(491a) Microplasma Reforming for Fuel Cell Feed

Microchemical reactor systems are known to intensify chemical reactions by significantly improving heat and mass transfer when compared to conventional sized reactors.  Plasmas have been used for chemical reactions for many years, but novel microplasmas (confined with a sub-mm critical dimension) offer strong hydrocarbon conversions and provide a favorable reaction environment due to high densities of reactive ions, radicals, and electrons.  Operation at atmospheric pressure and near-room temperature make microplasmas convenient for implementation.  We present a novel approach to further enhance chemical reaction intensification through the use of a microplasma reforming reactor.

The results of reforming experiments with a microfabricated microplasma reactor for producing hydrogen-rich product stream are reported.  These experiments demonstrate the potential of this approach for energy applications such as combustion or fuel cells where concerns for efficiency and portability are important.  To produce the microplasma reactors silicon microfabrication was used.  Photolithography and advanced deep reactive ion etching was used to produce microplasma reactors with microchannels widths varying from 25 to 250 mm.  A micro hollow cathode discharge (MHCD) configuration was designed with a void space in the cathode region with depths varying from 25 to 250 mm.  In these reactors, the void space or hollow was provided by the microchannel, which served as the center of plasma generation and the reaction zone within the reactor.

We examined the conversion of various simple hydrocarbons and alcohols into hydrogen.  It was found, consistent with literature reports, that an inert carrier such as nitrogen promotes decomposition of the organic species, encouraging the formation of hydrogen gas.  The experimental approach taken involved DC or pulsed DC high voltage power supplies interfaced to the reactor chip for plasma generation.  The gaseous feed was set using mass flow controllers.  Gas chromatography and mass spectrometry were implemented for analyzing the composition of the stream.  A computer interfaced with LabView software allowed simultaneous control and acquisition of data from the experiment.

Hydrocarbon conversions up to 50% were observed, as were various products depending on reactant and the conditions of reaction.  Under certain conditions, we observed selectivity of the reaction toward CO over CO₂; this behavior provides a compelling research direction for processing with less global environmental impact than conventional catalytic reforming processes which routinely yield CO₂. 

Experimental data will show that our reaction model can explain the key mechanisms that occurred; analysis of the data shows that reactions rates in the microplasma environment surpass those of conventional plasma reactors.  The realization of an energetically self-sustaining reforming process through extrapolating system modifications is possible with this model.  We conclude that microplasma activation overcomes inherent limitations imposed by catalytically-activated reactions such as catalysis deactivation through poisoning or carbon formation and the need for extended startup times to reach steady state.  Microplasma chemical processing is a viable approach for hydrocarbon reforming and merits consideration for a variety of chemical reaction applications.