CN114653210B - High-flux pervaporation membrane based on spraying method, and preparation method and application thereof - Google Patents
High-flux pervaporation membrane based on spraying method, and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a high-flux pervaporation membrane based on a spraying method, and a preparation method and application thereof. The compact separation layer of the pervaporation membrane obtained by the invention can prevent hydrated ions with larger kinetic diameters from passing through, and water molecules can directly pass through a continuous mass transfer channel with low diffusion resistance, so that the pervaporation membrane has high salt rejection rate, high water flux and high stability. The composite membrane can be used for desalting high-salinity wastewater treatment, brackish water, seawater desalination and the like and shows excellent wetting and pollution resistance.
Description
Technical Field
The invention belongs to the field of membrane separation water treatment, and particularly relates to a high-flux pervaporation membrane based on a spraying method, and a preparation method and application thereof.
Background
Compared with membrane separation technologies such as membrane distillation and forward osmosis, pervaporation has excellent wetting resistance and scaling resistance in the desalting process. The pervaporation technology is a promising desalination technology, the pervaporation membrane material is a key component in the separation process, and the water flux, the salt rejection rate and the stability are important indexes for measuring the performance of the membrane material. However, the current commercial membrane has the problems of low water flux, low salt rejection rate and poor stability, and the single hydrophilic and hydrophobic property greatly limits the application range. In order to solve the above problems, it is highly desirable to prepare a pervaporation membrane with high water flux, high salt rejection and high stability.
CN110559886B discloses a PIM-1/Pebax composite pervaporation membrane and a preparation method and application thereof, and is characterized in that: a novel material PIM-1 is mixed into Pebax, two hydrophobic materials are uniformly mixed through a solvent, and the composite membrane is prepared through phase inversion. CN107081068B discloses a pervaporation membrane and a preparation method thereof, which are characterized in that: s1, mixing raw materials including a porous material with the aperture of 0.3-0.5 nm, a polymer, a cross-linking agent, a catalyst and a solvent to form a membrane casting solution; and S2, compounding the base membrane with a polymer to form a cross-linked layer dispersed with a porous material, thereby obtaining the pervaporation membrane. But all the methods use separated organic matters/water as a guide, do not exert the potential of stable and efficient desalination of pervaporation, cannot selectively screen salt ions through a separation layer, and have complex preparation method and poor interface compatibility of the membrane surface.
Disclosure of Invention
Object of the Invention
In order to solve the problem of poor interface compatibility between a commercial membrane and a high polymer material obtained in the prior art, the invention aims to provide a high-flux pervaporation membrane based on a spraying method, a preparation method and application thereof.
The pervaporation membrane prepared by the method has the advantages of one or more two-resistance and three-high resistance, and is multipurpose, anti-wetting, anti-pollution, high in salt rejection rate, high in water flux and high in stability.
Technical scheme
The purpose of the invention is realized by the following technical scheme:
a spray-based high-flux pervaporation membrane comprising, in order: the compact layer is formed on the surface of a transition layer/porous supporting layer composite membrane formed by spraying the transition layer and the porous supporting layer by adopting a spraying method. The transition layer forms an interlocking structure between the hydrophobic layer and the hydrophilic layer, so that the adverse factors restricting the adhesion of the hydrophilic layer and the hydrophobic layer are solved, and the falling-off caused by the swelling of the coating in the pervaporation process is inhibited.
The compact layer is a hydrophilic layer, the thickness F3 is 2-10 mu m, the material is a hydrophilic polymer, and specifically, the hydrophilic polymer comprises any one of local polyvinyl alcohol (PVA), graphene Oxide (GO) and carbon nano tube (TNT). When in use, the hydrophilic polymer is mixed with a cross-linking agent which comprises but is not limited to 4-sulfophthalic acid (SPTA), sulfosuccinic acid (SSA) and Glutaraldehyde (GA) according to a certain proportion to form a spraying liquid.
The porous supporting layer is a hydrophobic layer, and the thickness F1 is 20-200 mu m; specifically, the porous support layer is made of materials including but not limited to Polytetrafluoroethylene (PTFE) microfiltration membranes, nanoporous anodic aluminum oxide membranes (NAAF) and chlorinated polyvinyl chloride (CPVC) ultrafiltration membranes, and the pore diameter is 20-300 nm.
The thickness F2 of the transition layer is 20-200 μm, preferably 20 μm. The material is a low interfacial energy polymer material, including but not limited to any one of polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN) and Polyamide (PA); when in use, the low-interface-energy high-molecular material is dissolved in the following organic solvents, including but not limited to N-methylpyrrolidone (NMP), tetrahydrofuran (THF) and N, N-Dimethylformamide (DMF).
The preparation method of the high-flux pervaporation membrane based on the spraying method comprises the following steps:
firstly, loading a low-interface-energy high polymer material on a porous supporting layer by a non-solvent induced phase conversion method, and forming a porous transition layer with micron-sized thickness on the supporting layer;
then coating the hydrophilic polymer solution on the porous transition layer by a spraying method;
and finally, crosslinking and drying in an oven to obtain the high-flux pervaporation membrane with the mechanical interlocking structure.
Specifically, the method comprises the following steps:
step (1), placing a low interfacial energy polymer material in an organic solvent for ultrasonic dissolution, then fully stirring for 24-48 h, standing for 12-24 h, and removing bubbles to obtain a transition layer membrane casting solution;
the low interfacial energy polymer material includes but is not limited to polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), and Polyamide (PA);
organic solvents include, but are not limited to, N-methylpyrrolidone (NMP), tetrahydrofuran (THF), N-Dimethylformamide (DMF);
the mass ratio of the low-interface-energy high polymer material of the membrane casting solution to the organic solvent is 1:4 to 1:10;
the ultrasonic duration is 15-30 min.
And (2) fixing the porous support layer on a glass plate, pouring a proper amount of membrane casting liquid on the porous support layer to construct a transition layer, and scraping the membrane by using a scraper to control the thickness of the transition layer to be F250-200 mu m. After scraping the membrane, quickly placing the membrane in deionized water at room temperature, soaking for 18-36 h, periodically changing water, and then placing the obtained porous supporting layer/transition layer composite membrane in a vacuum drying oven for drying;
the material of the porous support layer comprises but is not limited to a Polytetrafluoroethylene (PTFE) microfiltration membrane, a nano-porous anodic aluminum oxide membrane (NAAF) and a chlorinated polyvinyl chloride (CPVC) ultrafiltration membrane, and the pore diameter is 20-300 nm:
the dosage of the casting solution is 50-300 mu L/cm 2 ；
The thickness F1 of the porous support layer is 20-200 mu m; the thickness F2 of the transition layer is 20-200 μm; the thickness F3 of the dense layer is 2-10 μm.
The drying temperature is 50-80 ℃, and the drying time is 2.5-5.0 h;
putting a hydrophilic polymer into deionized water, heating in a water bath for 2-4 hours until a uniform solution is formed, sealing, storing and standing for 12-24 hours for defoaming, and then mixing and diluting the hydrophilic polymer and a cross-linking agent according to a certain pure substance mass ratio to form a spraying liquid;
the hydrophilic polymers include, but are not limited to, polyvinyl alcohol (PVA), graphene Oxide (GO), carbon nanotubes (TNT); the concentration of the hydrophilic polymer aqueous solution is 0.5 to 2.0 weight percent;
the water bath heating temperature is controlled to be 75-90 ℃;
crosslinking agents include, but are not limited to, 4-sulfophthalic acid (SPTA), sulfosuccinic acid (SSA), glutaraldehyde (GA);
the mass ratio of the hydrophilic polymer to the pure water solution of the cross-linking agent is 1:5 to 1:1.
and (4) spraying the spraying liquid onto the porous supporting layer/transition layer composite membrane obtained in the step (2) under a certain pressure, constructing a compact layer on the transition layer, and placing the formed hydrophilic polymer @ porous supporting layer/transition layer composite membrane in a vacuum drying oven for crosslinking for 2-4 h after the compact layer is formed, so as to finally form the high-flux pervaporation membrane.
The spraying pressure is 1.0-2.5 bar, the spraying distance is controlled at 8-10 cm, the angle between the spray pen and the film surface is 60-80 degrees, each spraying time is 2-4 s, and the spraying amount is 30-200 mu L/cm 2 。
The drying temperature of the step (4) is 70-100 ℃, and the drying time is 1.5-3.0 h.
The method for calculating the water flux of the membrane obtained in the step (4) is as shown in the formula (1):
J w is the water flux, kg.m -2 H; Δ m is the mass, kg, of the coolant increased per unit time; a is the effective area of the film, m 2 (ii) a T is a time unit, h.
The calculation method of the obtained membrane salt rejection rate is as shown in formula (2):
R s percent is salt cut; c p Is the coolant concentration, ppm; c f In stock solution salt concentration, ppm.
The method for judging the anti-wetting performance of the obtained film is as shown in the formula (3):
R w wetting coefficient,%; sigma i Mu S-cm for coolant conductivity -1 ；σ G Is a special distilled water quality standard three-level standard conductivity value of 5 mu S cm -1 。
If R is w Less than or equal to 1, the anti-wetting performance is better; if R is w >1, the anti-wetting property is poor.
The method for judging the anti-pollution performance of the obtained membrane is as shown in the formula (4):
R p contamination coefficient,%; delta F is the increase of the film thickness of the composite film before and after the test, and is mum; rho is a pollution index, is dimensionless and is 0-5 percent;
the high-flux pervaporation membrane based on the spraying method is applied to the fields of high-salinity wastewater treatment, brackish water, seawater desalination and the like.
(1) Has the beneficial effects that: compared with the prior art, the invention has the advantages that: the high-flux pervaporation membrane is prepared based on a spraying method, the operation is simple, the cost is low, the time consumption is short, the stability is high, the obtained hydrophilic polymer @ porous supporting layer/transition layer pervaporation membrane is prepared, the compact layer is made of the hydrophilic polymer and is a hydrophilic layer, the porous supporting layer is a hydrophobic layer, a transition layer made of a low-interfacial-energy high polymer material is constructed between the hydrophilic polymer @ porous supporting layer and the transition layer, an interlocking structure is formed, the adverse factor that the hydrophilic layer and the hydrophobic layer are adhered is avoided, and the problem that the coating swells and falls off in the pervaporation process is greatly inhibited.
(2) The transition layer is introduced into the porous supporting layer and the compact layer of the pervaporation composite membrane, and the low interface energy material of the transition layer overcomes the contradiction of poor interface compatibility between the compact layer and the supporting layer, so that the composite membrane can be applied to direct contact type pervaporation desalination, and the energy consumption of the pervaporation desalination process is reduced.
(3) The compact layer of the pervaporation composite membrane is made of hydrophilic polymer, can effectively screen macromolecules and hydrated ions, constructs a water molecule single channel, reduces mass transfer resistance, improves water flux, enhances the anti-pollution and anti-wetting capacity of the membrane surface, is superior to the pervaporation membrane used in the prior art, and has wide application prospect in the fields of high-salinity wastewater treatment, brackish water, seawater desalination and the like.
Drawings
FIG. 1 is a schematic diagram of a method for preparing a high flux pervaporation membrane based on a spray coating method;
FIG. 2 is a schematic structural diagram of a high flux pervaporation membrane according to the present invention;
wherein: 1-supporting layer, 2-transition layer, 3-compact layer, 4-water molecule and 5-salt ion;
FIG. 3 is an SEM photograph of the high-flux pervaporation membrane obtained in example 1, wherein the scale of (a) is 1 μm and the scale of (b) is 20 μm, showing that the pervaporation membrane obtained in this example has a dense PVA layer formed on the surface, and the appearance is smooth, flat and uniform.
FIG. 4 is a graph showing the effect of different cross-linking ratios of PVA to STPA on the results in example 4.
Detailed Description
The present invention will be described in detail below with reference to specific examples, but the present invention is not limited to the following examples, and various modifications and implementations are included within the technical scope of the present invention without departing from the content and scope of the present invention.
In the embodiment of the invention, a multi-factor response relation is comprehensively considered, and a mass transfer path and a crosslinking degree are used as main influence factors of the water flux of the pervaporation membrane, so that the thickness F2 of the transition layer and the crosslinking ratio are used as main variables.
The commercial membrane used as a control in the example of the invention is a hydrophobic PTFE microfiltration membrane with a membrane thickness of 50 μm and a pore size of 220nm, and is purchased from Taobao filter material dealers.
Example 1
A high flux pervaporation membrane based on a spraying method is prepared by the following steps:
and (1) putting 20g of PVDF into 100ml of NMP, carrying out ultrasonic treatment for 15min to dissolve the PVDF, then fully stirring for 24h, standing for 12h, and removing bubbles to obtain a transition layer membrane casting solution.
And (2) fixing the PTFE hydrophobic microfiltration membrane with the thickness F1 of 50 microns and the pore diameter of 220nm on a glass plate, pouring 6ml of membrane casting solution on the PTFE hydrophobic microfiltration membrane, and scraping the membrane by using a scraper, wherein the thickness F2 of the transition layer is controlled to be 50 microns. After scraping the membrane, quickly placing the membrane in deionized water at room temperature, soaking for 20h, periodically changing water, then placing the membrane in a vacuum drying oven at 80 ℃ for drying for 2.5h to obtain a membrane with an effective area of 20cm 2 The PVDF/PTFE composite membrane of (1).
And (3) dissolving 2g of hydrophilic polymer PVA in 98ml of deionized water, heating in a water bath at 90 ℃ for 4h until a uniform solution is formed, sealing, storing and standing for 12h for defoaming, and then mixing with a cross-linking agent STPA according to a pure mass ratio of 2:5 mixing and diluting to 0.75wt% aqueous PVA solution to form a spray.
And (4) as shown in figure 1, spraying the spraying liquid onto the PVDF/PTFE composite membrane obtained in the step (2) under the pressure of 2.5bar, wherein the spraying distance is 10cm, a spray pen and the membrane surface form 80 degrees, the spraying amount is 8.5ml after each spraying, and after the spraying is finished, placing the PVA @ PVDF/PTFE composite membrane into a vacuum drying box for crosslinking for 2 hours at the temperature of 100 ℃ to finally form a pervaporation membrane with the thickness F3 of a compact layer being 2 microns, as shown in figure 3.
Tested, examplesWater flux J with the resulting and commercial membranes w Salt rejection rate R s Wet coefficient R w Contamination coefficient R p As shown in table 1:
table 1 comparison of pervaporation membranes obtained in example 1 with commercial membranes
| Group of | J w /kg·m -2 ·h | R s /％ | R w /％ | R p /％ |
| Pervaporation membrane | 28.2 | 99.9 | 0.9 | 4.9 |
| Commercial film | 27.0 | 97.2 | 2.5 | 9.5 |
The results show that a 50 μm transition layer pervaporation membrane has a water flux J compared to a commercial membrane w Salt rejection rate R s Has no obvious promotion, but due to the existence of the compact layer and the transition layer, the anti-wetting and anti-pollution performance of the pervaporation membraneIs obviously improved. Thus, the pervaporation membranes obtained in example 1 all performed better than the commercial membranes.
Example 2
On the basis of example 1, the preparation of the PVDF/PTFE composite membrane in step (2) was changed, the amount of the cast membrane liquid was changed, the thickness of the transition layer was further changed, and the influence of the different thicknesses of the transition layer on the performance of the obtained pervaporation membrane was examined:
group 1: the film casting solution amount is 6ml, and the thickness of the transition layer is 50 mu m;
group 2: the liquid volume of the casting film is 3ml, and the thickness of the transition layer is 25 μm;
group 3: the liquid casting solution amount is 2.4ml, and the thickness of the transition layer is 20 mu m;
group 4: the amount of the casting solution was 0ml, and the thickness of the transition layer was 0 μm.
The water flux J of the obtained pervaporation membrane is tested w Salt rejection rate R s Wetting coefficient R w Contamination coefficient R p As shown in Table 2, it is shown that the mass transfer resistance of the transition layer is reduced, the mass transfer path of water molecules is reduced, the water-soluble efficiency of the water molecules and the PVA layer is improved, the retention time of potential pollutants on the surface of the membrane is reduced, the water flux and the anti-wetting and anti-pollution performance are further improved, and the optimal thickness of the transition layer is 20 μm as the thicknesses of the transition layers are sequentially reduced.
Table 2 example 2 comparison of pervaporation membranes to commercial membrane performance
| Group of | J w /kg·m -2 ·h | R s /％ | R w /％ | R p / |
| Group | ||||
| 1 | 28.2 | 99.9 | 0.9 | 4.9 |
| |
47.8 | 99.9 | 0.7 | 4.2 |
| |
72.4 | 99.9 | 0.2 | 2.2 |
| Group 4 | 27.4 | 99.3 | 2.4 | 5.6 |
| Commercial film | 27.0 | 97.2 | 2.5 | 9.5 |
Example 3
On the basis of example 1, the crosslinking ratio of PVA to STPA in step (3) was changed, the influence of the crosslinking ratio on the flux of the pervaporation membrane was examined, and the field verification was performed by setting 1 control group and 3 test groups.
The control group was a commercial film and the test group included a PVA to STPA crosslinking ratio of 1:1. 3: 5. 1:5, the results are shown in FIG. 4, and it can be seen that as the ratio of PVA to STPA cross-linking decreases from 1:1, the flux of the pervaporation membrane is the highest and reaches 73.6LMH; the anti-wetting performance is optimal, and the wetting phenomenon does not occur after 24 hours of operation. While the overall performance of the pervaporation membrane gradually decreased with decreasing STPA usage, both were superior to the commercial membranes.
Examples 4 to 6
The materials or process parameters adopted in each step are shown in Table 3, and the water flux J of the obtained pervaporation membrane is tested w Salt rejection rate R s Wetting coefficient R w Contamination coefficient R p As shown in table 4.
Table 3 table of materials or process parameters for examples 4-6
TABLE 4 comparison of the properties of the films obtained in examples 4 to 6
| Group of | J w /kg·m -2 ·h | R s /％ | R w /％ | R p /％ |
| Example 4 | 73.9 | 99.9 | 0.4 | 2.3 |
| Example 5 | 72.6 | 99.9 | 0.8 | 2.6 |
| Example 6 | 74.5 | 99.9 | 0.9 | 2.8 |
| Commercial film | 27.0 | 97.2 | 2.5 | 9.5 |
The results show that the membranes prepared in examples 4-6 by using different low interfacial energy polymer materials, organic solvents, hydrophilic polymers and crosslinking agents can obtain the same excellent high water flux, anti-wetting and anti-pollution performances as the above examples under the conditions of optimal transition layer thickness and crosslinking ratio, and the flux is far greater than that of the existing commercial membranes.
Claims (2)
1. A preparation method of a high-flux pervaporation membrane based on a spraying method is characterized by comprising the following steps:
putting a low-interfacial-energy polymer material into an organic solvent, dissolving the low-interfacial-energy polymer material by ultrasonic waves, fully stirring for 24 to 48h, and standing for 12 to 24h for defoaming to obtain a transition layer casting solution;
the low-interface energy high polymer material is polyvinylidene fluoride;
organic solvents include, but are not limited to, N-methylpyrrolidone, tetrahydrofuran, N-dimethylformamide;
in the casting solution, the mass ratio of the low-interface-energy high polymer material to the organic solvent is 1:4 to 1:10;
the ultrasonic duration is 15 to 30min;
fixing the porous support layer on a glass plate, pouring the casting solution obtained in the step (1) on the porous support layer to construct a transition layer, wherein the thickness of the transition layer is 20-200 mu m, and the transition layer forms an interlocking structure between the hydrophobic layer and the hydrophilic layer, so that adverse factors restricting adhesion of the hydrophilic layer and the hydrophobic layer are solved, and the coating is prevented from falling off due to swelling in a pervaporation process;
placing the obtained membrane in deionized water at room temperature, soaking for 18-36h, changing water regularly, and then placing the obtained porous supporting layer/transition layer composite membrane in a vacuum drying oven for drying;
the porous supporting layer is a hydrophobic layer, the thickness is 20 to 200 mu m, the material is a polytetrafluoroethylene microfiltration membrane, and the pore diameter is 20 to 300nm:
the dosage of the casting solution is 50 to 300 mu L/cm 2 ；
The drying temperature is 50 to 80 ℃, and the drying time is 2.5 to 5.0 hours;
putting a hydrophilic polymer into deionized water, heating in a water bath for 2 to 4 hours until a uniform solution is formed, sealing, preserving and standing for 12 to 24h for defoaming, and then mixing and diluting the hydrophilic polymer with a cross-linking agent in proportion to form a spraying liquid;
the hydrophilic polymer is polyvinyl alcohol; the concentration of the hydrophilic polymer aqueous solution is 0.5 to 2.0wt%;
the water bath heating temperature is controlled to be 75 to 90 ℃;
crosslinking agents include, but are not limited to, 4-sulfophthalic acid, sulfosuccinic acid, glutaraldehyde;
the mass ratio of the hydrophilic polymer to the pure water solution of the cross-linking agent is 1:5 to 1:1;
step (4) spraying a spraying liquid under pressure onto the porous supporting layer/transition layer composite membrane obtained in the step (2), constructing a compact layer on the transition layer, and after finishing, placing the formed hydrophilic polymer @ porous supporting layer/transition layer composite membrane in a vacuum drying oven for crosslinking for 2 to 4 hours to form a high-flux pervaporation membrane; the drying temperature is 70 to 100 ℃, and the drying time is 1.5 to 3.0 hours.
2. The application of the high-flux pervaporation membrane obtained by the preparation method of the high-flux pervaporation membrane based on the spraying method in the fields of high-salt wastewater treatment, brackish water and seawater desalination.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210354873.7A CN114653210B (en) | 2022-04-06 | 2022-04-06 | High-flux pervaporation membrane based on spraying method, and preparation method and application thereof |
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