Conversion of Methanol to Hydrocarbons in a Supercritical Fluid Reaction Medium

Abstract

This thesis work explores the effects of a supercritical fluid reaction medium on the catalytic performance of the methanol-to-hydrocarbons (MTH) reaction. The MTH reaction allows for the conversion of cheap and readily available methanol to light olefins and/or high octane gasoline. Historically, the MTH conversion has been carried out under gas phase conditions; however, under these conditions, several drawbacks have been observed which limit the useful application of this technology, including coking and heat management challenges. Supercritical fluid (SCF) reaction media have been successfully employed in other exothermic and mass transfer limited reactions, such as Fischer-Tropsch Synthesis and Higher Alcohol Synthesis, to mitigate the problems associated with traditional gas phase operation. Because of their intermediate physical properties, SCF media possess higher solvent strength and thermal conductivities than gases while also possessing gas-like diffusivities and viscosities, thus allowing for a single phase reaction environment in which both liquid products and heat are efficiently extracted from the catalyst without hindering the diffusion of gaseous reactants. To the best of the author’s knowledge, this work reports the first investigation of SCF application in the MTH reaction. Isooctane was selected as the SCF medium primarily because of its low reactivity over the traditional MTH catalyst, ZSM-5. The results of this investigation suggest that, compared to operation in a gas phase environment, conducting the MTH reaction in the presence of supercritical isooctane led to improved catalyst maintenance, as evidenced in part by increased hydrocarbon production with increasing time-on-stream as well as decreased coke accumulation. Further studies are needed to better understand the effects of an SCF environment on the MTH reaction under different operating conditions which exploit the unique properties of the SCF medium and for different MTH catalytic systems.