Reactor microchannel

Combined with the use of precious metal catalyzed washcoats deposited on the walls, microchannel reactors can realize nearly 10 times reduction in reactor size compared with that of a process that utilizes catalyst particles. The washcoat thickness is usually less than lOOjit and provides greater structural stability. This stability arises from smaller thermal expansion ratios and lower temperature gradients. 

MicroChannel reactors have some significant drawbacks. The most troublesome is clogging of the channels via incoming particulate matter or from fouling during the reaction process. Robustness is another common problem with microreactors. Because the unit is made at such a small internal scale, the resistance to mechanical shock is low. These issues usually render the microchannel reactor unsuitable for reactions that have precipitates as a product. For the Prox reaction, microchannel reactors are suitable provided there is no water condensation and the incoming reformate is particulate free, especially from carbon. Since microchannel reactors are often made from substrates that include stainless steel, Hastelloy, glass, silicon, polymers, and ceramics, another issue that could arise is chemical compatibility. 

The length of bubbles and slugs in Taylor flow has a direct impact on the reactor performance. The dependency of bubble 

In a T-mixer, the bubble length depends on the volume of the mixer chamber and the gas holdup. Garstecki et al. [54] 

Bretherton [63] expanded on this work and analytically derived an expression for the liquid film thickness in chaimels with a circular cross section for Cub 0.01 and negligible inertial effects  

Aussillous and Quere [64] have applied a scaling analysis to Bretherton s result for the Uquid film thickness and su ested an empirical equation for the liquid film thickness  

In cylindrical capillaries where the effects of gravity can be neglected, the liquid film around the bubble has a constant thickness, which increases with the capillary number. Under inertia-dominated flow conditions, the liquid film thickness decreases and then increases with increasing Reynolds number [65, 66]. Han and Shikazono [66] studied hydrodynamics of Taylor flow in circular tubes with different diameters of 0.3, 0.5, 0.7, 1.0, and 1.3 mm, and they proposed empirical correlations for the dimensionless film thickness for Re 2000  

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Microstructures on Macroscale MicroChannel Reactors for Medium- and Large-Size Processes... 

Scale-up of microchannel reactors is based on using the optimal channel dimensions rather than seeking the smallest or the largest microchannel. In some cases, the channels may range from 100 pm in hydrauhc diameter to a few millimeters. The classification of a rigorous size range to designate a reactor as microchannel is not necessary. 

The scale-up challenges for microchannel reactors are addressed through integrated mathematical models to describe all elements of the physics. Integrated... 

As described above, microchannel reactor scale-up requires integrated models, which include the reaction chemistry with heat transfer, pressure drop, flow distribution, and manufacturing tolerances. The culmination of scale-up models is their successful demonstration. 

Development of a CO remover employing microchannel reactor for polymer electrolyte fuel cells... 

Actually, various efforts have been made to develop the compact and efficient microchannel PrOx reactor for portable PEMFC applications. Goerke et al. [2] reported micro PrOx reactor employing stainless steel microchannel foil and Cu/Ce02 catalyst. They showed more than 99% CO conversion at less than 150 C and residence time of 14ms while CO selectivity was about 20%. Chen et al. [3] also developed microchannel reactor made of... 

We prepared microchannel reactor employing stainless steel sheet 400tan thick patterned microchannel by a wet chemical etching. The microchannel shape and dimension were decided by computer simulation of flow distribution and pressure drop of the reactants in the microchaimel sheet. Two different types of patterned plates with mirror image were prepared [5]. The plate has 21 straight microchannels which are 550/an wide, 230/an deep and 34mi long as revealed in Fig. 1(b). 

The experimental apparatus is consists of reformed gas feeding sections, CO PrOx reaction section in the reactor, and the analysis section with a gas chromatograph system. Simulated reformed gas composition was 75 vol.% H2, 24 vol.% CO2 and 1.0 vol.% CO. The dry reformed feed stream was fed with O2 (A.=l) into the microchannel reactor by MFC (Brooks 5850E). Water vapor (10vol.% of reformed gas) was also fed into the reactor by a s)ninge pump. 

For the practical use of this CO removal reactor, the microchannel reactor should be operated carefully to maintain operating temperature ranges because the reaction temperature is critical for the microchannel reactor performance such as CO conversion, selectivity and methanation as disclosed in the above results. It also seems that the present microchannel reactor is promising as a compact and high efficient CO remover for PEMFC systems. 

Fig. 3. CO conversion and selectivity with respect to reaction temperature in a microchannel reactor...

A microchannel reactor for CO preferential oxidation was developed. The reactor was consisted of microchannel patterned stainless steel plates which were coated by R11/AI2O3 catalyst. The reactor completely removed 1% CO contained in the Ha-rich reformed gas and controlled CO outlet concentration less than Ippm at 130 200°C and 50,000h. However, CH4 was produced from 180"C and CO selectivity was about 50%. For high performance of present PrOx reactor, reaction temperature should be carefully and uniformly controlled to reach high CO conversion and selectivity, and low CH4 production. It seems that the present microchaimel reactor is promising as a CO removal reactor for PEMFC systems. 

Kah, S., Honicke, D., Selective oxidation of 1-butene to maleic anhydride -comparison of the performance between microchannel reactors and fixed bed reactor, in Matlosz, M., Ehreeld, W., Baselt, J. P. (Eds.), Microreaction Technology - IMRET 5 Proc. of the 5th International Conference on Microreaction Technology, pp. 397-407, Springer-Verlag, Berlin (2001). 

Zech, T, Honicke, D., E ient ond reliable screening of catalysts for microchannel reactors by combinatorial methods, in Proceedings of the 4th International Conference on Microreaction Technology, IMRET 4, pp. 379-389 (5-9 March 2000), AIChE Topical Conf Proc., Atlanta, USA. 

Rouge, A., Spoetzl, B., Gebauer, K., Sghenk, R., Renken, a., MicroChannel reactors for fast periodic operation the catalytic dehydration of isopropanol,... 

J. P., Matlosz, M., Optimal design for flow uniformity in microchannel reactors, AIChE J. 48, 2 (2000) 345-358. 

Schenk, R., Steinfeld, N., Walter, S., Periodic operation in microchannel reactors, in Ehrfeld, W. (Ed.), Microreaction Technology 3rd International Conference on Microreaction Technology,... 

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