Biodiesel production from soybean oil in subcritical methanol using MnCO3/ZnO as catalyst

The MnCO3/ZnO catalyst with different Mn/Zn molar ratio were prepared using co-precipitation method and used for biodiesel synthesis in subcritical methanol. Prepared catalyst samples were characterized by basic strength, Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The triglyceride (TG) conversion and fatty acid methyl ester (FAME) yield were determined using high performance liquid chromatography (HPLC). The effects of Mn/Zn molar ratio, calcination temperature and time, catalyst amount, molar ratio of methanol to oil, and transesterification reaction temperature and time, in regards to the catalyst activity were investigated. Results showed that a maximum TG conversion of 99.25% and FAME yield of 94.20% were obtained using MnCO3/ZnO catalyst (Mn/Zn molar ratio of 1:1) calcined at 573 K for 0.5 h under such reaction conditions for biodiesel synthesis as 4 wt% of catalyst, methanol/oil molar ratio of 18:1, reaction temperature of 448 K, and reaction time of 1 h. The catalyst kept TG conversion above 91.54% and FAME yield above 86.26% after 17-cycle reuse in batch reaction without regeneration processes. Further reuse of catalyst is followed by deactivation mainly caused by the transformation of small particle ZnO to lamellate zinc glycerolate.