Synthesis,characterization and catalytic acitivity of ZSM-5 zeolites having variable silicon-to-aluminum ratios

摘要

Hydrogel prepared from sodium silicate and aluinum sulfate with silicon-to-aluminum molar ratios (Si/Al)in the range 15-100 were readily transformed into ZSM-5 zeolite when subjected to heating by a rapid crystallization method using tetrapropylammonium bromide (TPAcentre dotBr)template at pH 10.The crystallization of gel having Si/Al molar ratio of 10 was achieved with diffculty and represented the lower limit of Si/Al ratio,while the gel with Si/Al molar ratio of 10 was achieved with difficulty and represented the lower limit of Si/Al ratio,while the gel with Si/Al molar ratio of 9 could not be crystallized even after several attempts.FCalcination of hte synthesized zeolites was carried out at 873K and ion-exchange was achieved suing aqueous ammonium nitrate solution.All synthesized zeolites were found to be ZSM-5 as confirmed by XRD and supported by FT-IR characterization.The synthesized zeolites were found stable up to 1323K,and possess surface properties and pore sizes comparable to those of ZSM-5 zeolites.The catalytic activity fo hte synthewized zeolites was sevaluated at 343,353,363 and 373 K in a flow reactor.or the reaction of methanol and osibutene to produc methyl tertiary butly ether (MTBE),the activity increased with decreasing Si/Al molar ratio of the zeolites and with increasing reaction temperature.These xeolites were found to have methyl tertiary butly ether selectivity in the range of 90-98% that decreased with increase in reaction temperature.