Biodiesel production via non-catalytic SCF method and biodiesel fuel characteristics

Vegetable oil (m)ethyl esters, commonly referred to as "biodiesel," are prominent candidates as alternative Diesel fuels. Biodiesel is technically competitive with or offers technical advantages compared to conventional petroleum Diesel fuel. The vegetable oils, as alternative engine fuels, are all extremely viscous with viscosities ranging from 10 to 20 times greater than that of petroleum Diesel fuel. The purpose of the transesterification process is to lower the viscosity of the oil. Transesterifications of vegetable oils in supercritical methanol are performed without using any catalyst. The most important variables affecting the methyl ester yield during the transesterification reaction are the molar ratio of alcohol to vegetable oil and the reaction temperature. Biodiesel has become more attractive recently because of its environmental benefits. The cost of biodiesel, however, is the main obstacle to commercialization of the product. With cooking oils used as raw material, the viability of a continuous transesterification process and recovery of high quality glycerol as a biodiesel by product are primary options to be considered to lower the cost of biodiesel. Supercritical methanol has a high potential for both transesterification of triglycerides and methyl esterification of free fatty acids to methyl esters for a Diesel fuel substitute. In the supercritical methanol transesterification method, the yield of conversion increases to 95% in 10 min. The viscosity values of vegetable oils are between 27.2 and 53.6 mm(2)/s, whereas those of vegetable oil methyl esters are between 3.59 and 4.63 mm(2)/s. The flash point values of vegetable oil methyl esters are much lower than those of vegetable oils. An increase in density from 860 to 885 kg/m(3) for vegetable oil methyl esters or biodiesels increases the viscosity from 3.59 to 4.63 mm(2)/s. Biodiesel is an environmentally friendly fuel that can be used in any Diesel engine without modification. (c) 2005 Elsevier Ltd. All rights reserved.