Patent Application
20150298116
The present invention relates to a process for preparation of anion exchange membrane which is safe and convenient compared to conventional method. Particularly, this method relates to the preparation of quaternized anion exchange membranes (AEMs) via benzylic bromination of crosslinked methyl substituted aromatic polymer followed by amination and its application for water desalination. The developed anion exchange membrane exhibits significant desalination behavior and can be used for all applications where such ion exchange membranes are required.
Anion exchanges are generally prepared by quaternization of crosslinked chloromethylated polystyrene-DVB polymeric film. The synthesis of intermediate halomethylated (chloromethylated) polystyrene-DVB membrane involves the use of carcinogenic chloromethyl ether (CME).The use of CME for AEM preparation is hazardous to health.
The article “A novel positively charged composite membrane for nanofiltration prepared from poly (2,6-dimethyl-1,4-phenyleneoxide) by in situ amine crosslinking” published in J. Memb. Sci., 215, 25-32 (2003), by Tongwen et. al., describes the preparation of anion exchange resin from linear engineering plastics poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and its characterization. A base substrate made of aryl-brominated PPO polymers and a top layer made of benzyl- and aryl-brominated PPO polymers are taken together and subjected to in-situ amine crosslinking to obtain a membrane. The resultant membrane was characterized with pure water flux and rejection of electrolytes MgCl2 and NaCl. The properties of the nanofiltration membrane are significantly affected by the type of brominated polymers of the top layer, the amination time, and the composition of amination medium.
The article “Anion Exchange Membranes by Bromination of Benzylmethyl-Containing Poly(sulfone)s”, published in Macromolecules, 43, 2349-2356, (2010), by Jingling Yan and Michael A. Hickner, discloses the properties of anion-conducting membranes synthesized by halomethylation and quaternization of benzylmethyl-containing poly(sulfone)s. The benzylmethyl moieties serve as precursors to cationic sites, are introduced during polymer synthesis, thereby circumventing post modification of the polymer by chloromethylation.
The article entitled “Fundamental studies of a new series of anion exchange membranes: Membranes prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) and pyridine”, published in Journal of Membrane Science 279 (2006) 200-208, by Ming Gong et. al., describes the anion exchange membranes containing pyridinium groups was prepared by quaternization of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) membrane with pyridine. The prepared. AEM showed relatively low IEC, high water content and low membrane potential, which was due to the erosion of pyridine during the amination reaction.
Reference may be made to an article by Blanc, G. L., published in Bull. Soc. Chin., France, 33, 313, (1923), wherein they disclosed that the halomethylated aromatic hydrocarbons and polymeric analogues are promising key intermediate for the synthesis of many valuable chemicals for targeted applications for both laboratory and industrial scale. The halomethylation reaction particularly, Lewis acid catalyzed chloromethylation of aromatic group is an important intermediates step in realizing polymeric materials.
The article entitled “Porogenic Solvents Influence on Morphology of 4-Vinylbenzyl Chloride Based PolyHIPEs”, published in Macromolcules, 41, 3543-3546 (2008), by Peter Krajnc et. al., describes the poly(high internal phase emulsion) materials were prepared from concentrated emulsions containing 4-vinylbenzyl chloride as the reactive monomer and divinylbenzene as the cross-linker. The process of drying the polyHIPE materials also influenced the wet porosity. They have not attempted directly from methyl vinyl benzene.
The article entitled “A New Strategy to Microporous Polymers: Knitting Rigid Aromatic Building Blocks by External Cross-Linker”, published in Macromolcules, 44, 2410-2414 (2011), by Bien Tan et. al. They describes a series of microporous polymers via a low-cost versatile strategy, which involves “knitting” rigid aromatic building blocks, such as benzene, biphenyl, 1,3,5-triphenylbenzene, methylbenzene, chlorobenzene, and phenol using an external cross-linker. These materials are predominantly microporous and exhibit high surface areas. Moreover, different building blocks can generate materials with different pore structures, functional groups and application properties, which are significant for materials design. They used dimethoxymethane as linkers instead of CME.
The main object of the present invention is to provide a process for preparation of anion exchange membrane.
Another object of the present invention is to prepare styrene-co-divinylbenzene (Sty-co-DVB) type polymeric anion exchange membranes bearing quaternary ammonium groups in safe and eco-friendly manner.
Another object of the present invention is to provide a process to avoid the use of hazardous chloromethyl ether (CME) for chloromethylation of the aromatic ring of styrene moiety to introduce a —CH2Cl group.
Yet another object of the present invention is to provide a process to recognize that bromomethyl group (—CH2Br) would be even more efficient for quaternization.
Yet another object is to recognize that there is more than one way to introduce bromomethyl group (—CH2Br) essential for quaternization.
Yet another object is to recognize that bromination of the methyl group of the polymer formed from p-methylstyrene (p-MS) and divinylbenzene (DVB) would result in such a bromomethyl group.
Yet another object is to undertake such bromination reaction directly on inter-polymer films prepared by casting and melt extrusion process.
Yet another object is to demonstrate such equivalence of performance through electrodialysis-based desalination, keeping the cation exchange membrane constant.
Accordingly, the present invention provides a process for the preparation of inter-polymer anion exchange membrane wherein the said process comprising the steps of:
In an embodiment of the present invention binder used in step (b) is selected from the group consisting of polyethylene, chlorinated and fluorinated polymers, polycarbonate, polyester.
In one embodiment of the present invention polyethylene binder is selected from the group consisting of HDPE, LDPE, LLDPE or mixtures thereof.
In another embodiment of the present invention melted mixture of binder in step (b) is prepared by heating HDPE, LLDPE and xylene at temperature ranging between 140-160° C. to melt PE and homogenise followed by adding toluene into PE melt and cooling the mixture at temperature ranging between 80-90° C. to obtain melted mixture of binder.
Still in another embodiment of the present invention the films were of 0.1-0.3 mm thickness and contained 20-55% p-MS and 40-80% binder by weight.
Still in another embodiment of the present invention halogenation in step (c) at benzylic position involves chlorination or bromination or iodination and preferably bromination.
Still in another embodiment of the present invention bromination is carried out by N-bromosuccinimide or liquid bromine or 2:1 bromide-bromate.
Still in another embodiment of the present invention photoirradiation in step (c) is done by tungsten lamp, solar radiation, CFL lamp, LED lamp as light source.
Still in another embodiment of the present invention the degree of mono bromination of p-MS is 40-90%.
Still in another embodiment of the present invention the brominated film having 8-16% bromine by weight is quaternized employing tertiary amines and phosphines.
Still in another embodiment of the present invention the degree of quaternization is 80-100%.
Still in another embodiment of the present invention the membrane is conditioned prior to evaluation of membrane properties and membrane performance.
Still in another embodiment of the present invention Ion exchange membrane is having thickness of 0.1-0.3 mm, ion exchange capacity of 0.8-2.0 meq.g−1 dry weight, ionic resistance of 5-35 ohm.cm2, water uptake of 5-25% by weight, and transport number of 0.85-0.98.
Still in another embodiment of the present invention Ion exchange membrane is found suitable for electrodialytic desalination and is used for all applications where such ion exchange membranes are used.
The present invention relates to an improved process for the preparation of anion exchange membrane using two different approaches. The first approach relates to preparation of p-methylstyrene-co-divinylbenene (p-MS-co-DVB) polymer by radical polymerization with benzoyl peroxide (BPO) initiator in a solution additionally containing co-dissolved polyvinyl chloride (PVC), casting films from the above polymer solution carrying out benzylic bromination of the resultant polymeric film employing N-Bromosuccinimide (NBS) and thereafter subjecting the resultant film to amination to obtain quaternary ammonium sites. The second approach involves the preparation of inter-polymer film of p-MS-co-DVB polymer by radical polymerization with BPO through melt extrusion process with the mixture of high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) and conversion of this inter-polymer into thin film through blow film extrusion. Thereafter, the resulting thin film was subjected to benzylic bromination and subsequent amination to get quaternary ammonium group. In this way, two different processes have been adopted to prepare anion exchange membrane by greener route by avoiding hazardous chloromethylether. The thickness and ion exchange capacities of the AEMs prepared by former process was the range of 0.15-0.17 mm and 1.30-1.33 meq.g−1 while, by later process theses were 0.24-0.28 mm and 0.8-0.85 meq.g−1 respectively.
Novel Features of the Invention:
The main inventive steps involve the following:
Following are the examples given to further illustrate the invention and should not be construed to limit the scope of the present invention.
A mixture containing p-methylstyrene (5.60 g), DVB (divinyl benzene) (1.40 g), and benzoyl peroxide (BPO) as initiator (1% (w/w) with respect to monomer mixture) were added into a solution of PVC (3 g) in 30 ml of tetrahydrofuron (THF) under constant stirring at 65° C. for 4 hrs. The resultant hot solution was poured on a glass plate and a film was cast by ‘SS-304’ metal roller to get uniform thickness of the film in closed casting chamber. It was dried at 30° C. for 12 hrs. Thereafter, the film was peeled off from the glass plate and un-reacted monomer and solvent were removed through washing with methanol prior to further functionalization.
The experiment of Example-1 was repeated for the preparation of inter-polymer film by varying the composition of p-MS (5.95 g) and DVB (1.05 g), BPO (1% (w/w) with respect to monomer mixture), while keeping other parameter constant. The film was peeled off from the glass plate treated to remove unreacted monomer and solvent as similar method given in Example-1.
The experiment of Example-1 was repeated to prepare the inter-polymer film by varying the composition of p-MS (6.3 g) and DVB (0.70 g), BPO (1% (w/w) with respect to monomer mixture) while keeping other parameter constant. The film was peeled off from the glass plate and treated to remove unreacted monomer and solvent as similar method given in Example 1.
This example pertains to experiments on benzylic bromination of the inter-polymer films of examples 1-3. N-bromosuccinimide (NBS), (NBS: p-MS=2.5:1 w/w) and BPO (BPO: p-MS=0.02 (w/w)) were added into 800 ml of pure and mixed chlorinated solvents (CCl4; DCE; varying proportions of CCl4+DCE) and the solution poured into a cylindrical glass reactor. The inter-polymer films were allowed to react in immersed solution for 6 h at 80° C. under constant stirring in the presence of a 100 W tungsten lamp. The brominated films were then removed, washed with methanol and dried under ambient conditions. It was further dried under vacuum (5 mm Hg Exact value) at 30° C. and its Br-content was analyzed by Volhard method.
This example pertains to the quaternization of brominated films of example-4. The films were immersed in aqueous trimethylamine solution (30% w/w) in closed container at 30° C. for 24 h. The contents were occasionally shaken. The resultant membrane was washed thoroughly with water to remove the adhering amine. It was thereafter conditioned by immersing in 100 ml M HCl followed by water wash till neutral pH obtained, followed by immersing in 100 mll M NaOH, followed by water wash till once again neutral pH obtained. This cycle was repeated three times. The films were then kept standing in 100 ml 0.1 M NaCl solution for 24 h at 30° C. The adhering liquid on the membrane surface was wiped prior to measurement of membrane properties. (Table 1 and 2)
aBinder weight was 3 g in all the films
The granules of high density polyethylene (HDPE) (3.12 kg) and linear low density polyethylene (LLDPE) (0.780 kg) were added in a mixtruder (
The inter-polymer pellets of example-6 were kept in oven at 80° C. for 14 hrs to remove unreacted monomers and solvents. After curing, the inter-polymer pellets were converted into thin film of thickness 0.280 mm through blow film extruder.
This example pertains to experiments on benzylic bromination of the inter-polymer film of example 7. The p-MS-co-DVB/PE inter-polymer film was immersed in 500 ml of dichloro ethane at 30° C. for 24 h to swell the film prior to the bromination reaction and reaction was carried out using NBS: p-MS ratio (1:1 molar basis) in DCE solvent for 10 h in a similar manner as given in example 4. Thereafter, the film was taken out from the reactor and washed and cleaned in similar manner given in example 4 and Br content was measured
The quaternization of the brominated film of example 8 was carried out by the similar procedure given in example 5, except that the reaction temperature was 50° C. instead of room temperature. The resultant membrane was washed with water to remove the adhering amine and conditioned in similar way given in example 5. Thereafter, the ionic resistance and ion exchange capacity of this AEM was measured. (Table 3)
The EMF method was employed in the present study to estimate (tCl
ED experiments were performed in a laboratory-scale unit to assess the relative merits of AEM-7 and AEM-8 for the desalination of brackish water.
The Energy Consumption (EC) and Current Efficiency (CE) were obtained for AEM-7 and AEM-8. The data are presented in Table 6 shows that the values of EC and CE of AEM-7 developed in the present invention are marginally superior to the AEM-8. The EC was the lowest for AEM-7 while CE was the highest.
The IEC values of the membranes remained nearly identical for three cycles of regeneration. The IEC values were also checked after ED experiments and no significant differences were seen. Stability of the AEMs under thermal and oxidative conditions is also important for their practical application in electrochemical processes. After Fenton's test, the IEC and membrane weight showed a reduction while Rm increased. The data are tabulated in Table 8. It can be seen that the data of the AEM-7 is matched closely those of AEM-8. Both the membranes were also found to be hydrolytically stable.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3598/DEL/2012 | Nov 2012 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IN2013/000712 | 11/25/2013 | WO | 00 |
