Conversion of a low value industrial waste into biodiesel using a catalyst derived from brewery waste: An activation...

In this study, biodiesel was produced by using a heterogeneous acid catalyst made from brewer's spent yeast (BSY). BSY was initially activated by phosphoric acid followed by carbonization in inert atmosphere and sulfonation process to prepare the catalyst. It is completely characterized using sophisticated instruments to determine its physical and chemical properties. Subsequently, the effectiveness of the catalyst was analyzed by subjecting it to sonochemical esterification of an industrial low value waste product, palm fatty acid distillate (PFAD). The reactions were performed in the presence of ultrasound at a constant frequency of 25 kHz. An optimum methyl ester conversion of 87.8% was achieved at 8 wt% of catalyst, 21:1 methanol to PFAD molar ratio, 65 °C and 180 min of reaction time. The catalyst displayed a high catalytic stability up to four cycles due to firm SO₃H functional group attached onto the surface. Furthermore, a novel sonochemical kinetic model was proposed for surface esterification reaction on the catalyst. The reaction rate was found and it followed a pseudo-first-order reaction mechanism. Furthermore, a deactivation model was also proposed to account for the loss of activity upon catalyst reuse during sonochemical reaction.