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.
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