JPS5858111A - Dry separation membrane - Google Patents

Abstract

PURPOSE:To obtain a dry hollow yarn separation membrane for separating oxygen without shrinking said membrane, in drying a wet hollow yarn separation membrane comprising cellulose acetate, by preliminarily heat treating this separation membrane at a specifide temp. CONSTITUTION:A wet hollow yarn separation membrane comprising cellulose acetate is heat treated at 85-99 deg.C. In this case, the moisture content of this separation membrane is adjusted to about 35-55% and the membrane is dried by a freeze drying method or a solvent replacement method. Herein, when the heat treatment temp. is below the lower limit, shrinkage becomes large and the reversibility of a membrane structure is lost in a dry and a wet conditions and, when the temp. exceeds the upper limit, the membrane is largely shrunk during heat treatment and the performance thereof becomes unsuitable for practical purposes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry hollow fiber separation membrane used for separating or concentrating components of gaseous or liquid fluid mixtures. More specifically, in a dry hollow fiber separation membrane obtained by drying a wet hollow fiber separation membrane obtained by a wet method etc., the wet hollow fiber membrane before drying is heat treated at a temperature in the range of 85°C to 99°C.

The present invention relates to a dry hollow fiber separation membrane characterized in that the water content of the membrane is adjusted to 35% to 55%.

Most of the membranes used to separate or concentrate components from fluid mixtures were in a wet state because they were mainly used for ultrafiltration and reverse osmosis. On the other hand, hollow fiber separation membranes are often manufactured using a wet method or an air gap method.
Various methods of drying O 2 semipermeable membranes, which are already wetted with water or other solvents during the manufacturing process, have been studied, but for that purpose, it is not necessary to completely dry the membranes. However, in recent years, the field of application of separation membranes has expanded, and as applications for not only liquid-liquid separation but also gas separation have become popular, the demand for dry membranes has increased.

On the other hand, when preserving a stone layer film made of cellulose acetate,
During long-term storage, the permeation performance decreases due to the densification of the membrane due to water evaporation, or the separation performance decreases due to damage by microorganisms, so wet membrane a drying is necessary to protect the separation membrane from these factors. It seems that it has become a film and is attracting attention and demand.)9. When a separation membrane moistened with water or a solvent is dried with hot air or under reduced pressure, the membrane shrinks and the membrane performance S is markedly reduced, often rendering it unusable. When completely drying a wet film in this manner, a drying method and a wet film that do not cause shape change are required. When drying a wet membrane, two forces act on the membrane and change its structure.〇(1) In the process of evaporation of water in the micropores, a thin layer of water is formed on the inner wall of the pores, and this water Surface tension causes the micropores to contract, and thus the entire layer to contract.

(2) The water that swells the membrane material is detached from material a during the drying process, causing the membrane to shrink.

These contractions change the microstructure of the wet film,
It increases the dense layer on the membrane surface and reduces the permeation rate of gas or liquid. Various methods have been proposed for producing a dry film from a wet film without causing such deterioration in film performance. For example, in the special report No. 48-6033, the water in the wet membrane is replaced with a non-polar organic solvent instead of a water-immersed compatible solvent, and the shrinkage of fine particles and pores is reduced by drying the membrane with a non-polar organic solvent that has a lower surface tension than water. JP-A No. 47-116182 discloses a method of using a mixed aqueous solution of polyhydric alcohol and organic carboxyl alcohol, and JP-A-Sho-94079 discloses a method for preventing Fi!
A method of treating with an aqueous polyhydric alcohol solution at 1IC-110°C and drying is known. In addition, as an example of freeze-drying to avoid the generation of surface tension of liquid, JP-A-53-146-
Publication No. 274 proposes a method of freeze-drying while applying tension to the membrane.

As a result of extensive research into drying methods for wet hollow fiber separation membranes, the present invention has found that shrinkage during drying is related to the moisture content of the membrane and the heat treatment temperature of the wet membrane.

The present invention will be explained in detail below. When producing dry hollow fiber separation M from a cellulose acetate wet hollow fiber separation membrane, the heat treatment temperature is preferably 85°C to 99°C [87
~930, moisture content 2>135%~, 55%, preferably t
Membranes dried by freeze-drying or solvent replacement methods from wet 9-thread separation membranes adjusted to 40 to 50 inches have excellent gas permeability and separation ability, and when re-wetted with water, they have relatively high water permeability. The removability of salts and the like was also unchanged from before drying.

From the above, this dry-like membrane is effective for gas separation or liquid separation.On the other hand, this wet membrane is also superior to other wet membranes in hot air or air drying. I found out.

A wet hollow fiber separation membrane with a water content of 55 or more has a weak membrane structure, and even when dried from a solvent with a low surface tension, the micropores are deformed, the entire layer shrinks greatly, and the dry membrane becomes slow. The permeability is low, and the membrane structure is not reversible even when rewetted with water, and the water permeability is greatly reduced. - If the water ratio is less than 35, the dense layer on the surface of the wet film will be thick and it will not be practical even before drying. The heat treatment temperature of a wet hollow fiber separation membrane is related to the morphological stability during membrane drying.
If the water content is lower than '0, the shrinkage will be large, similar to when the water content is high, and the membrane structure will no longer be reversible during wetting and drying. It's becoming impractical.

The method for drying the wet membrane is to freeze the wet hollow fiber separation membrane and dry it under reduced pressure while maintaining it in a frozen state, or to replace the water in the wet hollow fiber separation membrane with a solvent with lower surface tension. After that, there is a method of evaporating the solvent to remove water and drying, but the method is not limited to these methods.

The moisture content of the wet membrane is a value calculated using the following formula.

w, Dry weight of membrane Weight of Wo membrane when hydrated The present invention will be described below with reference to Examples.

Example 1 40 parts by weight of cellulose triacetate, N-methyl-2
- A spinning solution consisting of 45 parts by weight of monolorin and 15 parts by weight of ethylene glycol is discharged into the atmosphere in the form of a hollow fiber, and then N-methyl-2-pyrrolidone:ethylene glycol:
The mixture was introduced into a coagulation bath with a water ratio of 20:10 to obtain a wet hollow fiber membrane. After washing the obtained wet hollow fiber membranes with water, heat treatment was performed under different temperature conditions to obtain hollow fiber membranes with different water contents and removal rates. This wet membrane was cooled to t''-40-0, and after freezing, it was freeze-dried under reduced pressure of o,its+ng or less to obtain a dry hollow fiber membrane.The gas separation performance of the obtained hollow fiber membrane was 1.
Isui/Liao! The permeation and separation characteristics of oxygen and nitrogen were investigated using G air. At the same time, the dried hollow fiber H was re-wetted with water,
The performance of rewetting 14s as a reverse osmosis membrane was investigated. For reverse osmosis performance, 3.5% NaCl aqueous solution, operating pressure 55'j'/
am"G Measured at a water temperature of 25℃.Heat treatment temperature was 85"
Hollow fiber membranes of C or higher showed good gas separation performance and reverse osmosis performance, but the hollow fiber membranes at 70°C and untreated showed a large degree of change during drying, and the gas permeability and reverse osmosis of the rewet membrane were poor. The performance decreased significantly, indicating that the membrane structure was not reversible. The results are shown in Table 1.

Example 2 Example 1 was carried out in exactly the same manner as in Example 1 except that cellulose diacetate was used instead of cellulose triacetate. The results are shown in Table 2.

Margins below Table 1 Table 2 Comparative Example The wet hollow fiber membrane obtained in Example 1 after heat treatment at 90°C was heated to 85°C.
An attempt was made to produce a dry separation membrane by drying it under hot air for 30 minutes, but the gas separation performance of the resulting membrane was poor.

Po21. Ox 10'qd-sec -mHg,
A 3.0, which was not satisfactory.

Example 3 The same method as in Example 1 was adopted, except that a spinning solution prepared using different ratios of cellulose triacetate, N-)lfk-2-pyrrolidone, and ethylene glycol was used (heat treatment temperature: 90 ℃) Moisture content is 34
Two types of hollow fiber membranes were obtained: % and 56%. Example 1
A dry hollow fiber membrane was obtained by drying in the same manner as above. The performance of these membranes was as shown in Table 3.

Procedural amendment (self-motivated) June 8, 1980 Public Patent Office M Go K Lij Spring ML Lord L Indication of the case 1981 Patent Review No. 158977 2 Name of the invention Kabuto-shu-part membrane & amendment Relationship with the case of the person who made the patent applicant Table 8, 2-2 Dojimahama, Kita-ku, Osaka Special # of the specification to be amended! In the axial column of Claim F, Details of the Invention (2) Specification @ page 1, line 13, "components of a gas or liquid fluid mixture" is corrected to "oxygen content".

(8) On the 1st page, lines 16 and 20, "dry hollow fiber" is corrected to "dry hollow fiber for oxygen separation."

(4) Correct ``Application of gas separation'' in the 11th line of the 2nd Arashi to ``M proportion ll! 1 concentrated resistance technique #M 姥.''

(5) In the 10th line of the same page, "dry hollow fiber" is corrected to "dry hollow fiber for oxygen separation."

(6) On page 4, line 15, "membrane" is corrected to "oxygen-selective passage membrane."

()) On page 4, line 18, “gas sphere or liquid” is replaced with “
Gas separation, especially several proposals.''

(8) Correct “gas” in the 6th line of the same 5ft to “oxygen”.

(9) “Gas” in the 6th and 7th lines of page 7 is replaced with “
+! ! Correct it to ``Elementary''.

8ft Tables 1 and 2, "Gas component #! 1 characteristics" is corrected to "Oxygen separation characteristics."

αυ Correct “Gas separation performance” in the 4th line of No. 9 wL to “Oxygen separation performance”.

(b) In Table 3 on page 9, ``Gas separation characteristics'' is corrected to ``Oxygen separation characteristics''.

Claims (1) Oxygen content # obtained by drying a wet hollow excess 1Ili layer heat-treated at 185°C to 99°C in a dry hollow excess 1Ili membrane for oxygen separation made of cellulose acetate.
Dry hollow fiber 4i membrane for 11.

(2) The dry hollow fiber separation membrane for bulk separation according to claim 1, which uses an AI precious hollow fiber molecule IA membrane having a water content of 35% to 55%.

Claims (2)

[Claims] (1) A dry hollow fiber separation membrane made of cellulose acetate, obtained by drying a wet hollow fiber separation membrane heat-treated at 85°C to 99°C. (2) The dry hollow fiber separation membrane according to claim 1, wherein the moisture content of the membrane is 35% to 55% d', which is a wet hollow fiber separation membrane.