A comprehensive review on apatite-derived catalysts for sustainable biodiesel production: Classification, features and challenges

Heterogeneous catalysis has a rich history in energy production through the transformation of oils and free fatty acids (FFA) into biodiesel which is composed of fatty acid alkyl esters and produced via transesterification and esterification reactions. Biodiesel, which possesses similar physicochemical properties to those of conventional petro-diesel, is considered a suitable alternative that can be blended with diesel and used in engines without modification. The production of biodiesel through transesterification/esterification reactions is dependent on suitable catalysts to accelerate the chemical reactions. As such, the development of new catalysts has been pursued over the past decades to find materials that can improve fatty acid alkyl esters (FAAE) yields. A variety of solid families have been used as efficient catalysts for biodiesel production. However, the review primary aims are to provide a first comprehensive overview and a database of various base and acid catalysts derived from apatites for biodiesel synthesis via transesterification of feedstocks containing low levels of fatty acid and esterification of highly acidic feedstocks. To achieve this goal, we present the different outlines of apatite materials and classify the derived catalysts into various categories in order to understand the unique characteristics of each one. This exploration also highlights biodiesel production methods, feedstocks and factors influencing biodiesel yields. Furthermore, we provide mechanistic insights, limitations and future perspectives.