Preferential oxidation systems

Lee, SH, Han, J, Lee, K-Y. Development of lOkWe preferential oxidation system for fuel cell vehicles. J. Power Sources 2002 109 394 2. 

The production of copper from sulphide minerals is accomplished with a preliminary partial roast of die sulphides before reaction widr air in the liquid state, known as mattes, to form copper metal (conversion). The principal sources of copper are minerals such as chalcopyrite, CuFeSa and bornite CuaFeSa, and hence the conversion process must accomplish the preferential oxidation of non, in the form of FeO, before the copper metal appears. As mentioned before, tire FeO-SiOa liquid system is practically Raoultian, and so it is relatively easy to calculate the amount of iron oxidation which can be canned out to form this liquid slag as a function of the FeO/SiOa ratio before copper oxidation occurs. The liquid slag has a maximum mole fraction of FeO at the matte blowing temperatures of about 0.3, at solid silica saturation. 

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. 

P. Ratnasamy, D. Srinivas, C. V. V. Satyanarayana, P. Manikandan, R. S. Sendiil Kumaran, M. Sachin, and V. N. Shetti, Influence of flie support on flie preferential oxidation of CO in hydrogen-rich stream reformates over flie CuO—Ce02—Zr02 system, J. Catal. 221, 455 65... 

PAFC systems are commercially available from UTC Power as 200-kW stationary power sources operating on natural gas. The stack cross section is 1 m (10.8 ft ). It is about 2.5 m (8.2 ft) tall and rated for a 40,000-h life. It is cooled with water/steam in a closed loop with secondary heat exchangers. Fuel processing is similar to that in a PEFC system, but a preferential oxidizer is not needed. These systems are intended for on-site power and heat generation for hospitals, hotels, and small businesses. 

Pfiefer et al. are developing a methanol fuel processor system using steam reforming for a 200 Wg fuel cell based power supply. The researchers are currently working on the methanol reformer reactors, heat exchangers, combustors, and preferential oxidation reactors (Figure 23) for the system. The reactor bodies are either stainless steel or copper. 

To estimate the relative reactivity of allylic, benzylic, and nonconjugative aliphatic alcohols toward the Ar3BiCl2/DBU system, intermolecular competitive oxidations were examined. As summarized in Scheme 20, cinnamyl and benzylic alcohols were preferentially oxidized in the presence of ethyl alcohol. The chemos-electivities observed for the Ar3BiCl2/DBU oxidant (Ar = o-tolyl) are considerably higher than those achieved by Dess-Martin periodinane [83, 84]. 

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. 

Schuessler et al. [85] of XCELLSiS (later BALLARD) presented an integrated methanol fuel processor system based on autothermal reforming, which coupled fuel/water evaporation with exothermic preferential oxidation (PrOx) of carbon monoxide. The reactor technology was based, in contrast to most other approaches, on a sintering technique. 

Wash coats made of various source aluminas were prepared by applying this procedure (Figure 2.96) [147]. The catalysts obtained after subsequent impregnation were applied to methanol steam reforming [25, 28], propane steam reforming [52], water-gas shift [84] and preferential oxidation [89], to name but a few reaction systems. 

R 20] The fuel processing system consists of a fuel evaporator, a reformer, a reactor for the preferential oxidation of carbon monoxide and a catalytic burner (Figure 4.48) [95],... 

This system includes several mixing and heat exchange units. A concept for an integrated, microtechnology-based fuel processor was proposed by PNNF [8]. As examples for unit operations which may be included in future integrated systems the same publication mentions reactors for steam reforming and/or partial oxidation, water-gas shift reactors and preferential oxidation reactors for carbon monoxide conversions, heat exchangers, membranes or other separation components. 

This trend is markedly different from that observed over almost all the catalytic oxidation systems reported so far, both based on a metal and on a radical precursor, which always preferentially convert benzylic alcohols with respect to the others, suggesting that a different mechanism is operating in the present case. 

Although a suitable acceptor for the transfer dehydrogenation of benzylic alcohols has not yet been found, under the present conditions the low conversion of benzylic alcohols is only an apparent drawback. Indeed, it has a positive side as it allows us to fine-tune the system s selectivity. This makes the catalytic system unique among all the others known, operating both under aerobic and anaerobic conditions, that preferentially oxidize benzylic alcohols with respect to nonacti-vated secondary ones. 

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