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 (Al ₂ O ₃ , MgO, ZrO ₂ , and TiO ₂ ) and ethanol to produce fatty acid alkyl esters. The potential of the sulfonated catalysts for esterification decreased in the following order: Ti-SO ₄  > Zr-SO ₄  > Al-SO ₄  > Mg-SO ₄ . Particularly, Ti-SO ₄ and Zr-SO ₄ 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 -SO ₃ H functional groups, additional Lewis acid sites formed by Ti and Zr oxides, and their appropriate pore size. Compared with HCl and H ₃ PO ₄ , the use of H ₂ SO ₄ for TiO ₂ treatment significantly enhanced ester formation. When using Ti-SO ₄ , 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.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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