Chemistries and processes for the conversion of ethanol into middle-distillate fuels

Ethanol is presently the most common liquid fuel derived from biomass. One way of meeting the growing demand for heavier middle-distillate fuels — diesel and jet fuels comprising hydrocarbons of typically 8–22 carbon atoms — is to derive these from ethanol. This Review describes the chemistries and processes involved in the conversion of ethanol into diesel and jet fuel drop-in replacements and blendstocks. This conversion of ethanol relies on reactions including dehydration (to olefins), dehydrogenation (to aldehydes), hydrogenation (of C=C and C=O bonds), acid-catalysed olefin oligomerization, metal-catalysed olefin oligomerization, aldolization and ketonization. We discuss the thermodynamics, kinetics, process integration and catalyst development of different approaches. Some routes, particularly those based on olefin oligomerization, have been realized on the pilot scale. Other routes are currently in laboratory stages. This Review provides a framework for understanding how to convert ethanol into distillate-range molecules and the key research problems to be addressed. Ethanol has emerged as a potential alternative feedstock for the synthesis of middle-distillate transportation fuels. This Review describes the chemistry of ethanol-to-distillate processes and challenges associated with improving current technologies and implementing new ones.