JPH0426887B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a reverse osmosis membrane made of a cellulose derivative with excellent liquid separation performance. [Prior art] Cellulose-based reverse osmosis membranes have been used not only for desalination of brine and seawater but also for ultrapure water since the asymmetric membrane was invented by Robb et al. in 1961 and put into practical use by Manjikian et al. in 1966. Its uses are increasingly expanding to include production of water, non-aqueous treatment, and recovery of valuable materials. However, in order for reverse osmosis membrane technology to become more widespread, it is important to improve the salt rejection rate and further increase the amount of permeated water in order to increase the economic efficiency of this technology, and it is desired. Cellulose-based reverse osmosis membranes are usually made from a solution of cellulose acetate as a raw material and a cellulose acetate solvent and additives, but in order to improve performance, it is important to select the solvent and especially without reducing the salt rejection rate. The selection of microporous forming agents, that is, additives that improve the amount of permeated water, has been intensively studied. Inorganic additives such as magnesium perchlorate and organic additives are known as additives, and their function is to allow water to pass through without affecting the separation layer that selectively excludes salts. It is thought to increase the number of pores and improve water permeability.
Furthermore, compared to inorganic additives, organic additives have the advantage that they have a simpler composition, can be formed into films near room temperature, and can provide higher performance. Such cellulose-based reverse osmosis membranes, particularly cellulose acetate-based reverse osmosis membranes, have excellent practical performance such as oxidation resistance, especially chlorine resistance, and are superior to cellulose-based reverse osmosis membranes and reverse osmosis membranes that have been improved in many ways to date. Membrane forming solutions for permeable membranes have been proposed. As an example of such a membrane forming solution, Japanese Patent Publication No. 49-27269 discloses a method in which an organic amine salt is added as a microporous forming agent to a membrane forming solution using cellulose acetate as a membrane material. Furthermore, in Japanese Patent Publication No. 59-40482, using cellulose acetate with an average degree of acetylation of 41.5% by weight or more,
A film-forming solution is proposed in which a mixture of an oxycarboxylic acid and an alcohol having a solubility in water of 5% by weight or more at room temperature is added as an additive. [Problems to be Solved by the Invention] However, with any of the techniques, it is currently difficult to obtain a reverse osmosis membrane with a predetermined rejection rate and sufficiently high water permeability. The present invention attempts to overcome the drawbacks of the prior art, and aims to provide a method for producing a reverse osmosis membrane that has a sufficient salt rejection rate and improved water permeability. [Means for Solving the Invention] The present invention has the following configuration to achieve the above object. That is, in the production of a reverse osmosis membrane made of a cellulose derivative, when a solution containing a cellulose derivative, a solvent, and a polyhydric carboxylic acid as an additive is used as a membrane-forming solution, the membrane-forming solution further contains a polyhydric carboxylic acid. The present invention relates to a method for manufacturing a reverse osmosis membrane characterized by containing a surfactant. A reverse osmosis membrane made of a cellulose derivative as used in the present invention refers to a membrane formed using cellulose acetate, cellulose acetobutyrate, methyl cellulose, ethyl cellulose, or the like as a main polymer component. Among these, cellulose acetate is particularly preferred. Cellulose acetate herein refers to cellulose diacetate, cellulose triacetate, acetate with an intermediate degree of substitution, or a blend of cellulose diacetate. Practical acetyl group concentration in cellulose acetate is usually 39.8 to 43.2%. Preferred solvents include dioxane, acetone, tetrahydrofuran, dimethylformamide, formamide, diacetone alcohol, and the like, which are water-soluble and are good solvents for cellulose derivatives. In addition, ketones such as methyl oxide, methyl ethyl ketone, and methyl isobutyl ketone, which are poorly water-soluble but are good solvents for cellulose derivatives; fatty acid esters such as methyl acetate and ethyl acetate;
Halogenated hydrocarbons such as methylene chloride and ethylene dichloride, nitroethane, and the like can be used in combination with the above-mentioned water-soluble solvent. As additives, it is possible to use inorganic and/or organic additives that are commonly used in the production of cellulose acetate reverse osmosis membranes.
Preferably, polyhydric carboxylic acids can be used, particularly preferably maleic acid and/or butanetetracarboxylic acid. These additives result in higher rejection rates and higher permeability when membranes are formed from solutions containing cellulose acetate in a single solvent or in a mixture of solvents. It is sometimes called a swelling agent because it is thought to increase the number of pores that contribute to water permeation. The feature of the present invention is that the following surfactants are added to the film-forming stock solution together with the above additives, and as a result, the film-forming solution is cast and solidified with the surfactant included. It is in. As surfactants, nonionic surfactants,
Amphoteric surfactants and anionic surfactants are preferably used. Specific examples include the following (A), (B), (C), (D), (E), and (F).
and (G) can be exemplified. (A) R-O(-CH ₂ CH ₂ O) _o --H (However, in the above formula, R is an aliphatic hydrocarbon having 12 to 18 carbon atoms, and n is an integer of 4 to 30.) (However, in the above formula, R is an aliphatic hydrocarbon having 8 to 9 carbon atoms, and n is an integer of 4 to 40.) (C) R-COO(-CH ₂ CH ₂ O) _o --H (However, in the above formula, R is an aliphatic hydrocarbon having 12 to 18 carbon atoms, and n is an integer of 4 to 40.) (However, in the above formula, a, b, and c are integers of 2 to 20 and have an average molecular weight of 2000 to 3000.) (However, R in the above formula is an aliphatic hydrocarbon having 12 to 18 carbon atoms.) (However, R in the above formula is an aliphatic hydrocarbon having 11 to 18 carbon atoms.) (However, M in the above formula is an inorganic metal group such as sodium.) The amount of these surfactants added is preferably 0.05 to 1.0 parts by weight, based on 100 parts by weight of the total amount of the film forming solution. , used in a range of 0.1 to 0.3 parts by weight.
If it exceeds 1.0 part by weight, the amount remaining in the cast film immediately before solidification increases, making it easy to form voids that become defects. If the amount is less than 0.05 part by weight, the effect of improving membrane performance due to addition is small. Conventionally known inorganic or organic additives have strong hydrophilic properties and allow water in the coagulating liquid to diffuse into the membrane during coagulation due to the effect of osmotic pressure, effectively increasing pores for water permeation. It is thought that it has the function of On the other hand, if we estimate the effect of adding the surfactant of the present invention, when the membrane forming solution comes into contact with the coagulation liquid and undergoes phase separation, it forms a finer phase separation structure, which is advantageous for water permeation. It is thought that the pores are increased, and the mechanism by which this additive exerts its effect is different from that of conventionally known additives, and therefore the synergistic effect with other conditions is also thought to be different. [Example] The invention will be explained below using Examples and Comparative Examples, but the invention is not limited thereto. The performance of reverse osmosis membranes is expressed in terms of salt rejection rate (Rej) and water permeation rate (Flux), but it is not possible to directly compare the performance of membranes with different values. However, in general, the performance of reverse osmosis membranes is
If they are constant, the salt rejection rate and water permeation rate will change contradictoryly depending on the manufacturing conditions, such as changes in heat treatment temperature.
It is known that the value of A ³ /B, which will be explained next, is approximately constant. A is the water permeability coefficient (g/ ^cm2・
sec・atm), B is the salt permeability coefficient (cm/sec), and the higher the salt rejection rate and the higher the water permeability, the larger the value of A ³ /B. Therefore, by using this index A ³ /B, the membrane performance can be compared. A and B are salt rejection rates (Rej) under actual operating conditions
It is calculated using the following formula using the amount of water permeation (Flux). A=Flux/(△p-δ×△π ⁾ ×119.6× ^10-5 B=(100-Rej)/Rej×Flux×115.7×10-5 △p is the actual operating pressure (Kg/ ^cm2 ) be. δ is a quantity called the reflection coefficient, and in the case of reverse osmosis membrane, it is 1
You can do it by setting it aside. Membrane performance is 30% saline solution containing 1500ppm salt.
The measurement was carried out by applying a pressure of Kg/cm ² and flowing it onto the membrane surface at a speed of 10 m/min. Example 1 41 parts by weight of dioxane and 27 parts by weight of acetone were added to 20 parts by weight of a mixture of threose triacetate with a degree of acetylation of 43.2% and cellulose diacetate with a degree of acetylation of 39.8% in a weight ratio of 2:3. In addition, 0.2 parts by weight of polyoxyethylene oleyl ether [C ₁₈ H ₃₅ O (CH ₂ CH ₂ O) ₃₀ H], which is a nonionic surfactant, and 2.8 parts by weight of kaleic acid were added to the dissolved liquid with 9 parts by weight of methanol. A membrane-forming solution was obtained by adding the solution dissolved in the solution. For film formation, the above film forming solution was cast onto a glass plate to a thickness of 0.2 mm using an applicator in an atmosphere of 20°C.
After drying for about 50 seconds, the film was immersed together with the glass plate in cold water at 10°C for about 20 minutes, and the film was peeled off from the glass plate. The obtained membrane was heat-treated in a hot water solution (80°C) for 5 minutes. The membrane performance of the membrane thus obtained is shown in Table 1.
This is shown in the section of Example 1. Comparative Example 1 A solution obtained by dissolving 3.0 parts by weight of maleic acid in 9 parts by weight of methanol was added to a solution in which the polymer, dioxane, and acetone were dissolved under the same conditions as in Example 1 to obtain a film forming solution. A film was formed under the same conditions as in Example 1, and the obtained film was heat-treated. The membrane performance of this membrane is as shown in the section of Comparative Example 1 in Table 1. At the same exclusion rate, the water permeability was reduced by 20% compared to Example 1. Example 2 Instead of using polyoxyethylene oleyl ether in Example 1, polyoxyethylene noniphenyl ether, which is a nonionic surfactant, was used. A film-forming solution was obtained under the same conditions as above, and a film was formed under the same conditions, and the resulting film was heat-treated. The membrane performance of this membrane is as shown in the section of Example 2 in Table 1. At the same exclusion rate, the water permeability is improved by 17% compared to Comparative Example 1. Example 3 10 parts by weight of cellulose triacetate with a degree of acetylation of 43.2%, 20 parts by weight of acetone, and 44 parts by weight of dioxane
Parts by weight of polyoxyethylene monostearate [C ₁₇ H ₃₅ COO
A solution obtained by dissolving 0.15 parts by weight of (CH ₂ CH ₂ O) ₄ H] and 3.85 parts by weight of butanetetracarboxylic acid in 10 parts of methanol was added to obtain a membrane forming solution. To form a film, use an applicator to cast the film-forming solution onto a glass plate to a thickness of 0.2 mm in an atmosphere of 20°C. After drying for about 10 minutes, the film is immersed together with the glass plate in water at 30°C for about 1 hour. This was done by peeling it off. The obtained membrane was placed in hot water (80
℃) for 5 minutes. The membrane performance of the membrane thus obtained was as shown in Example 3 in Table 1. Comparative Example 2 In Example 3, a solution obtained by dissolving 4 parts by weight of butanetetracarboxylic acid in 10 parts by weight of methanol was added to a solution in which the polymer, acetone, and dioxane were dissolved under the same conditions to obtain a membrane forming solution. A film was formed under the same conditions as in Example 3, and the resulting film was heat-treated. The membrane performance of the Uko membrane is as shown in the section of Comparative Example 2 in Table 1. At the same exclusion rate, the water permeability was reduced by 9% compared to Example 3. Example 4 41 parts by weight of dioxane and 25 parts by weight of acetone were added to 20 parts by weight of a mixture of cellulose triacetate with a degree of acetylation of 43.2% and cellulose diacetate with a degree of acetylation of 39.8% in a weight ratio of 2:3. Oxyethylene oxypropylene block polymer, a nonionic surfactant, is added to the dissolved solution. Average molecular weight 2220, ethylene oxide 10% by weight
Contains] 0.25 parts by weight, butanetetracarboxylic acid 3.75
A solution obtained by dissolving part by weight in 10 parts by weight of methanol was added to obtain a membrane forming solution. To form a film, the film-forming solution is cast on a glass plate to a thickness of 0.2 mm using an applicator in an atmosphere of 20°C, dried for about 60 seconds, and then immersed together with the glass plate in cold water at 10°C for about 20 minutes. This was done by peeling the film from the plate. The obtained membrane was heat treated in hot water (80°C) for 5 minutes. The membrane performance thus obtained is shown in the Example 3 section of Table 1. Comparative Example 3 A solution prepared by dissolving 4 parts by weight of butanetetracarboxylic acid in 10 parts by weight of methanol was added to a solution in which the polymer, dioxane, and acetone were dissolved under the same conditions as in Example 4 to obtain a membrane forming solution. A film was formed under the same conditions as in Example 4, and the resulting film was heat-treated. The membrane performance of this membrane is as shown in the section of Comparative Example 3 in Table 1, and the permeability is reduced by 14% compared to Example 4 at the same rejection rate. Example 5 In Example 4, lauryl betaine, an amphoteric surfactant, was used instead of the oxyethylene oxypropylene block polymer. A film-forming solution was obtained using the same conditions except for the same conditions, and a film was formed under the same conditions, and the obtained film was heat-treated. The membrane performance during this period is as shown in the section of Example 5 in Table 1. At the same exclusion rate, the water permeability was improved by 18% compared to Comparative Example 3. Example 6 In Example 5, alkylimidazolinium betaine, an amphoteric surfactant, was used instead of lauryl betaine. A film-forming solution was obtained using the same conditions except for the same conditions, and a film was formed under the same conditions, and the obtained film was heat-treated. The membrane performance during this period is as shown in the section of Example 6 in Table 1. At the same rejection rate, the water permeability is improved by 11% compared to Comparative Example 3. Example 7 In Example 6, sulfosuccinate, an anionic surfactant, was used instead of alkylimidazolinium betaine.

A film-forming solution was obtained using the following formula with the other conditions being the same, a film was formed under the same conditions, and the resulting film was heat-treated. The membrane performance of this membrane is as shown in the section of Example 7 in Table 1. At the same exclusion rate, the water permeability is improved by 5% compared to Comparative Example 3.

[Table] [Effects of the Invention] The membrane of the present invention has significantly improved water permeability of 5 to 19% compared to the conventional technology. Further, the present invention is effective by using only a small amount of a commercially available surfactant, and does not particularly change the manufacturing process. Therefore, a high quality film can be manufactured without increasing manufacturing costs.

Claims (1)

[Claims] 1. In the production of a reverse osmosis membrane made of a cellulose derivative, when a solution containing a cellulose derivative, a solvent, and a polyhydric carboxylic acid as an additive is used as a membrane forming solution, the membrane forming solution further contains A method for producing a reverse osmosis membrane, characterized by containing a surfactant. 2. The method for manufacturing a reverse osmosis membrane according to claim 1, wherein the surfactant is contained in a proportion of 0.05 to 1.0 parts by weight based on 100 parts by weight of the total amount of the membrane forming solution. 3. The method for producing a reverse osmosis membrane according to claim 1, wherein the surfactant is a nonionic surfactant. 4. The method for producing a reverse osmosis membrane according to claim 1, wherein the surfactant is an amphoteric surfactant. 5. The method for producing a reverse osmosis membrane according to claim 1, wherein the surfactant is an anionic surfactant. 6. The method for producing a reverse osmosis membrane according to claim 1, wherein the cellulose derivative is cellulose acetate. 7 The surfactant has the following formula (A), (B), (C), (D), (E),
2. The method for producing a reverse osmosis membrane according to claim 1, wherein at least one surfactant is selected from the surfactants having the structural formulas represented by (F) and (G). (A) R-O-( _CH2CH2O ) _-oH (However, in the above formula, R is an aliphatic hydrocarbon having 12 to 18 carbon atoms, and n is an integer of 4 _to 30.) (However, in the above formula, R is an aliphatic hydrocarbon having 8 to 9 carbon atoms, and n is an integer of 4 to 40.) (C) R-COO-(CH ₂ CH ₂ O)- _o H ( However, in the above formula, R is an aliphatic hydrocarbon having 12 to 18 carbon atoms, and n is an integer of 4 to 40.) (However, in the above formula, a, b, and c are integers of 2 to 20 and have an average molecular weight of 2000 to 3000.) (However, R in the above formula is an aliphatic hydrocarbon having 12 to 18 carbon atoms.) (However, R in the above formula is an aliphatic hydrocarbon having 11 to 18 carbon atoms.) (However, M in the above formula is an inorganic metal group such as sodium.)