NZ228443A

NZ228443A - Chlorine resistant semi-permeable membrane

Info

Publication number: NZ228443A
Application number: NZ22844389A
Authority: NZ
Inventors: Chinh N Tran; Hong C Chu; William G Light
Original assignee: Allied Signal Inc
Priority date: 1989-03-21
Filing date: 1989-03-21
Publication date: 1990-09-26

Description

<div id="description" class="application article clearfix"> New Zealand Paient Spedficaiion for Paient Number £28443 22 8 4 4 3 NO ?a p I Sag Priority Date(s); Complete Specification Filed: VAT> Classy Oi • /•/ ........ 5 /cP/. t S. .&QlD)ayb.<V.».. Publication Date: .... P. J95I .. ;i3S5>: «?■ P.O. Journa!, No: N. Z. No . " ' NEW ZEALAND ■* ?*%, Patents Act 1953 COMPLETE SPECIFICATION CHLORINE-RESISTANT SEMIPERMEABLE MEMBRANES : \ .Tts - We, ALLIED-SIGNAL INC./ a corporation organized under the laws of the State of Delaware, United States of America having a principle business at Columbia Road and Park Avenue, Morris Township, Morris County, New Jersey, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- - 1 - (Followed by 1A) 22 8 4 4 3 \k CHLORINE-RESISTANT SEMIPERMEABLE MEMBRANES BACKGROUND OF THE INVENTION The separation of various components found 1n liquids or 5 gases may be effected 1n a multitude of processes, the techniques for effecting the separation utilizing asymmetric or composite membranes Including selective permeation, ultrafiltration or reverse osmosis. A particular example of the latter type of separation involves a desalination process 1n which water which 1s 10 rendered potable or suitable for other purposes is obtained from sea water, contaminated water, brackish water or brine. This process 1s of especial value in areas of the world where the water found 1n the area 1s brackish or 1s saline 1n nature. The desalination of this water 1s necessary 1n order to provide large 15 amounts of potable or relatively nonsalty water for industrial, agricultural or home use. The desalination of the water is effected by forcing the water through a reverse osmosis membrane whereby the purified water 1s passed through the membrane and recovered, while the contaminants or salts do not pass through the 20 membrane, thus, In effect, being rejected by the membrane and recovered as the retentate. A reverse osmosis membrane, 1n order to be utilized for such a purpose, must possess certain characteristics applicable to the process. For example, the membrane must have a very high salt 25 rejection coefficient. In addition, another Important characteristic and a problem which must be addressed when utilizing the membrane, 1s the ability of the membrane to be resistant to chlorine attack. Another Important factor which 1s present 1n the use of a reverse osmosis membrane 1s that said membrane also 30 possess a high flux characteristic, that 1s, the ability to pass a relatively large amount of water through the membrane at relatively low pressures. If a membrane possesses these desirable characteristics, 1t will be commercially feasible 1n its applicability to the desalination process. 228443 Reverse osmosis membranes have been prepared and used from a wide variety of known polymeric materials. While many of these polymeric materials possess the ability of reducing the concentration of a solute to where the salt rejection capability 1s 1n 5 excess of 98SC, some do not possess the necessary flux rate whereby the volume of water which is required to be produced by the membrane per unit of membrane surface 1s sufficient for the application of the technology. As was hereinbefore set forth, many prior U.S. patents 10 describe various membranes which are useful 1n desalination processes. For example, U.S. Patents 3.567,632, 3,600,350, 3,710,945, 3,878,109, 3,904,519, 3,920,612, 3,951,815, 3,993,625 and 4,048,144 Illustrate various semipermeable membranes prepared from polyamldes. Likewise, U.S. Patents 3,260,691 and 3,480,588 15 disclose coating compositions which are obtained from the condensation products of aromatic primary diamines and aromatic tricarboxylic acid derivatives. Inasmuch as the semipermeable membrane which is used for the desalination process should be relatively thin in nature in order 20 to provide a desirable flux rate, it is necessary, 1n many Instances, that the reverse osmosis membrane be composited or laminated on a porous backing support material. This porous support backing material should 1n Itself possess certain characteristics which make 1t desirable for such a use. For 25 example, the porous support material should possess pore sizes which are sufficiently large enough so that the water or permeate can pass through the support without affecting or lessening the flux rate of the entire composite. Conversely speaking, the pore size should not be large enough so that the thin composite 30 semipermeable membrane will tend to fill up or penetrate too far Into the pores, thus distorting the shape of the thin film membrane with the attendant possibility of rupturing the membrane when operated under high pressure, thus causing said membrane to lose Its effectiveness in the reverse osmosis process. 35 In addition to the aforementioned U.S. patents, another U.S. Patent, namely 4,277,344, discloses an interfacial synthesized 228443 3 reverse osmosis membrane. This membrane 1s prepared from an 1nterfac1ally polymerized aromatic polyamlne which has been prepared from an essentially monomerlc polyacyl hallde and an essentially monomerlc arylene polyamlne. The composite membrane 5 1s prepared by coating a support material with a liquid layer comprising an aqueous solution containing the polyamlne reactant, contacting the liquid layer with essentially monomerlc volatHlzable polyfunctlonal acyl hallde dissolved in a liquid aliphatic or liquid halogenated aliphatic solvent and drying the 10 product formed thereby to form the desired membrane. In addition, the membrane may then be treated with an oxidizing agent and chlorine or a chlorine releasing agent to Improve its chlorine resistance. The patent teaches that the membrane contains a plurality of sites having the formula: 15 Ar(COHH-)2COOH in which Ar represents the aromatic nucleus residue of the polyfunctlonal aryl hallde. In addition, the membrane 1s 20 described as being lightly cross-linked 1n nature. The reaction 1s effected 1n the absence of any surface active agents and acid acceptors, the patentee stating that these compounds do not appear to provide any advantages 1n the context of the Invention and that 1t 1s preferred to carry out the interfacial polymerization 25 without the presence of surface active agents or acid acceptors. Furthermore, the structure of the membrane will be dependent upon the water provided for 1n the aqueous solution to serve as a reactant and states that the aryl hallde groups on the polyfunctlonal aryl hallde are 1n a competitive state during the 30 reaction with the aqueous solution of the polyamlne. The patentee theorizes that the acyl hallde groups can react either with water or with the primary amine groups or conversely that a sequential reaction occurs 1n which hydrolysis precedes condensation with an amine group. 22 8 4 4 SUMMARY OF THE INVENTION This Invention relates to composite membranes comprising of a permselectlve barrier on a porous support. More specifically, the Invention 1s concerned with membranes which exhibit an extensive 5 resistance to chlorine and oxidants degradation, a superior degree of solvent permeation rate and a superior degree of solute rejection. As was previously discussed, the use of membranes for the separation of gas from a gaseous mixture, liquid from liquid 10 mixture, gas from liquid mixture or sol Ids from liquids are important articles of commerce. This 1s especially true 1n the area of separation whereby water which is brackish or saline in nature or having other solid and/or organic materials dissolved therein may be rendered potable or suitable for use 1n other 15 Industrial or agricultural regions by passing the water through separation (permselectlve) membranes. The particular membranes which constitute the Inventive feature of the present application will comprise the reaction product resulting from the reaction of an aromatic polyamlne and an aromatic polycarboxyllc acid 20 chloride, said membrane being composited or coated on a porous support backing material. By utilizing these membranes 1n a separating (desalination) process, 1t 1s possible to treat water source over a relatively long period of time without replacement of the membrane, the long life of the membrane being, in part, due 25 to the resistance to degradation resulting from exposure to chlorine or other oxidizing agents are present in the water source. It 1s therefore an object of this Invention to provide a composite membrane, suitable for use 1n separation processes, 30 which possesses desirable characteristics. A further object of this invention 1s to provide a process for preparing a semipermeable membrane which 1s resistant to chlorine and other oxidizing agents, thus rendering the membrane suitable for use 1n separation processes such as desalination of 35 water where chlorine or other oxidizing agents are present 1n an amount sufficient to degrade other types of membranes. 22 8 4 4 3 5 In one aspect, an embodiment of this invention resides in a chlorine-resistant semipermeable membrane prepared by casting an aqueous solution of an aromatic polyamine which contains a polyhydrlc compound on a porous support backing material, removing 5 excess solution, contacting the coated porous support material with an organic solvent solution of an aromatic polycarboxylic acid hallde to form an Interfacial condensation reaction product on the surface of said porous support material, curing the resultant composite at curing conditions to form said chlorlne-10 resistant semipermeable membrane. A further embodiment of this Invention 1s found 1n a process for the preparation of a chlorine-resistant semipermeable membrane which comprises casting an aqueous solution of an aromatic polyamlne which contains a polyhydric compound and an acid 15 acceptor on a porous support backing material, removing excess solution, contacting the coated porous support material with an organic solvent solution of an aromatic polycarboxyllc acid hallde to form an interfacial condensation reaction product on the surface of said porous support material, curing the resultant 20 composite at curing conditions, washing the cured membrane with an alkaline compound at an elevated temperature and pH, leaching the washed composite at an elevated temperature with sodium bisulfite, treating the leached composite with a polyhydrlc compound, and recovering the resultant chlorine-resistant semipermeable 25 membrane. A specific embodiment of this invention is found 1n a chlorine-resistant semipermeable membrane prepared by casting an aqueous solution of m-phenylened1amine, said aqueous solution containing ethylene glycol and sodium carbonate on a polysulfone 30 backing material, removing excess solution, contacting the coated polysulfone with a naphtha solution of trimesoyl chloride, curing the resultant composite at a temperature in the range of from about 20° to about 150°C for a period of time in the range of from about 10 minutes to about 2 hours, subjecting the composite to 35 treatment with sodium carbonate at a temperature in the range of from about 20° to about 100°C at a pH in the range of from about 9 22 8 4 4 3 6 to about 11, leaching the treated membrane with sodium bisulfite at a temperature 1n the range of from about 20° to about 100°C. The leached membrane can be further treated with glycerine, or heat at 20°-1006C. 5 Other objects and embodiments will be found 1n the following further detailed description of the invention. DETAILED DESCRIPTION OF THE INVENTION As hereinbefore set forth, the present Invention 1s concerned 10 with semipermeable membranes which are resistant to chlorine and to a method for preparing these membranes. The membranes are prepared by casting an aqueous solution of an aromatic polyamlne on a porous backing support material, removing excess solution by drawing, rolling, sponging, air knifing or other suitable 15 techniques, and thereafter contacting the coated support material with an organic solvent solution of an aromatic polycarboxylic acid hallde. The organic solvent which is used to prepare this solution of the aromatic polycarboxyllc add hallde 1s Immiscible or sparingly mlsdble with the aqueous solution, thus permitting 20 the formation of an interfacial polymerized condensation reaction product onto the surface of the support material. The resulting composite 1s then cured to provide a semipermeable membrane which exhibits favorable characteristics with respect to salt rejection and flux as well as resistance to chlorine. 25 As was previously discussed, a membrane of this type 1s set forth 1n U.S. Patent 4,277,344. This membrane was described as containing a plurality of sites having the formula: Ar(C0NH-)2C00H 30 1n which Ar represents the aromatic nucleus residue of the polyfunctlonal aryl hallde utilized as one component thereof. It has now been discovered that by utilizing an aromatic polyamlne in an aqueous solvent solution which contains a polyhydrlc compound 35 and an acid acceptor in which the pH of the aqueous solution is kept in a range of from about 9 to about 11 will, when contacted 22 8 4 4 3 7 with an organic solvent solution of an aromatic polycarboxyllc acid hallde, result in the formation of a membrane which exhibits superior performances 1n term of permeation rate and separation characteristics over the membranes made according to the teaching 5 of U.S. Patent 4,277,344 which did not utilize polyhydrlc compounds. An additional difference between the membrane of the present Invention and the membrane of U.S. Patent 4,277,344, is that due to the high pH of the reaction medium and use of an add acceptor, any COOH units will be present in the salt form as 10 carboxylates rather than undissociated carboxyllc acid forms. In one embodiment, the chlorine resistant semipermeable membranes of the present Invention may be prepared by coating a porous support backing material with an aqueous solution of the aromatic polyamlne, said aqueous solution being of a composition 15 hereafter set forth 1n greater detail. The porous support backing material comprises a polymeric material containing pore sizes which are of sufficient size to permit the passage of permeate therethrough, but are not large enough so as to Interfere with the bridging over of the resulting ultrathln reverse osmosis 20 membrane. In the preferred embodiment of the Invention, the pore size of the porous support backing material will range from about 1 to about 5,000 millimicrons inasmuch as pores which are larger 1n diameter than 5,000 millimicrons will permit the ultrathln reverse osmosis membrane to sag Into the pore, thus disrupting the 25 flat sheet configuration which 1s a desirable characteristic of the membrane. Examples of porous support backing materials which may be used to prepare the desired membrane composite of the present Invention will Include such polymers as polysulfone, polycarbonate, mlcroporous polypropylene, the various polyamldes, 30 polylmlnes, polyphenylene ether, various halogenated polymers such as polyvinyl1d1ne fluoride, etc. The porous support backing material may be coated utilizing either a hand coating or continuous operation with an aqueous solution of monomerlc polyamlnes or to render the resulting 35 membrane more resistant to environmental attacks, of monomerlc substituted polyamlnes. These monomeric polyamlnes may comprise 228443 8 cyclic polyamlnes such as plperazlne, etc.; substituted cyclic polyamlnes such as methyl plperazlne, dimethyl plperazine, etc.; aromatic polyamlnes such as m-phenylened1am1ne, o- phenylenedlamlne, g-phenylenedlamine, etc.; substituted aromatic 5 polyamlnes such as chlorophenylenedlamine, N,N'd1methy-l,3 phenylenedlamine, etc.; multl-aromatic ring polyamlnes such as benzidine, etc.; substituted multi-aromatic ring polyamlnes such as 3,3'd1methylbenz1d1ne, 3,3'd1chlorobenz1d1ne, etc.; or a mixture thereof depending on the separation requirements as well 10 as the environmental stability requirements of the resulting membranes. The solution which 1s utilized as the carrier for the aromatic polyamlne will comprise water 1n which the aromatic polyamlne will be present 1n the solution 1n an amount 1n the range of from about 0.1 to about 5% by weight of the solution. 15 Another component of the aqueous solution will Include polyhydrlc compounds such as ethylene glycol, propylene glycol, glycerine, other longer carbon atom backbone glycols, I.e. (C^-C^). polyethylene glycol, polypropylene glycol, copolymers of ethylene glycol and propylene glycol, etc. used singly or mixed with each 20 other. The aqueous solution may also contain basic acid acceptors such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc. The polyhydrlc compound may be present 1n the aqueous solution 1n amounts ranging from about 5 to about 902 while the acid acceptor may be present 1n a relatively small 25 amount ranging from about 5 to about 500 parts per million. Furthermore, the pH of the aqueous solution 1s maintained 1n a relatively high range of from about 9 to about 11. After coating the porous support backing material with the aqueous solution of the aromatic polyamlne, the excess solution 1s 30 removed by suitable techniques previously discussed and the coated support material 1s then contacted with an organic solvent solution of the aromatic polycarboxyllc acid hallde. Examples of aromatic polycarboxyllc acid halldes which may be employed will Include d1- or tricarboxylic acid halldes such as trlmesoyl 35 chloride (1,3,5-benzene tricarboxylic acid chloride), Isophthaloyl chloride, terephthaloyl chloride, trlmesoyl bromide (1,3,5-benzene 22 8 4 4 3 9 tricarboxylic acid bromide), Isophthaloyl bromide, terephthaloyl bromide, trlmesoyl Iodide (1,3,5-benzene tricarboxylic acid Iodide), Isophthaloyl iodide, terephthaloyl Iodide, as well as mixtures of d1-tr1, tr1-tr1 carboxyllc acid halldes, that 1s, 5 trlmesoyl hallde and the Isomeric phthaloyl halldes. The di- or tricarboxylic acid halldes may be substituted to render them more resistant to further environmental attack. Again, in the preferred embodiment of the Invention, the aromatic polycarboxyllc acid hallde 1s present 1n the organic solvent solution 1n a range 10 of from about 0.01 to about 5* by weight of the solution. The organic solvents which are employed 1n the process of this Invention will comprise those which are Immiscible with water, Immiscible or sparingly mlsdble with polyhydrlc compounds and may comprise paraffins such as n-pentane, n-hexane, n-heptane, 15 cyclopentane, cyclohexane, methylcyclopentane, naphtha, etc. or halogenated hydrocarbon such as the freon series or class of halogenated solvents. It 1s to be understood that the above listing of polyhydrlc compounds, acid acceptors, aromatic substituted and unsubstituted polyamlnes, aromatic polycarboxyllc 20 acid halldes and organic solvents are only representative of the class of compounds which may be employed, and that the present Invention 1s not necessarily limited thereto. Inasmuch as the organic solvent and the aqueous solvent mixture for the aromatic polyamlne are substantially Immiscible or 25 Incompatible, the polymerization of the two components of the membrane will occur substantially only at the Interface between the solvent phases and thus an 1nterfac1ally polymerized reaction product comprising a thin film membrane will be formed thereat. The contact time required for the formation of the thin film 30 membrane will fluctuate over a relatively wide range of from about 1 second to about 60 seconds. Following the formation of the Interfacially polymerized reaction product on the surface of the porous support backing material, the resultant composite may be cured to remove any remaining solvent and reactants and firmly 35 affix the thin film membrane on the surface of the support. The curing of the composite membrane may be effected over a wide 22 8 4 4 3 10 temperature range, said temperature being from ambient (20o-25°C) up to about 150°C for a period of time ranging from about 1 minute to about 2 hours or more 1n duration. The operating parameters of time and temperature will be Interdependent, the primary criteria 5 for the curing of the membrane being that said curing time is sufficient to provide the desired membrane but being insufficient to affect the desired characteristics of the thin film membrane and the porous backing support material. For example, excessive heat or curing time may affect the pore size of the backing 10 material, thus resulting in a decrease of the desired flux rate of the membrane. The composite of chlorine-resistant membrane 1s then subjected to a post treatment 1n which the membrane 1s subjected to a wash utilizing an aqueous solution of a basic material at a 15 pH in the range of from about 9 to about U. The basicity of the solution 1s afforded by the presence of a basic compound such as sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, etc. The wash 1s effected at a temperature which may be in the range of from 20 about 20° to about 100°C for a period of time in the range of from about 1 to about 15 minutes. Following the wash of the membrane, 1t 1s then subjected to a leaching step 1n which any unreacted aromatic polyamlne which may still be present on the membrane will be removed. The removal of 25 the polyamlne 1s effected inasmuch as the amine may tend to oxidize and discolor the membrane as well as causing a subsequent handling problem of the membrane downstream 1n the equipment. The leaching of the unreacted aromatic polyamlne 1s effected by treating said membrane with a substance such as sodium bisulfite 30 at a temperature 1n the range of from about 20° to about 100°C again for a period of time 1n the range of from about 1 to about 5 minutes. In the preferred embodiment of the Invention the sodium bisulfite 1s present 1n the leached solution 1n a range of from about 0.5 to about 12. Additional leaching substances which may 35 be utilized will include organic acids such as sulfamic acid or mineral acids such as nitric acid, etc. 22 8 4 4 3 11 Following the leaching treatment, the chlorine-resistant semipermeable membrane is then further treated with a polyhydrlc compound such as glycerine which may be present in a range of from about 10 to about 502 V/V in order to protect the thin film 5 membrane from damage 1n handling as well as preventing the membrane from drying out, the latter leading to a loss of performance of the membrane when used 1n a separation process. It is contemplated within the scope of this Invention that chlorine-resistant semipermeable membranes may be prepared 1n a 10 continuous manner of operation. When this type of operation 1s employed, a porous support backing material of the type hereinbefore set forth 1n greater detail 1s continuously passed through a bath of an aqueous solution of the aromatic polyamlne which contains the polyhydric compound and acid acceptor. After 15 passage through the bath, the backing material is continuously withdrawn and the excess solution which may be present 1s removed by suitable techniques. The coated support material 1s then also continuously passed through the organic solvent solution of the aromatic polycarboxyllc acid hallde. The Interfacial 20 polymerization reaction will occur during the contact time by the solutions following which the composite comprising the interfacial polymerized reaction product in the form of a thin film semipermeable membrane on the surface of the porous support backing material will then be cured as, for example, by passage 25 through an oven which 1s maintained at the desired curing temperature, the passage through said oven being at a predetermined rate so as to avoid any possible damage to the composite membrane. Thereafter, the membrane 1s continuously withdrawn from the curing oven and continuously passed through the 30 washing, leaching and coating zones for the post treatment, and the desired membrane is subsequently recovered. The resultant chlorine-resistant semipermeable membrane may then be employed for the separation process desired such as the desalination of sea water or brackish water, other treatments of 35 water such as softening of hard water whereby salts are removed, boiling said water treatment, concentration of whey or fruit 12 22 8 4 4 3 juices, etc. The membranes which are 1n the form of flat sheets are particularly applicable for use in modules either 1n single sheet or multiple sheet units whereby the sheet or sheets are wound 1n a spiral type configuration. 5 The following examples are given for purposes of Illustrating the novel chlorine-resistant semipermeable membranes which have been prepared according to the process hereinbefore set forth and to the use thereof as separation agents. However, it is to be understood that these examples are provided merely for purposes of 10 Illustration and that the present invention 1s not necessarily limited thereto. EXAMPLE I 15 A chlorine-resistant semipermeable membrane was prepared by passing a sheet of porous polysulfone through an aqueous solution containing 256 by weight of m-phenylenediam1ne, 70 ppm of sodium carbonate and 52 by volume of ethylene glycol. The polysulfone sheet was 1n contact with the solution which had a pH of 9.85 for 20 a period of 30 seconds. The membrane now loaded with aqueous solution mixture was air dried at room temperature for a period of 15 minutes and thereafter was passed through a naphtha solution containing 0.152 by weight of trlmesoyl chloride for a period of 15 seconds. The membrane composite was then dried at a 25 temperature of 21.7°C 1n air for a period of 23 minutes. The post treatment of the membrane was effected by washing the membrane with a sodium carbonate solution which had a pH of 10.0 for a period of 5 minutes at room temperature. The leaching step of the post treatment was effected by treating the membrane 30 with a sodium bisulfite solution for a period of 5 minutes at a temperature of 40°C. Finally the membrane was coated with a 202 solution of glycerine. This membrane was designated as membrane A. 22 84 13 EXAMPLE II A second membrane was prepared 1n a manner similar to that set forth in Example I above by passing a sheet of polysulfone 5 through an aqueous solution of m-phenylened1 amine which was present 1n an amount of 2.12 by weight, said solution containing 70 ppm of sodium carbonate and 202 by volume of ethylene glycol, the pH of the solution being maintained at 9.4. The polysulfone was contacted with this solution for a period of 30 seconds 10 following which 1t was withdrawn and the excess solution was removed 1n a manner similar to that set forth above. The coated polysulfone was then passed through a solution of 0.12 by weight of trlmesoyl chloride 1n naphtha for a period of 15 seconds and thereafter dried at a temperature of 21.7°C in a forced air 15 atmosphere for a period of 20 minutes. The resultant membrane was post treated by rinsing with a sodium carbonate solution at room temperature for a period of 5 minutes, the pH of the solution being 10.0. Following this, the residual m-phenylened1amine was removed by treatment with a sodium 20 bisulfite solution at a temperature of 40°C for a period of 5 minutes and thereafter coated with a glycerine solution. This membrane was designated as membrane B. EXAMPLE III 25 A third membrane was also prepared by passing a sheet of polysulfone through an aqueous solution of m-phenylenediamine, said polyamlne being present in an amount of 2.12 by weight, the aqueous solution containing 70 ppm of sodium carbonate and 502 by 30 volume of ethylene glycol. The coated polysulfone was treated in a manner similar to that set forth above, that 1s, by being passed through a naphtha solution containing 0.152 by weight of trlmesoyl chloride under Identical conditions. The post treatment of the resultant membrane was also similar to that described above and 35 this membrane was designated as membrane C. 14 22 8 4 4 3 EXAMPLE IV For comparative results, a like membrane was prepared with the exception that the aqueous solution did not contain any ethylene glycol, being 1002 aqueous by nature. The remainder of the process was identical to that described above and the resultant membrane after post treatment was designated a membrane D. EXAMPLE V Again for comparative results, two membranes were prepared according to the method set forth in U.S. Patent 4,277,344. The first membrane was prepared by passing a sheet of polysulfone through an aqueous solution containing 2.02 by weight of m-phenylenedl amine for a period of 36 seconds. The coated polysulfone sheet was removed, the excess solution was also removed and the coated sheet passed through an organic solution of trlchlorotrlfluoroethane containing 0.12 weight per volume of trimesoyl chloride for a period of 10 seconds. The membrane was dried in air at a temperature of 23.3°C. A second membrane was also prepared according to the above paragraph and after drying with air was treated with a solution containing 100 ppm of hypochlorite for a period of 20 hours at room temperature and recovered. The first membrane in this example was designated membrane E and the second as membrane F. EXAMPLE VI The membranes which were prepared according to the above examples were placed 1n a cell and a synthetic brackish water feed containing 2 g/Hter of sodium chloride was passed across the surface of a membrane at a feed flow rate of 5.68 I1ters/m1nute. The test conditions which were employed during the experiments Included a pressure of 1516.85 kPa gauge on one side of the membrane while the other side of the membrane was maintained at </div>

Claims

<div id="claims" class="application article clearfix printTableText"> 15 22 8 4 4 3 atmospheric pressure. A temperature of 25°C was maintained throughout the experiment while keeping the pH of the feed at 5.5. The permeate, which was collected from the flowthrough, was measured and the rejection of sodium chloride and flux rate were 5 determined. The results of these tests are set forth 1n the table below. TABLE Membrane D A B C E F 10 Flux (l/m2/d) 929 1087.9 1344.6 1320.2 884.2 1052.9 Rejection (%) 98.5 98.6 98.7 95.3 96.3 95.99 It 1s to be noted from the above table that the membranes which were prepared according to the present Invention utilizing 15 ethylene glycol and sodium carbonate 1n the aqueous solution as well as a post treatment of the type set forth in greater detail in the above examples exhibited higher flux rates with comparable or greater salt rejections than were found when utilizing membranes which had been prepared according to U.S. Patent 20 4,277,344 or without the presence of ethylene glycol 1n the aqueous solution. 228443 16 WHAT WE CLAIM IS:

1. A chlorine-resistant semipermeable membrane prepared by casting an aqueous solution of an aromatic polyamlne which contains a polyhydrlc compound on a porous support backing 5 material, removing excess solution, contacting the coated porous support material with an organic solvent solution of an aromatic polycarboxyllc acid hallde to form an interfacial condensation reaction product on the surface of said porous support material, curing the resultant composite at curing conditions to form said 10 chlorine-resistant semipermeable membrane.

2. The chlorine-resistant semipermeable membrane as set forth 1n Claim 1 1n which said curing conditions include a •Substantially SubsicMfc7% temperature 1n the range of fromJabeut 20° to Jabotrt 150°C for a Substantially substantially period of time 1n the range of from4ab©trt 10 minutes toJabwt 2 15 hours.

3. The chlorine-resistant semipermeable membrane as set forth in Claim 1 in which said aromatic polyamlne comprises m-phenylenedlamine, 4-chlorophenylened1am1ne, 5-chlorophenylene-dlamlne, or mixtures thereof. 20

4. The chlorine-resistant semipermeable membrane as set forth 1n Claim 1 1n which said aromatic polycarboxyllc acid hallde comprises Isophthaloyl chloride, trlmesoyl chloride or terephthaloyl chloride.

5. The chlorine-resistant semipermeable membrane as set 25 forth 1n Claim 1 in which said polyhydrlc compound comprises ethylene glycol, glycerine, propylene glycol, or polyethylene glycol. 1 ' '( ...

6. The chlorine-resistant semipermeable membrane as set forth 1n Claim 1 further characterized 1n that said aqurooT^-a***-*-,. 30 solution contains an acid acceptor.

7. The chlorine-resistant semipermeable membrane as sey!^t E * forth in Claim 1 1n which the pH of said aqueous solution 1s in/,4V Substantially substaithalk/ I Substantially substantially ,, range of fromjabout 9 to about 11. U

8. The chlorine-resistant semipermeable membrane as se%? 35 forth 1n Claim 1 further characterized 1n that said membrane is^C^J^J subjected to treatment with an alkaline compound. .a 4 ft 228443 17

9. The chlorine-resistant semipermeable membrane as set forth 1n Claim 8 in which the cured membrane 1s washed at a Subitannall/ substantially temperature +s- 1n a range of fromJabeut 20°C toJabeut 100°C.

10. The chlorine-resistant semipermeable membrane as set 5 forth 1n Claim 1 further characterized 1n that said chlorine- resistant semipermeable membrane 1s subjected to a leaching treatment subsequent to treatment with said alkaline compound.

11. The chlorine-resistant semipermeable membrane as set forth 1n Claim 10 1n which said leaching treatment 1s effected 1n .10 the presence of solium bisulfite at an elevated temperature 1n the range of from^alJeu^'^O'C to

12. The chlorine-resistant semipermeable membrane as set forth 1n Claim to 1n which said chlorine-resistant semipermeable membrane 1s further treated with a polyhydric compound subsequent 15 to said leaching treatment to form a coating on said membrane.

13. A process for the preparation of a chlorine-resistant semipermeable membrane which comprises casting an aqueous solution of an aromatic polyamlne which contains a polyhydrlc compound and an acid acceptor on a porous support backing material, removing 20 excess solution, contacting the coated porous support material with an organic solvent solution of an aromatic polycarboxyllc acid hallde to form an Interfacial condensation reaction product on the surface of said porous support material, curing the resultant composite at curing conditions, washing the cured 25 membrane with an alkaline compound at an elevated temperature and pH, leaching the washed composite at an elevated temperature with sodium bisulfite, treating the leached composite with a polyhydrlc compound, and recovering the resultant chlorine-resistant semipermeable membrane.

14. A membrane according to Claim 1 substantially as herein described or exemplified.

15. A process according to Claim 13 substantially as herein described or exemplified. -iHh Any novel feature or novel combination of foaturoo dioeloood heroin> ALLIED-SIGNAL INC. "9^GI99o5 11J\1 llUUllljJ Ljini i By Their Attorneys HENRY HUGHES LIMITED BY </div>