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

Abstract

This work deals with the further development and optimization of a simulated countercurrent moving bed chromatographic reactor (SCMCR) for the oxidative coupling of methane (OCM). To optimize the adsorptive separation of OCM products from unreacted methane, different adsorbents were selected and tested. Hydrophobic carbon molecular sieve, examined along with other adsorbents (activated charcoal and zeolite with high silica/alumina ratio), appears to be the most suitable choice, both for methane storing and for efficient handling of the OCM separation. Three catalysts, Sm 2O 3, Y 1Ba 2Zr 3O 9.5, and Y 1Ba 2Ge 1O 3.5 have been studied in microcatalytic reactor experiments. The Y 1Ba 2Zr 3O 9.5 catalyst proved to be the best, giving 84% selectivity to C 2-products at a CH 4 O 2 ratio of 11 and nearly complete oxygen conversion. A detailed model of the SCMCR employing experimental information about the catalyst and adsorbent properties was developed to analyze the complex cyclic behavior of the SCMCR. It was found that observed methane loss, and therefore decreased conversion, are caused by incomplete desorption of methane in the carrier section of the SCMCR. This effect can be minimized by selecting a better adsorbent. The influence of the switching time and CH 4 O 2 ratio in the make-up feed, the two most important parameters in this system, on reactor performance was analyzed. It was shown that for the best catalyst (Y 1Ba 2Zr 3O 9.5) at optimal operating conditions the SCMCR can give 55% yield for C2 products at 75% methane conversion. Adaptive flow switching and the use of a non-uniform make-up feed appear to be promising methods for further optimization of the SCMCR.