Comparative effect of reaction time on biodiesel production from low free fatty acid beef tallow: a definition of product yield

Review of works in biodiesel production showed that performance of transesterification reaction has always been assessed with wrong notion of product yield. Various researchers defined yield in variety of conflicting ways. This paper addresses the existing confusion in using product yield as reaction performance criterion in biodiesel production. With reference to fundamentals of chemistry and chemical engineering, expression for fatty acid alkyl ester (FAAE) yield in transesterification was derived. The new model was used in comparison with the existing ones, to investigate the effect of transesterification reaction time via homogeneous and heterogeneous base catalyses of beef tallow. Firstly, the physicochemical properties of beef tallow were examined to determine its requirement for esterification pretreatment before the transesterification process. Calcium oxide was derived from eggshell and characterized as catalyst for biodiesel production from beef tallow. Biodiesel was produced at different reaction times and FAAE yield was calculated with all models. By comparison, new yield model gave the least results, with maximum FAAE yields of 94.2% and 87.5% recorded using homogeneous and heterogeneous catalyses respectively. Moreover, heterogeneous catalysis required much reaction time of 4 h to achieve this maximum yield compared to 1 h for homogeneous catalysis. Resolution of some notable limitations of the old models was proved possible using the new one. Yield should be explicitly defined and reported to aid result comparison and design choices in biodiesel production. [GRAPHICS] .