Modeling of methanol to olefins (MTO) process in a circulating fluidized bed reactor

Methanol is obtained commercially from natural gas. However, production of light olefins such as ethylene, propylene, etc. from natural gas is higher value-added gas conversion option and therefore, the conversion of methanol to olefins is of industrial importance. In the present work, this process is simulated in a circulating fluidized bed (CFB) reactor at 450 degreesC a nd at atmospheric pressure. The simulation combined the kinetic model with SAPO-34 as the catalyst and the core-annulus type hydrodynamic model. The m odeling studies indicated that the selectivity towards ethylene increased s ignificantly with increase in coke deposit on the catalyst. This was attrib uted to the 'cage effect' of the coke on the catalyst. However, the increas e in coke deposit on the catalyst also decreased the methanol conversion. A t 5 wt% coke on the catalyst, the methanol conversion and C-2 + C-3 light o lefin selectivity were optimum at 90 and 75 wt%, respectively. The influenc e of the exit geometry such as smooth exit, abrupt exit and exit with a pro jected end, on the solids hold-up and thereby on the methanol conversion an d light olefin yield were also studied. As the exit geometry varied from sm ooth to exit with projected end, the methanol conversion increased due to t he increased solids hold-up in the riser correspondingly increasing the lig ht olefin yield. The simulator also predicts the flow characteristics withi n the CFB. (C) 2001 Elsevier Science Ltd. All rights reserved.