CN112588121A

CN112588121A - Method for regulating and controlling dense layer on surface of ultrafiltration membrane

Info

Publication number: CN112588121A
Application number: CN202011288092.XA
Authority: CN
Inventors: 武少禹; 刘星
Original assignee: Anhui Encote Film Technology Co ltd; Nanjing Shuilian Tianxia Seawater Desalination Technology Research Institute Co ltd; Nanjing Delnamem Technology Co ltd
Current assignee: Anhui Encote Film Technology Co ltd; Nanjing Shuilian Tianxia Seawater Desalination Technology Research Institute Co ltd; Nanjing Delnamem Technology Co ltd
Priority date: 2020-11-17
Filing date: 2020-11-17
Publication date: 2021-04-02

Abstract

The invention discloses a method for regulating and controlling a dense layer on the surface of an ultrafiltration membrane. Specifically, in the process of preparing the asymmetric polymer ultrafiltration membrane by using a phase inversion method, a slit extrusion or a scraper is used for coating a polymer membrane casting solution on a non-woven fabric to form a liquid film with a certain thickness, before the liquid film is immersed in a coagulating bath and solidified into a solid membrane, a wind knife is used for introducing mixed solvents with different proportions and coagulating bath steam or air to the surface of the membrane, and the structure, the water permeability and the separation performance of the compact skin layer of the obtained asymmetric membrane can be regulated and controlled according to application requirements.

Description

Method for regulating and controlling dense layer on surface of ultrafiltration membrane

Technical Field

The invention belongs to the technical field of preparation of separation membrane materials, relates to a preparation method of an asymmetric polymer ultrafiltration membrane, and particularly relates to a method for regulating and controlling a dense layer on the surface of the ultrafiltration membrane.

Background

Energy and environmental issues, including water safety, global warming, and energy supply depletion, have attracted considerable attention in recent years. To date, various technologies have been initially explored to obtain clean water, capture "greenhouse" gases, and find alternative energy sources. Membrane separation has become one of the most important technologies by solving some of the pressing problems described above. Membrane separation technology is becoming more and more important in the separation industry, being applicable to the separation of various molecular weight components in gas or liquid phase, with the particular advantage that no heating is required, and therefore the energy usage is much lower than in conventional thermal separation processes. The liquid separation membrane comprises microfiltration, ultrafiltration, nanofiltration and reverse osmosis.

The present method for manufacturing organic high-molecular ultrafiltration membrane mostly adopts phase inversion technique, and the surface of the manufactured asymmetric membrane is compact skin layer, and the lower side of the compact layer is macroporous loose structure, so that the structure can greatly optimize the permeation rate of water and the retention property of solute. In order to optimize the separation performance, the control method of the dense layer usually requires a relatively complicated process involving the concentration of the casting solution, the kind of solvent, the kind and concentration of additives, the temperature of the casting solution, the kind and temperature of the coagulation bath, the operation speed of the apparatus, and even the water entry angle of the liquid thin film.

Disclosure of Invention

Aiming at the problem of regulating and controlling the compact skin layer on the surface of the asymmetric membrane, the invention aims to provide a new method; the method is used for treating the surface of the liquid film before the solid film is formed with steam or air containing different solvents or coagulating baths, so that the density and the thickness of the compact skin layer can be simply, conveniently and easily adjusted as required, and the water permeability and the retention performance of the film to different solutes are optimized.

The invention realizes the purpose through the following technical scheme:

a method for regulating and controlling a dense layer on the surface of an ultrafiltration membrane comprises the following steps:

s1: preparing a casting solution containing organic high molecular polymers and additives with certain concentration;

s2: coating the solution on the surface of the non-woven fabric by a scraper or a slit extrusion method to form a liquid film with a certain thickness;

s3: the film is subjected to air for a period of time;

s4: and (3) entering a coagulation bath tank, and solidifying the liquid film to form the solid asymmetric porous ultrafiltration membrane through the rapid exchange of the solvent in the liquid film and the coagulation bath in the coagulation bath tank.

Further, in step S1, the organic high molecular polymer includes polysulfone, polyethersulfone, polyvinyl chloride, polyethylene, polyvinylidene fluoride, and polyacrylonitrile.

Further, in step S3, before the liquid film is immersed in the coagulation bath to become a solid film, a mixture of solvents in different proportions and coagulation bath steam or air is introduced to the film surface by an air knife; the solvent comprises dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methyl pyrrolidone and tetrahydrofuran; the coagulation bath comprises water, ethanol, propanol, isopropanol and butanol.

More specifically, in the process of preparing the asymmetric ultrafiltration membrane by the phase inversion method, a slit extrusion or a scraper is used for coating the membrane casting solution on a non-woven fabric to form a liquid film with a certain thickness, before the liquid film is immersed in a coagulating bath and solidified to form a solid film, a wind knife is used for introducing mixed solvents with different proportions and coagulating bath steam to the surface of the liquid film, then the liquid film enters the coagulating bath to form the solid ultrafiltration membrane, and finally the solid ultrafiltration membrane is wound. The structure, water permeability and solute separation performance of the obtained asymmetric membrane can be optimized.

Has the advantages that: the method for regulating and controlling the dense layer on the surface of the ultrafiltration membrane can regulate and control the dense skin layer structure on the surface of the asymmetric membrane prepared by the method according to application requirements under the condition of not changing the existing formula, process and equipment, so that the optimization process of the water permeability and the separation performance of the membrane is simpler, more convenient, more effective and easier to implement.

Drawings

FIG. 1 is a schematic diagram of a process for preparing a flat-plate macromolecular asymmetric ultrafiltration membrane;

FIG. 2 is a schematic view of a hybrid steam generating device;

in the figure: 1. unwinding the non-woven fabric; 2. non-woven fabrics; 3. a casting film liquid material liquid tank and a scraper; 4. an air knife; 5. a liquid film scraped from the surface of the non-woven fabric; 6. a coagulation bath; 7. a solid ultrafiltration membrane; 8. a film product take-up shaft; 9. a hot air blower; 10. hot air generated by the air heater; 11. mixing the liquid; 12. a mixed liquid heating tank; 13. the steam is mixed.

Detailed Description

The following are preferred embodiments of the present invention, which are intended to be illustrative only and not limiting, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Preparing a casting solution:

dissolving and dispersing a certain amount of polysulfone resin in weighed dimethyl formamide (DMF) with a certain mass, stirring at 60 ℃ until PSF is completely dissolved, and defoaming in vacuum for 8 hours at room temperature. The coating is uniformly applied to the non-woven fabric by the coating equipment shown in fig. 1, wherein 1 is an unwinding shaft, 2 is a casting solution groove and a scraper for placing the whole roll of non-woven fabric with the thickness of about 100 microns as a supporting material, the casting solution is scraped into a liquid film 5 with the thickness of 200 microns on the non-woven fabric, then the liquid film enters a coagulating bath 6 to form a solid ultrafiltration membrane 7, and the whole process is completed by rolling 8. In stage 4, which is typically the portion of the polymer liquid film in contact with air, hot steam or air containing different chemical components is introduced.

Generation of mixed hot steam:

fig. 2 is a schematic diagram of a process for producing hot steam, wherein 9 is a hot air blower, hot air 10 with a certain temperature is introduced into a heating tank 12 filled with liquid 11 with different components, and the generated hot steam 13 is introduced onto the surface of the polymer liquid film through an air knife 4.

Water permeability test of the membrane:

the dead-end test cell was used, the test pressure was 0.1Mpa, the data was measured three times after 10 minutes of pre-compression, the water permeation volume per minute was collected and averaged to give a test cell membrane area of 22 cm 2.

Membrane retention test:

bovine serum albumin aqueous solution with the concentration of 1000ppm is prepared. The concentrations of raw water and permeated water were measured by ultraviolet spectrophotometry. The retention rate is calculated by the formula of retention rate (%) = (raw water concentration-permeate concentration)/raw water concentration x 100.

Comparative example: the polysulfone concentration is 18% (w/w), a 200 micron liquid film is scraped by a scraper from a non-woven fabric running at 10 m/min by using the casting film liquid at 25 ℃, the formed liquid film enters a pure water coagulating bath at 25 ℃ at an angle of 40 degrees horizontally after passing through a distance of 10cm, and finally the film is rolled. The pure water permeation rate of the obtained membrane is 36ml/min, and the retention rate is 92.5%.

Example 1: other conditions were the same as in comparative example, after the liquid film was scraped, hot air (relative humidity 20%) at a temperature of 70 ℃ was introduced to the surface of the liquid film by means of an air knife, the slit of the air knife was adjusted so that the air speed was 0.3 m/s, the air flow was 5 liters/s, and the air knife was 0.50 m from the surface of the film, and the pure water permeation rate and the rejection rate of the obtained film were as shown in Table 1.

Example 2: the other conditions were the same as in example 1, the air knife distance was 3.0 m, and the pure water permeation rate and the rejection rate of the obtained membrane are shown in Table 1.

Example 3: the other conditions were the same as in example 1, the solution in the mixed vapor generator was 70 ℃ pure water, the flow rate of the blower was 50 liters per second, the air knife slit was adjusted so that the air speed was 0.3 meters per second, the flow rate was 10 liters per second, and the air knife was 0.50 meters from the surface of the film. The pure water permeation rate and rejection of the obtained membrane are shown in Table 1.

Example 4: the conditions were the same as in example 3 except that the mixed vapor generator internal solution was a 50% (w/w) DMF aqueous solution at a temperature of 70 ℃ and the pure water permeation rate and rejection rate of the obtained membrane were as shown in Table 1.

Example 5: the conditions were the same as in example 3, the solution in the mixed vapor generator was pure DMF, and the pure water permeation rate and the rejection rate of the obtained membrane are shown in Table 1.

Example 6: the conditions were the same as in example 3 except that the mixed vapor generator internal solution was a 20% (w/w) DMF aqueous solution, and the pure water permeation rate and the rejection rate of the obtained membrane were as shown in Table 1.

Example 7: the other conditions were the same as those in example 6, the air knife distance was 3.0 m, and the pure water permeation rate and the rejection rate of the obtained membrane are shown in Table 1.

TABLE 1

Claims

1. A method for regulating and controlling a dense layer on the surface of an ultrafiltration membrane is characterized by comprising the following steps:

s3: the film is subjected to air for a period of time;

2. The method for regulating and controlling the dense layer on the surface of the ultrafiltration membrane according to claim 1, wherein in step S3, before the liquid thin membrane is immersed in the coagulation bath to become a solid membrane, a mixture of solvents with different proportions and coagulation bath steam or air is introduced to the surface of the membrane through an air knife.

3. The method for regulating and controlling the dense layer on the surface of the ultrafiltration membrane according to claim 1, wherein the organic high molecular polymer comprises polysulfone, polyethersulfone, polyvinyl chloride, polyethylene, polyvinylidene fluoride and polyacrylonitrile.

4. The method for regulating and controlling the dense layer on the surface of the ultrafiltration membrane according to claim 2, wherein the solvent comprises dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methyl pyrrolidone and tetrahydrofuran.

5. The method for regulating and controlling the dense layer on the surface of the ultrafiltration membrane according to claim 2, wherein the coagulation bath comprises water, ethanol, propanol, isopropanol and butanol.