Mono alkyl esters of long-chain fatty acids derived from
renewable lipid feedstock, such as vegetable oils or animal fats,
also known as biodiesel are well positioned to replace mineral
diesel. The outstanding technical problem with biodiesel is that it
is more susceptible to oxidation owing to its exposure to oxygen
present in the air and high temperature. This happens mainly due to
the presence of varying numbers of double bonds in the free fatty
acid molecules. The chemical reactivity of esters can therefore be
divided into oxidative and thermal instability, which can be
determined by the amount and configuration of the olefinic
unsaturation in the fatty acid chains. Many of the plant-derived
fatty oils contain polyunsaturated fatty acids that are more prone
to oxidation.
Increasing production of biodiesel from vegetable oils (edible)
places strain on food production, availability and price and leads
to food versus fuel conflict. Hence, this study evaluates biodiesel
derived from low cost non-edible oils, primarily available in
African continent, namely croton megalocarpus, moringa oleifera and
jatropha oils. The fuel related properties and oxidation stability
of croton oil methyl ester (COME), moringa oil methyl ester (MOME)
and jatropha oil methyl ester (JOME) were determined and compared
with global biodiesel standards such as ASTM D6751 and EN 14214.
Oxidation stability of COME, MOME and JOME with and without
antioxidants was analyzed using Rancimat method. The results showed
that most of the properties of COME, MOME and JOME fulfilled the
minimum requirements specified in the ASTM D6751 and EN 14214
biodiesel standards. However, COME and MOME did not fulfill the
oxidation stability requirements specified in EN 14214 (6 h), while
JOME displayed a remarkably high oxidation stability of 10.43 h.
Also, this study examined the effectiveness of three antioxidants
namely 1, 2, 3 trihydroxy benzene (PY), 3, 4, 5-tri hydroxy benzoic
acid (PG) and 2-tert butyl-4-methoxy phenol (BHA) on COME, MOME and
JOME. The result showed that, the effectiveness of these
antioxidants was in the order of PY≻PG≻BHA.