阅读说明：本技术 聚酰亚胺渗透汽化膜及其制备方法 (Polyimide pervaporation membrane and preparation method thereof ) 是由 刘京妮 孙旭阳 崔晶 钟璟 马文中 于 2018-07-06 设计创作，主要内容包括：本发明涉及一种聚酰亚胺渗透汽化膜及其制备方法,主要解决现有技术中渗透汽化膜耐溶剂性差、分离效率低导致薄膜使用寿命短,难以用于强极性溶剂的分离问题。本发明提供一种聚酰亚胺渗透汽化膜,包括支撑层和分离层；其中,所述分离层位于所述支撑层上,所述分离层为多层聚酰亚胺膜,所述支撑层为具有0.01μm以上孔隙结构的无机物或有机物；其特征在于所述多层聚酰亚胺膜由采用至少两种除溶剂法制得的聚酰胺酸膜经亚胺化得到,且除与支撑层接触的第一层外,其它层均采用在聚酰胺酸的不良溶剂中扩散的除溶剂方法的技术方案,较好地解决了该问题,可用于聚酰亚胺渗透汽化膜的工业化应用中。(The invention relates to a polyimide pervaporation membrane and a preparation method thereof, and mainly solves the problems that in the prior art, the pervaporation membrane is poor in solvent resistance, low in separation efficiency, short in service life and difficult to separate strong-polarity solvents. The invention provides a polyimide pervaporation membrane, which comprises a supporting layer and a separating layer; the separation layer is positioned on the support layer, the separation layer is a multilayer polyimide film, and the support layer is an inorganic substance or an organic substance with a pore structure of more than 0.01 mu m; the multilayer polyimide film is characterized in that the multilayer polyimide film is obtained by imidizing a polyamic acid film prepared by at least two solvent removal methods, and the other layers except the first layer in contact with the supporting layer adopt the technical scheme of the solvent removal method of diffusing in poor solvent of polyamic acid, so that the problem is solved well, and the multilayer polyimide film can be used for industrial application of polyimide pervaporation films.)

1. A polyimide pervaporation membrane comprises a support layer and a separation layer; the separation layer is positioned on the support layer, the separation layer is a multilayer polyimide film, and the support layer is an inorganic substance or an organic substance with a pore structure of more than 0.01 mu m; the multilayer polyimide film is obtained by imidizing at least two polyamic acid films prepared by a solvent removal method, and the polyamic acid films of the other layers except the first polyamic acid film in contact with the support layer are prepared by a method of diffusing the solvent removal method in a poor solvent of polyamic acid.

2. The polyimide pervaporation membrane according to claim 1, characterized in that said multilayer polyimide membrane is 2 to 10 layers; preferably 2 to 6 layers.

3. The polyimide pervaporation membrane according to claim 1, characterized in that the total thickness of said multilayer polyimide membrane is 2 to 80 μm.

4. The polyimide pervaporation membrane according to claim 1, wherein said support layer is selected from inorganic or organic substances having a pore structure of 0.01 to 1 μm.

5. The polyimide pervaporation membrane according to claim 1, characterized in that said support layer has a thickness of 0.5 to 100 mm; preferably 1 to 5 mm.

6. A method for preparing a polyimide pervaporation membrane according to any one of claims 1 to 5, comprising the following steps:

a) attaching a layer of polyamic acid solution to the surface of the supporting layer;

b) removing the solvent in the polyamic acid solution by a solvent removal method of heating or diffusing in a poor solvent of the polyamic acid to form a polyamic acid film;

c) imidizing the polyamic acid film obtained in the step b) into a polyimide film;

d) attaching a layer of polyamic acid solution on the surface of the polyimide film obtained in the previous step;

e) removing the solvent in the polyamic acid solution layer by a solvent removal method of diffusing in a poor solvent of the polyamic acid to form a polyamic acid film;

f) imidizing the polyamic acid membrane obtained in the step e) into a polyimide membrane to obtain the polyimide pervaporation membrane with two separation layers;

or repeating the step d), the step e) and the step f) on the polyimide membrane obtained in the step f) to obtain the polyimide pervaporation membrane with more than two polyimide membranes as a separation layer;

wherein the poor solvents in step b) and step e) are different from each other.

7. The method of claim 6, wherein the polyamic acid is selected from the group consisting of structures represented by the following general formula (1):

wherein Ar is₁、Ar₃Is a tetravalent aromatic radical having at least one carbon-six membered ring, Ar₂、Ar₄Is a divalent aromatic residue containing at least one carbon six-membered ring.

8. The method for preparing a polyimide pervaporation membrane according to claim 6, wherein the organic solvent used in the polyamic acid solution is at least one selected from the group consisting of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, toluene, and xylene; the solid content of the polyamic acid solution is 5-25%.

9. The method of preparing a polyimide pervaporation membrane according to claim 1, wherein the polyamic acid solution has a viscosity of 1 x 10³～5×10⁵cP。

10. Use of a polyimide pervaporation membrane according to any of claims 1 to 5.

11. A pervaporation separation device provided with a pervaporation membrane, wherein the pervaporation membrane is the polyimide pervaporation membrane according to any one of claims 1 to 5.

12. A separation method using the pervaporation separation device of claim 11.

Technical Field

The invention relates to a solvent-resistant polyimide pervaporation membrane with high pervaporation separation capacity and a preparation method thereof.

Background

Aprotic polar solvents such as Dimethylformamide (DMF), dimethylacetamide (DMAc) and the like are widely applied to the fields of pesticides, medicines, organic synthesis, synthetic leather and the like. However, such solvents have adverse effects on human health and the environment. Therefore, separation, recovery and disposal of the used amide solvent are important problems in the industrial field. Pervaporation (PV) technology is a new membrane separation technology, and is applied to the recovery of organic solvents. However, the general polymer membrane material is easy to swell or even dissolve in such solvents, so that the pervaporation separation technology is difficult to separate and recover such solvent systems, and therefore, a membrane material with good solvent resistance needs to be found.

Polyimide (PI) is a polymer material having an imide ring structure in the main chain developed in the 60 th 20 th century, and has excellent heat resistance, mechanical properties, and solvent resistance. The PI membrane has a certain research foundation in the membrane separation fields of nanofiltration, pervaporation and the like. In 1993, White and the like firstly prepare the PI into a nanofiltration membrane to be applied to an organic solvent system for recovering a solvent in a lubricating oil filtrate, wherein the rejection rate of the membrane on the lubricating oil reaches 95%, the purity of the permeated solvent reaches more than 99%, and the membrane shows good stability. The PI pervaporation membrane prepared by Qiao et al is used for separating isopropanol/water, the separation factor reaches 3508, and the permeation flux is 0.432 kg.m^-2·h^-1. Polotskaya et al synthesized PI composite membrane (BTDA-ODA/PAN) for separating 10% methanol/cyclohexane solution, and the result shows that the PI/PANI membrane has better selectivity to methanol and the permeation flux at 50 ℃ is 0.046 kg.m^-2·h^-1. In 2011, Park et al demonstrated that PI membranes have better tolerance in aprotic polar solvents such as DMF, DMAc and the like, further showing that PI is used as a pervaporation separation membraneSolvent resistance and wide prospect in the aspect of organic solvent separation.

Patent reports that the chemical imidization method for preparing the polyimide pervaporation membrane and separating the n-octane/n-heptane-thiophene system is relatively simple in process, but the chemical imidization method cannot enable the PI to reach a sufficient imidization degree, greatly reduces the stability of the PI membrane in an aprotic solvent, and is not suitable for separating the solvent system involved in the patent. The polyimide pervaporation membrane disclosed by the invention has the advantages of excellent solvent resistance, high separation efficiency, low energy consumption, lower theoretical cost than the conventional distillation and rectification process at the present stage and obvious advantages.

Disclosure of Invention

One of the technical problems to be solved by the invention is that the pervaporation membrane in the prior art has poor solvent resistance and low separation efficiency, so that the membrane has short service life and is difficult to separate and purify the strong polar organic solvent; the invention provides a polyimide pervaporation membrane which has the characteristics of excellent solvent resistance, high pressure difference resistance, difficulty in damage, high separation efficiency and easiness in processing, can keep stable performance in a strong polar solvent, and has a wide application prospect.

The second technical problem to be solved by the present invention is to provide a method for preparing a polyimide pervaporation membrane corresponding to the first technical problem.

The present invention provides a method for applying a polyimide pervaporation membrane, which is corresponding to the solution of the above technical problem.

The fourth technical problem to be solved by the present invention is to provide a pervaporation separation apparatus using a polyimide pervaporation membrane corresponding to one of the technical problems to be solved as a pervaporation membrane.

The fifth technical problem to be solved by the present invention is to provide a separation method using the pervaporation separation apparatus described in the fourth technical problem to be solved.

In order to solve one of the above technical problems, the technical scheme adopted by the invention is as follows: a polyimide pervaporation membrane comprises a support layer and a separation layer; the separation layer is positioned on the support layer, the separation layer is a multilayer polyimide film, and the support layer is an inorganic substance or an organic substance with a pore structure of more than 0.01 mu m; the multilayer polyimide film is characterized in that the multilayer polyimide film is obtained by imidizing a polyamic acid film prepared by at least two solvent removal methods, and the other layers except the first layer in contact with the supporting layer adopt a solvent removal method of diffusing in a poor solvent of polyamic acid.

In the technical scheme, the separation layer is a multilayer polyimide film, and the total thickness is preferably 2-80 μm.

In the technical scheme, the total number of layers of the multilayer polyimide film is preferably 2-10 layers, and more preferably 2-6 layers.

In the technical scheme, the supporting layer is preferably an inorganic or organic supporting layer with a pore structure of 0.01-1 μm, is preferably an inorganic ceramic supporting layer, and is more preferably an inorganic ceramic supporting layer with a pore structure of 0.1-1 μm.

In the technical scheme, the thickness of the supporting layer is preferably 0.5-100 mm, and more preferably 1-5 mm.

In the above technical solution, the solvent removing method used for the first layer of the multilayer polyimide film is preferably a self-heating method or a method of diffusing in a poor solvent of polyamic acid, and the solvent removing method used for the second layer and the above polyamic acid film is a method of diffusing in a poor solvent of polyamic acid.

In order to solve the second technical problem, the invention adopts the technical scheme that: a preparation method of a polyimide pervaporation membrane comprises the following steps:

a) attaching a layer of polyamic acid solution to the surface of the supporting layer;

b) removing the solvent in the polyamic acid solution by a solvent removal method of heating or diffusing in a poor solvent of the polyamic acid to form a polyamic acid film;

c) imidizing the polyamic acid film obtained in the step b) into a polyimide film;

d) attaching a layer of polyamic acid solution on the surface of the polyimide film obtained in the previous step;

e) removing the solvent in the polyamic acid solution layer by a solvent removal method of diffusing in a poor solvent of the polyamic acid to form a polyamic acid film;

f) imidizing the polyamic acid membrane obtained in the step e) into a polyimide membrane, and obtaining a polyimide pervaporation membrane with a separation layer which is two layers of polyimide membranes;

or repeating the step e) and the step f) to obtain a polyimide pervaporation membrane with the separation layer being more than two polyimide membranes;

wherein the poor solvents in step b) and step e) are different from each other.

In the above technical solution, the polyamic acid is preferably selected from the structures represented by the general formula (1):

general formula (1)

Wherein Ar is₁、Ar₃The tetravalent aromatic residue having at least one carbon six-membered ring, more preferably an aromatic residue represented by the following structural formula (1):

structural formula (1);

in the above structural formula (1), R₁Is preferably selected fromAnd the like.

Ar₂、Ar₄Preferably a tetravalent aromatic residue comprising at least one carbon six-membered ring, more preferably an aromatic residue represented by the following structural formula (2):

structural formula (2);

in the above structural formula (2), R₂H-, CH-, is preferably selected₃-、Cl-、Br-、F-、CH₃O-, COOH-, etc.

In the technical scheme, the mole ratio of the dianhydride monomer to the diamine monomer in the polyamic acid solution is preferably 0.95-1.05: 1.

in the above technical solution, the organic solvent used in the polyamic acid solution is preferably at least one selected from N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, toluene, and xylene.

In the technical scheme, the solid content of the polyamic acid solution is preferably 5-25%.

In the above technical solution, the viscosity of the polyamic acid solution is preferably 1 × 10³～5×10⁵cP。

In the above technical solution, the method for attaching a layer of polyamic acid solution to the support is preferably at least one of spin coating, doctor blade coating, or dipping.

In the above technical solution, the solvent removing method for preparing the multilayer polyimide film includes a heating method or a method of diffusing a solvent immersed in a poor solvent of polyamic acid.

In the above technical solution, in the preparation of the multilayer polyimide film, the solvent removing method used for the first layer is selected from a heating method or a method of diffusing in a poor solvent of polyamic acid, the solvent removing method used for the second layer and the above polyimide films is a method of diffusing in a poor solvent of polyamic acid, and the poor solvent used for the second layer and the above layers is different from that used for the first layer; more preferably, the poor solvents used for the second layer and the layers above are different from each other.

In the technical scheme, the temperature of solvent diffusion in the heating method is preferably 40-180 ℃, and is preferably 50-120 ℃; the time for removing the solvent by heat preservation is preferably 0.1-60 min.

In the technical scheme, the heating method is carried out in an environment protected by air or inert gas through solvent diffusion.

In the above technical solution, the poor solvent is preferably at least one of pure water, ethanol, acetone, and a polar aprotic organic solvent aqueous solution.

In the technical scheme, the imidization temperature in the high-temperature environment is 200-450 ℃, and preferably 240-350 ℃.

In the technical scheme, the imidization time in the high-temperature environment is 0.1-120 min, preferably 5-60 min.

In order to solve the third technical problem, the invention adopts the technical scheme that: an application method of the polyimide pervaporation membrane in any one of the technical schemes for solving the technical problems.

In the above technical scheme, the application method is not limited strictly, and those skilled in the art can utilize the method according to the existing process conditions, for example, the method is applied to separation of a strong polar organic solvent.

In order to solve the fourth technical problem, the invention adopts the technical scheme that: a pervaporation separation device is provided with a pervaporation membrane, wherein the pervaporation membrane is the polyimide pervaporation membrane in any one of the technical schemes for solving the technical problems.

In the above technical solution, the pervaporation separation device is not limited to other specific limitations, and those skilled in the art can design the pervaporation separation device according to the existing device, for example, but not limited to, the pervaporation membrane is a polyimide pervaporation membrane of the present invention.

In order to solve the fifth technical problem, the invention adopts the technical scheme that: a separation method using the pervaporation separation device according to any of the fourth technical means for solving the technical problems.

In the above technical schemes, the separation method is not particularly limited, and those skilled in the art can utilize the separation method according to the existing process conditions, for example, but not limited to, separating the aprotic polar solvent and the small molecule solvent mixture.

The polyimide pervaporation membrane and the preparation method thereof adopt an innovative processing technology, PI membranes with certain difference in compactness are obtained by different solvent removal modes to compound a separation layer, and the advantages of pervaporation performance of each layer of PI membranes are integrated, so that the pervaporation separation effect of efficiently separating medium and small molecules in a penetrant, stable pervaporation separation performance, strong solvent resistance and high temperature and high pressure resistance is achieved; the polyimide pervaporation membrane obtained by the technical scheme of the invention has the advantages of smooth surface, high yield, good separation effect, low energy consumption and good solvent resistance, can be used for separating a strong polar organic solvent to keep the separation effect, meets the application requirements of separation, recovery, purification and the like of the solvent in industrial production, and obtains better technical effect.

The test equipment and test conditions used in the present invention are:

apparent viscosity: BROOKFIELD DV-III ULTRA PROGRAM MABLE RHEOMETER, USA, at 25 deg.C using LV-4 rotor test.

Swelling degree: preparing a support-free PI film sample, cutting the PI film sample into squares, drying the PI film sample in an oven at 100 ℃ for 1h, and weighing the mass w₁Then soaking the mixture in a pure DMAc solvent at 60 ℃ for 48 hours, and weighing the mixture by mass w₂The degree of swelling is (w)₂-w₁)/w₁×100％。

Pervaporation performance: the pervaporation membrane is placed in a pervaporation membrane separator, the upper part of the membrane is filled with 90 wt% N, N-dimethylformamide aqueous solution, the cavity at the lower part of the membrane is a gas phase, a vacuum pump is connected, and a larger component pressure difference is kept between the feed liquid side and the permeate side, so that each component in the feed liquid penetrates through the pervaporation membrane and diffuses towards the permeate side, and the schematic diagram of the testing device is shown in figure 1. The feed solution temperature was 60 ℃ and the pressure after the membrane was 500Pa, and the quality of the permeate collected on the permeate side by the condenser was tested (M)_i) And the concentration of permeant therein (y)_i) The calculation formula is as follows:

a is the membrane area, m²(ii) a t is the operation time, h; j is the permeation flux, g/(m)²·h)。

x_i、x_j-the molar fractions of component i and component j in the stock solution; y is_i、y_j-the molar fractions of component i and component j in the permeate; generally i represents a component having a fast permeation rate.

In order to comprehensively express the pervaporation separation performance, a pervaporation separation index PSI is adopted, and PSI is alpha.J.

The PI pervaporation membrane obtained by adopting the technical scheme of the invention has good separation effect, excellent solvent resistance and low separation energy consumption, the swelling degree in an aprotic polar solvent is less than 5 wt%, and high permeation flux and better separation factor can be ensured at the same time, and the permeation flux is more than 350 g/(m)²H) separation factor > 20, separation index > 7000 g/(m)²H), a good technical effect is obtained.

Drawings

Fig. 1 is a pervaporation performance testing device.

The invention is further illustrated by the following examples.

Detailed Description

[ example 1 ]

1. Preparing stock solution: 14.7g of 2, 2' -bis [4- (4-aminophenoxyphenyl)]Dissolving propane (BAPP) and 1.8g 3-diaminobenzoic acid (DABA) in 146.1g N, N-dimethylacetamide, stirring until completely dissolved, adding 15.5g benzophenone dianhydride (BTDA) powder (molar ratio of dianhydride to diamine is 1:1), and stirring for full reaction to obtain final product with apparent viscosity of 5 × 10³A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a spin coating method, horizontally immersing the inorganic ceramic support in ethanol for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the solvent in a drying oven at 100 ℃ for 20min, and preserving the heat at 260 ℃ for 30min to perform imidization, thus obtaining the prepared PI pervaporation membrane a coated with the PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the temperature in a 100 ℃ oven for 20min, preserving the temperature at 260 ℃ for 30min, and carrying out imidization to obtain the pervaporation membrane coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 4%; the PI pervaporation membrane prepared by the method is tested to have the compact layer thickness of about 16 mu m and the permeation flux of 382 g/(m)²H), separation factor 22.72, PSI 8679 g/(m)²·h)。

[ example 2 ]

1. Preparing stock solution: dissolving 13.0g of p-Phenylenediamine (PDA) in 200.2g N, stirring until the mixture is completely dissolved, adding 37.1g of biphenyl tetracarboxylic dianhydride (BPDA) powder (the molar ratio of dianhydride to diamine is 1.05:1), and continuously stirring until the mixture fully reacts to obtain the product with the apparent viscosity of 4.8 x 10⁵A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a spin coating method, horizontally immersing the inorganic ceramic support in ethanol for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the solvent in a 50 ℃ oven for 60min, and preserving the heat at 240 ℃ for 60min to perform imidization, thus obtaining the PI pervaporation membrane a to be prepared with a PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a in ethanol for 10min to completely diffuse the solvent, taking out the prepared PI pervaporation membrane, then preserving the temperature in a 50 ℃ oven for 60min, preserving the temperature at 240 ℃ for 60min, and carrying out imidization to obtain the prepared PI pervaporation membrane b coated with a PI compact layer.

c) Coating a layer of PAA solution on the prepared PI pervaporation membrane b obtained in the step b) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane b in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the temperature in a 50 ℃ oven for 60min, preserving the temperature at 240 ℃ for 60min, and carrying out imidization to obtain the pervaporation membrane coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 2.5%; the PI pervaporation membrane prepared by the method is tested to have the thickness of about 23 mu m and the permeation flux of 316 g/(m)²H), separation factor 32.7, PSI 10333 g/(m)²·h)。

[ example 3 ]

1. Preparing stock solution: dissolving 24.0g of 4, 4-diaminodiphenyl ether (ODA) in 220.9g N-methyl-2-pyrrolidone, stirring until the mixture is completely dissolved, adding 39.3g of benzophenone dianhydride (BTDA) powder (the molar ratio of dianhydride to diamine is 0.99:1), and continuously stirring until the mixture is fully reacted to obtain the product with the apparent viscosity of 3.6 x 10⁵A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a blade coating method, horizontally immersing the inorganic ceramic support into an N-methyl-2-pyrrolidone aqueous solution (20 wt%) for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the solvent in an oven at 80 ℃ for 40min, and preserving the heat at 300 ℃ for 10min to perform imidization, thus obtaining the prepared PI pervaporation membrane a coated with a PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a into N-methyl-2-pyrrolidone aqueous solution (20 wt%) for 10min to completely diffuse the solvent, taking out the membrane, then preserving the heat in an oven at 80 ℃ for 40min, and preserving the heat at 300 ℃ for 10min to perform imidization, thus obtaining the prepared PI pervaporation membrane b coated with a PI compact layer.

c) Coating a layer of PAA solution on the prepared PI pervaporation membrane b obtained in the step b) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane b in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the heat in an oven at 80 ℃ for 40min, and preserving the heat at 300 ℃ for 10min to perform imidization, thus obtaining the prepared PI pervaporation membrane c coated with a PI compact layer.

d) And c) attaching a layer of PI film on the prepared PI pervaporation film c through the preparation process of the step c), thus obtaining the pervaporation film coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 5.2%; the PI pervaporation membrane prepared by the method is tested to have the thickness of about 80 mu m and the permeation flux of 51 g/(m)²H), separation factor 243, PSI 12393 g/(m)²·h)。

[ example 4 ]

1. Preparing stock solution: dissolving 24.0g of 4, 4-diaminodiphenyl ether (ODA)Dissolving in 146.6g N N-dimethylacetamide, stirring to dissolve completely, adding 24.9g pyromellitic dianhydride (PMDA) powder (molar ratio of dianhydride to diamine is 0.95:1), and stirring to react completely to obtain final product with apparent viscosity of 2.2 × 10⁵A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) covering a layer of PAA solution on an inorganic ceramic support by a dip-coating method, horizontally immersing the inorganic ceramic support in acetone for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the inorganic ceramic support in a 120 ℃ oven for 10min, and preserving the temperature at 350 ℃ for 20min to perform imidization, thus obtaining the prepared PI pervaporation membrane a covered with the PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by using a dipping and pulling method, horizontally immersing the prepared PI pervaporation membrane a in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the heat in a 120 ℃ oven for 10min, preserving the heat at 350 ℃ for 20min, and carrying out imidization to obtain the prepared PI pervaporation membrane b coated with the PI compact layer.

c) Coating a layer of PAA solution on the prepared PI pervaporation membrane b obtained in the step b) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane b in acetone for 10min to completely diffuse the solvent, taking out the membrane, then preserving the heat in a 120 ℃ oven for 10min, preserving the heat at 350 ℃ for 20min, and carrying out imidization to obtain the prepared PI pervaporation membrane c coated with the PI compact layer.

d) Coating a layer of PAA solution on the prepared PI pervaporation membrane c obtained in the step c) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane c in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the heat in a 120 ℃ oven for 10min, preserving the heat at 350 ℃ for 20min, and carrying out imidization to obtain the pervaporation membrane coated with a plurality of PI compact layers.

Testing the swelling degree of the PI film prepared by the method to be 20%; the PI pervaporation membrane prepared by the method is tested to have the compact layer thickness of about 62 mu m and the permeation flux of 133 g/(m)²H), separation factor 66.2, PSI 8804 g/(m)²·h)。

[ example 5 ]

1. Preparing stock solution: 12.9g of 4, 4-Biphenyldiamine (BZD) was dissolved in 660.7g N, N-dimethylacetamide, and after stirring until the solution was completely dissolved,adding 21.9g benzophenone dianhydride (BTDA) powder (molar ratio of dianhydride to diamine is 0.97:1), and stirring for reacting to obtain final product with apparent viscosity of 1 × 10³A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a spin coating method, taking out, then preserving heat for 1min in a baking oven at 100 ℃ to remove the solvent by a heating method, and preserving heat for 5min at 320 ℃ to perform imidization, thus obtaining the prepared PI pervaporation membrane a coated with a PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the temperature in a 50 ℃ oven for 60min, preserving the temperature at 240 ℃ for 60min, and carrying out imidization to obtain the pervaporation membrane coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 3.7%; the PI pervaporation membrane prepared by the method is tested to have the thickness of about 11 mu m and the permeation flux of 210 g/(m)²H), separation factor 54.1, PSI 11361 g/(m)²·h)。

[ example 6 ]

1. Preparing stock solution: 9.8g of 2, 2' -bis [4- (4-aminophenoxyphenyl)]Dissolving propane (BAPP) and 2.4g4, 4' -diaminodiphenylmethane (MDA) in 215.5g N, N-dimethylacetamide, stirring until the mixture is completely dissolved, adding 11.7g benzophenone dianhydride (BTDA) powder (molar ratio of dianhydride to diamine is 1.01:1), and continuously stirring until the mixture is fully reacted to obtain the product with apparent viscosity of 3 × 10³A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a dip-coating method, horizontally immersing the inorganic ceramic support in ethanol for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the inorganic ceramic support in a 60 ℃ oven for 30min, and preserving the heat at 250 ℃ for 40min to perform imidization, thus obtaining the prepared PI pervaporation membrane a coated with the PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the heat in a 60 ℃ oven for 30min, preserving the heat at 250 ℃ for 40min, and carrying out imidization to obtain the prepared PI pervaporation membrane b coated with a PI compact layer.

c) And (b) attaching a layer of PI film on the prepared PI pervaporation film b through the preparation process of the step b), thus obtaining the prepared pervaporation film c coated with a plurality of PI compact layers.

d) And c) attaching a layer of PI film on the prepared PI pervaporation film c through the preparation process of the step c), thus obtaining the prepared pervaporation film d coated with a plurality of PI compact layers.

e) And (b) attaching a layer of PI film on the prepared PI pervaporation film d through the preparation process of the step b), thus obtaining the prepared pervaporation film e coated with a plurality of PI compact layers.

f) And c) attaching a layer of PI film on the prepared PI pervaporation film e through the preparation process of the step c), thus obtaining the pervaporation film coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 8.0%; the PI pervaporation membrane prepared by the method is tested to have the thickness of about 49 mu m and the permeation flux of 57.1 g/(m)²H), separation factor 160.8, PSI 9181 g/(m)²·h)。

[ example 7 ]

1. Preparing stock solution: dissolving 20.0g of 4, 4-diaminodiphenyl ether (ODA) in 262.5g N, N-dimethylacetamide, stirring until the mixture is completely dissolved, adding 11.2g of benzophenone dianhydride (BTDA) powder and 15.1g of pyromellitic dianhydride (PMDA) powder (the molar ratio of dianhydride to diamine is 1.01:1), and continuously stirring until the mixture fully reacts to obtain the product with the apparent viscosity of 8 x 10⁴A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a blade coating method, horizontally immersing the inorganic ceramic support in ethanol for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the solvent in a baking oven at 100 ℃ for 20min, preserving the heat at 300 ℃ for 20min, and carrying out imidization to obtain the prepared PI pervaporation membrane a coated with the PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a into N, N-dimethylacetamide aqueous solution (15 wt%) for 10min to completely diffuse the solvent, taking out the prepared PAA solution, keeping the temperature in a 100 ℃ oven for 20min, keeping the temperature at 300 ℃ for 20min, and imidizing to obtain the pervaporation membrane coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 4.4%; the PI pervaporation membrane prepared by the method is tested to have the compact layer thickness of about 2 mu m and the permeation flux of 454 g/(m)²H), separation factor 29.2, PSI 13256 g/(m)²·h)。

[ example 8 ]

1. Preparing stock solution: dissolving 13g of p-Phenylenediamine (PDA) in 197.8g N-methyl-2-pyrrolidone, stirring until the solution is completely dissolved, adding 36.5g of 2,3,3',4' -diphenyl ether tetracarboxylic dianhydride (ODPA) powder dianhydride and diamine in a molar ratio of 0.98:1, and continuously stirring until the mixture fully reacts to obtain the product with the apparent viscosity of 1.4 multiplied by 10⁴A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a spin coating method, horizontally immersing the inorganic ceramic support into N-methyl-2-pyrrolidone aqueous solution (25 wt%) for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the temperature in a drying oven at 100 ℃ for 30min, preserving the temperature at 300 ℃ for 30min, and carrying out imidization to obtain the prepared PI pervaporation membrane a coated with a PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a in pure water for 10min to completely diffuse the solvent, taking out the membrane, then preserving the temperature in a 100 ℃ oven for 30min, preserving the temperature at 300 ℃ for 30min, and carrying out imidization to obtain the pervaporation membrane coated with a plurality of PI compact layers.

The swelling degree of the PI film prepared by the method is 5.9 percent; the PI pervaporation membrane prepared by the method is tested to have the dense layer thickness of about 25 mu m and the permeation flux of 411 g/(m)²H), separation factor 17.9, PSI 7357 g/(m)²·h)。

[ COMPARATIVE EXAMPLE 1 ]

1. Preparing stock solution: 24g of 4, 4-diaminodiphenyl ether (ODA) are dissolved in 3553g N, stirring to completely dissolve, adding 38.7g of benzophenone dianhydride (BTDA) powder dianhydride and diamine at a molar ratio of 1:1, and continuously stirring to fully react to obtain the final product with apparent viscosity of 1.7 × 10⁴A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane: coating a layer of PAA solution on a glass plate by a blade coating method, horizontally immersing the glass plate in pure water for 10min to completely diffuse the solvent, taking out the glass plate, then keeping the temperature in an oven at 100 ℃ for 10min, and keeping the temperature at 300 ℃ for 10min to perform imidization.

3. And stripping the imidized PI film from the glass plate to obtain the PI pervaporation film.

Testing that the swelling degree of the PI film prepared by the method is 3.9%; when the pervaporation performance test is carried out, the film is broken, and the pervaporation separation effect cannot be achieved.

[ COMPARATIVE EXAMPLE 2 ]

1. Preparing stock solution: dissolving 12.9g of 4, 4-Biphenyldiamine (BZD) in 660.7g N, N-dimethylacetamide, stirring until the mixture is completely dissolved, adding 21.9g of benzophenone dianhydride (BTDA) powder (the molar ratio of dianhydride to diamine is 0.97:1), and continuously stirring until the mixture fully reacts to obtain the product with the apparent viscosity of 1 x 10³A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) and (2) coating a layer of PAA solution on the inorganic ceramic support by a spin coating method, horizontally immersing the inorganic ceramic support in pure water for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the temperature in a 50 ℃ oven for 60min, preserving the temperature at 240 ℃ for 60min, and carrying out imidization to obtain the prepared PI pervaporation membrane a coated with the PI compact layer.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, taking out, then keeping the temperature in a drying oven at 100 ℃ for 1min, removing the solvent by a thermal drying method, and keeping the temperature at 320 ℃ for 5min for imidization to obtain the pervaporation membrane coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 4.2%; the PI pervaporation membrane prepared by the method is tested to have the thickness of about 9 mu m and the permeation flux of 237 g/(m)²H), separation factor 21.5, PSI 5095 g/(m)²·h)。

[ COMPARATIVE EXAMPLE 3 ]

1. Preparing stock solution: 14.7g of 2, 2' -bis [4- (4-aminophenoxyphenyl)]Dissolving propane (BAPP) and 1.8g 3-diaminobenzoic acid (DABA) in 146.1g N, N-dimethylacetamide, stirring until completely dissolved, adding 15.5g benzophenone dianhydride (BTDA) powder (molar ratio of dianhydride to diamine is 1:1), and stirring for full reaction to obtain final product with apparent viscosity of 5 × 10³A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a spin coating method, horizontally immersing the inorganic ceramic support in ethanol for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the solvent in a drying oven at 100 ℃ for 20min, and preserving the heat at 260 ℃ for 30min to perform imidization, thus obtaining the prepared PI pervaporation membrane a coated with a layer of polyimide membrane.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the PAA solution in ethanol for 10min to completely diffuse the solvent, taking out the PAA solution, then preserving the PAA solution in a 100 ℃ drying oven for 20min, preserving the heat at 260 ℃ for 30min, and carrying out imidization to obtain the pervaporation membrane coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 4.5%; the PI pervaporation membrane prepared by the method is tested to have the compact layer thickness of about 18 mu m and the permeation flux of 98 g/(m)²H), separation factor 23.40, PSI 2293.2 g/(m)²·h)。

[ COMPARATIVE EXAMPLE 4 ]

1. Preparing stock solution: 14.7g of 2, 2' -bis [4- (4-aminophenoxyphenyl)]Dissolving propane (BAPP) and 1.8g 3-diaminobenzoic acid (DABA) in 146.1g N, N-dimethylacetamide, stirring until completely dissolved, adding 15.5g benzophenone dianhydride (BTDA) powder (molar ratio of dianhydride to diamine is 1:1), and stirring for full reaction to obtain final product with apparent viscosity of 5 × 10³A uniform transparent viscous polyamic acid solution of cP (25 ℃).

2. Preparing a pervaporation membrane:

a) coating a layer of PAA solution on an inorganic ceramic support by a spin coating method, horizontally immersing the inorganic ceramic support in pure water for 10min to completely diffuse the solvent, taking out the inorganic ceramic support, then preserving the temperature in a baking oven at 100 ℃ for 20min, preserving the temperature at 260 ℃ for 30min to imidize, and obtaining the prepared PI pervaporation membrane a coated with a layer of polyimide membrane.

b) Coating a layer of PAA solution on the prepared PI pervaporation membrane a obtained in the step a) by a spin coating method, horizontally immersing the prepared PI pervaporation membrane a in pure water for 10min to completely diffuse the solvent, taking out the prepared PI pervaporation membrane, then preserving the temperature in a 100 ℃ oven for 20min, preserving the temperature at 260 ℃ for 30min, and carrying out imidization to obtain the polyimide pervaporation membrane coated with a plurality of PI compact layers.

Testing that the swelling degree of the PI film prepared by the method is 3.8%; the thickness of the compact layer of the polyimide pervaporation membrane prepared by the method is about 20 mu m, and the permeation flux is 355 g/(m)²H), separation factor 4.32, PSI 1533 g/(m)²·h)。