Biodiesel production from used cooking oil using a novel surface functionalised TiO2 nano-catalyst

A novel, efficient and recyclable mesoporous TiO2/PrSO3H solid acid nano-catalyst was synthesised by the post-synthetic grafting of propyl sulfonic acid groups onto a mixed phase of a TiO2 support. The synthesised nano-catalyst was characterised using FTIR, SEM, TEM, XPS, N2 adsorption–desorption isotherms, XRD, DSC, TGA, and CHNS analysis. The percentage of loading for propyl sulfonic acid on the TiO2 support was calculated using CHNS analysis and TGA. The catalytic performance of TiO2/PrSO3H on the production of the fatty acid methyl esters (FAME) via simultaneous esterification and transesterification reactions from used cooking oil (UCO) has been studied. The effects of different process parameters showed that 98.3% of FAME can be obtained after 9 hrs of reaction time with 1:15 molar ratio of oil to methanol, 60 °C reaction temperature and 4.5 wt% catalyst loading. It was also found that the one-pot post-surface functionalisation strategy with hydrophilic functional groups (-SO3H) enhanced the acid strengths of the nano-catalyst providing more acid sites for the reactants, and improving the accessibility of methanol to the triglycerides (TG)/free fatty acids (FFAs) by increasing the pore volumes/sizes of the nano-catalyst. The solid acid nano-catalyst was re-used in four consecutive runs without significant loss of catalytic efficiency. Finally, the synthesised biodiesel fuel satisfied ASTM and EN standards.