The molar ratio of alcohol to vegetable oil is one of the
important factors that affect the conversion efficiency as
well as production cost of biodiesel. The conversion
efficiency is defined as the yield of the process represented
in terms of percentage. Molar ratio is the ratio of number of
moles of alcohol to number of moles of glycerides in the oil.
Theoretically, transesterification reaction requires three
moles of alcohol for each mole of oil. However, in practice,
the molar ratio should be higher than that of stoichiometric
ratio in order to drive the reaction towards completion. That
is, 96 g of methanol is required for 910 g of rubber seed oil.
Canakci and Van Gerpan [1,13] advocate the use of large
excess quantities of methanol (15:1–35: 1) while using
the sulphuric acid as catalyst. The conversion efficiency of
first step in relation with molar ratio obtained during the
present study is shown in Fig. 1. The maximum conversion
efficiency is achieved very close to the molar ratio of 6:1.
With further increase in molar ratio there is only little
improvement in the conversion efficiency. The first step
reduces the viscosity of the oil. Also, it has been found that
the reduction in viscosity increases with increase in molar
ratio.