An overview of the current status of biodiesel
- Colorado School of Mines, Golden, CO (United States)
Vegetable oils (and animal fats) have been used as lighting fuels since Egyptian times, but recent testing shows that they are not suitable for diesel engines, causing poor spray and coking. Transesterification of the oils with methanol cleaves the oil/fat molecule into 3 parts and removes the glycerine, yielding a viscosity and other properties comparable to that of diesel. The resulting esters have been given the generic name {open_quotes}biodiesel.{close_quotes} Biodiesel can be made from vegetable oils and animal fats by transesterification with methanol or ethanol using Acid or base catalysts. Only minor variations in characteristics such as Cetane number and pour point occur with various feedstocks. The heat of combustion of biodiesel is 95% of that for conventional diesel (on a volume basis). The viscosity is no more than double that of No. 2 diesel. Biodiesel has a Cetane number of 50--80 (compared to typically 42 for diesel). The Cetane number is important in determining emissions. Biodiesel fuel requires no engine modification for use in conventional diesel engines. The engine characteristics have been widely tested in engines and fleets in the US, Brazil, and in Europe. Reduced emissions (except NOX) are reported for both blends and neat. Vegetable oils cost typically $2--$4/gal, and so require a subsidy to compete economically with diesel today. It is expected that this cost can be reduced with improved species and improved yields. The cost of biodiesel can also be reduced by using waste vegetable cooking oils which typically contain 4-8% free fatty acids that must be removed. Processing costs are estimated to be $0.50 above the feedstock cost, so that $2/gal vegetable oils would give biodiesel at $2.50/gal biodiesel. Biodiesel is certainly the best candidate for an alternate diesel fuel.
- Research Organization:
- National Renewable Energy Lab., Golden, CO (United States)
- OSTI ID:
- 140197
- Report Number(s):
- NREL/CP--200-5768-Vol.2; CONF-9308106--Vol.2; ON: DE94000435
- Country of Publication:
- United States
- Language:
- English
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