Glycerolysis treatment to enhance biodiesel production from low-quality feedstocks

Abstract

The depletion of diesel fuel and its association with the pollution problems forces the world to look for alternative ways for energy production. The most important alternative source of energy is biodiesel that has a composition and combustion properties similar to diesel. The main hurdle to the commercialization of biodiesel is its high sale price because of the high cost of feedstock. The cost of feedstock accounts for 75–80% of the total cost of biodiesel. Therefore, the use of cheap low-quality feedstock can lower the biodiesel price to a competitive price. However, the cheap feedstock often contains a large amount of free fatty acids (FFAs), which react with the base catalyst in the transesterification reaction to produce soap, form emulsions, reduce the yield, and decrease the biodiesel quality. Consequently, the treatment step is required to reduce the FFAs content to an acceptable level that the base transesterification reaction can be applied. The glycerolysis treatment was applied to reduce the FFAs in different feedstocks by using either the crude glycerol –a byproduct from biodiesel production after its purification– or the pure glycerol in the presence of potassium hydroxide (KOH) as a catalyst. The feedstocks were two types of used cooking oil that had 7.6 and 11.97 wt% of FFAs. The treatment could successfully decline the FFAs content to less than 1 wt% that was appropriate for base catalyst transesterification.