The processing of high density liquid hydrocarbon fuels appears to be the most promising method of supplying a hydrogen stream for feeding portable fuel cells. Furthermore, microchemical systems are a strong enabling aspect of compact fuel processors due to their advantageous heat and mass transport and inherent compactness. However, a number of crucial challenges exist for the realization of practical fuel processors. In this article, these challenges are addressed, and two examples are shown of how the challenges can be attacked in the context of implementation of microchemical systems. The examples involve (a) appropriate measurement of kinetics in microchannel-catalyst systems with preferential oxidation of carbon monoxide as a model, and (b) thermal integration of reactor components with a methanol steam reformer as a model.
Our recent studies of CO preferential oxidation (PrOx) identified systemic differences between the characteristic curves of CO conversion for a microchannel reactor with thin-film wall catalyst and conventional packed-bed lab reactors (m-PBR's). Strong evidence has suggested that the reverse water-gas-shift (r-WGS) side reaction activated by temperature gradients in m-PBR's is the source of these differences. In the present work, a quasi-3D tubular non-isothermal reactor model based on the finite difference method was constructed to quantitatively study the effect of heat transport resistance on PrOx reaction behavior. First, the kinetic expressions for the three principal reactions involved were formed based on the combination of experimental data and literature reports and their parameters were evaluated with a nonlinear regression method. Based on the resulting kinetic model and an energy balance derived for PrOx, the finite difference method was then adopted for the quasi-3D model. This model was then used to simulate both the microreactor and m-PBR's and to gain insights into their different conversion behavior.Simulation showed that the temperature gradients in m-PBR's favor the reverse water-gas-shift (r-WGS) reaction, thus causing a much narrower range of permissible operating temperature compared to the microreactor. Accordingly, the extremely efficient heat removal of the microchannel/thin-film catalyst system eliminates temperature gradients and efficiently prevents the onset of the r-WGS reaction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.