CN112604514A

CN112604514A - Super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane and preparation method and application thereof

Info

Publication number: CN112604514A
Application number: CN202011284755.0A
Authority: CN
Inventors: 申向; 刘秋菊; 刘鹏
Original assignee: Qujing Normal University
Current assignee: Qujing Normal University
Priority date: 2020-11-17
Filing date: 2020-11-17
Publication date: 2021-04-06
Anticipated expiration: 2040-11-17
Also published as: CN112604514B

Abstract

The invention discloses a super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane and a preparation method and application thereof, wherein the composite membrane is formed by compounding polytetrafluoroethylene particles and a polyvinylidene fluoride membrane; the preparation method comprises the following steps: and (2) standing and defoaming the casting solution dissolved with the polyvinylidene fluoride, dropwise adding the casting solution on a glass plate to scrape a liquid film, immersing the glass plate coated with the liquid film in a coagulating bath dispersed with polytetrafluoroethylene particles to be cured, and preparing the super-hydrophobic polyvinylidene fluoride oil-water separation composite film by an immersion phase conversion method. The super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane provided by the invention has a good separation effect on emulsions such as chloroform, toluene and isooctane, has retention rates higher than 99.8%, has excellent acid and alkali resistance, and can be further developed and used as a separation material for acidic or alkali oil-water mixtures.

Description

Super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane and preparation method and application thereof

Technical Field

The invention relates to the technical field of membranes, and particularly relates to a super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane, and a preparation method and application thereof.

Background

Oily wastewater is produced in large quantities in the fields of food processing, petrochemical industry, and the like. If the oily wastewater is directly discharged into the environment without being treated, serious ecological problems are caused, for example, waste oil discharged in rivers causes eutrophication of water bodies, death of aquatic organisms, and serious environmental pollution. How to efficiently realize the treatment of the oily wastewater is an urgent problem to be solved. In the treatment technology of oily wastewater, the membrane technology is a separation method developed in recent years, and has the advantages of high separation efficiency, low energy consumption, easy operation, no secondary pollution and the like. The selective separation characteristic of the membrane material can be utilized to treat various oil-containing wastewater systems, and particularly, the separation and purification of oil-in-water and water-in-oil emulsions can be better realized. Because the surface tension of water and oil are greatly different, in the membrane separation process, membrane materials with different water and oil wettability can selectively adsorb one phase and repel the other phase. Therefore, the hydrophilic-oleophobic membrane and the hydrophobic-lipophilic membrane can both realize oil-water separation operation, so that the wettability of the membrane surface to a certain phase is enhanced, and the separation efficiency can be obviously improved.

In the research on oil-water separation membranes, superhydrophobic/superhydrophilic type separation membranes are a hot point of research, and many research results have been obtained. The Chinese invention patent CN109126205A discloses an oil-water separation membrane, which is prepared by firstly preparing a spinning solution of Polystyrene (PS) and polymethyl methacrylate (PMMA), then dispersing carbon nano tubes treated by gamma-aminopropyltriethoxysilane in the solution, dripping poor solvent to promote phase separation, and then dripping the poor solvent on a substrate to prepare the PS/PMMA bionic porous membrane with the uniformly dispersed carbon nano tubes and a rough surface. And finally, immersing the porous membrane in an ether solution of 1H,1H,2H, 2H-perfluorodecyl mercaptan to modify the surface of the porous membrane with fluorine-containing groups. The finally obtained composite membrane has super-hydrophobic performance, but the preparation process of the method involves a more complex chemical modification process and the process is more complex. Wei et al [ Journal of Membrane Science 555(2018) 220-]A super-hydrophobic polyvinylidene fluoride (PVDF) composite membrane is prepared. PVDF powder was dissolved in a dimethylformamide solvent and applied to a glass plateAfter scraping the liquid film, the film was immersed in a solution containing different silicon dioxide (SiO)₂) And (3) solidifying and forming in alcohol-water mixed coagulation bath with nano-particle concentration. The method has the defects that the adopted nano particles have poor compatibility with the membrane material, the interaction force is weak, and the membrane performance stability is poor in the application process.

In conclusion, the existing preparation technology of the super-hydrophobic oil-water separation membrane has the problems of poor stability of nanoparticles on a base membrane structure, complex process and the like. Therefore, the development of a preparation technology of the super-hydrophobic composite membrane with simple process operation and high efficiency is of great significance.

Disclosure of Invention

In order to solve the technical problems, the invention provides a super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane and a preparation method and application thereof, and aims to overcome the defects of poor performance stability and complex process of the existing nano particle modified super-hydrophobic polyvinylidene fluoride membrane.

The invention provides a super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane which is formed by compounding polytetrafluoroethylene particles and a polyvinylidene fluoride membrane.

Further, the particle size of the polytetrafluoroethylene particles is 500nm-1600 nm.

The invention also provides a preparation method of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane, which comprises the following steps: and (2) standing and defoaming the casting solution dissolved with the polyvinylidene fluoride, dropwise adding the casting solution on a glass plate to scrape a liquid film, immersing the glass plate coated with the liquid film in a coagulating bath dispersed with polytetrafluoroethylene particles to be cured, and preparing the super-hydrophobic polyvinylidene fluoride oil-water separation composite film by an immersion phase conversion method.

Further, the mass fraction of the polyvinylidene fluoride in the casting solution dissolved with the polyvinylidene fluoride is 12-25%.

Further, the mass fraction of the polytetrafluoroethylene particles in the coagulation bath is 0.1% -1.5%.

And further, the curing time is 0.5-24h, after the curing is finished, the film is taken out of the coagulating bath, transferred to pure water for soaking and washing for at least 24h, taken out and dried to obtain the finished product of the super-hydrophobic polyvinylidene fluoride oil-water separation composite film.

Further, the preparation method of the polyvinylidene fluoride casting solution comprises the following steps: adding the dried polyvinylidene fluoride into an organic solvent, and stirring for 6-8h at 60-90 ℃ until the polyvinylidene fluoride is completely dissolved to obtain a transparent casting solution.

Further, the organic solvent is selected from at least one of N, N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide, and the mass average molecular weight of the polyvinylidene fluoride is 180000g/mol-540000 g/mol.

Further, the preparation method of the coagulation bath dispersed with polytetrafluoroethylene particles comprises the following steps: placing the polytetrafluoroethylene particles in a coagulant, and performing ultrasonic dispersion for 30-60min to obtain a coagulation bath containing the polytetrafluoroethylene particles, wherein the size of the polytetrafluoroethylene particles in the coagulation bath is 500-1600 nm.

Further, the coagulant is selected from at least one of methanol, ethanol, and isopropanol.

The invention also provides an application of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane as an oil-water separation membrane.

Compared with the prior art, the invention has the following beneficial effects:

(1) the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane provided by the invention is formed by compounding polytetrafluoroethylene particles and a polyvinylidene fluoride membrane, and due to strong interaction between the Polytetrafluoroethylene (PTFE) particles and the membrane, the separation membrane is endowed with good performance stability, and has good separation effect on emulsions such as chloroform, toluene, isooctane and the like, and the retention rate is higher than 99.8%. Because Polytetrafluoroethylene (PTFE) material has excellent acid and alkali resistance, the PVDF/PTFE super-hydrophobic composite membrane provided by the invention can be further developed and used as a separation material of an acidic or alkaline oil-water mixture.

(2) In the invention, polytetrafluoroethylene particles are dispersed in a coagulant to convert polyvinylidene fluoride (PVDF) into a film, and the Polytetrafluoroethylene (PTFE) particles are deposited on the surface of the film in the process. The hydrophobicity of Polytetrafluoroethylene (PTFE) particles causes the membrane material to exhibit superhydrophobic properties. Because the surface energy between the PTFE particles and the PVDF membrane material is relatively close, the deposited PTFE particles and the membranes have good similar compatibility and strong hydrophobic interaction force. Thereby overcoming the defect of poor compatibility between the nano particles and polyvinylidene fluoride (PVDF) in the prior art. The preparation technology of the super-hydrophobic membrane has the characteristic of simple process, and is particularly suitable for industrial production.

Drawings

Fig. 1 is a SEM picture of a cross-sectional structure of a composite membrane M3 prepared in example 3 of the present invention.

Fig. 2 is a SEM picture of the surface structure of the composite membrane M3 prepared in example 3 of the present invention.

FIG. 3 is a comparison of water contact angles of PVDF/PTFE composite membranes M1, M2, M3 and M4 prepared in examples 1 to 4 of the present invention and pure PVDF membranes prepared in comparative example 1.

FIG. 4 is a graph showing the adhesion behavior of water droplets on the surface of a pure PVDF membrane prepared in comparative example 1 of the present invention.

FIG. 5 is a water drop adhesion behavior diagram of the surface of PVDF/PTFE composite membrane M3 prepared in example 3 of the present invention.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

Example 1

(1) Preparing a casting solution: 3g of PVDF powder having a mass-average molecular weight of 352000 were weighed into 9g of N-methylpyrrolidone and stirred at 80 ℃ for 6h until complete dissolution. And (5) defoaming the solution at room temperature for 24 hours to obtain a uniform and transparent casting solution.

(2) Preparation of PTFE particle coagulation bath: 0.3g of PTFE particles with the average size of 1000nm are weighed, placed in 190g of absolute ethanol solvent, and subjected to ultrasonic dispersion for 60min to obtain a coagulation bath with uniformly dispersed particles.

(3) Preparation of PVDF/PTFE composite film (M1): and (3) dropwise adding the casting solution in the step (1) onto a glass plate, scraping the liquid film by using a film scraping knife with the size of 250 microns, and immediately transferring to the coagulating bath prepared in the step (2). After the liquid film was solidified in the coagulation bath for 30min, the sample was taken out and transferred to pure water for immersion washing for 24h to remove the residual coagulant. And finally, airing the sample in the air at room temperature to obtain a finished film product.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M1 membrane is 148 degrees.

Example 2

(1) Preparing a casting solution: the same as in example 1.

(2) Preparation of PTFE particle coagulation bath: 0.6g of PTFE particles with the average size of 1000nm are weighed, placed in 190g of absolute ethanol solvent, and subjected to ultrasonic dispersion for 60min to obtain a coagulation bath with uniformly dispersed particles.

(3) Preparation of PVDF/PTFE composite film (M2): the same as in example 1.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M2 membrane is 150 degrees.

Example 3

(1) Preparing a casting solution: the same as in example 1.

(2) Preparation of PTFE particle coagulation bath: 1.2g of PTFE particles with the average size of 1000nm are weighed, placed in 190g of absolute ethanol solvent, and subjected to ultrasonic dispersion for 60min to obtain a coagulation bath with uniformly dispersed particles.

(3) Preparation of PVDF/PTFE composite film (M3): the same as in example 1.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M3 membrane is 154 degrees. The morphological structure of the composite membrane is shown in fig. 1 and fig. 2.

Example 4

(1) Preparing a casting solution: the same as in example 1.

(2) Preparation of PTFE particle coagulation bath: 2.4g of PTFE particles with the average size of 1000nm are weighed and placed in 190g of absolute ethyl alcohol solvent, and ultrasonic dispersion is carried out for 60min, so as to obtain a coagulating bath with uniformly dispersed particles.

(3) Preparation of PVDF/PTFE composite film (M4): the same as in example 1.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M4 membrane is 151 degrees.

Example 5

(1) Preparing a casting solution: the same as in example 1.

(2) Preparation of PTFE particle coagulation bath: 1.2g of PTFE particles with an average size of 1000nm were weighed, placed in 190g of isopropanol solvent, and ultrasonically dispersed for 60min to obtain a coagulation bath in which the particles were uniformly dispersed.

(3) Preparation of PVDF/PTFE composite film (M5): the same as in example 1.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M5 membrane is 152 degrees.

Example 6

(1) Preparing a casting solution: the same as in example 1.

(2) Preparation of PTFE particle coagulation bath: 1.2g of PTFE particles having an average size of 1000nm were weighed, placed in 190g of a methanol solvent, and ultrasonically dispersed for 60min to obtain a coagulation bath in which the particles were uniformly dispersed.

(3) Preparation of PVDF/PTFE composite film (M6): the same as in example 1.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M6 membrane is 150 degrees.

Example 7

(1) Preparing a casting solution: 3g of PVDF powder having a mass-average molecular weight of 180000 are weighed into 9g of N-methylpyrrolidone and stirred at 80 ℃ for 6h until complete dissolution. And (5) defoaming the solution at room temperature for 24 hours to obtain a uniform and transparent casting solution.

(2) Preparation of PVDF/PTFE composite film (M7): 1.2g of PTFE particles with the average size of 1000nm are weighed, placed in 190g of absolute ethanol solvent, and subjected to ultrasonic dispersion for 60min to obtain a coagulation bath with uniformly dispersed particles.

(3) And (3) dropwise adding the casting solution in the step (1) onto a glass plate, scraping the liquid film by using a film scraping knife with the size of 250 microns, and immediately transferring the liquid film into the coagulating bath prepared in the step (2). After the liquid film was solidified in the coagulation bath for 30min, the sample was taken out and transferred to pure water for immersion washing for 24h to remove the residual coagulant. And finally, airing the sample in the air at room temperature to obtain a finished film product.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M7 membrane is 151 degrees.

Example 8

(1) Preparing a casting solution: 3g of PVDF powder having a mass-average molecular weight of 534000 were weighed into 9g of N-methylpyrrolidone and stirred at 80 ℃ for 6h until complete dissolution. And (5) defoaming the solution at room temperature for 24 hours to obtain a uniform and transparent casting solution.

(2) Preparation of PVDF/PTFE composite film (M8): 1.2g of PTFE particles with the average size of 1000nm are weighed, placed in 190g of absolute ethanol solvent, and subjected to ultrasonic dispersion for 60min to obtain a coagulation bath with uniformly dispersed particles.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M8 membrane is 153 degrees.

Comparative example 1

3g of PVDF powder having a mass-average molecular weight of 352000 were weighed into 9g of N-methylpyrrolidone and stirred at 80 ℃ for 6h until complete dissolution. And (5) defoaming the solution at room temperature for 24 hours to obtain a uniform and transparent casting solution. The casting solution was dropped on a glass plate, and the liquid film was scraped with a doctor blade having a size of 250 μm, and immediately transferred to the above-mentioned coagulation bath. After the liquid film was solidified in the coagulation bath for 30min, the sample was taken out and transferred to pure water for immersion washing for 24h to remove the residual coagulant. And finally, airing the sample in the air at room temperature to obtain a finished membrane product M.

The pure water contact angle of the prepared PVDF membrane was 138 ℃ as shown in FIG. 3.

Comparative example 2

The difference from example 3 is that the casting solution preparation in step (1): 5g of PVDF powder having a mass-average molecular weight of 352000 were weighed into 10g of N-methylpyrrolidone and stirred at 80 ℃ for 6h until complete dissolution. And (5) defoaming the solution at room temperature for 24 hours to obtain a uniform and transparent casting solution. The PVDF/PTFE composite membrane thus obtained is designated M9.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M9 membrane is 142 degrees.

Comparative example 3

The difference from example 3 is that in step (2), a coagulation bath of PTFE particles is prepared: 4.8g of PTFE particles with the average size of 1000nm are weighed, placed in 190g of absolute ethanol solvent, and subjected to ultrasonic dispersion for 60min to obtain a coagulation bath with uniformly dispersed particles.

The PVDF/PTFE composite membrane thus obtained is designated M10.

The pure water contact angle test of the prepared PVDF/PTFE composite membrane shows that the pure water contact angle of the M10 membrane is 146 DEG

Effect verification

(1) Analysis of behavior of water drop on film surface

Taking the pure PVDF membrane prepared in the comparative example 1 and the PVDF/PTFE super-hydrophobic polyvinylidene fluoride composite membrane prepared in the example 3 as experimental objects, dripping 5 microliters of pure water from a contact angle measuring instrument injector to enable the pure water to be suspended above the membranes; slowly moving the water drop down and contacting the membrane surface until the water drop is sufficiently contacted with the membrane surface; the syringe is then lifted.

It was found through this experiment that when the syringe was lifted, water droplets adhered to the surface of the pure PVDF membrane (fig. 4); whereas for PVDF/PTFE membranes it was found that water droplets adhered very poorly to the membrane surface, when the water droplets were pulled off the membrane surface, the water droplets did not pull off the needle, but rather adhered tightly to the micro-adjustment syringe needle. The PVDF/PTFE composite membrane has an ultra-low surface energy and hardly adheres to water drops (FIG. 5).

(2) Measurement of Water-oil separating Property

The membranes prepared in examples 1-8 and comparative examples 1-3 were used as the subjects. And clamping the membrane sample in a sand core filtering device, and measuring the separation performance of different oil-water emulsions under 0.09 MPa. The preparation method of the emulsion comprises the following steps: 0.5g span 80 and 2g water were weighed into 114ml oil solvent (including isooctane, chloroform or toluene) and magnetically stirred at room temperature for 3 h. The retention effect of the PVDF/PTFE membrane on the above emulsion is shown in Table 1 below.

TABLE 1

(3) Membrane stability assay

The prepared composite membrane is immersed in ethanol water solutions with different pH values, is measured after being washed for 48h by shaking, and is dried at room temperature, and the pure water contact angle is measured, and the results are shown in the following table:

the above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.

Claims

1. The super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane is characterized by being formed by compounding polytetrafluoroethylene particles and a polyvinylidene fluoride membrane.

2. The superhydrophobic polyvinylidene fluoride oil-water separation composite membrane of claim 1, wherein the polytetrafluoroethylene particles have a particle size of 500nm to 1600 nm.

3. The preparation method of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane according to claim 1, characterized by comprising the following steps: and (2) standing and defoaming the casting solution dissolved with the polyvinylidene fluoride, dropwise adding the casting solution on a glass plate to scrape a liquid film, immersing the glass plate coated with the liquid film in a coagulating bath dispersed with polytetrafluoroethylene particles to be cured, and preparing the super-hydrophobic polyvinylidene fluoride oil-water separation composite film by an immersion phase conversion method.

4. The preparation method of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane according to claim 3, wherein the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride casting membrane liquid is 12% -25%;

the mass fraction of the polytetrafluoroethylene particles in the coagulating bath is 0.1-1.5%.

5. The preparation method of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane according to claim 3, wherein the curing time is 0.5-24h, after the curing is completed, the composite membrane is taken out of a coagulating bath, transferred to pure water for soaking and washing for at least 24h, taken out and dried to obtain the finished product of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane.

6. The preparation method of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane according to any one of claims 3 to 5, wherein the preparation method of the polyvinylidene fluoride-dissolved casting solution comprises the following steps: adding the dried polyvinylidene fluoride into an organic solvent, and stirring for 6-8h at 60-90 ℃ until the polyvinylidene fluoride is completely dissolved to obtain a transparent casting solution.

7. The preparation method of the super-hydrophobic polyvinylidene fluoride oil-water separation composite membrane according to claim 6, wherein the organic solvent is at least one selected from N, N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide, and the polyvinylidene fluoride has a mass average molecular weight of 180000g/mol to 540000 g/mol.

8. The method for preparing the superhydrophobic polyvinylidene fluoride oil-water separation composite membrane according to any one of claims 3 to 5, wherein the method for preparing the coagulation bath in which polytetrafluoroethylene particles are dispersed comprises: placing the polytetrafluoroethylene particles in a coagulant, and performing ultrasonic dispersion for 30-60min to obtain a coagulation bath containing the polytetrafluoroethylene particles, wherein the size of the polytetrafluoroethylene particles in the coagulation bath is 500-1600 nm.

9. The method for preparing the superhydrophobic polyvinylidene fluoride oil-water separation composite membrane according to claim 8, wherein the coagulant is at least one selected from methanol, ethanol and isopropanol.

10. Use of the superhydrophobic polyvinylidene fluoride oil-water separation composite membrane of claim 1 as an oil-water separation membrane.