Comprehensive Review on the Biodiesel Production using Solid Acid Heterogeneous Catalysts

Biodiesel can be produced by domestic resources like straight vegetable oil, animal oil/fats, tallow and waste cooking oil. Its use, instead of the conventional diesel, contributes to the reduction of the CO2 emissions. Production of biodiesel occurring from base catalyzed transesterification of the oil, direct acid catalyzed transesterification of the oil and/or conversion of the oil to its fatty acids and then to biodiesel. Two types of catalytic mechanisms can be used for the biodiesel production. These are the homogenous and heterogeneous catalytic processes. However, heterogeneous catalysis can be identified as solid and enzymatic. In addition solid heterogeneous catalysts can be classified as acid or base. Ηeterogeneous solid acid catalysts are of a great importance for biodiesel production. The most known catalysts of this type are zeolites, mixed oxides, sulfonic acid group catalysts, sulfonic acid modified mesoporus silica, heteropoly acids and polyoxonetalates, supported and substituted heteropoly acids and solid acids catalysts based in waste carbon. The major advantages of this type of catalysts are their reusability, their non-toxic and non-corrosive attributes as well as decrement of the biodiesel production cost.