CO clean

Potrooms and anode baking Wet process phosphoric acid Coed cleaning and dryer Transfer, loading ... 

Table 4 lists a few selected catalysts for the SRE reaction in the middle temperature range, between 450 and 600 °C and high temperature range, above 600 °C. Under these conditions, the listed catalysts produce relatively large amounts of CO which is a poison to the PEM fuel cells. These catalytic processes would therefore require a multi-stage CO clean-up process in the downstream in order to produce pure H2 suitable for fuel cells. 

The main unit is the catalytic primaiy process reactor for gross production, based on the ATR of biodiesel. After the primary step, secondary units for both the CO clean-up process and the simultaneous increase of the concentration are employed the content from the reformated gas can be increased through the water-gas shift (WGS) reaction by converting the CO with steam to CO and H. The high thermal shift (HTS) reactor is operating at 575-625 K followed by a low thermal shift (LTS) reactor operating at 475-535 K (Ruettinger et al., 2003). A preferential oxidation (PROX) step is required to completely remove the CO by oxidation to COj on a noble metal catalyst. The PROX reaction is assumed to take place in an isothermal bed reactor at 425 K after the last shift step (Rosso et al., 2004). 

However, most fuel cell systems can tolerate methane concentrations up to at least 1% in the reformate, no special purification reactions are required. In contrast, hence, removing small residual amounts of carbon monoxide from pre-purifled reformate applying the methanation reaction may be considered as an alternative to the preferential oxidation of carbon monoxide, provided that the CO concentration is low enough to have no significant impact on the hydrogen yield. However, no applications of methanation for CO clean-up in micro structured devices appear to have been reported, hence the issue is not discussed in depth. Finally, during hydrocarbon reforming all hydrocarbon species (saturated and unsaturated) smaller than the feed molecule may be formed. 

Dudfield et al. [88] presented results generated in the scope of the Mercatox program funded by the European Community aimed at a combined methanol steam reformer/combustor with consecutive CO clean-up by PrOx. First, various catalysts were tested for the reaction as micro spheres in a test reactor which was similar to a macroscopic shell-and-tube heat exchanger (Figure 2.57). 

Membrane purification is an elegant alternative to catalytic CO clean-up systems because it has the capability of producing highly purified hydrogen [91]. Additionally,... 

In a second prototype, the reaction temperature was reduced to 250 °C, which reduced the carbon monoxide concentration from 1.2 to < 1%. Later, the first fuel processor prototype was linked to a meso-scale high-temperature fuel cell developed at Case Western University by Holladay et al. [117], which was tolerant to carbon monoxide concentrations up to 10%. Hence no CO clean-up was necessary to run the fuel processor. A 23 mW power output was demonstrated according to Holladay et al. [118], This value was lower than expected, which was attributed to several factors. First, the hydrogen supply was lower in the reformate. Second, the presence of carbon monoxide (2%) lowered the cell voltage. Third, the presence of carbon dioxide (25%) generated a magnified dilution effect at the gas diffusion layer material of the fuel cell, which was considerably less porous than conventional materials. 

Molten carbonate fuel cells Micro-electro-mechanical systems Microreactor Technology for Hydrogen and Electricity Micro-structured membranes for CO Clean-up Membrane reactor... 

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