Changing the balance of the MTO reaction dual-cycle mechanism: Reactions over ZSM-5 with varying contact times

The methanol to olefins (MTO) reaction was performed over ZSM-5 zeolite at 300 degrees C under various methanol weight hourly space velocity (WHSV) values. During these trials, the catalytic perfor mance was assessed, in addition to the formation and function of organic compounds retained in the zeolite. Analysis of reaction effluents and confined organics demonstrated a dual-cycle reaction mechanism when employing ZSM-5. The extent of the hydrogen transfer reaction, a secondary reaction in the MTO process, varied as the catalyst-methanol contact time was changed. In addition, C-12/C-13-methanol switch experiments indicated a relationship between the dual-cycle mechanism and the extent of the hydrogen transfer reaction. Reactions employing a low methanol WHSV in conjunction with a long contact time favored the hydrogen transfer reaction to give alkene products and promoted the generation and accumulation of retained organic species, such as aromatics and methylcyclopentadienes, which enhance the aromatic cycle. When using higher WHSV values, the reduced contact times lessened the extent of the hydrogen transfer reaction and limited the generation of methylcyclopentadienes and aromatic species. This suppressed the aromatic cycle, such that the alkene cycle became the dominant route during the MTO reaction. (C) 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.