CN105013331A - Preparation method of asymmetric PDMS/PVDF blend pervaporation membrane - Google Patents

Abstract

The invention discloses a preparation method of an asymmetric PDMS/PVDF blend pervaporation membrane, and relates to the technical field of membrane preparation. A membrane casting solution comprises polyvinylidene fluoride, N,N-dimethylacetamide, polydimethylsiloxane and tetrahydrofuran. According to the invention, polyvinylidene fluoride (PVDF) is adopted as a pore-forming membrane material, and polydimethylsiloxane (PDMS) is introduced for blending, such that the asymmetric PDMS/PVDF blend pervaporation membrane is prepared. According to the invention, the problems of low flux and poor strength of existing PDMS homogeneous symmetric membranes used in pervaporation are solved from the fundamental aspect, i.e., the membrane materials. The two hydrophobic membrane materials PVDF and PDMS are used for preparing the novel asymmetric PDMS/PVDF blend pervaporation membrane, such that the above properties of the PDMS pervaporation membrane can be improved.

Description

Preparation method of asymmetric PDMS/PVDF blend pervaporation membrane

technical field

The invention relates to the technical field of membrane preparation, in particular to a method for preparing an asymmetric PDMS/PVDF blended pervaporation membrane.

Background technique

Membrane separation technology has the following advantages, such as: compared with traditional separation technology, it has low energy consumption, low cost, high efficiency, and environmental protection. , absorption and other separation process coupling. In recent years, it has been widely used in industrial production and daily life, and people pay more and more attention to the research of membrane separation technology.

Polydimethylsiloxane (PDMS) is a chemically stable polymer organosilicon compound, which has heat and cold resistance, strong hydrophobicity, good movement and vibration, solvent resistance, high and low temperature resistance, and Ozone, hydrophobic and many other excellent properties. At the same time, PDMS is low in cost, non-toxic, and not volatile, so PDMS is widely used to prepare homogeneous and symmetrical pervaporation membranes that preferentially permeate organic matter.

However, the flux of PDMS membrane is not large enough and its strength is poor. For these deficiencies of PDMS membranes, it is common to improve the performance of the membrane by membrane modification, such as surface modification, blending, post-treatment and other methods to modify the membrane.

Polyvinylidene fluoride (PVDF) is a new type of fluorocarbon thermoplastic. As a membrane material, it has received great attention because of its excellent performance. Compared with other commercial polymer materials, it has high mechanical strength and thermal stability. Chemical resistance, and high hydrophobicity. Therefore, PVDF is widely used in the field of membrane separation. Asymmetric pervaporation membranes can be prepared by immersion precipitation method.

Contents of the invention

(1) Solved technical problems

Aiming at the deficiencies of the prior art, the present invention provides a method for preparing an asymmetric PDMS/PVDF blended pervaporation membrane. The present invention uses polyvinylidene fluoride (PVDF) as the porous membrane material, and introduces polydimethylsilane Oxygen (PDMS) was blended to prepare asymmetric PDMS/PVDF blended pervaporation membranes to improve the problems of insufficient flux and poor strength of PDMS membranes.

(2) Technical solution

To achieve the above object, the present invention is achieved through the following technical solutions:

A casting solution of an asymmetric PDMS/PVDF blended pervaporation membrane, the casting solution is composed of the following raw materials in parts by weight:

Polyvinylidene fluoride 10～18

N,N-Dimethylacetamide 50～60

The mass ratio of polydimethylsiloxane and tetrahydrofuran is 1:10

A method for preparing an asymmetric PDMS/PVDF blended pervaporation membrane casting liquid, comprising the following steps:

S1. Fully dissolve polyvinylidene fluoride and N,N-dimethylacetamide in a water bath at 80°C with mechanical stirring, take out the casting solution, seal it, and place it in an oven at 80°C for aging for 20- 30 hours;

S2. Dissolving polydimethylsiloxane in tetrahydrofuran and stirring at 25°C for 1-2 hours to mix the two evenly;

S3. Take the solution of step S1 out of the oven, cool to room temperature, add the solution of step S2, and stir for 3-5 hours at room temperature to mix the components evenly to obtain the casting solution.

The method for preparing the PDMS/PVDF blended pervaporation membrane by using the casting solution obtained above comprises the following steps:

S1. First, let the uniformly mixed casting solution stand for 24 hours to fully remove the air bubbles in the system, and use ultrasonic degassing or vacuum degassing for 1 to 2 hours;

S2. Apply the prepared film casting solution evenly on a clean and flat glass plate with a scraper, evaporate in the air, and then put the glass plate in a gel bath. After the film solidifies and separates from the glass plate, take it out and place it in a Soak in deionized water for 72 hours to completely remove the residual solvent in the film, and finally take it out and place it in a clean room to dry.

Preferably, in the preparation method of the asymmetric PDMS/PVDF blended pervaporation membrane casting solution, the aging time in step S1 is 24 hours.

Preferably, in the preparation method of the asymmetric PDMS/PVDF blended pervaporation membrane casting solution, the stirring time in step S3 is 4 hours.

Preferably, the method for preparing the PDMS/PVDF blended pervaporation membrane is characterized in that the air evaporation time in step S2 is 10, 30, 50, and 70 minutes respectively.

(3) Beneficial effects

The invention provides a method for preparing an asymmetric PDMS/PVDF blended pervaporation membrane. The invention uses polyvinylidene fluoride (PVDF) as a porous membrane material, and introduces polydimethylsiloxane (PDMS) for co- Mixing, preparing asymmetric PDMS/PVDF blended pervaporation membranes, aiming at the problems of insufficient flux and poor strength of existing PDMS membranes used for pervaporation, starting from the fundamental of membrane materials, PVDF and PDMS two kinds of hydrophobic A new type of asymmetric PDMS/PVDF blended pervaporation membrane was prepared to improve the mechanical strength and flux of PDMS pervaporation homogeneous symmetric membrane.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the present invention Examples, not all examples. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Casting liquid of the present invention is made up of the raw material of following weight portion:

Polyvinylidene fluoride 10～18

N,N-Dimethylacetamide 50～60

The mass ratio of polydimethylsiloxane and tetrahydrofuran is 1:10

The preparation steps of the PDMS/PVDF blended pervaporation membrane casting solution of the present invention are:

S1. Fully dissolve polyvinylidene fluoride and N,N-dimethylacetamide in a water bath at 80°C with mechanical stirring, take out the casting solution, seal it, and place it in an oven at 80°C for aging for 24 hours ;

S2. Dissolving polydimethylsiloxane in tetrahydrofuran and stirring at 25°C for 1-2 hours to mix the two evenly;

S3. Take the solution of step S1 out of the oven, cool to room temperature, add the solution of step S2, and stir for 4 hours at room temperature to mix the components evenly to obtain the casting solution.

The method of preparing the PDMS/PVDF blended pervaporation membrane from the casting solution obtained above, first, let the uniformly mixed casting solution stand for 24 hours to fully remove the air bubbles in the system, and use ultrasonic degassing or vacuum degassing for 1 to 2 hours ;Use a scraper to evenly apply the prepared casting solution on a clean, flat glass plate, evaporate it in the air, then put the glass plate into a gel bath, and after the film is solidified and separated from the glass plate, take it out and place it in a Soak in deionized water for 72 hours to completely remove the residual solvent in the film, and finally take it out and place it in a clean room to dry.

Example 1:

1. Weigh 10.00g PVDF, and dissolve it in 50.00g DMAc solvent in 80°C water bath with mechanical stirring. Maintain 80°C water bath and mechanical stirring until the polymer is completely dissolved, take out the casting solution, seal it, and place it in an oven at 80°C for aging for 24 hours.

Weigh 2.00 PDMS and dissolve in 20.00 g THF, and stir magnetically at 25°C for 1 hour to mix the two evenly.

Take the matured PVDF casting solution out of the oven, cool it to room temperature, add 22.00g of PDMS/THF solution, and stir it mechanically for 4 hours at room temperature to make the components evenly mixed.

2. Let the uniformly mixed casting solution stand for 24 hours to fully remove the air bubbles in the system. If necessary, ultrasonic degassing or vacuum degassing can be used.

3. Use a spatula to evenly coat the prepared casting solution on a clean and flat glass plate, and evaporate it in the air for 10, 30, 50, and 70 minutes respectively, then put the glass plate into the gel bath, and the gel will The bath is a double gel bath, soak in 30% DMAc, 5% THF and 65% deionized aqueous solution for 15 minutes, then soak in deionized water for 30 minutes, after the film is solidified and detached from the glass plate, take it out and soak in deionized water for 72 hours , to completely remove the residual solvent and additives in the membrane, during which the water is replaced every 24 hours. Afterwards, the film was taken out and placed in a clean room to dry for later use.

The test methods used in the following examples are mainly:

1. The ethanol permeation flux test of the membrane. Before the test, put the membrane into the test device to fix it, and then circulate it in 15wt% ethanol aqueous solution at 60°C for 1 hour. The permeation side maintains a vacuum of 90KPa, and the test is started. Parallel measurement 3 times, take the average value.

2. Mechanical performance test of the film: the mechanical strength of the film was tested with a material tensile testing machine (3365, Instron, USA). The loading speed is 20mm/min.

Comparative Test:

The film of the present invention with a thickness of 130 microns was compared with the existing PDMS film.

In this example, the gel bath is 30% DMAc, 5% THF and 65% deionized water. The asymmetric PDMS/PVDF blend pervaporation membrane performance and PDMS homogeneity obtained according to different air evaporation times in the gel bath The pervaporation membrane properties are listed in Table 1.

Table 1 Performance comparison of asymmetric PDMS/PVDF blend membrane and PDMS homogeneous membrane with different air evaporation time

It can be seen from the data in Table 1 that the ethanol permeation flux and mechanical strength of the PDMS/PVDF blended pervaporation membrane prepared by the method of this example are higher than those of the PDMS homogeneous pervaporation membrane, especially in the ethanol pervaporation membrane. The improvement is most evident in throughput. It can be seen from Table 1 that the structures of the membranes prepared under the conditions of 30% DMAc, 5% THF, and 65% deionized water in the gel bath with an evaporation time of 50 min and 70 min are relatively uniform, with many and uniform finger-like pore structures. It can effectively increase the permeation flux of ethanol and enhance the mechanical strength.

Example 2:

1. Weigh 10.00g PVDF, and dissolve it in 50.00g DMAc solvent in 80°C water bath with mechanical stirring. Maintain 80°C water bath and mechanical stirring until the polymer is completely dissolved, take out the casting solution, seal it, and place it in an oven at 80°C for aging for 24 hours.

Weigh 2.00 PDMS and dissolve in 20.00 g THF, and stir magnetically at 25°C for 1 hour to mix the two evenly.

Take the matured PVDF casting solution out of the oven, cool it to room temperature, add 22.00g of PDMS/THF solution, and stir it mechanically for 4 hours at room temperature to make the components evenly mixed.

2. Let the uniformly mixed casting solution stand for 24 hours to fully remove the air bubbles in the system. If necessary, ultrasonic degassing or vacuum degassing can be used.

3. Use a spatula to evenly coat the prepared casting solution on a clean and flat glass plate. After evaporating in the air for 10, 30, 50, and 70 minutes, put the glass plate into the gel bath. It is a double gel bath, soak in 35% DMAc and 65% deionized aqueous solution for 15 minutes, then soak in deionized water for 30 minutes, after the film is solidified and detached from the glass plate, take it out and soak it in deionized water for 72 hours to completely remove the film Solvents and additives remaining in the water, during which the water is replaced every 24 hours. Afterwards, the film was taken out and placed in a clean room to dry for later use.

In this example, the gel bath is 35% DMAc, 65% deionized water, and the properties of asymmetric PDMS/PVDF blended pervaporation membrane and PDMS homogeneous pervaporation membrane obtained according to different air evaporation times in the gel bath Listed in Table 2.

Table 2 Performance comparison of asymmetric PDMS/PVDF blend membrane and PDMS homogeneous membrane with different air evaporation time

It can be seen from the data in Table 2 that the ethanol permeation flux and mechanical strength of the PDMS/PVDF blended pervaporation membrane prepared by the method of this example are higher than those of the PDMS homogeneous pervaporation membrane, wherein the ethanol pervaporation flux Great improvement has been made. It can be seen from Table 2 that the ethanol flux of the membrane prepared under the conditions of 35% DMAc and 65% deionized water in the gel bath with an evaporation time of 70 min is larger than others.

Example 3:

1. Weigh 10.00g PVDF, and dissolve it in 50.00g DMAc solvent in 80°C water bath with mechanical stirring. Maintain 80°C water bath and mechanical stirring until the polymer is completely dissolved, take out the casting solution, seal it, and place it in an oven at 80°C for aging for 24 hours.

Weigh 2.00 PDMS and dissolve in 20.00 g THF, and stir magnetically at 25°C for 1 hour to mix the two evenly. Take the matured PVDF casting solution out of the oven, cool to room temperature, add 22.00g PDMS/THF solution, and mechanically stir for 4 hours at room temperature to make the components evenly mixed.

2. Let the uniformly mixed casting solution stand for 24 hours to fully remove the air bubbles in the system. If necessary, ultrasonic degassing or vacuum degassing can be used.

3. Use a spatula to evenly coat the prepared casting solution on a clean and flat glass plate. After evaporating in the air for 10, 30, 50, and 70 minutes, put the glass plate into the gel bath. Use deionized water, soak in deionized water for 30 minutes, after the film is solidified and detached from the glass plate, take it out and soak in deionized water for 72 hours to completely remove the residual solvent and additives in the film, and replace the water every 24 hours during this period. Afterwards, the film was taken out and placed in a clean room to dry for later use.

In this example, deionized water was used as the gel bath. The properties of asymmetric PDMS/PVDF blended pervaporation membranes and PDMS homogeneous pervaporation membranes obtained according to different air evaporation times in the gel bath are listed in Table 3.

It can be seen from the data in Table 3 that the ethanol permeation flux and mechanical strength of the PDMS/PVDF blended pervaporation membrane prepared by the method of this example are higher than those of the PVDF membrane, and the ethanol permeation flux is also stronger. As shown in Table 3, the ethanol flux of the membrane prepared under the condition that the gel bath is deionized water with an evaporation time of 10 minutes is larger than others.

Table 3 Performance comparison of asymmetric PDMS/PVDF blend membrane and PDMS homogeneous membrane with different air evaporation time

From the above experiments, it was found that in the process of preparing PDMS/PVDF blended pervaporation membranes, the pervaporation performance of the asymmetric PDMS/PVDF blended pervaporation membranes with air evaporation time of 50 min and 70 min was relatively better, and the air evaporation time The structure of the membrane prepared for 50min and 70min is relatively uniform, which is suitable for the requirements of pervaporation.

In summary, the beneficial effects of the present invention are as follows: The present invention provides a method for preparing an asymmetric PDMS/PVDF blended pervaporation membrane, using polyvinylidene fluoride (PVDF) as the porous membrane material, and introducing polydimethylsilane Oxygen (PDMS) is blended to prepare asymmetric PDMS/PVDF blended pervaporation membranes. Aiming at the problems of insufficient flux and poor strength of existing PDMS membranes used for pervaporation, start from the fundamentals of membrane materials. Two kinds of hydrophobic membrane materials, PVDF and PDMS, are used to prepare a novel asymmetric PDMS/PVDF blended pervaporation membrane to improve the mechanical strength, ethanol permeation flux and other properties of the PDMS homogeneous symmetrical pervaporation membrane; the solvent of the present invention It is DMAc without additives; the dense film thickness of the asymmetric PDMS/PVDF blended pervaporation membrane of the present invention is 2 μm-4 μm, and the porosity is greater than 60%; the asymmetric PDMS/PVDF blended pervaporation membrane of the present invention is mainly used for preferential permeability Organic pervaporation (PV). The results of pervaporation experiments show that the separation performance of the membrane prepared by the gel bath composition of 35wt% DMAc, 5wt% THF and 60wt% deionized water is the best when the evaporation time is 70min at room temperature.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is a relationship between these entities or operations. There is no such actual relationship or order between them. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be described in the foregoing embodiments. Modifications are made to the recorded technical solutions, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (6)

1. a casting liquid of asymmetric PDMS/PVDF blended pervaporation membrane, it is characterized in that, described casting liquid is made up of the raw material of following weight portion: Polyvinylidene fluoride 10～18 N,N-Dimethylacetamide 50～60 The mass ratio of polydimethylsiloxane and tetrahydrofuran is 1:10. 2. The preparation method of the asymmetric PDMS/PVDF blended pervaporation membrane casting liquid according to claim 1, is characterized in that, comprises the following steps: S1. Fully dissolve polyvinylidene fluoride and N,N-dimethylacetamide in a water bath at 80°C with mechanical stirring, take out the casting solution, seal it, and place it in an oven at 80°C for aging for 20- 30 hours; S2. Dissolving polydimethylsiloxane in tetrahydrofuran and stirring at 25°C for 1-2 hours to mix the two evenly; S3. Take the solution of step S1 out of the oven, cool to room temperature, add the solution of step S2, and stir for 3-5 hours at room temperature to mix the components evenly to obtain the casting solution. 3. the method for preparing the PDMS/PVDF blended pervaporation membrane by using the casting liquid obtained in claim 1 and 2, is characterized in that, comprises the following steps: S1. First, let the uniformly mixed casting solution stand for 24 hours to fully remove the air bubbles in the system, and use ultrasonic degassing or vacuum degassing for 1 to 2 hours; S2. Apply the prepared film-casting solution evenly on a clean and flat glass plate with a scraper, evaporate in the air for 10-70 minutes, then put the glass plate into a gel bath, and the film will solidify and separate from the glass After the board, take it out and soak it in deionized water for 72 hours to completely remove the residual solvent in the film, and finally take it out and put it in a clean room to dry. 4. The method for preparing asymmetric PDMS/PVDF blended pervaporation membrane casting solution according to claim 2, characterized in that the aging time in step S1 is 24 hours. 5. The method for preparing asymmetric PDMS/PVDF blended pervaporation membrane casting liquid according to claim 2, characterized in that the stirring time in step S3 is 4 hours. 6. the method for preparing PDMS/PVDF blended pervaporation membrane according to claim 3, is characterized in that, the air evaporation time described in step S2 is respectively 10,30,50,70min.