Continuous Flow Preferential Hydrogenation of an Octanal/Octene Mixture Using Cu/AlO Catalysts.

γ-Alumina-supported catalysts with varying copper loadings (5-25 wt %) were prepared by incipient wet impregnation and characterized by various characterization techniques. These catalysts were tested for the selective hydrogenation of octanal in a mixture containing 10 wt % octanal and 2 wt % octene diluted in octanol. The reactions were carried out in a continuous flow fixed-bed reactor in a down flow mode with varying pressures, liquid hourly space velocities, and hydrogen (H)-to-aldehyde molar ratios. The catalyst activities were assessed over a temperature range between 100 and 180 °C using hydrogen gas as the hydrogen source. The results obtained showed that under these experimental conditions, copper preferentially hydrogenates the aldehyde and the copper content exhibited no significant influence on the catalyst activity or product selectivity. Kinetic modeling revealed that both octanal and octene hydrogenation were first-order reactions, although octene conversion was very low until octanal conversion had reached a significant level. The activation energy for octanal hydrogenation is higher than the octene hydrogenation. A maximum octanal conversion of >99% was obtained at 160 °C, and the best selectivity toward octanol of 99% was achieved at 100 °C (53% conversion). The pressure played a small role with regards to octanal conversion and selectivity toward octanol, whereas it exhibited a significant influence on the octene conversion. Increasing the hydrogen-to-aldehyde ratio was found to have a direct influence on both octanal and octene conversion.