Sulfur dioxide production

Conversion Processes. A number of options exist for handling concentrated sulfur dioxide streams. One option is the sale of a Hquid sulfur dioxide product. Alternatively, the sulfur dioxide can be converted to elemental sulfur or to sulfuric acid. 

Snyder, J. D., and Subramaniam, B., Numerical simulation of a periodic flow reversal reactor for sulfur dioxide production. Chem. Eng. Sci. 48, 4051-4064 (1993). 

The basic steps in the contact process are (1) production of sulfur dioxide (2) cooling and, for smelters, cleaning of the process gas (3) conversion of the sulfur dioxide to sulfur trioxide (4) cooling of the sulfur trioxide gas and (5) absorption of the sulfur trioxide in sulfuric acid.28 Figure 25.8 is a photograph of a contact process plant. A simplified diagram of a double absorption contact sulfuric acid process is shown in Fig. 25.9. Because sulfur dioxide is produced by several processes, it is convenient to separate the discussion of sulfur dioxide production from its conversion to sulfuric acid. 

The Flakt-Boliden version of the citrate process uses thermal regeneration of the citrate absorbing solution to obtain stripped citrate solution and a stream of up to 90% sulfur dioxide. Recovery of a sulfur dioxide product gives flexibility to the final stage of processing as to whether liquid sulfur dioxide, sulfuric acid, or sulfur are obtained as the final product. This process has recently been reexamined [42]. 

Sulfur Dioxide Production at 25°0 (98.2% H2S04, 1 x 10-5 moles/litre of solute)... 

The only olefin-sulfur dioxide product sold commercially is sulfolene by Phillips Petroleum Co. The linear polymers remain to be commercially produced. It is interesting to note that a polysulfone, i.e., poly(phenylene sulfone), has been sold commercially since 1966 [8]. 

Coal is the most familiar of the fossil fuels not necessarily because of its use throughout the preceding centuries (Galloway, 1882) but more because of its common use during the nineteenth century. Coal was largely responsible not only for the onset but also for the continuation of the industrial revolution. Coal occurs in various forms defined in a variety by rank or type (Chapter 2) and is not only a solid hydrocarbonaceous material with the potential to produce considerable quantities of carbon dioxide as a result of combustion, but many coals also contain considerable quantities of sulfur (Table 22.1). Sulfur content varies (Table 22.2) but, nevertheless, opens up not only the possibility but also the reality of sulfur dioxide production (Manowitz and Lipfert, 1990 Tomas-Alonso, 2005). 

About 25% of sulfur dioxide production is used to make sodium hydrosulfite. 

Product removal during reaction. Sometimes the equilibrium conversion can be increased by removing the product (or one of the products) continuously from the reactor as the reaction progresses, e.g., by allowing it to vaporize from a liquid-phase reactor. Another way is to carry out the reaction in stages with intermediate separation of the products. As an example of intermediate separation, consider the production of sulfuric acid as illustrated in Fig. 2.4. Sulfur dioxide is oxidized to sulfur trioxide ... 

Example 4.4 Butadiene sulfone (or 3-sulfolene) is an intermediate used for the production of solvents. It can be produced from butadiene and sulfur dioxide according to the reaction ... 

This is an exothermic, reversible, homogeneous reaction taking place in a single liquid phase. The liquid butadiene feed contains 0.5 percent normal butane as an impurity. The sulfur dioxide is essentially pure. The mole ratio of sulfur dioxide to butadiene must be kept above 1 to prevent unwanted polymerization reactions. A value of 1.2 is assumed. The temperature in the process must be kept above 65°C to prevent crystallization of the butadiene sulfone but below lOO C to prevent its decomposition. The product must contain less than 0.5 wt% butadiene and less thM 0.3 wt% sulfur dioxide. 

This procedure may result in a concentration of cumene hydroperoxide of 9—12% in the first reactor, 15—20% in the second, 24—29% in the third, and 32—39% in the fourth. Yields of cumene hydroperoxide may be in the range of 90—95% (18). The total residence time in each reactor is likely to be in the range of 3—6 h. The product is then concentrated by evaporation to 75—85% cumene hydroperoxide. The hydroperoxide is cleaved under acid conditions with agitation in a vessel at 60—100°C. A large number of nonoxidising inorganic acids are usehil for this reaction, eg, sulfur dioxide (19). 

The furnace is constmcted with a steel shell lined with high temperature refractory (see Refractories). Refractory type and thickness are deterrnined by the particular need. Where combustion products include corrosive gases such as sulfur dioxide or hydrogen chloride, furnace shell temperatures are maintained above about 150—180°C to prevent condensation and corrosion on the inside carbon steel surfaces. Where corrosive gases are not present, insulation is sized to maintain a shell temperature below 60°C to protect personnel. 

Plant investment and maintenance costs are relatively high for a new iodine plant in the United States or in Japan because of the deep weUs required for brine production and disposal as weU as the corrosive nature of the plant streams. The principal materials cost is for chlorine and for sulfur dioxide, although in the United States the additives used for the brines, such as scale inhibitors and bactericides, also have a considerable influence on costs. 

Minerals. Iron-bearing minerals are numerous and are present in most soils and rocks. However only a few minerals are important sources of iron and thus called ores. Table 2 shows the principle iron-bearing minerals. Hematite is the most plentiful iron mineral mined, followed by magnetite, goethite, siderite, ilmenite, and pyrite. Siderite is unimportant in the United States, but is an important source of iron in Europe. Tlmenite is normally mined for titania with iron as a by-product. Pyrite is roasted to recover sulfur in the form of sulfur dioxide, leaving iron oxide as a by-product. 

Nickel sulfate also is made by the reaction of black nickel oxide and hot dilute sulfuric acid, or of dilute sulfuric acid and nickel carbonate. The reaction of nickel oxide and sulfuric acid has been studied and a reaction induction temperature of 49°C deterrnined (39). High purity nickel sulfate is made from the reaction of nickel carbonyl, sulfur dioxide, and oxygen in the gas phase at 100°C (40). Another method for the continuous manufacture of nickel sulfate is the gas-phase reaction of nickel carbonyl and nitric acid, recovering the soHd product in sulfuric acid, and continuously removing the soHd nickel sulfate from the acid mixture (41). In this last method, nickel carbonyl and sulfuric acid are fed into a closed-loop reactor. Nickel sulfate and carbon monoxide are produced the CO is thus recycled to form nickel carbonyl. 

PPS dust should be treated as a nuisance particulate. The OSHA permissible exposure limit for respirable dust is 5 mg/m for dust containing no asbestos and less than 1% siUca. The principal decomposition products released during mol ding of PPS and their permissible exposure limits are given in Table 10. Sulfur dioxide and carbonyl sulfide are the most significant off-gases for production of mucous membrane irritation. 

One method for using sodium alumiaate to desulfurize flue gas containing sulfur dioxide is described (45). This procedure led to a process where aluminum sulfate [10043-01-3] could be generated as a by-product of flue gas desulfurization (46). 

Emissions control systems play an important role at most coal-fired power plants. For example, PC-fired plants sited in the United States require some type of sulfur dioxide control system to meet the regulations set forth in the Clean Air Act Amendments of 1990, unless the boiler bums low sulfur coal or benefits from offsets from other highly controlled boilers within a given utiUty system. Flue-gas desulfurization (FGD) is most commonly accomphshed by the appHcation of either dry- or wet-limestone systems. Wet FGD systems, also referred to as wet scmbbers, are the most effective solution for large faciUties. Modem scmbbers can typically produce a saleable waUboard-quaUty gypsum as a by-product of the SO2 control process (see SULFURREMOVAL AND RECOVERY). 

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