JPH0365221B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing gas separation membranes or dry membranes required in the first stage of membrane compositing, modification, etc., and its purpose is to manufacture membranes without deteriorating permeation performance. To provide a way to dry. BACKGROUND OF THE INVENTION Dry separation membranes are required in several applications. For example, gas separation membranes used for separating and concentrating mixed gases, separation membranes for artificial lungs, and other membranes are known that allow liquid and gas to come into contact with each other through the membrane to allow gas permeation and exchange. Further, in the case of reverse osmosis membranes, it is often used to compose membranes for the purpose of imparting mechanical strength to thin membranes. Alternatively, the surface of the membrane has been modified or modified by graft polymerization or other methods, but in either case, the membrane must be dried. Most other conventional ultrafiltration membranes for liquid separation are produced by wet membrane formation and are handled in a wet state.
There are problems in terms of transportation and storage, and dry film production is desired. However, if a wet-formed membrane is simply dried with hot air or the like, the amount of water permeation or gas permeation will be significantly reduced. Therefore, various studies have been made to improve the water permeability of dry membranes before and after the drying process. For example, a method is known in which the film is immersed in an aqueous surfactant solution after wet film formation and before entering the drying process. However, since the surfactant remains after treatment, a long period of cleaning is required before use, and if the membrane is left dry, the remaining surfactant makes it difficult to modify or modify the membrane surface. Become. There are also examples of using polyhydric alcohols in addition to surfactants, but these have the same problems as above. Furthermore, a method has been proposed in which a immersion process in hot water of 80° C. or higher is added after wet film formation and before the drying process. However, in this method, even if the dried membrane is re-wetted with an aqueous alcohol solution, the water permeation amount only recovers to the value before drying. In the case of polysulfone, an example in which an alcohol aqueous solution is used to rewet a dried membrane without any pretreatment has been reported, but in this case as well, the water permeability remains at the level before drying. Therefore, when drying again, the amount of permeation decreases, so this method of restoring membrane performance is insufficient for gas separation membranes. Treatment with vapors of alcohol, ketones, etc. has also been proposed, but this is not an easy process because the membrane will deform and deteriorate unless the vapor concentration is strictly controlled. In addition, gas separation membranes, ultrafiltration membranes and proposed for membranes. Although this method achieves certain effects, the process becomes complicated. In other words, since the liquid used as a coagulating liquid is a highly cohesive liquid such as water (solubility parameter 23.4), it is difficult to exchange a highly cohesive liquid with a low coagulant liquid within the membrane, and It is necessary to take measures such as immersing the membrane in a refluxing liquid with low cohesion, or replacing the membrane with a suitable liquid with low cohesion such as alcohol during the process, and then replacing it with a liquid with low cohesion. [Purpose of the Invention] In view of the above-mentioned problems, the inventors started research with the aim of finding a method for manufacturing a dry membrane with a simple process that does not cause a decrease in permeation performance that could not be obtained conventionally. The present invention was completed as a result of intensive research based on the idea that a dried membrane with a desired permeability can be obtained by not only preventing the membrane from shrinking during drying but also by allowing the membrane to swell before drying. It is ivy. [Structure of the invention] The present invention provides that the mixed drying liquid is dioxane or boiling point
A lower alcohol mixed solution containing 3 to 50% by weight of an organic solvent at 100°C or less, which is miscible with water and has a solubility parameter of 9.5 to 14.5,
This method of producing a dry separation membrane is characterized in that the separation membrane is moistened with the mixed drying liquid and then dried. Regarding the separation membrane to which the present invention is applied, the type of material polymer is not particularly limited. In addition to cellulose polymers, there are, for example, polyamide, polyimide, polyetherimide, polysulfone, polyethersulfone, polyacrylonitrile, and the like. Regarding the shape of the membrane, any shape such as a flat plate, a tube, or a hollow fiber can be used. It may be a membrane whose surface has been modified or a composite membrane with a thin layer. Further, the membrane may be in a wet state or may be in a dry state in advance. The present invention can be applied even after the membrane has already been assembled into a module such as a spiral. The mixed drying liquid used in the present invention contains 3 to 50% by weight of dioxane or an organic solvent with a boiling point of 100°C or less.
It is a mixed solution of lower alcohol containing. If the boiling point of the organic solvent is 100°C or higher, the film will not dry smoothly. However, the boiling point of dioxane is 100℃
It was confirmed that it is a preferable organic solvent for use in the present invention, although it is slightly more expensive. The organic solvent is preferably one that exhibits swelling or solubility with respect to the membrane material polymer. If the amount of organic solvent is less than 3% by weight, no significant effect will be observed, and if it is more than 50% by weight, various problems will occur depending on the nature of the organic solvent. That is, if the organic solvent dissolves the membrane material polymer, deformation and shrinkage of the membrane will occur. Alternatively, if the organic solvent is insoluble in water and the membrane is previously wetted with water, replacement within the membrane with the mixed drying liquid will not proceed smoothly. Depending on the conditions, phase separation of the liquid may occur within the membrane, and if this is dried as is, the performance of the membrane will be non-uniform. In many cases, separation membranes are manufactured by a wet method, and the coagulating liquid in that case is mostly water or an aqueous solution. Therefore, if the present invention is applied to make this into a dry membrane, it is an important issue whether or not the replacement of water and mixed drying liquid within the membrane proceeds smoothly. The organic solvent may be used alone or in combination. Examples include ethers such as diexane, esters, and ketones. The lower alcohol used in the present invention also has a boiling point of 100℃
The following is desirable, and it may be used alone or as a mixture. For example, methyl alcohol and ethyl alcohol can be mentioned. The mixed drying liquid must be miscible with water. Miscibility in the present invention means, as described above, that there are no problems such as phase separation or substitution that does not proceed smoothly within the membrane. The solubility parameter of the mixed drying liquid is 9.5 ~
Must be in 14.5. The solubility parameter referred to herein is calculated by proportionally distributing the solubility parameters of each solvent based on the mixing weight ratio. For example, the solubility parameter values of lower alcohol in the mixed drying liquid are a ₁ and
a ₂ , ..., a _n , and the weight percent values are x ₁ , x ₂ ,
..., x _n . Also, the solubility parameters of the organic solvent are b ₁ , b ₂ ,...
..., b _o and the weight percent values are y ₁ , y ₂ , ..., y _o , the solubility parameter δ of the mixed drying liquid is δ = ( _n 〓 ⁱ⁼¹ a _i x _i + _o 〓 ^{i =1} b _i y _i )/100. If the value of the solubility parameter of the mixed drying liquid is less than 9.5, the miscibility with water decreases, resulting in the above-mentioned problem of water exchange or phase separation within the membrane. If it is larger than 14.5, the shrinkage of the membrane during drying will be large, making it difficult to obtain a dry membrane with a high permeation rate of gas or liquid. If the organic solvent mixed with the lower alcohol is one that is azeotropic with the alcohol, drying will proceed more smoothly, so it is preferably used. Generally, the solubility parameters of the organic solvent that swells or dissolves the membrane material and the high molecular weight polymer of the membrane material are close to each other. In general, the larger the solubility parameter of the organic solution, the greater the degree of shrinkage of the film when drying the film moistened with the organic solvent. The fractionation or pore size of the dry membrane is determined by subtracting this swelling and shrinkage, so the situation differs depending on the membrane material and is not limited, but the optimal value of the solubility parameter of the mixed drying liquid depends on the membrane material polymer material. Assuming that the value is between 9.5 and 9.5, it is a good idea to search. No special method is required to moisten the separation membrane with the mixed drying liquid. Even if the membrane has already been dried or the membrane has been moistened with the coagulating liquid after wet membrane formation, it may be simply immersed in the mixed drying liquid at room temperature. Unless the inside of the membrane is already wet with a liquid that is immiscible with the mixed drying liquid and needs to be removed, do not immerse the membrane in a refluxed mixed drying liquid. It is possible to achieve the desired effect without taking measures such as replacing the inside of the membrane with another liquid that is miscible with the mixed drying liquid in advance. Depending on the shape of the membrane or membrane module, dipping alone may take time; in such cases, it is effective to circulate the mixed drying liquid through the membrane or membrane module. If the membrane is already dry, the mixed drying liquid may be introduced into the membrane by spraying. Although the extent varies depending on the membrane material and the composition of the mixed drying liquid, it is sufficient that when the membrane is moistened with the mixed drying liquid by immersion, etc., the properties of the obtained membrane change depending on the temperature and time at which it is left in the wet state. Caution must be taken. When it is desired to increase the permeability as much as possible, it is particularly important to pay attention to the case where there is an optimum value for the immersion time. That is, if the immersion time is too short, the effect will be small, and if the immersion time is prolonged, the permeability of the obtained membrane will increase once, but may eventually tend to decline and settle to a certain value. Although not limited to this, in order to simplify the work and process, it is desirable to adjust the mixing and drying liquid so that the optimum time falls within 30 minutes to 1 hour. As for the method of drying the membrane moistened with the mixed drying liquid, no special measures are required and air drying may be used, but heating, reduced pressure, etc. may also be applied. Drying is preferably carried out by circulating an inert gas such as hot air. [Effects of the Invention] According to the present invention, the membrane can be dried in a simple process without deteriorating the permeation performance, so it is suitable as an industrial method for producing a dry membrane. The method of the present invention can be applied not only to membranes of various shapes as described above, but also to gas separation membranes, liquid separation membranes, reverse osmosis membranes, or porous membranes serving as their base materials.
It can be applied to various applications such as ultrafiltration membranes. Furthermore, the present invention can be applied to the production of membranes with advanced functions by combining with other methods. For example, the membrane can be chemically modified or other compounds can be attached or bonded to the membrane surface simultaneously with drying.
In this case, the mixed dry solution contains specific reagents or compounds. An example of such a reagent is sulfuric acid. For the purpose of producing a composite membrane, it is also possible to carry out polymerization or crosslinking reactions of other compounds within the membrane and on the membrane surface at the same time as drying. For example, crosslinking of polyethyleneimine can be mentioned. Furthermore, as mentioned above, the present invention can be applied to dried membranes, so it can be used not only to dry membranes made by a wet process, but also to improve the molecular weight cutoff or pore size of a membrane made by a dry process or a dry membrane. It can also be used for adjustment purposes. [Example] Examples of the present invention will be described below with reference to Examples. Example 1 A resin solution was prepared by heating and dissolving 14 parts by weight of aromatic polysulfone P-1700 (manufactured by Union Carbide) in 86 parts by weight of N-methyl-2-pyrrolidone at 70°C for 4 hours. After defoaming, the resin solution was cast onto a glass plate at room temperature and further immersed in water at 18°C to solidify, thereby obtaining a wet flat membrane separation membrane with a thickness of 11 to 130 μm. The water permeability of the membrane was 1230 (/hrm ² atm). Next, add 95 parts by weight of ethyl alcohol to 1.4 parts by weight.
- It was immersed in a wet state for a predetermined time in a mixed drying liquid at 18°C consisting of 5 parts by weight of dioxane, and dried with hot air at 80°C for 15 to 30 minutes to obtain a dry film. Table 1 shows the water permeability of the membrane. (Method for measuring dry film) After drying, the film was soaked in ethyl alcohol at room temperature for 1 minute and washed with water to obtain a wet film. The amount of water permeated through this membrane was measured 5 minutes after the start of water permeation using ion-exchanged water under conditions of 18 to 22°C and 1 Kg/cm ² . The same method was used below. Comparative Example 1 After soaking the same wet aromatic polysulfone separation membrane as in Example 1 in ethyl alcohol for a predetermined time, Example 1
A dry film was obtained by drying in the same manner as above. Table 1 shows the water permeability of the membrane. In this way, it can be seen that in the case of polysulfone, the rate of improvement in water permeability is almost doubled by adding only 5% by weight of 1,4-dioxane.

【table】

[Table] (a) Example of concentration in ethyl alcohol solution 2 Amorphous thermoplastic polyetherimide ultem
1000 (manufactured by General Electric Company) was dissolved in 80 parts by weight of N-methyl-2-pyrrolidone by heating at 95°C for 4 hours to prepare a resin solution. After defoaming, use the same method as in the example to reduce the wet thickness to 110~
A 130μ flat membrane separation membrane was obtained. The water permeability of the membrane is 670
(/hrm ² atm). Next, a predetermined amount of a predetermined organic solvent was dissolved in ethyl alcohol to prepare a mixed drying liquid. The wet membrane was immersed in this material at 18° C. for a predetermined time and dried in the same manner as in Example (1) to obtain a dry membrane. The water permeability of the membrane is shown in Table 2. Comparative Example 2 After immersing the same wet polyetherimide separation membrane as in Example 2 in ethyl alcohol for a predetermined time, Example 1
A dried film was obtained in the same manner as above. The water permeability of the membrane is the second
Shown in the table. In this way, it can be seen that in the case of polyetherimide, the effect of increasing the amount of water permeation appears when the amount of 1,4-dioxane added is considerably larger than that of polysulfone. Here, 1,4-dioxane is a good solvent for polyetherimide, but diethyl ether is not. Also, if the product is immersed for too long, water permeability will decrease.

[Table] (a) Concentration comparison example in ethyl alcohol solution 3 To confirm the validity of the obtained water permeability value regarding rewetting of the membrane by immersion in ethyl alcohol and washing with water, which is performed as a pretreatment for water permeation measurement. The following experiment was conducted. Wet polymalphone membranes and polyetherimide membranes were prepared in the same manner as in Examples 1 and 2, and dried as they were with hot air at 80° C. for 1 hour to obtain dry membranes. Each of these membranes was rewetted in the same manner as in Example 1, and the water permeability was measured and found to be as low as 10 or less. Therefore, it can be seen that although the water permeability improves by rewetting, the obtained values can be sufficiently used as a relative evaluation of the water permeability of the dry membrane.

Claims (1)

[Claims] 1. The mixed drying liquid is a lower alcohol mixed solution containing 3 to 50% by weight of dioxane or an organic solvent with a boiling point of 100°C or lower, is miscible with water, and has a solubility parameter of 9.5 to 14.5. . A method for producing a dry separation membrane, which comprises moistening the separation membrane with the mixed drying liquid and then drying the separation membrane.