Methanol synthesis from hydrogen, carbon monoxide, and carbon dioxide over a CuO/ZnO/Al 2O 3 catalyst : I. Steady-state kinetics experiments

Abstract

The steady-state synthesis of methanol over a commercial low-pressure CuO/ZnO/Al 2O 3 catalyst was studied in a fixed-bed, steady-flow reactor with a well mixed fluid phase at pressures of 2.89 MPa and 4.38 MPa, temperatures between 483 K and 513 K, and varying CO/H 2/CO 2 compositions. Additional experiments were conducted by replacing carbon monoxide with helium in the feed gas to determine the effect of carbon dioxide on the methanol formation rate. Carbon dioxide was found to contribute significantly to the total production rate of methanol. It was found that the optimum carbon dioxide concentration occurred near 2 mole percent carbon dioxide in the feed. Higher carbon dioxide concentrations resulted in decreasing methanol production rate. In the limited number of experiments in which carbon monoxide was replaced with helium in the synthesis gas, no optimum carbon dioxide concentration, in the range of 2–8 mole percent carbon dioxide in the feed, was found beyond which the methanol production rate decreased. Thus it appears that carbon dioxide inhibits carbon monoxide hydrogenation when above 2 mole percent in the feed but not its own hydrogenation to methanol. Significantly more water was produced during the helium experiments than during those experiments in which carbon monoxide was present in the synthesis gas mixture. Thus, the water—gas shift reaction appeared to proceed in the reverse direction in the helium experiments and in the forward direction when carbon monoxide was present in the feed.