Preparation method of spongy solvent-resistant polyacrylonitrile ultrafiltration membrane

Abstract

The invention belongs to a method for preparing a novel polyacrylonitrile ultrafiltration membrane by adopting a phase inversion method. 8%-19% of polyacrylonitrile, 6%-13% of polyaniline and 1%-6% of protonic acid are blended and dissolved in dimethyl sulfoxide to serve as a membrane casting solution, m-cresol serves as an active agent, water, polyvinylpyrrolidone (PVP) and alcohol or polyvinyl alcohol serve as additives, the solvent tolerance of the ultrafiltration membrane is improved by doping the polyaniline and the protonic acid, and the membrane is prepared. M-cresol optimizes the structure of polyaniline, the additive changes the structure of the ultrafiltration membrane, and the spongy solvent-resistant polyacrylonitrile ultrafiltration membrane is prepared by a one-step method. The solvent resistance and the pressure resistance of the polyacrylonitrile membrane are greatly improved, the preparation process is simplified, and the membrane performance can be effectively regulated and controlled in the preparation process.

Description

Technical Field

[0001] The present invention relates to a method for preparing a polymer material membrane, in particular to a method for preparing a polyacrylonitrile ultrafiltration membrane with good solvent tolerance and pressure resistance. Background Art

[0002] Polyacrylonitrile (PAN) is an inexpensive organic polymer. As a membrane material, PAN exhibits excellent chemical stability, high hydrophilicity, good solubility in solvents, and excellent film-forming properties. However, traditional PAN membranes suffer from low thermal stability and solvent resistance. The treatment of organic wastewater has become a key issue in current environmental governance. Solvent-resistant polymer membranes can effectively treat wastewater containing organic pollutants. Therefore, research on solvent-resistant polymer membranes is of great practical significance.

[0003] Due to its inherent electrical conductivity, polyaniline is widely used in different industries, but its structure and properties will also change depending on its degree of oxidation. Patent CN 104419012B utilizes the conductive properties of polyaniline to first prepare doped polyaniline, and then blend it with polyacrylonitrile to prepare a composite membrane for precious metal recovery. In addition, polyaniline has good solvent tolerance. Its application in liquid separation membranes is mainly concentrated in pervaporation membranes. It has been used in processes such as isopropyl alcohol dehydration, acetic acid dehydration, and mixed solvent separation. Patent CN 2022104953398 uses alkali modification and thermal cross-linking treatment to make polyacrylonitrile ultrafiltration membranes have good solvent tolerance, but the preparation process conditions are relatively harsh and it does not have a sponge-like structure. Summary of the Invention

[0004] Aiming at the insufficient pressure resistance and solvent resistance of polyacrylonitrile ultrafiltration membrane, the present invention proposes a preparation method of sponge-shaped solvent-resistant polyacrylonitrile ultrafiltration membrane by blending polyaniline with polyacrylonitrile.

[0005] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] First, 8%-19% polyacrylonitrile, 6%-13% polyaniline, 1%-6% protonic acid, 1%-9% active agent and additives are blended in dimethyl sulfoxide at 80-120° C. and stirred and dissolved for 6-10 hours to form a casting solution; then, the casting solution is cooled to 10-40° C. and degassed, and then coated on a non-woven fabric substrate with a scraper and placed in a gel bath at 50-80° C. for phase inversion to form an ultrafiltration membrane; and the formed ultrafiltration membrane is rinsed with pure water to obtain a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane.

[0007] The active agent is m-cresol;

[0008] The polyaniline is an oxidized form containing alternating benzene rings and quinone rings in the molecular chain, and the specific molecular formula is:

[0009]

[0010] Y cannot be equal to 0 or 1.

[0011] Preferably, the additive is one or more of water, alcohols, polyvinyl pyrrolidone (PVP), and polyvinyl alcohol.

[0012] Preferably, the alcohol is usually methanol, ethanol, ethylene glycol, glycerol, n-butanol, etc.

[0013] Preferably, the protonic acid is typically camphorsulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, or sulfosalicylic acid.

[0014] Preferably, the gel time is 1-60 seconds.

[0015] Preferably, the scraping film thickness is 10-100 μm

[0016] Preferably, the rinsing temperature is 30-60° C., and the rinsing time is 1-10 minutes.

[0017] Preferably, the non-woven fabric substrate is made of polypropylene (PP) or polyethylene terephthalate (PET).

[0018] The present invention improves the solvent tolerance of the membrane through the hydrogen bonding between the benzene rings in the doped polyaniline and the polyacrylonitrile. The addition of protonic acid can adjust the ratio of benzene rings to quinone rings in the polyaniline, thereby regulating the strength of the hydrogen bonding between the polyaniline and the polyacrylonitrile. Secondly, meta-cresol can optimize the molecular structure of the polyaniline in the solvent system, so that its molecular chain obtains an extension effect, and a better cross-linked network is obtained after combining with the polyacrylonitrile. The addition of additives and the temperature difference effect between the gel bath and the casting solution synergistically change the structure of the ultrafiltration membrane, changing it from a finger-like pore structure to a sponge-like structure, thereby improving the pressure resistance and porosity of the membrane. The present invention greatly improves the solvent resistance and pressure resistance of the polyacrylonitrile membrane, simplifies the preparation process, and can effectively regulate the membrane performance during the preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron micrograph of a cross-section of the ultrafiltration layer structure of the ultrafiltration membrane prepared in Example 19 of the present invention;

[0020] Figure 2 This is a scanning electron micrograph of a cross-section of the ultrafiltration layer structure of the ultrafiltration membrane prepared in Example 20 of the present invention; DETAILED DESCRIPTION

[0021] The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

[0022] The retention performance and water system flux of the ultrafiltration membrane prepared by the present invention were tested in a pure water system using bovine serum albumin at 0.3 MPa.

[0023] The calculation formula of membrane flux is shown in (1).

[0024]

[0025] Where J is the flux of the membrane (L / (m 2 ·h)), V is the volume of the collected permeate (L), A is the effective area of ​​the membrane (m 2 ), T is the time (h) required to collect V volume of permeate.

[0026] The calculation method of the membrane retention performance is shown in (2).

[0027]

[0028] Wherein R is the retention rate of the membrane, Cp is the COD value of the bovine serum albumin aqueous solution on the permeate side, and Cf is the COD value of the bovine serum albumin aqueous solution on the feed side.

[0029] The solvent resistance of the ultrafiltration membrane prepared in the present invention is tested by measuring the swelling parameters of the membrane and the flux stability in the solvent system.

[0030] The swelling degree can be used to test the solvent tolerance of the ultrafiltration membrane. The test method is as follows:

[0031] Cut five 1cm x 5cm sample strips from each ultrafiltration membrane, dry them to constant weight, and record the mass m1. Then, immerse each strip in isopropyl alcohol for 24 hours, remove it, quickly wipe off the surface solvent, and weigh it, recording the mass m2. Calculate the expansion Sr according to the formula.

[0032]

[0033] The average value of the swelling degrees Sr obtained from the five samples is the final swelling degree of the ultrafiltration membrane.

[0034] The flux stability of the solvent system was measured at 0.3 MPa. After continuous operation for 300 h in analytically pure n-heptane and methanol solvent systems, the membrane flux attenuation rate was measured as the flux stability parameter.

[0035] Examples 1-12

[0036] A non-woven fabric made of PET is used as the support layer, and a polyacrylonitrile-doped polyaniline sponge-like ultrafiltration membrane is prepared according to the steps described in claim 1:

[0037] Polyacrylonitrile, polyaniline, protonic acid, m-cresol and additive water were dissolved in dimethyl sulfoxide at 80°C with stirring for 10 hours to form a casting solution. The casting solution was then cooled to 30°C and degassed. The membrane thickness was controlled to 50 μm by a scraper. After coating on a non-woven fabric substrate, the membrane was placed in a gel bath and phase inverted at 50°C to form an ultrafiltration membrane. The gel time was 5 seconds, the rinse temperature was 60°C, and the rinse time was 5 minutes. The specific parameters are shown in Table 1.

[0038] Table 1 Relationship between the changes in casting solution component parameters and bovine serum albumin retention rate in Examples 1-12

[0039]

[0040]

[0041] It can be seen from Examples 1-3 that the increase of proton acid improves the retention rate of the membrane; it can be seen from Examples 3 and 7 that m-cresol plays a certain role in the combination of polyacrylonitrile and polyaniline; Examples 3, 5, and 6 can show the influence of the concentrations of polyacrylonitrile and polyaniline on the retention; Examples 2, 8, and 9 can show that at a concentration of 9% polyaniline and 4% proton acid, increasing the m-cresol concentration does not improve the retention rate; Examples 10-12 can show that the concentration of additive water has little effect on the membrane retention.

[0042] Examples 13-18

[0043] A PAN concentration of 13%, a polyaniline concentration of 8%, a protonic acid concentration of 3%, a m-cresol concentration of 1%, and additives were dissolved in dimethyl sulfoxide at 120°C with stirring for 8 hours to form a casting solution. The casting solution was then cooled to 25°C and degassed. The membrane thickness was controlled to 50 μm by a scraper. After coating on a non-woven fabric substrate, the membrane was placed in a gel bath for phase inversion at 60°C to form an ultrafiltration membrane. The gel time was 5 seconds, the rinse temperature was 55°C, and the rinse time was 8 minutes. The specific parameters are shown in Table 1.

[0044] Table 2 Relationship between the changes in additive components and the retention rate of bovine serum albumin in Examples 13-18

[0045] Example additive concentration Bovine serum albumin retention rate 13 water 3％ 80％ 14 Water + PVP 3％+3％ 90％ 15 PVP 3％ 88％ 16 Water + glycerol 3％+3％ 82％ 17 PVP+ethanol 3％+3％ 92％ 18 Glycerol 3％ 70％

[0046] It can be seen from Examples 13-18 that the addition of PVP can greatly improve the performance of the membrane, and multiple additives have better effects.

[0047] Example 19

[0048] A PAN concentration of 14%, a polyaniline concentration of 11%, a protonic acid concentration of 4% and a meta-cresol concentration of 1% were dissolved in dimethyl sulfoxide at 80°C with stirring for 10 hours to form a casting solution. The casting solution was then cooled to 30°C and degassed. A membrane thickness of 50 μm was controlled by a scraper. After coating on a non-woven fabric substrate, the membrane was placed in a gel bath for phase inversion at 50°C to form an ultrafiltration membrane. The gel time was 5 seconds and the rinsing temperature was 60°C for 5 minutes.

[0049] The ultrafiltration membrane scraped out without additives has a finger-like pore structure such as Figure 1 .

[0050] Example 20

[0051] The concentration of additive water was increased by 3% and the concentration of PVP was increased by 2%. Other steps were the same as those in Example 19.

[0052] The ultrafiltration membrane prepared by adding additives has a sponge-like structure and has better pressure resistance, such as Figure 2 .

[0053] Swelling test and flux stability test were performed on Examples 1-5.

[0054] Table 3 Swelling test of Examples 1-5

[0055]

[0056] Table 4 Flux change rate after continuous operation of Examples 1-5 for 300 h in different solvent systems

[0057]

[0058]

[0059] Table 4 shows the chemical stability of the prepared membranes in specific solvent environments. Negative values ​​indicate a decrease in the corresponding flux, while positive values ​​indicate an increase in the corresponding flux. The decrease or increase in flux is caused by the combined effects of membrane swelling and compaction.

[0060] Combining Tables 3 and 4, it can be seen that adjusting the concentrations of proton acid and polyaniline has a significant effect on the solvent resistance of the ultrafiltration membrane. At the same time, it can be seen that adding m-cresol to change the morphology of the polyaniline molecular chain can promote the stability of the membrane in the solvent.

[0061] The above-mentioned specific implementation methods are used to illustrate the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the scope of protection of the claims shall fall within the scope of protection of the present invention.

Claims

1. A preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane, characterized in that: First, 8%-19% polyacrylonitrile, 6%-13% polyaniline, 1%-6% protonic acid, 1%-9% surfactant and additives are blended and stirred in dimethyl sulfoxide at 80-120 °C for 6-10 hours to form a casting solution; Then, the casting solution is cooled to 10-40 °C and degassed, coated on a non-woven substrate with a doctor blade, and then entered into a gel bath for phase inversion within the range of 50-80 °C to form an ultrafiltration membrane; The formed ultrafiltration membrane is rinsed with pure water to obtain a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane; The surfactant is m-cresol; The polyaniline is in an oxidized form with alternating benzene rings and quinone rings in the molecular chain, and the specific molecular formula is: where Y cannot be equal to 0 or 1.

2. The preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane according to claim 1, characterized in that, The additives are one or more of water, alcohols, polyvinylpyrrolidone (PVP), and polyvinyl alcohol.

3. The preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane according to claim 2, wherein The alcohols are usually methanol, ethanol, ethylene glycol, glycerol, n-butanol, etc.

4. The preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane according to claim 1, characterized in that, The protonic acid is usually such as camphorsulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, sulfosalicylic acid, etc.

5. The preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane according to claim 1, characterized in that , The gel time is 1-60 seconds.

6. The preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane according to claim 1, characterized in that, The coating thickness is 10-100 μm.

7. The preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane according to claim 1, characterized in that, The rinsing temperature is 30-60 °C, and the rinsing time is 1-10 minutes.

8. The preparation method of a sponge-like solvent-resistant polyacrylonitrile ultrafiltration membrane according to claim 1, characterized in that, The non-woven substrate material is polypropylene (PP), polyethylene terephthalate (PET).

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