abstracts - Институт катализа им. Г.К. Борескова

OP-III-32- high-activity zone - in which alkane molecules are activated with a formation of free alkylradicals;- high-selectivity zone - in which highly reactive radicals undergo selective transformationinto desired product(s).A proper design of SDCS includes a selection of efficient catalysts for each zone and aspatial organization of components, which provides with a fast transfer of reactive free-radicalintermediates from one zone to another. The latter means that the probability of anysecondary by-processes of free radical transformation should be diminished. This requires acareful selection of solid components of catalytic system (including reactor material, "inert"supports and packing), as well as a detailed analysis of gas-phase radical transformations.The directions and kinetics of gas-phase radical processes are analyzed by using apropane conversion as an example. In this case, reactive n- and/or iso-propyl radicals canform both in the gas phase and in heterogeneous processes. In order to achieve the highestpossible efficiency of the overall process, the time of radical transfer from the zone of theirformation to the zone of their controlled transformation into desired products must be shorterthan characteristic time of the fastest reaction of radicals (lifetime) in the gas phase.The lifetimes using the available kinetic data for gas-phase reactions of n- and iso-propylradicals at temperatures up to 1000 K are analyzed. Both mono-molecular (H-atomelimination and cracking) and bi-molecular reactions (recombination, disproportionation,oxidation, etc.) are taken into consideration. Corresponding lifetimes can be calculated asfollows:-1τ 1 = k 1andτ 2 = (k 2 C) -1where τ 1 and τ 2 - characteristic times for mono- and bi-molecular reaction respectively;k 1 and k 2 - corresponding rate constants;C - concentration of molecule-partner (in bi-molecular reaction).The comparison of calculated τ 1 and τ 2 values with characteristic times for heterogeneoustransformations and mass-transfer (inter- and intra-particle) can lead to conclusions onpossible contribution of different elementary reactions to the overall process. For instance,characteristic time for inter-particle diffusion τ D can be estimated asτ D = δ 2 /D ≈ 0.01 d 2 /D392