Transesterification process is carried out in the presence of catalysts. Both acid and base catalysts are used and their selection
is made according to the characteristics of feedstock. The virgin
vegetable oils, yellow grease (used cooking oil), or animal fats are
reacted with alcohol in the presence of acid or base catalysts. The
catalyst is used to expedite the reaction rate and to get better
quality biodiesel [36]. The base catalysts are preferred over acid catalysts, owing to their capability of completion of reaction at higher
speed, requirement of lower reaction temperature, and their higher
conversion efficiency as compared to acid catalysts [62–65]