Elemental sulfur H2SO4 production

Elemental sulfur is mined along the U.S. Gulf Coast by the Frasch process (Figure 24-2). Most of it is used in the production of sulfuric acid, H2SO4, the most important of all industrial chemicals. Sulfur is used in the vulcanization of rubber and in the synthesis of many important sulfur-containing organic compounds. 

Most elemental sulfur is converted to sulfuric acid (H2SO4), a key chemical in the production of a wide variety of products, such as fertilizers, automobile batteries, detergents, pigments, fibers, and synthetic rubber, as shown here. 

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]... 

The SO2 gas produced by many regenerable processes can be converted in an auxiliary plant into any of several byproducts, including liquid SO2, H2SO4, and elemental sulfur. The marketability of these products depends on local demand and economic factors. Transporta-... 

Sulfur is a rather exceptional element for several aspects. It can assume various oxidation states [1] and in these oxidation states it exists in a great number of different chemical forms. Sulfur is a constituent of a large number of industrial products (H2SO4, rubber vulcanization, for instance) and is also at the origin of a major pollutant (SO2) [2]. Sulfur can exist in more than ten allotropic forms at room temperature, that is, in a variety not found with any other element [3-5]. Orthorhombic sulfur is the most stable form at room temperature. It contains crown-shaped Sg molecules, which are stacked in a complex array. It can also be mentioned that the liquid and gaseous phases of sulfur are very complex [6, 7]. Undoubtedly, the existence of catenated species is a general feature of sulfur chemistry and is the basic reason for its complexity. 

The deeply colored solutions of sulfur in oleum have been known for a long time (39), but it was not until the identification of the sulfur cations Sg , and that the nature of these solutions became clear (66). In 95-100% H2SO4 sulfur forms a colloidal solution but after 12 hr at 75° the element dissolves as Sg molecules. In 5% oleum, oxidation is observed and Sig + is formed. In 10% and 157 oleum, sulfur is oxidized first rather rapidly to a mixture of S g and Sg " and then very slowly to SOg. In 30% oleum, Sjg and Sg produced initially are further oxidized to 84 + and finally to SOg. In more concentrated oleums (45 and 65%), Sg " and 84 are the initial products, and as 84 " appears to be rather stable in these solvents further oxidation to 8O2 is very slow. Changes in concentration of the various species with time and with 8O3 concentration are complicated by disproportionation reactions. Thus, 8g disproportionates to 8O2 and 8ig in oleum containing less than 15% 80g, and 84 + disproportionates to 8g + and SO2 in oleum conteining less than 407, SO3. 

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