Oleic acid esterification with methanol to methyl oleate under light irradiation using modified alginate capsules loaded with a solid acid catalyst

Abstract

Sulfated ZrO2 and amorphous carbon-based solid acid catalysts were prepared by a literature method and were estimated to contain 54 and 240 μmol g-cat−1 acid sites, respectively. The capsule shell was modified by various methods to increase its permeability to oleic acid, and methoxy functionalization of the alginate shell with methanol gave the biggest increase and also improved the oleic acid esterification to methyl oleate by the capsules loaded with the solid acid catalyst. The amount of solid acid catalyst loaded in the capsule was optimized, and the capsules loaded with the amorphous carbon-based solid acid catalyst showed a higher methyl oleate formation rate and yield than the capsules loaded with sulfated ZrO2 and active carbon powder under light irradiation. This is probably because the number of acid sites on the amorphous carbon-based catalyst was greater than that on the sulfated ZrO2 catalyst. In addition, the amorphous carbon-based catalyst was directly heated under light irradiation because it was black, whereas the sulfated ZrO2 catalyst was heated by the reaction media that was heated by the active carbon powder absorbing the irradiated light.