Although homogeneous catalysis is the traditional and very efficient process to convert lipids into alkyl esters, it has a number of disadvantages. The catalyst cannot be reused and has to be discarded after the reaction. In addition, catalyst residues have to be removed from crude biodiesel using several water washing steps that increases the production cost and complicates the purification of the glycerol. Recently an excellent review was published dealing with heterogeneous
catalyst for biodiesel production (Di Serio et al, 2008). Various processes are available using heterogeneous catalysts which are simplifying the purification costs of the biodiesel and the glycerol. The advantage of heterogeneous catalysis is that the catalyst can be either recovered by filtration and/or decantation or applied in a fixed bed reactor and the post-treatment of the biodiesel and glycerol is easier.