MEMS-Based Reactors

Current pressure drop measurements also show that they are no higher than that of a conventional 400cpsi monolith. 

MEMs reactor technology is still developing. The most common application for these systems is in portable devices that are suitable for military use. Like micro-channel reactors, the small internal dimensions can create problems with fouling and plugging of the flow paths. 

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Jensen stresses the great flexibility in reactor design that can be achieved by means of microfabricahon, in particular when parallel, MEMS-based mask processes are followed, having a mulhtude of miniature designs on one mask [75], This should invigorate the innovahve nature of reactor design and allow one to overcome... 

Without being itself a screening device, the reactor of Jensen et al. [6, 42, 43] also has to be mentioned because they opened up a completely new field in catalysis by combining MEMS (micro-electro-mechanical systems) technology with a chip-based catalytic reactor (Fig. 4.10). A mixing-tee was equipped with heaters and temperature and flow sensors, thus giving on-stream information about the reaction conditions. 

Preferential Carbon Monoxide Oxidation 2 [PrOx 2] Single-plate Reactor Based on MEMS Technology... 

Bednarova et al. [87] designed a single-plate PrOx reactor for a 1 W fuel cell based on MEMS technology, similar to [PrOx 1], The results of the simulation work described above were applied to optimize the reactor performance. The plate carried a pre-mixer and 29 channels each 12 mm long, 500 pm wide and 400 pm deep. Flow uniformity was verified by simulations. Full conversion of carbon monoxide was achieved at much lower temperature with [PrOx 1] and the selectivity towards carbon dioxide was 40%. 

Franz et al. [93] developed a palladium membrane micro reactor for hydrogen separation based on MEMS technology, which incorporated integrated devices for heating and temperature measurement. The reactor consisted of two channels separated by the membrane, which was composed of three layers. Two of them, which were made of silicon nitride introduced by low-pressure chemical vapor deposition (0.3 pm thick) and silicon oxide by temperature treatment (0.2 pm thick), served as perforated supports for the palladium membrane. Both layers were deposited on a silicon wafer and subsequently removed from one side completely... 

A third way to build up pFCs based on MEMS-polymers such as poly-dimethylsiloxane (PDMS) or polymethyl methacrylate (PMMA) or PCB-materials such as polyimid (PI) or FR4. These polymers can be micro-machined by molding or by laser ablation. Shah et al. [22,23] have developed a complete PEMFC system consisting of a PDMS substrate with micro-flow channels upon which the MEA was vertically stacked. PDMS micro-reactors were fabricated by employing micro-molding with a dry etched silicon master. The PDMS spin coated on micro-machined Si was then cured and peeled off from the master. The MEA employed consisted in a Nafion - 12 membrane where they have sputtered Pt through a Mylar mask. Despite an interesting method, this FC gave poor results, a power density of 0.8 mW cm was achieved. 

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