5.2. Effect of molar ratio
The alcohol to oil ratio is a chief criterion as it controls the
phase of reacting system whether system is one or two phase. It is
reported in literature that, on decreasing the molar ratio, system
approaches single phase system from two phase. Zanuttini et al.
[61] studied kinetics of esterification of Butia Yatay coconut oil and
based on many preliminary experiments, alcohol to oil ratio was
between 7:1 and 12:1 and only single phased mixture was
obtained. Centrifugation was done to enhance the separation of
products. Generally, fatty acids and esters settle down and other
matter like alcohol and glycerol gets separted and lies in upper
phase. The resulted biodiesel had acid values ranged in 109 and
140 mg KOH/g. Yin et al. [62] suggested that, larger the alcohol:oil
ratio, reaction achieves its equilibrium in lesser time. They
observed that the more yield was obtained with molar ratio under
7:1 but as it was kept above this value, declining trend in yield was
observed. Excessive alcohol doesnot help in yield rather, it results
in unnecessary rise in cost of process because recovery becomes
difficult. The best molar for maximum yield ranges between 6:1
and 9:1 but some authors also reported using alcohol in range of
3:1–20:1 M ratio depending upon oil used and other reaction
conditions