Homogeneous Catalysis for Biodiesel Production-A Review

Biodiesel is a low-emissions diesel substitute fuel made from renewable resources and waste lipid. The most common way to produce biodiesel is through transesterification, especially alkali-catalyzed transesterification. When the raw materials (oils or fats) have a high percentage of free fatty acids or water, the alkali catalyst will react with the free fatty acids to form soaps. The water can hydrolyze the triglycerides into diglycerides and form more free fatty acids. Both of the above reactions are undesirable and reduce the yield of the biodiesel product. This problem is overcome by use of acid catalysts. The present review looks into various aspects of biodiesel production using homogeneous alkali and acid based catalysts. The main factors affecting the yield of biodiesel, i.e. alcohol quantity, reaction time, reaction temperature and catalyst concentration, are also discussed. The flow schemes for continuous production of base catalyzed and acid catalyzed biodiesel production are discussed. Scope for future work is also presented.