Two-Step Conversion of Neem (Azadirachta indica) Seed Oil into Fatty Methyl Esters Using a Heterogeneous Biomass-Based Catalyst: An Example of Cocoa Pod Husk

In this study, the viability of using calcined cocoa pod husk ash (CCPHA) as a catalyst for the transesterification of neem seed oil (NSO) into biodiesel was investigated. Prior to transesterification to biodiesel, the oil was pretreated with Fe₂(SO₄)₃ via esterification to reduce its high acid value content. The Box-Behnken design (BBD) and central composite design (CCD) of response surface methodology (RSM) were used to investigate the individual and interactive effects of the methanol/oil ratio, catalyst amount, and reaction time on the acid value and biodiesel yield, respectively. Results of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and elemental analysis showed that the catalytic action of the CCPHA produced was due to its K content and microstructural development when calcined at 700 °C for 4 h. The acid value of the NSO could be reduced from 11.57 to 1.80 mg of KOH/g of oil using optimum values of the methanol/oil ratio of 2.19 (v/v), catalyst amount of 6 wt %, and reaction time of 15 min while maintaining the reaction temperature constant at 65 °C. The results confirmed that neem seed oil methyl ester (NSOME), which satisfied ASTM D6751 and EN 14214 standards, could be produced at an optimum yield of 99.3 wt % using the methanol/oil ratio of 0.73 (v/v), catalyst amount of 0.65 wt %, and reaction time of 57 min while maintaining the reaction temperature constant at 65 °C. The results of this study demonstrated the prospect of developing an heterogeneous base catalyst from cocoa pod husk (CPH) for biodiesel production, which may reduce the total cost of production