JPS5940482B2 - Manufacturing method of cellulose acetate semipermeable membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cellulose acetate semipermeable membranes for use in reverse osmosis or ultralacrimation.

The so-called reverse osmosis method, in which the solution is separated into parts with different solution compositions by bringing the solution into contact with a semipermeable membrane and applying pressure to selectively allow the solvent or the solvent and some solutes to permeate through the membrane. Membrane separation techniques such as ultrafiltration have been rapidly becoming popular in recent years.

One of the most important factors for increasing the efficiency of membrane separation is the separation performance of the semipermeable membrane used.

The separation performance of a semipermeable membrane is expressed by the solute exclusion rate (also called retention rate) and solvent permeation rate shown below.

In addition to separation performance, semipermeable membranes are required to have various properties such as high mechanical strength and chemical resistance.

Many studies have already been conducted and proposed on membrane materials and membrane manufacturing methods as semipermeable membranes for membrane separation processes such as reverse osmosis and ultralacrimation, but a fully satisfactory semipermeable membrane has not yet been obtained. do not have.

Semipermeable membranes currently on the market include cellulose acetate semipermeable membranes and aromatic nylon semipermeable membranes for reverse osmosis, and cellulose acetate semipermeable membranes, ethyl cellulose semipermeable membranes, and sulfonate semipermeable membranes for ultrafiltration. Most of the products are semipermeable membranes made of acrylonitrile-based polysulfone and acrylonitrile-based copolymers.

In particular, cellulose acetate semipermeable membranes have excellent separation performance as semipermeable membranes for reverse osmosis.

Conventionally, cellulose acetate semipermeable membranes have an acetylation degree of 38 to 38.
Semipermeable membranes made of cellulose diacetate containing 408 to 40 parts by weight have generally been used, but so-called cellulose triacetate, which has a degree of acetylation of 43 parts by weight or more, has higher salt rejection than cellulose diacetate. In recent years, a method for manufacturing semipermeable membranes for reverse osmosis using cellulose triacetate or a mixture of cellulose triacetate and cellulose diacetate as a membrane material has been developed to take advantage of its properties such as efficiency, mechanical strength, chemical resistance, and heat resistance. is presented.

For example, in Japanese Patent Publication No. 45-14891, the degree of acetylation is 4.
The membrane material is a mixed cellulose acetate with an average degree of acetylation of 41.5 to 42.7%, which is a mixture of 3.2% and 39.8% cellulose tri- and diacetate, and is made of acetone-1,4-dioxane. A 3.5% NaCl aqueous solution was cast at 1500 psi (approximately 105
kg/d) to achieve a salt rejection rate of 98.7-99.6%.
, water permeability rate 11.9~6.8 gfd (approximately 0.48~0
．． This paper presents a method for obtaining a semipermeable membrane for reverse osmosis that exhibits a separation performance of 28 m 7 days).

However, although this method has a high salt rejection rate, the water permeation rate is low.
A semipermeable membrane with sufficiently satisfactory separation performance has not been obtained.

A method for producing a semipermeable membrane using cellulose acetate as a membrane material, which has a higher average degree of acetylation than cellulose diacetate, which is made by mixing cellulose acetates with different degrees of acetylation, is disclosed in Japanese Patent Application Laid-Open No. 49/1989.
-17377, the average degree of acetylation is in the relatively low range of 40.9 to 41.4%, and it does not seem to fully exhibit the characteristics of high acetylation. do not have.

JP-A-50-35073 discloses a membrane-forming solution in which a mixture of cellulose acetate with a degree of acetylation of 43.2% and 39.8%, respectively, is used as membrane material, and oxycarboxylic acid and methanol as non-solvents are added as additives. proposed a method of casting a semipermeable membrane for reverse osmosis, but the water permeation rate is still not high enough, and if the average degree of acetylation of the mixed cellulose acetate is 41.8% or more, the rejection rate is low. It has the disadvantage of being extremely poor.

JP-A-48-38350 discloses cellulose triacetate,
JP-A No. 50-35074 discloses that cellulose acetate, a mixture of cellulose triacetate and cellulose diacetate, is used as a membrane material, and a dibasic carboxylic acid monoester and methanol as non-solvents are added to the membrane forming solution. Although methods of casting semipermeable membranes for permeation have been proposed, none of them have been able to obtain a semipermeable membrane with a sufficiently high water permeation rate.

JP-A-50-32080 has an acetylation degree of 43.2.
% of cellulose triacetate as the membrane material and a membrane forming solution containing non-solvent oxalic acid and methanol as additives. The water permeation rate of the membrane cannot be said to be sufficiently high.

The present inventors conducted research for the purpose of improving the drawbacks of cellulose acetate semipermeable membranes, and as a result, the average degree of acetylation was 41.
．． A membrane-forming solution in which cellulose acetate with a high degree of acetylation of 5 or more parts is used as a membrane material, and in addition to a solvent, an ester of a non-solvent oxycarboxylic acid and alcohol and a monohydric or polyhydric alcohol are added as additives. The present inventors have discovered that a semipermeable membrane with excellent separation performance can be obtained by casting a semipermeable membrane from the above, and have accomplished the present invention.

That is, to describe the constitution of the present invention in detail, 5 to 15 parts by weight, preferably 7 to 10 parts by weight, of cellulose acetate having an average degree of acetylation of 41.5% by weight or more is mixed with 60 to 80 parts by weight, preferably 65 to 76 parts by weight. parts by weight of a water-soluble organic solvent, e.g.
Dissolved in known solvents for cellulose triacetate, such as 4-dioxane, acetone-1,4-dioxane, dimethyl sulfoxide, and acetic acid, alone or in a mixture, and as an additive,
Non-solvents such as methyl lactate, ethyl lactate, methyl glycolate, ethyl glycolate, and other esters of oxycarboxylic acids and alcohols having a solubility in water of 5 or more moieties at room temperature, methanol, ethyl alcohol, ethylene glycol, A mixture with monohydric or polyhydric alcohol such as propylene glycol or glycerin at a mixing ratio of 1:4 to 2:
A film-forming solution prepared by adding 5 to 30 parts by weight, preferably 10 to 25 parts by weight, of 1 is prepared on a smooth surface such as a glass plate or a porous support such as a woven fabric in a room temperature atmosphere of 10 to 30°C. to form a film at a relative linear velocity of 0.5 to 40 cm/sec, and left to stand for 0.1 to 3 minutes to evaporate part of the solvent, and then 0 to 30°C, preferably 10 to 20°C. This is a method of manufacturing a semipermeable membrane by immersing the membrane in water for at least 10 minutes to dissolve the remaining solvent and additives into the water.

The advantages of the present invention are as follows: (1) A semipermeable membrane for reverse osmosis with a high water permeation rate can be obtained.

2) By changing the composition of the membrane forming solution, from reverse osmosis to ultrafiltration, the NaCl rejection rate can be increased from 98% to 1.
A wide range of semipermeable membranes with coefficients below 0 can be manufactured.

3) Even if the same membrane-forming solution is used, semipermeable membranes of a wide range of grades can be manufactured by changing the casting speed.

4) Normally, cellulose acetate semipermeable membranes for reverse osmosis require so-called heat treatment by immersing them in hot water after membrane formation in order to obtain the necessary salt rejection rate; however, according to the manufacturing method of the present invention, By controlling the composition of the solution and the conditions during film casting, the salt rejection rate can be arbitrarily controlled, and no heat treatment is required.

Furthermore, the salt rejection rate of the cellulose acetate semipermeable membrane produced by the method of the present invention does not change even when immersed in hot water at 80°C, so it can be used stably even at high temperatures.

EXAMPLES The present invention will be specifically explained below with reference to Examples.

The membrane performance was measured using the measuring device shown in FIG.

That is, a sample solution is supplied from a liquid tank 1 equipped with a heat exchanger 16 and an agitator 17 to a measurement cell 10 by a high-pressure pump 4, and a membrane permeate is sampled from a permeate sampling valve 11.

In addition to the above, this device includes a liquid tank discharge valve 2, a high pressure pump supply valve 3, an accumulator 5, a safety valve 6, a pressure gauge 7,
13, a bypass valve 8, a measurement channel inlet valve 9, a measurement channel outlet valve 12, a pressure regulating valve 14, and a flow meter 15.

Further, the measurement cell 10 is shown in an enlarged view in FIG.

The measurement cell consists of an upper cell body 18 and a lower cell body 19, and a semipermeable membrane 24 and a P paper 2 are placed between the upper part 18 and the lower part 19.
5 and supported by a porous support plate 26, the upper part 18 and the lower part 19 are completely sealed by the supply liquid seal O ring 22 and the permeate seal O1J ring 23, and then installed in the above-mentioned measuring apparatus.

The feed liquid being measured enters through the inlet 20 and exits through the outlet 21.

The liquid that has passed through the membrane exits from the outlet 27.

Example 1 Cellulose triacetate (TAC manufactured by Daicel) with acetylation degree of 43.3wt% and acetylation degree of 39.8wt
% of diacetic acid) v loin (E-398 manufactured by EASTMAN)
-3)5. Average degree of acetylation consisting of lJ 41.6wt
% of cellulose acetate mixed with acetone 20.4g, 1.4%
- A film-forming solution prepared by adding 12 g of ethyl lactate and 18 g of methanol to 102 g of a solution dissolved in 71.4 g of dioxane was spread on a glass plate to a thickness of 0.2 mm at room temperature.
It was cast at a crn speed of 7 seconds, left to stand for 2 minutes to evaporate part of the solvent, and then immersed in water at 20°C and left to stand for about an hour to obtain a semipermeable membrane.

The sample was removed from this semipermeable membrane and the measuring device shown in Figure 1 (
effective membrane area 10.8cIrL), 0.35%N
When aC1 aqueous solution was supplied at a pressure of 40 kg/i,
The water permeation rate was 2.4 m per day, and the salt rejection rate was 90.4.

Examples 2 to 3 and Comparative Examples 1 to 2 Example 1 except that the mixing ratio of cellulose acetate was changed to change the average degree of acetylation in the range of 39.8 wt% to 43.3 wt%. Table 1 shows the results of a similar experiment.

In the membrane forming method of the present invention, a good semipermeable membrane can be obtained by using cellulose acetate having a degree of acetylation of 41.5 or higher as the membrane material.

Examples 4 to 6 and Comparative Examples 3 to 6 Table 2 shows the results of experiments carried out in the same manner as in Example 2, except that various carboxylic acid esters were used instead of ethyl lactate.

Semipermeable membranes with good performance were obtained only from the membrane-forming solution containing the oxycarboxylic acid ester.

Examples 7 to 10 Table 3 shows the results of experiments carried out in the same manner as in Example 2, except that other monohydric or polyhydric alcohols were used instead of methanol.

By changing the type of alcohol, a wide range of semipermeable membranes can be obtained, from reverse osmosis membranes to ultra-E membranes.

Examples 11 to 13 Table 4 shows the results of carrying out the same procedure as in Example 2, except that instead of the casting speed of 5 cfrL/sec in Example 2, various casting speeds were used.

According to the production method of the present invention, semipermeable membranes of different grades can be easily obtained from the same membrane forming solution by changing the casting speed.

Examples 14-16 9 g of cellulose triacetate with a degree of acetylation of 43.3 wt% was dissolved in various acetone-1,4-dioxane mixed solvents shown in Table 5, and ethyl lactate 12y and methanol 13
Table 5 shows the results obtained in the same manner as in Example 1 except that a film forming solution prepared by adding g was used.

Example 17 10 g of cellulose triacetate with a degree of acetylation of 43.3 wt%
The procedure was carried out in the same manner as in Example 1 except that a membrane forming solution prepared by dissolving 11 g of acetone and 54 g of 1,4-dioxane and adding 12 g of ethyl lactate and 13 g of methanol thereto was used. As a result, the water permeation rate was 1. The salt rejection rate was 117 FL/El and 94.0%.

Example 18 9 g of cellulose triacetate with a degree of acetylation of 43.3 wt% was dissolved in 13 g of acetone and 63 I of 1,4-dioxane,
A film-forming solution prepared by adding 7 g of ethyl lactate and 8 g of methanol was formed into a film on a glass plate at a casting speed of 5 cIrt/sec at room temperature, left for 2 minutes to evaporate part of the solvent, and then 0°C. A semipermeable membrane obtained by immersing it in water for about 1 hour was measured under the same conditions as in Example 1, and the water permeation rate was 1.91 m.
On the 7th, the salt rejection rate was 89cm.

Examples 19-20 The semipermeable membranes prepared according to Examples 2 and 8 were immersed in hot water at 80°C for 15 minutes, and then measured under the same conditions as Example 1, giving the results shown in Table 6.

There is no significant change in performance due to hot water immersion.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a membrane performance measuring device, and FIG. 2 is a schematic diagram of a measurement cell. 1...Liquid tank, 2...Liquid tank discharge valve,
3... High pressure pump supply valve, 4...
High pressure pump, 5... Accumulator, 6...
...Safety valve, 7...Pressure gauge, 8...
Bypass valve, 9...Measurement channel inlet valve,
10...Measurement cell, 11...Permeate sampling valve, 12...Measurement channel outlet valve, 13...Pressure gauge, 14... ... Pressure regulating valve, 15 ... Flow meter, 16 ... Heat exchanger, 17 ... Stirrer, 18 ... Upper part of cell body, 19 ... ...Bottom part of cell body, 20...
・・Supply liquid inlet, 21 ・・・Supply liquid outlet, 22・
...Feed liquid seal 0 ring, 23 ... Permeate seal 01J ring, 24 ... Semipermeable membrane, 25
...P paper, 26 ... Porous support plate, 2
7...Permeate outlet.

Claims (1)

[Claims] 1. Dissolve 5 to 15 parts by weight of cellulose acetate with an average degree of acetylation of 41.5 parts or more in 60 to 80 parts by weight of a water-soluble organic solvent, and dissolve 5 to 15 parts by weight of cellulose acetate having an average degree of acetylation of 41.5 parts or more in water, and dissolve 5 to 15 parts by weight of cellulose acetate having an average degree of acetylation of 41.5 parts or more in water, and dissolve 5 to 15 parts by weight of cellulose acetate, which has an average degree of acetylation of 41.5 parts or more, in 60 to 80 parts by weight of a water-soluble organic solvent. A mixture of an ester of an oxycarboxylic acid and an alcohol and a monohydric or polyhydric alcohol at a mixing ratio of 1:4 to
A method for producing a cellulose acetate semipermeable membrane, which comprises casting a membrane forming solution in a room temperature atmosphere of 10 to 30°C from a membrane forming solution containing 5 to 30 parts by weight of 2:1.