Oxygenated Diesel Fuels from Waste Vegetable Oil

Abstract

Vegetable oils and animal fats (triglycerides) were the first liquid fuels used in the rise of civilization, and now again are a potential source of alternate diesel fuel. They are 20 times as viscous as diesel fuel, however, and so form carbon deposits on diesel cylinders and injectors. They are also typically %3- $S/gallon, and so are too expensive to compete economically with diesel today. A number of solutions have been proposed for these problems, including transesterification, dilution, pyrolysis and Microemulsification The viscosity can be lowered by transesterification of the triglycerides with methanol or ethanol to form fatty acid esters. This cleaves the fat molecule and removes the glycerine, yielding a viscosity comparable to that of diesel. The heat of combustion is 95% of that for conventional diesel (on a volume basis). They have a Cetane number of 50-80 (compared to 42 for diesel). The cost of the fuel can be reduced by using waste vegetable cooking oils. There are 350 million gallons of waste vegetable oil produced annually in the U.S.A., and various quantities available in other countries. We have developed a process for making the esters from waste vegetable oils and we call the fuel M-Diesel. The oil is reacted with sodium hydroxide dissolved in methanol. A sufficient quantity of alkali is used to neutralize the fatty acids in the waste oil plus 0.3% excess. A batch of 300 gallons was made for testing. We have tested the fuel in a Denver public bus and find power comparable to that of diesel. A 30% blend with diesel reduced smoke opacity to 60% of that from diesel, while neat M-Diesel reduced the opacity to 26% of that of diesel.