CN117379997A - Preparation method of polyimide-based organic silicon composite membrane for dehydrating pervaporation isopropanol - Google Patents
Preparation method of polyimide-based organic silicon composite membrane for dehydrating pervaporation isopropanol Download PDFInfo
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- 239000004642 Polyimide Substances 0.000 title claims abstract description 70
- 229920001721 polyimide Polymers 0.000 title claims abstract description 70
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 title claims abstract description 61
- 239000012528 membrane Substances 0.000 title claims abstract description 56
- 239000002131 composite material Substances 0.000 title claims abstract description 39
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 28
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 28
- 239000010703 silicon Substances 0.000 title claims abstract description 28
- 238000002360 preparation method Methods 0.000 title claims abstract description 27
- 238000005373 pervaporation Methods 0.000 title claims abstract description 21
- 238000005507 spraying Methods 0.000 claims abstract description 55
- 239000000758 substrate Substances 0.000 claims abstract description 38
- 239000007788 liquid Substances 0.000 claims abstract description 30
- 239000002904 solvent Substances 0.000 claims abstract description 26
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 23
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims abstract description 20
- 238000005266 casting Methods 0.000 claims abstract description 15
- 238000000108 ultra-filtration Methods 0.000 claims abstract description 14
- 239000004745 nonwoven fabric Substances 0.000 claims abstract description 7
- 238000007790 scraping Methods 0.000 claims abstract description 4
- 238000000034 method Methods 0.000 claims description 18
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 15
- 238000010438 heat treatment Methods 0.000 claims description 15
- 230000018044 dehydration Effects 0.000 claims description 13
- 238000006297 dehydration reaction Methods 0.000 claims description 13
- 239000008367 deionised water Substances 0.000 claims description 11
- 229910021641 deionized water Inorganic materials 0.000 claims description 11
- 229920001296 polysiloxane Polymers 0.000 claims description 11
- 239000002994 raw material Substances 0.000 claims description 8
- 239000003054 catalyst Substances 0.000 claims description 6
- 239000000178 monomer Substances 0.000 claims description 6
- 238000003756 stirring Methods 0.000 claims description 6
- 238000006243 chemical reaction Methods 0.000 claims description 5
- 238000002156 mixing Methods 0.000 claims description 5
- 239000003921 oil Substances 0.000 claims description 5
- 238000001291 vacuum drying Methods 0.000 claims description 4
- 238000005345 coagulation Methods 0.000 claims description 3
- 230000015271 coagulation Effects 0.000 claims description 3
- 239000011521 glass Substances 0.000 claims description 3
- 229920000728 polyester Polymers 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 2
- 238000007789 sealing Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 1
- 230000000694 effects Effects 0.000 abstract description 26
- 239000002699 waste material Substances 0.000 abstract description 4
- 230000015572 biosynthetic process Effects 0.000 abstract description 3
- 239000000463 material Substances 0.000 abstract description 3
- 238000004544 sputter deposition Methods 0.000 abstract description 2
- 238000001035 drying Methods 0.000 abstract 1
- 238000013007 heat curing Methods 0.000 abstract 1
- 238000000926 separation method Methods 0.000 description 23
- 239000010410 layer Substances 0.000 description 22
- 230000004907 flux Effects 0.000 description 15
- 239000007921 spray Substances 0.000 description 11
- 239000002346 layers by function Substances 0.000 description 9
- 238000001878 scanning electron micrograph Methods 0.000 description 9
- 238000000576 coating method Methods 0.000 description 6
- 230000007547 defect Effects 0.000 description 5
- 238000000151 deposition Methods 0.000 description 4
- 230000008021 deposition Effects 0.000 description 4
- 239000011148 porous material Substances 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 238000004528 spin coating Methods 0.000 description 3
- 230000008093 supporting effect Effects 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 239000002390 adhesive tape Substances 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 238000005234 chemical deposition Methods 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 125000000962 organic group Chemical group 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 229920001558 organosilicon polymer Polymers 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 238000000614 phase inversion technique Methods 0.000 description 1
- 229920000307 polymer substrate Polymers 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 1
- 238000009718 spray deposition Methods 0.000 description 1
- 238000012876 topography Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
- B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
- B01D71/64—Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0011—Casting solutions therefor
- B01D67/00113—Pretreatment of the casting solutions, e.g. thermal treatment or ageing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0013—Casting processes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0083—Thermal after-treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
- B01D69/122—Separate manufacturing of ultra-thin membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
- C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
- C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
- C07C29/78—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by condensation or crystallisation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/26—Spraying processes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/56—Use of ultrasound
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- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Dispersion Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Crystallography & Structural Chemistry (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention provides a preparation method of a polyimide-based organic silicon composite membrane for dehydrating pervaporation isopropanol, and belongs to the technical field of organic silicon composite membranes. The preparation method comprises the steps of preparing polyimide casting solution by polyimide and N, N-dimethylformamide, pouring the polyimide casting solution on non-woven fabrics, scraping the film, performing phase inversion to obtain a porous polyimide ultrafiltration film, drying to obtain a porous polyimide base film, and spraying organosilicon sol on the surface of the porous polyimide base film by adopting an ultrasonic spraying method to perform heat curing treatment to obtain the polyimide base organosilicon composite film. According to the invention, ultrasonic spraying is adopted, liquid is lightly coated on the surface of the substrate, the sputtering rebound phenomenon does not occur, the uniformity of film formation is easier to control, the material waste can be reduced, and the organosilicon sol is a double-solvent system of isopropanol and water, so that a uniform and complete organosilicon active layer is formed on the surface of the substrate through the Malagony effect, and finally, the ultrathin, uniform and defect-free preparation of the microporous organosilicon active layer is realized.
Description
Technical Field
The invention relates to the technical field of organic silicon composite films, in particular to a preparation method of a polyimide-based organic silicon composite film for dehydrating pervaporation isopropanol.
Background
The preparation processes of the organic silicon composite film reported at present comprise a hot coating method, a spin coating method, a liquid flow method, a spraying method, a thermal plasma chemical deposition method and the like. Wherein, the support used for preparing the film by the hot coating method is almost all Al 2 O 3 The application of the method is limited by complex preparation process, poor repeatability and high preparation cost of the inorganic materials; the spin coating method has certain requirements on the affinity of the support body and sol, the surface smoothness and the size and shape of the base film, so that the spin coating method is limited to the preparation research of the organic silicon film in the laboratory range; the thickness of the BTESE layer is difficult to regulate and control by a liquid flow method membrane preparation method, and the experimental repeatability is poor; in the sol-gel spraying method, due to the existence of air flow, sol droplets are sputtered to the periphery when falling on a substrate, so that the difficulty of controlling the uniformity of a functional layer is high, and unnecessary raw material waste is generated; the thermal plasma chemical vapor deposition method has the advantages that organic groups in the organic silicon network are easy to decompose, so that the separation performance of the membrane is reduced.
Disclosure of Invention
In view of the above, the present invention provides a method for preparing a polyimide-based organosilicon composite membrane for dehydration of pervaporation isopropanol, which utilizes a fine ultrasonic spraying method (ultrasonic atomization and spray deposition) to lightly deposit an ultralow-viscosity organosilicon sol on the surface of a polyimide substrate, and the prepared organosilicon layer is uniform and complete and has adjustable thickness, and can reduce raw material waste compared with the conventional spraying method.
The preparation method of the polyimide-based organic silicon composite membrane (XP 84-BTESE membrane) for dehydrating pervaporation isopropanol provided by the invention comprises the following steps:
(1) Preparation of polyimide casting solution: vacuum drying polyimide, fully removing residual moisture in the raw materials, mixing with N, N-dimethylformamide, sealing, placing in an oil bath pot, heating and stirring at 50 ℃ in an oil bath until the polyimide is completely dissolved to obtain polyimide casting film liquid, and placing in a dryer for overnight removal of bubbles;
(2) Preparation of a porous polyimide ultrafiltration membrane: under the condition of constant temperature and constant humidity, flattening and fixing the polyester non-woven fabric on a clean glass plate, slowly pouring the polyimide casting solution with bubbles removed in the step (1) above the non-woven fabric, scraping the film, immediately immersing the scraped film in a pure water coagulation bath at 21 ℃ for 20min to finish phase conversion, transferring the film into clean deionized water, immersing for 1h, and fully removing residual casting solution solvent in the film to obtain a porous polyimide ultrafiltration film with smooth and flawless surface;
(3) Preparation of a porous polyimide base film: fixing the porous polyimide ultrafiltration membrane prepared in the step (2), and placing the porous polyimide ultrafiltration membrane in an oven for heat treatment to obtain the porous polyimide base membrane (XP 84 base membrane);
(4) Preparation of porous polyimide-based organic silicon composite film: fixing the porous polyimide base film prepared in the step (3), adopting an ultrasonic spraying method, setting the spraying flow to be 0.3-0.5mL/min, spraying the organosilicon sol on the surface of the porous polyimide base film at the substrate temperature of 30-70 ℃, repeating the ultrasonic spraying step after the solvent is completely volatilized, and thermally curing the composite film at the temperature of 150-200 ℃ for 10min after spraying for 1-3 times to obtain the polyimide base organosilicon composite film.
Preferably, the polyimide in the step (1) is dried in vacuum at 110-130 ℃ for 10-15 h.
Preferably, the mass ratio of the polyimide in the step (1) to the N, N-dimethylformamide is 20-25: 70-80.
Preferably, the constant temperature and humidity conditions in the step (2) are as follows: the ambient temperature was 21℃and the ambient humidity was 20RH%.
Preferably, the thickness of the scratch film in the step (2) is 250 μm.
Preferably, the temperature of the heat treatment in the step (3) is 150-200 ℃, and the time of the heat treatment is 10-15 min.
Preferably, in the step (4), the organosilicon sol is prepared by mixing silsesquioxane monomer with isopropanol, adding deionized water and hydrochloric acid catalyst under the condition of continuous stirring, heating in a water bath, and completing the reaction.
More preferably, the ratio of isopropanol to deionized water in the organic silicon sol is 73-82:9-18; the concentration of sol in the organic silicon sol is 5.0wt%; the molar ratio of HCl to silsesquioxane monomer in the hydrochloric acid catalyst is 0.01:1.
Preferably, in the ultrasonic spraying in the step (4), the spraying parameters are set as follows: the spraying height is 60mm, the left and right speed is 10000mm/min, the front and back steps are 2mm, the front and back speed is 10000mm/min, and the left and right stroke is 110mm.
Compared with the prior art, the invention has the following beneficial effects: the invention provides a preparation method of polyimide-based organic silicon composite film for dehydrating pervaporation isopropanol, which adopts ultrasonic spraying, liquid is lightly coated on the surface of a substrate, the sputtering rebound phenomenon can not occur, the uniformity of film formation is easier to control, and the waste of materials can be reduced. In addition, the organosilicon sol is a double-solvent system of isopropyl alcohol and water, and the marangoni effect of the double-solvent system is beneficial to forming a uniform and complete organosilicon active layer on a substrate.
Drawings
FIG. 1 is a SEM image of the surface and cross-section of XP84-BTESE film prepared in examples 1, 2 and 3;
FIG. 2 shows the different binary solvents (IPA +.H 2 O) PV performance diagram of XP84-BTESE film prepared in proportion;
FIG. 3 is a SEM image of the surface and cross-section of XP84-BTESE film prepared in examples 1, 4, 5;
FIG. 4 is a graph of the PV performance of XP84-BTESE films prepared from different substrate temperatures for examples 1, 6, and 7;
FIG. 5 is a SEM image of the surface and cross-section of XP84-BTESE film prepared in examples 1, 6 and 7;
FIG. 6 is a graph of PV performance of XP84-BTESE films prepared from different spray flows for examples 1, 8, and 9;
FIG. 7 is a SEM image of the surface and cross-section of XP84-BTESE film prepared in examples 1, 8 and 9.
Detailed Description
The invention is further illustrated below with reference to examples.
Example 1
A preparation method of polyimide-based organic silicon composite membrane (XP 84-BTESE membrane) for dehydrating pervaporation isopropanol comprises the following steps:
(1) Preparation of polyimide casting solution: firstly, the polyimide raw material is dried in vacuum for 12 hours at 120 ℃ to fully remove residual moisture in the raw material. Then 22g of dried polyimide raw material (P84) is taken in a clean blue mouth bottle, 78g of N, N-Dimethylformamide (DMF) is added into the bottle, the blue mouth bottle is screwed in an oil bath pot, heating and stirring are carried out at 50 ℃ until P84 raw material particles are completely dissolved in DMF, a casting solution is obtained, and finally the casting solution is placed in a dryer for overnight removal of bubbles.
(2) Preparation of a porous polyimide ultrafiltration membrane: the porous polyimide ultrafiltration membrane is prepared in a constant temperature and humidity walk-in chamber, and the environment temperature in the walk-in chamber is set to be 21 ℃ and the environment humidity is set to be 20RH%. The preparation method comprises the steps of adopting a phase inversion method to prepare a porous polyimide ultrafiltration membrane, firstly flatly fixing a polyester non-woven fabric on a clean glass plate, then slowly pouring a P84 casting solution above the non-woven fabric, scraping the film to form a film with the thickness of 250 mu m, immediately immersing the scraped film in a pure water coagulation bath at the temperature of 21 ℃ for 20min to finish the phase inversion process, then transferring the film into clean deionized water for immersing for 1h, fully removing residual casting solution solvent in the film, and finally obtaining the porous polyimide ultrafiltration membrane with smooth and flawless surface.
(3) Preparation of XP84 base film: and fixing the porous polyimide ultrafiltration membrane by using a steel plate die, and placing the steel plate die in a baking oven at 150 ℃ for heat treatment for 10min to finally obtain the XP84 base membrane.
(4) Preparation of porous polyimide-based organic silicon composite film: flattening and fixing the XP84 base film on a heating table of ultrasonic spraying equipment by using a transparent adhesive tape, and spraying the organosilicon sol on the surface of the XP84 film by using an ultrasonic spraying method;
the organosilicon sol is prepared by mixing silsesquioxane monomers with isopropanol, heating in a water bath, adding deionized water and a hydrochloric acid catalyst into the mixture under the condition of continuous stirring, and completing the reaction to obtain organosilicon polymer sol; the ratio of isopropanol to deionized water in the organic silicon sol is 73:9; the concentration of sol in the organic silicon sol is 5.0wt%; the molar ratio of HCl to silsesquioxane monomer in the hydrochloric acid catalyst is 0.01:1.
In the ultrasonic spraying, the spraying mode of the ultrasonic spraying equipment is selected to be left and right spraying, and the set spraying parameters are as follows: spraying height: 60mm, speed of left and right: 10000mm/min, step back and forth: 2mm, speed front-back: 10000mm/min, and the left and right strokes are 110mm; and (3) after the solvent in the sol on the surface of the film is completely volatilized, repeating the ultrasonic spraying step, spraying for 3 times, and thermally curing the composite film at 200 ℃ for 10min, and then taking out the composite film to finally obtain the XP84-BTESE film.
Examples 2 to 9
The polyimide-based silicone composite membrane for dehydration of pervaporation isopropanol was prepared by changing the mass ratio of isopropanol and deionized water in the silicone sol in step (4) of example 1, the spray flow rate, the substrate temperature and the number of spray times, and the other steps were the same as in example 1. The specific parameters in examples 1 to 9 are shown in Table 1.
TABLE 1
From the contents of Table 1, examples 1, 2, and 3 investigate the effect of spray number on XP84-BTESE film; examples 1, 4, 5 investigate the effect of mass ratio of isopropanol and deionized water in the organosilicon sol on XP84-BTESE films; examples 1, 6, 7 investigate the effect of substrate temperature on XP84-BTESE films; examples 1, 8, 9 investigate the effect of spray flux on XP84-BTESE film.
SEM images of the surface and cross-section of XP84-BTESE films prepared in examples 1, 2 and 3 are shown in FIG. 1. As can be seen from fig. 1, the surface morphology of the organic silicon functional layer is uniform and complete, the hollow defects in the organic silicon functional layer gradually decrease with the increase of the spraying times, and the hollow defects of the organic silicon functional layer disappear when the spraying times are 3 times. This is because the silicone sol infiltration can compensate for the hollow defect generated by the previous coating during the coating process.
Examples 1, 4, 5 different binary solvents (IPA/H) 2 O) the PV performance of the XP84-BTESE film prepared in the proportion is shown in figure 2. As can be seen from fig. 2, the permeation flux and the separation factor still show the trade-off effect, and when the IPA content in the sol is fixed to 73vol%, the water content in the sol is reduced, the permeation flux of the XP84-BTESE membrane is increased, and the separation factor is decreased. With binary solvents (IPA/H) 2 Compared with sol with the ratio of O) being 73:9, IPA/H 2 XP84-BTESE film prepared from sol with the O volume ratio of 73:18 has unstable performance, and uneven deposition of BTESE layer leads to poor separation effect. The water content in the sol is kept unchanged, and the permeation flux of the XP84-BTESE film is reduced when the IPA content is reduced.
SEM images of the surface and cross-section of XP84-BTESE films prepared in examples 1, 4 and 5 are shown in FIG. 3. As can be seen from FIG. 3, the IPA/H in the sol is observed from the surface topography 2 The surface of the film with the O volume ratio of 73:9 is the most smooth, which shows that the IPA/H 2 The membrane prepared by the O proportion has the best uniformity, and the membrane has the best pervaporation isopropanol dehydration performance, so that the deposition effect of the BTESE layer is verified to have a larger influence on the separation performance of the organic silicon composite membrane. Other binary solvents (IPA/H) 2 The surface of the organosilicon composite film prepared by the sol with the ratio of O) has obvious granular agglomeration.
Examples 1, 6, 7 the PV performance graphs of XP84-BTESE membranes prepared from different substrate temperatures are shown in fig. 4, and it can be seen from fig. 4 that the separation factor and permeation flux of the XP84-BTESE membranes still have a significant trade-off relationship with the change of the substrate temperature, and the permeation flux of the membranes gradually increases and the separation factor gradually decreases with the increase of the substrate temperature. At a substrate temperature of 70 ℃, the sol drops fall on the base and dry rapidly, the drops do not spread to the surrounding area without direct spraying, so that the organosilicon layer has defects, and the separation factor of the XP84-BTESE film is low. When the temperature of the substrate is reduced to 50 ℃, the volatilization time of the solvent in the sol on the surface of the substrate is increased, but the evaporation rate of the solvent is still obviously faster than the flow rate of the liquid, so that the BTESE layer is not uniform and complete enough, and a good separation effect is not achieved. When the temperature is continuously reduced to 30 ℃, the solvent volatilization rate and the liquid fluidity rate of the surface of the substrate reach balance, the liquid drops mutually merge into a complete liquid film, and the sol liquid drops flow to the area which is not directly covered by the liquid drops by means of the Marangoni effect, so that the complete and defect-free BTESE separation layer is obtained. XP84-BTESE film prepared at a substrate temperature of 30℃has the best separation effect.
SEM images of the surface and cross section of XP84-BTESE films prepared in examples 1, 6 and 7 are shown in FIG. 5. As can be seen from FIG. 5, a significant change in the thickness of the BTESE layer with increasing substrate temperature can be observed in the cross section images of the films. The thickness of the BTESE layer was about 730nm at a substrate temperature of 70℃and 400nm and 300nm, respectively, at a reduced substrate temperature of 50℃and 30℃and decreased with a reduced substrate temperature. This is due to the fact that as the substrate temperature changes, so too does the flow rate and volatilization rate of the sol at the substrate surface. At a substrate temperature of 70 ℃, the volatilization rate of the solvent in the sol falling on the surface of the substrate is very fast, the liquid drops do not spread to the periphery, the coverage area of the solute in the sol is small, and the BTESE layer is thicker. When the temperature is reduced to 50 ℃, the volatilization rate of the solvent in the liquid drop is reduced, the time for the liquid drop to diffuse to the surrounding is also increased, and therefore the thickness of the formed BTESE layer is reduced. When the substrate temperature is 30 ℃, the solvent volatilization speed and the flow speed of sol liquid drops reach balance, and a defect-free 300 nm-thick functional layer is formed on the surface of the XP84 base film.
The PV performance graphs of XP84-BTESE films prepared by different spraying flows in examples 1, 8 and 9 are shown in FIG. 6, and as can be seen from FIG. 6, when the spraying flow is lower than 0.3mL/min, the amount of sol falling on the surface of a substrate is too small, fine liquid drops cannot form a complete wet layer, the XP84-BTESE film prepared by the spraying flow of 0.3mL/min has a good separation effect, the separation factor is 950, which indicates that the prepared BTESE functional layer is complete under the flow, so that 0.3mL/min is considered as the minimum threshold of the spraying flow for realizing the pinhole-free coverage of the sol on the substrate. The XP84-BTESE membrane prepared by spraying the flow of 0.4mL/min has the best separation performance, and the flux of 0.49kg/m 2 h, the separation factor increases to 1282, so we speculate that as the spray flux increases, so does the separation factor of the silicone composite membrane. However, when the spray flux was continuously increased to 0.5mL/min, the membrane flux was 0.46kg/m 2 h, separation factor 822. As the spray flow increases, the thickness of the BTESE layer also increases slightly. The organosilicon composite membrane does not show obvious trade-off effect under the three spraying flow rates, and the reason is presumed to be considered from the following two aspects that firstly, the polymer base membrane can shrink during the high-temperature heat treatment, and organosilicon particles penetrating into the porous polymer pore diameter can play a role in supporting the membrane pore, so that the trade-off effect is not obvious due to the mutual balance of the pore diameter shrinkage of the base membrane and the supporting effect of the organosilicon particles in the membrane pore in the spraying flow rate range used by us.
The SEM images of the surface and the cross section of the XP84-BTESE films prepared in examples 1, 8 and 9 are shown in FIG. 7, and as can be seen from the SEM images of the surface, the surface of the organosilicon composite film prepared by 3 spraying flows is very flat and uniform, which shows that the spraying flows have little influence on the surface morphology of the film in the spraying condition range of 0.3-0.5 mL/min. As can be seen from SEM sectional images, the thicknesses of the BTESE layers corresponding to the spray flow rates of 0.3, 0.4 and 0.5mL/min were 200, 300 and 370nm, respectively, and as the spray flow rate increases, the amount of solute falling on the surface of the base film also increases, so the thickness of the BTESE functional layer gradually increases. Although the membrane BTESE layer prepared was the thinnest under spray conditions of 0.3mL/min, the permeation flux of the membrane was not the highest in the pervaporation test. This is probably because although thinner BTESE layers reduce certain mass transfer resistance, polyimide is a polymeric material that has severe shrinkage cavity during high temperature curing and the base membrane has a large impact on permeation flux. And the XP84 film is a porous film, part of organic silica sol can downwards permeate into the aperture of the base film in the spraying process, and when the BTESE layer is cured at a high temperature of 200 ℃, organic silica particles permeated into the aperture of the base film can play a role in supporting film holes, so that the shrinkage effect of the base film is reduced, and therefore, the XP84-BTESE film does not show obvious track-off effect.
IPA/Water dehydration performance test of XP84-BTESE films prepared in examples 1 to 9 was as follows: the 90wt% aqueous isopropanol solution was subjected to pervaporation dehydration test at 60 ℃ and the results are shown in table 2:
TABLE 2
| Flux [ kg/m ] 2 h] | Separation factor | |
| Example 1 | 0.45 | 1282 |
| Example 2 | 0.67 | 767 |
| Example 3 | 0.71 | 726 |
| Example 4 | 0.6 | 209 |
| Example 5 | 0.71 | 140 |
| Example 6 | 1.2 | 111 |
| Example 7 | 1.34 | 94 |
| Example 8 | 0.39 | 950 |
| Example 9 | 0.46 | 822 |
From the contents of fig. 1-7 and tables 1-2, the following conclusions can be drawn:
when the spraying times are increased, the lower penetration of the sol can make up the tiny defect of the upper layer, the film forming effect is better by properly increasing the coating times, but the thickness of the organic silicon functional layer is increased along with the increase of the spraying times, the mass transfer resistance is increased, the penetration flux of the composite film is reduced, the organic silicon layer is easy to crack when the thickness is overlarge, and when the spraying times are 3 times, the film forming effect is optimal.
Binary solvent (IPA/H) in organosilicon sol 2 Influence of O) ratio on deposition effect of BTESE functional layerImportantly, the organosilicon sol has ultralow viscosity, so that the organosilicon sol has great difficulty in realizing large-area uniform deposition of an organosilicon functional layer on a polymer substrate, the surface tension of liquid is required to be reduced in a coating technology, the spreadability of the sol on the surface of the substrate is better, the substrate is completely covered by the organosilicon sol because of the requirement of a smaller volume of liquid, and the solvent in the liquid volatilizes more uniformly. The invention adopts a double-solvent system of water and organic solvent, the Marangoni effect of the double-solvent system also plays a role in promoting the formation of a uniform and complete liquid film, the Marangoni effect is utilized to enable the liquid to be diffused to an area which is not directly covered by liquid drops, and the main factors influencing the Marangoni linear velocity are surface tension, the volume fraction of low-surface tension liquid, the volatilization speed of binary solvent and the like. IPA/H 2 The organic silicon composite membrane prepared by the sol with the O volume ratio of 73:9 has the best separation effect.
The substrate temperature affects both the liquid rheological property of the organosilicon sol falling on the surface of the base film and the volatilization rate of the solvent in the sol, and is important to the influence of the BTESE layer film effect, so that the substrate temperature is also an important factor affecting the separation effect of the organosilicon composite film. When the substrate temperature is 30 ℃, the solvent volatilization rate and the liquid fluidity rate of the substrate surface reach balance, the liquid drops mutually merge into a complete liquid film, and the sol liquid drops flow to the area which is not directly covered by the liquid drops by means of the Marangoni effect, so that the complete and defect-free BTESE separation layer is obtained.
In order to realize complete pinhole-free coverage of the sol on the surface of the substrate, a minimum threshold of spraying flow for realizing complete coverage of the sol on the XP84 base film needs to be explored, and experiments prove that 0.3mL/min is the minimum threshold of spraying flow for realizing pinhole-free coverage of the sol on the substrate. The XP84-BTESE membrane prepared by spraying the flow of 0.4mL/min has the best separation performance, and the flux of 0.49kg/m 2 h, the separation factor is 1282.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (9)
1. A method for preparing a polyimide-based organic silicon composite membrane for dehydrating pervaporation isopropanol, which is characterized by comprising the following steps:
(1) Preparation of polyimide casting solution: vacuum drying polyimide, fully removing residual moisture in the raw materials, mixing with N, N-dimethylformamide, sealing, placing in an oil bath pot, heating and stirring at 50 ℃ in an oil bath until the polyimide is completely dissolved to obtain polyimide casting film liquid, and placing in a dryer for overnight removal of bubbles;
(2) Preparation of a porous polyimide ultrafiltration membrane: under the condition of constant temperature and constant humidity, flattening and fixing the polyester non-woven fabric on a clean glass plate, slowly pouring the polyimide casting solution with bubbles removed in the step (1) above the non-woven fabric, scraping the film, immediately immersing the scraped film in a pure water coagulation bath at 21 ℃ for 20min to finish phase conversion, transferring the film into clean deionized water, immersing for 1h, and fully removing residual casting solution solvent in the film to obtain a porous polyimide ultrafiltration film with smooth and flawless surface;
(3) Preparation of a porous polyimide base film: fixing the porous polyimide ultrafiltration membrane prepared in the step (2), and placing the porous polyimide ultrafiltration membrane in an oven for heat treatment to obtain the porous polyimide base membrane;
(4) Preparation of porous polyimide-based organic silicon composite film: fixing the porous polyimide base film prepared in the step (3), adopting an ultrasonic spraying method, setting the spraying flow to be 0.3-0.5mL/min, spraying the organosilicon sol on the surface of the porous polyimide base film at the substrate temperature of 30-70 ℃, repeating the ultrasonic spraying step after the solvent is completely volatilized, and thermally curing the composite film at the temperature of 150-200 ℃ for 10min after spraying for 1-3 times to obtain the polyimide base organosilicon composite film.
2. The method for preparing a polyimide-based silicone composite membrane for pervaporation isopropanol dehydration according to claim 1, wherein the polyimide vacuum drying in step (1) is vacuum drying at 110 to 130 ℃ for 10 to 15 hours.
3. The method for preparing a polyimide-based organosilicon composite membrane for pervaporation isopropanol dehydration according to claim 1, wherein the mass ratio of polyimide to N, N-dimethylformamide in the step (1) is 20-25: 70-80.
4. The method for preparing a polyimide-based silicone composite membrane for pervaporation isopropanol dehydration according to claim 1, wherein the conditions of constant temperature and humidity in step (2) are: the ambient temperature was 21℃and the ambient humidity was 20RH%.
5. The method for producing a polyimide-based silicone composite membrane for pervaporation isopropanol dehydration according to claim 1, wherein the thickness of the doctor film in step (2) is 250 μm.
6. The method for preparing a polyimide-based silicone composite membrane for dehydration of pervaporation isopropanol according to claim 1, wherein the temperature of the heat treatment in the step (3) is 150 to 200 ℃, and the time of the heat treatment is 10 to 15 minutes.
7. The method for preparing polyimide-based organosilicon composite membrane for pervaporation isopropanol dehydration according to claim 1, wherein the organosilicon sol in step (4) is obtained by mixing silsesquioxane monomer with isopropanol, adding deionized water and hydrochloric acid catalyst into the mixture under continuous stirring, heating in water bath, and completing the reaction.
8. The method for preparing a polyimide-based silicone composite membrane for pervaporation isopropanol dehydration according to claim 7, wherein the ratio of isopropanol to deionized water in the silicone sol is 73-82:9-18; the concentration of sol in the organic silicon sol is 5.0wt%; the molar ratio of HCl to silsesquioxane monomer in the hydrochloric acid catalyst is 0.01:1.
9. The method for preparing polyimide-based silicone composite membrane for pervaporation isopropanol dehydration according to claim 1, wherein in the ultrasonic spraying in the step (4), the spraying parameters are set to be ： The spraying height is 60mm, the left and right speed is 10000mm/min, the front and back steps are 2mm, the front and back speed is 10000mm/min, and the left and right stroke is 110mm.
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