JPS59166208A - Manufacture of gas separating membrane - Google Patents

Abstract

PURPOSE:To manufacture an anisotropic membrane having excellent oxygen- enriching performance by treating a porous membrane under an atmosphere contg. a specific solvent. CONSTITUTION:The anisotropic membrane is manufactured from high polymer materials having >=3 separation factor of oxygen to nitrogen such as poly (4- vinylpyridine), polysulfon, polycarbonate, cellulose acetate and cellulose ether. The material is dissolved in an organic solvent contg. a nonsolvent, and pushed out into the air through a spinneret, then introduced into an aq. coagulation bath to obtain a porous membrane. The obtained membrane is treated by passing the membrane through a gaseous atmosphere contg. a solvent for the material of the membrane, by dipping the membrane in a soln. contg. said solvent, or by spraying the soln. By this treatment, the defects of the membrane such as pinholes are mended, and the separation factor is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an anisotropic membrane for gas separation, and is particularly effective for obtaining oxygen-enriched air from air.
The present invention relates to a method for manufacturing an anisotropic membrane with a large amount of gas permeation and excellent selectivity.

Methods for separating specific gases from gas mixtures using membranes are already well known, and can be roughly divided into methods using homogeneous membranes and methods using porous membranes. In the method using a uniform membrane, separation of the mixed gas occurs due to the difference in the dissolution rate and diffusion rate of the gas in the membrane, whereas in the case of a porous membrane, there are many pores of around 100X, and the difference in the mean free path of the gas molecules causes separation of the mixed gas. A separation takes place. As an example of the latter, asymmetric hollow fibers made of cellulose derivatives are described in JP-A-51-112917, -! A dry semipermeable membrane with a surface active layer and an inner porous layer mainly composed of polyacrylonitrile was published in Japanese Patent Application Laid-Open No. 5
6-111005. However, although these are all asymmetric membranes (anisotropic membranes), separation is performed due to the difference in mean free path of gas molecules, as described above. On the other hand, in the anisotropic film of the present invention,
This is the first time that a membrane of this type is used to separate mixed gases based on the difference in gas dissolution rate and diffusion rate in the membrane.

It becomes possible to obtain oxygen-enriched air from air.

As an example of these, two types of functional membrane materials have been developed, but both are mainly composite membranes that share separation characteristics, molding characteristics, and shape retention.

There are few examples of anisotropic membranes, and even if there are, there are practical or manufacturing problems. For example, a cellulose ester anisotropic membrane for the purpose of enriching oxygen in the air was developed in JP-A-57-7.
Although it is disclosed in the specification of No. 206, it has a manufacturing drawback in that very labor-intensive methods such as freeze-drying and solvent substitution methods have to be used in order to maintain the anisotropic structure. There is. Furthermore, the performance characteristics of the membrane are not necessarily satisfactory, and there is a dilemma that an anisotropic membrane with high biselectivity has a low oxygen permeation rate, and a membrane with a high oxygen permeation rate has low selectivity.

The inventors of the present invention have conducted extensive research into the manufacturing method and form of porous support membranes in order to improve the performance of composite membranes, and surprisingly, they have developed the present invention by focusing on a specific porous membrane. .

In other words, the present invention uses a gas specially designed to treat a porous membrane in an atmosphere containing at least one of the polymeric substances forming the acid component of the membrane. This is a method for manufacturing a separation membrane. .

According to the method of the present invention, it is possible to easily manufacture a gas separation membrane. By the treatment of the method of the present invention, the two surface layers are transformed into a substantially uniform film, resulting in an anisotropic film capable of enriching oxygen in the air. A membrane with good oxygen enrichment performance that exhibits a high oxygen permeation rate and a high separation coefficient (ratio of oxygen permeation rate to nitrogen permeation rate) can be obtained.

The polymeric substance that forms the porous membrane of the present invention is one that has membrane-forming ability and has excellent oxygen enrichment performance as a material (
There are no particular limitations as long as the material has a high oxygen permeation rate and a high separation coefficient. When the membrane form is hollow fiber, the membrane area per unit volume can be increased, so it is advantageous to focus on the separation coefficient rather than the oxygen permeation rate.
Specifically, poly(4-vinylpyridine), polysulfone, polycarbonate, cellulose acetate, cellulose ether, etc. having a separation coefficient of 6 or more can be mentioned. Further, the polymer substance may be a single polymer,
It may still be a copolymer.

Other polymeric substances may be mixed to such an extent that these polymeric substances account for 50% or more of the total weight.

Among these polymeric substances, ethyl cellulose (hereinafter referred to as E'C), which has a relatively high oxygen permeation rate, and polysulfone, which has a relatively high separation coefficient, are particularly preferably used.

The porous membrane of the present invention is manufactured by extruding a solution of a polymeric substance in an organic solvent containing a non-solvent as an additive into the air through a spinneret, and then introducing it into an aqueous coagulation bath containing the solvent. The membrane structure is stabilized by forming a membrane and then subjecting it to hot water treatment.

It can be manufactured by drying.

The above method for manufacturing a porous membrane is merely an example, and some of the steps may be omitted or changed as necessary, and other steps may be added.

The case where the porous membrane is an ethyl cellulose porous hollow fiber will be described in more detail below.

There are no particular limitations on the solvent for ethylcellulose, but specific examples include N-methyl-2-pyrrolidone (hereinafter referred to as NMP), dimethylformamide (hereinafter referred to as D'MF),
Dimethylacetoamide (hereinafter referred to as DMic), acetone, ethanol.

Benzene, toluene, cyclohexene, etc.! a[' can be put.

In addition, additives may be used as long as they are non-solvents for ethylcellulose and can facilitate the creation of porosity during the formation of hollow fiber membranes, but they can also be water-soluble substances that can be removed in the washing process and are used in organic solvent solutions of ethylcellulose. More preferred are those that exhibit a thickening effect on.

Specific examples include polyhydric alcohols such as polyethylene glycol, ethylene glycol (hereinafter referred to as EG), glycerin, and surfactants such as Triton X 100. In actual selection, care must be taken regarding the combination of solvent and additive.

The composition of the spinning dope varies slightly depending on the solvent and additives selected, but the ethyl cellulose concentration is between 20 and 20.
40% by weight, the amount of additives is 3% or more, and if the spinning stock solution has uniform stringiness at the spinning temperature, it may be added up to 50%, but usually about 60% or less is necessary for stringiness. It is preferable in this respect.

/If the polymer concentration is too low, the viscosity of the stock solution decreases, making it difficult to form a hollow fiber membrane by the cis injection method.
This is not preferable because the spinnability (threadability) of the discharged stock solution flow is reduced. On the other hand, if the polymer concentration is too high, the degree of porosity of the resulting hollow fiber membrane will be small (depending on the amount of additives), and the viscosity of the raw solution will be high, so it will be difficult to set the spinning temperature high, and the dry-wet spinning method will be used. It is thought that the formation of a dense layer on the surface of the hollow fiber membrane in the dry section is excessively promoted. Therefore, such a hollow fiber membrane has a low oxygen permeation rate and is not preferable.

Although the spinning stock solution of the present invention differs somewhat depending on the combination of solvent and additives and its composition, the viscosity of the stock solution has a high temperature dependence (for example, B C / N M P / E G = 60155,
/15 system, the apparent flow activation energy is 19.
3 kcal/rn31). In other words, when the temperature of the stock solution decreases, the viscosity of the stock solution increases rapidly and gels.

This property applies when hollow fiber membranes are formed using the gas injection method.

Very advantageous. It also has the characteristic that it undergoes phase separation as it gels, forming an opaque gel. Therefore, the spinning temperature (die temperature)
Settings are also important. If the set temperature is too low, the spinnability will be lost and the spinning state will become unstable, and the coagulated yarn will become extremely weak, which is disadvantageous in terms of handling. If the set temperature is still too high, the viscosity of the stock solution will be too low, making it difficult to form a hollow fiber membrane by the gas injection method.

If the spinning temperature is set high and the hollow fibers in the sol state extruded from the two spindles are introduced into the coagulation bath before gelation and phase separation progress, a hollow fiber membrane with a relatively dense surface can be obtained; Set the spinning temperature lower.

If the dry length (distance from the mouth surface to the solidified liquid level 1) is increased, the hollow fiber membrane will have a relatively coarse membrane structure.

By setting the twisting spinning temperature higher or shortening the dry length, selectivity can be shown by simply twisting (α>1)
A hollow fiber membrane is obtained.

Although it varies depending on the conditions, the spinning temperature is 50 to 160°
The C2 dry length is selected within the range of 0 q to 50 a'o.

Next, as the coagulation bath, an aqueous solution of the used solvent is preferably used. Usually, it is preferable that the bath composition contains 5% or more of a solvent. If the ratio of solvent is too small, the formation of a so-called skin layer during coagulation tends to be excessively promoted, and as with the case of using a high concentration stock solution, the separation coefficient (α
) is good, but tends to result in hollow fiber membranes with low oxygen permeation rates.

There is no particular limitation on the coagulation bath temperature, but it is 10 to 60°C.
bath temperature is preferably used. The higher the bath temperature, the rougher the film structure will be on average;

Similar to the hollow fiber membrane obtained from the high concentration stock solution mentioned above.

It is thought that it is easy to form a so-called uniform membrane with a very small surface porosity, and the hollow fiber membrane has a large separation coefficient but a low oxygen permeation rate.

The trench hot water treatment temperature is preferably in the range of 50 to 100'C. This hot water treatment step is important in terms of fixing the membrane structure formed by coagulation. That is, solvents and additives remaining in the hollow fiber membrane are removed and heat treatment is performed to suppress dimensional changes (shrinkage) of the hollow fiber during drying.

The relationship between the manufacturing conditions and oxygen enrichment performance of the ethyl cellulose porous hollow fiber of the present invention has been described above.
It is also possible to produce porous hollow fibers (with a separation coefficient close to that of ethyl cellulose, 3.3). However, if an attempt is made to create a hollow fiber membrane having a completely uniform layer, the thickness of the dense layer inevitably increases, resulting in a decrease in oxygen permeability.

Therefore, if manufacturing conditions are selected so that the dense layer becomes thinner, the separation coefficient of the hollow fibers after drying will be lower than the original properties of ethyl cellulose. The dense layer gradually becomes a completely uniform layer.

As mentioned above, the ethyl cellulose porous hollow fiber, which is an example of the present invention, exhibits a certain degree of performance as an oxygen-enriching membrane even when dried as is, but it is treated in an atmosphere containing a selected solvent. As a result, defects such as pinholes in the porous hollow fibers can be repaired, and a membrane with a higher separation coefficient can be obtained.

In the case of an ethyl cellulose porous membrane, the solvent used for treating the porous membrane is as described above.

NMP, DMF', DMAc, acetone, ethanol.

In addition to methanol, benzene, toluene, cyclohexene, chloroform, etc., dimethyl sulfoxide, cyclohexane, etc., which have a swelling effect, are used.

The porous membrane is treated by a method such as passing the porous membrane through a gas atmosphere containing these solvents, immersing it in a solution containing these solvents, or immersing the porous membrane in a solution containing these solvents.

When a solution is used, it is usually diluted with a non-solvent for the porous membrane. Specifically, it is selected from water, an aqueous solution containing a salt or a surfactant, n-hexane, impentane, and the like.

The concentration of the solvent at this time depends on the type of solvent used.

Although it varies depending on the immersion time and temperature, it is usually selected in the range of 1% or more, preferably 5% or more. If the concentration is less than 1φ, the treatment effect will be poor and this is not preferable.

The processing time is not particularly limited, but is usually 1 minute or less.

Furthermore, it is preferable to set the solvent concentration, temperature, etc. so that the treatment effect can be improved in 10 seconds or less. Generally, the longer the processing time, the more solution is taken in.

This is not preferable as the dense layer of the porous membrane becomes thicker and the subsequent drying process becomes burdensome.

The processing temperature is usually selected in the range of 15 to 5°C,
In order to adjust the solubility of the processing solution, the temperature may be selected within the range of 0 to 15°C and 65 to 70°C.

In these treatments, the hollow fibers are wound once after being treated with hot water.
Although it may be carried out afterwards, it is particularly preferable to carry out the continuous processing directly in connection with the spinning.

It is desirable that the treated hollow fiber membrane be at least slightly surface-dried in a non-contact dryer. More hot air if necessary,
It is dried using a heated roller or the like and then wound up.

The drying temperature is usually selected within the range of 0 to 80'C.

Performance evaluation of the obtained hollow fiber membrane was performed using a small glass tube module. Specifically, a small module made by bundling n (numbers) of hollow fiber membranes with outer diameter OD (picture) and effective length/(an) is filled with oxygen whose pressure is regulated to 1.0 heel/an・G from a cylinder. The oxygen flow rate per unit time q (me/e e c
) was measured using a thin film flowmeter. The permeation direction is from the outer surface of the hollow fiber to the inner surface, and the oxygen permeation rate Qo2 (m3/m2・hr*
atm ) using the following formula.

The nitrogen permeation rate QN2 was also evaluated and measured in the same manner, and the separation coefficient (α-QO2/QN2) was calculated from these values.

Examples 1 to 2 and Comparative Example 1 Commercially available ethyl cellulose (Kanto Kagaku, reagent 100 cps
) and 350 parts of NMP were stirred and dissolved at 120'C. Do not continue stirring at the same temperature EG14
0 parts were added dropwise and mixed to obtain a homogeneous solution. The viscosity of this solution was 90 poise at 120'C, gelatinized at 85C and virtually no longer showed stringiness. After filtering, removing and encapsulating this stock solution, the spinning temperature (cutter temperature) of a double-tube type hollow fiber Kawaguchi was maintained at 100°C and the dry length was maintained at 20 mm.

Next, it was immersed in a coagulation bath of 50'C consisting of a 30 wt% NMP aqueous solution, washed with water, and subjected to hot water treatment at 50'A for 50 seconds. Then, after being continuously immersed in a mixed solution of ethanol/water = 5D150 (wt%) for about 0.5 seconds, it was passed through a non-contact hot air drying tube.
It was brought into contact with hot air at 52° C. in a countercurrent flow, dried, and wound up. Comparative Example 1, which had not yet been subjected to the immersion treatment, was wound up in the same manner as an untreated hollow fiber membrane. The obtained hollow fiber membrane had an outer diameter of 601 μ, a membrane thickness of 67 lt, and a circularity ratio (minor axis/long axis) of 97, regardless of whether it was treated or not.

The performance of the obtained hollow fiber membranes is shown in Table 1 along with those obtained by changing only the mixing ratio of ethanol/water.

Table 1 Examples 3 to 6 Spinning and solvent treatment were performed in the same manner as in Example 1 using a spinning dope having the same composition. As a condition.

The other conditions were the same as in Example 1, except that the hot air drying temperature was 58"C, the coagulation bath composition and the hot water treatment temperature were different.The performance of the obtained hollow fiber membrane was compared to that of the untreated hollow fiber membrane. It is shown in Table 2 along with its performance.

Table 2 *QO2= [m7m21hr-atm] α-Qo
2/ Q10. .

Examples 7 to 9 E C/DM F/E in the same manner as Example 1
A spinning dope having a G ratio of 30155/15 (wt%) was prepared. The viscosity of this stock solution was 477 poise at 110°C. This stock solution was discharged in the same manner as in Example 1 at a spinning temperature of 85°C, 1 dry length of 5 dishes, and a nitrogen injection pressure of 19 w H2O. Then 50 wt/I)]) 6 consisting of an aqueous M F solution
After being immersed in a coagulation bath at 0°C, it was washed with water and further subjected to hot water treatment at 50°C for 50 seconds. Subsequently, immersion treatment was performed in the same manner as in Example 1 by changing the composition of the treatment solution.

Note that the temperature of the treatment liquid at this time was maintained at 5°C.

The oxygen enrichment performance of these hollow fiber membranes is summarized in Table 6 together with the performance of the untreated membrane.

Table Example 10 Polysulfone (Product name: ``Unyl Polysulfone'' p-
5500) 245 copies to 350 copies of NMP 120'c
The big thing melted. K while continuing to stir at the same temperature.
5 parts of Gl[) was added dropwise and mixed to obtain a homogeneous solution.

The viscosity of this solution was 7 D'a and 739 voids.

After this spinning stock solution was subjected to excessive defoaming, it was discharged into the air using a double tube type hollow fiber nozzle. At the same time, nitrogen was injected into the hollow fiber at an injection pressure of 2 filtration + nmH2O.

At this time, the spinning temperature was 75° C. and the dry length was maintained at 15 mto. Next, 6% by weight of N, MP aqueous solution was filtered.
After being immersed in a coagulation bath at 0°C, it was washed with water and further subjected to hot water treatment at 50°C for 50 seconds. and continuously acetone/
After being immersed in a water-60/40 (weight ratio) mixture for about 2 seconds, it was passed through a non-contact type hot air drying tube at 58°C.
in countercurrent contact with hot air.

It was dried and rolled up. The obtained hollow fiber membrane had an outer diameter of 291μ
The film thickness was 60 μm, and the circularity (breadth axis/long axis) was 99%.

The oxygen enrichment performance of the hollow fiber membrane that was dried and wound without being subjected to dipping treatment was Qo2 = 1.42 m3/m2. hr-atm
, α=1.0, whereas the hollow fiber membrane subjected to the immersion treatment had QQ2=0.051 m3/m2. h
The separation performance was significantly improved with r, atm, ct = 2.8.

Claims (3)

[Claims] (1) A method for producing a gas separation membrane, which comprises treating a porous membrane in an atmosphere containing at least a solvent for a polymeric substance that is one component of the membrane. (2) The method for producing a gas separation membrane according to item 1 above, wherein the porous membrane has a hollow fiber shape. (3) The method for producing a gas separation membrane according to item 1 above, wherein the polymeric substance is ethyl cellulose.