Single-Event Microkinetics for Methanol to Olefins on H-ZSM-5
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- 作者：Pravesh Kumar ; Joris W. Thybaut ; Stian Svelle ; Unni Olsbye ; Guy B. Marin
- 刊名：Industrial & Engineering Chemistry Research
- 出版年：2013
- 出版时间：January 30, 2013
- 年：2013
- 卷：52
- 期：4
- 页码：1491-1507
- 全文大小：653K
- 年卷期：v.52,no.4(January 30, 2013)
- ISSN：1520-5045
文摘
A single-event microkinetic (SEMK) model was developed for the conversion of methanol to olefins (MTO) and used in the assessment of experimental data obtained on H-ZSM-5 with a Si/Al ratio of 200. The experiments were performed at temperatures from 643 to 753 K, space times between 0.5 and 6.5 kgcat路s mol鈥? and at atmospheric pressure. Dimethyl ether (DME) and primary olefins formation through aromatic hydrocarbon pool and higher olefins formation via the alkene homologation cycle, was implemented in terms of elementary steps. The single-event concept, in combination with thermodynamic constraints allowed a significant reduction of the number of adjustable parameters. A further reduction was achieved by calculation of the single-event pre-exponential factors based on statistical thermodynamics. Physicochemical constraints along with Boudart鈥檚 criteria were used to limit the parameter space. Twenty one activation energies of kinetically significant reaction families and eight protonation enthalpies corresponding to methanol, DME and olefins were estimated via regression to the experimental data. The SEMK model well describes the product distribution, relying on model parameters with a precise physical meaning. The trends in activation energies obtained, are as could be expected from the considered reaction family, and the type of carbenium ions involved as reactant and product. Olefin protonation enthalpies decrease from 鈭?1.2 kJ/mol for ethene to 鈭?0.3 kJ/mol for heptene. A reaction path analysis established that ethene originates exclusively from the aromatic hydrocarbon pool, while propene is formed both via the aromatic hydrocarbon pool and the alkene homologation cycle.