Preparation method of modified polytetrafluoroethylene-based anion exchange membrane

Abstract

The invention discloses a new technology, and particularly relates to a preparation method of a quaternized silanized zirconium dioxide nanofiber modified polytetrafluoroethylene-based anion exchange membrane, which comprises the following preparation steps: modifying zirconium dioxide nanofiber by using a silane coupling agent to improve the hydrophilicity of the zirconium dioxide nanofiber, quaternizing the modified zirconium dioxide nanofiber to obtain a quaternized silanized zirconium dioxide nanofiber modified polytetrafluoroethylene-based anion exchange membrane, and drying the quaternized silanized zirconium dioxide nanofiber modified polytetrafluoroethylene-based anion exchange membrane to obtain the quaternized silanized zirconium dioxide nanofiber modified polytetrafluoroethylene-based anion exchange membrane. And mixing with polytetrafluoroethylene, extruding, calendaring, and longitudinally and transversely stretching, so as to obtain the composite anion exchange membrane. According to the prepared composite film, the properties such as hydrophilicity, mechanical strength and ionic conductivity are greatly improved, and it is indicated that the composite film has good application prospects in the industries of alkaline electrolyzed water, fuel cells and water treatment.

Description

Technical Field

[0001] The invention relates to the technical field of membrane materials, and in particular to a quaternary ammonium silanized zirconium dioxide modified polytetrafluoroethylene-based anion exchange membrane and a preparation method thereof. Background Art

[0002] As a zero-carbon energy carrier, hydrogen is gaining more and more attention. Since hydrogen rarely exists in the form of a single substance in nature, it needs to be produced through industrial processes. Compared with other technologies such as fossil fuel reforming, water electrolysis hydrogen production technology has the advantages of high hydrogen purity and zero carbon emissions, making it the most promising source of green hydrogen. Among the various water electrolysis hydrogen production technologies, alkaline water electrolysis hydrogen production technology AWE is the earliest technology to be industrialized. It was applied as early as the beginning of the 20th century and is currently the most mature and economical water electrolysis hydrogen production technology. Anion exchange membrane water electrolysis technology (AEMWE) has attracted widespread attention due to its ability to use low-concentration alkaline conditions (≤1M) or pure water and produce high-purity hydrogen.

[0003] Anion exchange membrane is a kind of polymer membrane containing alkaline active groups and having selective permeability to anions, also known as ion selective permeability membrane. Anion exchange membrane consists of three parts: polymer main chain with fixed groups, namely polymer matrix (also known as base membrane), positively charged active groups (ie cations) and anions that can move freely on the active groups. Generally, cations such as -NH3, -NR2H or -PR3 are used as active exchange groups, and OH is generated at the cathode. - As a carrier, it moves to the anode through the selective permeability of the anion exchange membrane.

[0004] Polytetrafluoroethylene (PTFE) has excellent chemical stability, high temperature resistance and good mechanical properties, which makes it have long-term stability and reliability in high-concentration alkali solution, not prone to aging or corrosion, and suitable as the basic material of anion exchange membrane. However, polytetrafluoroethylene itself is a hydrophobic material and lacks hydrophilic groups, which makes its performance in ion conduction poor.

[0005] As an important inorganic material, zirconium dioxide nanofibers have attracted much attention due to their unique structural characteristics, excellent chemical and thermal stability, and excellent optical and electronic properties. When applied to composite films, their high hydrophilicity can improve surface wettability and enhance their toughness. Summary of the invention

[0006] The present invention aims to provide a quaternary ammonium silanized modified polytetrafluoroethylene-based anion exchange membrane and a preparation method thereof in view of the deficiencies in the prior art.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0008] A modified polytetrafluoroethylene-based anion exchange membrane and a preparation method thereof, comprising the following method:

[0009] (1) Preparation of silanized zirconium dioxide nanofibers: Mix the zirconium dioxide nanofibers in a mixed solution containing ethanol and water, then slowly add 3-methoxysilyl propylamine, and reflux for 6-10 hours after ultrasonic treatment. Use hydrochloric acid solution to adjust the pH of the system to 3-6. After centrifugation, wash with anhydrous ethanol for multiple times to remove excess 3-methoxysilyl propylamine, and bake at 60-80°C for 8-12 hours to obtain silanized zirconium dioxide nanofibers.

[0010] (2) Preparation of quaternized silanized zirconium dioxide nanofibers: The silanized zirconium dioxide nanofibers obtained in step (1) are dispersed in water, and glycidyl trimethylammonium chloride is added thereto. The mixture is stirred at 50-70° C. for 20-26 hours, and the reaction product is precipitated in acetone, filtered, and dried to obtain quaternized silanized zirconium dioxide nanofibers.

[0011] (3) Preparation of composite film: The quaternized silanized zirconium dioxide nanofibers dried in step (2) and polytetrafluoroethylene (PTFE) fine powder are mixed, and then additives are added and mixed thoroughly to obtain a mixed powder, which is then put into an extruder. The powder is pushed and extruded into a strip-shaped mixture, which is then rolled into a film sheet under a rolling machine. After heating and volatilization to remove the additives, the composite film is stretched longitudinally and transversely to obtain a composite film.

[0012] The beneficial effects of the present invention are:

[0013] (1) The present invention uses a silane coupling agent to modify the zirconium dioxide nanofibers, which greatly improves the hydrophilicity of the membrane, and the high strength and toughness of the zirconium dioxide nanofibers themselves enhance the mechanical strength of the membrane;

[0014] (2) The composite anion exchange membrane prepared by the present invention greatly improves the ionic conductivity of the membrane by introducing quaternary ammonium groups as conductive groups;

[0015] (3) The present invention uses polytetrafluoroethylene as the substrate of the membrane, which greatly improves the mechanical strength of the membrane, improves the mechanical properties and dimensional stability of the membrane, and prolongs the service life of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the SEM image of PTFE before modification; Figure 2 This is the SEM image of PTFE after modification; Figure 3 This is the contact angle test diagram before PTFE modification; Figure 4 This is the contact angle test diagram after PTFE modification. DETAILED DESCRIPTION

[0018] Example 1

[0019] (1) Preparation of silanized zirconium dioxide nanofibers

[0020] 1g of zirconium dioxide nanofibers were mixed in 100ml of a solution containing 95% ethanol and 5% water, followed by slow addition of 1g of 3-methoxysilylpropylamine, followed by ultrasonic treatment for 10min and reflux treatment for 8h. The pH of the system was adjusted to 4.5 using a 12-1mol / L hydrochloric acid solution. Finally, the system was centrifuged at 4000r / min for 30min, and then washed with anhydrous ethanol for 3 times to remove excess 3-methoxysilylpropylamine, and then dried at 80°C for 12 hours to obtain silanized zirconium dioxide nanofibers.

[0021] (2) Preparation of quaternized silanized zirconium dioxide nanofibers

[0022] 3 g of silanized zirconium dioxide nanofibers were dispersed in 30 ml of water, and 6 g of glycidyl trimethylammonium chloride was added thereto, and stirred at 60° C. for 24 h. The reaction product was then precipitated in acetone, and then filtered and dried in an oven at 60° C. to obtain quaternized silanized zirconium dioxide nanofibers.

[0023] (3) Preparation of composite films

[0024] Mix 2g of quaternized silanized zirconium dioxide nanofibers and 200g of PTFE fine powder, add 40g of liquid paraffin and mix thoroughly to obtain a mixed powder, then put it into an extruder for molding, the temperature is 50℃, the plunger descends at a speed of 76mm / min, the pressure is 3.5MPa, the mixed material is slowly pressed into a cylindrical block, and then put into a calender for calendering 5 times to obtain a 0.5nm raw tape, and the calendering roller is kept at 70℃. Select a piece of the smoother part of the raw tape, use a bidirectional film stretching machine to first stretch the raw tape in the longitudinal direction, and then change to the transverse direction after stretching to 1 times the size, and then give stress in the longitudinal direction. After several longitudinal and transverse stretching, the film reaches 3 times the size, and a composite film can be obtained.

[0025] Example 2

[0026] (1) Preparation of silanized zirconium dioxide nanofibers

[0027] Same as step (1) of Example 1

[0028] (2) Preparation of quaternized silanized zirconium dioxide nanofibers

[0029] Same as step (2) of Example 1

[0030] (3) Preparation of composite films

[0031] Mix 5g of quaternized silanized zirconium dioxide nanofibers and 200g of PTFE fine powder, add 20g of liquid paraffin and mix thoroughly to obtain a mixed powder, then put it into an extruder for molding, the temperature is 50℃, the plunger descends at a speed of 76mm / min, and the pressure is 3.5MPa. The mixed material is slowly pressed into a cylindrical block and then put into a calender for calendering 5 times to obtain a 0.5mm raw tape, and the calendering roller is kept at 70℃. Select a piece of the smoother part of the raw tape, use a bidirectional film stretching machine to first stretch the raw tape in the longitudinal direction, and then change to the transverse direction after stretching to 1 times the size, and then give stress in the longitudinal direction. After several longitudinal and transverse stretching, the film reaches 3 times the size, and a composite film can be obtained.

[0032] Example 3

[0033] (1) Preparation of silanized zirconium dioxide nanofibers

[0034] Same as step (1) of Example 1

[0035] (2) Preparation of quaternized silanized zirconium dioxide nanofibers

[0036] Same as step (2) of Example 1

[0037] (3) Preparation of composite films

[0038] Mix 2g of quaternized silanized zirconium dioxide nanofibers and 200g of PTFE fine powder, add 20g of liquid paraffin and mix thoroughly to obtain a mixed powder, then put it into an extruder for molding, the temperature is 50℃, the plunger descends at a speed of 76mm / min, and the pressure is 3.5MPa. The mixed material is slowly pressed into a cylindrical block and then put into a calender for calendering 5 times to obtain a 0.5mm raw tape, and the calendering roller is kept at 70℃. Select a piece of the smoother part of the raw tape, use a bidirectional film stretching machine to first stretch the raw tape in the longitudinal direction, and then change to the transverse direction after stretching to 1 times the size, and then give stress in the longitudinal direction. After several longitudinal and transverse stretching, the film reaches 3 times the size, and a composite film can be obtained.

[0039] Comparative Example 1

[0040] This comparative example is basically the same as Example 1, the only difference being the content of quaternized silanized zirconium dioxide nanofibers in the composite film. The results show that the composite film with 2g of quaternized silanized zirconium dioxide nanofibers has a better effect in alkaline electrolysis of water, because the quaternized silanized zirconium dioxide nanofibers with 5g added are not evenly dispersed in the composite film, resulting in agglomeration problems.

[0041] Comparative Example 2

[0042] The comparative example is basically the same as Example 1, the only difference is the content of the additive liquid paraffin in the composite film. The results show that the composite film with 40g of liquid paraffin added has the most suitable film-forming effect. This is because the composite film with 20g of liquid paraffin added has some traces of breaking during extrusion, and there are obvious cracks on the strip material after calendering, and the product has no plasticity.

Claims

1. A method for preparing a modified polytetrafluoroethylene-based anion exchange membrane, characterized in that: The specific steps include: (1) Preparation of silanized zirconium dioxide nanofibers: Mix the zirconium dioxide nanofibers in a mixed solution containing ethanol and water, then slowly add 3-methoxysilyl propylamine, and reflux for 6-10 hours after ultrasonic treatment. Use hydrochloric acid solution to adjust the pH of the system to 3-6. After centrifugation, wash with anhydrous ethanol for multiple times to remove excess 3-methoxysilyl propylamine, and bake at 60-80°C for 8-12 hours to obtain silanized zirconium dioxide nanofibers. (2) Preparation of quaternized silanized zirconium dioxide nanofibers: The silanized zirconium dioxide nanofibers obtained in step (1) are dispersed in water, and glycidyl trimethylammonium chloride is added thereto. The mixture is stirred at 50-70° C. for 20-26 hours, and the reaction product is precipitated in acetone, filtered, and dried to obtain quaternized silanized zirconium dioxide nanofibers. (3) Preparation of composite film: The quaternized silanized zirconium dioxide nanofibers dried in step (2) and polytetrafluoroethylene (PTFE) fine powder are mixed, and then additives are added and mixed thoroughly to obtain a mixed powder, which is then put into an extruder. The powder is pushed and extruded into a strip-shaped mixture, which is then rolled into a film sheet under a rolling machine. After heating and volatilization to remove the additives, the composite film is stretched longitudinally and transversely to obtain a composite film.

2. The method for preparing a polytetrafluoroethylene-based anion exchange membrane according to claim 1, characterized in that: Preferably, the molar ratio of the silica nanofibers to 3-methoxysilylpropylamine used in step (1) is 1:

1.

3. The method for preparing a polytetrafluoroethylene-based anion exchange membrane according to claim 1, characterized in that: Preferably, the length of the zirconium dioxide nanofibers used in step (1) is between 400 nm and 3 μm.

4. The method for preparing a polytetrafluoroethylene-based anion exchange membrane according to claim 1, characterized in that: The additives in step (3) are hydrocarbons in the petroleum refining process, including petroleum ether, solvent oil and paraffin oil.

Images