Claus reaction sulfur production from

Among the most effective of the modifications to Claus operating procedure is accurate temperature control of the catalyst beds. Gamson and Elkins (27) in the early 1950 s showed that equilibrium sulfur conversion efficiencies in the catalytic redox reaction rise dramatically as operating temperatures are lowered toward the dewpoint of sulfur. While some highly efficient subdewpoint Claus type processes are now in use the bulk of sulfur production from H2S still requires that the converters be operated above the dewpoint. Careful control of converter bed temperature has, however, contributed to improved efficiencies. This has in large part resulted from better instrumentation of the Claus train and effective information feed back systems. 

Reverse-flow operation for Sulfur Production over Bauxite Catalysts by the Claus Reaction has been considered in Refs 9 and 31. The rate of H2S oxidation by SO2 on bauxite catalysts is very high even at ambient gas inlet temperature, but sulfur condensing at low temperatures blocks the active catalyst surface, and the reaction stops because of catalyst deactivation. In a reverse-flow reactor the periodic evaporation of condensed sulfur from the outlet parts of the catalyst bed occurs. Although it is difficult to remove all the sulfur condensed within the catalyst pellets at the bed edges, after a certain time a balance between the amount of sulfur condensed and evaporated is attained. Using a reverse-flow reactor instead of the two-bed stationary Claus process provides an equal or better degree of... 

Many of the metal oxide materials used for making ceramic membranes, particularly the porous type, have also been used or studied as catalysts or catalyst supports. Thus, they are naturally suitable to be the membrane as well as the catalyst. For example, alumina surface is known to contain acidic sites which can catalyze some reactions. Alumina is inherently catalytic to the Claus reaction and the dehydration reaction for amine production. Silica is used for nitration of benzene and production of carbon bisulfide from methanol and sulfur. These and other examples are highlighted in Table 9.6. 

The technology of Claus conversion of hydrogen sulfide to sulfur was developed in Germany in about 1880. However, it was not until 1940 that this process was commercially adopted in the U.S. By 1967, annual sulfur production in the U.S.A., from this process had already reached 4.8 million tonnes, and by 2000, it was double the U.S. Frasch production (Table 9.2). Two reactions are employed in Claus units. The first is a simple combustion of one-third of the hydrogen sulfide stream in air, carried out in a waste heat boiler to capture the heat evolved as steam (Eq. 9.18). 

If a process gas is supplied to the cathode with an H,S level of 2000 ppm, a CO, level of 1%, and an H,0 level of 12% (a saturated natural gas composition), it is assumed that 99% of the H,S is removed by reaction (5), and if the process and sweep gas flowrates are equal, then there exist an activity ratio of a oJa of 665 in the anolyte before significant (e.g. 1%) of the carbonate is oxidized. This assiunes equivalent electrode kinetics for the cathodic and anodic reactions. When compared to the activity ratio of Ocos a of 26.9, this shows the thermodynamic preference for the oxidation of to elemental sulfur by equation (8) when there is an absence of reductant at the anode. This mode of operation is preferable for commercial application, with direct production of elemental sulfur vapor, eliminating this need for a Claus reactor for sulfur production. The net effect, under these conditions, is continuous removal of H,S from the process gas accompanied by enrichment of the process gas with H, and direct generation of elemental sulfrur. ITie only reagent required is electric power at a potentially attractive rate, which will be shown. 

Hydrt en sulfide, H2S, is sometimes contained in natural gas with a fraction up to 25 % or is a byproduct of various petrochemical processes and is usually considered a waste gas. The widely used treatment of H2S according to the Claus process only allows for sulfur production plus it leaves waste in the form of SO and polluted water. Therefore H2S is projected to gain economic importance if decomposed in a waste-free process to hydrogen and sulfur. Achievable hydrogen from this resource is estimated to amount to 1 million tons per year [12]. The endothermal reaction... 

The Claus process, which involves the reaction of sulfur dioxide with hydrogen sulfide to produce sulfur in a furnace, is important in the production of sulfur from sour natural gas or by-product sulfur-containing gases (see Sulfurremoval and recovery). 

The production of COS in the front end reaction furnace presents special problems since sulfur in this form may be difficult to remove in the downstream catalytic beds under conditions that are optimal for the Claus redox reaction between H2S and SO COS (and CS2) were known to be generated from hydrocarbon impurities carried over in the acid gas feed thus the efficiency of the up-stream sweetening process became an important factor. The reaction of CO2, a common constituent of the acid gas feed, with H2S and/or sulfur under furnace temperature conditions has also been shown to be an important source of COS. 

The study of adsorptive reactors for the Claus process represents a departure from most previous studies in that the equilibrium position is already well on the product side, with a conversion of 93 % being achievable for isothermal operation of gas with 10 mol% H2S without additional measures [30]. The need to attain conversions in excess of 99.5 % to ensure that the residual sulfur emissions meet environmental specifications [31] nevertheless makes the reaction system an interesting candidate for adsorptive equilibrium displacement. 

The oxidation of ammonia to nitrous gases is a fast high-temperature reaction for the production of nitric acid (Ostwald process). The Claus process is an important petrochemical process for obtaining sulfur from H2S, which results from the desulfurization of petroleum and natural gas (hydrodesulfurization). One-third of the H2S is combusted to SO2, which reacts with the remaining H2S (see Table 8-1). 

Various reaction mechanisms have been proposed for the formation of carbonyl sulfide and carbon disulfide and for their subsequent hydrolysis to hydrogen sulfide and carbon dioxide (Paskall and Sames, 1992). The plant data available indicate that carbonyl sulfide is formed primarily from the reaction between elemental sulfur and carbon monoxide, which in turn are derived from hydrogen suUide and carbon oxides present during combustion of the feed gas in the Claus thermal stage. The production of carlxin disulfide in the thermal stage is usually attributed to the presence of hydrocarbons in the feed gas because carbon disulfide is produced commercially by reacting elemental sulfur with saturated hydrocarbons. The... 

Inspection of Table 8-4 shows that the Claus plant tail gas typically contains 30-35% water vapor. Although the selective oxidation reaction (8-1) is not reversible, its products (H2O and S) can react by the reverse of reaction 8-3 to reduce the net conversion to sulfur. Since the reverse reaction is favored by the presence of water vapor, reducing the water vapor concentration in the gas from 30 to 35% to 1.5 to 4% by cooling aids in obtaining a high conversion. About 80-90% of the H2S entering the Selectox reactor is converted to sulfur, the conversion being limited primarily by the increase in temperature due to the heat of reaction. 

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