Title of Invention	A PROCESS FOR THE PREPARATION OF IMPROVED HETEROGENEOUS ION-EXCHANGE SPACER
Abstract	The invention relates to a process for the preparation of improved heterogeneous ion-exchange spacer. The ion-exchange spacer is used in the electrodialysis process for desalting of solution having low salt content. The heterogeneous ion-exchange(cation or anion) spacer is prepared from polymer net selected from Polyethylene, polyvinyl chloride, polypropylene or nylon coated with suspended fine powder of cation/anion exchange resin in polyvinyl chloride solution in tetrahydrofuran or cyclohexane.

Title of Invention

A PROCESS FOR THE PREPARATION OF IMPROVED HETEROGENEOUS ION-EXCHANGE SPACER

Abstract

The invention relates to a process for the preparation of improved heterogeneous ion-exchange spacer. The ion-exchange spacer is used in the electrodialysis process for desalting of solution having low salt content. The heterogeneous ion-exchange(cation or anion) spacer is prepared from polymer net selected from Polyethylene, polyvinyl chloride, polypropylene or nylon coated with suspended fine powder of cation/anion exchange resin in polyvinyl chloride solution in tetrahydrofuran or cyclohexane.

Full Text	The present invention relates to a process for the preparation of improved heterogeneous ion-exchange spacer. The main usage of the invention is in the preparation of heterogeneous ionexchange spacer through a new process and it is an excellent material to be used in electrodialysis process for demineralization of solutions (organics or inorganics) having low salt content eg. separation of sodium formate from pentaerythritol/ removal of inorganic acids from glyoxal etc. Electrodialysis process for desalination of brackish water containing total dissolved solids (TDS) upto 5000 mg/lit.(5000 ppm is economical to the potable level of ~ 500 mg/lit. or 500 ppm in TDS Ion-exchange spacer can be applied in electrodialysis units to desalt the solutions containing salt of concentration less than 500 mg/lit. Reference may be made to O.Kedem et al in an article "Ion conducting spacer for improved Electrodialysis", Desalination 19 (1976) 465-470, which reveals the preparation of ion conducting spacer by knitting anion and cation fibers separately, adding a thin nylon-fiber for stability of shape during swelling. The thickness of the two layers is approximately 2.5 mm. In the cell, the two knits become slightly interpenetrating. The drawbacks of this process are (i) the process is cumbersome and time consuming, (ii) the thickness of the spacer is too high which increases the compartment thickness and hence, due to which electrical resistance in the diluate ompartments may also increase and ,,(iii) addition of nylon fibre for s!oape stability increases one unit operation. K P Govindan et al in an article "Demineralization by electrodialysis using amphoiytic ion-conducting spacers. Desalination, 38 (1981) 517-527 describes the preparation of ionconducting spacers in 8 to 9 steps by (i) first preparing interpolymers based on polyethylene-styrene-divinyl benzene, the preparation of said interpolymer has been made a subject matter of Indian Pat. No. 124573 (Dec. 1969) and require temperature (ii) moulding the interpolymer into 10 mesh netting of 1 mm thickness (iii) dissolving chlorosulphonic acid in solvent like ethylene dichloride or chloroform (iv) sulphonation of the interpolymer netting with the above solution for preparing cation conducting spacer, (v) dissolving anhydrous aluminium chloride in chloromethyl ether (vi) mixing this with chloroform (vii) chloromethylation of in chloroform of the nett ng with this mixture (viii) ammination of the chloromethylated netting with trimethyl amine for the preparation of anion conducting spacer etc. the chemicals like chlorosulphonic acid, chloromethyl ether, trimethyl amine, chloroform etc. are all highly hazardous and disposal of these causes pollution problem. The different interpolymer compositions they prepared were (la) interpolymer of polyethylene (PE), styrene (St) and divinylbenzene (DVB), (Ib) interpolymer of polyethylene-styrene and/vinylbenzyl chloride (VBC) and divinylbenzene, (2a) the interpolymer of polyethylene, styrene, maleic anhydride (MA) and divinylbenzene, (2b) the interpolymer of polyethylene, vinylbenzylchloride, maleic anhydride and divinylbenzene and (3) the interpolymer of PE, VBC acrylonitrile (CAN) and DVB. The drawbacks of this process are (i) this methods requires at least 8 to 9 steps to prepare conducting spacer, making the process un economical and time consuming (ii) the chemicals like chlorosulphonic acid, chloromethyl ether, trimethyl amine used in this process are hazardous and disposal of such chemicals without proper etlluent treatment causes atmosphere, soil and water pollution, (iii) extra effluent treatment plant is necessary to solve environmental pollution problem; O. Kedem et al in an article "EDS-sealed cell electrodialysis". Desalination, 46 (1983) 291-299, discloses the preparation of an anion-conducting spacer by impregnation of a multifilament net with a crosslinked anion-exchanger which is prepared by chloromethylation of substituted polystyrene, which is then absorbed in the^metv catalytically crosslinked, followed by further chloromethylation and animation with trimethylamine. The drawbacks of this method are (i) chemicals used for chloromethylation of substituted polystyrene are highly carcinogenic and hazardous, proper precautions are needed for proper handling and disposal of unreacted chemicals and (ii) cross linking with a catalyst also need critical control of conditions E. Korngold et al. in an article "Novel ion-exchange spacer for improving electrodialysis I. Reacted spacer", Journal of Membrane Science, 138 (1998) 165-170, describes the reparation of ion-exchange spacer by sulfochlorination of a commercial polypropylene spacer having thickness = 25mils, mesh type = diamond, strand count = 10 per inch , surface area=1000 cm2. The spacer is introduced into a 5 lit. glass vessel containing 4 lit. of trichloroethylene at 65-70°C The sulfochlorination is done by bubbling sulfur dioxide (3 lit./h) and chlorine (1 lit./hr) through the reaction mixture for 25-45 hrs. until the sulfur content reached 4.1% by weight. Two 100W light bulbs are used to provide energy for the photochemical reaction. The spacer is then washed by immersing it in chloroform, after which it is allowed to stand in dimethylarninopropylamine overnight for drying, it is then quaternized by immersing it in dimethylformamide saturated with methyl bromide at 15-25°C for one day. Finally, it is washed with methanol to eliminate all traces of chemicals. This gives an anion-exchange spacer of 0.45 meq./gm. A cation-exchange spacer is made by immersing the sulfochlorinated spacer in IN NaOH overnight. The capacity of the cation-exchange spacer is 0.71 meq/g. The drawbacks of this process are (i) ion exchange spacer is prepared after 4-5 days (ii) it involves many steps to prepare the ion-exchange spacer, (iti) it requires chemicals which needs safety handling and disposal and (iv) the exchange capacity of anion and cation exchange spacers are low R Messalem et al in their article "Novel ion-exchange spacer for improving electrodialysis II. Coated spacer", Journal of Membrane Science, 138 (1998) 171-180, describe the preparation of ion exchange spacer by coating a commercially availed spacer with suspension of ground ion exchange resin in dissolved polyvinyl alcohol cross-linked with hexamethoxymethylmeiamine (HMMM) and polyethyleneimine. For cationexchange spacer they added Procion Red dye as the cross-linking agent. The spacer netting is pretreated in concentrated sulturic acid, to enhance adhesion of the hydrophilic layer. They also describe the preparation of cation-conducting spacers, by dissolving sulphonated polysulfone (SPS) in a mixed solution of N-methyl pyrolydone (NMP) and ethanol at a weight ratio of 9:1, into which the spacers are dipped, then drying the coating at 80°C. For the preparation of anion-conducting spacer, the spacers are dipped into a 5% solution of bromomethylated polysuL , iBMPS) and polystyrene (PS), in N-methyl pyrolydone, (NMP) and methylene chloride (weight ratio 3:7). The coated spacer is then aminated in a mixture of trimethylamine, methanol and distilled water for two days in a refrigerator. The drawbacks of this process are (i) the selected binder polyvinyl alcohol being a water soluble polymer has to be cross-linked with HMMM and polyethyleneimine for anion-exchange spacer and Procion Red dye for cation-exchange spacer involving additional steps as well as chemicals for their application in aqueous medium. The main object of the present invention is to provide a process for the preparation of improved heterogeneous ion-exchange spacer, which obviates the drawbacks as detailed above. Another object of the present invention is to prepare heterogeneous cation-exchange spacer from suitable net (polyethylene, polyvinylchloride, polypropylene) coated with suspended fine powder of cation-exchange resin in polyvinyl chloride solution in tetrahydrofuran or cyclohexanone. Another object of the present invention is to prepare heterogeneous anion exchange spacer from polyethylene, polyvinyl chloride or polypropylene net coated with suspended fine powder of anion-exchange resin in a solution of polyvinyl chloride in tetrahydrofuran or cyclohexanone. Another object of the present invention is to prepare heterogeneous amphoteric ionexchange spacer from polyethylene, polyvinylchloride or polypropylene net coated with suspended fine powdered cation and anion exchange resin in a solution of polyvinyl chloride in tetrahydrofuran or cyclohe,xanone. Another object of the present invention is to use the above ion-exchane spacers in the electrodialysis process for desalting of solution having low salt content. Accordingly, the present invention provides a process for the preparation of improved heterogenous ion-exchange spacer which comprises: (a) preparing a suspension of ion-exchange resin selected from anion exchange, cation exchange and mixture thereof having mesh size -200+300 to -400+500 BSS in a solution prepared by dissolving binder selected from polyvinyl chloride, polysulphone in an organic solvent, (b) coating of above said mixture obtained in step (a) on a polymer net made of polymer selected from polyethylene, polyvinyl chloride, polypropylene or nylon at a temperature ranging from 25 to 35°C, © removing the excess coating material to keep the opening of the net free by air blower and drying the ion-exchange spacer. In an embodiment of the present invention.the anion-exchange resin is selected from chloromethylated and amminated copolymer of styrene-divinylbenzene, having quaternary ammonium as functional group. In yet another embodiment of the present invention, the cation-exchange resin is sulphonated copolymer of styrene-divinylbenzene, having sulphonic acid as functional group. In yet another embodiment of the present invention, the organic solvent used for dissolving binder is selected from Tetrahydrofuran or cyclohexane In yet another embodiment of the present invention the net used is made of polymer selected from polyethylene, polyvinyl chloride, polypropylene or nylon. In yet another embodiment of the present invention the net used is made of .polymer selected from PE, PVC, PP or xylene. The present invention provides a process for the preparation of improved heterogeneous ion-exchange spacer which comprises the preparation of cation-exchange spacer of size in the range 70 x 42 cm to 200 x 120 cm from suspended fine powder of cation exchange resin, which is a sulphonated copolymer of styrene-divinylbenzene containing sulphonic acid as functional group, in a solution prepared by dissolving polyvinyi chloride or polysulfone as binder in cyclohexanone or tetrahydrofuran as solvent coated on a suitable met made from polyethylene (PE). or polyvinyi Chloride or polypropylene or nylon having opening 50 to 75% and thickness 0.4 to 0.6 mm, in three steps, the first step involves the suspension of 4 to 40 gm fine powder cation-exchange resin having mesh size - 200 + 300 to - 400 + 500 BSS in a solution prepared by dissolving 40 to 4 gm of polyvinyi chloride or polysulfone in 200 to 500ml tetrahydrofuran or cyclohexanone, the second step is the coating of the mixture, prepared in the first step,-on a Jiet made from poryethylene-(P£); or poiyvinylchloride'-or polypropylene or nylon at temperature 25 to 35°C, finally the removal of excess coating material to keep the opening of the net free by air blower and drying of the spacer and anion-exchange spacer of size in the range 70 x 42 cm to 200 x 120 cm from suspended fine powder strong base anion exchange resin, which is a chloromethylated and amminated copolymer of styrene-divimHbenzene containing quaternary ammonium as functional group, in a solution prepared by dissolving polyvinyi chloride or polysulfone 1 s binder in cyclohexanone or tetrahydrofuran as solvent coated on a suitable net made from polyethylene (PE) or polyvinyl chloride or polypropylene or nylon having opening M) to 75% and thickness 0.4 to 0.6 mm. in three steps, the first step involves the suspension of 4 to 40 gm tine powder anion-exchange resin having mesh size - 200 + 300 to - 400 + 500 BSS in a solution prepared by dissolving 40 to 4 gm of polyvinyl chloride or polysulfone in 200 to 500ml tetrahydrofuran or cyclohexanone, the second step is the coating of the mixture, prepared in the first step, on a net made from polyethylene (PE) or polyvinylchloride or polypropylene or nylon at temperature 25 to 35IIC. finally the removal of excess coating material to keep the opening of the net free by air blower and drying of the spacer and amphoteric ion-exchange spacer of size in the range 70 x 42 cm to 200 x 120 cm from suspended mixture of fine powder strong acid cation exchange resin as described herein and strong base anion exchange resin as described herein, in a solution prepared by dissolving polyvinyl chloride or polysulfone as binder in cyclohexanone or tetrahydrofuran as solvent coated on a suitable net made from polyethylene (PE) or polyvinyl chloride or polypropylene or nylon having opening 50 to 75% and thickness 0.4 to 0.6 mm, in three steps, the first step involves the suspension of 4 to 40 gm fine powder cation -exchange resin and anion-exchange resin having mesh size - 200 + 300 to - 400 + 500 BSS , with resin ratios 40:60 to 60:40 in a solution prepared by dissolving 40 to 4 gm of polyvinyl chloride or polysulfone in 200 to 500ml tetrahydrofuran or cyclohexanone, the second step is the coating of the mixture, prepared in the first step, on a net made from polyethylene (PE) or polyvinylchloride or polypropylene or nylon at temperature 25 to 35°C, finally the removal of excess coating material to keep the opening of the net ft , »y air blower and drying of the spacer. 8 . In an embodiment of the present invention cation-exchange spacer of size in the range 70 x 42 cm to 200 x i 20 cm may be prepared from suspended powdered strong acid cationexchange resin, which is a sulphonated copolymer of styrene-divinylbenzene, having suiphonic acid as functional group, of quantity in the range selected from 4 to 40 gm in solution of polyvinyl chloride (PVC) or polysulfone (PS) quantity of which may be in the range selected from 40 to 4 gm dissolved in tetrahydrofuran (THF) or cyclohexanone, volume of which may be in the range selected from 200 to 500 mi. In another embodiment of the present invention anion-exchange spacer of size in the range 70 x 42 cm to 200 x 120 cm may be prepared from suspended powdered strong base anion-exchange resin, which is a chloromethylated and amminated copolymer of styrene-divinylbenzene, having quaternary ammonium as functional group, of quantity in the range selected from 4 to 40 gm in solution of polyvinyl chloride (PVC) or polysulfone (PS) quantity of which may be in the range selected from 40 to 4 gm dissolved in tetrahydrofuran (THF) or cyclohexanone, volume of which may be in the range selected from 200 to 500 ml. In yet another embodiment of the present invention amphoteric ion-exchange spacer of size in the range 70 x 42 cm to 200 x 120 cm may be prepared from suspended powdered strong acid cation-exchange resin and anion-exchange resin of quantity in the range selected from 4 to 40 gm with resin ratios in the range selected from 40:60 to 60:40 in solution of polyvinyl chloride (PVC) or polysulfone (PS) quantity of which may be in the range selected from 40 to 4 gm dissolved in tetrahydrofuran (THF) or cyclohexanone, , volume of which may be in the ranges , ;ed from 200 to 500 ml. In still another embodiment of the present invention the dip coaling technique may be used to prepare ion-exchange spacer In still another embodiment of the present invention, the net used to obtain the ionexchange spacer, may be made of polyethylene (PE) or polyvinyl chloride (PVC) or polypropylene (PP) or nylon having openings 50 to 75% with thickness 0.4 to 06 mm. In still another embodiment of the present invention, the powdered cation-exchange resin having mesh size in the range selected from -200 + 300 to -400 + 500 BSS, may be used to obtain cation-exchange spacer. In still another embodiment of the present invention the powdered anion-exchange resin having mesh size in the range selected from - 200 + 300 to - 400 + 500 BSS, may be used to obtain anion-exchange spacer. In still another embodiment of the present invention the mixture of powdered cation and anion-exchange resins having mesh size - 200 + 300 BSS to - 400 + 500 BSS, with resin ratios in the range selected from 40:60 to 60:40, may be used to obtain amphoteric ionexchange spacer. In still another embodiment of the present invention, binder used for ion-exchange resin, may be selected from polyvinyl chloride (PVC) or polysulfone (PS). In still another embodiment of the present invention the binder polyvinyl chloride (PVC) or polysulfone (PS) was dissolved in tetrahydrofuran (THF) or cyclohexanone. In still another embodiment of the present invention, the process may be carried out at ambient temperature between 25-35°C. In still another embodiment, the capacity of the cation-exchange spacer may be in the range 0.5-to 1.5 meq/ gm dry spacer. I n still another embodiment, the exchange capacity of the anion-exchanue membrane may be in the range of 0.8 to I 8 meq/gm dry spacer In still another embodiment, the total exchange capacity of the amphoteric ion-exchange spacer may be in the range of to 1.5 meq/gm dry spacer In still another embodiment, the thickness of the spacer obtained may be in the range of 0.6 to 08 mm The process of preparation of ion-exchange spacer may be described in the following three steps. In the first step polymeric solution is prepared by dissolving 40 to 4 gm of polyvinyl chloride (PVC) (Indovin 67GEF092,K-value 67,Inherent viscosity 0 92) or polysulfone (PS) in 200 to 500ml solvent like tetrahydrofuran (LR grade, boiling range 65-67°C, refractive index = 1 407) or cyclohexanone. In the second step 4 to 40 gm fine powdered ion-exchange resin of mesh size in the range - 200 + 300 to - 400 + 500 BSS is dispersed in the binder solution. The resin: binder ratio is in the range 80: 20 to 20 : 80. The strong acid cation exchange resin (Indion 225 total exchange capacity 4 5meq/g), which is a sulphonated copolymer of styrene-divinylbenzene containing sulphonic acid as Functional group, is used for preparing cation-exchange spacer. The strong base anion-exchange resin (Indion FFTP, total exchange capacity 3.4 meq/g), which is a chloromethylated and aminated copolymer of styrene-divinylbenzene containing quaternary ammonium as functional group, is used for anion-exchange spacer and a mixture of cation-exchange and anion-exchange resin in the ratio 40: 60 to 60 : 40 is used for amphoteric ion-exchange spacer. In the third step a suitable net made of polyethylene (PE) or polyvinyl chloride (PVC) or polypropylene or nylon having openings 50 to 75% and thickness 0.4 to 0.6 is coated with the solution prepared in the first step by dipping it into the solution The excess coating material is removed to keep t h e opening of the net tree by air-blower and then the spacer is allowed to dry The process qualifies as a simple three steps process, to prepare ion exchanger spacer with good exchange capacity and low thickness, thus obviates the need of preparing interpolymers and then introducing strongly acidic or basic groups using chemicals thus avoiding number of steps involved in the preparation. In this method, the simple inventive steps adopted are (i) in the first step, preparation of binder solution by dissolving polyvinyl chloride or polysulfone in tetrahydrofuran or cyclohexanonerthus obviates the cumbersome process for the preparation of interpolymer net.(ji) In4he second step, suspension of fine powder ion-exchange resin, either cation or anion or both, in the binder solution prepared in the first step thus obviates the need of converting the interpolymer net into conducting spacer by chemical treatment using highly carcinogenic chemicals like chlorosulphonic acid, chloromethylether, chloroform, trimethyl amine etc. The second step also obviates the need of chloromethylation of substituted polystyrene, which is absorbed in a catalytically cross-linked multifilament net, which needs proper precautions for handing and disposals, (iii) In the third and final step, coating of a net of appropriate thickness and openings, prepared from polyethylene or polyvinyl chloride or polypropylene or nylon, with the solution prepared in the first two steps, and removal of excess coating material to keep free the openings of the net using air blower and drying of the spacer, thus obviates the need of cumbersome and time consuming process of knitting anion and cation fibers separately and adding a thin nylon-fiber, thus increasing one unit operation, for stability of sh u: during swelling. All these three steps thus obviate the need of the steps involved in the preparation of reacted spacers, which requires sulfochlorination of a polypropylene spacer using chemicals like trichloroethylene, sulfur dioxide, chlorine, dimethylaminopropylamine. dimethylformamide, methanol, NaOH etc. making the process longer. These steps also obviate the need of using polyvinyl alcohol (PVA) cross-linked with hexamethoxymethylmelamine in which polyethyleneimine is added, as binder for coating a net with ground ion-exchange resin suspended in the solution of binder. The steps also obviate the need of the steps involving dissolution of sulphonated polysulfone (SPS) in a mixed solution of N-methyl pyrolydone (NMP) and ethanol into which the spacer are dipped, and then dried to give the cation-conducting spacer or for anion-exchange spacer, coating of the spacer with 5% solution of bromomethylated polysulfone (BMPS) and polystyrene (PS) in N-methyi pyrolydone (NMP) and methylene chloride, followed by ammination of the coated spacer with trimethyl ammine, methanol and distilled water making the process longer. The following examples are given by way of illustrations and should not be construed to limit the scope of the present invention. EXAMPLE-1. 4 g polyvinyl chloride (PVC) was dissolved in 200 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 16 gm of powdered cation-exchange resin of mesh size - 200 + 300 BSS was dispersed thoroughly. A 70 cm x 42 cm polyethylene net with 50% opening and thickness 0.4 mm is dipped in this solution. The viscous coating covers a large part of the opehi; , the net. Air is blown in order, to confine the coating to the strands of the net and keep the openings free The spacer is then dried at •t( rc The properties of the cation-exchange spacer are Thickness : 0.6 mm Moisture 28% Exchange capacity 1 45 meq/g dry spacer Performance : Tested in an ED stack containing 7 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm" By applying 2V/cell pair water with total dissolved solids (IDS) 1000 ppm, 750 ppm. 500 ppm can be reduced to 128 ppm. 100 ppm and 60 ppm respectively at the flow rate of 1.0 lit./hr. The experiment was carried out at 25°C . EXAMPLE-2 8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 32 gm of powdered cation-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene net with 75% opening and thickness 0.5 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the cation-exchange spacer are Thickness : 0.7 mm Moisture 25% xchaime capacity I 40 mei\|/g d i v spacei. Performance . Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm Bv applying 2V7cell pair water with total dissolved solids (IDS) 1000 pprn. 750 ppm. 500 ppm can be reduced to 130 ppm. 100 ppm and 80 ppm respectively at the flow rate of 2.0 lit./lir. 2 I l i t / h r and 2.3 l i t / h r The experiment was carried out at 30UC EXAMPLE-3 10 a polyvinyl chloride (PVC) was dissolved in 500 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 40 gm of powdered cation-exchange resin of mesh si/e - 400 + 500 BSS was dispersed thoroughly A 200 cm x 120 cm nylone net with 60% opening and thickness 06 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the cation-exchange spacer are Thickness : 0.8 mm Moisture : 30% Exchange capacity : 1.50 meq/g dry spacer. Performance : Tested in an ED stack containing 15 ceil pairs of anion and cation exchange membranes having effective single membrane area 80 cm2 By applying 2V/'cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be 1-5 reduced to 120 ppm. l)0 ppm and 65 ppm respectively at the ilo\v tale -of 1.9 lit./hr. The experiment was carried out at 32"C. EXAMPLE-4 32 g polyvinyl chloride (PVC) was dissolved in 400 ml of cyclohexanone solvent taken in a closed container. To this solution 8 gm of powdered cation-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene net with 60% opening and thickness 04 mm is dipped in this solution. The viscous coating, covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the cation-exchange spacer are Thickness : 0.65 mm Moisture : 8% Exchange capacity : 05 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V7cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm? 500 ppm can be reduced to 130 ppm. 105 ppm ami 80 ppm respectively at the flow rate of 1.5 lit./hr. !61it../hr. and 1.52 lit./hr. The experiment was carried out at 35 °C . EXAMPLE-5 16 g polysulfone was dissolved in 400 mi of tetrahydroftiran (THF) solvent taken in a closed container. To this solution 24 gm of powdered cation-exchange resin of mesh size - 400 + 500 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinylchloride net with 55% opening and thickness 0 42 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the cation-exchange spacer are _ Thickness : 0 60 mm Moisture : 29% Exchange capacity : 1.20 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm, 500 ppm can be reduced to 130 ppm, 105 ppm and 70 ppm respectively at the flow rate of 2.0 lit./hr, 2.07lit./hr. andl.81it./hr. The experiment was carried out at 32 °C . EXAMPLE-6 20 g polyvinyl chloride was dissolved in,.5'", ^1 of cyclohexanone solvent .taken in a closed container. To this solution 30 gm of powdered cation-exchange resin of mesh size ... 300 + 400 BSS was dispersed thoroughly. A 200 cm x 120 cm polyvinyl chloride net with 60% opening and thickness 0.5 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the cation-exchange spacer are Thickness : 0.72 mm Moisture : 27% Exchange capacity : ( 30 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm7 By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be reduced to 125 ppm, 100 ppm and 65 ppm respectively at the flow rate of 2.05 lit./hr, 2.00lit./hr. and 1.9 lit./hr. The experiment was carried out at 28 °C . EXAMPLE-7 16 g polysulfone (PS) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 24 gm of powdered cation-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene (PP) net with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and kefep the openings free. The spacer is then dried at40()C. The properties of the cation-exchange spacer are Thickness 0 65 mm Moisture : 20% I'xchange capacity : I 20 meq/g drv spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm'. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be reduced to 130 ppm, 100 ppm and 60 ppm respectively at the flow rate of 2.1 lit./hr, 1.9!it./hr. and 1.8 lit./hr. The experiment was carried out at 29 °C . EXAMPLE-8 8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 32 em of powdered cation-exchange resin of mesh size - 400 + 500 BSS was dispersed thoroughly. A 150 crn x 100 cm nylon net with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40 C. The properties of the cation-exchange spacer are Thickness : 0.7 mm Moisture : 30% Exchange capacity : 1.50 meq/g dry spacer Performance Tested in an F.D stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cnr Bv applying 2 V/celi pair water with total dissolved solids (IDS) 1000 ppm. 750 pptn. 500 ppm can be reduced to 120 ppm, 100 ppm and 60 ppm respectively at the flow rate of 2.0 lit./hr 2 I lit Vhr. and 2.2 lit./hr The experiment was carried out at 28 °C EXAMPLE-9 10 g polyvinyl chloride (PVC) was dissolved in 500 ml of cyclohexanone solvent taken in a closed container. To this solution 40 gm of powdered cation-exchange resin of mesh si/c 300 + 400 BSS was dispersed thoroughly A 200 cm x 120 cm polyvinyl chloride net with 55% opening and thickness 0.42 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C The properties of the cation-exchange spacer are Thickness : 0.65 mm Moisture : 21% Exchange capacity : 1 45 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solid , DS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 130 ppm. 95 ppm and 62 ppm respectively at the flow rate of 2.02 lit /hr. : Olit /hr and 2.05 lit./hr The experiment was carried out at 32 C . EXAMPLE-10 8 u polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container To this solution 32 gm of powdered anion-exchange resin of mesh si7.e - 300 + 400 BSS was dispersed thoroughly A 150 cm \ 100 cm polyethylene net with 75% opening and thickness 05 mm is dipped in this solution The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free The spacer is then dried at 4()"C The properties of the anion-exchange spacer are Thickness : 0.72 mm Moisture : 30% Exchange capacity : 1.72 meq/g dry spacer Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V7cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be reduced to 120 ppm, 90 ppm and 60 ppm respectively at the flow rate of 2.4 lit./hn 2.5lit./hr. and 2.45 lit./hr. The experiment was carried out at 32° C EXAMPLE-11 10 g polyvinyl chloride (PVC) was dissolved in 500 ml of tetrahydrofuran (THF) solvent taken in a closed container To this solution 40 gm of powdered anion-exchange resin of mesh size - 400 + 500 BSS was dispersed thoroughly A 200 cm x 120 cm polyethylene net with 60% opening and thickness 0.6 mm is dipped in this solution The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the anion-exchange spacer are Thickness 0.8 mm Moisture 29% Exchange capacity : 1 80 meq/g dry spacer Performance : Tested in an ED stack containing 15 ceil pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm, 500 ppm can be reduced to 125 ppm, 95 ppm and 40 ppm respectively at the flow rate of 2.45 lit./hr. 2.41it./hr. and 2.3 lit./hr. The experiment was carried out at 32°C . EXAMPLE-12 32 u polwinyl chloride (PVC) was dissolved in 400 ml of cvclohexanone solvent taken in a closed container. To this solution 8 gm of powdered anion-exchange resin of mesh "00 + 400 BSS was dispersed thoroughly A I n cm I no cm polyethylene net y..ith 60% opening and thickness 0 4 mm is dipped in this solution The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the anion-exchange spacer are Thickness : 0.60 mm Moisture i 2% Exchange capacity : 08 meq/g dry spacer Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2 By applying 2V, cell pair water with total dissolved solids (IDS) !000 ppm, 750 ppm, 500 r.pm can be reduced to 125 ppm, 100 ppm and 70 ppm respectively at the flow rate of 1.6 lit./hr, 1.65 lit./hr. and 1.70 lit./hr. The experiment was carried out at 35 °C . EXAMPLE-13 16 g polysulfone was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 24 gm of powdered anion-exchange resin of mesh size - 400 + 500 BSS was dispersed thoroughly A 150 cm x 100 cm polyvinyl chloride net with 55% opening and thickness 0 42 mm is dipped in this solution The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the anion-exchange spacer are Thickness 0 62 mm Moisture : 3!°o Exchange capacity : I 44 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm' By applying 2V/cell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm, 500 ppm can be ieduced to 1.30 ppm. 100 ppm and 70 ppm respectively at the flow rate of 2 30 lit./hr. 2 20lit./hr and 2.30 lit./hr The experiment was carried out at 32 °C . EXAMPLE-14 20 g polyvinyl chloride was dissolved in 500 ml of cyclohexanone solvent taken in a closed container. To this solution 30 gm of powdered anion-exchange resin of mesh size - .300 + 400 BSS was dispersed thoroughly. A 200 cm x 120 cm polyvinyl chloride net with 60% opening and thickness 0.5 mm is dipped in this solution The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the anion-exchange spacer are Thickness : 0 70 mm Moisture : 30% Exchange capacity : 1.42 meq/g dry spacer. Performance : Tested in an ED stack ,r. aining 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm. 500 ppm can be reduced to 120 ppm. 104 ppm and 76 ppm respectively at the flow rate of 2.20 lit./hr. 2.251it./hr. and 2.21 lit./hr. The experiment was carried out at 28 °C . EXAMPLE-15 16 g polvsulfone (PS) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 24 gm of powdered anion-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene (PP)r net with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the anion-exchange spacer are Thickness : 0.60 mm Moisture : 29% Exchange capacity : 1.40 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 125 ppm, 100 ppm and 50 ppm respectively at the flow rate of 2.25 lit./hr, 2.21it./hr. and 1.5 lit./hr. The experiment was carried out at 29 °C . EXAMPLE-16 8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydroftiran (THF) solvent taken in a closed container. To this solution 32 gm of powdered anion-exchange resin of mesh size - 400 + 500 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene (PP) net with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the anion-exchange spacer Thickness . 0.72 mm Moisture : 31% Exchange capacity : 1.75 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm? 500 ppm can be reduced to 100 ppm, 80 ppm and 40 ppm respectively at the flow rate of 1.8 lit./hr, 1.91it./hr. and 2.2 lit./hr. The experiment was carried out at 32 °C . EXAMPLE-17 10 g polyvinyl chloride (PVC) was dissolved in 500 ml of cyclohexanone soNfent taken in a closed container. To this solution 40 gm of powdered anion-exchange resin of mesh size .?00 + 400 BSS was dispersed thoroughly. A 200 cm x I 20 cm polvvinvl chloride net with 55% opening and thickness 0.42 mm is dipped in this solution The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free The spacer is then dried at -40°C The properties of the anion-exchange spacer Thickness : 0.60 mm Moisture : 30% F.xchange capacity : 1 80 meq/g dry spacer Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 125 ppm, 90 ppm and 45 ppm respectively at the flow rate of 2 35 lit./hr, 2.30lit./hr. and 2.35 lit./hr. The experiment was carried out at 35 °C . EXAMPLE-18 8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydroruran (THF) solvent taken in a closed container To this solution 192 gm of powdered anion-exchange resin of mesh size - 300 + 400 BSS and 12.8 gm of powdered cation-exchange resin of mesh size - 400 + 500 BSS were dispersed thoroughly. A 150 cm x 100 cm polyethylene net with 75% opening and thickness 05 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. 1 he properties of the amphoteric ion-exchange spacer are Thickness : 0.72 mm Moisture : 28% Total exchange capacity 1 60 meq/g dry spacer Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm caiUw reduced to 110 ppm, °0 ppm and 40 ppm respectively at the flow rate of 2.3 IttJhr, 2 4lit ,/hr. and 2.35 lit./hr I he experiment was carried out at 32°C . EXAMPLE-19 16 g polysuifone (PS) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken hi a closed container. To this solution 12 gm of powdered anion-exchange resin of mesh si7.e - 400 + 500 BSS and 12 gm of powdered cation-exchange resin of mesh size -'400 + 500 BSS was dispersed thoroughly A 150 cm x 100 cm polyproplene net with 60% opening and thickness 0.4 mm is dipped in this solution The viscous coating covenra large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the amphoteric ion-exchar . spacer are Thickness : 0.6 mm Moisture : 26.1% Total exchange capacity 1 23 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm. By applying ZVVcell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm. 500 ppm can be - reduced to 130 ppm, 100 ppm and 60 ppm respectively at the flow rate of 2.4 lit./hr, 2.2 lit./hr and 2.3 lit./hr. (he experiment was carried out at 32°C EXAMPLE-20 16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahvdrofuran (THF) solvent taken in a closed container. To this solution 9.6 cm of powdered anion-exchange resin of mesh size - 300 + 400 BSS and 14.4 gm of powdered cation-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinyl chloride net with 60% opening and thickness 0.4 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the amphoteric ion-exchange spacer are Thickness : 0 62 mm Moisture : 25% Total exchange capacity : 1.20 meq/g dry spacer. Performance : Tested in an ED stack ccv , ing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2Vcell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm. 500 ppm can be reduced to 130 ppm. 105 ppm and 60 ppm respectively at the flow rate of 2.2 lit./hr. 22!lit/hr and 2.0 lit,/hr. The experiment was carried out at 33°C EXAMPLE-2I 16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THH solvent taken in a closed container. To this solution 14.4 gm of powdered anion-exchange resin of mesh size - 300 + 400 BSS and 9.6 gm of powdered cation-exchange resin of mesh size 300-+ 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene net with 60% opening and thickness 0.4 mm is dipped in this solution The viscous coating covers a large part of the opening of the net, Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the amphoteric ion-exchange spacer are Thickness : 0.61 mm Moisture : 26% Total exchange capacity 1.40 meq/g dry spacer Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 125 ppm, 100 ppm and 50 ppm respectively at the flow rate of 2.3 lit./hr. 2 4 l i t / h r and 2.1 lit./hr The experiment was carried out at 35°C HXAMPLE-22 16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tctrahydrotiiran (THF) solvent taken in a closed container. To this solution 12 gm of powdered anion-exchange resin of mesh size - 300 + 400 BSS and 12 gm of powdered cation-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene net with 60% opening and thickness 0.4 mm is dipped in this solution The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the amphoteric ion-exchange spacer are Thickness 0 60 mm Moisture : 27% Total exchange capacity : I 23 mcq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm7 By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 130 ppm, 105 ppm and 70 ppm respectively at the flow rate of 2.5 lit./hr, 2.2lit./hr. and 2.1 lit./hr. The experiment was carried out at 32°C . EXAMPLE-23 16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 12 gm of powdered anion-exchange resin of mesh size - 300 + 400 BSS and 12 gm of powdered cation-exchange resin of mesh size - "500 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinyl chloride net with 60% opening and thickness 0.4 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the amphoteric ion-exchange spacer are Thickness : 0 62 mm Moisture 26% Total exchange capacity : 1.24 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and -cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 125 ppm, 100 ppm and 65 ppm respectively at the flow rate of 2.4 lit./hr, 2.1 lit./hr. and 2.3 lit./hr. The experiment was carried out at 33°C . EXAMPLE-24 8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 16 gm of powdered anion-exchange resin of mesh size - 300 + 400 BSS and 16 gm of powdered cation-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene net with 60% opening and thickness 04 mm is ,4>ed in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40 °C. The properties of the amphoteric ion-exchange spacer are Thickness : 0.60 mm Moisture : 29% Total exchange capacity : 1.5 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2. By applying 2V/cell pair water with total dissolved solids (IDS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 120 ppm, 100 ppm and 50 ppm respectively at the flow rate of 2.3 lit./hr, 2.4 lit./hr and 2.3 lit./hr. The experiment was carried out at 30°C . EXAMPLE-25 8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a closed container. To this solution 12.8 gm of powdered anion-exchange resin of mesh size - 300 + 400 BSS and 19.2 gm of powdered cation-exchange resin of mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinyl chloride net with 60% opening and thickness 0.4 mm is dipped in this solution. The viscous coating covers a large part of the opening of the net. Air is blown in order to confine the coating to the strands of the net and keep the openings free. The spacer is then dried at 40°C. The properties of the amphoteric ion-exchange spacer are Thickness : 0.62 mm Moisture 27% Total exchange capacity : 1.4 meq/g dry spacer. Performance : Tested in an ED stack containing 15 cell pairs of anion and cation exchange membranes having effective single membrane area 80 cm2 By applying 2V/cell pair water with total dissolved solids (IDS) 1000 ppm, 750 ppm, 500 ppm can be reduced to 130 ppm, 105 ppm and 60 ppm respectively at the flow rate of 2 3 lit./hr, 2.4 litVhr. and 2.3 lit./hr The experiment was carried out at 34°C . The main advantages of the present invention are: 1. It is a very simple two steps process. 2. Process is highly flexible from the viewpoint of selection of net materials. 3. Wide variation in net design is possible. 4. Use of least quantity and number of chemicals. 5. It is possible to vary the ion exchange capacity of the spacers from a very low to very high value. 6. Moisture content of the spacers can be widely varied. 7. Process is such that the maximum utilization of the material is possible 8. Single technique may be adopted for the preparation of both the types (cationic or anionic) of spacers. 9 Spacer size may be flexible from small to medium to big depending upon the requirement. 10 Long life of the spacers 11 The same solution used for coating on a net for preparing ion-exchange spacer can be used also for preparing heterogeneous ion-exchange membranes by coating on a cloth, which is a subject matter of another patent We claim: 1. A process for the preparation of improved heterogeneous ion-exchange spacer which comprises; (a) preparing a suspension of ion-exchange resin selected from anion exchange, cation exchange and mixture thereof having mesh size -200+300 to -400+500 BSS in a solution prepared by dissolving binder selected from polyvingly chloride, polysulphone in an organic solvent, (b) coating of above said mixture obtained in step (a) on a polymer net made of polymer selected from Polyethylene, polyvinyl chloride, polypropylene or nylon at a temperature ranging from 25 to 35°C, © removing the excess coating material to keep the opening of the net free by air blower and drying the ion-exchange spacer. 2. A process as claimed in claim 1, wherein anion-exchange resin is chloromethylated and amminated copolymer of styrene-divinylbenzene, having quaternary ammonium as functional group. 3. A process as claimed in claims 1 to 2, wherein cation-exchange resin is sulphonated copolymer of styrene-divinylbenzene, having sulphonic acid as functional group. 4. A process as claimed in claims 1 to 3, wherein the organic solvent used for dissolving binder is selected from Tetrahydrofuran or cyclohexane. 5. The process as claimed in claimsl to 4, wherein the dip coating technique is used to prepare ion-exchange spacer. 6. The process as claimed in claims 1 to 5, wherein the net used to obtain the ion-exchange spacer is having openings 50 to 76% with thickness 0.4 to 0.6 mm. 7. The process as claimed in claims 1 to 6, wherein the mixture of powdered cation and anion-exchange resins having mesh size - 200 + 300 BSSS to 400 + 500 BSS, with resin ratios in the range selected from 40:60 to 60:40 is used to obtain amphoteric ion- exchange spacer. 8. The process as claimed in claims 1 to 7, wherein the capacity of the cation-exchange spacer is in the range 0.5 to 1.5 meq/gm dry spacer. 9. The process as claimed in claims 1 to 8, wherein the exchange capacity of the anion-exchange membrane is in the range of 0.8 to 1.8 meq/gm dry spacer. 10. The process as claimed in claims 1 to 9, wherein the total exchange capacity of the amphoteric ion-exchange spacer is in the range of to 1.5 nieq./gm dry spacer. 11. The process as claimed in claims 1 to 10, wherein the thickness of the spacer obtained is in the range of 0.6 to 0.8 mm. 12. A process for the preparation of improved heterogeneous ion-exchange spacer substantially as herein described with reference to the examples accompanying this specification.

Full Text

The present invention relates to a process for the preparation of improved heterogeneous
ion-exchange spacer.
The main usage of the invention is in the preparation of heterogeneous ionexchange
spacer through a new process and it is an excellent material to be used in
electrodialysis process for demineralization of solutions (organics or inorganics) having
low salt content eg. separation of sodium formate from pentaerythritol/ removal of
inorganic acids from glyoxal etc. Electrodialysis process for desalination of brackish
water containing total dissolved solids (TDS) upto 5000 mg/lit.(5000 ppm is economical
to the potable level of ~ 500 mg/lit. or 500 ppm in TDS Ion-exchange spacer can be
applied in electrodialysis units to desalt the solutions containing salt of concentration less
than 500 mg/lit.
Reference may be made to O.Kedem et al in an article "Ion conducting spacer for
improved Electrodialysis", Desalination 19 (1976) 465-470, which reveals the
preparation of ion conducting spacer by knitting anion and cation fibers separately,
adding a thin nylon-fiber for stability of shape during swelling. The thickness of the two
layers is approximately 2.5 mm. In the cell, the two knits become slightly
interpenetrating. The drawbacks of this process are (i) the process is cumbersome and
time consuming, (ii) the thickness of the spacer is too high which increases the
compartment thickness and hence, due to which electrical resistance in the diluate
ompartments may also increase and ,,(iii) addition of nylon fibre for s!oape stability
increases one unit operation.
K P Govindan et al in an article "Demineralization by electrodialysis using amphoiytic
ion-conducting spacers. Desalination, 38 (1981) 517-527 describes the preparation of ionconducting
spacers in 8 to 9 steps by (i) first preparing interpolymers based on
polyethylene-styrene-divinyl benzene, the preparation of said interpolymer has been
made a subject matter of Indian Pat. No. 124573 (Dec. 1969) and require temperature (ii)
moulding the interpolymer into 10 mesh netting of 1 mm thickness (iii) dissolving
chlorosulphonic acid in solvent like ethylene dichloride or chloroform (iv) sulphonation
of the interpolymer netting with the above solution for preparing cation conducting
spacer, (v) dissolving anhydrous aluminium chloride in chloromethyl ether (vi) mixing
this with chloroform (vii) chloromethylation of in chloroform of the nett ng with this
mixture (viii) ammination of the chloromethylated netting with trimethyl amine for the
preparation of anion conducting spacer etc. the chemicals like chlorosulphonic acid,
chloromethyl ether, trimethyl amine, chloroform etc. are all highly hazardous and
disposal of these causes pollution problem. The different interpolymer compositions they
prepared were (la) interpolymer of polyethylene (PE), styrene (St) and divinylbenzene
(DVB), (Ib) interpolymer of polyethylene-styrene and/vinylbenzyl chloride (VBC) and
divinylbenzene, (2a) the interpolymer of polyethylene, styrene, maleic anhydride (MA)
and divinylbenzene, (2b) the interpolymer of polyethylene, vinylbenzylchloride, maleic
anhydride and divinylbenzene and (3) the interpolymer of PE, VBC acrylonitrile (CAN)
and DVB. The drawbacks of this process are (i) this methods requires at least 8 to 9 steps
to prepare conducting spacer, making the process un economical and time consuming (ii)
the chemicals like chlorosulphonic acid, chloromethyl ether, trimethyl amine used in this
process are hazardous and disposal of such chemicals without proper etlluent treatment
causes atmosphere, soil and water pollution, (iii) extra effluent treatment plant is
necessary to solve environmental pollution problem;
O. Kedem et al in an article "EDS-sealed cell electrodialysis". Desalination, 46 (1983)
291-299, discloses the preparation of an anion-conducting spacer by impregnation of a
multifilament net with a crosslinked anion-exchanger which is prepared by
chloromethylation of substituted polystyrene, which is then absorbed in the^metv
catalytically crosslinked, followed by further chloromethylation and animation *with
trimethylamine. The drawbacks of this method are (i) chemicals used for
chloromethylation of substituted polystyrene are highly carcinogenic and hazardous,
proper precautions are needed for proper handling and disposal of unreacted chemicals
and (ii) cross linking with a catalyst also need critical control of conditions
E. Korngold et al. in an article "Novel ion-exchange spacer for improving electrodialysis
I. Reacted spacer", Journal of Membrane Science, 138 (1998) 165-170, describes the
reparation of ion-exchange spacer by sulfochlorination of a commercial polypropylene
spacer having thickness = 25mils, mesh type = diamond, strand count = 10 per inch ,
surface area=1000 cm2. The spacer is introduced into a 5 lit. glass vessel containing 4 lit.
of trichloroethylene at 65-70°C The sulfochlorination is done by bubbling sulfur dioxide
(3 lit./h) and chlorine (1 lit./hr) through the reaction mixture for 25-45 hrs. until the sulfur
content reached 4.1% by weight. Two 100W light bulbs are used to provide energy for
the photochemical reaction. The spacer is then washed by immersing it in chloroform,
after which it is allowed to stand in dimethylarninopropylamine overnight for drying, it is
then quaternized by immersing it in dimethylformamide saturated with methyl bromide at
15-25°C for one day. Finally, it is washed with methanol to eliminate all traces of
chemicals. This gives an anion-exchange spacer of 0.45 meq./gm. A cation-exchange
spacer is made by immersing the sulfochlorinated spacer in IN NaOH overnight. The
capacity of the cation-exchange spacer is 0.71 meq/g. The drawbacks of this process are
(i) ion exchange spacer is prepared after 4-5 days (ii) it involves many steps to prepare
the ion-exchange spacer, (iti) it requires chemicals which needs safety handling and
disposal and (iv) the exchange capacity of anion and cation exchange spacers are low
R Messalem et al in their article "Novel ion-exchange spacer for improving
electrodialysis II. Coated spacer", Journal of Membrane Science, 138 (1998) 171-180,
describe the preparation of ion exchange spacer by coating a commercially availed spacer
with suspension of ground ion exchange resin in dissolved polyvinyl alcohol cross-linked
with hexamethoxymethylmeiamine (HMMM) and polyethyleneimine. For cationexchange
spacer they added Procion Red dye as the cross-linking agent. The spacer
netting is pretreated in concentrated sulturic acid, to enhance adhesion of the hydrophilic
layer. They also describe the preparation of cation-conducting spacers, by dissolving
sulphonated polysulfone (SPS) in a mixed solution of N-methyl pyrolydone (NMP) and
ethanol at a weight ratio of 9:1, into which the spacers are dipped, then drying the coating
at 80°C. For the preparation of anion-conducting spacer, the spacers are dipped into a 5%
solution of bromomethylated polysuL , iBMPS) and polystyrene (PS), in N-methyl
pyrolydone, (NMP) and methylene chloride (weight ratio 3:7). The coated spacer is then
aminated in a mixture of trimethylamine, methanol and distilled water for two days in a
refrigerator. The drawbacks of this process are (i) the selected binder polyvinyl alcohol
being a water soluble polymer has to be cross-linked with HMMM and
polyethyleneimine for anion-exchange spacer and Procion Red dye for cation-exchange
spacer involving additional steps as well as chemicals for their application in aqueous
medium.
The main object of the present invention is to provide a process for the preparation of
improved heterogeneous ion-exchange spacer, which obviates the drawbacks as detailed
above.
Another object of the present invention is to prepare heterogeneous cation-exchange
spacer from suitable net (polyethylene, polyvinylchloride, polypropylene) coated with
suspended fine powder of cation-exchange resin in polyvinyl chloride solution in
tetrahydrofuran or cyclohexanone.
Another object of the present invention is to prepare heterogeneous anion exchange
spacer from polyethylene, polyvinyl chloride or polypropylene net coated with suspended
fine powder of anion-exchange resin in a solution of polyvinyl chloride in
tetrahydrofuran or cyclohexanone.
Another object of the present invention is to prepare heterogeneous amphoteric ionexchange
spacer from polyethylene, polyvinylchloride or polypropylene net coated with
suspended fine powdered cation and anion exchange resin in a solution of polyvinyl
chloride in tetrahydrofuran or cyclohe,xanone.
Another object of the present invention is to use the above ion-exchane spacers in the electrodialysis process for desalting of solution having low salt content. Accordingly, the present invention provides a process for the preparation of improved heterogenous ion-exchange spacer which comprises:
(a) preparing a suspension of ion-exchange resin selected from anion exchange, cation exchange and mixture thereof having mesh size -200+300 to -400+500 BSS in a solution prepared by dissolving binder selected from polyvinyl chloride, polysulphone in an organic solvent,
(b) coating of above said mixture obtained in step (a) on a polymer net made of polymer selected from polyethylene, polyvinyl chloride, polypropylene or nylon at a temperature ranging from 25 to 35°C,
© removing the excess coating material to keep the opening of the net free by air blower
and drying the ion-exchange spacer.
In an embodiment of the present invention.the anion-exchange resin is selected from
chloromethylated and amminated copolymer of styrene-divinylbenzene, having
quaternary ammonium as functional group.
In yet another embodiment of the present invention, the cation-exchange resin is
sulphonated copolymer of styrene-divinylbenzene, having sulphonic acid as functional
group.
In yet another embodiment of the present invention, the organic solvent used for
dissolving binder is selected from Tetrahydrofuran or cyclohexane
In yet another embodiment of the present invention the net used is made of polymer
selected from polyethylene, polyvinyl chloride, polypropylene or nylon.

In yet another embodiment of the present invention the net used is made of
.polymer selected from PE, PVC, PP or xylene.
The present invention provides a process for the preparation of improved
heterogeneous ion-exchange spacer which comprises the preparation of cation-exchange
spacer of size in the range 70 x 42 cm to 200 x 120 cm from suspended fine powder of
cation exchange resin, which is a sulphonated copolymer of styrene-divinylbenzene
containing sulphonic acid as functional group, in a solution prepared by dissolving
polyvinyi chloride or polysulfone as binder in cyclohexanone or tetrahydrofuran as
solvent coated on a suitable met made from polyethylene (PE). or polyvinyi Chloride or
polypropylene or nylon having opening 50 to 75% and thickness 0.4 to 0.6 mm, in three
steps, the first step involves the suspension of 4 to 40 gm fine powder cation-exchange
resin having mesh size - 200 + 300 to - 400 + 500 BSS in a solution prepared by
dissolving 40 to 4 gm of polyvinyi chloride or polysulfone in 200 to 500ml
tetrahydrofuran or cyclohexanone, the second step is the coating of the mixture, prepared
in the first step,-on a Jiet made from poryethylene-(P£); or poiyvinylchloride'-or
polypropylene or nylon at temperature 25 to 35°C, finally the removal of excess coating
material to keep the opening of the net free by air blower and drying of the spacer and
anion-exchange spacer of size in the range 70 x 42 cm to 200 x 120 cm from suspended
fine powder strong base anion exchange resin, which is a chloromethylated and
amminated copolymer of styrene-divimHbenzene containing quaternary ammonium as
functional group, in a solution prepared by dissolving polyvinyi chloride or polysulfone
1
s binder in cyclohexanone or tetrahydrofuran as solvent coated on a suitable net made
from polyethylene (PE) or polyvinyl chloride or polypropylene or nylon having opening
M) to 75% and thickness 0.4 to 0.6 mm. in three steps, the first step involves the
suspension of 4 to 40 gm tine powder anion-exchange resin having mesh size - 200 +
300 to - 400 + 500 BSS in a solution prepared by dissolving 40 to 4 gm of polyvinyl
chloride or polysulfone in 200 to 500ml tetrahydrofuran or cyclohexanone, the second
step is the coating of the mixture, prepared in the first step, on a net made from
polyethylene (PE) or polyvinylchloride or polypropylene or nylon at temperature 25 to
35IIC. finally the removal of excess coating material to keep the opening of the net free
by air blower and drying of the spacer and amphoteric ion-exchange spacer of size in the
range 70 x 42 cm to 200 x 120 cm from suspended mixture of fine powder strong acid
cation exchange resin as described herein and strong base anion exchange resin as
described herein, in a solution prepared by dissolving polyvinyl chloride or polysulfone
as binder in cyclohexanone or tetrahydrofuran as solvent coated on a suitable net made
from polyethylene (PE) or polyvinyl chloride or polypropylene or nylon having opening
50 to 75% and thickness 0.4 to 0.6 mm, in three steps, the first step involves the
suspension of 4 to 40 gm fine powder cation -exchange resin and anion-exchange resin
having mesh size - 200 + 300 to - 400 + 500 BSS , with resin ratios 40:60 to 60:40 in a
solution prepared by dissolving 40 to 4 gm of polyvinyl chloride or polysulfone in 200 to
500ml tetrahydrofuran or cyclohexanone, the second step is the coating of the mixture,
prepared in the first step, on a net made from polyethylene (PE) or polyvinylchloride or
polypropylene or nylon at temperature 25 to 35°C, finally the removal of excess coating
material to keep the opening of the net ft , »y air blower and drying of the spacer.
8 .
In an embodiment of the present invention cation-exchange spacer of size in the range 70
x 42 cm to 200 x i 20 cm may be prepared from suspended powdered strong acid cationexchange
resin, which is a sulphonated copolymer of styrene-divinylbenzene, having
suiphonic acid as functional group, of quantity in the range selected from 4 to 40 gm in
solution of polyvinyl chloride (PVC) or polysulfone (PS) quantity of which may be in the
range selected from 40 to 4 gm dissolved in tetrahydrofuran (THF) or cyclohexanone,
volume of which may be in the range selected from 200 to 500 mi.
In another embodiment of the present invention anion-exchange spacer of size in the
range 70 x 42 cm to 200 x 120 cm may be prepared from suspended powdered strong
base anion-exchange resin, which is a chloromethylated and amminated copolymer of
styrene-divinylbenzene, having quaternary ammonium as functional group, of quantity in
the range selected from 4 to 40 gm in solution of polyvinyl chloride (PVC) or
polysulfone (PS) quantity of which may be in the range selected from 40 to 4 gm
dissolved in tetrahydrofuran (THF) or cyclohexanone, volume of which may be in the
range selected from 200 to 500 ml.
In yet another embodiment of the present invention amphoteric ion-exchange spacer of
size in the range 70 x 42 cm to 200 x 120 cm may be prepared from suspended powdered
strong acid cation-exchange resin and anion-exchange resin of quantity in the range
selected from 4 to 40 gm with resin ratios in the range selected from 40:60 to 60:40 in
solution of polyvinyl chloride (PVC) or polysulfone (PS) quantity of which may be in the
range selected from 40 to 4 gm dissolved in tetrahydrofuran (THF) or cyclohexanone,
, volume of which may be in the ranges , ;ed from 200 to 500 ml.
In still another embodiment of the present invention the dip coaling technique may be
used to prepare ion-exchange spacer
In still another embodiment of the present invention, the net used to obtain the ionexchange
spacer, may be made of polyethylene (PE) or polyvinyl chloride (PVC) or
polypropylene (PP) or nylon having openings 50 to 75% with thickness 0.4 to 06 mm.
In still another embodiment of the present invention, the powdered cation-exchange resin
having mesh size in the range selected from -200 + 300 to -400 + 500 BSS, may be used
to obtain cation-exchange spacer.
In still another embodiment of the present invention the powdered anion-exchange resin
having mesh size in the range selected from - 200 + 300 to - 400 + 500 BSS, may be
used to obtain anion-exchange spacer.
In still another embodiment of the present invention the mixture of powdered cation and
anion-exchange resins having mesh size - 200 + 300 BSS to - 400 + 500 BSS, with resin
ratios in the range selected from 40:60 to 60:40, may be used to obtain amphoteric ionexchange
spacer.
In still another embodiment of the present invention, binder used for ion-exchange resin,
may be selected from polyvinyl chloride (PVC) or polysulfone (PS).
In still another embodiment of the present invention the binder polyvinyl chloride (PVC)
or polysulfone (PS) was dissolved in tetrahydrofuran (THF) or cyclohexanone.
In still another embodiment of the present invention, the process may be carried out at
ambient temperature between 25-35°C.
In still another embodiment, the capacity of the cation-exchange spacer may be in the
range 0.5-to 1.5 meq/ gm dry spacer.
I n still another embodiment, the exchange capacity of the anion-exchanue membrane may
be in the range of 0.8 to I 8 meq/gm dry spacer
In still another embodiment, the total exchange capacity of the amphoteric ion-exchange
spacer may be in the range of to 1.5 meq/gm dry spacer
In still another embodiment, the thickness of the spacer obtained may be
in the range of 0.6 to 08 mm
The process of preparation of ion-exchange spacer may be described in the
following three steps. In the first step polymeric solution is prepared by dissolving 40 to
4 gm of polyvinyl chloride (PVC) (Indovin 67GEF092,K-value 67,Inherent viscosity
0 92) or polysulfone (PS) in 200 to 500ml solvent like tetrahydrofuran (LR grade, boiling
range 65-67°C, refractive index = 1 407) or cyclohexanone. In the second step 4 to 40 gm
fine powdered ion-exchange resin of mesh size in the range - 200 + 300 to - 400 + 500
BSS is dispersed in the binder solution. The resin: binder ratio is in the range 80: 20 to
20 : 80. The strong acid cation exchange resin (Indion 225 total exchange capacity
4 5meq/g), which is a sulphonated copolymer of styrene-divinylbenzene containing
sulphonic acid as Functional group, is used for preparing cation-exchange spacer. The
strong base anion-exchange resin (Indion FFTP, total exchange capacity 3.4 meq/g),
which is a chloromethylated and aminated copolymer of styrene-divinylbenzene
containing quaternary ammonium as functional group, is used for anion-exchange spacer
and a mixture of cation-exchange and anion-exchange resin in the ratio 40: 60 to 60 : 40
is used for amphoteric ion-exchange spacer. In the third step a suitable net made of
polyethylene (PE) or polyvinyl chloride (PVC) or polypropylene or nylon having
openings 50 to 75% and thickness 0.4 to 0.6 is coated with the solution prepared in the
first step by dipping it into the solution The excess coating material is removed to keep
t h e opening of the net tree by air-blower and then the spacer is allowed to dry
The process qualifies as a simple three steps process, to prepare ion
exchanger spacer with good exchange capacity and low thickness, thus obviates the need
of preparing interpolymers and then introducing strongly acidic or basic groups using
chemicals thus avoiding number of steps involved in the preparation. In this method, the
simple inventive steps adopted are (i) in the first step, preparation of binder solution by
dissolving polyvinyl chloride or polysulfone in tetrahydrofuran or cyclohexanonerthus
obviates the cumbersome process for the preparation of interpolymer net.(ji) In4he
second step, suspension of fine powder ion-exchange resin, either cation or anion or both,
in the binder solution prepared in the first step thus obviates the need of converting the
interpolymer net into conducting spacer by chemical treatment using highly carcinogenic
chemicals like chlorosulphonic acid, chloromethylether, chloroform, trimethyl amine etc.
The second step also obviates the need of chloromethylation of substituted polystyrene,
which is absorbed in a catalytically cross-linked multifilament net, which needs proper
precautions for handing and disposals, (iii) In the third and final step, coating of a net of
appropriate thickness and openings, prepared from polyethylene or polyvinyl chloride or
polypropylene or nylon, with the solution prepared in the first two steps, and removal of
excess coating material to keep free the openings of the net using air blower and drying
of the spacer, thus obviates the need of cumbersome and time consuming process of
knitting anion and cation fibers separately and adding a thin nylon-fiber, thus increasing
one unit operation, for stability of sh u: during swelling. All these three steps thus
obviate the need of the steps involved in the preparation of reacted spacers, which
requires sulfochlorination of a polypropylene spacer using chemicals like
trichloroethylene, sulfur dioxide, chlorine, dimethylaminopropylamine.
dimethylformamide, methanol, NaOH etc. making the process longer. These steps also
obviate the need of using polyvinyl alcohol (PVA) cross-linked with
hexamethoxymethylmelamine in which polyethyleneimine is added, as binder for coating
a net with ground ion-exchange resin suspended in the solution of binder. The steps also
obviate the need of the steps involving dissolution of sulphonated polysulfone (SPS) in a
mixed solution of N-methyl pyrolydone (NMP) and ethanol into which the spacer are
dipped, and then dried to give the cation-conducting spacer or for anion-exchange spacer,
coating of the spacer with 5% solution of bromomethylated polysulfone (BMPS) and
polystyrene (PS) in N-methyi pyrolydone (NMP) and methylene chloride, followed by
ammination of the coated spacer with trimethyl ammine, methanol and distilled water
making the process longer.
The following examples are given by way of illustrations and should not be
construed to limit the scope of the present invention.
EXAMPLE-1.
4 g polyvinyl chloride (PVC) was dissolved in 200 ml of tetrahydrofuran (THF) solvent
taken in a closed container. To this solution 16 gm of powdered cation-exchange resin of
mesh size - 200 + 300 BSS was dispersed thoroughly. A 70 cm x 42 cm polyethylene
net with 50% opening and thickness 0.4 mm is dipped in this solution. The viscous
coating covers a large part of the opehi; , the net. Air is blown in order, to confine the
coating to the strands of the net and keep the openings free The spacer is then dried at
•t( rc
The properties of the cation-exchange spacer are
Thickness : 0.6 mm
Moisture 28%
Exchange capacity 1 45 meq/g dry spacer
Performance : Tested in an ED stack containing 7 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm" By applying
2V/cell pair water with total dissolved solids (IDS) 1000 ppm, 750 ppm. 500 ppm can be
reduced to 128 ppm. 100 ppm and 60 ppm respectively at the flow rate of 1.0 lit./hr.
The experiment was carried out at 25°C .
EXAMPLE-2
8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent
taken in a closed container. To this solution 32 gm of powdered cation-exchange resin of
mesh size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene
net with 75% opening and thickness 0.5 mm is dipped in this solution. The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free. The spacer is then dried at
40°C.
The properties of the cation-exchange spacer are
Thickness : 0.7 mm
Moisture 25%
xchaime capacity I 40 mei|/g d i v spacei.
Performance . Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm Bv applying
2V7cell pair water with total dissolved solids (IDS) 1000 pprn. 750 ppm. 500 ppm can be
reduced to 130 ppm. 100 ppm and 80 ppm respectively at the flow rate of 2.0 lit./lir.
2 I l i t / h r and 2.3 l i t / h r
The experiment was carried out at 30UC
EXAMPLE-3
10 a polyvinyl chloride (PVC) was dissolved in 500 ml of tetrahydrofuran (THF) solvent
taken in a closed container. To this solution 40 gm of powdered cation-exchange resin of
mesh si/e - 400 + 500 BSS was dispersed thoroughly A 200 cm x 120 cm nylone net
with 60% opening and thickness 06 mm is dipped in this solution. The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the cation-exchange spacer are
Thickness : 0.8 mm
Moisture : 30%
Exchange capacity : 1.50 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 ceil pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2 By applying
2V/'cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be
1-5
reduced to 120 ppm. l)0 ppm and 65 ppm respectively at the ilo\v tale -of 1.9 lit./hr.
The experiment was carried out at 32"C.
EXAMPLE-4
32 g polyvinyl chloride (PVC) was dissolved in 400 ml of cyclohexanone solvent taken
in a closed container. To this solution 8 gm of powdered cation-exchange resin of mesh
size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene net
with 60% opening and thickness 04 mm is dipped in this solution. The viscous coating,
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the cation-exchange spacer are
Thickness : 0.65 mm
Moisture : 8%
Exchange capacity : 05 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V7cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm? 500 ppm can be
reduced to 130 ppm. 105 ppm ami 80 ppm respectively at the flow rate of 1.5 lit./hr.
!61it../hr. and 1.52 lit./hr.
The experiment was carried out at 35 °C .
EXAMPLE-5
16 g polysulfone was dissolved in 400 mi of tetrahydroftiran (THF) solvent taken in a
closed container. To this solution 24 gm of powdered cation-exchange resin of mesh size
- 400 + 500 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinylchloride net
with 55% opening and thickness 0 42 mm is dipped in this solution. The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the cation-exchange spacer are _
Thickness : 0 60 mm
Moisture : 29%
Exchange capacity : 1.20 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm, 500 ppm can be
reduced to 130 ppm, 105 ppm and 70 ppm respectively at the flow rate of 2.0 lit./hr,
2.07lit./hr. andl.81it./hr.
The experiment was carried out at 32 °C .
EXAMPLE-6
20 g polyvinyl chloride was dissolved in,.5'", ^1 of cyclohexanone solvent .taken in a
closed container. To this solution 30 gm of powdered cation-exchange resin of mesh size
... 300 + 400 BSS was dispersed thoroughly. A 200 cm x 120 cm polyvinyl chloride net
with 60% opening and thickness 0.5 mm is dipped in this solution. The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the cation-exchange spacer are
Thickness : 0.72 mm
Moisture : 27%
Exchange capacity : ( 30 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm7 By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be
reduced to 125 ppm, 100 ppm and 65 ppm respectively at the flow rate of 2.05 lit./hr,
2.00lit./hr. and 1.9 lit./hr.
The experiment was carried out at 28 °C .
EXAMPLE-7
16 g polysulfone (PS) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in
a closed container. To this solution 24 gm of powdered cation-exchange resin of mesh
size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene (PP)
net with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and kefep the openings free. The spacer is then dried
at40()C.
The properties of the cation-exchange spacer are
Thickness 0 65 mm
Moisture : 20%
I'xchange capacity : I 20 meq/g drv spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm'. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be
reduced to 130 ppm, 100 ppm and 60 ppm respectively at the flow rate of 2.1 lit./hr,
1.9!it./hr. and 1.8 lit./hr.
The experiment was carried out at 29 °C .
EXAMPLE-8
8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent
taken in a closed container. To this solution 32 em of powdered cation-exchange resin of
mesh size - 400 + 500 BSS was dispersed thoroughly. A 150 crn x 100 cm nylon net
with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40 C.
The properties of the cation-exchange spacer are
Thickness : 0.7 mm
Moisture : 30%
Exchange capacity : 1.50 meq/g dry spacer
Performance Tested in an F.D stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cnr Bv applying
2 V/celi pair water with total dissolved solids (IDS) 1000 ppm. 750 pptn. 500 ppm can be
reduced to 120 ppm, 100 ppm and 60 ppm respectively at the flow rate of 2.0 lit./hr
2 I lit Vhr. and 2.2 lit./hr
The experiment was carried out at 28 °C
EXAMPLE-9
10 g polyvinyl chloride (PVC) was dissolved in 500 ml of cyclohexanone solvent taken
in a closed container. To this solution 40 gm of powdered cation-exchange resin of mesh
si/c 300 + 400 BSS was dispersed thoroughly A 200 cm x 120 cm polyvinyl chloride
net with 55% opening and thickness 0.42 mm is dipped in this solution. The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free. The spacer is then dried at
40°C
The properties of the cation-exchange spacer are
Thickness : 0.65 mm
Moisture : 21%
Exchange capacity : 1 45 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solid , DS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 130 ppm. 95 ppm and 62 ppm respectively at the flow rate of 2.02 lit /hr.
: Olit /hr and 2.05 lit./hr
The experiment was carried out at 32 C .
EXAMPLE-10
8 u polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent
taken in a closed container To this solution 32 gm of powdered anion-exchange resin of
mesh si7.e - 300 + 400 BSS was dispersed thoroughly A 150 cm \ 100 cm polyethylene
net with 75% opening and thickness 05 mm is dipped in this solution The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free The spacer is then dried at
4()"C
The properties of the anion-exchange spacer are
Thickness : 0.72 mm
Moisture : 30%
Exchange capacity : 1.72 meq/g dry spacer
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V7cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm. 500 ppm can be
reduced to 120 ppm, 90 ppm and 60 ppm respectively at the flow rate of 2.4 lit./hn
2.5lit./hr. and 2.45 lit./hr.
The experiment was carried out at 32° C
EXAMPLE-11
10 g polyvinyl chloride (PVC) was dissolved in 500 ml of tetrahydrofuran (THF) solvent
taken in a closed container To this solution 40 gm of powdered anion-exchange resin of
mesh size - 400 + 500 BSS was dispersed thoroughly A 200 cm x 120 cm polyethylene
net with 60% opening and thickness 0.6 mm is dipped in this solution The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free. The spacer is then dried at
40°C.
The properties of the anion-exchange spacer are
Thickness 0.8 mm
Moisture 29%
Exchange capacity : 1 80 meq/g dry spacer
Performance : Tested in an ED stack containing 15 ceil pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm. 750 ppm, 500 ppm can be
reduced to 125 ppm, 95 ppm and 40 ppm respectively at the flow rate of 2.45 lit./hr.
2.41it./hr. and 2.3 lit./hr.
The experiment was carried out at 32°C .
EXAMPLE-12
32 u polwinyl chloride (PVC) was dissolved in 400 ml of cvclohexanone solvent taken
in a closed container. To this solution 8 gm of powdered anion-exchange resin of mesh
"00 + 400 BSS was dispersed thoroughly A I n cm I no cm polyethylene net
y..ith 60% opening and thickness 0 4 mm is dipped in this solution The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the anion-exchange spacer are
Thickness : 0.60 mm
Moisture i 2%
Exchange capacity : 08 meq/g dry spacer
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2 By applying
2V, cell pair water with total dissolved solids (IDS) !000 ppm, 750 ppm, 500 r.pm can be
reduced to 125 ppm, 100 ppm and 70 ppm respectively at the flow rate of 1.6 lit./hr, 1.65
lit./hr. and 1.70 lit./hr.
The experiment was carried out at 35 °C .
EXAMPLE-13
16 g polysulfone was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in a
closed container. To this solution 24 gm of powdered anion-exchange resin of mesh size
- 400 + 500 BSS was dispersed thoroughly A 150 cm x 100 cm polyvinyl chloride net
with 55% opening and thickness 0 42 mm is dipped in this solution The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the anion-exchange spacer are
Thickness 0 62 mm
Moisture : 3!°o
Exchange capacity : I 44 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm' By applying
2V/cell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm, 500 ppm can be
ieduced to 1.30 ppm. 100 ppm and 70 ppm respectively at the flow rate of 2 30 lit./hr.
2 20lit./hr and 2.30 lit./hr
The experiment was carried out at 32 °C .
EXAMPLE-14
20 g polyvinyl chloride was dissolved in 500 ml of cyclohexanone solvent taken in a
closed container. To this solution 30 gm of powdered anion-exchange resin of mesh size
- .300 + 400 BSS was dispersed thoroughly. A 200 cm x 120 cm polyvinyl chloride net
with 60% opening and thickness 0.5 mm is dipped in this solution The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the anion-exchange spacer are
Thickness : 0 70 mm
Moisture : 30%
Exchange capacity : 1.42 meq/g dry spacer.
Performance : Tested in an ED stack ,r. aining 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm. 500 ppm can be
reduced to 120 ppm. 104 ppm and 76 ppm respectively at the flow rate of 2.20 lit./hr.
2.251it./hr. and 2.21 lit./hr.
The experiment was carried out at 28 °C .
EXAMPLE-15
16 g polvsulfone (PS) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken in
a closed container. To this solution 24 gm of powdered anion-exchange resin of mesh
size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene (PP)r
net with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free. The spacer is then dried at
40°C.
The properties of the anion-exchange spacer are
Thickness : 0.60 mm
Moisture : 29%
Exchange capacity : 1.40 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 125 ppm, 100 ppm and 50 ppm respectively at the flow rate of 2.25 lit./hr,
2.21it./hr. and 1.5 lit./hr.
The experiment was carried out at 29 °C .
EXAMPLE-16
8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydroftiran (THF) solvent
taken in a closed container. To this solution 32 gm of powdered anion-exchange resin of
mesh size - 400 + 500 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene
(PP) net with 55% opening and thickness 0.45 mm is dipped in this solution. The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free. The spacer is then dried at
40°C.
The properties of the anion-exchange spacer
Thickness . 0.72 mm
Moisture : 31%
Exchange capacity : 1.75 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm? 500 ppm can be
reduced to 100 ppm, 80 ppm and 40 ppm respectively at the flow rate of 1.8 lit./hr,
1.91it./hr. and 2.2 lit./hr.
The experiment was carried out at 32 °C .
EXAMPLE-17
10 g polyvinyl chloride (PVC) was dissolved in 500 ml of cyclohexanone soNfent taken
in a closed container. To this solution 40 gm of powdered anion-exchange resin of mesh
size .?00 + 400 BSS was dispersed thoroughly. A 200 cm x I 20 cm polvvinvl chloride
net with 55% opening and thickness 0.42 mm is dipped in this solution The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free The spacer is then dried at
-40°C
The properties of the anion-exchange spacer
Thickness : 0.60 mm
Moisture : 30%
F.xchange capacity : 1 80 meq/g dry spacer
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 125 ppm, 90 ppm and 45 ppm respectively at the flow rate of 2 35 lit./hr,
2.30lit./hr. and 2.35 lit./hr.
The experiment was carried out at 35 °C .
EXAMPLE-18
8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydroruran (THF) solvent
taken in a closed container To this solution 192 gm of powdered anion-exchange resin
of mesh size - 300 + 400 BSS and 12.8 gm of powdered cation-exchange resin of mesh
size - 400 + 500 BSS were dispersed thoroughly. A 150 cm x 100 cm polyethylene net
with 75% opening and thickness 05 mm is dipped in this solution. The viscous coating
covers a large part of the opening of the net Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
1 he properties of the amphoteric ion-exchange spacer are
Thickness : 0.72 mm
Moisture : 28%
Total exchange capacity 1 60 meq/g dry spacer
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm caiUw
reduced to 110 ppm, °0 ppm and 40 ppm respectively at the flow rate of 2.3 IttJhr,
2 4lit ,/hr. and 2.35 lit./hr
I he experiment was carried out at 32°C .
EXAMPLE-19
16 g polysuifone (PS) was dissolved in 400 ml of tetrahydrofuran (THF) solvent taken hi
a closed container. To this solution 12 gm of powdered anion-exchange resin of mesh
si7.e - 400 + 500 BSS and 12 gm of powdered cation-exchange resin of mesh size -'400 +
500 BSS was dispersed thoroughly A 150 cm x 100 cm polyproplene net with 60%
opening and thickness 0.4 mm is dipped in this solution The viscous coating covenra
large part of the opening of the net. Air is blown in order to confine the coating to the
strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the amphoteric ion-exchar . spacer are
Thickness : 0.6 mm
Moisture : 26.1%
Total exchange capacity 1 23 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm*. By applying
ZVVcell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm. 500 ppm can be -
reduced to 130 ppm, 100 ppm and 60 ppm respectively at the flow rate of 2.4 lit./hr, 2.2
lit./hr and 2.3 lit./hr.
(he experiment was carried out at 32°C
EXAMPLE-20
16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahvdrofuran (THF) solvent
taken in a closed container. To this solution 9.6 cm of powdered anion-exchange resin of
mesh size - 300 + 400 BSS and 14.4 gm of powdered cation-exchange resin of mesh size
- 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinyl chloride net
with 60% opening and thickness 0.4 mm is dipped in this solution. The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the amphoteric ion-exchange spacer are
Thickness : 0 62 mm
Moisture : 25%
Total exchange capacity : 1.20 meq/g dry spacer.
Performance : Tested in an ED stack ccv , ing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2Vcell pair water with total dissolved solids (IDS) 1000 ppm. 750 ppm. 500 ppm can be
reduced to 130 ppm. 105 ppm and 60 ppm respectively at the flow rate of 2.2 lit./hr.
22!lit/hr and 2.0 lit,/hr.
The experiment was carried out at 33°C
EXAMPLE-2I
16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THH solvent
taken in a closed container. To this solution 14.4 gm of powdered anion-exchange resin
of mesh size - 300 + 400 BSS and 9.6 gm of powdered cation-exchange resin of mesh
size 300-+ 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene net
with 60% opening and thickness 0.4 mm is dipped in this solution The viscous coating
covers a large part of the opening of the net, Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the amphoteric ion-exchange spacer are
Thickness : 0.61 mm
Moisture : 26%
Total exchange capacity 1.40 meq/g dry spacer
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 125 ppm, 100 ppm and 50 ppm respectively at the flow rate of 2.3 lit./hr.
2 4 l i t / h r and 2.1 lit./hr
The experiment was carried out at 35°C
HXAMPLE-22
16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tctrahydrotiiran (THF) solvent
taken in a closed container. To this solution 12 gm of powdered anion-exchange resin of
mesh size - 300 + 400 BSS and 12 gm of powdered cation-exchange resin of mesh size -
300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyethylene net with
60% opening and thickness 0.4 mm is dipped in this solution The viscous coating covers
a large part of the opening of the net. Air is blown in order to confine the coating to the
strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the amphoteric ion-exchange spacer are
Thickness 0 60 mm
Moisture : 27%
Total exchange capacity : I 23 mcq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm7 By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 130 ppm, 105 ppm and 70 ppm respectively at the flow rate of 2.5 lit./hr,
2.2lit./hr. and 2.1 lit./hr.
The experiment was carried out at 32°C .
EXAMPLE-23
16 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent
taken in a closed container. To this solution 12 gm of powdered anion-exchange resin of
mesh size - 300 + 400 BSS and 12 gm of powdered cation-exchange resin of mesh size -
"500 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinyl chloride net
with 60% opening and thickness 0.4 mm is dipped in this solution. The viscous coating
covers a large part of the opening of the net. Air is blown in order to confine the coating
to the strands of the net and keep the openings free. The spacer is then dried at 40°C.
The properties of the amphoteric ion-exchange spacer are
Thickness : 0 62 mm
Moisture 26%
Total exchange capacity : 1.24 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and -cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (TDS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 125 ppm, 100 ppm and 65 ppm respectively at the flow rate of 2.4 lit./hr, 2.1
lit./hr. and 2.3 lit./hr.
The experiment was carried out at 33°C .
EXAMPLE-24
8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent
taken in a closed container. To this solution 16 gm of powdered anion-exchange resin of
mesh size - 300 + 400 BSS and 16 gm of powdered cation-exchange resin of mesh size -
300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyproplene net with
60% opening and thickness 04 mm is ,4>ed in this solution. The viscous coating covers
a large part of the opening of the net. Air is blown in order to confine the coating to the
strands of the net and keep the openings free. The spacer is then dried at 40 °C.
The properties of the amphoteric ion-exchange spacer are
Thickness : 0.60 mm
Moisture : 29%
Total exchange capacity : 1.5 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2. By applying
2V/cell pair water with total dissolved solids (IDS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 120 ppm, 100 ppm and 50 ppm respectively at the flow rate of 2.3 lit./hr, 2.4
lit./hr and 2.3 lit./hr.
The experiment was carried out at 30°C .
EXAMPLE-25
8 g polyvinyl chloride (PVC) was dissolved in 400 ml of tetrahydrofuran (THF) solvent
taken in a closed container. To this solution 12.8 gm of powdered anion-exchange resin
of mesh size - 300 + 400 BSS and 19.2 gm of powdered cation-exchange resin of mesh
size - 300 + 400 BSS was dispersed thoroughly. A 150 cm x 100 cm polyvinyl chloride
net with 60% opening and thickness 0.4 mm is dipped in this solution. The viscous
coating covers a large part of the opening of the net. Air is blown in order to confine the
coating to the strands of the net and keep the openings free. The spacer is then dried at
40°C.
The properties of the amphoteric ion-exchange spacer are
Thickness : 0.62 mm
Moisture 27%
Total exchange capacity : 1.4 meq/g dry spacer.
Performance : Tested in an ED stack containing 15 cell pairs of anion and cation
exchange membranes having effective single membrane area 80 cm2 By applying
2V/cell pair water with total dissolved solids (IDS) 1000 ppm, 750 ppm, 500 ppm can be
reduced to 130 ppm, 105 ppm and 60 ppm respectively at the flow rate of 2 3 lit./hr, 2.4
litVhr. and 2.3 lit./hr
The experiment was carried out at 34°C .
The main advantages of the present invention are:
1. It is a very simple two steps process.
2. Process is highly flexible from the viewpoint of selection of net materials.
3. Wide variation in net design is possible.
4. Use of least quantity and number of chemicals.
5. It is possible to vary the ion exchange capacity of the spacers from a very low to
very high value.
6. Moisture content of the spacers can be widely varied.
7. Process is such that the maximum utilization of the material is possible
8. Single technique may be adopted for the preparation of both the types (cationic or
anionic) of spacers.
9 Spacer size may be flexible from small to medium to big depending upon the
requirement.
10 Long life of the spacers
11 The same solution used for coating on a net for preparing ion-exchange spacer
can be used also for preparing heterogeneous ion-exchange membranes by coating
on a cloth, which is a subject matter of another patent

We claim:
1. A process for the preparation of improved heterogeneous ion-exchange spacer which
comprises;
(a) preparing a suspension of ion-exchange resin selected from anion exchange, cation exchange and mixture thereof having mesh size -200+300 to -400+500 BSS in a solution prepared by dissolving binder selected from polyvingly chloride, polysulphone in an organic solvent,
(b) coating of above said mixture obtained in step (a) on a polymer net made of polymer selected from Polyethylene, polyvinyl chloride, polypropylene or nylon at a temperature ranging from 25 to 35°C,
© removing the excess coating material to keep the opening of the net free by air blower and drying the ion-exchange spacer.
2. A process as claimed in claim 1, wherein anion-exchange resin is chloromethylated and amminated copolymer of styrene-divinylbenzene, having quaternary ammonium as functional group.
3. A process as claimed in claims 1 to 2, wherein cation-exchange resin is sulphonated copolymer of styrene-divinylbenzene, having sulphonic acid as functional group.
4. A process as claimed in claims 1 to 3, wherein the organic solvent used for dissolving binder is selected from Tetrahydrofuran or cyclohexane.
5. The process as claimed in claimsl to 4, wherein the dip coating technique is used to prepare ion-exchange spacer.
6. The process as claimed in claims 1 to 5, wherein the net used to obtain the ion-exchange spacer is having openings 50 to 76% with thickness 0.4 to 0.6 mm.

7. The process as claimed in claims 1 to 6, wherein the mixture of powdered cation and
anion-exchange resins having mesh size - 200 + 300 BSSS to 400 + 500 BSS, with
resin ratios in the range selected from 40:60 to 60:40 is used to obtain amphoteric ion-
exchange spacer.
8. The process as claimed in claims 1 to 7, wherein the capacity of the cation-exchange spacer is in the range 0.5 to 1.5 meq/gm dry spacer.
9. The process as claimed in claims 1 to 8, wherein the exchange capacity of the anion-exchange membrane is in the range of 0.8 to 1.8 meq/gm dry spacer.
10. The process as claimed in claims 1 to 9, wherein the total exchange capacity of the amphoteric ion-exchange spacer is in the range of to 1.5 nieq./gm dry spacer.
11. The process as claimed in claims 1 to 10, wherein the thickness of the spacer obtained is in the range of 0.6 to 0.8 mm.
12. A process for the preparation of improved heterogeneous ion-exchange spacer substantially as herein described with reference to the examples accompanying this specification.

Documents:

472-DEL-2003-Abstract-(08-05-2009).pdf

472-del-2003-abstract.pdf

472-DEL-2003-Claims-(08-05-2009).pdf

472-del-2003-claims.pdf

472-DEL-2003-Correspondence-Others-(08-05-2009).pdf

472-del-2003-correspondence-others.pdf

472-del-2003-correspondence-po.pdf

472-DEL-2003-Description (Complete)-(08-05-2009).pdf

472-del-2003-description (complete).pdf

472-del-2003-form-1.pdf

472-del-2003-form-18.pdf

472-DEL-2003-Form-2-(08-05-2009).pdf

472-del-2003-form-2.pdf

472-DEL-2003-Form-3-(08-05-2009).pdf

472-del-2003-form-3.pdf

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Patent Number

236262

Indian Patent Application Number

472/DEL/2003

PG Journal Number

43/2009

Publication Date

23-Oct-2009

Grant Date

14-Oct-2009

Date of Filing

27-Mar-2003

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	GAURANG SHAMBHUPRASAD TRIVEDI	CENTRAL SALT AND MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR-364002(GUJARAT) INDIA.
2	PARAMITA RAY	CENTRAL SALT AND MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR-364002(GUJARAT) INDIA.
3	BHARATI GUNVANT SHAH	CENTRAL SALT AND MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR-364002(GUJARAT) INDIA.
4	SAMIR KUMAR ADHIKARY	CENTRAL SALT AND MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR-364002(GUJARAT) INDIA.
5	RAMAMURTI RANGARAJAN	CENTRAL SALT AND MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR-364002(GUJARAT) INDIA.
6	PUSHPITO KUMAR GHOSH	CENTRAL SALT AND MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR-364002(GUJARAT) INDIA.

PCT International Classification Number

B01D 61/44

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA