Modeling of the simulated countercurrent moving-bed chromatographic reactor used for the oxidative coupling of methane

Abstract

The oxidative coupling reaction of methane (OCM) is a potential industrial reaction for the efficient production of ethylene. Replacement of current technologies requires significant product yield improvements. A novel experimental reactor, the simulated countercurrent moving-bed chromatographic reactor (SCMCR), has reported OCM yields which exceed conventional reactors [ Tonkovich et al. , 1993, Science 262 , 221 ; Tonkovich and Carr, 1995, Chem. Engng Sci. (in press) ]. An understanding of the SCMCR operation is aided by concurrent mathematical modeling. The model mimics the experimental reactor configuration and operation. Four sections are used in the SCMCR, each containing one reaction column and two separation columns connected in series. The feed is switched from section to section at a rate less than a single section breakthrough time, and a make-up feed is used after the first cycle. Reaction occurs in the first column and is followed by rapid product and reactant separation in the ensuing section columns. The model does not incorporate the realistic and complex kinetics arising from the OCM, rather a simplified reaction term is used to qualitatively gain insight into the operation of the SCMCR. The effects of the feed switching time and the make-up feed rate are investigated. The reactant conversion has a maximum at intermediate values of both parameters. This agrees with experimental trends, where the methane conversion and the C 2 yield are also maximized at similar intermediate values of the switching time.