KINETICS OF THE HIGHER ALCOHOL SYNTHESIS OVER A K-PROMOTED CUO/ZNO/AL2O3 CATALYST

Abstract

Detailed kinetic experiments of higher alcohol synthesis over K-promoted CuO/ZnO/Al2O3 catalysts have been performed using an internal recycle reactor operated at 4 MPa and between 548 and 578 K. It was found that a 0.5 % K-promoted catalyst, a stoichiometric H-2/CO ratio (approximately 2), and a low (2%) CO2 concentration were favorable for isobutanol yield. In contrast, for the synthesis of methanol, a higher K loading, H-2/CO ratio, and CO2 concentration were found to be favorable. The results suggest that isobutanol synthesis requires a balanced level of oxidation (Cu-0/Cu1+), as confirmed by in situ X-ray photoelectron spectroscopy, while methanol synthesis requires a greater degree of oxidation (more Cu1+). Contact time experiments showed the selectivity of aldehydes to pass through a maximum, suggesting the intermediacy of aldehydes in a classic ''aldol'' condensation mechanism. In extended time-on-stream experiments, initial deactivation was accounted for by a loss in BET surface area and a loss in Cu/Zn ratio. Greater deactivation at higher temperatures resulted in lower final activities; nevertheless steady-state isobutanol yields increased significantly at higher temperatures.