Selective and stable production of ethylene from propylene over surface-modified ZSM-5 zeolites

This study is the first to examine the selective production of ethylene from propylene (propylene-to-ethylene, PTE) with using various structural types of zeolites. The catalytic performances of these zeolite catalysts were tested in a continuous fixed-bed reactor system with respect to ethylene selectivity and catalyst stability during the overall reaction period. Among these zeolite catalysts, ten-membered ring zeolites with three-dimensional pore structures (ZSM-5 and ZSM-11) exhibited stable catalytic performances with considerable ethylene selectivity compared to other zeolite catalysts. The ZSM-5 zeolite, thus selected, was further studied in the PTE reaction with different silica-alumina ratios (Si/Al-2, SARs), a surface modification with phosphorus, and under different reaction conditions in order to investigate the effect of acidity, surface properties, and process variables on the catalytic activity as well as to additional improve the ethylene selectivity. From these studies, the PTE reaction was found to depend strongly on the reaction condition, SAR and surface P modification in the ZSM-5 zeolite. The phosphorous-modified ZSM-5 catalyst exhibited the highest ethylene selectivity of more than 70% with moderate propylene conversion of 36.3% at a low propylene space velocity and a low partial pressure condition.