H2S breakthrough capacity

Rgure 21.1 Dependence of normalized H2S breakthrough capacity (per unit pore volume of carbon) on the surface pH (as described by Bandosz and coworkers [43, 48]). 

Table 21.1 summarizes the H2S breakthrough capacity results obtained on few commercial activated carbons. The results are done using the same tests (ASTM D6646-01) so the comparison is meaningful. 

H2S breakthrough capacities at various concentrations of H2S in the challenge gas (2% oxygen 312 K) [125], Reprinted with pennission from A. Bagreev, S. Katikaneni, S. Parab, T.J. Bandosz. 

The model equations were solved using a numerical method witli known parameters (qs and k) of H2S adsorption corrected for hydrodynamics conditions. The parameters for VOC adsorption and L-V model parameters for H2O adsorption where found by fitting the experimental and calculated data. The results of these fittings are present on Fig. 28, where numbers in the plot legends represent the port location. The initial concentration of H2S was 0.15 ppm. Comparison of the H2S breakthrough capacities received finm the Lab test and the Plant... 

Yazdanbakhsh et al. [158] reported the H2S breakthrough capacity of copper-exchanged Engelhard Titanosilicate-2 (ETS-2). The adsorbent efficiency remains unchanged up to 950 °C. Below 750 °C, the adsorption capacity at breakthrough is 0.7 mol of H2S per mol of copper while >750 °C the capacity of the adsorbent is halved. The change in H2S capacity is due to Cu + reduction by the H2 which is formed through the thermal dissociation of H2S. 

A kinetics reaction order of about 0.5 with respect to O2 was found in several studies when H2S was in excess, and of zero order for H2S/O2 < 1 [130,131]. The reaction is first order with respect to H2S. The reaction can be performed at temperatures as low as ambient. The presence of water vapor enhances the breakthrough capacity [132]. At first, only elemental sulfur was found as a reaction product, but later, with some carbons, SO2 and H2SO4 were also observed [130,133]. The formation of H2SO4 requires the presence of water vapor usually, a relative humidity of 80% is used. The selectivity to sulfur oxides increases with increasing reaction temperature. However, H2SO4 is obtained exclusively with some carbons, even at room temperature (e.g., with activated carbon fibers [134]... 

ZnO has been widely used for more than 30 years as an H2S removal agent from natural gas.176 The achieved dynamic capacity was 22-24 wt% (370 °C, 400 h 1), with a maximum possible sulfur loading of 33 wt%, which corresponds to the complete conversion of ZnO to ZnS. If the concentration of sulfur in the feed gas is very small, then on-site regeneration is not necessary for some applications. For such cases, upon breakthrough, the absorbent bed is replaced with a fresh batch of ZnO and then sulfur removal continues. From this point of view, the use of ZnO as a... 

Gangwal eta . [25] investigated zinc ferrite and zinc ferrite/copper oxide adsorbents for the removal of H2S from coal gas for molten carbonate fuel cell (MCFC) appHcations at 540-800 °C. H2S concentrations are much higher, that is, 13 400 ppmv, and must be below 10 ppmv in the product gas. A typical breakthrough performance was achieved at 600 °C for 3 ppmv, leading to a capacity of 11.8 g of S per 100 g of sorbent Further investigations on improved adsorbents have been reported [26-28]. 

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