Biofuels in Perspective

Process Technologies for Biodiesel Production 79
been installed with an overall production capacity of over 5 million tons per year. 4 But
also the major palm oil producing countries like Malaysia and Indonesia have a series of
biodiesel plants already installed with a capacity of over 1 million tons per year. Similar
activities can be found in China and India with their huge demand for transport fuel, but
also in the vegetable oil producing countries like Brazil and Argentina.
5.3 Feedstocks for Biodiesel Production
Today a production capacity of almost 30 million tons of biodiesel exists worldwide. On
the other hand there is a total annual production of vegetable oils of approx. 110 million
tons per year, which is mainly used for food purposes. As the production of vegetable oils
cannot be increased in such a way as there is the demand for biodiesel, competition with
the food market will be inevitable. Also concern on unsustainable production of oil plants
like palm oil has led to extrensive discussions leading to the search for non-edible oil seeds.
Basically all vegetable oils and animal fat can be used as feedstock for biodiesel production.
Most of these oils and fats have a similar chemical composition, they consist of triglycerides
with different amounts of individual fatty acids. The major fatty acids are those with
a chain length of 16 and 18 carbons, whereas the chain could be saturated or unsaturated.
Methyl esters produced from these fatty acids have very similar combustion characteristics
in a diesel engine, because the major components in fossil diesel fuel are also straight chain
hydrocarbons with a chain length of about 16 carbons (hexadecane, ‘cetane’). The major
differences between the methyl esters from different feedstocks refer to the amount of unsaturated
fatty acids. The best combustion characteristics as well as oxidation stability come
from saturated fatty acids; however, cold temperature behaviour is worse due to the high
melting points of these fatty acids. On the other hand, high unsaturation of fatty acids leads
to optimum low temperature properties, but the oxidation and storage stability is worse.
The major feedstocks for the biodiesel production today are rape seed oil (Canola),
soybean oil and palm oil. The fuel properties of the methyl esters out of these oils are
quite similar except for the poor cold temperature behaviour of palm oil because of the
high portion of saturated fatty acids. However, depending on the climate conditions of a
country, an optimum mix of methyl esters out of these feedstocks can be used. Also a
series of other vegetable oils has quite similar fatty acid distribution and can also be used
as blend. Only coconut oil and palm kernel oil have fatty acids with 12 or 14 carbons as
major components. Therefore the methyl esters out of these fats have lower boiling points,
but could be used perfectly as ad-mixture to common biodiesel.
Especially in Asian countries like India and China the use of non-edible seed oils for
biofuel production is very popular; in that case there would be no competition with the
food production, especially when these oil plants are grown on marginal areas not suitable
for food production. Especially Jatropha curcas L. has attracted enormous attention within
the last years, especially in India, Indonesia and in the Philippines. As there would be
no competition with the food production and also with the traditional agricultural areas
Jatropha could fill the gap between actual vegetable oil production and demand for biofuels.
Another interesting feedstock for biodiesel production is oil produced from algae, which
could be grown in open ponds or in closed tubes. The productivity is estimated to be
much higher per area than with traditional oil seeds and furthermore there is no need for
agricultural land, it can be produced at any place, where water and sunlight are existing.