Preparation method of benzoxazole-polyimide copolymer gas separation membrane

Abstract

The invention discloses a preparation method of a benzoxazole-polyimide copolymer gas separation membrane, which comprises the following steps: a solvent and two aromatic diamines are added into a flask, one aromatic diamine is hydroxyl-containing aromatic diamine; adding dianhydride after dissolving, and reacting to generate a hydroxyl polyamide acid solution; filtering the hydroxyl polyamide acid solution in a filter, pouring on a tool plate, drying, performing thermal imidization in a drying oven, and cooling to obtain a hydroxyl polyimide-polyimide copolymer film; and placing the hydroxyl polyimide-polyimide copolymer film in a tubular furnace, and carrying out thermal rearrangement reaction in an argon atmosphere to generate the benzoxazole-polyimide copolymer film. According to the gas separation membrane obtained by the method, the gas permeability is remarkably improved, and the carbon dioxide separation capability is improved.

Description

Technical Field

[0001] The invention relates to the technical field of gas separation membranes, and in particular to a method for preparing a benzoxazole-polyimide copolymer gas separation membrane. Background Art

[0002] In recent years, the increase in carbon dioxide emissions has led to the intensification of the greenhouse effect and global warming, resulting in a series of climate and environmental problems. CO2 emission reduction has become the focus of attention of countries around the world and an important issue that human society needs to solve urgently. Traditional carbon dioxide separation and capture methods have problems such as complex processes, high energy consumption and high pollution. Membrane separation technology is a new separation technology for removing CO2 from flue gas and energy gas, which has great potential in CO2 capture.

[0003] Membrane materials are key components of membrane separation technology, and the development of high-performance gas separation membranes is of great significance. Membrane materials used for CO2 separation should have high permeability, high selectivity, high mechanical strength, high stability, and good film-forming properties. There is a certain restrictive relationship between the selectivity and permeability that determine the separation effect of membrane materials.

[0004] Traditional membrane materials have low separation performance. Under certain conditions, CO2 will induce polymer chain plasticization, which makes the increase in the permeation rate of other gases greater than the increase in the permeation rate of CO2, thereby reducing gas selectivity and resulting in a decrease in the separation coefficient, affecting its application range. Summary of the invention

[0005] In order to overcome the above-mentioned defects in the prior art, the present invention provides a method for preparing a benzoxazole-polyimide copolymer gas separation membrane.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] A method for preparing a benzoxazole-polyimide copolymer gas separation membrane comprises the following steps:

[0008] Step 1, adding a solvent and two aromatic diamines into a flask, wherein one aromatic diamine is a hydroxyl-containing aromatic diamine; adding dianhydride after dissolving, and generating a hydroxy polyamic acid solution after reaction;

[0009] Step 2, after filtering the hydroxy polyamic acid solution in a filter, pouring it onto a tool plate, drying it, thermally imidizing it in an oven, and cooling it to obtain a hydroxy polyimide-polyimide copolymer film;

[0010] Step 3: placing the hydroxy polyimide-polyimide copolymer film in a tube furnace to generate a benzoxazole-polyimide copolymer film by thermal rearrangement reaction in an argon atmosphere.

[0011] Furthermore, in step 1, the solvent is N-methylpyrrolidone; and the two aromatic diamines are 4,4-hexafluoroisopropylphthalic anhydride and 4,4'-diaminodiphenyl ether.

[0012] Furthermore, in step 1, the dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0013] Furthermore, in step 1, the molar ratio of the two aromatic diamines is 1:1, and the molar amount of dianhydride is equal to the sum of the molar amounts of the two aromatic diamines.

[0014] Furthermore, in step 1, the solvent and the two aromatic diamines are dissolved under nitrogen purge.

[0015] Furthermore, in step 2, the pore size of the filter is 0.4 to 0.6 microns.

[0016] Furthermore, in step 2, the tool plate is a glass plate.

[0017] Furthermore, in step 2, the step of thermal imidization in an oven includes: keeping the oven temperature at 50°C for 3 hours, keeping the oven temperature at 100°C for 1 hour, keeping the oven temperature at 200°C for 1 hour, and keeping the oven temperature at 250°C for 30 minutes.

[0018] Furthermore, in step 3, the tube furnace is a quartz tube furnace.

[0019] Furthermore, in step 3, when the thermal rearrangement reaction occurs, the temperature of the tube furnace is 400-500°C, and the argon gas flow rate is 250-350 cm 3 / min.

[0020] The beneficial effects of the present invention are as follows: the gas separation membrane obtained according to the method, in a solid state, thermally converts the hydroxyimine group into a benzoxazole structure, increases the rigidity of the polymer skeleton, and the generated microcavities increase the diffusion pathways of the membrane, significantly increases the gas permeability, and improves the gas separation performance of the copolymer membrane under harsh conditions. The benzoxazole-polyimide copolymer gas separation membrane prepared according to the method of the present invention has a very high CO2 / N2 separation performance, and improves the ability of the membrane to separate carbon dioxide. DETAILED DESCRIPTION

[0021] A preferred embodiment is given below to more clearly and completely illustrate the present invention.

[0022] A method for preparing a benzoxazole-polyimide copolymer gas separation membrane comprises the following steps:

[0023] Step 1, preparing a hydroxy polyamic acid solution.

[0024] Add solvent and two aromatic diamines into a flask, one of which is a hydroxyl-containing aromatic diamine; add dianhydride after dissolving, and generate a hydroxy polyamic acid solution after reaction. Specifically:

[0025] 5mmol 4,4-hexafluoroisopropylphthalic anhydride, 5mmol 4,4'-diaminodiphenyl ether and 100ml N-methylpyrrolidone were added to a three-necked flask, and the mixture was dissolved in the three-necked flask under nitrogen purge; then 10mmol 3,3',4,4'-biphenyltetracarboxylic dianhydride was added to the three-necked flask, and the mixture was stirred to generate a hydroxy polyamic acid solution after reaction.

[0026] The molar ratio of 4,4-hexafluoroisopropylphthalic anhydride to 4,4'-diaminodiphenyl ether is 1:1, and the molar amount of 3,3',4,4'-biphenyltetracarboxylic dianhydride is equal to the sum of the molar amounts of 4,4-hexafluoroisopropylphthalic anhydride and 4,4'-diaminodiphenyl ether.

[0027] Step 2, preparing a hydroxy polyimide-polyimide copolymer membrane.

[0028] The hydroxy polyamic acid solution is filtered in a filter, poured onto a tool plate, dried, thermally imidized in an oven, and cooled to obtain a hydroxy polyimide-polyimide copolymer film. Specifically:

[0029] The hydroxypolyamic acid solution was filtered through a filter with a pore size of 0.5 microns and then poured onto a dry glass plate. After being dried at 80°C under ventilation, the solution was peeled off from the glass plate and placed in an oven for thermal imidization. After being cooled to room temperature, a hydroxypolyimide-polyimide copolymer membrane was obtained.

[0030] The step of thermal imidization in an oven includes: keeping the temperature at 50°C for 3 hours, keeping the temperature at 100°C for 1 hour, keeping the temperature at 200°C for 1 hour, and keeping the temperature at 250°C for 30 minutes. The oven can be a vacuum oven.

[0031] Step 3, preparing a benzoxazole-polyimide copolymer gas separation membrane.

[0032] The hydroxy polyimide-polyimide copolymer film is placed in a tube furnace and undergoes a thermal rearrangement reaction in an argon atmosphere to generate a benzoxazole-polyimide copolymer film.

[0033] In the tubular furnace, the hydroxyl polyimide in the hydroxyl polyimide-polyimide copolymer film undergoes a thermal rearrangement reaction, and the ortho-hydroxyl group of the aromatic imine bond attacks the carbonyl group in the imine to form an intermediate fusion ring, forming a carboxyl-benzoxazole structure, and generating a benzoxazole-polyimide copolymer.

[0034] The heating rate of the tube furnace is 4-6°C / min. When the thermal rearrangement reaction occurs, the temperature of the tube furnace is 400-500°C, and the argon flow rate is 250-350cm 3 / min.

[0035] The tube furnace may be a quartz tube furnace.

[0036] The performance test of the benzoxazole-polyimide copolymer membrane obtained by the method showed that the prepared benzoxazole-polyimide copolymer membrane had good CO2 / N2 separation performance, with a CO2 permeability of 25.8 Barrer and a selectivity of 38.

[0037] Compared with the existing gas separation membrane, the performance of the gas separation membrane obtained by the method of the present invention is improved.

[0038] The preparation method of the present invention has the following advantages:

[0039] 1. The gas separation membrane obtained by this method, in a solid state, thermally converts the hydroxyimine group into a benzoxazole structure, thereby increasing the rigidity of the polymer skeleton, and the generated free volume elements or microcavities enhance the membrane diffusion pathway, significantly increasing the gas permeability, and improving the gas separation performance of the copolymer membrane under harsh conditions.

[0040] 2. The benzoxazole-polyimide copolymer gas separation membrane prepared according to the method of the present invention has a very high CO2 / N2 separation performance and improves the ability to separate carbon dioxide.

[0041] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a benzoxazole-polyimide copolymer gas separation membrane, characterized in that: It includes the following steps: Step 1, adding a solvent and two aromatic diamines into a flask, wherein one aromatic diamine is a hydroxyl-containing aromatic diamine; adding dianhydride after dissolving, and generating a hydroxy polyamic acid solution after reaction; Step 2, after filtering the hydroxy polyamic acid solution in a filter, pouring it onto a tool plate, drying it, thermally imidizing it in an oven, and cooling it to obtain a hydroxy polyimide-polyimide copolymer film; Step 3: placing the hydroxy polyimide-polyimide copolymer film in a tube furnace to generate a benzoxazole-polyimide copolymer film by thermal rearrangement reaction in an argon atmosphere.

2. The method for preparing a benzoxazole-polyimide copolymer gas separation membrane according to claim 1, characterized in that: In step 1, the solvent is N-methylpyrrolidone; the two aromatic diamines are 4,4-hexafluoroisopropylphthalic anhydride and 4,4'-diaminodiphenyl ether.

3. The method for preparing the benzoxazole-polyimide copolymer gas separation membrane according to claim 2, characterized in that: In step 1, the dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride.

4. The method for preparing a benzoxazole-polyimide copolymer gas separation membrane according to claim 3, characterized in that: In step 1, the molar ratio of the two aromatic diamines is 1:1, and the molar amount of dianhydride is equal to the sum of the molar amounts of the two aromatic diamines.

5. The method for preparing the benzoxazole-polyimide copolymer gas separation membrane according to claim 1, characterized in that: In step 1, the solvent and the two aromatic diamines are dissolved under nitrogen purge.

6. The method for preparing a benzoxazole-polyimide copolymer gas separation membrane according to claim 1, characterized in that: In step 2, the pore size of the filter is 0.4 to 0.6 microns.

7. The method for preparing a benzoxazole-polyimide copolymer gas separation membrane according to claim 1, characterized in that: In step 2, the tool plate is a glass plate.

8. The method for preparing a benzoxazole-polyimide copolymer gas separation membrane according to claim 1, characterized in that: In step 2, the step of thermal imidization in an oven includes: keeping the oven temperature at 50°C for 3 hours, keeping the oven temperature at 100°C for 1 hour, keeping the oven temperature at 200°C for 1 hour, and keeping the oven temperature at 250°C for 30 minutes.

9. The method for preparing a benzoxazole-polyimide copolymer gas separation membrane according to claim 1, characterized in that: In step 3, the tube furnace is a quartz tube furnace.

10. The method for preparing a benzoxazole-polyimide copolymer gas separation membrane according to claim 1, characterized in that: In step 3, when the thermal rearrangement reaction occurs, the temperature of the tube furnace is 400-500°C, and the argon gas flow rate is 250-350 cm 3 / min.