Hexanoic acid upgrading into hexyl hexanoate: An efficient way to obtain a new sustainable biofuel

Abstract

Hexyl hexanoate emerges as a promising candidate for integration into diesel fuel blends. To achieve a green synthesis of hexyl hexanoate, a straightforward process was proposed, utilizing hexanoic acid and hydrogen as reactants, both potentially obtainable from renewable sources. 5 % Ru/C, 5 % Pt/C and 10 % Pd/C were tested for the hydrogenation/esterification of hexanoic acid. Among these, 10 % Pd/C proved to be the most effective catalyst: after a 6-hour reaction at 573 K under 20 bar of H2, hexanoic acid exhibited a partial conversion (84.7 %) into a mixture of hexyl hexanoate, water, hexanoic acid, and 1-hexanol (58.7 %, 12.9 %, 14.9 %, and 13.5 % wt, respectively), resulting in a hexyl hexanoate yield of 69.8 %. Following the removal of 10 % Pd/C, the addition of AlCl3·6H2O to the reaction mixture was considered for enhancing hexyl hexanoate production, through further conversion of previously unreacted hexanoic acid and 1-hexanol. A remarkable increase in hexanoic acid conversion (94.2 %) and hexyl hexanoate yield (from 69.8 % to 88.8 %) was achieved, along with an increase in the hexyl hexanoate purity of the final product (86.8 %). An efficient, clean, and resource-saving synthesis of hexyl hexanoate from hexanoic acid was achieved, supported by the recoverability and reusability of both catalysts, boding well for an effective and widespread use of such ester in diesel fuel blends.