Transesterification of Spent Frying Oils over Aluminium Orthophosphate-Potassium Ribbed Bi-Functional Catalyst: Reaction Optimisation Study

This paper reports the optimisation study of a batch scaled ethanolysis conversion of waste frying oil carried out over aluminium phosphate-potassium bi-functional catalysts. All synthesised catalysts were analysed for their structural and surface chemical properties thereby following N₂ adsorption-desorption isotherm and CO₂ and NH₃-temperature programmed desorption techniques respectively. X-ray diffraction and x-ray photoelectron spectroscopy were also adopted for phase identification and atomic quantification studies respectively. Ethanolysis experiments were carried out eliminating reaction rate limitations caused by solid-liquid interfacial mass transport and intraparticle diffusion. Other operating parameters were also examined in the study. These included; reaction temperature, catalyst percentage loading on support, catalyst weight and reactants molar ratio (β).

Results from the preliminary study revealed that 98.2% ethyl ester yield was achieved over a catalyst sample with highest K₃PO₄ content. Even so, ethanolysis reactions carried out over such catalysts may homogeneously progress due to abnormal increased concentrations of leached K⁺. Homogeneous catalytic behaviour was less pronounced over those with low to medium levels of K₃PO₄ content. The study highlights a catalyst sample with a medium level of K₃PO₄ content as the most heterogeneous catalyst.

Finally, reaction governing parameters were reasonably optimised for a best catalytic performance at conditions of β=12:1, SS = 1200r.min⁻¹, dp≤140µm, cat = 50g.L⁻¹ and were found to be optimal. The study identifies aluminium phosphate 15wt% potassium-ribbed catalyst as a quite active bi-functional catalyst for transesterification of spent frying oils.