaction time in the step S5 is 2-5 min.
Preferably, in the step S6, the crosslinking and curing reaction temperature is 50-70 ℃, and the crosslinking and curing reaction time is 20-30 min.
According to the method, polytetrafluoroethylene is used as a supporting layer of the composite nanofiltration membrane, and trimesoyl chloride and triethylene tetramine monomer are subjected to interfacial polymerization reaction on the surface of a polytetrafluoroethylene microporous membrane, so that a polyamide separation functional layer is polymerized on the surface of the polytetrafluoroethylene microporous membrane. The polytetrafluoroethylene material has the reputation of the king plastic, has excellent performances of acid and alkali resistance, solvent resistance, high mechanical strength and the like, and can be used in harsh environments by adopting the polytetrafluoroethylene microporous membrane material as a supporting layer of the composite nanofiltration membrane. Because the polytetrafluoroethylene material is a hydrophobic material, the hydrophobic material can prevent water molecules from permeating the polytetrafluoroethylene microporous membrane and is not suitable for filtration, the hydrophilic polytetrafluoroethylene microporous membrane is prepared by carrying out hydrophilic modification treatment on the polytetrafluoroethylene microporous membrane by utilizing sodium dodecyl benzene sulfonate.
Because the microstructure of the polytetrafluoroethylene microporous membrane presents a fiber-node structure, the fiber-node structure of the polytetrafluoroethylene microporous membrane shrinks after the polytetrafluoroethylene microporous membrane is heated in the subsequent heat treatment step, and the separation functional layer covered above the polytetrafluoroethylene microporous membrane is damaged in the shrinking process of the polytetrafluoroethylene microporous membrane, so that the mechanical strength of the separation functional layer is reduced, and the separation functional layer is easy to crack in the filtering operation process of the composite nanofiltration membrane, so that the interception performance of the composite nanofiltration membrane is reduced. As shown in fig. 1, which is a microscopic scanning electron microscope image of a ptfe microporous membrane, it can be seen that the ptfe microporous membrane has a fiber-node structure on its surface, and many slits on its surface, which are closed during the shrinkage process of the ptfe microporous membrane. The polytetrafluoroethylene microporous membrane is modified, the butyl titanate is used as a precursor to prepare the nano titanium dioxide colloid, and the nano titanium dioxide colloid particles are deposited in gaps on the surface of the polytetrafluoroethylene microporous membrane, so that the gaps on the surface of the polytetrafluoroethylene microporous membrane are filled, and the polytetrafluoroethylene microporous membrane is prevented from shrinking under the condition of heat. However, the problem caused by filling the gaps on the surface of the polytetrafluoroethylene microporous membrane with the nano titanium dioxide colloidal particles is that the gaps and holes on the surface of the polytetrafluoroethylene microporous membrane are blocked, and the water flux is seriously reduced.
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FIG. 1 is a microscopic SEM image of the surface of a polytetrafluoroethylene microporous membrane of the invention.
Detailed Description
The technical solution of the present invention is further illustrated by the following specific examples. In the present invention, unless otherwise specified, raw materials, equipment, and the like used are commercially available or commonly used in the art, and the methods in the examples are conventional in the art unless otherwise specified.
Example 1
The preparation method of the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane comprises the following steps:
s1, preparing chitosan microspheres:
adding chitosan into acetic acid solution with mass concentration of 5.0%, and dissolving by magnetic stirring to obtain chitosan solution with mass concentration of 3.0%; uniformly mixing and stirring liquid paraffin and span 80 to obtain an oil phase solution, wherein the addition amount of the span 80 is 6.0 wt% of the liquid paraffin, dripping a chitosan solution into the oil phase solution, the volume ratio of the chitosan solution to the oil phase solution is 1:8, heating to 50 ℃, emulsifying for 20min by magnetic stirring, then adding a glutaraldehyde crosslinking agent for crosslinking reaction for 2.5h, the addition amount of the glutaraldehyde crosslinking agent is 5.0wt% of chitosan, and performing suction filtration, washing and drying to obtain chitosan microspheres;
s2, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution with the concentration of 0.5wt%, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 20min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s3, preparing a modified polytetrafluoroethylene microporous membrane:
adding butyl titanate into absolute ethyl alcohol, and uniformly stirring and mixing to obtain a butyl titanate solution with the mass concentration of 6.0%; adding glacial acetic acid and distilled water into absolute ethyl alcohol, uniformly stirring to obtain a mixed solution, wherein the volume ratio of the glacial acetic acid to the distilled water to the absolute ethyl alcohol is 1:3:8, dropwise adding a hydrochloric acid solution to adjust the pH value to 3, adding chitosan microspheres into the mixed solution according to the mass-to-volume ratio of 1g/50mL, ultrasonically oscillating to uniformly disperse the chitosan microspheres in the solution to obtain a suspension, immersing a hydrophilic polytetrafluoroethylene microporous membrane into the suspension according to the bath ratio of 1:30, then dropwise adding a butyl titanate solution into the suspension, wherein the mass ratio of the butyl titanate to the chitosan microspheres is 1:0.4, uniformly stirring, heating in a water bath to 55 ℃, carrying out heat preservation reaction for 2h, standing for 8h, taking out, and then placing the microporous membrane into an oven to carry out drying treatment for 1h at 60 ℃ to obtain modified polytetrafluoroethylene;
s4, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution, wherein the mass concentration percentage of the triethylene tetramine in the aqueous phase solution is 2.5%, the mass concentration percentage of the sodium dodecyl sulfate is 0.05%, and the mass concentration percentage of the triethylamine is 0.5%; immersing the modified polytetrafluoroethylene microporous membrane into the aqueous phase solution for 30min to obtain an intermediate membrane body;
s5, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution with the mass concentration of 0.6%, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction for 4min at room temperature to obtain a nascent state polytetrafluoroethylene composite nanofiltration membrane;
s6, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction at 70 ℃ for 20min, taking out, and cooling at room temperature to obtain the nano-composite polytetrafluoroethylene nanofiltration membrane.
Example 2
The preparation method of the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane comprises the following steps:
s1, preparing chitosan microspheres:
adding chitosan into acetic acid solution with mass concentration of 5.0%, and dissolving by magnetic stirring to obtain chitosan solution with mass concentration of 3.0%; uniformly mixing and stirring liquid paraffin and span 80 to obtain an oil phase solution, wherein the addition amount of the span 80 is 6.0 wt% of the liquid paraffin, dripping a chitosan solution into the oil phase solution, the volume ratio of the chitosan solution to the oil phase solution is 1:8, heating to 40 ℃, emulsifying for 40min by magnetic stirring, then adding a glutaraldehyde crosslinking agent for crosslinking reaction for 2.5h, the addition amount of the glutaraldehyde crosslinking agent is 5.0wt% of chitosan, and performing suction filtration, washing and drying to obtain chitosan microspheres;
s2, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution with the concentration of 0.1 wt%, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 50min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s3, preparing a modified polytetrafluoroethylene microporous membrane:
adding butyl titanate into absolute ethyl alcohol, and uniformly stirring and mixing to obtain a butyl titanate solution with the mass concentration of 6.0%; adding glacial acetic acid and distilled water into absolute ethyl alcohol, uniformly stirring to obtain a mixed solution, wherein the volume ratio of the glacial acetic acid to the distilled water to the absolute ethyl alcohol is 1:3:8, dropwise adding a hydrochloric acid solution to adjust the pH value to 2, adding chitosan microspheres into the mixed solution according to the mass-to-volume ratio of 1g/50mL, ultrasonically oscillating to uniformly disperse the chitosan microspheres in the solution to obtain a suspension, immersing a hydrophilic polytetrafluoroethylene microporous membrane into the suspension according to the bath ratio of 1:30, then dropwise adding a butyl titanate solution into the suspension, wherein the mass ratio of the butyl titanate to the chitosan microspheres is 1:0.3, uniformly stirring, heating in a water bath to 45 ℃, carrying out heat preservation reaction for 5h, standing for 6h, taking out, and then placing the microporous membrane into an oven to carry out drying treatment for 1h at 60 ℃ to obtain modified polytetrafluoroethylene;
s4, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution, wherein the mass concentration percentage of the triethylene tetramine in the aqueous phase solution is 1.5%, the mass concentration percentage of the sodium dodecyl sulfate is 0.05%, and the mass concentration percentage of the triethylamine is 0.5%; immersing the modified polytetrafluoroethylene microporous membrane into the aqueous phase solution for 10min to obtain an intermediate membrane body;
s5, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution with the mass concentration of 0.3%, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction for 3min at room temperature to obtain a nascent state polytetrafluoroethylene composite nanofiltration membrane;
s6, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction at 50 ℃ for 30min, taking out, and cooling at room temperature to obtain the nano-composite polytetrafluoroethylene nanofiltration membrane.
Example 3
The preparation method of the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane comprises the following steps:
s1, preparing chitosan microspheres:
adding chitosan into acetic acid solution with mass concentration of 5.0%, and dissolving by magnetic stirring to obtain chitosan solution with mass concentration of 3.0%; uniformly mixing and stirring liquid paraffin and span 80 to obtain an oil phase solution, wherein the addition amount of the span 80 is 6.0 wt% of the liquid paraffin, dripping a chitosan solution into the oil phase solution, the volume ratio of the chitosan solution to the oil phase solution is 1:8, heating to 45 ℃, emulsifying for 30min by magnetic stirring, then adding a glutaraldehyde crosslinking agent for crosslinking reaction for 3h, wherein the addition amount of the glutaraldehyde crosslinking agent is 5.0wt% of chitosan, and performing suction filtration, washing and drying to obtain chitosan microspheres;
s2, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution with the concentration of 0.3 wt%, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 40min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s3, preparing a modified polytetrafluoroethylene microporous membrane:
adding butyl titanate into absolute ethyl alcohol, and uniformly stirring and mixing to obtain a butyl titanate solution with the mass concentration of 6.0%; adding glacial acetic acid and distilled water into absolute ethyl alcohol, uniformly stirring to obtain a mixed solution, wherein the volume ratio of the glacial acetic acid to the distilled water to the absolute ethyl alcohol is 1:3:8, dropwise adding a hydrochloric acid solution to adjust the pH to 2.5, adding chitosan microspheres into the mixed solution according to the mass-to-volume ratio of 1g/50mL, ultrasonically oscillating to uniformly disperse the chitosan microspheres in the solution to obtain a suspension, immersing a hydrophilic polytetrafluoroethylene microporous membrane into the suspension according to the bath ratio of 1:30, then dropwise adding a butyl titanate solution into the suspension, wherein the mass ratio of the butyl titanate to the chitosan microspheres is 1:0.5, uniformly stirring, heating in a water bath to 50 ℃, carrying out heat preservation reaction for 3h, standing for 10h, taking out, and then placing in an oven to carry out drying treatment for 1h at 60 ℃ to obtain a modified polytetrafluoroethylene microporous membrane;
s4, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution, wherein the mass concentration percentage of the triethylene tetramine in the aqueous phase solution is 3.0%, the mass concentration percentage of the sodium dodecyl sulfate is 0.05%, and the mass concentration percentage of the triethylamine is 0.5%; immersing the modified polytetrafluoroethylene microporous membrane into the aqueous phase solution for 20min to obtain an intermediate membrane body;
s5, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution with the mass concentration of 0.8%, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction for 5min at room temperature to obtain a nascent state polytetrafluoroethylene composite nanofiltration membrane;
s6, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction at 60 ℃ for 25min, taking out, and cooling at room temperature to obtain the nano-composite polytetrafluoroethylene nanofiltration membrane.
Example 4
The preparation method of the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane comprises the following steps:
s1, preparing chitosan microspheres:
adding chitosan into acetic acid solution with mass concentration of 5.0%, and dissolving by magnetic stirring to obtain chitosan solution with mass concentration of 3.0%; uniformly mixing and stirring liquid paraffin and span 80 to obtain an oil phase solution, wherein the addition amount of the span 80 is 6.0 wt% of the liquid paraffin, dripping a chitosan solution into the oil phase solution, the volume ratio of the chitosan solution to the oil phase solution is 1:8, heating to 45 ℃, emulsifying for 30min by magnetic stirring, then adding a glutaraldehyde crosslinking agent for crosslinking reaction for 2h, wherein the addition amount of the glutaraldehyde crosslinking agent is 5.0wt% of chitosan, and performing suction filtration, washing and drying to obtain chitosan microspheres;
s2, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution with the concentration of 0.3 wt%, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 40min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s3, preparing a modified polytetrafluoroethylene microporous membrane:
adding butyl titanate into absolute ethyl alcohol, and uniformly stirring and mixing to obtain a butyl titanate solution with the mass concentration of 6.0%; adding glacial acetic acid and distilled water into absolute ethyl alcohol, uniformly stirring to obtain a mixed solution, wherein the volume ratio of the glacial acetic acid to the distilled water to the absolute ethyl alcohol is 1:3:8, dropwise adding a hydrochloric acid solution to adjust the pH to 2.5, adding chitosan microspheres into the mixed solution according to the mass-to-volume ratio of 1g/50mL, ultrasonically oscillating to uniformly disperse the chitosan microspheres in the solution to obtain a suspension, immersing a hydrophilic polytetrafluoroethylene microporous membrane into the suspension according to the bath ratio of 1:30, then dropwise adding a butyl titanate solution into the suspension, wherein the mass ratio of the butyl titanate to the chitosan microspheres is 1:0.2, uniformly stirring, heating in a water bath to 50 ℃, carrying out heat preservation reaction for 3h, standing for 5h, taking out, and then placing in an oven to carry out drying treatment for 1h at 60 ℃ to obtain a modified polytetrafluoroethylene microporous membrane;
s4, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution, wherein the mass concentration percentage of the triethylene tetramine in the aqueous phase solution is 1.0%, the mass concentration percentage of the sodium dodecyl sulfate is 0.05%, and the mass concentration percentage of the triethylamine is 0.5%; immersing the modified polytetrafluoroethylene microporous membrane into the aqueous phase solution for 20min to obtain an intermediate membrane body;
s5, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution with the mass concentration of 0.2%, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction for 2min at room temperature to obtain a nascent state polytetrafluoroethylene composite nanofiltration membrane;
s6, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction at 60 ℃ for 25min, taking out, and cooling at room temperature to obtain the nano-composite polytetrafluoroethylene nanofiltration membrane.
Comparative example 1
Comparative example 1 a preparation method of a polytetrafluoroethylene composite nanofiltration membrane comprises the following steps:
s1, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution with the concentration of 0.5wt%, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 20min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s2, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution, wherein the mass concentration percentage of the triethylene tetramine in the aqueous phase solution is 2.5%, the mass concentration percentage of the sodium dodecyl sulfate is 0.05%, and the mass concentration percentage of the triethylamine is 0.5%; immersing a hydrophilic polytetrafluoroethylene microporous membrane into the aqueous phase solution for 30min to obtain an intermediate membrane body;
s3, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution with the mass concentration of 0.6%, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction for 4min at room temperature to obtain a nascent state polytetrafluoroethylene composite nanofiltration membrane;
s4, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction at 70 ℃ for 20min, taking out, and cooling at room temperature to obtain the nano-composite polytetrafluoroethylene nanofiltration membrane.
Comparative example 2
Comparative example 2 the preparation method of the polytetrafluoroethylene composite nanofiltration membrane comprises the following steps:
s1, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution with the concentration of 0.5wt%, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 20min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s2, preparing a modified polytetrafluoroethylene microporous membrane:
adding butyl titanate into absolute ethyl alcohol, and uniformly stirring and mixing to obtain a butyl titanate solution with the mass concentration of 6.0%; adding glacial acetic acid and distilled water into absolute ethyl alcohol, uniformly stirring to obtain a mixed solution, wherein the volume ratio of the glacial acetic acid to the distilled water to the absolute ethyl alcohol is 1:3:8, dropwise adding a hydrochloric acid solution to adjust the pH value to 3, immersing a hydrophilic polytetrafluoroethylene microporous membrane into the mixed solution according to the bath ratio of 1:30, then dropwise adding a butyl titanate solution into the mixed solution, wherein the volume ratio of the butyl titanate solution to the mixed solution is 1:2, uniformly stirring, heating in a water bath to 55 ℃, carrying out heat preservation reaction for 2 hours, standing for 8 hours, taking out, and placing in an oven to carry out drying treatment for 1 hour at 60 ℃ to obtain a modified polytetrafluoroethylene microporous membrane;
s3, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution, wherein the mass concentration percentage of the triethylene tetramine in the aqueous phase solution is 2.5%, the mass concentration percentage of the sodium dodecyl sulfate is 0.05%, and the mass concentration percentage of the triethylamine is 0.5%; immersing the modified polytetrafluoroethylene microporous membrane into the aqueous phase solution for 30min to obtain an intermediate membrane body;
s4, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution with the mass concentration of 0.6%, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction for 4min at room temperature to obtain a nascent state polytetrafluoroethylene composite nanofiltration membrane;
s5, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction at 70 ℃ for 20min, taking out, and cooling at room temperature to obtain the nano-composite polytetrafluoroethylene nanofiltration membrane.
And (3) performance testing:
1. respectively preparing a magnesium sulfate aqueous solution with the concentration of 1g/L and a sodium chloride solution with the concentration of 1g/L, using the magnesium sulfate solution and the sodium chloride solution as to-be-detected solutions, and testing the interception performance of the composite nanofiltration membrane on the magnesium sulfate and the sodium chloride by adopting a membrane performance evaluation device under the test conditions of water pressure of 0.3MPa and temperature of 25 ℃. And (3) collecting filtrate after the membrane performance evaluation device operates for 30min, measuring the volume of the penetrating fluid and the ion concentration of the penetrating fluid collected in unit time, and then calculating the ion rejection rate and the penetration flux of the composite nanofiltration membrane, wherein the test results are shown in table 1. The retention and permeation flux were calculated as follows:
R＝(1-Cp/Cf) X is 100%; wherein R represents a retention rate (%), CpDenotes the permeate mass concentration (g/L), CfRepresents the mass concentration (g/L) of the feed liquid. J is V/At; wherein J represents a permeation flux L/m2h, V denotes the volume of permeate collected (L), A denotes the effective area of the membrane (m)2) And t represents the permeation time (h).
TABLE [ 1 ]
2. Respectively preparing a magnesium sulfate aqueous solution with the concentration of 1g/L and a sodium chloride solution with the concentration of 1g/L, using the magnesium sulfate solution and the sodium chloride solution as to-be-detected solutions, and testing the interception performance of the composite nanofiltration membrane on the magnesium sulfate and the sodium chloride by adopting a membrane performance evaluation device under the test conditions of water pressure of 0.3MPa and temperature of 25 ℃. And (3) collecting filtrate after the membrane performance evaluation device operates for 48 hours, measuring the volume of the penetrating fluid and the ion concentration of the penetrating fluid collected in unit time, and then calculating the ion rejection rate and the penetration flux of the composite nanofiltration membrane, wherein the test results are shown in table 2.
TABLE [ 2 ]
The results of the tests show that the polytetrafluoroethylene composite nanofiltration membrane prepared by the embodiment of the invention has the magnesium sulfate rejection rate of more than 98% and the sodium chloride rejection rate of more than 86%, and the polytetrafluoroethylene composite nanofiltration membrane has excellent ion interception and separation effects. Compared with the polytetrafluoroethylene composite nanofiltration membrane in the embodiment, the composite nanofiltration membrane in the comparative example 1 has poorer retention performance and stability on salt solution, and the retention rate of the composite nanofiltration membrane in the comparative example 1 on ions of the salt solution after 48 hours of filtration operation is greatly reduced, so that the invention proves that the lasting stability of the polytetrafluoroethylene composite nanofiltration membrane on the retention of the ions of the salt solution can be obviously improved by filling the gaps and holes of the polytetrafluoroethylene membrane with silicon dioxide colloid particles. The permeation flux of the comparative example 2 is always at a lower level compared with that of the example, because the pores of the polytetrafluoroethylene microporous membrane are blocked by the silica colloid particles, the water flux of the composite nanofiltration membrane can be obviously improved by mixing the chitosan microspheres among the silica colloid particles.
The above embodiments are merely some examples of the individual experiments selected in the present invention, and are not limited to the above embodiments, and various modifications can be appropriately made within a certain range. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.
Claims (8)
1. A preparation method of a heat-resistant condensation polymerization tetrafluoroethylene composite nanofiltration membrane is characterized by comprising the following steps:
s1, preparing chitosan microspheres:
adding chitosan into an acetic acid solution, and dissolving by magnetic stirring to obtain a chitosan solution; uniformly mixing and stirring liquid paraffin and span 80 to obtain an oil phase solution, dripping a chitosan solution into the oil phase solution, heating to 40-50 ℃, emulsifying for 20-40min by magnetic stirring, then adding a glutaraldehyde crosslinking agent for crosslinking reaction for 2-3h, and carrying out suction filtration, washing and drying to obtain chitosan microspheres;
s2, activating a hydrophobic polytetrafluoroethylene microporous membrane:
adding sodium dodecyl benzene sulfonate into deionized water, stirring and dissolving to prepare a sodium dodecyl benzene sulfonate solution, completely immersing the hydrophobic polytetrafluoroethylene microporous membrane into the sodium dodecyl benzene sulfonate solution, soaking for 20-50min, taking out, and then placing in the air for drying to obtain a hydrophilic polytetrafluoroethylene microporous membrane;
s3, preparing a modified polytetrafluoroethylene microporous membrane:
adding butyl titanate into absolute ethyl alcohol, and uniformly stirring and mixing to obtain a butyl titanate solution; adding glacial acetic acid and distilled water into absolute ethyl alcohol, uniformly stirring, dropwise adding a hydrochloric acid solution to adjust the pH to 2-3, then adding chitosan microspheres, uniformly dispersing the chitosan microspheres in the solution by ultrasonic oscillation to obtain a suspension, immersing a hydrophilic polytetrafluoroethylene microporous membrane into the suspension, then dropwise adding a butyl titanate solution into the suspension, uniformly stirring, heating in a water bath to 45-55 ℃, carrying out heat preservation reaction for 2-5h, standing for 5-10h, taking out, and then placing in an oven for drying treatment to obtain a modified polytetrafluoroethylene microporous membrane;
s4, dipping in aqueous phase solution: adding triethylene tetramine into deionized water, stirring and dissolving to prepare a triethylene tetramine solution, adding sodium dodecyl sulfate and triethylamine into the triethylene tetramine solution, and stirring and mixing uniformly to obtain an aqueous phase solution; immersing the modified polytetrafluoroethylene microporous membrane into the aqueous phase solution for 10-30min to obtain an intermediate membrane body;
s5, soaking in organic phase solution: adding trimesoyl chloride into a normal hexane solvent, stirring and dissolving to prepare a trimesoyl chloride solution, immersing an intermediate membrane body into the trimesoyl chloride solution, and carrying out interfacial polymerization reaction at room temperature to obtain a nascent-state polytetrafluoroethylene composite nanofiltration membrane;
s6, thermal curing and crosslinking: and (3) placing the nascent state polytetrafluoroethylene composite nanofiltration membrane in an oven for curing and crosslinking reaction, taking out the nascent state polytetrafluoroethylene composite nanofiltration membrane, and cooling the nascent state polytetrafluoroethylene composite nanofiltration membrane at room temperature to obtain the nano-porous polytetrafluoroethylene composite nanofiltration membrane.
2. The method for preparing the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane according to claim 1, wherein the glutaraldehyde crosslinking agent is added in an amount of 5.0wt% of the chitosan in the step S1.
3. The method for preparing a heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane according to claim 1, wherein the concentration of the sodium dodecyl benzene sulfonate solution in the step S2 is 0.1-0.5 wt%.
4. The preparation method of the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane according to claim 1, wherein the mass ratio of the butyl titanate to the chitosan microspheres in the step S3 is 1: 0.2-0.5.
5. The method for preparing the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane according to claim 1, wherein the mass concentration percentage of triethylene tetramine in the aqueous solution in the step S4 is 1.0-3.0%.
6. The method for preparing a heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane according to claim 1, wherein the concentration of the trimesoyl chloride solution in the step S5 is 0.2-0.8 wt%.
7. The preparation method of the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane according to claim 1, wherein the interfacial polymerization reaction time in the step S5 is 2-5 min.
8. The preparation method of the heat-resistant polycondensation tetrafluoroethylene composite nanofiltration membrane according to claim 1, wherein the crosslinking curing reaction temperature in the step S6 is 50-70 ℃, and the crosslinking curing reaction time is 20-30 min.
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