Design of adiabatic fixed-bed reactors for the partial oxidation of methane to synthesis gas. Application to production of methanol and hydrogen-for-fuel-cells

Abstract

Adiabatic fixed-bed reactors for the catalytic partial oxidation (CPO) of methane to synthesis gas were designed at conditions suitable for the production of methanol and hydrogen-for-fuel-cells. A steady-state, one-dimensional heterogeneous reactor model was applied in the simulations. Intra-particle concentration gradients were taken into account explicitly, by solving the continuity equations in the catalyst pellet at each position along the fixed-bed reactor co-ordinate. The reactor designs are based on supported Ni catalysts, which catalyse the indirect formation of synthesis gas via total oxidation followed by steam reforming and water–gas shift. In both cases water was added as a reactant. Atmospheric, air-based fixed-bed CPO reactors for fuel-cell applications are feasible due to low catalyst temperatures. At high-pressure methanol conditions, however, catalyst deactivation will be very important as a result of the calculated high catalyst temperatures. The influence of the steam-reforming rate was investigated separately by performing simulations with the kinetic reforming models proposed by Numaguchi and Kikuchi (Chem. Eng. Sci. 43 (1988) 2295) and Xu and Froment (AIChEJ. 35 (1989) 88). The influence of the oxidation kinetics was studied as well. Application of different reforming models leads to significantly different maximum catalyst temperatures. Also, the possible occurrence of gas-phase reactions was investigated: homogeneous reactions will be very important at conditions suitable for methanol production.