Kinetic study and modeling of the hetero-homogeneous pyrolysis and oxidation of isobutane around 800 K. Part I. Pyrolysis in an unpacked pyrex reactor

Abstract

Isobutane pyrolysis is studied in an unpacked Pyrex reactor at 20–100 torr initial pressures and 750–793 K. Results are interpreted in terms of a long chain radical mechanism and the reaction is modeled. The reaction selectivity or ratio of the initial production rate of isobutene (or hydrogen) to that of propene (or methane) is practically given by the ratio of the rate constant of abstraction of a tertiary hydrogen atom of isobutane to that of a primary one. A sensitivity analysis clearly shows that self‐inhibition is essentially due to methylallyl radicals produced by hydrogen abstraction from isobutene. The model has been manually adjusted to experimental results and most of the adjusted rate constants are in agreement with literature data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 425–437, 1998

Kinetic study and modeling of the hetero-homogeneous pyrolysis and oxidation of isobutane around 800 K. Part II. Pyrolysis in pyrex reactors packed with platinum foils or PbO-treated pyrex rods

“…In this limiting case, the initial order of reaction would be unity for every product, which is consistent with the results obtained in the unpacked reactor [1]. The difference in the activation energies of CH 4 and H 2 formation is about as found in the un-Ϫ1 5 kcal mol packed vessel [1]; last, we would get:…”

“…A general description of the apparatus and experimental techniques has been given elsewhere [1,2] and only salient details will be presented here.…”

“…Isobutane pyrolysis in packed reactors may be interpreted by the free-radical scheme proposed for the un-444 ZILS, MARTIN, AND PERRIN packed reactor [1] completed by step (w). The following simplified scheme may therefore be proposed at small conversion:…”

“…The chains may be terminated either homogeneously in the gas-phase volume or heterogeneously on the walls of the vessel. In the first part of this work [1], it has been shown that isobutane pyrolysis in an unpacked Pyrex vessel is a typical freeradical chain reaction, with volume terminations only. The object of this second part is to learn more about wall effects and surface terminations in isobutane pyrolysis.…”

“…3 and 4). The initial orders of product formation at are 773 K given in Table II: they are near 2 instead of 1.1 in the unpacked vessel [1]. The reaction was studied at different temperatures and activation energies were determined at small conversion and initial concentration of isobu-…”