Reaction selectivity in a porous catalyst pellet: analysis of a kinetic model of two parallel, first order, irreversible reactions with a second order inhibition kinetic term in one of them

摘要

This work deals with the analysis of a kinetic model of two parallel, first order, irreversible reactions that include a second order inhibition term in one of them. The continuity differential equation taking account of isothermal diffusion and reaction of A in a spherical catalyst pellet, was formulated. The numerical solution of the latter equation yielded useful results related to the variation of the effectiveness factor (#eta#) and the selectivity (S) (S=[k_1C_A/(1+KC_A)~2]/[k_2C_A+k_1C_A/(1+KC_A)~2]) for the desired reaction (i.e. A +b_1 B->C) versus the Thiele modulus (#phi#). Parametric studies involved the investigation of the effects of k=k_2/k_1, the ratio of the intrinsic specific reaction rata constants, and the inhibition strength factor (i.e.KC_A), upon the #eta# vs. #phi# and the S vs. #phi# curves. The #eta# vs. #phi# curve turns faster towards lower #eta# values for high k values, especially at high inhibition KC_A values. Intraparticle diffusion imparts a pronounced effect upon selectivity, fact contrasting markedly from the standard case of two parallel reactions without inhibition, where selectivity is independent of diffusion resistance. The S vs. #phi# curves show a step increase occurring at specified values of #phi# that increase at high inhibition strengths. The relative selectivity S'(=S/S_0) vs. #phi# curves (where S_0 is the selectivity for reactant concentration at catalyst surface) increases monotonically with k and KC_A values and go though a maximum for high #phi# values.