Optimisation of biodiesel production via in-situ esterification for spent bleaching earth waste (SBEW) using response surface methodology

Spent Bleaching Earth Waste (SBEW) is a solid waste generated during the degumming and bleaching of edible oils containing up to 40%(wt.). SBEW is utilised in biodiesel production via in-situ esterification in a deep eutectic solvent (DES). Optimisation of the reaction time (80 to 160 min) and DES/Methanol ratio (5 to 25%) were carried out using response surface methodology (RSM) involving central composite design (CCD) at a fixed temperature (65 °C). A quadratic model was set up to predict the biodiesel yield. The high value of R² was 0.99 and R²adj 0.98 for FAME yield, indicating that the fitted model agrees with predicted and actual crude and FAME yield. The RSM result exhibit that the optimized condition for the in-situ esterification process was 160 min with a 5% DES/methanol ratio. The predicted FAME yield was 96.13%, and the actual experimental value was 97.56%. The produced biodiesel from spent bleach earth shows the property fulfilled the standard requirements EN14214 and ASTM D6751.