Catalytic conversion of alcohols as a potential source of synthetic hydrocarbon Fuels

Abstract

Establishing non-petroleum pathways to fuel production is currently of global concern. The Mobil Methanol-To-Gasoline (MTG) process pioneered the possibility of generating hydrocarbons from alcohols over solid acid catalysts. Coupled with the need to upgrade Fischer-Tropsch products, of which oxygenates form a significant fraction, the potential to convert oxygenates to synthetic fuels addresses some significant issues in the energy industry. The main purpose of this study was to investigate the transformation of two alcohols of industrial importance over solid acid catalysts, as part of a wider investigation into the use of alcohols derived from Fischer-Tropsch processes as an alternative feedstock to synthetic fuel production. I-propanol and 2-butanol were reacted over a commercially available ZSM-5 type zeolite catalyst (Zeolyst CBV3024E), an industrially used ZSM-5 type zeolite catalyst, and y-alumina (by itself and as part of a dual bed study with the industrial ZSM-5 type catalyst) in a fixed bed continuous flow bench-scale reactor at atmospheric pressure (270°C and 320°C, weight hourly space velocities (WHSVs) 0.24 -1.50 h-1). Regular sampling and gas chromatographic analysis of the hydrocarbon products allowed for significant data interpretation. The y-alumina catalyst produced corresponding olefins in most cases, but the acidity of the medium that developed at 270°C and WHSV 0.48 h-1 was sufficient for dehydration and oligomerisation with both of the abovementioned alcohols. The industrial ZSM-5 type catalyst exhibited lower hydrogen transfer activity than the commercial Zeolyst ZSM-5 catalyst. This proved beneficial to higher hydrocarbon yields, as less hydrogenation of lower olefins occurred. Hydrogen transfer activity was found to decrease with time on stream for both catalysts, possibly due to deactivation of the stronger Brensted acid sites. This decrease occurred faster with the industrial catalyst than it did with the commercial Zeolyst catalyst. This period of strong acid site activity was reduced with the use of lower temperature and higher WHSV, which benefitted oligomerisation.