CA1263572A - Sulfonated polysulfone composite semipermeable membranes and process for producing the same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A sulfonated polysulfone composite semipermeable membrane comprising a support membrane having laminated thereon in unity a semipermeable membrane composed of a sulfonated polysulfone formed by sulfonating a polysulfone composed of a recurring unit shown by formula (A) (A)

Description

~L2~35~

SULFONATED POLYSULFONE COMPOSITE SEMIPERMEABLE MEMBRANES
AND PROCESS FOR PRODUCING THE SAME

FIELD OF THE INVENTION

This invention relates to a composite semipermeable membrane composed of a sulfonated polysulfone and a process for producing the same. More particularly, the invention relates to a composite semipermeab]e membrane comprising a semipermeable membrane composed of a sulfonated polysulfone formed on a ultrafiltration membrane as a support and a process for producing the same.
BACKGROUND OF THE INVENTION
A linear polysulfone copolymer having a recurring unit shown by formula ~A) ~ O ~ ~ ~ (A) wherein n is an integer of 1 or more, and a recurring unit shown by rormula (B) -O ~ ~ ~ S2 ~ (B) t ~, ii3~7%

is already described in Japanese Patent Publication ~o.
21458/71 and the sulfonated product of the above-described copolymer is already described in Japanese Patent .~pplica-tion (OPI) ~o. 48222/80; the term "OPI" indicates an unexam-ined published patent application open to public inspection.
That is, it is described in the above-described published specification that by sulfonating the above-described poly-sulfone copolymer by dissolved it in concentrated sulfuric acid, a hydrophilic sulfonated polysul~one wherein the recurring units shown by formula (A~ are substantially wholly sulfonated but the recurring units shown by formula (B) wholly remain as a substantially un-sulfonated state.
Also, a sulfonated product o a polysulfone having a recurring unit shown by formula (C) ~ H { ~ (C) is described in U.S. Patent 3,709,841. Furthermore, there is described a process of producing a composite semipermea-ble membrane for reverse osmosis composed of a th~n membrane having semipermeability laminated on a ultrafiltration mem-brane by coating a solution of the above-described sul-fonated polysulfone on a dense layer on the surface of an 3~

anisotropic ultrafiltration membrane and evaporating oEf the solvent in Japanese Patent A~plication (OPI) Nos. 99973/75 and 146379/76, corresponding to Great Britain published applications GB1473857-A and GB1495887-A respectively, available to the public prior to June 12, 1985. Similarly, there is described a process of obtaining a composite semipermeable membrane by previously filling the fine pores of an anisotropic ultrafiltration membrane having the recurring unit shown by above-described formula (C) with an ~ aquPous solution of làctic acid, coating the ultrafiltration membrane with a solution oE a sulfonated product of a polysulfone having the recurring unit shown by above-described formula (C), and then evaporating off the solvent in Office of Water Rese~rch _and Technology- Department of the Interiorj Report No. 2001-20.
SUMMARY OF TBE INVENTION
As a resul~ of various investigations, the inventors have discovered that a composite semipermeable membrane can be obtained by sulfonating a polysulfone having the recurring unit shown by abo~e-described formula ~A) and forming a thin film-form semipermeable membrane of the sulfonated polysulfone on a support membeane an-1 that the composite semipermeable membrane thus ~ormed is particularly useful as a reverse osmosis membrane or an ultrafiltration membrane having excellent chlorine eesistance and pH resistance.
The inventors have further discovered that a reverse osmosis membrane or a composite semipermeable membrane having very excellent properties and per~ormance as compared to conventional composite semipermeable membranes 2S well as having, in a preferred case, the rejection of a very high sodium chloride in a treatment of an aqueous sodium chloride solution and also excellent pH resistance and heat resis-tance can be obtained by forming a film of a sulfonated polysulfone copolymer prepared by sulfonating a linear polysulfone copolymer having the recurring unit shown by above-described formula (A) and the recurring unit shown by above-described formula (B) on a ultrafiltration membrane as a support membrane.
Moreover, the inventors have discovered that in the case of producing a composite semipermeable membrane by forming a thin film-form semipermeable membrane composed of the above-described ~ulfonated polysulfone or sulfonated polysulfone copolymer on a ultrafiltration membrane as a support membrane, the properties of ~he composite semiperme-able membrane thus obtained, in particular, the rejection of a solute in the membrane-forming treatment of the membrane-forming solution and the flux can be controlled in wide ranges by incorporating a certain water-soluble organic or inorganic compound in the membrane-forming solution contain-ing the above-described polysulfone or polysulfone copoly-mer.
The invention has been attained based on these dis-. .

7~

coveries.
Thus, 2ccording to a .irst embodiment of this inven-tion, there is provided a sulfonated polysulfone composite semipermea~le membrane comprising a support membrane having laminated thereon in unity a semipermeable membrane composed of a sulfonated polysulfone formed by sulfonating a poly-sulfone comprising a recurring unit represented by formula (A) ~ ~ 2 { O } ( ) wherein n is an integer of 1 or more.
According to a second embodiment of this invention, there is provided a sulfonated polysulfone CompQSite semi-permeable membrane comprising a support membrane having laminated thereon in unity a semipermeable membrane com-prising a recurring unit shown by above-described formula (A) and a recurring unit shown by formula (B) ~ ~ S2 ~ ~ ~ S2 { (B) ~.~63~

According to a third embodiment of this invention, there is provided a process for producing a sulfonated polysul.one composlte semiper~eable membrane which comprises coating a support membrane, preferably dried, with a mem-brane-forming solution ~ontaining a sulfonated polysulfone which is a polymer prepared by sulfonating a polysulfone comprising a recurring unit shown by formula (A) ~ 2 ~ ~ } (A) ~{~

wherein n is an integer of 1 or more, and, preferably, has a logarithmic viscosity of 0.2 to 10 measured at 30C about the solution of 0.5 g of the polymer dissolved in 100 ml of N-methyl-2-pyrrolidone and an ion exchange capacity of 0.2 to 2.3 milli-equivalent/g, an alkylene glycol alkyl ether which may contain a small amount of a non-protonic polar organic solvent, and a water-soluble and low volatile com-pound as an additive, and then evaporating off the solvent from the membrane-forming solution thus coated.
According to a fourth embodiment of this invention, there is provided a process for producing a sulfonated polysulfone composite semipermeable membrane which comprises coating a support membrane, preferably dried, with a memb-rane-forming solution containing a sulfonated polysulfone copolymer which is a polymer (hereinafter, is referred to as a sulfonated polysulfone copolymer) prepared by sulfonating a linear polysulfone copolymer comprising a recurring unit shown by formula (A) ~ S2 ~ ~ (A) ~ ~ n wherein n is an integer of 1 or more, and a recurring unit shown by formula (B) -O ~ S2 ~ ~ S02_ ~0 ~ (B) and, preferably, has a logarithmic viscosity of 0.2 to lO
measured at 30C about the solution of 0.5 g of the polymer in lOO ml of ~-methyl-2-pyrrolidone and an ion exchange capacity of 0.2 to 2.3 milli-equivalent/g, an alkylene glycol alkyl ether which may contain a small amount of a non-protonic polar organic solvent, and a water-soluble and ~Z~

low-volatile compound as an additive, and then evaporating o~f the solvent from the membrane-forming solution thus coated.
DESCRIl'TION OF THE PPEFERRED E~BODIM~IT
5Then, Lhe invention is explained in de_ail.
The sulfonated polysulfone for use in the process (the above-described third embodiment) of this invention is a hydrophilic polymer obtained by sulfonating the polysul-fone having the recurring unit shown by above-described lQformula (A). The sulfonated polysulfone is obtained by adding the polysulfone having the recurring unit shown by aforesaid formula (A) in concentrated sulfuric acid of 97 ~o 98% in concentration and mildly stirring the mixture for several hours at room ~k:emperature. After the reaction is 15over, the viscous reaction mixture thus obtained is added to water and then the sulfonated polysulfone can be easily separated by filtration.
In this invention, it is necessary that the sul-fonated polysulfone has a logarithmic viscosity of 0.2 to 2010, preferably 0.5 to 8 measured at 30C about the solution of 0.5 g of the polymer dissolved in 100 ml of ~-methyl-2-pyrrolidone. If the logarithmic viscosity is less than 0.2, the molecular weight of the sulfonated polysulfone is too small to form a uniform thin film having no defects such as 25pinholes, etc. Also, if the logarithmic viscosity is larger than 10, ~he viscosity of the membrane-forming solution becomes too high to form a film.
Furthermore, it is necessary that the above-de-scribed sulfonated polysulfone has an ion exchange capacity of 0.2 to 2.3, preferably 0.3 to 2.0 milli-equivalent per gram of the dry polymer.
When in a polysulfone composed of the recurring unit only shown by formula (A), all the aromatic rings each disposed between the two ether bonds are monosulfonated, the theoretical ion exchange capacity of such a sulfonated poly-sulfone is 2.4 milli-equivalent/g but in the sulfonated polysulone for use in this invention, the aromatic rings are partially sulfonated.
If the ion e:~change capacity is over 2.3 milli-equivalent/g, the sulfonated polysulfone has water solubili-ty and hence is unsuitable for making a semipermeable membrane ~hich is frequently used for treating liquids containing aqueous media. On the other hand, if the ion exchange capacity is less than 0.2 milli-equivalent/g, it sometimes happens that the effect of this invention is not obtained.
The sulfonated polysulfone ~opolymer for use in another process (above described fourth embodiment) of this invention can be easily obtained by dissolving a linear polysulfone copolymer composed of the recurriny unit sho~n by above-described formula tA) and the recurring unit shown by above-described formula (B) in concentrated sulfuric acid and ~ildly stirring the mixture for sever~l hours at room temperature. In this case, .he aromatic rings each disposed between the ether bonds in tne recurring unit shown by for-mula (A) are substantially wholly monosulfonated but since the recurring units shown by formula (B) substantially wholly remain in non-sulfonated state, the extent o the sulfonation of the linear polysulfone can be easily control-led by changing the ratio of the recurring unit of formula(A) to the recurring unit of formula (B) in the copolymer.
In this invention, it is preferred that the linear polysulfone copolymer which is a precursor for the sul-fonated polysulfone copolymer is composed of more than 10 mole% the recurring unit of formula (A) and less than 90 mole% the recurring unit of formula (B).
Also, in this invention, it is also necessary that the sulfonated polysulfone copolymer has the logarithmic viscosity of 0.2 to 10, preferably 0.5 to 8 (measured by the same manner as described about the above-described sul-fonated polysulfone) as the case of the above-described sulfonated polysulfone. If the logarithmic viscosity is less than 0.2, the molecular weight of the sulfonated poly-sulfone copolymer is too small to form a uniform thin film having no defect such as pinholes. On the other hand, if ~.~Eii~i~2 the logarithmic viscosity is larger than 10, the viscosity ol the membrane-forming solution is too high ~o form a film.
Also, it is necessary that the aforesaid sulfonated polysulfone copolymer has an ion exchange capacity of 0.2 to 52.3, preferably 0.3 to 2.0 milli-equivalent per gram of the dry polymer. If the ion exchange capacity of the sulfonated polysulfone capacity is over 2.3 milli-equivalent/g, the copolymer becomes water-soluble, which is unsuitable for making a semipermeable membrane which is frequently used for 10treating aqueous liquids. Also, if the ion exchange capaci-ty is less than 0.2 milli-equivalent/g, it sometimes happens that the effect of this invention is not obtained.
The sulfonic acid group contained in the above-de-scribed sulfonated pc,lysulfone or sulfonated polysulfone 15copolymer for use in the process of this invention is shown by formula -S03M, wherein M represen-s a hydrogen atom, an alkali metal, or a tetraalkyl ammonium group.
For example, when a polysulfone composed of the recurring unit shown by formula (A) is sulfonated and then 20the sulfonated polysulfone is washed with water and dried, a sulfonated polysulfone having a free sulfonic acid group can be obtained. Also, when the sulfonated polysulfone is treated by an aqueous solution, a methanol solution, an ethanol solution, etc., of an alkali metal hydroxide or an 25alkali metal alcoholate, the sulfonic acid group can be converted into an alkali metal salt. This is also applica-ble to the case of the sulfonated polysulfone copolymer.
Exam les of the above-described alXali metal hydroxide are sodi~lm hydroxide, potassium hydroxide, lithium hydroxide, etc., and examples of the alkali metal alcoholate are sodium methylate, potassium methylate, potassium ethylate, etc.
Also, when the sulfonated polysulfone or sulfinated polysulfone copolymer is similarly treated with a solution of a tetraalkylammonium such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, etc., the sulfonic group of the polymer can be converted into the corresponding tetraalkylammonium salt. The above sulfonic acid group occupies a large part of the total ion-exchange groups, preferably at least 70% and most preferably at least 90%.
The remaining ion-exchange group can be an ion-exchange group other than the sulfonic acid group, such as carboxylic acid group, so long as the sulfonic acid group content per the total ion-exchange group is fallen within the above-described range.
The composite semipermeable membrane of this inven-tion can be obtained by dissolving the above-described sulfonated polysulfone or sulfonated polysulfone copolymer and a water-soluble and low-volatile compound as an additive in an alkylene glycol alkyl ether which may contain a small amount of a non~protonic polar organic solvent to form a membrane-forming solution, coating a support membrane, preferably, dried with the membrane-forming solution, and then evaporating off the solvent from the coated membrane-~orming solution.
As the organic solvent for preparing the membrane-forming solution, an alkylene glycol alkyl ether having an al~ylene group of 2 to 4 carbon atoms and an alkyl group of l to 4 carbon atoms is particularly preferably used in this invention. This is because the solvent has an excellent dissolubility for both the sulfonated polysulfone and the sulfonated polysulfone copolymer for use in this invention and shows a high volatility as well as does not dissolve a polysulfone series ultrafiltration membrane which can be suitably used as a support membrane in this invention.
Specific examples of such an alkylene glycol alkyl ether are alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, methylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol mono-ethyl ether, etc., and alkylene glycol dialkyl ethers suchas ethylene glycol dimethyl ether, ethylene ~lycol methyl-ethyl ether, ethylene glycol diethyl ether, etc. In particular, ethylene glycol monomethyl ether is preferred in this invention since the solvent is excellent in dissolving power for the sulonated polysulfone and the sulfonated æ
i7 polysulfone copoly~er and shows a hlgh volatility.
According to the nature of the sulfonated polysul-fone or the sulfonated polysulfone copolymer .or use in this invention, it sometimes happens that such a polymer is reluctant to be dissolved in the above-described alkylene glycol alkyl ether or is simplified swelled by the solvent but it has now been discovered that such a polymer is dis-solved well in the aforesaid alkylene glycol alkyl ether when a small amount of a non-protonic polar organic solvent is added to the solvent. Preferred examples of the non-protonic polar organic solvent are dimethyl sulfoxide, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethyl-acetamide, etc. It is preferred that the proportion of the non-protonic polar organic solvent in such a mixed solvent is less than 5 parts by weight, particularly less than 3 parts by weight per 100 parts by weight of the aforesaid alkylene glycol alkyl ether. If the proportion of the non-protonic polar organic solvent is larger than 5 parts by weight per 100 parts by weight of the aforesaid alkylene glycol alkyl ether, when the membrane-forming solution is coated on a dry polysulfone ultrafiltration membrane as a support membrane, the ultrafiltration membrane is dissolved in the solution or swelled by the solution, whereby a composite semipermeable membrane having good performance cannot be obtained.

~:63~2 The use of the mixed solvent of the alkylene glycol alkyl ether and a small amount of the foregoing non-protonic polar organic solvent as a solvent for the membrane-forming solution is advantageous since after coating a support me~brane with the membrane-Iormins solution, substantially all the solvents can be removed at room temperature or by slight heating in the step of evaporating off the solvent from the coated membrane-forming solution as will be de-scribed hereinafter and also a uniform thin film having no defects can be formed.
The concentration of ~he sulfonated polysulone or the sulfonated polysulfone copolymer in the membrane-forming solution depends upon the thickness of the semipermeable membrane composed of the copolymer in the composite semiper-meable membrane thus obtained but is usually in the range of0.05 to 10~ by weight, preferably 0.1 to 5% by weight.
The membrane-forming solution in this invention con-tains specific additives. As one of these additives, at least one kind of organic solvent selected from polyhydric alcohols, polyalkylene glycols, carboxylic acids or the salts thereof, and hydroxycarboxylic acids or the salts thereof can be used. It is necessary that the organic com pound as the additive is soluble in water and low volatile as well as is soluble in the membrane-forming solution.
Thus, polyhydric alcohols having 2 to 5 carbon atoms, low ~.~ii3~;72 molecular weight polyalkylene glycols, carboxylic acids or the salts thereof, and hydroxycarboxylic acids or the salts thereof can be preferably used. Speci-ic examples of ~hese organic additives are polyhydric alcohols such as ethylene glycol, propylene glycol, glycerol, l,a-butanediol, etc.;
polyalkylene glycols such as die~hylene glycol, triethylene glycol, dipropylene glycol, etc.; carboxylic acids such as citric acid, oxalic acid, etc.; hydroxycarboxylic acids such as lactic acid, hydroxybutyric acid, etc.; and the salts of the carboxylic acids or the hydroxycarboxylic acids, such as, the sodium salts, potassium salts, etc.
Also, an inorganic salt which is soluble in water and soluble in the membrane-forming solution can be used as the additive in this i~lvention. Examples of the inorganic salt are lithium chloride, lithium nitrate, magnesium perchlorate, etc.
The concentration of these additives in the mem-brane-forming solution is usually in the range of 0.1 to 80 by weight.
The function of the additives in the formation of the composite semipermeable membrane has not yet been clari-fied but it is considered the additive relates to the size of fine pores of the semi~ermeable membrane formed by the sulfonated polysulfone or the sulfonated polysulfone copoly-mer and also when the membrane-forming solution is coated on ~7~

an ultrafiltration membrane as a support membrane, the solvent and the additive in the membrane-~or~ing solution modiry the surace of the ultrafiltration membrane. Thus, by suitably selecting the Xind and the amount of the additive, the performance of the composite semipermeable membrane, in particular, the rejection of the solute and the flux can be controlled in wide ranges in this invention.
In the process of this invention, the membrane-forming solution thus prepared is then coated on a dried ultrafiltration membrane as a support membrane. The dry ultrafiltration membrane can be obtained by heating a wet ultrafiltration membrane prepared by a wet method.
As the materials for the support membranes in this invention, polymers having durability can be used without particular restriction but polysulfone series ultrafiltra-tion membrane are particularly preferred. Specifically, there are ultrafiltration membranes composed of the polysul-fone having the recurring units shown by aforesaid formula (B) or (C).
Particularly, the above-described support membrane showing a pure water flux of higher than 3 m3/m2.day, preferably higher than 5 m3/m2.day under a pressure of 3.5 kg/cm can be preferably used.
In the process of this invention, an alkylene glycol alkyl ether or a mixture of an alkylene glycol alkyl ether ~63572 and a small amount of ~he aforesaid non-protonic polar organic solvQnt is used ~s the solvent ror the membrane-forming solution as described above and hence the solvent of the me~brane-rorming solution can be evaporated off after coating usually without need of heating or at suhstantially room temperature but after coating the membrane-forming solution on the support membrane, the membrane is, if neces-sary, heated for evaporating off the solvent. The heating temperature may be suitably selected according to the kind o the solvent used but the temperature lower than 150C are sufficient.
For accelerating the evaporation of the solvent after coating the membrane-forming solution on a support membrane, the membrane-forming solution may be previously heated before applying to the support membrane.
The thickness of the thin film-form semipermeable membrane composed of the sulfonated polysulfone or the sul-fonated polysulfone copolymer in the composite semipermeable membrane thus obtained depends upon the concentration of the polymer in the membrane-forming solution used and the coat-ing thickness or the membrane-forming solution on the support membrane but is as thin as possible for increasing the flu~ of the composite semipermeable membrane and is as thick as possible for increasing the strength of the composite semipermeable membrane. Accord-~26~i~ ~

ingly, although there is no particular restriction on the -thic~ness of the semipermeable membrane composed of the sulfonated polysulfone or the sulfonated polysulfone copoly-mer, the thickness is preferably in the range of 0.01 to 5 ~m.
According to the kind of additive~s) used, the additive(s~ sometime remain in the composite semipermeable membrane thus obtained but these additives are removed from the membrane by immersing the composite semipermeable mem-brane in water and passing water through the membrane or byusing the composite semipermeable membrane as it is for the treatment of an aqueous liquid.
The composite semipermeable membrane of this inven-tion having the sem:ipermeable membrane composed of the sulfonated polysulfone is particularly excellent in chlorine resistance and pH resistance and is suitable for use as a reverse osmosis membrane or a ultrafiltration membrane.
Also, the composite semipermeable membrane of this invention having the semipermeable membrane composed of the sulfonated polysulfone copolymer is also excellent in chlorine resis-tance and pH resistance and is suitable for use as a reverse osmosis membrane. In particular, the composite semipermea-ble membrane obtained using the sulfonated product of the linear polysulfone copolymer wherein the recurring unit shown by formula (A) is in the range of 50 to lO mole% and ~2~i357~

the recurring unit shown by formula (B) is in the range of 50 to 90 mole% shows a hish rejection of sodium chloride by the trea ment at low pressure and has a sufriciently large flux. Also, by applying, i~ necessary, the operation of drying and rewetting to the composite semipermeable mem-brane, the rejection thereof can be further increased.
Moreover, according to the process of this inven-tion, the performance of the composite semipermeable mem-bxane obtained, in particular, the rejection thereof for a solute and the flux can be controlled in wide ranges by properly selecting the kind and concentration of the additive(s) added to the membrane-forming solution and hence the planning of the composite semipermeable membrane suita-ble for desired use can be easily made.
Then, the following examples are intended to illus-trate the present invention but not to limit it in any way.
In addition, the rejection of solute by the com-posite semipermeable membrane and the flux of the membrane are obtained by the following equations by treating an aqueous sodium chloride solution of a concentration of 5,000 ppm under the conditions of 25C in temperature and 20 kg/
cm in pressure.

Rejection = (1 - (a)/(b)) x 100 ~%) Flux = (c) (m3)/~(d) (m2) x (e) (day)]

~herein (a) is a concentration of the solute in the membrane pe~me ted solution; (b) is a concentration of the feed solution, (c) is an amount of permeated solution ; (d) is an effective membrane area; and (e) is a permeating period of time.

(1) Production of polysulfone:
A polysulfone having the recurring unit shown by ~ormula (Al) -0 ~ ~ S2 ~ (Al) was prepared by the process described in Japanèse Patent Publication ~o. 21458/~1.
That is, 13.2 g (0.12 mole) of hydroquinone was placed in a flask equipped with a stirrer, a nitrogen gas inlet, a water outlet, and a thermometer and then 100 ml of sulforane and 50 ml of xylene were added thereto. The mixture was refluxed for one hour at 150C wi~l stirring under heating by a mantle heater, during which about 3 ml of water was discharged.
Then, the temperature was reduced to 110C and then 34.5 g (0.12 mole) of 4,4'-dichlorodiphenylsulfone and 20.7 g (0.15 mole) of potassium carbonate were added to the mixture to initiate the polymerization reaction. After i'72 refluxing the mixture or 50 minutes at 150C, the tempera-ture was increased to 200C within a period of 50 minutes while withdrawing water and further the mixture was refluxed for 30 minutes at 200 to 215C. The amount of the dis-charged water during the reaction was 3.6 ml.
After confirming that when a part of the reaction mixture was coated on a glass plate and immersed in water, it could form a film, 80 ml of sulforane was added to the reaction mixture and after lowering the temperature to 100C, 20 ml of dichloromethane was added to the mixture.
The reaction mixture thus obtained was poured in pure water to solidify polysulfone and the mixture was allowed to stand overnight. The polysulfone was separated, crushed by means of a mixer, and after washing with pure water and isopropyl alcohol, dried for 6 h~urs at 80C.
The polysulfone thus obtained was russet granular materials and the logarithmic viscosity thereof measured at 47C about a solution of 0.5 g of the polymer in 100 ml of p-chlorophenol was 1.40. Hereinafter, the measurement conditions for the logarithmic viscosity o the polysulfone are the same.

(2) Production of sulfonated polysulfone:
To 80 ml of concentrated sulfuric acid of 97~ in concentration was added 10 g of the polysulfone obtained as described above and the mixture was mildly stirred for 4 ~;~635~2 hours at room temperature to perform the reaction, whereby a black-brown viscous reaction mixture was obtained. The product was poured in ice bath to solidify the sulonated polysulfone thus obtained, the sulfonated polysulfone was 5 collected, washed with water and then allowed to stand overnight in 800 ml of an aqueous solution of 0.5N sodium hydroxide. Then, the polymer was collected, washed with water until the washings became neutral, and then dried in vacuo for 7 hours at 30C.
The logarithmic viscosity of the light-yellow granu-lar sulfonated polysulfone thus obtained was 3.0 and the ion exchange capacity thereof was 1.92 milli-equivalent/g.

(3) Production of composite semipermeable membrane:
An anisotropic ultrafiltration membrane composed of the polysulfone having the recurring unit shown by the above-described formula (C) and having a pure water flux of 20 m3/m2-day at a pressure of 3.5 Xg/cm2 was allowed to stand for 5 minutes in a dryer at 60C to provide a dry ultrafiltration membrane.
The above-described sulfonated polysulfone was dis-solved in ethylene glycol monomethyl ether, foreign matters were removed using a filter paper of 10 ~m in pore size to provide a polymer solution of 1.0% by weight in concentra-tion, and further 10 g of 1,4-butanediol to 90 g of the solution followed by stirring to provide a homogeneous ~2~3~7~:

membrane-forming solution. The memorane-forming solution contained 0.9% by weight the sulfonated polysulfone and 10 by weight the additive.
The me~brane-forming solution was coated on the abo~e-described dry ultrafiltration membrane and arter allowing to stand the ultrafiltration membrane to evapo-rating off almost all the solvent, the membrane was heated for 5 minutes at 60C to provide a composite semipermeable membrane having a semipermeable membrane of 0.3 ~m in thickness.
The performance of the composite semipermeable membrane was 50.0% in rejection and 5.9 m3/m2~day in 1ux.
EXA~PLE 2 By following the same procedure as Example 1 e~cept that lactic acid was used as the additive and the concentra-tion of lactic acid in the membrane-forming solution was 10%
by weight, a composite semipermeable membrane was obtained.
The rejection and the flux of the composite semipermeable membrane were 50.3% and 5.9 m3/m2-day.

By following the same procedure as Example 1 except that 1,4-butanediol or glycerol was used as the additive at a concentration in the membrane-forming solution shown in Table 1, composite semipermeable membranes of this invention were obtained. The performances of the composite semiperme-~j,~jj7~

able membranes thus obtained are shown in Tablz 1.

Table 1 Additive Amount Added Re'ectionFl~x (wt~)* ~%) ~ (m3/m~ day) 1,4-Butanediol 5 65.0 3.2 " 10 49.7 5.1 " 30 31.2 8.4 " 70 20.6 11.4 Glycerol 2.5 28.9 7.4 " 10 14.1 13.0 (*~: Concentration in the membrane-forming solution.
:

By following the same procedure as Example 1 using the ~additive shown in Table 2, composite semipermeable membranes were produced.
I5~ In the evaluation of the performances of these products thus obtained, a permeating test was performed at a temperature~of~ 25C ~and a pressure of 20 kg/cm using an ;aqueous sucrose solution at a concentration of 500 ppm as a base~llquid. The results are shown in Table 2.

~ ~ , :

~: ;

~63~5~2 Table 2 Addl.iveAmount .~ddeReiec~ion~Fl x (wt~)* (~) (m /m day) 1,4-sutanediol 10 67.8 3.2 " ~o ag.o 6.6 ~ 70 40.9 9.2 Lactic Acid 10 66.1 3.8 Glycerol 10 63.0 4.2 (*): Concentration in the membrane-forming solution.

~Acid resistance]

The semipermeable membrane obtained in Example 1 was immersed in distilled water for 2 hours and then in an aqueous 0.5N hydrochloric acid solution for 2 hours at 25C, and thereafter, the mernbrane performance was measured about an aqueous sodium chloride solution under the same condi-tions as in Example 1. The rejection of the membrane was 50.0%, the flux thereof was 5.8 m3/m2-day, which did not substantially differ from the case of without immersing the aqueous hydrochloric acid solution. Thus, it can be seen that the composite semipermeable membrane of this invention thus prepared is excellent in acid resistance.
~Alkali resistance~
The composite semipermeable membrane obtained in Example 1 was immersed in distilled water for 2 hours and 5i7;2 then in aqueous 0.5~ sodium hydroxide solution for 2 hours at 25C, and then the membrane performance thereo~ was measured about an aqueous sodium chloride solution under the conditions as in Example 1. The rejection of the membrane was 50.0% and the flux thereo~ was 6.0 m /m day, which were substantially same as those of the membrar.e without im-mersing the aqueous sodium hydroxide solution. Thus~ it can be seen that the ~omposite semipermeable membrane of this invention is excellent in alkali resistance.
[Chlorine resistance~
The composite semipermeable membrane obtained in Example 3 using 1,4-butanediol in a concentration of 5g by ! weight was immersed in distilled water for 2 hours and then in an aqueous solution containing 100 ppm of chlorine for 4 weeks at 25C. Thereafter, the membrane performance was measured about an aqueous so~ium chloride solution under the same conditions as in Example 1. The rejection of the membrane was 67.0% and the flux thereof was 3.1 m3/m2.day, which were substantially same as the composite semipermeable membrane without being immersed in the aqueous solution con-taining chlorine. Also, when the change of the performance of the composite semipermeable membrane with the passage of tlme for half a year~as examined, no substantial change was obser~ed.
After similarly immersing the composite semipermea-ble membrane in an aqueous solution having a chlorine ~:~635i7~

concentration of 10,000 ppm for 4 weeks, the rejection was 68.0% and the flux was 3.0 m3/m2-day.
Thus, it can be seen that the composite semipermea-ble membrane of this invention is excellent in chlorine5 resistance.
E~AMPLE 6 (1) Production of linear polysulfone copolymer:
According to -the process described in Japanese Pat-ent Publication ~o. 21458/71, a linear polysulfone copolymer10 composed of 57 mole~ recurring unit shown by formula (Al) and 43 mole% recurring unit shown by formula (B) was prepared.
That is, 15.0 g (0.06 mole) of 4,4'-dihydroxydi-- phenylsulfone and 8.1 g (0.08 mole) of hydroquinone were placed in a flask equipped with a stirrer, a nitrogen gas inlet, a water discharging pipe, and a thermometer and then 200 ml of sulforan and 100 ml of xylene were added thereto.
Then, the mixture was refluxed for one hour at 155C while stirring under heating by means of a mantle heater, whereby 5.6 ml of water was discharged in this case.
Then, the temperature of the mixture was lowered to 110C and 40.2 g (0.14 mole) of 4,4'-dichlorodiphenylsulfone and 27.6 g (0.20 mole) of potassium carbonate were added thereto to initiate a polymerization reaction. ~fter re-fluxing the mixture for one hour at 162C, the temperature of the mixture was increased to 200C while withdrawing water during 2.5 hours and then the mixture was further refluxed for 4 hours at 200 to 215C. During the reaction, 2.0 ml of water was withdrawn.
After confirming that when a part of the reaction mixture thus obtained was coated on a glass plate and the glass place was immersed in water, the reaction mixture could form a film, the temperature of the reaction mixture was lowered to 100C and 20 ml of dichloromethane was added thereto. The reaction mixture thus obtainea was poured in pure water to solidify polysulfone copolymer thus formed.
The copolymer was recovered, washed with pure water and then acetone, and dried for 6.5 hours ~t 80C.
The linear polysulfone copolymer thus obtained was a light yellow granular material and the logarithmic viscosity thereof was 0.84.
(2) Production of sulfonated polysulfone copolymer:
To 80 ml of concentrated sulfuric acid of 97~ in concentration was dissolved 10 g of the polysulfone copoly-mer obtained as described above and the solution was stirred for 4 hours at room temperature to cause a reaction, whereby a blac~-brown viscous reaction mixture was obtained. The product was poured in an ice bath to solidify the sulfonated polysulfone copolymer thus formed. After washing with water, the product was allowed to stand overnight in 800 ml .

~:6;~57~2 of an aqueous O.SN sodium hydroxide solution. Therea~ter, the product was washed with water until the washings bec~me neuiral and th2n dried in vacuo for 5 hours at 60C.
The logarithmic viscosity and the ion exchange capacity of the light-yellow granular sulfonated polysul~~one copolymer thus obtained were 0.84 and 1.2 milli-equivalent/
g, respectively.
(3) Production of composite semipermeable membrane:
The sulfonated polysulfone copolymer obtained as described above was dissolved in ethylene glycol monomethyl ether to provide a solution of 1.0% by weight of the copolymer and to 90 g of the solution was added glycerol so ~hat the concentration thereof became 2.5% by weight follow-ed by stirring to provide a homogeneous membrane-forming solution.
The membrane-forming solution was coated in a dry ultrafiltration membrane as used in Example 1 and after evaporating off almost all the solvent from the coating solution, the membrane was heated at 60C for about 5 minutes to provide a composite semipermeable membrane of this invention having a semipermeable film of 0.3 ~m thick-ness.
The performance of the composite semipermeable mem-brane thus obtained was 82.0% in rejection and 2.5 m3/m2.day in flux.

~263~

By following the same procedure as Example 6 e~cept that 1,4-butanediol was used as the additive and the concentration thereof in the membrane-forming solution was 10% by weight, a composite semipermeable membrane was obtained. The performance of the composite semipermeable membrane was 85.6% in rejection and 1.4 m /m .day in flux.

By following the same procedure as the case of preparing the polysulfone copolymer in Example 6, various polysulfone copolymers each having a different ratio of the recurring unit shown by formula (Al) to the recurring unit shown by formula (B) were prepared, these copolymers were sulfonated to sulfonated polysulfone copolymers, composite semipermeable membrane were prepared.by the same manner as in Example 6 using these sulfonated copolymers.
The performances of these composite semipermeable membranes are shown in Table 3.

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~ ~63S7~

CO~PAR~TIVE ~XAMPLE 1 A polysulfone (P-1700, trade name, made by Union Carbide Corporation) having the recurring unit shown by formula (C) de~cribed before was sulfonated according to the method reported by A. ~oshay et 21 in Journal of Applied Polymer Science, 20, 1885 (1976).
That is, 60 g of the above-described polysulfone was dissolved in 300 ml of 1,2-dichloroethane to provide a poly-sulfone solution. Apart from this, 11.5 ml (0.07 mole) of triethyl phosphate and 83 ml of 1,2-dichloroethane were placed in a 200 milliliter Erlenmyer flask having a stop cock and 6 mol (0.16 mole) of sulfur trioxide was added thereto with stirring under cooling by an icè bath to provide a sulfur triox~de solution.
In a flask equipped with a stirrer, two dropping funnels, and a calcium chloride tube, the above-described polysulfone solution and sulfur trioxide solution were added dropwise through the dropping funnels, respectively, to the dichloroethane in the flask with stirring over a period of one hour, ~nd then the mixture thus formed was further stir-red for 2 hours at room temperature. The polymer thus deposited was collected by filtration, washed with isopropyl alcohol and then pure water, and then dried for 13 hours at The logarithmic viscosity of the sulfonat~d polysul-~one co olymer thus obtained measured at 30C as a 0.15% by weigh~ ~-methyl-2 pyrrolidone solution thereof was 0.91 and rhe ion exchange capacity thereor was 1.0 milli-equivalent/
g-The sulfonated polysulfone was dissolved in ethylene glycol monomethyl ether to provide a membrane-forming solu-tion having a concentration thereof of 1.0% by weight.
On the other hand, a wet ultrafiltration membrane as used in Example 1 was immersed in an aqueous 10% lactic acid solution without being dried and thereafter dried for 24 hours at room temperature to provide a dry ultrafiltration membrane.
The above-described membrane-forming solution was coated on the dry ultrc~filtration membrane and a composite semipermeable membrane was obtained by the same manner as in Example 6.
he performance of the composite semipermeable membrane was 83.2~ in rejection and 0.5 m3/m2-day in flux.

In a 1.0 wt% ethylene glycol monomethyl ether solu-tion of the sulfonated product of the polysulfone copolymer composed of 43 mole~ the recurring unit shown by formula (Al) and 57 mole~ the recurring unit shown by formula (B) obtained in Example 8 was dissolved glycerol or 1,4-butanediol in various concentrations to provide various membrane-forming solutlons.
Then, composite semipermeable membranes were pre-pared using these membrane-forming solutions by the sa~e manner as E~ample 6. The performance of .he membranes are shown in Table 4.

Table 4 Additive Amount Added Reiection 3Fl~x (wt%)* ~ m /m day) 1,4-Butanediol 10 90.0 1.8 ~ " 30 80.6 3.5 ~ . 50 45.6 7.3 " 70 13.1 15.6 Glycerol 5 51.1 5.5 " 10 34.7 9.4 " 15 19.3 11.4 ~ 20 11.7 14.7 ~*): Concentration in the membrane-forming solution.

By following the same procedure as Example 8 except that in the case of preparing a composite semipermeable membrane using a 1.0 wt% ethylene glycol monomethyl ether solution of the sulfonated product of the polysulfone copolymer composed of 43 mole% the recurring unit shown by formula ~Al) and 57 mole% the recurring unit shown by for-~;263~

mula (3), tne conce,~tration of the copolymer in the mem-brane-forming solution was changed, composite semipermeabl2 membranes were prepared. The performances of the composite semipermeable membranes thus ob-tained are shown in Table 5.

Table 5 Concentration of Copolymer in Membrane-Formin~ Solution Reiection 3Fl~x (wt%) t~) (m /m day) 5.0 46.9 5.7 - l.0 38.9 7.6 0.5 4~.1 8.2 0.1 21.0 10.2 ÆXAMPLE 11 In a mixed solvent composed of 99 g of ethylene glycol monomethyl ether ~nd 1 g of N,N-dimethylformamide was dissolved 1 9 of the sulfonated product of the polysulfone copolymer composed of 17 mole% the recurring unit shown by formula (Al) and 83 mole% the recurring unit shown by for-mula (B) as obtained in Example 8 and after further adding there~o 2.5 g of glycerol, insoluble matters were removed using a filter paper of 10 ~m in pore size to provide a homogeneous membrane-forming solution.
The membrane-forming solution thus formed was coated on a dry ultrafiltration membrane at a temperature of 25C

by the same manner as in Example 6 and after evaporating off almost all the solvent at 25C, the membrane was heated to 60C for 5 minutes to completely remove the solvent to provide a composite semipermeabLe membrane.
The p~rformance of the composite semipermeable mem-brane thus obtained was 92.8~ in rejection and 0.5 m3/m2. day in flux.
EXA~lPLE 12 By following the same procedure as Example 6 except that resercinol was used in place of hydroquinone, a poly-sulfone copolymer composed of 57 mole% a recurring unit ~shown by formula (A2) O~S02~>-- (A2 ) O ~

and 43 mole% a recurring unit shown by formula (B) was pre-pared. The polysulfone copolymer thus obtained was sul-fonated by the same manner as in Example 6 to provide a sulfonated polysulfone copolymer. The logarithmic viscosity and the ion exchange capacity of the sulfonated polysulfone copolymer were 0.93 and 0.98 milli-equivalent/g, respective-ly.

~63~;i7~

A composite semipermeable membrane having a semiper-meable membrane of ().3 ~m in film thickness was prepared using tne sulfonat~d copolymer by ~he same manner as in Example 6. The performance of the composite semipermeable 5membrane was 90.3% in rejection and 1.8 m3/m2.day in flux.

By following the same procedure as Example 6 except that catechol was used in place of hydroquinone, a polysul-fone copolymer composed of 57 mole~ a recurring unit shown 10by formula (A3) O O~S02~ (A2 ) and 43 mole% a recurring unit shown by formula (B) was prepared and the copolymer thus obtained was sulfonated by the same manner as in Example 6. The logarithmic viscosity 15and the ion exchange capacity of the sulfonated polysulfone copolymer were 1.02 and 1.03 milli-equivalent/g, respective-ly .
Then, a composite semipermeable membrane having a semipermeable membrane of 0.3 ~m in thickness was prepared 20using the sulfonated copolymer by the same manner as in Example 6. The performance of the composite semipermeable membrane was 90.1% in rejection and 1.8 m3/m2-day in ~lux.
EXAMPLE l In concentrated sulfuric acid of 97% in concentra-tion was dissolved 10 g of the polysulfone copolymer com-posed of 43 mole% the recurring unit shown by formula (Al) and 57 mole~ the recurring unit shown by formula (B) as obtained in Example 8 and the solution was stirred for 4 hours to cause reaction, whereby a black brown viscous reaction mixture was obtained. After the reaction was over, the reaction mixture thus obtained was poured in an ice bath to solidify the sulfonated copolymer, which was collected, washed with pure water until the washing became neutral, and dried for 7 hours at 6C~C to provide a sulfonated polysul-fone copolymer having a logarithmic viscosity of 1.03 and an ion exchange capacity of 1.0 milli-equivalent/g.
In 99.5 g of ethylene glycol monomethyl ether was dissolved 1.0 g Gf the sulfonated polysulfone copolymer and further 2.5 g of glycerol was dissolved in the solution to provide a membrane-forming solution. Then, a composite semipermeable membrane was prepared using the membrane-forming solution by the same manner as in Example 6.
The performance of the composite semipermeable mem-brane was 90.3~ in re~ection and 1.7 m3/m2.day in flux.

- ~63~72 [Evaluation of heat resistance]
Each of the composite semipermeable membrane obtain-ed in Example 6 and the composite semipermeable membrane composed of 43 mole% the recurring unit shown by formula (Al) and 57 mole% the recurring unit shown by formula (B) obtained in Example 8 was immersed in hot water of 95C for 30 minutes and thereafter, the rejection and the ~lux there-of were measured. Furthermore, the operation of immersing hot water for 30 minutes as above was repeated five times and the rejection and the flux were measured.
The results were as follows. That is, the perfor-mance of the composite semipermeable membrane in Example 6 was 82.0~ in rejection and 2.5 m /m day in flux before the hot water treatment ancl was 82.3 to 82.6% in rejection and 2.4 to 2.5 m3/m2. day in flux in the aforesaid hot water immersion of five times, which showed that the performance of the membrane did not substantially change during the hot water treatment.
Also, the performance of the composite semipermeable membrane in Example 8 was 94.0% in rejection and 1.5 m3/
m day in flux before the hot water treatment and was 95.5 to 95.8% in rejection and 1.2 to 1.4 m /m day in flux in the aforesaid hot water immersion of five times, which also showed that the performance thereof did not substantially change during ~he hot water treatment.

~:~ Ei3~

[Acid resistance]
The above-described composite semiDermea'Dle membrane in ~xample 8 was immersed in distilled water for 2 hours and then after further i~mersing the membrane in an aqueous 0.5N
hydrochloric acid solution of 25C for 2 hours, the perfor-mance of the membrane about an aqueous sodium chloride solution was measured under the same conditions as in Exam-ple 1. The results are shown in Table 6.

Table 6 Before Immersion Ater Immersion 10~_Treatment of Treatment (I)* (II)** (I)* (II)**
Acid Resistance 93.0 1.6 93.0 1.6 Alkali Resistance 92.8 1.2 93.0 - 1.2 Note: *: Rejection (%) 15**: Flux (m3/m day~

As shown in Table 6, it can be seen that the perfor-mance of the composite semipermeable membrane does not change before and after the immersion and hence the membrane is excellent in acid resistance.
[Alkali resistance~
The above-described composite membrane as in Example 8 was immersed in distilled water for 2 hours and then after further immersing the membrane in an aqueous 0.5N sodium 3~i7~

hydroxide solution for 2 hours, the performance of the membrane was measured. The results are shown in Table 6 before.
As shown in the table, it can be seen that the per-formance of the membrane does not change before and after the immersion and hence the membrane is excellent in alkali resistance.
[Chlorine resistance~
The composite semipermeable membrane using 1,4-butanediol in a concentration of 10% by weight as obtained in Example 9 was immersed in distilled water for 2 hours and after immersing the membrane in an aqueous solution contain-ing 100 ppm of chlorine for 4 weeks at 25C, the per~ormance of the membrane about an aqueous sodium chloride solution was measured under the same conditions as in Example 1. The rejection was 90.6% and the flux was 1.8 m3/m2 day, which were substantially same as -those before the immersion.
Also, when the same test as above was performed using an aqueous solution containing 10,000 ppm o~ chlorine, the rejection was 88.3% and the flux was 2.2 m /m .day.
Furthermore, when the change in performance of the membrane with the passage of time was detected but no sub-stantial change was observed. Thus, it can be seen that the composite semipermeable membrane of this invention is excel-lent in chlorine resistance.

[Drying resistance]
The composite semipermeable membrane using the poly-sulfone composition composed of 43 mole% recurring unit of formula (A1) and 57 mole% recurring unit of formula (B) as obtained in Example 8 was immersed in distilled water for 2 hours, and after immersing the membrane in an aqueous 0.5N
hydrochloric acid solution of 25C for 2 hours and then washing it with distilled water, the membrane was dried for 2 hours at 25C. When the dry membrane was immersed in water to be re-wetted, the performance of the membrane was 99.5% in rejection and 0.3 m3/m2-day in flux.
REFERENCE_EXAMPLE
When the ~olysulfone ultrafiltration membrane having the recurring unit sho~n by above-described formula (C) as used in Example 1 was used for treating an a~ueous 0.5%
sodium chloride solution at a temperature of 28C and a pressure of 20 kg/cm2, the rejection was 0.2% and the flux w s 17.1 m3/m2-day. However, when the ultrafiltration membrane was immersed in ethylene glycol monomethyl ether and dried for 6 minutes at 60C, the performance of the membrane was 2.0% in rejection and 0.9 m3/m2-day in flux.
Also, when the above-described ultrafiltration membrane was immersed in the solution of ethylene glycol monomethyl ether involving 10~ by ~eight of glycerol, and dried for 6 minutes at 60C, the performance of the membrane ~3~i7:~

was 0.8% in rejection and 9.3 m /m ~day in flux.

By following the s~me procedure as Example 9 except that an anisotropic ultrafiltra.ion memDrane compos-d of a polysulfone having the recurring unit shown by rormula (B) and showing a pure water flux of 20 m3/m2.day under a pressure of 3.5 kg/cm2, composite semipermeable membranes were obtained.
The performances of these composite semipermeable membranes are shown in Table 7.

Table 7 Additivemount Added Reiection 3Fl x ~wt~)* (%) (m /m day) 1,4-Butanediol 10 91.0 1.7 " 30 80.8 3.2 " 50 46.2 7.5 " 70 14.2 15.0 Glycerol 5 51.3 5.6 " lO 34.6 9.9 " 15 l9.1 10.3 " 20 11.3 16.1 (*): Concentration in the membrane-forming solution.

(1) Production of polysulfone:

7~

A linear polysulfone copolvmer composed of 57 mole%

of the recurring unit shown by rormula (Al) 1~~S2 <,~ (Al) wherein n is an integer of 1 or more, and 43 mole% of the recurring unit shown by formula (B) ~ ~ S2 - ~ ~ S2 { ~ (B) was prepared by the process described in Japanese Patent Publication No. 21458/710 That is, 25~0 g (0.1 mole~ of 4,4'-dihydroxyphenyl-sulfone was placed in a flask equipped with a stirrer, anitrogen gas inlet, a water outlet and a thermometer and then 200 ml of sulforane and 100 ml of xylene were added thereto. The mixture was refluxed for one hour at 150C
with stirring under heating by a mantle heater, during which about 5.3 ml of water was discharged.
Then, the temperature was reduced to 110C and then 28~8 g (0.1 mole) of 4,4'-dichlorodiphenylsulfone and 10.3 g (0~08 mole) of potassium carbonate were added to the mixture to initiate the polymerization reaction. After refluxing ~ 2~i3~

the mixture for 1 hour at 162C, the temperature was in-creased to 200C within a period of 2.5 hours while with-drawins water and further the mixture was rerluxed ~or 4 hours at 200 to 215C. The amount of the discharged water during the reaction was 2.0 ml.
After confirming that when a part .of the reaction mixture was coated on a glass plate and immersed in water, it could form a film, the tempe~ature was lowered to 100C
and 20 ml of dichloromethane was added to the mixture. The reaction mixture thus obtained was poured in pure water to solidify polysulfone After washing with pure water and then acetone, the polysulfone was dried for 6.5 hours at ~0 C .
The linear polysulfone thus obtained was light-yellow granular materials and the logarithmic viscositythereof was 0.90.
(2) Production of sulfonated polysulfone:
To 80 ml of concentrated sulfuric acid of 97% in concentration was added 10 g of the polysulfone obtained as described above and the mixture was mildly stirred for 4 hours at room temperature to perform the reaction, whereby a black-brown viscous reaction mi~ture was obtained. The product was poured in ice bath to solidify the sulfonated polysulfone thus obtained, the sulfonated polysulfone was collected, washed with water and then allowed to stand ~i3~72 overnight in 800 ml of an aqueous solution of 0.5~ sodium hydroxide. Then, ~he polymer was collected, washed with water until the washings became neutral, and then dried in vacuo for 5 hours at 60C.
The logarithmic viscosity of the light-yellow sranu-lar sulfonated polysulfone thus obtained was 1.03 and the ion exchange capacity thereof was 1.0 milli-equivalent/g.
(3) Production of composite semipermeable membrane:
By following the same procedure as Example 6 except that the sulfonated polysulfone obtained above was used, a composite semipermeable membrane was obtained.
The performance of the composite semipermeable mem-brane thus obtained was 83.3% in rejection and 2.3 m3/m2-day in flux.
` EXAMPLE 18 By following the same p~ocedure as Example 9 except that the sulfonated polysulfone obtained in Example 17 above was used, composite semipermeable membranes of this inven-tion were obtained. The performances of the composite semipermeable membranes thus obtained are shown in Table 8.

~2~3S~2 Table 8 Additive Amount Added Rejec~onFl~x (wt%)* (%) (m3/~ day~
1,4-Butanediol 10 90.0 1.7 " 30 ~3.0 3.~
" 50 43.3 7.0 " 70 15.6 16.0 Glycerol 5 50.8 5.5 " 10 38.0 10.3 " 15 20.4 11.0 " ~0 10.1 18.8 (*): Concentration in the membrane-forminy solution.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims (26)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A sulfonated polysulfone composite semipermeable membrane for reverse osmosis or ultrafiltration comprising polysulfone series ultrafiltration support membrane having a pure water flux of higher than 3 m3/m2 ? day under a pressure of 3.5 kg/cm2 and having laminated thereon a 0.01 to 5 µm semipermeable membrane composed of a sulfonated polysulfone formed by sulfonating a polysulfone composed of a recurring unit shown by formula (A) (A) wherein n is an integer of 1 or more.

2. The polysulfone semipermeable membrane as claimed in claim 1, wherein the sulfonated polysulfone has a logarithmic viscosity of 0.2 to 10 measured at 30°C about a solution of 0.5 g thereof dissolved in 100 ml of N-methyl-2-pyrrolidone and an ion exchange capacity of 0.2 to 2.3 milli-equivalent/g.

3. The polysulfone semipermeable membrane as claimed in claim 1, wherein the sulfonated polysulfone has a sulfonic acid group represented by the formula -SO3M (wherein M

represents a hydrogen atom, an alkali metal or a tetraalkyl ammonium).

4. A process for producing a sulfonated polysulfone composite semipermeable membrane for reverse osmosis or ultrafiltration which comprises coating a support membrane having a pure water flux of higher than 3 m3/m2?day under a pressure of 3.5 kg/cm2 with a membrane-forming solution contain-ing a sulfonated polysulfone formed by sulfonating a poly-sulfone composed of a recurring unit shown by formula (A) (A) wherein n is an integer of 1 or more, an alkylene glycol alkyl ether which may contain a small amount of a non-protonic polar organic solvent, and a water-soluble and low volatile compound as an additive and then evaporating off the solvent from the coated membrane-forming-solution.

5. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 4, wherein the sulfonated polysulfone has a logarithmic viscosity of 0.2 to 10 measured at 30°C about a solution of 0.5 g thereof dissolved in 100 ml of N-methyl-2-pyrrolidone and has an ion exchange capacity of 0.2 to 2.3 milli-equivalent/g.

6. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 4, wherein the sulfonated polysulfone has a sulfonic acid group represented by the formula -SO3M (wherein M represents a hydrogen atom, an alkali metal, or a tetraalkyl ammonium).

7. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 4, wherein the additive is at least one of polyhydric alcohols, polyalkylene glycols, carboxylic acids, the salts of carboxylic acids, hydroxycarboxylic acids, and the salts of hydroxycarboxylic acids.

8. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 4, wherein the additive is at least one of inorganic salts.

9. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 4, wherein the support membrane is a polysulfone series ultrafiltration membrane.

10. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 4, wherein the concentration of the additive in the membrane-forming solution is from 0.1 to 80% by weight.

11. A sulfonated polysulfone composite semipermeable membrane for reverse osmosis or ultrafiltration comprising a polysulfone series filtration support membrane having a pure water flux of higher than 3 m3/m2 ? day under a pressure of 3.5 kg/cm2 and having laminated thereon a 0.01 to 5 µm semipermeable membrane composed of a sulfonated polysulfone copolymer formed by sulfonating a linear polysulfone copolymer composed of a recurring unit shown by formula (A) (A) wherein n is an integer of 1 or more, and a recurring unit shown by formula (B) (B)

12. The sulfonated polysulfone composite semipermeable membrane as claimed in claim 11, wherein the linear polysulfone copolymer is composed of more than 10 mole% of the recurring unit of formula (A) and less than 90 mole% the recurring unit shown by formula (B).

13. The sulfonated polysulfone composite semipermeable membrane as claimed in claim 11, wherein the sulfonated polysulfone copolymer has a logarithmic viscosity of 0.2 to 10 measured at 30°C about a solution of 0.5 g thereof dissolved in 100 ml of N-methyl-2-pyrrolidone and has an ion exchange capacity of 0.2 to 2.3 milli-equivalent/g.

14. The sulfonated polysulfone composite semipermeable membrane as claimed in claim 11, wherein the sulfonated poly-sulfone copolymer has a sulfonic acid group shown by the formula -SO3M (wherein M represents a hydrogen atom, an alkali metal, or a tetraalkyl ammonium).

15. A process for producing a sulfonated polysulfone composite semipermeable membrane for reverse osmosis or ultra-filtration which comprises coating a support membrane having a pure water flux of higher than 3 m3/m2 ? day under a pressure of 3.5 kg/cm2 with a membrane-forming solution containing a sulfonated polysulfone copolymer formed by sulfonating a linear polysulfone copolymer composed of recurring unit shown by formula (A) (A) wherein n is an integer of 1 or more, and a recurring unit shown by formula (B) (B) an alkylene glycol alkyl ether which may contain a small amount of a non-protonic polar organic solvent, and a water-soluble and low volatile compound as an additive and then evaporating off the solvent from the coated membrane-forming solution.

16. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 15, wherein the linear polysulfone copolymer is composed of more than 10 mole% of the recurring unit of formula (A) and less than 90 mole% of the recurring unit of formula (B).

17. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 15, wherein the sulfonated polysulfone copolymer has a logarithmic viscosity of 0.2 to 10 measured at 30°C about a solution of 0.5 g thereof dissolved in 100 ml of N-methyl-2-pyrrolidone and has an ion exchange capacity of 0.2 to 2.3 milli-equivalent/g.

18. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 15, wherein the sulfonated polysulfone copolymer has a sulfonic acid group shown by the formula -SO3M (wherein M represents a hydrogen atom, an alkali metal, or a tetraalkyl ammonium).

19. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 15, wherein the additive is at least one of polyhydric alcohols, polyalkylene glycols, carboxylic acids, the salts of carboxylic acids, hydroxycarboxylic acids, and the salts of hydroxy-carboxylic acids.

20. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 15, wherein the additive is at least one of inorganic salts.

21. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 15, wherein the support membrane is a polysulfone series ultra-fitration membrane.

22. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 15, wherein the concentration of the additive in the membrane-forming solution is from 0.1 to 80% by weight.

23. A process for producing a sulfonated polysulfone composite semipermeable membrane which comprises coating a support membrane with a membrane-forming solution containing a sulfonated polysulfone formed by sulfonating a polysulfone composed of a recurring unit shown by formula (A) (A) wherein n is an integer of 1 or more, an alkylene glycol alkyl ether which contains a small amount of a non-protonic polar organic solvent, and a water-soluble and low volatile compound as an additive and then evaporating off the solvent from the coated membrane-forming solution.

24. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 23, wherein said solution contains the non-protonic polar organic solution in a proportion of the non-protonic polar organic solvent in a mixed solvent of less than 5 parts by weight.

25. A process for producing a sulfonated polysulfone composite semipermeable membrane which comprises coating a support membrane with a membrane-forming solution containing a sulfonated polysulfone copolymer formed by sulfonating a linear polysulfone copolymer composed of a recurring unit shown by formula (A) (A) wherein n is an integer of 1 or more, and a recurring unit shown by formula (B) (B) an alkylene glycol alkyl ether which contains a small amount of a non-protonic polar organic solvent, and a water-soluble and low volatile compound as an additive and then evaporating off the solvent from the coated membrane-forming solution.

26. The process for producing a sulfonated polysulfone composite semipermeable membrane as claimed in claim 25, wherein said solution contains the non-protonic polar organic solution in a proporiton of the non-protonic polar organic solvent in a mixed solvent of less than 5 parts by weight.