JPS59169510A - Anisotropic hollow yarn membrane - Google Patents

Abstract

PURPOSE:An anisotropic hollow yarn membrane suitable for preparing oxygen enriched air from air, obtained by spinning an org. solvent solution containing ethyl cellulose as a main component and having a specific solvent and a specific additive mixed therein. CONSTITUTION:210pts. of commercial ethyl cellulose is added to 385pts. of dimethylformamide being a solvent and dissolved therein at 210 deg.C under stirring. Succeedingly, 105pts. of ethylene glycol as a non-solvent additive is dripped and mixed in the obtained solution at the same temp. to prepare an org. solvent solution having a uniform composition. After this solution containing ethyl cellulose as a main component is filtered and defoamed, it is emitted into air by using a double wall type hollow yarn forming spinneret to be spun into a hollow yarn and, at the same time, N2 is injected into the hollow yarn. In the next step, the hollow yarn is immersed in a coagulation bath comprising a 30% aqueous dimethylformamide solution and the coagulated yarn is washed and subjected to hydrothermal treatment at 50 deg.C and the treated one is dried. By this method, an anisotropic hollow yarn membrane which has a dense outer surface layer part and an inner layer part comprising a reticulated porous layer with the peak position of a pore distribution of 300-5,000Angstrom and of which the oxygen permeation speed is 0.2m<3>/m<2>, hr, atm or more and separation coefficient is 2.3 or more, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an anisotropic hollow fiber membrane mainly composed of ethylcellulose, which has a large gas permeation rate and is particularly effective for obtaining oxygen-enriched air from air. The present invention also relates to an anisotropic hollow fiber membrane with 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 jf of the gas in the membrane, and in the case of a porous membrane, there are many pores of about 100A, and the mean free path of the gas molecules is As an example of the latter, asymmetric hollow fibers made of cellulose derivatives are disclosed in Japanese Patent Application Laid-open No. 51-112917.
In addition, a dry semipermeable membrane having a surface active layer and an inner porous layer mainly composed of polyacrylonitrile is disclosed in JP-A No. 5
6. -111005. Only 1
7. 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. In contrast, the anisotropic membrane of the present invention, which has a dense layer with substantial pores and no I2 in the outer surface layer, separates mixed gases based on the difference in the rate of dissolution and diffusion of gas into the membrane. Yes, for the first time using such a membrane.

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

In addition, various functional membrane materials have been developed as examples of these materials, but all of them are mainly composite membranes that share separation properties, molding properties, and shape retention properties.

There are few examples of anisotropic membranes, and even if there are, there are practical or manufacturing problems. For example, if the purpose is to enrich oxygen in the air, 1. The cellulose ester anisotropic turtle was published in Japanese Unexamined Publication +18
No. 57-7206, the method is freeze-dried to maintain the anisotropic structure.

It has the disadvantage of manufacturing by using a very labor-intensive method such as the common medium substitution method.

In addition, in terms of membrane performance characteristics, [2 is also not satisfactory; 9 Anisotropic membranes with high selectivity have a low oxygen permeation rate;
The dilemma was that a membrane with a high oxygen permeation rate would have low selectivity.

The present inventors have previously investigated in detail oxygen selective filtering membrane elements. As a result, they discovered an anisotropic hollow fiber membrane made of ethyl cellulose and achieved an extremely high oxygen permeation rate while retaining the essential selectivity of ethyl cellulose.122 The present invention was achieved.

That is, the present invention is a hollow fiber membrane mainly composed of ethylcellulose, which has a dense layer in the outer surface layer, and the peak position of the pore size distribution in the inner layer and inner surface layer is 300 to 50D.
It is a network porous layer in the OA range. It is an anisotropic hollow fiber membrane having an oxygen permeation rate of 0.2 m''/m'·hr -atm or more and a separation coefficient (permeation rate ratio of oxygen to nitrogen) of 23 or more.

The ethyl cellulose used in the present invention is particularly silicified, and the forming component of the hollow fiber membrane is mainly ethyl cellulose, but other polymeric substances may be added and mixed within the range that does not significantly deteriorate the material properties to improve processability and quality. It can be changed. Specifically, it has excellent separation performance for cellulose acetate, polysulfone, etc. Polymers with good moldability are preferably used.

The ethyl cellulose anisotropic hollow fiber membrane of the present invention has a dense layer without substantial pores in the outer surface layer, and the peak position of the pore size distribution in the inner layer and inner surface layer is between '500 and
It is a network porous layer in the range of 5000A. A dense layer with no substantial pores is a layer that exhibits the inherent selectivity of ethyl cellulose and substantial circular selectivity with respect to gases, specifically the separation coefficient (permeation rate ratio of oxygen to nitrogen). ) is a layer exhibiting selectivity of 23 or more. The thickness of this dense layer also determines the gas permeability.

In the case of a substantially dense layer such as the anisotropic hollow fiber membrane of the present invention, the oxygen permeability coefficient specific to ethyl cellulose can be calculated by actual measurement (or by excluding the oxygen permeation rate). The smaller the thickness, the higher the permeation rate, which is preferable, but if the thickness is too small, problems will arise in terms of mechanical strength.

001-5μ, preferably 001-2μ.

The oxygen permeation rate in the present invention is 0.2 m'/m',
hr, atm or more'', which means that in the case of a complete dense layer,
This corresponds to a thickness of approximately 0.2 μm or less.

The peak position of the pore size distribution in the inner layer and inner surface layer is
It is a network-like porous layer in the range of 0 to 50 DO'A, and shows virtually no selectivity for gases passing through this layer.

Although this porous layer does not directly affect performance, there is a deep relationship between the peak position of the pore size distribution of the porous layer and the density and thickness of the dense layer. In other words, when the peak position of the pore size distribution is less than 500A, the thickness of the dense layer becomes thick and the gas permeation rate decreases, whereas when it exceeds 5000A, the dense layer becomes too thin and the dense layer is incomplete. Therefore, the separation coefficient decreases significantly. In other words, the density and thickness of the dense layer, which determine performance, can be controlled by the peak position of the pore size distribution of the porous layer, so the peak position of the pore size distribution of the porous layer is very important. A range is preferred.

More preferably, it is in the range of 500 to 5 DOOA.

In addition, this porous layer supports the dense layer and the hollow fiber membrane and 1-
It plays a role in maintaining the necessary mechanical strength.

Although it depends on the outer diameter of the hollow fiber membrane, it is usually 500μ or less.

Preferably, the diameter is in the range of 10 to 200μ.

Specifically, the anisotropic hollow fiber membrane of the present invention is produced by extruding an organic solvent solution of ethyl cellulose 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. Stabilize the membrane structure by forming a thread membrane structure and further applying hot water treatment 17. It can be manufactured by drying after that.

The above method for producing an anisotropic hollow fiber membrane has a thin dense layer with no substantial pores in the outer surface layer, and a peak position of the pore size distribution in the inner layer and inner surface layer in the range of 300 to 5000 A. This is just one example of a method for manufacturing an anisotropic hollow fiber membrane that is a network-like porous layer; some of the steps may be omitted or changed as necessary, and other steps may be added. .

There are no particular limitations on the solvent for ethylcellulose, but specific examples include N-methyl-2-pyrrolidone (hereinafter abbreviated as NM'P), dimethylformamide (hereinafter abbreviated as MF), and dimethylacetamide (hereinafter abbreviated as DMAC). t omitted
), acetone, ethanol, benzene, toluene, etc. .

In addition, additives may be used as long as they are non-solvents for ethylcellulose and can facilitate the formation of porosity during the formation of hollow fiber membranes, but they can also be water-soluble substances that can be removed in the water washing process and can be 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 abbreviated 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 somewhat depending on the solvent and additives selected, but the concentration of the polymer containing ethyl cellulose as a living body is 20 to 40% by weight.

The amount of additive is 3L (1) or more, and if the spinning stock solution has uniform stringiness at the spinning temperature, it may be added up to 50 days, but usually 30% or less is the point for stringability. It's so ugly.

If the polymer concentration is too low, the viscosity of the stock solution decreases, making it difficult to form a hollow fiber membrane using the gas 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, depending on the amount of additives, the degree of porosity of the resulting hollow fiber membrane will be small, and the spinning temperature will be set high due to the high viscosity of the raw solution, resulting in a wet-dry spinning method. 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 suitable.

Furthermore, the viscosity of the spinning dope mainly composed of ethyl cellulose is highly temperature dependent, although it varies somewhat depending on the combination of solvent and additives and its composition. In other words, when the temperature of the stock solution decreases, the viscosity of the stock solution increases rapidly and gelation tends to occur. This characteristic is very advantageous when forming hollow fiber membranes by the gas injection method. In addition, phase separation occurs along with gelation 12. It has the characteristic of being an opaque gel. This property of phase separation due to temperature change alone is useful when forming a porous structure.

In other words, setting the spinning temperature (die temperature) is also an important factor in forming the membrane structure of the present invention.

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. Moreover, if the set temperature is too high, the viscosity of the stock solution will become 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 nine spindles are introduced into the coagulation bath before gelation and phase separation progress, a hollow fiber membrane with a relatively dense surface will be obtained; Set the spinning temperature lower.

If the dry part (distance from the mouth surface to the solidified liquid level) is lengthened, the hollow fiber membrane will have a relatively rough membrane structure.

In other words, by appropriately selecting the spinning temperature and drying zone, it is possible to obtain the anisotropic hollow fiber membrane of the present invention having a dense layer in the surface layer having no substantial pores. Although it varies depending on the composition of the stock solution, polymer concentration, etc., the spinning temperature is selected from 50 to 160° C.9 and the dry length is selected from the range of 0.2 cm to 50 cm.

Next, as the coagulation bath, an aqueous solution of the used solvent is preferably used. Usually, the bath composition preferably contains 5% or more of a solvent. If the proportion of the 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) of 9
It's good, but it tends to be a hollow fiber membrane with a low oxygen permeation rate.

There are no particular limitations on the temperature of the coagulation bath, but a bath temperature of 10 to 60°C is preferably used. The higher the bath temperature, the rougher the membrane structure will be on average; conversely, a lower temperature bath will tend to form a so-called dense layer with a very small surface porosity, similar to the hollow fiber membranes obtained from high-concentration stock solutions. 9, it is easy to obtain a hollow fiber membrane with a large separation coefficient.

The hot water treatment temperature is preferably in the range of 50 to 100'a. This hot water treatment step is important in terms of fixing the membrane structure formed by coagulation.

Solvents and additives remaining in the hollow fiber membranes are removed and heat treatment is performed to suppress dimensional changes during drying of the hollow fibers.

After the hydrothermal treatment, the hollow fiber membrane is dried in a conventional manner, ie, by contacting it with hot air or a heated roller surface. The drying temperature is usually selected within the range of 30 to 100°C.

The pore size distribution of the hollow fiber membrane in the present invention was measured by mercury porosimetry. In other words, the cumulative pore volume (V
) and pore diameter (r), cLV/'d (Jog
It was obtained by calculating the relationship between r ) and r.

The peak of the pore size distribution corresponds to the point where the slope is the largest in the relationship diagram between cumulative pore volume and pore size.

0 calculated from the measured oxygen permeation rate. Performance evaluation of the obtained hollow fiber membrane was performed using a small glass tube module. Specifically, oxygen regulated to 1.0y/♂G is supplied from a cylinder to a small module made by bundling n (n) hollow fiber membranes with an outer diameter OD (lightning) and an effective length of 7 (c+n). Schiff passes through the hollow fiber membrane to the module υ
The resulting oxygen flow rate q (Hz/unit) per unit time was measured using a thin film flow meter. The permeation direction was from the outer surface of the hollow fiber to the inner surface, and the oxygen permeation rate QO7 (ze/ml·hr-atm) was calculated from the following formula using the outer surface area of the hollow fiber membrane as the effective membrane area.

In addition, the nitrogen permeation rate QN was evaluated and measured using the same method, and from these values, the separation coefficient (α=Q, O, /QN,
) was calculated.

Examples 1 to 3 Commercially available ethyl cellulose (Kanto Yfk-gaku, Reagent I
The mixture was stirred and dissolved in 210 parts (DOcps) of 385 parts iDMF at 120°C. EoIDs section while continuing to stir at the same temperature?
A mixed solution was obtained. The viscosity of this solution is 110
575 poise at 75"C and gelatinized L7 at 75"C. It virtually no longer showed any stringiness. After degassing this stock solution'fr filtration filter, it was passed through a double-tube type hollow fiber nozzle into the air. At the same time, nitrogen was injected into the hollow fiber at a pressure of 18.5
Injected with mm H,O. At this time, the spinning temperature (mouth temperature) was maintained at 90° C., and the dry length was maintained at 5 holes. then 50
After being immersed in a 30° C. coagulation bath consisting of a wt % DMF aqueous solution, it was washed with water and further subjected to hot water treatment at 50° C. for 50 seconds. Subsequently, it was dried with hot air at 40°C and then rolled up.

The obtained hollow fiber membrane had an outer diameter of 602 μm, a membrane thickness of 52 μm, and a circularity (shorter axis/longer axis) of 98%. The structure of this hollow fiber membrane is shown in Figures 1 to 3, and its performance, peak position of pore size distribution, and calculated value of dense layer thickness are also shown along with hollow fiber membranes obtained by changing the spinning temperature and hot water treatment temperature. It is shown in Table 1.

Table 1 *QO3 oxygen permeation rate Cm"/m' ・hr-atm
[Comparative Examples 1 to 2] Ethyl cellulose concentrations were 65 parts and 28 parts by the same method as in Example 1 except that NM and P were used instead of DMF as the solvent (the amount of additive EG added was 10 parts and 20 parts, respectively).
A spinning stock solution of tI)) was prepared. The viscosity of each is 41
The solution was 0 poise/14 D'0.168 poise/120°C, and was a homogeneous solution.

In the case of stock solution No. 55, the spinning temperature was 120°C, the dry length was 50 mm, and the nitrogen injection pressure was 15 dishes H2 using the same spindle as in Example 1.
The sample was discharged at 0°C, immersed in an IO'c coagulation bath consisting of a 30% NMP aqueous solution, washed with water, and further subjected to hot water treatment at 90°C for about 1 second. Subsequently, it was dried with hot air at 65°C and then rolled up. The performance of the obtained hollow fiber membrane was excellent with a separation coefficient of 27, but an oxygen permeation rate of 0.0'0'7 m'
/m”, hr, and atm.

When the pore size distribution of this hollow fiber membrane was measured by mercury intrusion method, the peak position of the pore size distribution was 2ooX. On the other hand, 2
For 8% stock solution, spinning temperature 93°C2 dry length 7 mm
, discharged at a nitrogen injection pressure of 14 mm H, O, immersed in a coagulation bath of 30% NMP aqueous solution at 50°C, and then washed with water.
Further, it was subjected to hot water treatment at 90"C for about 1 second. Then, it was dried with hot air at 65°C.

The performance of this hollow fiber membrane is that the oxygen permeation rate is 50 m'/m
Although the 9-separation factor was 10, which showed almost no separation performance, the pore size distribution of this hollow fiber membrane was measured by mercury intrusion method, and the peak position of the pore size distribution was found to be 6DOOA. Ta.

Example 4 122 parts of ethylcellulose used in Example 1 and cellulose triacetate (manufactured by Eastman, CA455-85)
s) 55 parts were dissolved in 485 parts of NMP at 120°C with stirring. While stirring at the same temperature, 140 parts of EG was added dropwise and mixed to obtain a uniform solution.

The viscosity of this solution was 560 voids at 120°C.

It gelatinized at 90° C. and showed virtually no stringiness.

This stock solution was spun at a spinning temperature of 100°C and a dry length of 20 mm.

Nitrogen was injected at an injection pressure of 18.5 mm H, and was discharged in the same manner as in Example 1.
After coagulation by immersion in a coagulation bath at °0 and washing with water,
A second hot water treatment was performed. Then, it was subsequently dried with hot air at @40°C and rolled up.

The obtained hollow fiber membrane had an outer diameter of 417μ and a membrane thickness of 63μ.

The roundness was 96eI). Further, the peak position of the pore size distribution of the hollow fiber membrane measured by mercury intrusion method was 700A.

The performance of the obtained hollow fiber membrane is QO, = 0.24 (
m/m', hr, atm), a = 2.8, and compared with the case of x Circe/L/O-su alone, Qo and U decreased, but α was improved. Moreover, the mechanical properties (the tensile strength of the hollow fiber membrane) were rather improved.

[Brief explanation of drawings]

1 is an electron micrograph of a cross section of the anisotropic hollow fiber membrane obtained in Example 1 of the present invention, and FIGS. 2 and 3 are electron micrographs of the outer surface layer and inner surface layer of the cross section shown in FIG. 1, respectively. The magnification of Fig. 1 is 1000x, and Fig. 2.6 was taken at 10000x.

Claims (1)

[Claims] It is a hollow fiber membrane whose main component is ethyl cellulose. The outer surface layer has a dense layer, and the inner layer and inner surface layer are network-like porous layers in which the peak position of the pore size distribution is in the range of 500 to 5000 mm. Oxygen permeability is 0.2 m” /
m'-hr, atm or more and a separation coefficient (permeation rate ratio of oxygen to nitrogen) of 26 or more.