Biodiesel

In Vitro Cell.Dev.Biol.—Plant (2009) 45:229–266
DOI 10.1007/s11627-009-9204-z
INVITED REVIEW
Biodiesel production, properties, and feedstocks
Bryan R. Moser
Received: 18 December 2008 / Accepted: 24 February 2009 /Published online: 25 March 2009 / Editor: Prakash Lakshmanan; David Songstad
# The Society for In Vitro Biology 2009
Abstract Biodiesel, defin ed as the mono-alkyl esters ofvegetable oils or animal fats, is an environmentally
attractive alternative to conventional petroleum diesel fuel
(petrodiesel). Produced by transesterification with a mono-
hydric alcohol, usually methanol, biodiesel has many
important technical advantages over petrodiesel, such as
inherent lubricity, low toxicity, derivation from a renewable
and domestic feedstock, superior flash point andbiode-
gradability, negligible sulfur content, and lower exhaust
emissions. Important disadvantages of biodiesel include
high feedstock cost, inferior storage and oxidative stability,
lower volumetric energy content, inferior low-temperature
operability, and in some cases, higher NOx exhaust
emissions. This review covers the process by which
biodiesel is prepared, the types of catalysts thatmay be
used for the production of biodiesel, the influence of free
fatty acids on biodiesel production, the use of different
monohydric alcohols in the preparation of biodiesel, the
influence of biodiesel composition on fuel properties, the
influence of blending biodiesel with other fuels on fuel
properties, alternative uses for biodiesel, and value-added
uses of glycerol, a co-product ofbiodiesel production. A
particular emphasis is placed on alternative feedstocks for
biodiesel production. Lastly, future challenges and ou tlook
for biodiesel are discussed.
Keywords Alternative feedstocks . Biodiesel . Fatty acid
methy l esters . Fuel properties . Methanolysis .
Transesterification
Introduction
Biodiesel is defined by ASTM International as a fuel
composed of monoalkylesters of long-chain fatty acids
derived from renewable vegetable oils or animal fats
meeting the requirements of ASTM D6751 (ASTM
2008a). Vegetable oils and animal fats are principally
composed of triacylglycerols (TAG) consisting of long-
chain fatty acids chemically bound to a glycerol (1,2,3-
propanetriol) backbone. The chemical process by which
biodiesel is prepared is known as thetransesterification
reaction, which involves a TAG reaction with a short-chain
monohydric alcohol normally in the presence of a catalyst
at elevated temperature to form fatty acid alkyl esters
(FAAE) and glycerol (Fig. 1). The conversion of TAG to
biodiesel is a stepwise process whereby the alcohol initially
reacts with TAG as the alkoxide anion to produce FAAE
and diacylglycerols (DAG, reaction[1], Fig. 1), which react
further with alcoho l (alkoxide) to liberate another molecule
of FAAE and generate monoacylglyerols (MAG, reaction
[2], Fig. 1). Lastly, MAG undergo alcoholysis to yield
glycerol and FAAE (reaction [3], Fig. 1), with the
combined FAAE collectively known as biodiesel. Three
moles of biodiesel and one mole of glycerol are produced
for every mole of TAG thatundergoes complete conver-
sion. The transesterification reaction is reversible, although
the reverse reaction (production of MAG from FAAE and
Disclaimer: Product names are necessary to report factually on
available data; however, the USDA neither guarantees nor warrants
the standard of the product, and the use of the name by USDA implies
no approval of the product to the exclusion of others thatmay also be
suitable.
B. R. Moser (*)
United States Department of Agriculture,
Agricultural Research Service,
National Center for Agricultural Utilization Research,
1815 N University St,
Peoria, IL 61604, USA
e-mail: Bryan.Moser@ars.usda.gov


MOSER
Figure 1. Transesterification of
triacylglycerols to yield fatty
acid alkyl esters (biodiesel).
230
O
O
O
O
catalyst
R'
+...