Title of Invention

"A PROCESS FOR PREPARATION OF IMPROVED CATION EXCHANGE RESINS BEADS"

Abstract

Is invention relates to a process for the preparation improved cation exchange resin beads based on sulphonated crosslinked styrene copolymer. The process comprises in the synthsis of copolymer in the form of herical beads by polymerisation of styrene with a copoylmer selected from maleic anhydride, acrylic acid or methacrylic acid and then the beads so obtained are objected to the step of sulphonation.

Full Text

FIELD OF INVENTION This invention relates to a process for preparation of improved cation exchange resins beads with improved ion exchange capacity. More specifically but without implying any limitation thereto, the invention relates to a process for preparation of crosslinked sulphonated styrene based copolymer which has application in areas like a self indicating ion exchange resin and as a reusable indicator in acid-base titrations. PRIOR ART Ion exchange resins are, generally, crosslinked polymers having exchangeable cationic and anionic groups. They are widely used for the deionisation of water, softening of water, recovery of precious metals like gold and uranium, ion exchange chromatography, in medicine and in catalysis. The ion exchange resins are mostly used in the form of spherical beads. According to a process known in the art, the resins in the form of spherical beads are prepared by aqueous suspension polymerisation. In this process, the monomers together with the initiator are dispersed as droplets in water. A disadvantage of the above process for preparation of the resin is that only those monomers which are immiscible with water can be used for the preparation of the beads. According to another process known in the art the resin is prepared by nonaqueous suspension polymerization. A disadvantage of the above process for the preparation of the resin is that the heat dissipation during this process is poor compared to the aqueous suspension process. Another disadvantage of the above process for preparation of the resin is that this involves more health hazards compared to the aqueous suspension process. Still another process known in the art the resin is prepared by reverse aqueous suspension polymerization. A disadvantage of the above method is that beads can be prepared only for water miscible monomers. A combination of water miscible and immiscible monomers can never be prepared. OBJECTS OF INVENTION The primary object of the present invention is to propose a process for preparation of resin, more specifically, for preparation of crosslinked sulfonated styrene based copolymer beads having improved ion exchange capacity. Another object of the present invention is to propose a process for preparation of a resin which imparts acid-base indicating capability to the resin which in turn enables the resin to give an indication by the colour change when the resin is exhausted and requires regeneration. Still another object of the present invention is to propose a process for preparation of the resin which can be used as a reusable indicator in acid-base titrations. STATEMENT OF INVENTION According to this invention there is provided a process for the preparation of improved cation exchange resin beads based on sulphonated crosslinked styrene copolymker comprising the steps of: a) synthesis of copolymer is carried in presence of stabilizer, a crosslinker, preferably divinyl benzene and an initiator, preferably azobis isobutyro nitrile in preferred concentration of 0.5 weight percentage in the form of spherical beads characterized by polymerisation of styrene with a monomer selected from maleic anhydride, acrylic acid or methacrylic acid in the ratio of 1:2; b) sulphonation is carried out with sulphuric acid at around 70° C for about 6 hours for styrene maleic anhydride and at room temperature for a longer duration for styrene-acrylic acid and styrene-methacrylic acid at a temperature of 60 to 70° C. A disadvantage of the above process for the preparation of the resin is that the heat dissipation during this process is poor compared to the aqueous suspension process. Another disadvantage of the above process for preparation of the resin is that this involves more health hazards compared to the aqueous suspension process. Still another process known in the art the resin is prepared by reverse aqueous suspension polymerization. A disadvantage of the above method is that beads can be prepared only for water miscible monomers. A combination of water miscible and immiscible monomers can never be prepared. OBJECTS OF INVENTION The primary object of the present invention is to propose a process for preparation of resin, more specifically, for preparation of crosslinked sulfonated styrene based copolymer beads having improved ion exchange capacity. Another object of the present invention is to propose a process for preparation of a resin which imparts acid-base indicating capability to the resin which in turn enables the resin to give an indication by the colour change when the resin is exhausted and requires regeneration. Still another object of the present invention is to propose a process for preparation of the resin which can be used as a reusable indicator in acid-base titrations. STATEMENT OF INVENTION According to this invention there is provided a process for the preparation of improved cation exchange resin beads based on sulphonated crosslinked styrene copolymker comprising the steps of: a) synthesis of copolymer in tne form or spherical beads by polymerisation of styrene with a monomer selected from maleic anhydride, acrylic acid or methacrylic acid in the ratio of 1:2; b) sulphonation a temperature of 60 to 70° C. BRIEF DESCRIPTION OF INVENTION The process of the present invention provides a method for the preparation of a cation exchange resin which is a crosslinked sulfonated styrene based copolymer having carboxyl acid group. The copolymers synthesized are styrene- inaleic anhydride(SMAn), styrene-acryh'c acid (SAA)and styrene- methacrylic acid(SMA). After sulphonation with sulfuric acid, the former have three and the latter two have two functional groups per repeat unit for exchange, whereas the commercial resins have only one exchangeable group. In other words, the exchange capacity of the resin prepared by the process of the present invention is much higher than the exchange capacity of the existing comparable resins. The copolymers are synthesized by the polymerisation of styrene with maleic anhydride or acrylic acid or methacrylic acid monomers using azobis isobutyro nitrile as initiator and divinyl benzene as crosslinker. The synthesis.and sulphonation of styrene-maleic anhydride copolymer are shown in Fig.l(a) and synthesis and sulphonation of styrene- acrylic acid or styrene -methacrylic acid copolymers are shown in Fig.l(b). The molar ratio of styrene to the other monomer is 1:2 in the case of styrene - maleic anhydride and 1:1 in the case of the other two copolymers namely styrene -acrylic acid and styrene- methacrylic acid. The ratio can be varied to get copolymers of desired composition. The weight percentage of the crosslinker is 10% with respect to the total weight of the two monomers in all the cases which was sufficient to give enough crosslinking to the beads. The conventional aqueous suspension polymerisation used for the synthesis of spherical polymer beads can not be used as such in the synthesis of these copolymer beads due to the solubility of the second monomer in water. The polymerisation process has therefore been improved in the process of the present invention. In the process of the present invention the solubility of the second monomer in the aqueous phase is suppressed by saturating it with sodium chloride. The styrene monomer which is hydrophobic and the carboxylic monomer which is hydrophilic are dissolved in methyl isobutyl ketone. Conventional suspension stabilizers like poly(vinyl alcohol) are ineffective in the present system. Therefore, magnesium hydroxide has been prepared in situ and used as the stabilizer. The processing parameters such as stirring speed and temperature have been standardized to get beads of 0.5 to 1.0 mm diameter. The sulphonated styrene acrylic acid beads prepared by the process of the present invention exhibit an unusual acid-base indicating property. The beads show yellow colour in acid which changes to purple colour at the equivalence point. During sulphonation the copolymer undergoes cyclic dehydration giving rise to this acid-base indicating property. In the known ion exchange resins, indicator properties are generally introduced by either chemically reacting the resin with common indicators or by physically mixing indicator with it. As against these, the resin prepared by the process of the present invention has inherent acid- base indicating properties without requiring any specific chemical processing for this purpose. The beads prepared by the process of the present invention can therefore be used as reusable indicators in acid base titrations. The resin prepared by the process of the present invention has the additional advantage of the self indication of the utilisation by the colour change. DESCRIPTION OF THE PROCESS According to the proposed process for the preparation of resin in the form of beads, the process comprises of the following steps:- Synthesis of Copolvmer Beads a) Charging a mixture containing 60 g to 70g, preferably 60g to 65g of sodium chloride, and 1 .0g to 2.0g, preferably 1 .0g to 1.2 g magnesium chloride which is carried out in a container containing 150 ml to 180 ml, preferably 150ml to 160ml of water. (b) Heating the mixture as prepared by step(a) to a temperature in the range of 60-80 degree Celsius preferably around 75 °C and also stirring the mixture in the speed range of 400- 600 rotations per minute preferably around 500 rpm. (c) Adding 5 ml to 10.0 ml preferably 5.0ml to 6.0ml of I N NaOH to precipitate magnesium hydroxide in situ. (d) Preparing a dispersed phase mixture in another container containing styrene+ acrylic acid or styrene + methacrylic acid in the preferred molar ratio of 1:1 or styrene+ maleic anhydride in the preferred molar ratio 1:2, a crosslinker preferably divinyl benzene in weight percentage of 10 with respect to the total weight of the two monomers , and an initiator preferably azobis isobutyro nitrile in weight percentage of 0.5 with respect to the total weight of the two monomers and dissolving all these in 20 to 30 ml methyl isobutyl ketone at room temperature. (e) Adding the dispersed mixture slowly to the aqueous mixture while the stirring is going on. (f) Increasing the stirring speed preferably to preferably around 800 rpm and the temperature 75° C to 80° C . (g) The beads started appearing in 30 minutes but the stirring to continue for another 30 minutes for completion of the reaction. (h) Cooling the contents to room temperature and then washing with dilute hydrochloric acid to dissolve the magnesium hydroxide, filtering followed by washing 3 to 4 times with water. (i) Washing the beads with dioxane or chloroform or carbon tetrachloride or with acetone to remove any unreacted monomers followed by drying. Sulphonation of Beads (j) The beads are obtained by steps (i) are sulphonated by suspending the beads in concentrated sulfuric acid at 60 to 70 C° for 6 hours for styrene- maleic anhydride and at room temperature for a longer duration for styrene - acrylic acid or styrene- methacrylic acid till the beads get a brownish colour after putting in water. (k) Washing the beads obtained by step(j) several times with water to make it free of acid. The process of the present invention is illustrated with the following example which is intended to be taken as a typical example to illustrate the process and is not intended to be taken as restrictively to imply any limitation to the scope of the present invention. WORKING EXAMPLE A 500 ml three necked flask is fitted with a thermometer, a stirrer and condenser. It is charged with 150 ml water containing 60 g sodium chloride and 1 g magnesium chloride. The contents are heated to 75 °C and 5 ml of 1N sodium hydroxide is added to precipitate the magnesium hydroxide under vigorous stirring. The dispersed phase mixture containing 22 ml styrene, 6 ml divinyl benzene, 12 ml acrylic acid, 250 mg azobis isobutyro nitrile and 20 ml methyl isobutyl ketone are added and stirred at high speed at 75-80° C. The beads are formed within 30 min but the stirring is continued for another 30 min for the completion of the reaction. The magnesium hydroxide is dissolved by the addition of dilute hydrochloric acid and the beads are filtered and washed several times with water. The styrene-acrylic acid beads are then washed with dioxane or acetone to remove any unreacted monomers. They are then dried to constant weight. The yield is around 75%. The beads are then sieved using standard test sieves. The bead size ranges from 0.5-1.0 mm. The styrene - maleic anhydride beads and the styrene-methacrylic beads were also prepared by the same aqueous suspension polymerization as given above. The size of the beads is in the same range as in the case of styrene acrylic acid. The beads are sulphonated by suspending the beads in concentrated sulfuric acid. In the case of styrene acrylic acid and styrene methacrylic acid beads sulphonation has been carried out with sulfuric acid at room temperature for about 10 hours. The sulphonation of styrene maleic anhydride hsa been carried out in sulfuric acid at 60- 70° C for 6 hours. The colourless beads change to brown in concentrated acid which is later washed with water several times to make it free of acid. The beads are characterized by Fourier Transform Infrared Spectroscopy (FTIR) and carboxylic acid exchange capacity. The 1R spectra give the characteristic absorptions for O-H stretch (3500cm-1 ;strong, broad) and C=0 stretch (1720 cm-1) for the styrene acrylic acid and styrene methacrylic acid copolymers. The styrene maleic anhydride copolymer gives the characteristic absorptions for the anhydride group at 1850 cm-1 and 1775 cm-1. The sulphonated beads are also characterized by FTIR and by determination of the exchange capacity. The IR spectra shows the characteristic absorptions for sulphonic acid groups: a very broad absorption between 3000- 3500 cm-1 for the O-H stretching and two sharp absorptions at 1260 cm-1 and 1097 cm-1 for the S=O stretching. However, in the case of sulphonated styrene acrylic acid, the IR spectra shows a shift in the carbonyl group stretching frequency i.e. the peak at 1720 cm-1 in the unsulphonated polymer has shifted to 1671 cm-1 in the sulphonated polymer. This shows that some chemical change has happened in this copolymer during sulphonation in addition to the aromatic sulphonation. It appears that the acrylic acid part of the polymer undergoes partial cyclisation with the aromatic ring giving a conjugated structure which result in the unusual acid- base indicating property of this copolymer. The exchange capacity of all the copolymer beads are determined by standard method and given in Table 1. The exchange with sodium hydroxide solution gives the total exchange capacity since both sulphonic and carboxylic protons exchange with sodium hydroxide. The exchange capacity with sodium chloride solution gives only the exchange of the sulphonic acid groups. The exchange with calcium chloride solution has been carried out after converting the resin to the sodium form. Table 1. Exchange Capacity and Elemental Composition of Copolymer Beads (Table Removed) SAA = styrene- acrylic acid SMA = styrene- methacrylic acid SMAn = styrene- maleic anhydride SSAA = sulphonated styrene- acrylic acid SSMA = sulphonated styrene- methacrylic acid SSMAn = sulphonated styrene- maleic anhydride The exchange capacity has been determined by equilibration method. A known weight of the beads are taken in a stoppered bottle and equilibrated with a known volume of standard alkali for 12 hours. A definite volume of the alkali is later pipetted out without the beads and titrated with standard acid. The capacity is calculated in milliequivalents per gram. The exchange capacity of a commercial resin is also measured by the same method and given in Table 1. It can be seen that the total capacity of all the beads are higher than that of the commercial resins. The exchange capacity was also determined using sodium chloride solution by elution method. For this a known weight of the beads in the H-form were taken in a column and 250 ml 0.25 N NaCl solution was passed through the column at a flow rate of 2 ml/min. The eluant was collected in a conical flask and the acid produced was estimated by titrating with standard NaOH. The exchange capacity with NaCl is lower than that with NaOH, because, the carboxylic acid proton does not exchange with NaCL The total exchange capacity is lower than the theoretical value and is due to the chemical change happened during sulphonation as mentioned above. The Ca2+ uptake of the beads were estimated by taking a known weight of the polymer in sodium form in a column and 0.25 N CaCl2 was passed through the column at a flow rate of 2 ml/min. The resin bed was then washed with distilled water and the Ca2+ was eluted by passing 1.0 N HC1 solution. The calcium content was evaluated by EDTA method. The indicator properties of the beads were evaluated by carrying out the titrations with standard hydrochloric acid and standard sodium hydroxide of different concentrations using the beads as reusable indicator. The values obtained were same as that obtained with phenolphthalein indicator. Thus, the beads can be used as reusable indicators in acid-base titrations. It is to be understood that the process of the present invention is susceptible to adaptations, modifications by those skilled in the art. Such adaptations, modifications are to be covered within the scope of the present invention which is set forth by the following claims. WE CLAIM; 1. A process for the preparation of improved cation exchange resin beads based on sulphonated crosslinked styrene copolymker comprising the steps of: a) synthesis of copolymer is carried in presence of stabilizer, a crosslinker, preferably divinyl benzene and an initiator, preferably azobis isobutyro nitrile in preferred concentration of 0.5 weight percentage in the form of spherical beads characterized by polymerisation of styrene with a monomer selected from maleic anhydride, acrylic acid or methacrylic acid in the ratio of 1:2; b) sulphonation is carried out with sulphuric acid at around 70° C for about 6 hours for styrene maleic anhydride and at room temperature for a longer duration for styrene-acrylic acid and styrene-methacrylic acid at a temperature of 60 to 70° C. 2. A process for the preparation of improved cation exchange resin beads as claimed in claim 1 wherein the molar ratio of styrene monomer to the other monomer is 1:2 in the case of styrene maleic anhydride copolymer and is 1:1 in the case of styrene acrylic acid and styrene methacrylic acid. 3. A process for the preparation of improved cation exchange resin beads as claimed in claim 1 wherein the weight percentage of divinyl benzene is 10. 4. A process for the preparation of improved cation exchange resin beads as claimed in claim 1 wherein the synthesis of copolymer is carried out in the presence of a stabilizer, preferably freshly prepared magnesium hydroxide at intermediate stage of reaction by hydrolysis of magnesium chloride. 5. A process for the preparation of an improved cation exchange resin as prepared by the process substantially described and illustrated herein.

Documents:

1886-del-1998-abstract.pdf

1886-del-1998-claims.pdf

1886-del-1998-correspondence-others.pdf

1886-del-1998-correspondence-po.pdf

1886-del-1998-description (complete).pdf

1886-del-1998-form-1.pdf

1886-del-1998-form-19.pdf

1886-del-1998-form-2.pdf

1886-del-1998-form-3.pdf

1886-del-1998-gpa.pdf