(460b) Steam Reforming and Combustion Kinetics of N-Hexadecane for Modeling and Simulation of A Novel Catalytic Reformer
AIChE Annual Meeting
Wednesday, November 7, 2007 - 3:50pm to 4:10pm
Fuel steam reforming to produce hydrogen has gained research interest due to its application in the solid oxide fuel cells (SOFC). Catacel Corporation, in partnership with the University of Toledo, has developed a Flexible Fuel Reformer (FFR), a compact multi channel heat exchanger unit in which reforming and combustion reactions are carried out simultaneously on adjacent catalyst coated channels. Kinetic study and modeling was carried out for both reactions to design FFR.
We evaluated the reforming and combustion kinetics of n-hexadecane (a surrogate fuel for diesel) over a rhodium on alumina catalyst (NM4) which was prepared by wet impregnation method on a commercially available support. Reforming of hexadecane was studied over a range of temperatures and steam to carbon (S/C) ratios, and then the reaction rate was modeled using power law kinetics. Combustion kinetics of hexadecane was studied with excess industrial grade air on the NM4 catalyst, and again modeled using power law kinetics.
The kinetic models were used in a numerical simulation describing the conversion within combustion and reforming channels as a function of position. These results indicated that combustion reaction liberates excess heat which results in higher temperature of both reactions, since heat transfer between two reactions is excellent. These simulation results also showed that reforming reaction was fast and reached completion in half of the reactor length. To overcome this effect, combustion flow rates were adjusted to stretch reforming reaction across entire length. Since the goal is to operate reforming reaction nearly isothermal to get consistent hydrogen yield, the effect of dilution on the combustion feed was evaluated.
Although simple kinetic models were initially used, experimental results also showed that hydrogen yield decreased above 700°C with further increase in temperature and that the catalyst deactivates with time on stream. In order to better capture actual catalyst performance, more extensive kinetic models (e.g. coke formation as a side reaction) are being investigated. The development of these models is supported through characterization of used catalyst via XRD, TGA and TPR.