Autothermal reforming of methanol: Experiments and modeling

A bench-scale fixed-bed reactor for the autothermal reforming (ATR) of methanol under near-adiabatic conditions was constructed to experimentally demonstrate the conversion of methanol to hydrogen over a copper-based catalyst. Axial distribution of air through multiple porous ceramic membranes was employed to limit the peak temperature within the catalyst bed, which is critical for the stability of copper-based catalysts. Methanol conversion, product selectivities, and temperatures were measured at discrete axial positions as a function of H2O:C ratios, feed temperatures, pressures, and two different air distributor designs. The effect of space velocity was implicitly studied via the axial composition profile measurements while the O2:C ratio was adjusted to achieve an overall methanol conversion exceeding 90%. The use of a copper-based catalyst with distributed air injection resulted in low CO effluent concentration of ca. 1.3% at a feed temperature of 200 °C, H2O:C ratio of 1.0, O2:C ratio of 0.11, and total pressure between 2 and 5 bar. Distributed air injection limits the peak bed temperature to 280 °C while injection of air over a narrow front results in a peak temperature of ca. 575 °C. The CO composition was found to be primarily a function of temperature and H2O:C ratio, with CO yield minimized at low temperature and high H2O:C. The system was simulated using an adiabatic 1D reactor model comprising kinetic rate expressions of Peppley et al. [B.A. Peppley, J.C. Amphlett, L.M. Kearns, R.F. Mann, Appl. Catal. A: Gen. 179 (1999) 31–49]. Very good agreement between data and model was achieved by assuming the oxidation reaction to be instantaneous (limited by oxygen supply). The results support a phenomenological view that the exothermic oxidation reactions occur in a narrow zone in close proximity to the porous membranes, leaving the bulk of the catalyst between membrane tubes in the reduced state and therefore active for conducting the endothermic reforming reactions.