Homogenous Acidic and Basic Catalysts in Biodiesel Synthesis: A Review

Several techniques, in which different homogenous catalysts and procedures, that are in use for transesterification of a vegetable oil or an animal fat have been successful in synthesizing biodiesel, although with some certain limitations. For such a purpose, among the catalysts employed are acidic as well as basic catalysts. It has been found that acidic catalysts can be tolerant with a high content of free fatty acids found in those low value feedstock oils/fats to be transesterified, although some sort of pretreatment by means of esterification might be required in order to synthesize biodiesel. Moreover, with employing homogenous acidic catalysts, it seems that biodiesel purification procedures are simplified; thus, reducing synthesis cost. In fact, these features of homogenous acidic catalysts render them advantageous over basic ones. With basic homogenous catalysts this; however, has not been possible due to the development of saponification reaction. To effectively perform, such catalysts require that the content of free fatty acids in the feedstock oil/fat is minimal. This requirement is also applicable to the moisture level in the feedstock. In terms of corrosive effects; nevertheless, acidic catalysts are disadvantageous compared to basic ones.