Solar energy and TiO2 nanotubes: Biodiesel production from waste cooking olive oil

TiO2 nanotubes have been used as practical heterogeneous nano-catalyst for biodiesel production from waste cooking olive oil using solar energy. Several critical parameters namely the reaction time and temperature and volume ratio of methanol to oil were optimized to obtain high-quality biodiesel fuel. By using an optimum volume ratio of methanol to WCOO of 8.0:1.0 at 60 degrees C within 4 h, the highest conversion of 91.2 +/- 0.7% was obtained. Solar energy was applied to heat the reaction vessel by parabolic trough reflectors, and photovoltaic panels were employed to power a small electric motor for the stirring of the reaction mixture. After completion of the reaction, the nanocatalyst was separated by a centrifuge. The catalyst could be reused up to four times with a 3% reduction in yield of the final product. The variation of five pollutant emissions for a blend of biodiesel: diesel (20:80 vol/vol %) showed a net decrease of the total hydrocarbons, carbon monoxide, and carbon dioxide emissions compared to the pure diesel fuel.