Main technologies in biodiesel production: State of the art and future challenges

Biodiesel is a fuel safe, renewable, non-toxic, biodegradable and much less contaminant for the environment than conventional diesel. Moreover, it represents a strategic source of energy especially for the countries that have not oilfields. For these reasons, even if the cost of biodiesel is still greater than diesel from petroleum, many governments sustain this production. The cost of biodiesel is mainly affected by the cost of the feedstock but also an improvement of the adopted technology can contribute in reducing the costs. Therefore, it is imperative: to employ less expensive feedstock, that is, unrefined or waste oils; to use not edible oil coming from alternative sources as, for example, algae or Jathropa Curcas; to improve the actual technology based on the use of homogeneous alkaline catalysts through a better understanding of the reaction mechanism, to develop new biphasic kinetic models; to adopt techniques of process intensification; to introduce the use of heterogeneous catalysts, possibly finding a catalyst promoting in one step both esterification of free fatty acids and transesterification of tri-glycerides; to find new remunerative uses for the by-product glycerol. In this paper, all the mentioned aspects will be considered by reporting some of the most relevant results obtained in the last years.