Biodiesel synthesis from photoautotrophic cultivated oleoginous microalgae using a sand dollar catalyst

Abstract

The aim of this study was to synthesize a calcined sand dollar (CSD), Clypeaster reticulatus as a green mixed oxide CaO–MgO solid catalyst through a thermal degradation method for transesterification of Nannochloropsis oculata (N. oculata) microalgae derived crude oil. The catalysts characterizations were carried out by TG/DTA, XRD, FTIR, TPD-CO₂, SEM and ICP–AES analysis, respectively. Formation of binary phase solid oxides i.e. CaO and MgO were confirmed at a calcination temperature of 800 °C. The effect of the reaction parameters i.e. catalyst amount, methanol/oil molar ratio, reaction temperature and time were evaluated for the transesterification reaction. The photoautotrophic microalgae propagation produced lipids with 25.8 ± 4.5% of total lipids, 18.5 ± 1.8% of crude lipids and 12.8 ± 2.6% of neutral lipids, respectively. Interestingly, the produced N. oculata biodiesel using this process revealed an insignificant change in FAME composition, which comprised mostly C16:0 and C16:1, similar to conventional biodiesel. Under the conditions tested, the catalyst showed a 90% yield of fatty acid methyl ester (FAME) at ideal reaction variables of 3 wt% of catalyst loading, 60 °C, 30 : 1 of methanol/oil, and 3 h reaction time.