Use of waste materials for biodiesel production

Waste raw materials obtained by several sources of both food and agro industries could be considered for biofuel production. In the last years, this topic has growing in interest. At this purpose, our research, has been focused on the development of new technologies to obtain biodiesel from the mentioned wastes feedstock. In particular from oleins, that are mixtures of free fatty acids (FFAs) and triglycerides. Therefore, we are studying the way to produce biodiesel in two steps: an esterification reaction of FFAs with glycerol and a transesterification with methanol of the whole mixture. The esterification of FFAs with glycerol has the advantage of using a relatively high temperature favouring the stripping of water formed during the esterification. In this way esterification equilibrium is shifted to the right. Then, the mixture of mono-, di- and triglycerides, obtained by esterification with glycerol, can be submitted to transesterification with methanol, in the usual way, to produce biodiesel. Catalysts promoting esterification, normally, are mineral acids or heterogeneous Bronsted acid catalysts. At this purpose, the classical sulphonated polystyrene acid resins cannot be used at temperature greater than 120°C. Therefore, a new class of sulfonated polymers, with enhanced temperature resistance, has been developed by selective and quantitative sulfonation of olefinic butadiene units in multiblock copolymers syndiotactic polystyrene-co-1,4-cis-polybutadiene. This catalytic system has been successfully tested in the above mentioned esterification reaction and compared to classic commercial strong acid catalysts like Amberlyst®, Nafion® and sulfuric acid.