(350d) A Study on Catalytic Combustion of Methanol-Air Mixture in Microreactors

Power generation from a thermoelectric (TE) element coupled with a
catalytic microcombustor is being investigated in
recent decades [1]. Lean hydrogen/air and methanol/air mixtures share a
desirable property that they ignite at room temperature on Pt/alumina
catalysts [2]. This allows combustor coupled TE devices to be operated at
relatively lower temperatures [3]. Since methanol is liquid at room temperature
and is safer to handle than hydrogen, it is a preferred fuel for coupled TE
device.

Hydrogen micro-combustion can be operated at highly fuel-lean
conditions and a wide range of flowrates, which
allows the coupled device to be operated at desirable temperatures and high
efficiency. Our interest is to investigate methanol combustion in catalytic microreactors. Mcnally et al. [4]
tested different fuels in a monolith coated with Pt
nanoparticles, and found that methanol alone could self-ignite at room
temperature. They developed an integrated device with TE element operating with
temperature difference of 55 ^oC. The aim
of this work is to further analyze behavior of methanol combustion in catalytic
micro-reactors, delineate regions of operation and hence determine optimal
design for integrated microreactor-TE device.

A detailed numerical study coupled with experimental validation is
performed for combustion of lean methanol/air mixtures on Pt/Alumina
catalyst in a microreactor. An appropriate kinetic model for methanol catalytic
combustion under microreactor conditions is not yet established in literature.
The kinetic parameters of available models are adjusted to match the reactor
level data from literature. A reactor model for the multi-channel
micro-combustor with and without internal heat recycle is developed, and the
resulting species and energy conservation equations are solved to get the
optimum operating conditions, quenching limits and maximum steady state
temperatures reached by the system. Furthermore, favorable operating conditions
for thermal coupling of the combustor with TE device for energy generation will
be investigated. Finally, the effect of including copper spreader adjacent to the
walls of the combustor will be analyzed to ensure thermal uniformity as
desirable by the TE device. This study provides an insight to build an integrated
power generating device with catalytic micro combustor fueled by methanol for
higher power outputs.

References

[1]         A. C. Fernandez-Pello,
“Micropower generation using combustion: Issues and approaches,” Proc.
Combust. Inst., vol. 29, no. 1, pp. 883–899, 2002.

[2]         Z. Hu, V. Boiadjiev, and
T. Thundat, “Nanocatalytic spontaneous ignition and self-supporting
room-temperature combustion,” Energy and Fuels, vol. 19, no. 3, pp.
855–858, 2005.

[3]         J. A. Federici, D. G.
Norton, T. Brüggemann, K. W. Voit, E. D. Wetzel, and D. G. Vlachos, “Catalytic
microcombustors with integrated thermoelectric elements for portable power
production,” J. Power Sources, vol. 161, no. 2, pp. 1469–1478, 2006.

 [4]        D.
Mcnally, M. Agnello, B. Pastore, J. R. Applegate, E. Westphal, and S. D.
Bakrania, “Nanoparticle Catalyzed Microreactors,” vol. 2015, 2015.