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°C and at atmospheric pressure. The simulation combined the kinetic model with SAPO-34 as the catalyst and the core-annulus type hydrodynamic model. The modeling studies indicated that the selectivity towards ethylene increased significantly with increase in coke deposit on the catalyst. This was attributed to the ‘cage effect’ of the coke on the catalyst. However, the increase in coke deposit on the catalyst also decreased the methanol conversion. At 5 wt% coke on the catalyst, the methanol conversion and C2+C3 light olefin selectivity were optimum at 90 and 75 wt%, respectively. The influence of the exit geometry such as smooth exit, abrupt exit and exit with a projected end, on the solids hold-up and thereby on the methanol conversion and light olefin yield were also studied. As the exit geometry varied from smooth to exit with projected end, the methanol conversion increased due to the increased solids hold-up in the riser correspondingly increasing the light olefin yield. The simulator also predicts the flow characteristics within the CFB.