Methyl Esterification of Oleic Acid in Supercritical Methanol with Methyl Formate

Abstract

Fatty acid methyl esters, which are used as biodiesel, can be produced by methyl esterification of fatty acids in supercritical methanol. However, in a reverse reaction, methyl esters are hydrolyzed to regenerate fatty acids due to the presence of water, which is produced by the esterification reaction, making it difficult to reduce the fatty acid content sufficiently. In this study, oleic acid was treated in supercritical methanol at 310 °C/20 MPa with a flow-type reactor by adding methyl formate to improve the yield of methyl ester. As a result, adding methyl formate improved the methyl ester yield approximately from 90 to 95 wt% compared with the treatment using methanol only. Methyl formate was hydrolyzed instead of fatty acid methyl esters, producing formic acid and methanol. Formic acid can be decomposed into gases such as H2 and CO2 by thermal decomposition in supercritical methanol. As these reactions consume water, removing it from the reaction system, the reaction equilibrium was considered to be shifted in the direction to improve the methyl ester yield.