Synthesis and Characterization of ZSM-22 Zeolites and Their Catalytic Behavior in 1-Butene Isomerization Reactions

Abstract

ZSM-22 zeolites, having a Si/Al ratio of 45, have been synthesized by sol-gel methods using 1,6-diaminohexane as a templating agent. The structures of these materials have been characterized by X-ray diffraction, transmission electron microscopy and electron diffraction, scanning electron microscopy, and adsorption techniques. Based on these analyses, these materials are determined to be of the Theta-1 structure type. Titration with pyridine base shows that these catalysts have a Brønsted to Lewis ratio of 7.0. Temperature programmed desorption experiments with NH 3 show that both strong and weak acid sites are present in this material and that the ratio of strong acid sites to weak acid sites is 1.1. From this information a total of 0.96 H + sites/u.c. has been calculated for this material, suggesting that these catalysts have relatively low acidity. The unique unidirectional pore structure and accompanying high Si/Al ratio of ZSM-22 provide for a potentially useful isomerization catalyst. These materials are used in this study for the isomerization of 1-butene, where shape selectivity is believed to be important in this first order reaction. Other kinetic information is obtained through deactivation studies and from studies of the effect of flow rates and temperature on conversion, selectivity, and yields of isobutylene. Yields and selectivities of 39.5 and 89%, respectively, have been obtained with this catalyst system.