Production of Biodiesel from Waste Cooking Oil Using KOH/Al2O3 as a Heterogeneous Catalyst

The catalytic performance of potassium hydroxide supported on alumina (KOH/Al2O3) for transesterification of waste cooking oil (WCO) was investigated. XRD, FTIR, and SEM techniques were used to characterize the catalyst after it had been synthesized using the wet impregnation method. The properties of the WCO and the produced biodiesel were evaluated. The main fatty acids of WCO were linoleic (45.61%), elaidic (33.86%), palmitic (10.32%), and stearic acid (4.80%), the acid value (2.29 mg KOH/g), FFA (1.15%), density at 25 °C (0.91 g/cm3), viscosity at 40 °C (34.09 mm2/s), water content (0.0017%), and flash point (206 °C). The XRD pattern of the catalyst showed diffraction peaks of KAlO2 attributed to the orthorhombic crystal system having a 12.46% degree of crystallinity. The SEM micrographs confirmed the amorphous nature of the catalyst. The presence of K–O and Al–O bonds in the catalyst was confirmed by the FTIR. A biodiesel yield of 86.6% was achieved with the following variables: oil to methanol ratio of 1:4, catalyst loading of 1.5% (w/v%), reaction temperature of 55 °C, and a reaction time of 1 h. The results appeared to show a decreasing pattern of yield after 4 cycles of reaction from 86.60 to 51.50%. The fuel properties were density (0.8919 g/cm3), viscosity (7.428 cSt), flash point (65 °C), acid number (0.54 mg KOH/g) and water content (0.0196%). Furthermore, the properties of the prepared biodiesel have been found to comply with the ASTM and EN standard specifications. This catalyst showed promising results for manufacturing biodiesel from low-cost feedstock.