Green heterogeneous base catalyst from ripe and unripe plantain peels mixture for the transesterification of waste cooking oil

Abstract

Economical feedstocks such as agricultural wastes, food wastes, and waste cooking oil were used for biodiesel production to expand their application. Thus, a solid base catalyst was synthesized from a mixture of ripe and unripe plantain peels at a calcination temperature of 500 °C for 4 h. The catalyst was characterized using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) analysis, Fourier Transform Infrared (FT-IR) spectroscopy, Energy dispersive X-ray (EDX) analysis, and Brunauer-Emmett-Teller (BET) method. The waste cooking oil (WCO) used in this study was first pretreated with 3% (v/v) of H2SO4 via esterification reaction due to its high acid value. The esterified WCO was converted to biodiesel via transesterification reaction, and the process was then modeled and optimized using Taguchi L9 orthogonal array design method considering reaction temperature, reaction time, catalyst amount, and methanol/WCO molar ratio as the input variables. Based on the results, the synthesized catalyst predominantly contained potassium phases with 45.16 wt.%. The morphology of the catalyst revealed a crystalline mesoporous nanocomposite. At the end of WCO esterification, the acidity of the oil decreased from 5 to 1 mg KOH/g. The optimal conditions established for the transesterification process were catalyst amount of 0.5 wt.%, methanol/WCO molar ratio of 6:1, reaction temperature of 45 °C, and reaction time of 45 min with a corresponding biodiesel yield of 97.96 wt.%. The quality of the biodiesel produced satisfied the specifications (ASTM D6751 and EN 14,241) recommended for biodiesel fuels. Hence, a blend of ripe and unripe plantain peels could serve as an efficient heterogeneous base catalyst in producing biodiesel from WCO.