Storage and thermal stability of biodiesel produced from manketti nut oil of Southern Africa origin with the influence of metal contaminants and antioxidants

Abstract

Biodiesel has widely been produced from common edible oils; however, food versus fuel conflicts has motivated researchers to search for other less common feedstock for production of biodiesel. Thus, this study investigates the suitability of biodiesel made from less common manketti nut oil in terms of its thermal and long-term storage stability. Also, since biodiesel is stored in containers made of different metals; the influence of metal contaminants on the storage stability of biodiesel is also examined. Manketti Oil Methyl Ester (MOME) is synthesized by the transesterification process and characterized as per biodiesel global standards. MOME is doped with antioxidants (1, 2, 3 tri-hydroxy benzene (Pyrogallol, PY) and 3, 4, 5-tri hydroxy benzoic acid (Propyl Gallate, PG)) at different ratio to analyse its influence on the stability of MOME. Also, 2 ppm of selected metals (Co, Cu, Fe, Mn, and Ni) is doped to MOME samples with and without antioxidants and stored for 6 months in open and closed 500 ml plastic bottles. Oxidation stability is measured once a month to monitor stability of MOME. Thermogravimetric analysis is conducted to examine thermal stability of MOME. The results show that freshly-synthesized MOME has oxidation stability of 4.24 h below the European EN 14214 (8 h) and South African SANS 1935 (6 h) standards. On adding antioxidant PY and PG at 200 ppm concentration, the oxidation stability increases to 13 h and 8.5 h respectively. The result of MOME contaminated with metals shows that Cu has the highest damaging effects on oxidation stability during storage. Additionally, thermal stability analysis results exhibit that MOME has excellent thermal stability of 211.33 °C.