Development of Carbon-Based Solid Acid Catalysts Using a Lipid-Extracted Alga, Dunaliella tertiolecta, for Esterification.

Novel carbon-based solid acid catalysts were synthesized through a sustainable route from lipid-extracted microalgal residue of Dunaliella tertiolecta, for biodiesel production. Two carbon-based solid acid catalysts were prepared by surface modification of bio-char with sulfuric acid (H₂SO₄) and sulfuryl chloride (SO₂Cl₂), respectively. The treated catalysts were characterized and their catalytic activities were evaluated by esterification of oleic acid. The esterification catalytic activity of the SO₂Cl₂-treated bio-char was higher (11.5 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) than that of commercial catalyst silica-supported Nafion SAC-13 (2.3 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) and H₂SO₄-treated bio-char (5.7 mmol Prod.∙h⁻¹∙g Cat. ⁻¹). Reusability of the catalysts was examined. The catalytic activity of the SO₂Cl₂-modified catalyst was sustained from the second run after the initial activity dropped after the first run and kept the same activity until the fifth run. It was higher than that of first-used Nafion. These experimental results demonstrate that catalysts from lipid-extracted algae have great potential for the economic and environment-friendly production of biodiesel.