Sulfonic acid exchange resins stability

From the literature it is well known that this etherification reaction requires an acidic catalyst. In industrial processes ion-exchange resins with sulfonic acid groups are in use. The structure of this cross-linked resin is depicted in Fig. 8.6 To have a catalyst that can compete with the existing materials we decided to prepare a catalyst that also contains sulfonic acid groups. To compile the requirements for the new catalyst, kinetic data for MTBE synthesis [11, 17] and information on chemical [18] and mechanical [19] stability of ion-exchange resins under the reac-... 

Both sulfuric acid and hydrofluoric acid catalyzed alkylations are low temperature processes. Table 3-13 gives the alkylation conditions for HF and H2SO4 processes. One drawback of using H2SO4 and HF in alkylation is the hazards associated with it. Many attempts have been tried to use solid catalysts such as zeolites, alumina and ion exchange resins. Also strong solid acids such as sulfated zirconia and SbFs/sulfonic acid resins were tried. Although they were active, nevertheless they lack stability. No process yet proved successful due to the fast deactivation of the catalyst. A new process which may have commercial possibility, uses... 

Nafion, a perfluorinated sulfonated polymer, is a typical example of an ion-exchangeable resin with high promise as a catalyst support. Its properties are significantly different from those of common polymers (stability towards strong bases, and strong oxidizing and reducing acids and thermal stability up to at least 120 °C if the counter ion is a proton, and up to 200-235 °C if it is a... 

The mechanical stability and ion exchange capacity of these condensation resins were modest. A better approach is to prepare a suitable crosslinked base membrane, which can then be converted to a charged form in a subsequent reaction. Ionics is believed to use this type of membrane in many of their systems. In a typical preparation procedure, a 60 40 mixture of styrene and divinyl benzene is cast onto a fabric web, sandwiched between two plates and heated in an oven to form the membrane matrix. The membrane is then sulfonated with 98 % sulfuric acid or a concentrated sulfur trioxide solution. The degree of swelling in the final membrane is controlled by varying the divinyl benzene concentration in the initial mix to control crosslinking density. The degree of sulfonation can also be varied. The chemistry of the process is ... 

More recently, Biswas and Chatteijee have prepared polystyrene electro-philically substituted with phthalic anhydride pyromellitic diianhydride tri-mellitic anhydride and 1,2,3,4-tetrahydrophthalic anhydride by Friedel-Crafts reaction. These anhydride-modified polystyrenes have further been converted into sulfonic acid resins by conventional sulfonation reaction. The thermal stabilities of these modified polymers are comparatively better than that of unmodified polystyrene. Ion-exchange capacities also compare favourably with the polystyrene-based commercial resins. 

Furfural-salicylic acid and furfural-P-naphthalenesulfonic acid resins possess thermal stabilityexceeding that of KU-1 (sulfonated phenol-formaldehyde resin) and approaching that of KU-2 (sulfonated SDVB copolymer). The heat resistance of toluenesulfonic acid-furfural resin is quite similar to that of KU-2 resin. The improved thermal stability of furfural-based cation-exchange resins is attributed to the presence of heterocyclic and aromatic rings in these resins. 

Ethers. The polycondensation of diphenyl ether and furfural (1 1.5mole ratio) in presence of sulfuric acid yields a resin which has been sulfonated by sulfuric acid at 50 °C for 10 h to give a cation-exchange resin The swelling and the exchange capacity of the product increase with the amount of sulfuric acid present during the polycondensation and are higher for a resin obtained by polycondensation in carbon tetrachloride than the one prepared in absence of solvent. The thermal stability of sulfonated diphenyl ether-furfural resin is more than that of KU-1 and comparable to that of KU-2. The sulfonic acid resin derived from the copolymer obtained by the polymerization of diphenyl ether and furfural at a mole ratio of 1 2 in carbon tetrachloride has optimum adsorption and catalytic activity... 

Styrene. The condensation of furfural with styrene in presence of zinc chloride followed by sulfonation with sulfuric acid yields a bifunctional cation-exchange resin (SFS) containing —SO3H and —COOH groups The resin has a total capacity of 4.2 meq/g and a sal-splitting capacity of 3.1 meq/g and can be used up to 100 °C without any appreciable fall in capacity In column operation the bed volume of the resin has been observed to be constant in a series of cycles carried out, indicating the stability of the resin in different regenerant and influent solutions. 

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