Enhanced catalytic performance in butylene cracking by hierarchical surface silicon-rich ZSM-5

Abstract

In the process of butylene catalytic cracking, the amount, location and strength of acid sites of the catalyst play an important role in suppressing the undesired reactions. Hydrothermal dealumination is widely used to adjust the acidity of catalyst. Also, the steaming treatment has a significant impact on the physico-chemical properties of the catalyst, such as leading to mesoporosity at the perimeter of zeolite crystals through dealumination process. The mesoporosity is beneficial to long working life-span of catalyst, while it can increase the external surface acid sites of ZSM-5, subsequently resulting in non-shape selective catalytic reactions on the external surface of the catalyst. Coke and large-molecular hydrocarbons or intermediates can be produced relatively easily at external surface acid sites because of the absence of spatial constraints. The external acid sites of catalyst can be deactivated through chemical liquid deposition of SiO2 onto the surface of catalyst using the tetramethoxysilane (TMOS) as silica source. Combing hydrothermal treatment and TMOS modification, a hierarchical surface silicon-rich ZSM-5 zeolite without pore-opening narrowed was prepared. Compared with the catalytic performance of untreated catalyst, this new catalyst has achieved a high total yield of propylene and ethylene and showed excellent hydrothermal stability. Side reactions and coking were restrained simultaneously during the butylene cracking process.