JPH027690B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an acrylonitrile (hereinafter referred to as AN) separation membrane having excellent mechanical strength. In recent years, separation techniques for various substances using semipermeable membranes have been attracting attention in a wide range of application fields, such as wastewater treatment, seawater desalination, food industry, and medical fields, and even greater development is expected in the future. Such separation techniques include ultrafiltration, ultrafiltration,
Various techniques such as reverse osmosis have been proposed. In other words, it goes without saying that the performance required of the membrane differs depending on the purpose of separation mentioned above, but the commonly required performance is a high permeation rate of the aqueous medium, and a high permeation rate for the separation target. The mechanical and chemical strength required to withstand the operating pressure of actual membrane separation is high. Although there are a large number of semipermeable membranes currently known, the reality is that there are not necessarily many membranes that can satisfy the above-mentioned performances to a practical level. For example, even cellulose acetate membranes, which are relatively practical, have drawbacks, particularly in terms of chemical resistance and microbial decomposition resistance. On the other hand, AN-based polymer membranes inherently have excellent chemical performance, so various membrane formation methods have been proposed. Those are JP-A-49-
No. 53258 (method for differentiating coagulation values of coagulants on both sides of membrane), JP-A-49-62380 (sheath-core composite spinning method), JP-A-50-92359 (method using mixed solvent) ) and Japanese Patent Application Laid-Open No. 117682/1982 (method of evaporating the solvent after forming into a sol membrane and then removing the solvent), etc., these membrane manufacturing methods are known for their membrane separation performance and membrane permeation performance. Moreover, it has inherent disadvantages in terms of membrane productivity, etc., and cannot be said to be industrially advantageous. On the other hand, JP-A-54-131666 discloses that an AN-based separation membrane can be obtained by a wet film-forming method using a film-forming stock solution of dimethylformamide, which is a solvent for AN-based polymers, and formamide, which is a non-solvent. (mixture of dimethylformamide and formamide) and JP-A-54-132480 (specified desolvation conditions). However, even if these conditions are satisfied, it is difficult to guarantee practical membrane performance and pressure resistance with good reproducibility. In other words, AN-based separation membranes have an extremely dense, asymmetric structure consisting of a thin surface active layer (skin layer) and a porous support layer with excellent water permeability, which gives them excellent membrane performance. Although this is an essential condition for the production of membranes with a mixed system of dimethylformamide and formamide, strict production conditions must be set in order to produce separation membranes with this membrane structure with good reproducibility. Not only is this necessary, but it also requires extremely advanced membrane-forming technology, and hollow fibers are unable to obtain a sufficiently perfect circular shape and cannot withstand the actual membrane separation operating pressure. Here, the present inventors investigated a wide range of film forming conditions and solvent removal conditions that could guarantee even better film performance, and found that, surprisingly, N-methylpyrrolidone and By using a mixed system with an organic swelling agent, not only was it possible to increase the water permeability and improve the separation rate, which could not be obtained with a mixed stock solution of dimethylformamide and formamide, but also it was possible to reproduce the membrane performance. The properties and mechanical strength were also very good, and stable membrane performance could be guaranteed, thus completing the present invention. That is, an object of the present invention is to provide a method for producing an AN-based separation membrane that has an excellent water permeation rate and can adjust separation performance within a suitable range. Another object of the present invention is to provide an industrially advantageous manufacturing method that can guarantee stable membrane performance. Still another object of the present invention is to
The object of the present invention is to provide a method for manufacturing a separation membrane that allows designing of membrane separation performance according to various application fields such as ultrafiltration, reverse osmosis substrates, and gas separation substrates. The purpose of the present invention described above is to manufacture a separation membrane from an AN-based polymer membrane-forming stock solution, in which the polymer is selected from N-methylpyrrolidone, formamide, ethylene glycol, diethylene glycol, triethylene glycol, or polyethylene glycol with a molecular weight of 1000 or less. This can be achieved by using a membrane-forming stock solution dissolved in a mixed system with one or more organic swelling agents. In the present invention, N- is a solvent for AN-based polymers.
Although it is not clear by what mechanism of action the use of a stock solution containing methylpyrrolidone and an organic swelling agent improves the mechanical performance of the membrane and the reproducibility of membrane performance, N-methyl Pyrrolidone cannot dissolve AN-based polymers at room temperature, and even if it does dissolve AN-based polymers at high temperatures, the viscosity of the polymer solution is higher than that of dimethylformamide, making it a poor solvent compared to dimethylformamide. In addition, the gelation point of the membrane forming stock solution prepared using a mixed system of N-methylpyrrolidone and an organic swelling agent is high, and N-methylpyrrolidone exerts a slow coagulation effect on the AN polymer. This seems to be to facilitate the sol-gel conversion as the temperature decreases after shaping the membrane-forming stock solution of the AN-based polymer into a desired shape, thereby facilitating the formation of a dense separated active layer. Here, the AN-based polymer used as a starting material for the separation membrane according to the present invention is one obtained by a known method, and contains AN alone or AN units in an amount of 80% by weight or more, more preferably 90 to 95% by weight. % bonds are preferred. Also, it takes
The molecular weight of the AN-based polymer is preferably such that the intrinsic viscosity [η] measured in DMF at 30°C is in the range of 0.4 to 4. The film-forming property is poor even if the molecular weight is too large. As the monomer to be copolymerized with AN, known comonomers that can be copolymerized with AN can be used, such as conjugated diene monomers such as butadiene and isoprene; styrene, α-methylstyrene, and chlorostyrene. Aromatic vinyl monomers such as methacrylonitrile and vinylidene cyanide; Acrylic acid esters such as methyl acrylate, ethyl acrylate, and butyl acrylate; Methyl methacrylate and ethyl methacrylate , methacrylic acid esters such as butyl methacrylate; vinyl halides and vinylidenes such as vinyl chloride, vinyl bromide, vinylidene chloride, and vinylidene bromide; vinyl acetate,
Examples include vinyl esters such as vinyl propionate; ethers such as ethyl vinyl ether and butyl vinyl ether. First, the above AN-based polymer is dissolved in a solvent to prepare a film-forming stock solution. As the solvent used in the present invention, it is essential to use N-methylpyrrolidone containing formamide, ethylene glycol, diethylene glycol, triethylene glycol, or polyethylene glycol having a molecular weight of 1000 or less as an organic swelling agent. Such an organic swelling agent and N
- The mixing ratio of methylpyrrolidone is determined by the composition, molecular weight, polymer concentration in the membrane forming stock solution, temperature of the stock solution, etc. of the AN polymer, but it also depends on the performance of the final membrane (water permeation rate, separation rate, etc.). ) The mixing of organic swelling agent and N-methylpyrrolidone is approximately
It is preferable to select from the range of 95:5 to 80:20. In particular, it is preferable to select from the range of 95:5 to 90:10. In addition, the concentration of AN-based polymer in the above membrane forming stock solution is
10-35% by weight based on the total amount of the stock solution, preferably
It is to be maintained at 20-30% by weight. In this way, it is made of AN polymer and a mixed solvent.
The AN-based polymer membrane forming stock solution is dissolved and defoamed. Lysis can be performed in any manner. Next, the membrane-forming stock solution prepared in this manner is formed into a membrane-like substance such as a flat membrane, tube, or hollow fiber. Next, the sol film thus formed is passed through an inert atmosphere to remove the solvent. The solvent removal treatment conditions in the present invention are such that after the sol-like film is brought into contact with an inert atmosphere, the sol-like film is brought into contact with an inert atmosphere, and then the water-soluble solvent that is compatible with the solvent is contained at 50°C or lower, preferably from 20°C to 40°C. It is preferable to remove the solvent by immersing it in an aqueous solution in the range of .degree. In addition, as the water-soluble solvent and inert medium used in the present invention,
For example, dimethylacetamide, dimethylsulfoxide, dimethylacetamide, γ-butyl lactone, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, formamide, nitric acid, or inorganic salts such as rhodan salt can be used alone or in mixtures.
It is industrially advantageous to preferably use the same composition as the mixed system. Air, nitrogen, oxygen, etc. can be used as the inert medium, and air is usually used. The solidified film produced through such solvent removal treatment is washed with water, stretched, and heat treated. Such stretching is at 50℃
As mentioned above, it is preferable to stretch uniaxially or biaxially at 70° C. or higher by 0.8 to 1.5 times based on the size of the solidified film. In addition, heat treatment is 50 to 120℃,
More preferably, it is carried out at 70 to 100°C in a water and/or polyethylene glycol or glycerin bath.
If the heat treatment temperature is less than 50°C, the effects of improving hot water resistance, anti-compaction properties, drying reusability, and membrane separation ability based on the structural fixation of the polymer cannot be fully expected; If the temperature exceeds 120°C, it is undesirable because the water permeation rate will decrease. As described above, by employing the method of the present invention in which a stock solution prepared by dissolving an AN polymer in N-methylpyrrolidone containing an organic swelling agent is shaped and solidified, the separation active part and the supporting part can be separated. An asymmetric structured membrane that is formed by different mechanisms, has a smooth separation active surface, and has high separation performance can be obtained. Further, due to the action of N-methylpyrrolidone, the coagulation phenomenon progresses slowly, resulting in a highly circular structural membrane. Furthermore, the separation membrane according to the present invention can contain oxygen, helium,
For separation and concentration of argon, neon, nitrogen monoxide, hydrogen sulfide, sulfur dioxide gas, nitrogen dioxide, methane, ethane, propane, ethylene, propylene, butylene, and other low-molecular gaseous compounds, as well as gas separation in gas-liquid mixtures. It can also be effectively applied as a base material for composite membranes for other gas separations. In order to provide a better understanding of the invention, representative examples of the invention will now be presented. Note that the water permeation rate and salt rejection rate described in the following examples were measured or calculated by the following method. (1) Water permeation rate {F: ^m2 / ^m2・day・(Kg/ ^cm2 )} Polyethylene glycol 4000 (manufactured by Wako Pure Chemical Industries)
A 0.5% aqueous solution of
A sample (hardened and molded with epoxy resin about 5 cm from the opposite end of the loop) is attached to the pressurizing device, the test drug is put into the outer surface of the test sample, and the test liquid side and the permeated liquid side ( The permeate flows out from the hollow part of the hollow fiber) and the pressure difference is 50Kg/ ^cm2.
The amount of permeated liquid was measured, and the water permeation rate per unit membrane area, unit time, and unit pressure (unit differential pressure) was calculated. The higher the water permeation rate (F), the higher the permeation rate and the higher the efficiency of the reverse osmosis membrane. (2) Salt rejection rate (R:%) Calculated using the following general formula (). R = (1-C/C ₀ ) x 100 () However, C ₀ indicates the polyethylene glycol 4000 concentration of the test liquid, and C indicates the polyethylene glycol 4000 concentration in the permeated liquid at the time when 5% of the test liquid amount has permeated. Indicates concentration. Such numerical value (R)
The larger the value, the greater the salt removal capacity. In addition, the membrane performance is such that the above F value and R value are 3.0~
10 ^-4 m ² /m ²・day・(Kg/cm ² ) or more and 30% or more, more optimally F is 6.0×10 ^-4 or more and R
is more than 50% practical. Example 1 Consisting of 92% AN and 8% methyl acrylate
A membrane-forming stock solution was prepared by dissolving 28 parts of an AN-based polymer ([η] = 1.20 as measured in dimethylformamide at 30°C) in 72 parts of the mixture shown in Table 1 below and defoaming it. This membrane-forming stock solution is spun through an annual spinneret maintained at 90°C and passed through the air.
After running for 10 mm, it was introduced into an aqueous solution (30° C.) containing 30% of the above solvent, and subjected to solvent removal and coagulation treatment. The solidified hollow fibrous membrane was continuously taken out from the coagulation bath, washed with water, treated with hot water at 80°C, stretched, and dried. The results of evaluating the membrane performance of the AN-based separation membrane thus obtained are shown in Table 1. Table 1 also shows the membrane performance when dimethylformamide was used as the solvent, when no organic swelling agent was added, and when polyethylene glycol 2000 was added.

[Table] As is clear from the results in Table 1, it is understood that the hollow fibrous separation membrane produced by satisfying the membrane-forming dope composition recommended by the present invention significantly improves its performance. Also, regarding the separation membranes No. 1 and No. 4 above, the pressure and F
When we examined the relationship with the value, we found that in No. 1, there was a sudden decrease in the F value from around 58Kg/cm ² , but in No. 4, no decrease in F value was observed even when it exceeded 100Kg/cm ² . Ta. Example 2 Consisting of 92% AN and 8% methyl acrylate
An AN-based polymer was dissolved in a mixed solvent consisting of N-methylpyrrolidone and ethylene glycol, and defoamed to prepare a membrane-forming stock solution. At this time, membrane forming stock solutions were prepared by changing the mixing ratio of N-methylpyrrolidone and ethylene glycol to five levels. A film was formed using this film forming stock solution in the same manner as in Example 1. The results of evaluating the membrane performance of the obtained AN-based separation membrane are shown in Table 2.

[Table] Example 3 28 parts of three types of AN copolymer consisting of AN and methyl acrylate with different copolymer compositions were mixed with 90% N-methylpyrrolidone and ethylene glycol.
A membrane forming stock solution was prepared by dissolving in 72 parts of a 10% mixture and defoaming. Both of these membrane forming stock solutions were heated at 90°C.
After spinning through a sheath-core type spinneret maintained at
Solvent removal and coagulation treatments were performed. At this time, an aqueous solution at 30°C containing 60% of the mixture was introduced into the core. The solidified hollow fiber membrane was continuously removed from the bath, washed with water, treated with hot water at 80°C, stretched, and dried.
Table 3 shows the results of evaluating the membrane performance of the obtained AN-based separation membrane.

【table】

Claims (1)

[Claims] 1. When producing a separation membrane from an acrylonitrile polymer membrane stock solution, a membrane formed by dissolving the polymer in a mixed system of N-methylpyrrolidone and the following organic swelling agent. A method for producing an acrylonitrile separation membrane characterized by using a stock solution. [Organic swelling agent: compound selected from formamide, ethylene glycol, diethylene glycol, triethylene glycol, or polyethylene glycol with a molecular weight of 1000 or less] 2. The mixing ratio of N-methylpyrrolidone and the organic based swelling agent is 95:5 to 80. :20. 3. The manufacturing method according to claim 1, wherein the acrylonitrile polymer contains 90-95% by weight of acrylonitrile. 4. The manufacturing method according to claim 1, wherein the separation membrane is a flat membrane. 5. The manufacturing method according to claim 1, wherein the separation membrane is a hollow fiber membrane.