External Mass and Heat Transfer Limitations of the Partial Oxidation of Methane over a Pt/MgO CatalystConsequences for Adiabatic Reactor Operation

A kinetic model for the partial oxidation of methane to syngas over a highly active Pt/MgO catalyst was developed using hyperbolic rate equations. The formation of syngas was derived to occur via primary methane combustion to CO 2 and H 2 O and secondary steam and CO 2 reforming of methane to CO and H 2 . On the basis of this kinetic model the performance of an adiabatic reactor was simulated. A sensitivity analysis with respect to radiation and heat conductivity of the catalyst bed on axial temperature and concentration profiles was performed assuming T inlet = 873 K and u reactor,873K = 3 m s - 1 . A hot-spot temperature on the surface of ca. 1700 K at 1 bar and 2600 K at 25 bar and large gradients between surface and gas-phase temperature were calculated. No significant contribution of radiation to the heat transfer was predicted. The effective heat conductivity of the catalyst bed is an important factor to decrease hot-spot temperatures. The maximum temperature amounts to 1380 K (1 bar) and 2100 K (25 bar), assuming a heat conductivity of the catalyst bed of 0.15 J s - 1 m - 1 K - 1 . Equilibrium conversion and selectivity is obtained with a bed of less than 1 mm length.