(390c) Micro-Structured Reactor Technology for Portable Fuel Processors

The introduction of heat-exchange capabilities into chemical reactors is a well-known measure taken to improve the thermal management of numerous processes ? hot spot formation may be suppressed and heat losses are minimised, which helps to improve the overall process efficiency. Apart from the safe management of hazardous reactions, the application of micro-structured reactor technology enhances the heat and mass transfer, which reduces the reactor size demand [1]. Especially small scale portable power generation systems require compact hydrogen supply in case fuel cell technology is applied [2]. Fuel processing is a viable option to meet the limited space demands of portable auxiliary power units (APUs) due to the high energy density of liquid or even solid fuels. A fuel processor requires energy supply for both fuel evaporation, steam generation and for the reforming process itself ? the latter in case an endothermic process such as steam reforming is applied. At IMM, all components required for building a fuel processor are addressed. Commercial and home-made catalyst coatings [3] are under investigation for the steam reforming and partial oxidation of propane [4], for methanol [5] and ethanol steam reforming as well as for the catalytic combustion of these fuels, which serves as energy source for steam reforming and evaporation processes. The catalytic CO clean-up has been addressed by catalyst screening for water-gas shift [6], preferential oxidation [7] and methanation reactions based upon noble metal catalyst technology. In selected cases 1,000 hours stability testing is performed on selected catalyst coatings at weight hourly space velocities, which are sufficiently high to meet the demands of future fuel processing reactors. The thermal and mechanical stability of the wash-coatings throughout temperature cycles, exposure to moisture and mechanical shocks has been demonstrated [8]. However, alternative routes of generating catalyst coatings such as sol-gel techniques are under investigation as well. Integrated plate heat-exchanger reactors for the combined propane steam reforming / propane combustion, methanol steam reforming / anode off-gas combustion and for the steam generation fed by hydrocarbon combustion are operated at temperatures exceeding 750°C (in case of hydrocarbon reforming) and up to a size range of 5 kWel of the fuel cells supplied. Cooling capabilities have been introduced into reactors designed for the partial oxidation of propane, the water-gas shift [9], [10] and the preferential oxidation of carbon monoxide. Balance-of-plant components such as cross-flow and counter-flow heat-exchangers working up to 900°C, evaporators, condensers and pre-heaters for fuel cells and fuel processors do complete this list. Short system start-up time demand is one of the requirements most difficult to meet in the case of portable systems. Owing to the lack of sufficient buffer battery power, combustion processes need to be applied for start-up. Because micro-structured plate heat-exchangers bear the potential of multi-task design, unique features may be introduced into the fuel processor components, which reduce the start-up time demand. System assembly is the final challenging task. At IMM, a complete fuel processor capable of feeding a 5 kWel fuel cell and working with autothermal reforming of iso-octane as a model substance for gasoline has been assembled and successfully put into operation. Other, smaller fuel processing systems in the power range below 1 kWel are under development. An overview of the work focussing on integrated components such as heat-exchanger reactors for combined fuel combustion / fuel reforming and integrated complete fuel processor solutions working with and without catalytic CO-clean-up will be presented.

Literature

[1] Kolb G., Hessel V, ?Review: Micro-structured reactors for gas phase reactions? Chem. Eng. J. 98, (2004) 1. [2] Hessel V., Löwe H., Müller, A., Kolb G., 2005, 'Chemical Micro Process Engineering- Processing, Applications and Plants', Wiley, Weinheim, ISBN-13 978-3-527-30998-6, p.281 ff. [3] Zapf R., Becker-Willinger C., Berresheim K., Bolz H., Gnaser H., Hessel V., Kolb G., Löb P., Pannwitt A.-K., Ziogas A., Trans I Chem E Part A, 81 (2003) 721. [4] Kolb, G.; Zapf, R.; Hessel, V.; Löwe, H., 2004, ?Propane Steam Reforming in Micro-channels ? Results from Catalyst Screening and Optimisation?, Appl. Cat. A: General, 277, 155-166. [5] Cominos V., Hardt S., Hessel V., Kolb G., Löwe H., Wichert M., Zapf R., Chem. Eng. Comm. 192 (2005) 685. [6] Kolb G., Pennemann H., Zapf R., Catal. Today 110 (2005) 121 [7] Cominos V., Hessel V., Hofmann C., Kolb G., Zapf R., Ziogas A., Delsman E.R., Schouten J.C., Catal. Today 110 (2005) 140 [8] Zapf R. and Kolb G., Chem Eng. Techn., in prep. [9] TeGrotenhuis, W.E. King, D.L., Brooks, K.P., Holladay B.J., Wegeng, R.S. 6th International Conference on Microreaction Technology, 2002, AIChE, NY, 2002, p. 18 [10] Baier T. and Kolb G., Chem Eng. Sci., submitted for publ.