Determination of the Activation Energy of the Thermal Isomerization of Oleic Acid with Raman Spectroscopy and Partial Least Squares Regression

Unsaturated fatty acids have cis and trans isomers. The naturally stable isomer is the cis isomer, which is changed to the trans isomer by a thermal reaction. The reaction order, reaction constant, and activation energy are required to confirm the reaction mechanism. Therefore, the concentrations of the cis and trans isomers must be determined simultaneously. In the present study, oleic acid (cis isomer) and elaidic acid (trans isomer) were measured using Raman spectroscopy and partial least squares regression. The thermal reaction of oleic acid was performed at several temperatures. The reaction was determined as a first-order reaction. The reaction rate constants at several temperatures were determined as 1.3 × 10−3 to 5.2 × 10−3/h at 100 °C to 160 °C by plotting the logarithm of the oleic acid concentration against reaction time. The activation energy obtained by the Arrhenius plot was 31 kJ/mol.