(578a) Partial Oxidation Of Methane And Propane With Sulfur Effects Over Rh-Coated Monolith : Spatially Resolved Intra-Channel Species And Temperature Measurements And Modeling

Fuel reformers convert hydrocarbons to hydrogen- and carbon monoxide-rich synthesis gas, and are useful for enabling a range of technologies including fuel cells, automotive catalysis and advanced combustion. Catalyzed monolith-supported fuel reformers can have very high species and temperature gradients, and varying reforming chemistries along the device axis. This gradient-rich reactor poses a challenge to reformer models, which are needed for device and system design. Transient reformer operation can create complex spatiotemporal gradients and further complicate reformer analysis. Given these complexities, the limited ability to understand reformer chemistry through integrated inlet-outlet measurements is apparent. In-situ diagnostics that resolve intra-reformer gradients and distributions are needed to improve the understanding and models of these devices.

We have made measurement of the species and temperature distributions within operating reformers. Specifically, methane and propane partial oxidiation and sulfur effects have been studied on channelized-monolith-supported Rh-based reformers. Intra-reformer species distributions have been measured with the spatially resolved capillary inlet mass spectrometer, SpaciMS; a minimally invasive diagnostic capable of resolving transient species distributions within operating reactors. Temperature distributions have been measured with fine-wire thermocouples and several optical-fiber-based techniques. The ability of thermocouples to resolve high thermal gradients is seriously limited by thermal-conductivity induced broadening, and further complicated by varying thermal expansion at different locations through the device. Optical-fiber techniques effectively eliminate these challenges and more accurately resolve the high thermal gradients of fuel reformers. We have applied fiber-optic based temperature measurements based on phosphorescence and pyrometry for intra-reactor measurements.

Applications of these diagnostics to methane partial oxidation allowed the species and temperature distributions through the reformer to be resolved on the level of 0.2 mm in our previous study. Initially the catalytic partial oxidation process started slowly at the catalyst front, was followed by much faster reactions in an exothermic oxidation zone, and subsequently an endothermic reforming zone using the products of the combustion zone. These measurements suggest subsequent major reaction zones, but do not rule out simultaneous reactions too. The initial slow reaction zone lengthened with increasing space velocity. Other than moving its inception location, space velocity had little effect on the oxidation zone; less than 15% of the total hydrogen production occurred in the oxidation zone where the major products were heat, CO, CO2 and H2O. Increasing space velocity decreased activity in the reforming zone, which had minor CO2 reforming in addition to the dominant steam reforming. Variations in the species and temperature profiles may indicate dominant-chemistry transitions and unknown chemistries. For instance, some process in the middle of the reforming zone reduced both heat consumption and syn-gas generation, and was more apparent at higher space velocities. In the presentation we will compare the methane and propane reformer chemistries, and describe sulfation effects and our modeling efforts.