Many different alcohols can be used in this reaction including, methanol, ethanol,
propanol, and butanol. The methanol application is more feasible because of its low cost
and physical as well as chemical advantages such as being polar and having the shortest
chain alcohol [Ma and Hanna, 1999]. The utilization of different types of catalyst
improves the reaction rate and final yield. There are various types of transesterification
reactions such as homogeneous, heterogeneous, and non-catalyst reaction. But, each of
them has their own advantages or disadvantages. Kulkarni et al. (2006) evaluated the
effects of various variables on conversion of methyl ester from low quality waste
cooking oil and high FFA with 12-tungstophosphoric acid (TPA) as catalyst. The results
indicated that this kinds of catalyst is nontoxic, recyclable, inexpensive, and user and
environmentally friendly.