Hetero‐homogeneous pyrolysis of isobutane and platinum wall‐effects in conditioned or unconditioned reactors

Abstract

The pyrolysis of isobutane has been studied a t 500°C in a "Pyrex" static reactor packed with platinum. It is shown that both dehydrogenation and demethanation rates are strongly depressed by the metal packing. The reaction rates are very sensitive to the amount of cabonaceous coating which is deposited on the walls. As this amount increases, both rates first increase, go through a maximum and decrease. These observations are compared with those previously made on propane pyrolysis in a "Pyrex" reactor packed with stainless steel. The present results are interpreted on the basis of a hetero-homogeneous chain mechanism in which the selectivity of the free-radical reaction is not altered referring to the unpacked reactor. 0

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

“…As shown in a previous article [2] and by contrast with the PbO-treated reactor, the rate of isobutane pyrolysis in the Pt reactor is very sensitive to the surface conditioning of the packing and to the amount of carbon deposits arising from prior pyrolyses of this reactant. In order to get reproducible results, it was necessary to condition the reactor walls with oxygen and hydrogen as mentioned in the experimental section.…”

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

“…This reactor will be subsequently termed the PbO-treated reactor. A second Pyrex vessel was packed with small platinum foils to a s/v of 2 (1 cm ) about…”

“…The effect of temperature on the initial rates was also examined and data of Figure 5 (method 2) as well as concentration-time profiles (method 1) give convergent values of the activation energies (see Table V) if the platinum packing is lightly conditioned. By contrast, a heavily conditioned reactor, that is a reactor in which isobutane has been pyrolyzed during 500 torr two days [2] and in which measured reaction rates are typically increased by a factor 3 at gives acti-773 K, vation energies much smaller than the lightly conditioned reactor (Table V). This result enlightens the importance of wall-seasoning in rate measurements.…”

“…Isobutane Pyrolysis in the Pt Reactor: Initial Rates (in Obtained by the Graphical ) or by the One-Minute Concentration Profile(2) and Initial Activation Energies E a for…”