INFLUENCE OF FRAMEWORK SUBSTITUTION OF AL3-ZEOLITE( BY FE3+ AN THE SORPTION CHARACTERISTICS OF BETA)

The sorption characteristics of Al-beta (SiO2 : Al2O3 = 39) and Fe-bet a (SiO2 : Fe2O3 = 39-46) zeolites in both sodium and protonic forms ha ve been compared. Sorption capacities at P/P-0 = 0.8 and 298 K for wat er, hexane, cyclohexane and butylamine (BA) yielded estimates of the v oid volume of the beta zeolites. Sorption kinetics with these probe mo lecules also confirmed the highly crystalline nature of the samples. B A sorption isotherms in both the zeolites in the temperature range 333 -483 K have also been measured to characterize the acidic centres in t he zeolites. Analysis of the BA sorption data in terms of different so rption models yielded useful information on the nature of sorbent surf ace and sorption centres. Sorption selectivities were also compared by evaluation of the chemical potential of the sorption at isotherm temp eratures. Isosteric heats (Q(st)) of BA sorption were evaluated by the application of a thermodynamic approach to the sorption energetics. O ver the entire coverage Q(st) values varied within 40-60 kJ mol(-1) fo r H/Al-beta and within 18-40 kJ mol(-1) for H/Fe-beta zeolites.