A detailed mechanism for initial phases of oxidation and pyrolysis of methyl tert-butyl ether (MTBE)

Author

Wen-Chiun Ing, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

9-30-1990

Degree Name

Master of Science in Environmental Science - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Richard B. Trattner

Third Advisor

Henry Shaw

Abstract

The lead phasedown in gasoline in both the U. S. and in Europe, the failure of other nonlead oxygenates (e.g. ethanol...) to significantly improve octance ratings and therefore to serve as replacement for tetra ethyl lead in gasline, and the U. S. Environmental Protection Agency's restrictions on gasoline RVP (Reid Vapor Pressure) to decrease tropospheric ozone concentrations are the factors causing the rapid growth in MTBE demand. There is however no detailed chemical kinetic study on the thermal or oxidative reactions of MTBE for full understanding the behavior and characteristics of MTBE and its degradation products during combustion processes.

Detailed mechanisms were developed for the oxidation reactions of MTBE (methyl tert-butyl ether) and compared with the experimental data done by Norton et.al.^<14> in this work. The unimolecular and bimolecular including chemical activation processes versions of Quantum RRK theory were used to develop kinetic mechanisms for the MTBE oxidations. Sensitivity analysis on this reaction mechanism was performed to identify the important reaction channels and to improve the fit of the mechanism on experimental observation.

The model results give a satisfactory fit for the conversion of MTBE with the experimental data. This mechanism clearly indicates the acceptable path toward the formation of the major experimentally observed products, isobutylene and methanol. The molecular elimination path is dominant when temperature are below rs,900 K in the MTBE oxidation system. Our mechanism explains why Daly et a/.^<24> and Choo et a4^<25> concluded that the decomposition reaction of MTBE is a four-center molecular elimination at the condition of temperature around 700 K. We determine rate constants for important reactions at 1 atm and temperature between 800 and 1200 K :

(CH₃)₃COCH₃--k₁-->(CH₃)₂C = CH₂ + CH₃OH

k₁ = 7.72 x 10¹³exp(-29700/T) sec^-1

(CH₃)₃COCH₃ --k₂--> (CH₃)₃C • +CH₃O*

k₂ = 3.66 x 10¹⁷exp(-39600/T) sec^-1

The difference between the calculation result and high pressure limit increases when the temperature is above 1000 K at atmospheric pressure. The reaction of (C₃COC --> C₃C • +CH₃O-) therefore becomes important as the temperature increasing and becomes dominant when the temperature is higher than 1800 K.

Recommended Citation

Ing, Wen-Chiun, "A detailed mechanism for initial phases of oxidation and pyrolysis of methyl tert-butyl ether (MTBE)" (1990). Theses. 2759.
https://digitalcommons.njit.edu/theses/2759