Single-Event MicroKinetics (SEMK) for Methanol to Hydrocarbons (MTH) on H-ZSM-23
•A Single-Event Microkinetic (SEMK) model is developed for ZSM-23.•Alkylation/cracking steps forming primary carbenium ions are additionally accounted for on ZSM-23 compared to ZSM-5.•Steady state kinetics are derived from data affected by deactivation as the product distribution is conversion independent.•The aromatic hydrocarbon pool cycle toward light olefins formation is suppressed on ZSM-23 as compared to ZSM-5.•The alkylation-cracking reactions become more important as compared to methylation reactions with increase in space time.
A Single-Event MicroKinetic (SEMK) model was constructed for the Methanol to Hydrocarbon (MTH) reaction on ZSM-23 with a Si/Al ratio of 26. The experimental data were acquired at 400 °C, atmospheric pressure using space times between 19.2 and 57.7 kgcat smol−1. Starting from a previously established fundamental reaction mechanism for MTH on ZSM-5, an extended reaction network, also involving primary carbenium ion alkylation/cracking reactions, was considered. The reaction network in terms of elementary steps for di-methyl ether (DME) and olefins formation from the aromatic hydrocarbon pool as well as from the alkene homologation cycle was implemented. The single-event concept together with thermodynamic constraints allowed to reduce the number of adjustable parameters to 33, from which only 2 activation energies for (s,p) and (t,p) alkylation/cracking, 6 alkene protonation heats, the total concentration of aromatic hydrocarbon pool and the stability difference between secondary and primary carbenium ion had to be determined by regression. The model explains well the product distribution with physically realistic parameter values. The estimated alkene protonation heats increase from 10.4 kJ mol−1 for ethene to 64.1 kJ mol−1 for hexene. A contribution analysis indicated that the alkene-homologation cycle is the dominant reaction pathway for olefins formation on ZSM-23.
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Journal: Catalysis Today - Volume 215, 15 October 2013, Pages 224–232