KINETICS OF THYMOL HYDROGENATION OVER A NI-CR2O3 CATALYST

The kinetics of thymol hydrogenation over commercial nickel-chromia catalyst with formation of four menthol diastereoisomers have been investigated in a batch reactor at constant hydrogen pressure (0.4-4 MPa) at temperatures between 373 and 433 K in n-hexane and cyclohexane solutions. The rate of thymol consumption was independent of conversion. Initially mainly more thermodynamically unstable cis isomers (neomenthol and neoisomenthol) were produced and only at relatively high conversions trans isomers (menthol and isomenthol) were formed. However the stereoselectivity values at a particular conversion were seen to be independent of hydrogen pressure and reaction temperature. The observed kinetic regularities were modeled based on an elementary step mechanism.