OP-II-3

KN-1description, that can be characterized as empirical, may suffer from a poor validityand low predictive power beyond the above mentioned limits.In this work an approach to non-contradictory description of the OCM kinetics isformulated and discussed. It consists in the modeling of the OCM kinetics based onthe independent mechanistic data that demonstrate the redox nature of the targetprocess. The latter presumes that the main reaction pathways, such asandCH 4 (+ O 2 ) → CH 3 • (→ C 2 H 6 )C 2 H 6 (+ O 2 ) → C 2 H 4can be described in the framework of Mars-van Krevelen type kinetic schemes. Thesecond main assumption consists in the assignment of "blocks" of elementary freeradicalreactions (with corresponding rate constants) to the key parts of the overallcatalytic process (such as reduction and re-oxidation of active sites, formation of byproducts,etc.). This allows one to assign a certain physical meaning to apparentparameters that enter into the kinetic equations and to pre-evaluate the reasonablelimits of their values.This approach was tested on typical OCM catalysts (PbO/Al 2 O 3 , NaWMn/SiO 2 ,Ln-Mg-oxides) and demonstrated its ability to describe not only "smooth" kineticcurves and general trends (reaction rate vs. temperature, GHSV, reactant partialpressures; product selectivities vs. conversion, etc.), but also some non-trivial effects(such as competitive/stimulating reciprocal influence of hydrocarbons, non-linearselectivity trends, complex effects of additives, such as peroxides, etc.).It was concluded that although the detailed multi-step and the empiricaldescriptions of the OCM kinetics are conceptually different, they both reflect somebasic features of the process under consideration and are complementary. Beingused simultaneously, they can substantially improve the accuracy, the validity andthe predictive power of the kinetic description of the process under consideration.References[1]. M.L. Mitchell and R.H. Waghorne. US Patent No. 4205194 (1980).[2]. T. Fang and C. Yeh. J. Catal., 1981, v.69, p.227.[3]. G.E. Keller and M.M. Bhasin. J. Catal., 1982, v.73, p.9.23