Production of biodiesel via esterification of coffee waste-derived bio-oil using sulfonated catalysts.

Catalytic esterification of acid-rich coffee waste-derived bio-oil was performed using sulfonated metal oxide catalysts (AlO, MgO, ZrO, and TiO) and ethanol to produce fatty acid alkyl esters. The potential of the sulfonated catalysts for esterification decreased in the following order: Ti-SO > Zr-SO > Al-SO > Mg-SO. Particularly, Ti-SO and Zr-SO resulted in 91.2 % (peak area %) and 85.2 % esters, respectively. This is attributed to the contributions of well-dispersed Brønsted acid sites created by -SOH functional groups, additional Lewis acid sites formed by Ti and Zr oxides, and their appropriate pore size. Compared with HCl and HPO, the use of HSO for TiO treatment significantly enhanced ester formation. When using Ti-SO, increasing the catalyst-to-feedstock ratio (1/2 ∼ 1/10) significantly increased the esters' selectivity (38.7 %∼94.7 %). Ethanol utilization caused a superior selectivity for esters than methanol, while the increasing temperature favored ester production. This study proposes an eco-friendly and practical method for biodiesel generation.