Use of bioethanol for biodiesel production

Faced with the energy crisis and environmental degradation, due to the massive use of fossil energy sources, biodiesel is an attractive alternative to diesel fuel. With a view to developing local biodiesel production, using bioethanol as a sustainable reactant for biodiesel production, rather than methanol, is leading to increasing interest, notably in emerging countries. Indeed, bioethanol, which is less toxic than methanol, is produced from local and renewable agricultural resources, being more sustainable and providing access to greater energy independence. However, some issues are limiting the process like purification problems, or the presence of water in bioethanol leading to a drop in yield. Although several studies have already been published on ethyl ester production, most of them primarily focus on homogeneous alkaline catalysis, and report various data. Therefore, this paper aims at presenting a review of previous studies on the subject. The aim of this article was to analyze all the literature data available on ethyl ester production, to gain a clearer insight into the advances made in the process, and bring out prospects for developing ethyl ester production, along with the limitations. This paper compares the different catalytic pathways that have been investigated for ethyl ester production. It discusses the effect of the main reaction parameters on the yield, the purification issues, and the characteristics and specifications of ethyl esters. This study shows that all authors formerly agreed in saying that ethyl esters separation and purification were a limiting stage. But these limitations can be overcome as high yields over 90% can be obtained by optimizing all the reaction parameters. Moreover, the negative effect of the water contained in bioethanol remains controversial. Finally, ethyl esters proved to be a viable alternative to diesel fuel being more sustainable than methyl esters. Some aspects of their production are worth a closer look for shifting the use of bioethanol to large-scale production. (C) 2011 Elsevier Ltd. All rights reserved.