ABSTRACT
Single stage alkali-catalyzed transesterification of vegetable oils having free fatty acid (FFA) content above 0.5% promotes saponification which lowers the biodiesel yield by deactivating the catalyst. A strong solid base KF/Eggshell catalyst, which is capable of circumventing saponification while producing biodiesel in a single stage from neem oil having FFA content of 4.2% was synthesized. The catalyst was synthesized by a thermal treatment of chicken eggshell at 900oC, followed by a wet impregnation of potassium fluoride (KF). The catalyst synthesis process factors such as; eggshell calcination time, potassium fluoride (KF) dosage, catalyst calcination temperature and time were optimized using a response surface methodology (RSM). The optimal synthesis conditions were found to be 2 h eggshell calcination time, KF dosage of 29 wt. %, catalyst calcination temperature of 600oC for 2 h. The KF/Eggshell catalyst was characterized. BET analysis revealed that, the catalyst is mesoporous with a pore width of 3.24nm, pore volume of 0.045 cm3/g and specific surface area of 128 m2/g. The SEM micrograph showed that, the crystallites of the catalyst are systemically arranged; as such, present its high specific surface area to the reacting species. Also, the XRD diffractogram showed presence of a highly basic KCaF3 crystal in the catalyst. Process factors of a transesterification reaction utilizing the KF/Eggshell catalyst such as; catalyst dosage, oil-methanol ratio, reaction temperature and time were also optimized. Biodiesel yield of 95% was obtained at the optimal process conditions of 6 wt. % catalyst dosage, 15:1 methanol-oil ratio, 2h reaction time and 600C reaction temperature. The analyzed physicochemical properties of the produced biodiesel meet the ASTM D6751 commercial standard for diesel engine. The chemical constituents of the produced biodiesel were analysed using GCMS and FTIR, the results revealed that saponification reaction was successfully circumvented. A magnetic form of the catalyst, KF/Eggshell-Fe3O4 was synthesized by a co-precipitation method for the purpose of enhancing its reusability. The magnetic KF/Eggshell-Fe3O4 catalyst produced 92% yield of the biodiesel after the fifth run, whereas the non-magnetic KF/Eggshell catalyst produced 79% yield for the same run. This significant difference confirmed that, the acquired magnetic property of the catalyst improved its recovery and reusability.