Ethylbenzene Transformation over a ZSM-5-Based Catalyst in a Riser Simulator

The transformation of ethylbenzene has been studied over a ZSM-5-type catalyst in a riser simulator that mimics the operation of a fluidized-bed reactor. The study was conducted at 350, 375, 400, 450, and 500 degrees C for reaction times of 3, 5, 7, 10, 13, and 15 s. The effect of reaction conditions on the ratio of cracking to disproportionation products (C/D), the distribution of diethylbenzene (DEB) isomers (m-DEB and p-DEB), and the ratio of benzene/diethylbenzenes (B/DEB) are reported. The experimental results were modeled using quasi-steady-state approximation. Disproportionation was determined to dominate at low temperatures (350-400 degrees C), while cracking reaction becomes significant as higher temperatures (>400 degrees C). Thus, two mechanisms were postulated to represent the disappearance of ethylbenzene during the transformation reaction (one mechanism for low temperature, and another for the complete temperature range considered). Kinetic parameters that were used for the disappearance of ethylbenzene during the transformation reaction, and in its conversion into cracking and disproportionation products, were calculated using the catalyst activity decay function, based on the time-on-stream (TOS). The apparent activation energies were determined to decrease: E-cracking > E-disproportionation.