H2S contamination

Apart from the intercollisional dips (which are not accounted for in a binary theory) and the effects of the ortho-H2 contamination, the agreement between theory and measurement is generally better than 10%. 

Carbon-supported Pt can also be used as the anode catalyst. However, this requires pure H2. Contaminants such as carbon monoxide (CO) poison the catalyst, because CO can strongly adsorb on Pt, blocking the catalytic sites and reducing platinum s catalytic activity. In H2 produced from the reforming of other fuels, CO is always present. Thus, to improve contaminant tolerance, carbon-supported PtRu was developed and now is always used as the anode catalyst. Ru can facilitate the oxidation of CO, releasing the catalytic sites on Pt through the following reactions ... 

With respect to H2S contamination, it has been recognized for many years that the major impact is upon the fuel cell electrode kinetics [40], When H2S is added to humidified H2, EIS can be used to study the H2S contamination. Information gathered includes the effects of the H2S concentration, the exposure time, and the reversibility of the contamination. H2S can strongly adsorb on a Pt catalyst surface, blocking the active sites and then causing irreversible contamination. 

Ecell is positive, and the spontaneous direction for the cell reaction is left to right therefore, iron will corrode. Note that the driving potential for corrosion (Ecell) in the H2S contaminated water is about twice that in the uncontaminated water (a comparison can be made with Example 5). 

The corrosion rate of the widely employed N-80 steel in the H2S contaminated mud is very rapid it can reach 2.5 nun/year (100 mpy). The rate is dependent on the hydrogen sulfide concentration, pH of the medium, and the temperature condition of the environment. 

Another kind of membrane material is represented by a group of nanoporous, hydrogen-selective carbon molecular sieve membranes, which exhibit excellent permeation characteristics and hydrogen permeabilities competitive with metallic membranes (Harale et al., 2007). Furthermore, they are unaffected by CO or hydrogen sulfide (H2S) contamination. Nevertheless, their hydrothermal stability is not guaranteed at r > 623 K. 

Garzon et al. (2006) investigated the effect of sulfur (in the form of H2S) contaminant in the anode fuel stream in fuel cell performance. 1 ppm H2S was supplied to the anode and severe performance losses were reported after 4 h of operation as the exposure time increased, cell performance deteriorated and after 21 h of anode exposure to H2S, the fuel cell was disabled ( 0.2 A cm at the end of the test compared to 1.1A cm at 0.6 V vs RHE under normal cell operation). 

The impact of CO on the PEMFC anode performance has been widely studied experimentally and by modelling, and maity mitigation methods have been proposed. In recent years, the impacts of H2S and NHj have become an important subject of research. It is well accepted that the major impact of CO and H2S contaminants on the hydrogen-fed PEMFC anode is a kinetic effect due to poisoning of the electrocatalyst, while NHj mainly affects the ionomeric membrane by reducing ionomer conductivity.In both cases, significant performance degradation can be induced. In order to enhance CO tolerance, bimetallic catalysts such as Pt-Ru, Pt-Mo and Pt-Sn have been proposed however, the... 

The dilute sulfur slurry leaving the absorber is piped to the top of the oxidizer-settler. This vessel is operated at atmospheric pressure and is almost full of liquid. Details of this vessel are shown in Figure 9-38. The downward flow of slurry is regenerated by exposure to air bubbles rising from an air sparger. The moisture laden, partly spent air vents directly to the atmosphere. This effluent air is virtually free of any H2S contamination. 

Some disadvantages of the fluidized beds are the complexity in operability, difficult separation of the fine catalyst particles from the exhaust gas (imposing significant capital costs for cyclones and oil scrubbers) and erosion problem due to the high linear velocities (Dry, 1996). Moreover, H2S contamination of the synthesis gas feed means complete deactivation. 

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