Kinetics of the hydrogenation of citral over supported ni catalyst

The hydrogenation kinetics of an unsaturated aldehyde, citral, was investigated in a semibatch reactor operating at 60-77 °C and at atmospheric pressure. Crushed alumina supported nickel was used as a catalyst and ethanol as a solvent. The kinetic experiments revealed that the conjugated double bond is the most reactive one, giving citronellal as a primary product, which is partially acetalized with ethanol. The acetalization can be suppressed by hydrogen spillover on the support. Hydrogenation of the carbonyl group in citronellal gave citronellol as the secondary reaction product with high yields (92.5-94.9%). In long time experiments the hydrogenation of citronellol to 3,7-dimethyloctanol was confirmed. The parallel hydrogenation part of citral through nerol and geraniol was observed to be almost negligible. Based on the qualitative results, a reaction scheme was written and pseudo-first order rate equations were derived. Approximate values for the rate constants were obtained by applying non-linear regression analysis on the kinetic data.