Biodiesel from blended microalgae and waste cooking oils: Optimization, characterization, and fuel quality studies

Petrodiesel is an unsustainable and undependable fuel owing to its environmental concerns and depleting reserves. Biodiesel is a sustainable alternative fuel to petrodiesel with a better fuel quality and minimum environmental impacts. However, cost-effective biodiesel production requires the use of a sustainable feedstock and process optimization. This study explored biodiesel yield optimization from mixed microalgae oil (MO) and waste cooking oil (WCO). The use of mixed feedstock for biodiesel production relieves the rising demands; lowers feedstock costs; and improves the fuel quality, engine performance, and pollutants emission characteristics. MO was extracted from dried microalgae biomass by the Soxhlet method using hexane. The MO and WCO were purified and characterized, and an oil blend with suitable properties (best in kinematic viscosity, density, higher heating value, and acid value compared to other blends) was selected. The transesterification experiments designed by central composite design were optimized using the response surface methodology. Experimental results underwent regression analysis to develop a quadratic model equation for predicting the optimum level of parameters and biodiesel yield. Model fitness and variables effects on biodiesel yield were studied using analysis of variance. The optimization experiment achieved 98.82% oil conversion rate at the catalyst loading of 2.0 w/v%, molar ratio of 12:1 v/v, reaction temperature of 60 degrees C, and reaction time of 100 min. A triplicate validation experiments achieved 97.72% conversion rate, which is very close to the model predicted result (99.1%). Biodiesel from MO-WCO showed a better cetane number (77.76), iodine value (12.90 gI2/100 g), acid value (0.049 mg KOH/g), HHV (43.25 MJ/kg), kinematic viscosity (4.50 mm2/s), pour point (-2.5 degrees C), and flash point (180 degrees C). In conclusion, the study revealed that transesterification of blended MO-WCO led to a maximum biodiesel and the reaction time and temperature were found to be the most significant factors affecting the yield of biodiesel. Furthermore, biodiesel from blended MO-WCO is a sustainable and environmentally friendly alternative fuel source which can contribute towards a promising industrial scale biodiesel production in the future.