Production and Characterisation of Biodiesel from Waste Cooking Oil: A Sustainable Approach Using Transesterification

The present study addresses South Africa’s urgent requirement for sustainable energy solutions, considering its reliance on fossil fuels and environmental issues. It explores the production and characterisation of biodiesel derived from Waste Cooking Oil (WCO) through alkali-catalysed transesterification. WCO represents a waste product that could be converted into Fatty Acid Methyl Esters (FAME) using a potassium hydroxide catalyst with methanol as the transesterifying agent. Standard physical analyses, including FT-IR spectra, were conducted to assess the biodiesel fuel quality. Fourier Transform Infrared Spectroscopy (FTIR) proved that methyl esters were synthesised by detecting ester functional groups in the biodiesel composition. The properties of WCO-biodiesel align with the American Society for Testing and Materials (ASTM) standards, such as a density of 0.870 kg/m³, viscosity of 4.69 mm²/s and calorific value of 38,450 kJ/kg. The rheological properties of the ternary blends containing butanol and propanol improved viscosity, shear stress and density throughout a broad temperature range. WCB 20Bu20Pr20 blend showed better physico-chemical properties as compared with other blends. The viscosity for ternary blends lies well within the range prescribed by ASTM D6751, i.e. 1.9 - 6.0mm²/s at 40°C, with WCB20Bu15Pr15 and WCB20Bu20Pr20 having very favourable values of 2.371 mm²/s and 2.320 mm²/s, respectively. This study demonstrates how WCO can be transformed into clean-burning biofuels that provide a sustainable solution to South Africa's energy security needs and environmental protection goals. Major Findings: WCB exhibited a reduced viscosity (from 31.62mm²/s to 4.69mm²/s), a modestly increased calorific value (38,450 kJ/kg), and a safer flash point (89.5°C) compared to diesel. The ternary blends (WCB20Bu10Pr10, WCB20Bu15Pr15, WCB20Bu20Pr20) exhibited favourable rheological behaviour in terms of reduced viscosity, shear stress, and density at elevated temperatures. WCB20Bu20Pr20 demonstrated the most desirable characteristics that include low viscosity (1.004mm²/s at 90°C), minimal shear stress (0.759 Pa), and reduced density (0.771 g/cm³).