Page 166 - Biofuels Refining and Performance

Chapter
5

Fuel and Physical Properties

of Biodiesel Components

Gerhard Knothe

5.1 Introduction
Biodiesel is an alternative diesel fuel (DF) derived from vegetable oils
or animal fats [1, 2]. Transesterification of an oil or fat with a monohy-
dric alcohol, in most cases methanol, yields the corresponding mono-
alkyl esters, which are defined as biodiesel. The successful introduction
and commercialization of biodiesel in many countries around the world
has been accompanied by the development of standards to ensure high
product quality and user confidence. Some biodiesel standards are ASTM
D6751 (ASTM stands for American Society for Testing and Materials)
and the European standard EN 14214, which was developed from pre-
viously existing standards in individual European countries.
The suitability of any material as fuel, including biodiesel, is influenced
by the nature of its major as well as minor components arising from pro-
duction or other sources. The nature of these components ultimately deter-
mines the fuel and physical properties. Some of the properties included in
standards can be traced to the structure of the fatty esters in the biodiesel.
Since biodiesel consists of fatty acid esters, not only the structure of the
fatty acids but also that of the ester moiety can influence the fuel proper-
ties of biodiesel. The transesterification reaction of an oil or fat leads to a
biodiesel fuel corresponding in its fatty acid profile with that of the parent
oil or fat. Therefore, biodiesel is largely a mixture of fatty esters with each
ester component contributing to the properties of the fuel.
Properties of biodiesel that are determined by the structure of its
component fatty esters and the nature of its minor components include

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