Adsorption of hydrogen sulfide

Adsorption Processes. The processes based on adsorption of hydrogen sulfide onto a fixed bed of soHd material are among the oldest types of gas treating appHcations (4). Two common sorbent materials for low concentration gas streams are iron oxide and zinc oxide. 

Figure 7.5 Adsorption of hydrogen sulfide on typical molecular sieve material.

The adsorption of hydrogen sulfide at 25° reached H2S/Cr3+= 0.12 before any hydrogen sulfide was detected beyond a sample of chromia that had been activated to 130°. None was desorbed in heating the chromia to 400°. 

An interesting effect of autocatalysis by deposited sulfur was identified by Steijns and coworkers [27, 28]. Studying adsorption of hydrogen sulfide on various adsorbents, they found that deposition of sulfur at the beginning of the removal process increases the catalytic activity of the carbon. Then, when sulfur starts to block microporosity, a rapid decrease in activity follows. It was postulated that elemental sulfur is rather in the form of radical chains than Sg rings [28]. Steijns and Mars found that the catalytic activity per square meter of total surface area is approximately proportional to the amount of adsorbed sulfur. On the other hand, no evidence of sulfur autocatalysis was found by Ghosh and ToUefson [20, 21]. 

Adsorption of Hydrogen Sulfide. IR studies of hydrogen sulfide adsorption on alumina suggest that (18, 19) hydrogen bonding produces the following structure ... 

Irreversible adsorption of hydrogen sulfide has been reported (2, 20). It is proposed that hydrogen sulfide adsorption could also take place via O2- sites ... 

The effect of the polarizing power of the cation on the Claus activity (Figure 5) could result from the fact that the basic sites (O2-) associated with Li+ are more effective in dissociative adsorption of hydrogen sulfide than those associated with Na+ or K+. 

Adsorption of hydrogen sulfide from moist digester Gas (CH4 = 60% CO2 = 40%) containing either 5,000, 2,000 or 1,000 ppm of H2S was studied at 311 and 333K in the presence of 1 or 2 percent of oxygen on three different activated carbons of proprietary suriace chemistries [125], Analysis of the perfonnance of carbons indicates that the capaci of all adsorbents is enhanced when the H2S concentration decreases. Tire effect of the temperature does not reveal the common trend due to the various mechanisms of oxidation depending on the chemistry of the surfaces [60]. All adsorbents were basic, which is favorable for H2S adsorption as described in section... 

Feng, W. et al., Adsorption of hydrogen sulfide onto activated carbon fibers effect of pore structure and surface chemistry. Environ. Sci. Technol. 2005,39(24), 9744-9749. 

Sirkecioglu, A. Altav, Y., and Erdem-Senatalar, A., Adsorption of hydrogen sulfide and sulfur dioxide on bigadic clinoptilolite, Sep. Sci. Technol., 30(13), 2747-2762 (1995). 

The dissociative adsorption of hydrogen sulfide has been shown to occur in the gas phase according to the above reactions at elevated temperatures [49]. Although the conductivity of the solid electrolyte membrane can increase due to oxidation of the adsorbed SH and H2S (i.e., reaction (5.16)), the formation of a stable platinum sulfide film can lead to fuel cell failure [38]. 

The severity of the PEM degradation depends on the amount of adsorption of hydrogen sulfide on the MEA. A recent study reported the potentially important finding that the introduction of a small quantity of Ru (ruthenium) or WO3 into the carbon support can inhibit Pt-S formation and improve the tolerance of the MEA to H2S [52][94]. 

Possible reactions of hydrogen sulfide with nickel can have different natures formation of bulk nickel sulfides via chemical reactions, reaction (5.7) surface sulfuration either via physical adsorptions of hydrogen sulfide molecules, reaction (5.8), or via chanisorptions of sulfur atoms, reaction (5.9) [18]. 

Examples The roasting of ores, the chemical adsorption of hydrogen sulfide by metal oxides (forming sulfides), the conversion of a metal oxide with a volatile non-metal oxide into a salt (e.g., the chemical adsorption of sulfur dioxide and oxygen by calcium oxide), the reductive chlorination of ilmenite (iron titanate) whereby iron chloride and titanium oxide are formed. In some processes a second solid reactant is present (e.g., carbon) that also reacts with the gaseous reactant, forming another gaseous reactant (e.g., carbon monoxide). 

In feedstock purification - mainly desulfurization - the development was from adsorption of sulfur-compounds on active carbon to catalytic hydrogenation of sulfur-compounds followed by adsorption of hydrogen sulfide on hot zinc oxide. This concept has been of major importance for the development of processes based on reforming at severe conditions including reforming of naphtha. See also Sect. 6.3.1. 

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