Design of a biolubricant by the enzymatic esterification of the free fatty acids from castor oil with neopentylglycol

Abstract

The optimization of the esterification of the free fatty acids (FFAs) from castor oil with neopentylglycol (NPG) catalyzed by the commercially immobilized lipase from Thermomyces lanuginosus (Lipozyme® TL IM) is herein reported. An 95 ± 3.3 % acid consumption was achieved at 55 °C, 6 wt% biocatalyst content and a substrates molar ratio (acid/alcohol)) of 2:1 after 24 h of reaction in a solvent-free medium. The addition of 1 M heptane seemed to lead to biocatalyst inactivation. The final product was composed of over 85 % of diesters of NPG, 5 % of monoesters of NPG and 5 % estolides (estolide number of 7), together to 2 % of unreacted FFAs. This product improved the feedstock viscosity index from 87.15 to 119.21 and the oxidative stability from 0.18 h to 24 h. It also exhibited a lower friction coefficient (0.0518 against 0.0592) and a lower wear scar diameter (117.99 against 136.78) than the commercial lubricant 15 W-50. Lipozyme® TL IM retained approximately half of its initial FFAs conversion after eight consecutive reaction cycles of 24 h.