CA1262994A

CA1262994A - Membranes

Info

Publication number: CA1262994A
Application number: CA000468558A
Authority: CA
Inventors: Richard A. Hann; David R. Holmes
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1983-11-23
Filing date: 1984-11-23
Publication date: 1989-11-14
Also published as: ES537916A0; AU3574484A; GR81009B; ES8604028A1; DK555284D0; DK555284A; AU580271B2

Abstract

Abstract Membranes Divalent metal salts of sulphonated polyarylethersulphones and solutions thereof in a specified solvent mixture, for example a mixture of an alkylene carbonate, an ether and a carboxylic acid, hydroxy-substituted hydrocarbon compound or water can be used to produce membranes, such as asymmetric semi-permeable membranes for reverse osmosis. The divalent metal may be an alkaline earth metal, particularly barium. Membranes having a desirable combination of nigh salt rejection at a high water flux are also disclosed. These membranes may be used for the desalination of sea water and purification of brackish waters and industrial effluents.

Description

-1~ H.32942 Membranes ..
This invention relates to membranes, more particularly to asymmetric semi permeable membranes, materials used for the production of such membranes, processes for the production of such membranes and the use of the membranes for the treatment of solutions and suspensions.
Membranes which are useful in separation processes such as ~lltrafiltration and reverse osmosis may be prepared from polymeric materials. Asymmetric semi-permeable membranes, which can be used for reverse-osmosis, can be prepared by casting a solution of a film-forming ion-exchange material on a support and then coagulating the film using a non-sol~ent for the ion-exchange material. Asy~metric semi-per~eable membranes are characterised by having a thin dense layer which function~ as the active layer of the me~brane and a thicker porous layer which functions as a reinforcing support for the active layer.
8ritish Patent Specification No 1258851 discloses sulphonated polyarylethersulphones having a specified structure. These materials are disclosed as being io~ exchange resins and as being suitable for the production of membranes for a number of applicatlons including electrodialysis 3 fuel cell applications, osmosis and reverse osmosis.
European Patent Specification No 8894 discloses alternative sulphonated polyarylethersulphones which may be prepared by a simple and readily controlled sulphonation technique and these materials also may be used to produce membranes for desalination and other processes.
In a membrane used for reverse osmosis, a combination of high salt rejection at a high water flux is commercially very desirable but is difficult to achieve. Generally it is found tha~
a membrane giving a high salt re~ection provides only a low water flu~ and that a membrane giving a high water flux provides only a low salt re~ection.
Furthermore, it ls desirable for the membrane to have a good resistance to attack by the constituents of the liquid being treated, since this minimises the time required to replace deterlorated 3S membranes. If the membrane does not have the re~uired resistance, it is necessary to subjec~ the liquid to a pretreatment to remove the harmful constituents, for example acld, alkali or c'nlorine.

-2- H32942 Such pretreatments are undesirable since they add to the cost of the total treatment process.
According to the present invention there is provided an asy~etric semi-permPable membrane wherein the support layer and the active layer are both formed from the same sulphonated polyarylethersulphone wherein the membrane has a salt re~ection and flux which are such that ~he ratio Flux ~in m.day 1) has a value of at least 0.05 (100 - % salt re~ection) The membrane properties are conveniently determined in a reverse osmosis cell using a 0.2% by weight aqueous solution of sodium chlorlde at a pressure of 40 bar (4MNm 2) and a temperature of 25~
For convenience hereafter, the relationship Flux (100 - % salt re~ection) will be referred to as the "membrane factor". Membranes in accordance with the present invention typically have a membrane factor of at leas~ 0.01 and usually at least 0.15. Preferred membranes are those having a membrane factor of at least 0.2 and especially those having a membrane factor of at least 0.5.
It will be appreciated that a membrane factor of 0.05 is achieved by a ~embrane having a salt re~ection of 85% at a flux of 0.75 m.day 1, and that other mRmbranes having a greater salt rejection at a lower flux, or a lower salt re~ection at a higher flux, may al80 have this membrane factor. Similarly, a membrane havi~g a ~alt re~ection of 90~ at a flux of one m.day 1 has a membrane factor of 0.1 whils~ a salt rejection of 90% at a flux of 1.Sm.day 1 corresponds to a membrane factor of 0.15. Preferred membranes having a me~brane factor of at least 0,2 include those having a salt rejection of 95% at a flux of one m.day~1 or a salt rejection of 90 at a flux of two m.day 1. Especially preferred membranes, which have a membrane factor of at least O.S, include those having a salt re~ection of 98% at a flux of one m.day 1 or a salt re~ection of 97 at a flux of 1.5 m.day 1.
The membranes of the present invention have improved resistance to aggressive materials, for example acid and alkali.
Thu8, ~he membranes of the present invention can be used to treat ~, 2~

-3- H32942 ;~ water coneaining aggre~sive materials ~hich cause deeerioration of membranes formed from other materlals.
The membranes may be of any thickness provided they possess the comblnation of salt rejec~ion and water flux required to achieve a membrane factor of the specified minimum value. The membrane ~hickness can be in the range fro~ 20 to 300 micrometres and we have obtained particularly useful properties with membranes of thickness ln the range from 50 up to 250 micrometres, especially in the range 75 up to 200 micrometres.
The membrane is formed from a sulphonated polyarylether-sulphone (here~naf~er simply sulphonated polysulphone ) and useful membranes can be obtained with a sùlphonated polysulphone containing repeat units of the formula I ~ h - 0 ~ Ph - S0 wherein Ph ls a phenylene residue, preferably a para-phenylene residue wherein at least s~me of the groups Ph are sulphonated;
m is 1 or 2 and the value of m can differ along the polymer ~ chain;
``~ 20 M is a hydrogen atom, a metal atom and/or a group MR4, wherein the groups M may be the same or different and the proportion of the groups M is sufficient to combine with the unsatisfied valencies of the groups -S03; and R is an al~yl group.
Whilst the value of m m~y be either one or two, we have produced particul~rly satisfactory membranes using a copolymer in which the value of m i9 one for some repea~ units and is two for other repeat units.
The group M will be dependent on any treatment to which the membrane has been subjected during its preparation or subsequent use and not all of the groups M need be the same. Thus, the group M may be a mixture, for example of hydrogen, sodium and barium atoms.
The sulphonated polysulphone may be the sulphonated copolymer of European Paeent Specification No 8894, which ls a material having repeat units of the formula:-II ~ phl _ o _ ph2 _ 0 _ phl _ S0

-4- a32g42 together with the repeat units of the formula III ~ ph1 _ o _ phl _ S02 _ phl _ o _ phl _ S0 wherein phl represen~s a phenylene residue, preferably a para-phenylene residue;
ph2 repre~ents a phenylene residue, preferably a para-phenylene residue, having one or two groups -S03M;
M is a hydrogen atom, a metal atom and/or a group NR4, wherein the groups M may be the sa~e or different and the proportion of the groups M is sufflciene to combine with the unsatisfied valencies of the group -S03; and R is a~ alkyl group.
The sulphonated polysulphone may also include a proportion of unsulphonated copolymer having repeat units of the formula IV tphl _ 0 _ phl _ 0 _ phl _ S0 ~

together with the repeat units of the formula III9 wberein Phl i3 as deined.
In the repeat unlts of the formula II, when ph2 is an ortho- or para- phenylene residuel there is typically only one group -S03M whereas when ph2 is a meta-phenylene residue there are typically two groups -S03M. When ph2 is an ortho-phenylene residue, the -S03M group is located in a pssition which is para-to one ether group and meta- to the other ether group, any further sulphonation occurring ~o locate the -S03M in positions meta- to each other. When ph2 is an ortho-phenylene residue, the -S03M
group i8 located in a position ortho- to one ether group and meta-to the other ether group. When ph2 i6 a me~a-phenylene residue, the -S03M groups are located in the po6itions ortho- to one ether group and para- to the other ether group.
As is described in European Patent Spacificatlon No 8894, the sulphonated copolymers m2y be prepared by s~lphonating a copoly~er consisting of repeat units III and IV. The sulphonation is readily effected by dissolving the copoly~er in concentrated sulphuric acid (98% w/w) at ambiene temperature and agitating the mixture for a sufficient time for sulphon2tion of essentially all of the sub-units

-5- H32942 - O - Ph1 - O - in the repeat units of for~ula IV. The copolymers which are subjected to sulphonation sultably have from 1 to 99 mole Z
of units IV and correspondingly from 99 to 1 mole ~ of units III, and especially from 5 to 80 mole ~ of units IV and correspondlng from 95 to 20 ~ole % of units III. Sulphonation is desirably effected to convert at least 90~ o-E the units IV to the units II.
The sulphonated copoly~ers used to produce membranes in accordance with the first aspect of the present invention are : polymeric materials of high molecular weight such that the reduced viscosity (R~) of the polymer, measured as a 1% by weight solutlon of ~he polymer in dimethylformamide at 25C, is at least 0.2 and preferably at least 0.4. The polymer may be such as to give an RV
of up to 2.5 but it is generally preferred that the RV of the polymer does not e~ceed 2Ø
The copolymer which is to be sulphonated is conveniently prepared using a mi~ure of mono~ers to produce the desired repeat units III and IV and hence the units III and IV are distributed in a random fashion along the poly~er chain. ~ence, ln ~he sulphonated copolymer, the unit~ II (and IV) and III are also distributed in a rando~ fashioQ along the polymer chain.
We have found that the membranes can be prepared by ~asting a solution of a divalent me~al salt of the sulphonated polysulphone.
~ ence, as a further aspect of the present inventlon, there is provided a sulphonated polysulphone derivatlve oontaining repeat units of the formula:-V t Ph1 ~ ~ Ph3- ~ Phl ~ S02 ~

~ogether with the repeat units of the formula III ~Ph1 ~ ~ Ph1 ~ S02 ~ Ph1 ~ ~ Phl ~ S02 ~

and optionally with a minor propvrtion of repeat units of the formula IV t Ph1 ~ - ph1 _ o _ ph1 _ S0 wherein

-6 ~329~2 ph1 represents a phenylene residue, preferably a para phenylene residue;
Ph3 represents a phenylene residue, preferably a para-phenylene residue, having one or two groups -S03Ml; and `~ 5 M1 is a divalent metal in a proportion sufficient,to cGmbine with the unsatisfied valencies of the group -S03.
~; If uni~s of the formula IV are present, they are preferably present in a molar proportion of not more than 25% molar oE the unlts IV and V and especially not more 10% molar of the units IY and V.
The ~etal M1 is preferably an alkaline earth metal and we especially prefer that Ml is barium.
~,' Membranes in accordance with the presen~ invention can be prepared from a solution contalning a ~ulphonated polyarylethersulphone, and a divalent metal in a specific solvene lS mixtureO
~` More specifically there is provided a solution containinga sulphonated polyarylethersulphone and a divalent metal in a solvent mixture containing at least three componen~s each of which is a non-solvent or poor solvent for the ~ulphona~ed polyarylethersulphone ,nd which are a~ a liquid or a low ~elting solid containing at least one hydroxylic group and having a delta-E with a value of at least 8;
b~ a liquid or a low melting solid havlng a delta-D with a value of at least 8 and a delta-P with a value of not more than 3;
c) a liquid or a lo~ melting Rolid having a delta-P wi~h a value of at least 8.5 and a delta-H with a value of not more than 3;
wherein the solvent mixture forms a single liquid phase and none of the components of the solvent mixture reacts or complexes with a~other of the components of the solvent mixture or -~ith the sulphonated polyarylethersulphone.
The sulphonated polyarylethersulphone is preferably a ~aterial aq described herein and ~he divalent metal is preferably barlum. The sulphonated polyarylethersulphone may be dlssolved in the solvent mix~ure as the divalent metal salt thersof or the salt may be for~ed in the solvent mixture.

2f~

-7- H32942 By "low melting solid" is meant a material which is solid at ambient temperature and has a melting point of not more than 50C.
In the solvent mixture, delta-~, delta-D and delta-P are components of the solubility parameter of each material which is a component of the solvent mixture and are related by the expression (delta-0)2 =~ (delta-H)2 * ( delta-D)2 ~ (delta-P)2 where delta-O is the solubility parameter and is given by ~he expression (delta-) = ( ~ ) where L~ Ev is the molar cohesive energy which approximates to ~ H-RT;
b H is the latent heat of vaporisation;
R i8 the gas constant;
15T is the absolute temperature; and is the molar volume.
~ ore specically, delta-H i9 the hydrogen bonding component of the solubility parameter, delta-D is the dispersion component of the solubility parameter and delta-P is the polar component of the solubility parameter.
~ The concept oE solubility parameters is discussed in many ; papers in ~he scientific literature including, lnter alia, a paper by C.M. Ha~sen in Ind. Eng. Chem. Prod. Res. Dev. 8, March 1969, pages 2 to 11. Other papers in which solubility parameters are considered are, inter alla, Chemical Reviews, 75 (1975), pages 731 to 753 and ~irk~Othmer "~ncylopedia of Chemlcal Technology", Second Edition, Supplemental VoLume (1971) pages 889 to 910.
A tabulation of values of delta-~, delta-D and delta-P i9 gi~en in the Hansen paper and these may be used to determine suitable liquids for use as components (a), (b) and (c) of the solvent mixture.
Preferred materials for use as component (a) of the solvent mixture have a delta-~ of at least 8 , a delta-D of not more than

8 and a delta-P of at least 6. Especially preferred materials have a delta~H of greater than 10, a delta-D of less than 8 and a delta-P
of at least 6. From the ~ansen paper, few ~aterials have a delta-~

of the required value and only diethylene glycol, dipropylene glycol, methanol and water satisfy the requirements for the preferred materials.
Preferred materials for use as component (b) of the solvent mixture have a delta-D wi~h a value at least 8, a delta-P of not more than 3 and a delta-~ of not more than 4. Materials satisfying the preferred requirements lnclude, inter alia, 1,4-dioxane, and several halohydrocarbons. Furan and tetrahydrofuran have the preferred values of delta-D, delta-P and delta-~ but are excluded due to the tendency of these materlals to comple~ with the sulphonated polysulphone. Many hydrocarbons, particularly cyclic hydrocarbons, bave the preferred values of delta-D, delta-P and delta-~ but do not f orm a single phase mixture with most materials used as components (a) and (c) of the solvent mixture.
Preferred materials for use a~ component (c) o the solvent mixture have a delta-P of at least 8.5 , a delta-H of not more than 3 and a delta-D of at least 7.5. Materials satisfying the preferred requirements include inter alla, propylene carbonate, and ethylene carbonate.
The components of the solvent mixture are non-solvents or poor solvents for the sulphonated polysulphone and the divalent metal salt thereof and the polymer is typically soluble in each of the components in an a~ount of not more than 5% by weight preferably less than 1% by weight, especially less than 0.1% by welght.
The sulphonated polysulphone and the divalent metal salt thereof is preferably soluble in the solvent mixture in an amount of at least 10% by weight, more preferably at least 15% by welght, especially at leas~ 20% by welght, for example 25 to 30% by weight.
The quantity of poly~er dissolved in the solvent mixture should be such that the resulting solution can be cast into a satisfactory me~brane and this will be dependen~ not only on the components of the solve~t mixture but also on the ~olecular weight of the polymer and the degree of sulphonation of the polymer.
The co~ponents of the solvent mi2ture and the proportions thereof, are preferably such that the solvent mixture has a delta-~of value ln the range from 4.5 to 5.5; a delta-P of value in the range from 4 to 8 and a delta-D of value in the range from 7.5 to 9.

-9- H32942 A sol~ent mixture which may be used is one containing a) RlOH or RlCOOH, where Rl is a hydrogen atom or a hydrocarhyl group;
b) an ether, particularly a cycllc ether; and c) an alkylene carbonate.
In the solvent mixture, the hydroxylic compound which is component {a) is preferably one in which Rl i~ a hydrogen atom or a lower alkyl group, for exa~ple an alkyl group containing l to 6 carbon atoms. The hydroxylic compound is preferably a compound of ! lO the formula RlOH, and is especially ~ater. We have found that 1,4-dioxane is particularly suitable for use as component ~b) of the solvent mixture. The alkylene carbonate which i8 component (c) of j the solvent mixture is preferably one in which the alkylene group contains two or three carbon atoms and may be, for example, propylene carbonate or ethylene carbonate.
Membranes can be for~ed by casting and coagulating the solution of the sulphonated polysulphone and divalent metal in the solvent mixture and it is preferred that the solvent mixture contains at least one component which has sufficient volatllity so that this component at least partially evaporates during the casting of the sol~tion, prior to immersing the cast film and support in the coagulatlon bath. It is al90 preferred that the salt of the sulphonated polysulphone has a reduced solubility in the residual solvent mixture which results as a consequence of the at leas~ partial evaporation of the volatlle component or components.
The solvent mixture may consist of four or more componen'ts but, Eor convenience of preparing the solvent mixture, it i8 preferred to minimise the number of components and hence the solve~t mixture typically consists of three components.
A wide range of solvent mixtures can be used. For sulphonated polyarylethersulphones as dlsclosed herein with reference to European Patent Specification No 8894, and the divalent metal salts thereof, we have obtained a solvent mixture having satisfactory characteristics from a mixture consisting of propylene carbonate, 1,4-dioxane and ~ater. This mixture suitably contains at least 15%
by weight o propylene carbonate, at least 15~ by weight of l,4-dioxane, and not more than 25% by weight o water, the total amounts

-10- H32942 of the three components aggregating to lOO% by weight. We particularly pre~er ~hat the mixture con~ains 5 to 20~ by wei~ht of water, 20 to 70% by weight of propylene carbonate and 20 to 66% by weight of 1,4-dioxane, the total amounts of the three components aggregating to 100% by weight.
The most suitable mixtures for any particular sulphonated material depend not only on the basic polymer struc~ure, that is the unsulphonated material, but also upon the sulphonation ratio of the polymer and also the nature of the metal salt produced. By sulphonation ratio we mean the ratio of the number of sulphonated phenylene residues in the sulphonated polymer to the number of unsulphonated phenylene residues in the sulphonated polymer. The sulphonation ratio can b~ determined by titration. In general, polymers having lower sulphonation ratios require solvent mixtures in which the value of delta-~ snd delta-P for the solvent mlxture is reduced. For the solvent mixture propylene carbonate, 1,4-dioxane and water, this is achieved with a mixture having a lower wster content and a higher 1,b~-dioxane content. The mo~t suitable mixtures for any glven sulphonated polymer and metal salt thereof can be readily ascertained by trial. Thus, we have found that with a sulphonated polyarylethersulphone and the barium salt thereof containing units II and III as specified herein, and essentially free of the units IV, in which the proportion of units II are such as to glve a sulphonation ratio of 1:10, the preEerred mixture oonsls~s of propylene carbonate, 1,4-dloxane and water in the weignt ratios of 5:3:1.
The solution may be prepared by dlssolving the sulphonated polysulphone, including the divalent metal qalt thereof 9 in any suitable form, for e~a~ple powder, chips, granules9 in the solvent ~i~ture to form a ~olution containing from 10% to 40~ by ~eight of the sulphonated polysulphone. Dissolution of the polymar may be effected at ambient temperature but lower or higher temperatures may be ~Ised if deslred.
The polymer which is dissolved in the solvent mixture may be added as the pre-formed divalent metal salt ~hereof. However, some of the divalent metal salts, for example the barium salts, are not readily soluble, or are insoluble in the solvent mixture.

J~

Solutions of such salcs can be ob~ained by dissol~Jing the sulphonated polysulphone, in ~he acid form, ln the solvent mixture and contacting the solution obtained with a compound of a divalent metal to form the deslred salt of the divalent metal and sulphonated polysulphone.
`` 5 The compound of a divalent metal is preferably a compound of a metal ~; of Group IIA of the Perlodic Table, such as magnasium or calcium, but we prefer to use a barium compound. The divalent metal compound may be an oxide, hydroxide or carbonate but other compound~ which ~ are capable of reacting wlth the sulphonic acid group may also be `~ 10 used. We have obtained ~embranes having a combination oE high salt re~ection at a high water flux using barium oxide as the metal compound.
Using a procedure in which the solutlon of the sulphonated polysulphone is reacted with a compound of a divalent metal, the compound of the divalent metal is preferably used in an amount sufficient to react with at least 25% oE the sulphonic acid groups in ehe sulphonated polysulphone. ~owever, it is particularly preferred to use the compound of the divalent metal in an amount sufficient ~o react ~ith at least 80%, and especially with essentially 1002, of the sulphonic acid groups.
The compound of the divalent ~etal is preferably added to the solu~ion of the sulphonated polysulphone in the stoichiometric ~ proportion to ensure essentially complete reaction. The reactlon; of the divalent metal compound wlth the solution contalnlng the sulphonated polysulphone may be effected at essentlally a~bient temperature but higher or~lower temperatures may be used if des,ired, ~or example in the range 0C to lOO~C.
The solution of the sulphonated polysulphone and divalent metal in the solvent mixture can be cast and coagulated to form a membrane.
More specifically, a sulphonated polysulphone in the acid form is dissolved in a solvent mixture containing a) at least one al~ylene carbonate;
b) at least one ethe~; and c) at least one hydroxyl compound selected from RlCOOH and Rloa~

~r~

the s~lution is contacted with a compound of a divalent metal to form a sal~ of the divalent me~al and the sulphonated polysulphone, any solid unreacted quanti~y of the compound of the divalent metal is separated from the solution, the solution is cast onto a support to form a film of the solution on the support, the film and support are immersed in a coagula~ion ba~h and a membrane is recovered wherein Rl is a hydrogen atom or a hydrocarbyl group.
The solution of the metal salt of the sulphonated polysulphone is formed into a membrane by casting on a support.
Ca~tlng onto the support may be effected at essentially ambient temperature but lower or higher temperatures ~ay be used if desirad.
The support may be for example a non-porous plane surface such as a gla~s or metal plate or, alternatively, may be a porous support such as a fabric and, where appropriate, it may have some other shape.
Sufficient of the solution is cast on to the support in conventional ~anner to give a film of the desired thickness which 0ay be ad~usted as necessary by suitable mechanical means. It is preferred to produce a film having a thickness of a~ least 20 micrometres and not more than 300 micrometres, most preferably from 50 up to 250 micro~etres, and especially from 75 up to 200 micrometres. Alternatively, fine hollo~
fibres may be produced by extruding the solution through a die having a cen~ral mandrel, allowing some of the solvent ~o evaporate and then pasQing the f~bres through a coagulation bath.
It is advantageous to allow at least partial evapora~lon of at least one component of the solvent mixture from the supported liquld fllm by exposing the latter to the atmosphere for a sho~t time, 10 seconds to 5 minutes, before immersing the supported film in a coagulatlon bath. The coagulation bath ~ay contain an aqueous solutlon, for example a solution of an inorganic salt such as sodium chloride or sodium nltrate, or may be a non-solYent liquld, or liquid mixture, for example formed from one or more of the components of the solve~t mixture. Preferably the coagulation bath is pure water.
The te~perature of the coagulation bath is generally between -20C
and 60C, and iq preferably about 0C. The coagulation treatment may be between 1 minute and several hours, for example between 5 and 60 minu~es.
After ~he coagulation treatment, a membrane is recovered.

In the case of a non-porous support, the membrane l~ detached from the support but ln the case of a porous support, the membrane remains adhered to the support. The recovered membrane may be subjected to heat treatment in order to relax the stru~ture. Such a treatment preferably lncludes an im~ersion in an aqueous solution of an inorganic salt at an elevated temperature, typically from 70C to 150C. This heat treament may be sffected wlth the membrane belng held under pre~sure (4 to 100 kN/m2), between porous supports such as porous graphite, sintered stainless steel or filter paper on a non-porous support. Once prepared, and after any heat treatment, the membrane is preferably washed with distilled water to remove free ; ionic species and is then stored in distilled water until required.
The ~embranes as prepared by casting are formed from the sulphonated polysulphone in the form of the divalent metal salt thereof. Ho~ever, if the coag~lation bath, and any subsequent heat treatment baths, contain an inorganic salt, ion exchange may occur between the divalent metal ions in the membrane and the ~etal ions in the ~olution.
Before being used for treatment of liquids, the membranes may ~e treated with a suitable acid to convert the salt of the sulphonated polysulphone into the acid form thereof, and it should be appreciated that the present invention is not restricted to the sulphonated polysulphone in the acid for~ or in the form of any specific metal salt.
To reduce the possibility of variations ln membrane properties, it is de3irable that all stages in the prepar~tion of the castlng solution and the ca~ting and coagulation steps are effected under carePully controlled conditions of time, temperature and humidity. During the cas~ing and subsequent evaporation, it is preferred that the humidity does not exceed about 65% relative humidity, for example in the range 35 to 50~ relative humidity.
Membranes obtained by the method of the invention may be used for ~he treat~ent of a wide variety of aqueous or non-aqueous solutions or suspensions by conventional reverse osmosls or ultra-filtràtion techniques. In particular, they may be used ~or thedesalina~ioQ of sea water and for the purifica~ion of brackish waters and industrial effluents~

-14- ~329~2 Membranes formed from qulphonated polysulphones are more resistant to the presence of agressive materials such as acids and alkalis. Hence, uslng membranes formed from sulphonated polysulphones, aqueous solutions may be treated in the presence of aggressive materials at levels which can cause deterioration of membranes for~ed from oeher materials such as cellulosics.
The accompanying drawing is a diagrammatic representation of a reverse o~mosis cell in which the membranes of the present invent-Lon may be used.
The cell comprises a closed vessel 1 which is divided lnto two sections internally by a membrane 2. The membrane 2 is in contact with a sheet 3 of a porous material for example filter paper, and sheet 3 is supported by a porous plate 4 which is not semi-permeable and which assists in preventing mechanical deformation of the membrane 2. The membrane 2, the sheet 3 and porous plate 4 are clamped at their edges to prevent leaking around the edges. The vessel 1 ~s ~` divided by the membrane 2 into a large section 5 and a small section`i 6~ The large section 5 is provided with two pipelines 7 and 8 for the supply and removal of liquid. The small section 6 is provided with a pipeline 9. In use, liquid under pressure, for example sea water at a pressure of 4MNm 2, is passed into section 5 of the vessel 1 through pipeline 7 and i~ withdrawn through pipeline 8.
The pressure is sufficlent to cause reverse osmosis and some water passes through the membrane 2 into the section 6 from which it is withdrawn through the pipeline 9. The apparatus can be operated at ambient temperature (about 25C) b~t higher temperatures may be~u~ed.
In a continuous process, a further pipeline may be connected to section 6 of the vessel 1 whereby a continuous Plow of a carrier liquid, which i9 the liquid being collected, is passed through section 6. Other modifications and variations may be effected in the manner k~own to those skilled in the are.
It is preferred ~hat the ~embrane possesses a combination of high salt rejection (at least 90%) at a high water flux tat leas~ 1 m.day~~ owever, ~or some applications, for example dewaterlng, a lower salt re~ection can be tolerated and hence it is not essential for such applica~ions that the membrane used does provide such a combina~ion of salt rejection and flux characteristics.

-15~ H32942 Various aspects of the present invention are lllustrated, but not limited, by the following Examples, in which all parts and percentages are by weight unless otherwle indicated.

A sulphonated polyarylethersulphone copolymer as described in European Patent Publication No 8894, containing 33% mole of units II in which Ph is a para-phenylene residue and M is a hydrogen atom, 67~ mole of units III, having a sulphonation ratio of 1:10, and a reduced viscoslty (as defined herein) of 0.82, was dissolved, 10 at a tempera~ure of 25C, in a 5:3:1 parts by weight propylene carbonate/1,4-dioxana/water mixture to give a 25~ parts by we~ght solution of the copolymer in the solvent mixture.
Barium oxide ~B~ Technical Grade, of purity greater than 95~ and particle size less than 10 micrometres) was added ~o the solution in the stoichiometric amount required to convert the sulphonic acid groups into the corresponding barium salt form. The mixture was stirred at 25C for 10 hours by which time all of the solid barium oxide had dissolved. The solu~ion was filtered through a gauze with a mesh size of 30 mlcro~etres and then centr~fuged a~ 2000 rOp.m. for 20 to 30 minutes.
The solution obtained was cas~ on to a glass plate and the thickness of the film was adjusted manually using a brass spreader bar. rhe film so formed was exposed to the atmosphere at the ambient ~emperature for one ~inute before being coagulated by immersion in distilled water at 0C for 30 minutes. The membrane was washed with distilled water and then stored in distilled water until tested.
The membrane was tested using an apparatus of the type here-inbefore described and in which the membrane was placed in contact with a porous support and the exposed side, being the side exposed to the air during casting, was subjected to a co~inuous feed of 0.2 aqueous sodium chloride solution pumped across the surface of the membrane at a pressure of about 4MNm 2 and a ~emperature of 25C.
The liquid passing through the membrane was analysed.

The procedure of Example 1 was repeated with the difference that calcium oxide (Example 2) or magnesium oxide (Example 3) were used rather than barium oxide.

16- ~32942 COMPARAl'IVE EXAMPLES A AND B
The procedure of Example 1 was repeated with the dlfference ~ha~ no metal compound was used (Comparative Example A) or aluminlum oxide was used (Comparative Example B).
The results of tes~ing the ~embranes of Examples 1 to 3, and the Co~parative Examples are given in Table One.
. .
TABL~ ONE
':' .. __ ~ , , , _ , Example or S.R. Flux Co~parative (%~ (m.day 1) 10 Example (a) (b) .`' ~ __ __ 1 95 ~.4 2 93.7 0.18 3 87.3 0.47 A 88 0.27 No~es to Table`One (a) S.R. is Z sal~ re~ection and i8 determined measuring the " conductivity of tbe solution fed to the membrane cell and by measuring ,1 the cond1lctivity of the solution permeating the membrane and u~ing 20 the relation~hip:-% sal~ reJection - ~1 ~ )x 100.
' ~ conductivity of feed (b) Flux is the volume tin m3) of the solution which passes through a membrane area of one m2 in one day and i5 expressed as m.day 1.

A sulphonated polyarylethersulphone copoly~er as described in ~xample 1 was dissolved, at a eempera~ure of 25C, in a 5:3:1 parts by weight propylene carbonate/1,4-dioxane/water migture ~o gi~e a 26.6% by weight solution of ~he copolymer in the solvent mixture.
Barium oxide taS used in Example 1) was added to the solution in an amount calculated to give complete reaction with the sulphonic acld groups. The mixture was stirred at 25C for 10 hours by which time all of the solid barium oxlde had dissolved. The solution was .

Eiltered and centri~uged as in Ex~mple 1.
The produc~lon of a membrane from the solution was efEected inside a cabinet in which humidlty and te~perature were controlled.
The solution was c~st on ~o a glass plate, and the ~hickness of the film formed on the plate was adjusted ~anually using a brasR
spreader bar. This operation required from 3 to 12 seconds to complete .
After 60 seco~d~ evaporation in alr of known humidity, coagulation of the fil~ was affected by immersion for 20 minute~ in water a~ about 1C.
The ~ecovered membrane was washed, ~tored and te~ted as de~cribed in Example 1. Further details of the me~brane preparation conditioQs, and the results of testing the membranes produced, are summari~ed in Table T~o.
TABL~ TW0 I , ... _ ____ __ . ___ Production Con~ litio~s Membrane Properties Example Ca~t ng Quench Thick~ess S.R. Flux M.~.
Humidi~y Temp Temp (~) (C) (C) (m-6~ (a) (~) (b) (mday~l) (c) _ . _ .
4 39 21.5 0.8 86 93.5 1.1 0.17 43 21.5 1.0 87 94.2 1.55 0.27 6 45 21.5 0.3 76 97.3 1.36 0.50 7 47 22 0.8 131 97.8 1.19 0.54 8 47.5 22 0.9 94 98~6 0.85' 0.61 9 ~5 ~2 0.8 149 98.8 0.79 0.66 44 2~ 0.7 102 95.5 1.34 0.30

11 44 22.5 1.0 61 96.7 0.8 0.24

12 43.5 23 0.6 200 95~4 1.0 0.22

13 40.5 22.5 0.6 120 96.3 1.66 0.45

14 41.5 22 0.5 50 95.4 O.g6 0,21 IS* 41.5 19.5 0.6 90 97.3 0.93 0.34 16* 41.5 19.5 ~.6 96 93.3 1.42 0.21 17* 41 20 0.5 170 94.3 loO 0.18 18* 42 20 0.5 88 96 1.0 0.25 19* 42 20 0.8 116 90.6 2.2 0~23 20~ 43 20 0.7 109 98.3 0~9 0.53 ~2~
-18~ ~32942 Note3 to Table Two (a) and (b) are aR defined in Notes to Table One.
(c) M.F. is the ~embrane factor and i8 given by the relationship Flux (in m.day 1) (100 - % qalt re~ection) In the Examples marked *, the barium salt was prepared the day before casting was carried ou~, in the remaining Examples the barium salt was prepared and the solution was cast on the same day.
EXAMPLES 21 A~D 22 The procedure of Examples 4 to 20 was repeated using zinc oxide (Example 21) or bariu~ oxide (~xample 22). Casting was affected at a humidity of 62% and a temperature of 20.5~C. For co~parlson (Co~parative Example C), the procedure wa~ repeated with the exception that a pre-formed sodium salt of the sulphonated polysulphone was used rathar than the acid form of the sulphonated polysulphone ~ith subsequent addition of the metal oxlde. The membrane thickness was 0.15m~.
The results obtained ar~ Ret out in Table Three.
TABLE THR~E

~xampleS.R. Flu~
or Comp.(a) (b) Example (Z~ (m.dayl) .
21 67.2 0.72 22 93.0 0.74 ........ 32.8 1.78 Notes to Table Three (a3 and (b) are a~ defined in Notes ~o Table One.
~AMPLES 23 AND 24 A sulphonated polyarylethersulphone copolymer a8 described in European Patent Publication No. 8894, contalning 40 mole % of uni~s -l9- ~329~2 II and 60 mole % of units III, having a sulphonation racio of 1:8 and a reduced viscosity of 1.54 was dissolved~ at a temperature of 25C, in a 5:3:1 parts by weight propylene carbonate/1,4-dioxane/water mixture.
The ~olutions obtained were reacted with barium oxide, formed into membranes 0.l5mm thic~ and tested as in Examples 4 to 20, further details being give~ in Table Four.
TABLE FOUR
~.~
~:: ~ .. ___ . . . __ C.S. Casting Cor ditlons Memb ~ es 10 Example co~cn ~umidity Temp. S.R. Flux M.F.
_ (d) (g) (C) (a)(b) .: (%) (%)(m.day~l) (c) .. _ , . , .. __ _ ....
23 20 66 21 94.3 1.0 0.18 24 ~6 80 22 .5 94.7 0.~9 0.035 Notes to Table ~our (a) and (b) are as defined in Notes to Table One.
. (C) i9 as defined in Notes to Table Two.
(d) C.S. concn 1~ the concentration in welght %, of the sulphonated polarylether~ulphone copolymer, dlssolved in the solution.

Membranes were produced as described in ~xa~ples 4 to 20, at a humidity of 65Z and a temperature of 21C. The membranes were 0.15mm thick. As in Che preceding Examples, the membranes were not heat treated.
The membranes were tested, immersed in various solutions for several days and tested once more. For the purposes of co~parlson tests were also carrled out on a commercially available cellulose acetate membrane which, as supplied, had been su~jected to a heat treatment.
The results of the tests are set out in Table Five.

~Z~iZ~
-20- ~32942 TABL~ FIV~
-j. . . ~ . _ ., ~ample ~embrane Soln Time S.R, Flux or Comp. ~aterial (days) ~a) (b) Exa~ple (e) 'f' (h) (%) (m.day 1 ~ . -- _.
SPS Cl2 91.5 0.42 26 SPS Cl2 856.7 0.39 27 SPS HCl O97.5 0.57 28 SPS ~Cl 680 0,49 29 SPS NaO~ O9408 0.42 lQ 30 SPS NaOH 660.9 0.65 31 SPS NaCl O91.7 0.59 32 SPS NaCl 664.1 0.51 D CA Cl2 O88.0 2.32 E CA C12 988.7 1.73 F CA ~Cl O81.8 2.56 G CA ~Cl 6 O N.D.
CA NaO~ O82.6 2.89 I CA NaOH 6 O N.D.
_ . . .. _.
Notes to Table Five -(a) and (b) are aff defined in ~ote3 to Table One (e) SPS i8 the sulphollated polyarylethersulphone copolymer of ~xample 1.
C~ is a commercially available cellulose acetate membrane (f) Cl2 is water containing 100 p.p.m. of di~solved chlorine ~Cl is IN hydrochloric acid NaOH is lN aqueous ~odium hydroxide solutioa NaCl i~ a 0.2% by weight aqueou~ solution of sodium chloride.
~h) O indicate~ the test was effected before immar~lng the membrane in the test ~olution.
6, 8 and 9 indlcate that the test was effected after im~ersing the me~brane ln the ~est solution for the number of days indicated.
N.D. indicates Chat the quantity was not determined~

Claims

1. An asymmetric semi-permeable membrane wherein the support layer and the active layer are both formed from the same sulphonated polyarylethersulphone wherein the membrane has a salt rejection and flux which are such that the ratio has a value of at least 0.05.

2. The membrane of claim 1 wherein the ratio has a value of at least 0.1.

3. The membrane of claim 2 wherein the ratio has a value of at least 0.5.

4. The membrane of claim 1 whereof the sulphonated polyarylethersulphone contains repeat units of the formula wherein Ph is a phenylene residue and at least some of the groups Ph have one or two groups -SO3M;
m is 1 or 2 and the value of m can differ along the polymer chain;
M is a hydrogen atom, a metal atom or a group NR4, wherein the groups M may be the same or different and the proportion of the groups M is sufficient to combine with the the unsatisfied valencies of the groups -S03; and R is an alkyl group.

5. The membrane of claim 4 whereof the sulphonated polyarylsulphone contains repeat units of the formula II together with the repeat units wherein Ph1 is a phenylene residue;
Ph2 is a phenylene residue having one or two groups -SO3M; and M is a hydrogen atom, a metal atom or a group NR4, wherein the groups M may be the same or different and the proportion of the groups M is sufficient to combine with the unsatisfied valencies of the groups -SO3; and R is an alkyl group.

6. The membrane of Claim 5 whereof the sulphonated polyarylsulphone contains additionally repeat units IV wherein Ph1 is a phenylene residue.

7. A sulphonated polysulphone derivative containing repeat units of the formula V together with the repeat units of the formula III and repeat units of the formula IV wherein Ph1 is a phenylene residue;
Ph3 is a phenylene residue having one or two groups SIAM
M1 is a divalent metal in a proportion sufficient to combine with the unsatisfied valencies of the groups -SO3; and repeat units IV are present in the molar proportion of 0 to 25% molar of the units IV and V.

8. The sulphonated polysulphone derivative of claim 7 wherein M1 is barium.

9. A solution containing a sulphonated polyarylethersulphone and a divalent metal in a solvent mixture containing a) at least one alkylene carbonate;
b) at least one ether; and c) at least one hydroxyl compound selected from R1COOH and wherein R1 is a hydrogen atom or a hydrocarbyl group.

10. The solution of claim 9 wherein the solvent mixture contains propylene carbonate, 1,4-dioxane and water; the sulphonated polyarylethersulphone contains repeat units of the formula II together with the repeat units III wherein Ph1 is a phenylene residue;
Ph2 is a phenylene residue having one or two groups -SO3M;
M is a hydrogen atom, a metal atom or a group NR4, wherein the groups M may be the same or different and the proportion of the groups M is sufficient to combine with the unsatisfied valencies of the groups -SO3; and R is an alkyl group; and the divalent metal is barium.

11. The solution of claim 10 wherein the solvent mixture contains at least 15% by weight of propylene carbonate, at least 15%
by weight of 1,4-dioxane and not more than 25% by weight of water, the total amounts of the three components aggregating to 100% by weight.

12. A process for producing n solution containing a sulphonated polyarylethersulphone and a divalent metal which comprises dissolving a sulphonated polarylethersulphone, in the acid form, in a solvent mixture containing;

a) at least one alkylene carbonate;
b) at least one ether; and c) at least one hydroxyl compound selected from R1COOH and R1OH, and contacting the solution obtained with a compound of the divalent metal wherein R1 is a hydrogen atom or a hydrocarbyl group.

13. A process for the production of a membrane which comprises casting onto a support the solution of claim 9 immersing in a coagulation bath, the cast film of the solution on the support, and recovering a membrane from the coagulation bath.

14. The process of claim 13 wherein the supported cast film is exposed to the atmosphere for from 10 seconds to 5 minutes and then immersed is the coagulation bath.

15. A process for the desalination of sea water, or for the purification of brackish waters and industrial effluents, by effecting reverse osmosis or ultrafiltration using the membrane of claim 1,

16. A reverse osmosis or ultrafiltration apparatus comprising a membrane as defined in claim 1.