Influencing selectivity in the oxidative coupling of methane by modulating oxygen permeation in a variable thickness membrane reactor

Onoja, Ojotule P. and Wang, Xiaodong and Kechagiopoulos, Panagiotis N. (2019) Influencing selectivity in the oxidative coupling of methane by modulating oxygen permeation in a variable thickness membrane reactor. Chemical Engineering and Processing: Process Intensification, 135. pp. 156-167. ISSN 0255-2701

Abstract

The Oxidative Coupling of Methane (OCM) has been considered for years as a promising alternative for the production of higher hydrocarbons, namely ethane and ethylene. Nonetheless, OCM’s inherent conversion-versus-selectivity limitations have not allowed till now for economical C2 yields to be achieved. Reactor engineering studies guided by a detailed mechanistic description of the reaction can directly contribute to obtaining an understanding of these limitations. In this work, a Variable Thickness Membrane Reactor (VTMR) is proposed, wherein O2 permeation along the reactor is modulated, aiming at maximizing C2 selectivity. 1D and 2D reactor simulations are carried out to compare the performance of this reactor to conventional co-feed Packed Bed Reactors (PBR) and Membrane Reactors without variable thickness (MR). Particular attention is given on the impact of gas phase reactions on C2 selectivity, while the effect of surface exchange kinetics on both sides of the membrane and bulk diffusion of O2 across the membrane is discriminated. When identical operating conditions (T = 1073 K, P = 1 atm, Space time = 7.85 s) and reactor geometry (Length = 0.1 m, Diameter = 0.01 m) were evaluated, the optimization performed of the VTMR configuration achieved a C2 selectivity of 67.26%, in comparison to 47.86% and 29.87% for the MR and PBR, respectively, highlighting the potential of the concept.