L21. THERMOCHEMICAL KINETIC ANALYSIS ON THE REACTION OF ALLYLIC ISOBUTENYL RADICAL WITH O2 :AN ELEMENTARY REACTION MECHANISM FOR ISOBUTENE OXIDATION
Chiung-Ju Chen and Joseph W. Bozzelli
Department of Chemical Engineering, Chemistry and Environmental Science,
New Jersey Institute of Technology, Newark, NJ 07102
Kinetics of the addition reactions of the allylic isobutenyl radical with molecular oxygen to form the energized adduct CH2=C(CH3)CH2OO× and the reactions of the adduct to products have been analyzed by using quantum Rice-Ramsperger-Kassel (QRRK) theory for k(E) and modified strong collision analysis for fall-off. Thermochemical and reaction path parameters are determined by molecular orbital calculations (PM3 and ab-initio) and by group additivity estimation. An elementary reaction mechanism is constructed to model the experimental system - isobutene oxidation. Detailed Chemical activation reaction analysis is done on the important reaction systems: allylic isobutenyl radical + O2, isobutene + HO2, isobutene + OH, isobutene-OH + O2 and allylic isobutenyl radical + HO2. All reactions in the mechanism incorporate reverse rates calculated from thermodynamic parameters and microscopic reversibility. Results show that several important equilibrium are achieved with product formation effected by slower (bleed) reaction out of the equilibrium systems. Important equilibrium exist for:
CH2=C(CH3)CH3 +O2 <=> CH2=C(CH3)CH2OO× and
CH2=C(CH3)CH2OO× <=> CH2=C(C× H2)CH2OOH.
Rate constants for formation of important products, acetone, methacrolein, epoxides, the five-member cyclic intermediate,cyclic-CH2C× (CH3)CH2OO- , and the four-member cyclic intermediate, cyclic-C(CH3)CH2OO-, are determined. Predictions are in good agreement with experimental data.
