Interaction of heterogeneous and homogeneous kinetics with mass and heat transfer in catalytic reforming of logistic fuels

A modeling and simulation concept is presented for a better understanding of the interaction of heterogeneous and homogeneous conversion with mass and heat transfer in compact, autothermal reformers of logistic fuels for the production of hydrogen-rich synthesis gas. The model couples elementary-step based reaction mechanisms with a two-dimensional parabolic description of the flow field in a representative number of monolith channels and of heat transport in the entire solid structure of the reactor including catalyst, heat shields, insulation, and reactor wall. The concept is applied to analyze conversion, selectivity, and temperature profiles in partial oxidation of iso-octane, a gasoline surrogate, over a rhodium/alumina monolithic catalyst. The counter-intuitive flow rate effect on hydrogen yield is explained by the ratio of chemical heat release to physical heat loss. Coking tendency is related to the C/O ratio, the flow rate, and the occurrence of homogeneous fuel conversion. C/O ratios close to unity and reasonably high flow rates are found to maximize hydrogen yield at minimum production of coke precursors.