Hydrogen generation for fuel-cell power systems by high-pressure catalytic methanol-steam reforming

Results of kinetic studies of methanol-steam reforming on a commercial low-temperature shift catalyst, BASF K3-110, are reported. A comprehensive Langmuir-Hinshelwood kinetic model of methanol-steam reforming on Cu/ZnO/Al2O3 catalyst was used to simulate a methanol-steam reformer operating at pressures up to 45 bar. At constant temperature and steam-to-methanol ratio, increasing the pressure results in an increase in the initial rate of the reaction and a corresponding improvement in reformer performance. This is partially offset as the equilibrium conversion decreases with increasing pressure. The rate of reaction is highest at low conversion. The result is that there is a large heat demand near the entrance of the catalyst bed which causes a strong endothermic effect and a corresponding temperature minimum. In the worst case, this temperature minimum can be below the dewpoint temperature of the operating fluid causing a loss in reformer performance due to condensation in the pores of the catalyst. The situation is exacerbated by the potential for thermal damage to other regions of the catalyst bed if the heating temperature is increased to overcome the endothermic effect. Catalyst deactivation at elevated pressures was also studied in an 80 hour experiment at 260 degrees C. Increasing the operating pressure did not accelerate the rate of deactivation for the typical gas compositions encountered during normal reformer operation. No catalyst fouling was observed for experimental pressures as high as 40 bar at steam-to-methanol ratios greater than unity even though the tendency for carbon formation increases with pressure. Catalyst selectivity improved at lower conversion due to kinetic effects. The equilibrium CO concentration, however, does not vary significantly with pressure because of the stoichiometry of the water-gas shift reaction.