Abstract
This study presents a
brief overview of the composition and properties of various oils used in
biodiesel production and the alkali, acidic and enzymatic transesterification
reactions used in production. Nowadays, vegetable and microalgae oils are
mostly used in biodiesel production. Recently, however, animal fats, processed
oils, industrial oils and yeast and bacterial oils have also gained importance.
Although all fats and oils are roughly similar, their saturated fatty acids
(SFA), polyunsaturated fatty acids (PUFA), monounsaturated fatty acids (MUFA),
free fatty acids (FFA), cholesterol or glycerol contents may be different and
affect the production and efficiency of the biodiesel. Triglycerides are the
most significant lipids in biodiesel production. Triglycerides in vegetable
oils dominantly contain C18:1ω9 and C18:2ω6 fatty acids. Whereas, triglycerides
in animal fats mostly include C16:0 and C18:1ω9 fatty acids. Microalgae are
rich in long-chain fatty acids such as C20 and C22. Also, fatty acids such as
C14:0, C16:1ω7, C18:0, C20:0, C22:0, C24:0, C22:1ω9, C18:3ω6, C20:4ω6 and
C20:5ω6 are present in oils and fats. However, their proportions change from
feedstock to feedstock. Rendered animal-originated fats include larger
quantities of FFA than waste vegetable oils and, as known, excessive amounts of
FFA generate soap in reactions with the alkaline catalyst, reducing biodiesel
efficiency. For this reason, generally vegetable and microalgal oils containing
a large number of triglycerides and less FFA are preferred for biodiesel
production. Bacteria can synthesize branched fatty acids. It has been reported
that biodiesel produced from branched fatty acids has advantages according to
biodiesel produced from other lipids. Consequently, the use of correct and reliable
lipids in biodiesel production is very important for the quality of fuel.