Base catalysts are highly sensitive to water contents,
which cause soap formation, and separation becomes difficult. The
acid values of most of the non-edible oils are higher than the performance range of base catalysts. So, in such cases acid catalysts are
used. But the problems associated with these catalysts are, requirement of higher amount of alcohol, higher reaction temperature and
pressure, and slower reaction rate [9]. Reactor corrosion and environmental issues are also the hurdles in the use of acid catalysts
[116].