Application of Agricultural Waste-Based Catalysts to Transesterification of Esterified Palm Kernel Oil into Biodiesel: A Case of Banana Fruit Peel Versus Cocoa Pod Husk

Abstract

This study aimed at modeling and optimizing the production of fatty acid methyl esters from esterified palm kernel oil using two heterogeneous biowaste catalysts namely calcined banana peel ash (CBPA) and calcined cocoa pod husk ash (CCPHA). The central composite design of response surface methodology (RSM) was employed for investigating the individual and interactive effects of the process input variables (methanol/oil ratio, catalyst weight and reaction time) on the palm kernel oil methyl esters (PKOME) yield. The same optimal conditions (methanol/oil ratio 0.8 v/v, catalyst weight 4 wt% and reaction time 65 min) were predicted by RSM for the transesterification reaction catalyzed by CBPA and CCPHA at constant temperature of 65 °C. The observed PKOME yields under the optimal condition using the two catalysts were 99.5 and 99.3 wt% for CBPA and CCPHA, respectively. The developed quadratic models were appraised using different statistical indicators such as coefficient of determination (R2) and average absolute deviation (AAD). R2 of 0.9064 and 0.8245 and AAD of 0.5526 and 0.6901 computed for CBPA and CCPHA-catalyzed transesterification reactions, respectively, showed both models gave good predictions. In both cases, methanol/oil ratio was the most significant factor on the PKOME yield. The PKOME produced using the two catalysts satisfied both the ASTM D6751 and EN 14214 standard specifications. Both banana fruit peel and cocoa pod husk could adequately serve as low-cost feedstock for PKOME synthesis.