The Effect of Coke Deposition of Catalyst on the Reaction of Methanol to Olefins

TG,NH3-TPD and BET methods were used to characterize the coked methanol to olefins(MTO) catalyst.With the increase of coke deposition amount,strong acid sites decreased while the weak acid sites almost maintained on the catalyst.Micropore specific surface area and volume of MTO catalyst declined with the growth of coke deposition.The regression of micropore specific surface area and volume showed that the coke was intra-pore monolayer adsorbed on catalyst.With the increase of coke amount,the methanol conversion kept constant first,then decreased sharply,and the selectivity of lower olefins increased first,then decreased gradually in MTO reaction.It is shown from the comprehensive analysis of acid characteristics results and methanol conversion of MTO reaction that the moderate and weak acid sites in catalyst did make methanol conversion efficiently.Although the strong acid sites could not affect methanol conversion,they could lead to unwanted secondary reactions of lower olefins.There existed an appropriate coke amount on MTO catalyst to help obtaining the maximum selectivity of lower olefins and to keep the certain methanol conversion.