Dual bed catalytic reactor system for direct conversion of methane to liquid hydrocarbons

Abstract

The feasibility of upgrading natural gas that primarily consists of methane to valuable chemicals, especially liquid fuel has been investigated for years. However, the high cost and inefficient processes have hampered the widespread exploitation of natural gas. Accordingly, a system comprising of a dual-bed catalytic has been investigated in this study to overcome the limitations and permit the direct conversion of methane to liquid hydrocarbons. In this dual-bed system, methane is converted in the first stage to Oxidative Coupling of Methane(OCM) products over La/MgO and the second bed comprises of H-ZSM-5 that has been tested as an oligomerization function to convert the OCM products to liquid hydrocarbons. The influence of SiO2/Al2O3 ratio of H-ZSM-5, temperature and CH4/O2 ratio on the process has been studied. The results implied that the Bronsted acid sites of H-ZSM- 5 were the active centers responsible for the oligomerization of primary ethylene products. Oxygen was absolutely necessary for the formation of the methyl radicals from methane, but it should be provided at a controllable manner in order to avoid undesired oxidation. The partial destruction and dealumination of H-ZSM-5 at higher temperature had caused the deactivation of the H-ZSM-5 catalyst for the oligomerization reaction. Investigation on the catalytic activity of various metals loaded H-ZSM-5 showed that incorporating nickel into H-ZSM-5 significantly enhances the yield of liquid hydrocarbons. The central composite design (CCD) coupled with response surface methodology (RSM) was successfully applied to map the response and to obtain the optimal reaction design. The results indicated that the optimum C5+ yield of 8.91% was attained at reaction temperature = 742 ºC, CH4/O2 ratio = 9.7 and Ni loading = 0.67 wt%. This exploration suggests that the concept of this dual-bed catalytic system is an interesting candidate for application in methane utilization to produce liquid hydrocarbons