Potential renewable oxygenated biofuels for the aviation and road transport sectors

Currently two major biofuels are present in the global fuel market; bioethanol which is largely produced by the fermentation of sugars or starches and biodiesel which is produced from the transesterification of vegetable oils such as rapeseed, soybean or palm. A number of key issues limit the applicability of these biofuels as substitutes in the road transport sector. These include the insufficient land area required to grow the feedstock needed alongside food crops, for bioethanol the poor energy density and for biodiesel the variability of the resulting fuel depending on the source and growing conditions, the oxidative instability of most biodiesel fuels and the poor low temperature behavior. This last issue also limits the applicability of these esters in the aviation sector. In an attempt to address these issues a range of possible renewable fuels were synthesized from esterified fermentation products potentially derivable from cellulosic sugars. These mono-and diesters were then examined for their potential as a replacement for aviation kerosene, mineral diesel or petrol. To determine the most suitable replacements, where appropriate, the fuels density, kinematic viscosity, melting point, boiling point, flash point, miscibility, solubility in water, the oxidative stability, lubricity and cetane number were examined and compared to their fossil fuel counterparts. From this study it emerges that the majority of the dibutyl diesters have physical properties which make them ideal replacements for diesel fuel, with the exception of the cetane number, where blends with diesel or cetane improving additives would need to be used to bring the fuels up to specification. Butyl butyrate has the potential to be used in a blend with petrol and was the only fuel tested fully compatible with aviation kerosene. The fuels tested also displayed superior lubricity to other alternative hydrocarbon fuels and as such have the potential to be used as additives for hydrocarbon fuels. (C) 2012 Elsevier Ltd. All rights reserved.