The fatty acid composition of the oil plays a significant role
when biodiesel is used as fuel in diesel engine[12]. Saturated fatty
acid esters have higher cetane values and oxidation stability but
poorer low temperature flow properties than those of unsaturated
ones[15,22]. The crude roselle oil consisted of a high proportion of
unsaturation, comprised primarily of oleic and linoleic acids and a
lower proportion of saturation, comprised mainly of palmitic acid.
In this study, the average molecular weight of the oil, from its composition, was calculated to be 854.1 g.
As in most other vegetable oils, the viscosity of the crude roselle
oil was very high compared to diesel (about 11.8 times higher). To
avoid any negative impacts on diesel engine performance, the viscosity had to be reduced to an acceptable level; therefore, alkalicatalyzed transesterification was performed. Several researchers
have established that free fatty acid (FFA) and moisture contents
in oils were significant factors affecting alkali-catalyzed transeste-rification[2,9,23]. The oil should have a low FFA content, and all
materials used in the reaction should be substantially anhydrous
[2]. Reports in the literature indicate that the FFA content in the
oil should be less than 1% prior to alkali-catalyzed transesterification[13,14]. The oil used in this study had an FFA content below 1%
and contained minute traces of water. Therefore, this oil had suitable characteristics to be used as a feedstock to produce biodiesel
by a one-step process, alkali-catalyzed transesterification.