OPTIMUM YIELD OF THE PURELY HETEROGENEOUS OXIDATIVE DIMERIZATION OF METHANE

The optimal C-2-yield per pass for the purely heterogeneous catalytic oxidation of methane by O-2 on Sm2O3 under continuous cofeed operation : eta(opt) less than or equal to 0.22 +/- 0.03, is computed from actua l kinetic data for all the pseudoelementary chemical reactions involve d. The optimization dispenses with adjustable kinetic parameters, and explores the combined effects of CH4 and O-2 flow rates, catalyst mass , residence time, and temperature variations on the objective function eta=methane conversion x C-2-selectivity for the scheme: CH4 (+O-2) d ouble right arrow CH3 (-->) 1/2C(2)H(6) double right arrow 1/2C(2)H(4) double right arrow CO. The fact that the derived eta(opt) value essen tially coincides with the largest C-2-yields reported on a myriad cata lysts under vastly different conditions: (1) proves that the ceiling t o selectivity is sorely determined by the competition among heterogene ous processes and (2) implies a substrate-independent selectivity patt ern for the species formed in O-2 dissociative chemisorption. We brief ly analyze the physical basis of these propositions and of the prospec ts of improving C-2-yields beyond 25%. (C) 1997 Academic Press.