Biodiesel synthesis from spent frying vegetable oils over heterogeneous inorganic catalysts

Abstract

Biodiesel derived from renewable plant seed oils and animal fats is a promising alternative to fossil diesel fuel. Commercially, triglyceride transesterification and free fatty acid esterification with short chain alcohols over soluble catalysts are crucial procedures for biodiesel synthesis. Such technologies are ecologically deplorable due to necessary removal of caustic catalysts from the product. Introducing separable solid heterogeneous catalysis systems has promoted less pronounced related operational problems. Even so, processing low quality feedstock over solid acid-base catalysis systems may add unavoidable processing cost. In this respect, the main goal of the research is to develop a new bi-functional heterogeneous catalytic system for biodiesel production from spent frying oils. K3PO4 was utilised in ethanolysis production of biodiesel from waste cooking oil in this dissertation. Biodiesel processing variables were optimised by following a two level-surface response coupled to central composite design methodology. The study suggested that leaching and catalyst agglomeration are the primary cause of catalyst deteriorations and product degradation. For the first time, aluminium and calcium phosphate-potassium ribbed bi-functional catalysts were synthesised for biodiesel processing. The catalysts were produced following dipping impregnation of γ-Al2O3 and seashell in aqueous solutions of K3PO4.The used seashell were used in raw and calcined forms respectively. Synthesised catalysts were comprehensively characterised and evaluated. Leaching of active species in the liquid phase was investigated over all synthesised catalysts. Results revealed that K3PO4 contents of 15,10and 25wt% on γ-Al2O3, calcined and raw seashell were the maximum synthesis ratios at which the resultant solids maintained their heterogeneous behaviour. Extensive ethanolysis reactions were carried out over pre-selected catalyst samples with secured heterogeneous behaviour in an attempt to select the most proficient and durable catalytic system for applications concerning biodiesel synthesis. Biodiesel processing parameters were optimised in an attempt to ensure the true chemical kinetic as a single rate determining step of the overall reaction. Catalyst characterisation coupled to biodiesel formation rate data collected, demonstrated that K3PO4/raw seashell catalyst was the most feasible, sustainable and active bi-functional catalysis system for biodiesel applications.