Kinetics of the Homogeneous Reverse Water-gas Shift Reaction at High Temperature

The high-temperature rate of reaction of the homogeneous, reverse water-gas shift reaction, rWGSR, has been evaluated in quartz reactors with rapid feed pre-heating at low-pressure and high-pressure conditions. The form of the powerlaw rate expression was consistent with the Bradford mechanism. The Arrhenius expressions for the reaction rate constant corresponding to the empty reactor were in very good agreement with the low-pressure results of Graven and Long, but yielded rate constants roughly four times greater than those obtained in our packed reactor and those reported by Kochubei and Moin and by Tingey. Reactor geometry was not responsible for these differences because CFD simulations revealed similar residence time distributions and comparable conversions when the same kinetic expression was used to model the rWGS reaction in each reactor. The empty NETL reactor and the Graven and Long reactor may not have attained an invariant value of the concentration of the chain carrier (H) at low reaction times, however, which led to an overestimation of the rate constant. Conversions attained in an Inconel® 600 reactor operating at comparable conditions were approximately two orders-of-magnitude greater than those realized in the quartz reactor. This dramatic increase in conversion suggests that the Inconel® 600 surfaces, which were depleted of nickel during the reaction, catalyzed the rWGSR.