Temperature-dependent secondary conversion of primary products from methanol aromatization in a two-stage fluidized bed

Methanol to aromatics (MTA) following dual cycles concept unavoidably produced considerable amounts of olefinic intermediates and paraffinic by-products. Their formation and further conversion were vital to improving aromatics production. In this study, a two-stage fluid bed packed with fluid Zn/ZSM-5 catalyst in each stage was used to investigate the MTA reaction at 470 degrees C in the first stage and the secondary conversion of MTA primary products at temperatures from 270 degrees C to 550 degrees C in the second stage with time on stream. During the MTA reaction, the decrease of catalyst acidity was beneficial to controlling hydrogen transfer, thus blocking propane formation. During the secondary conversion of MTA products, at temperatures below 390 degrees C, the alkylation and hydrogen transfer reactions dominated and thus olefins were converted into more alkylbenzene as well as the undesired propane and butane. As the temperature increased from 430 degrees C to 550 degrees C, the aromatization of light hydrocarbon and the dealkylation of alkylbenzene were facilitated, producing more benzene and toluene but increasing methane and ethane yields. Meanwhile, the dehydrogenation and cracking of propane and butane were favored by high temperature and strong acidity so that the yields of ethene and propene increased. It was clarified that the characteristics of secondary conversion of MTA products varied and depended on reaction temperature and catalyst acidity. Based on these findings, the concept of regional functionalization of fluidized bed reactor was proposed for intensification of MTA process based on the reconfiguration of the temperature and acidity of catalyst stream during the fluidized bed reaction-regeneration cycle.