Sulfur Trioxide and Oleum

Materials of Construction. Resistance of alloys to concentrated sulfuric acid corrosion iacreases with increasing chromium, molybdenum, copper, and siUcon content. The corrosiveness of sulfuric acid solutions is highly dependent on concentration, temperature, acid velocity, and acid impurities. An excellent summary is available (114). Good general discussions of materials of constmction used ia modem sulfuric acid plants may be found ia References 115 and 116. More detailed discussions are also available (117—121). For nickel-containing alloys Reference 122 is appropriate. An excellent compilation of the relatively scarce Hterature data on corrosion of alloys ia Hquid sulfur trioxide and oleum may be found ia Reference 122. 

Sulfur trioxide and oleums of all strengths are important substances in the field of major hazards. Their main feature is the violent and exothermic reaction between SO3 and water that occurs in both the liquid and vapor phase. 

Du Pont Chemicals. 1988. Sulfur Trioxide and Oleum Storage and Handling. 

Grint, G., and G. Purdy. 1990. Sulfur Trioxide and Oleum Hazard Assessment, Journal cf Loss Prevention in the Process Industries, vol. 3, pp. 177—184. 

Kapias, T. 1999. Modelling Accidenttil Releases of Sulfur Trioxide and Oleum, PhD thesis, UMIST, Manchester, U.K... 

Sulfation and Sulfonation. a-Olefin reactions involving the introduction of sulfur-containing functional groups have commercial importance. As with many derivatives of olefins, several of these products have appHcations in the area of surfactants (qv) and detergents. Typical sulfur reagents utilized in these processes include sulfuric acid, oleum, chlorosulfonic acid, sulfur trioxide, and sodium bisulfite. 

Detergent All late. In the 1940s, sodium dodecylben2ene sulfonate [25155-30-0] (DDES) produced by the alkylation of ben2ene with propylene tetramer followed by sulfonation with oleum [8014-95-7] (H2SO4 mixture with sulfur trioxide) or sulfur trioxide and then neutrali2ation... 

Gas leaving the economizer flows to a packed tower where SO is absorbed. Most plants do not produce oleum and need only one tower. Concentrated sulfuric acid circulates in the tower and cools the gas to about the acid inlet temperature. The typical acid inlet temperature for 98.5% sulfuric acid absorption towers is 70—80°C. The 98.5% sulfuric acid exits the absorption tower at 100—125°C, depending on acid circulation rate. Acid temperature rise within the tower comes from the heat of hydration of sulfur trioxide and sensible heat of the process gas. The hot product acid leaving the tower is cooled in heat exchangers before being recirculated or pumped into storage tanks. 

Modem plants manufacture chlorosulfuric acid by direct union of equimolar quantities of sulfur trioxide and dry hydrogen chloride gas. The reaction takes place spontaneously with evolution of a large quantity of heat. Heat removal is necessary to maintain the temperature at 50—80°C and thus minimize unwanted side reactions. The sulfur trioxide may be in the form of 100% Hquid or gas, as obtained from boiling oleum, ie, fuming sulfuric acid, or may be present as a dilute gaseous mixture as obtained direcdy from a contact sulfuric acid plant (24). The hydrogen chloride gas can be in the form of 100% gas or in a diluted form. 

Solutions of sulfur trioxide in cone, sulfuric acid (oleum) are available with various proportions of dissolved sulfur trioxide, and the 3 entries in Handling Chemicals Safely 1980 deal with the properties and hazards of solutions with 65, 30 and 20% of sulfur trioxide, respectively. As expected, the reactivity and oxidising power increase with the content of sulfur trioxide. 

The use of aqueous foams to control fume or vapour release from reactive chemicals is discussed. An acid-resistant foam NF2 controlled fume emission from 35% and 65% oleum, and from titanium tetrachloride, but was not effective for sulfur trioxide and chlorosulfuric acid. An alcohol-resistant foam NF1 suppressed ammonia vapour emission by 80%, and Universal fire foam reduced evaporation of ethylene oxide, vinyl chloride and methanethiol, and reduced vapour emission of 1,3-butadiene by 60%. Safety aspects of foam blanketing are discussed [1]. Equipment and application techniques are covered in some detail [2],... 

Equipment needed for the above procedures is not always available in the standard laboratory. A useful and widely used method for preparing solutions of dinitrogen pentoxide in nitric acid involves the distillation of mixtures of oleum and potassium nitrate in absolute nitric acid. Another method uses a solution of sulfur trioxide and ammonium nitrate in nitric acid. Although the original report states that solutions of 28 2 % dinitrogen pentoxide in nitric acid can be prepared via this method, a later report suggests that concentrations higher than 30 % are not attainable. 

In the von Pechmann synthesis, originally used to prepare pyran-2-one-5-carboxylic acid (coumalic acid), 2-hydroxybutane-l,4-dioic acid is converted into 3-oxopropanoic acid by treatment with oleum (sulfur trioxide and cone, sulfuric acid), and this product then self-condenses in the acidic medium to give pyran-2-one-5-carboxylic acid (Scheme 4,8a). Pyran-2-one is obtained by decarboxylating coumalic acid by heating it over copper at 650 °C. 

Forty milliliters of 60% oleum are placed in a non-vitre-ous vessel and cooled to about —10°C in an ice-salt bath. Twenty grams of finely powdered and carefully dried potassium add fiuoride are added in small portions with stirring. A viscous mass is obtained which fumes slightly in air heating slowly to 100°C (hood) drives off the excess sulfur trioxide and hydrogen fluoride. 

Concentrated or fuming sulfuric acid (oleum) is widely used for the direct sulfonation of aromatic compounds (see Chapter 7, p. 97).5,6 The active sulfonating agent in sulfuric acid is the electrophile sulfur trioxide, and the sulfonating power of sulfuric acid is proportional to the concentration of S03. Consequently, fuming sulfuric acid, which contains excess sulfur trioxide, is a more powerful sulfonating agent than concentrated sulfuric acid. The sulfonation of an aromatic hydrocarbon is depicted in Scheme 26. 

Regeneration of high concentrations of sulfuric acid may also be achieved by addition of oleum or sulfur trioxide to diluted acid. The inventory of acid in circulation is increased by a corresponding amount (Eq. 9.26). A third method of reconcentration, useful when the acid consumption occurs as a part of, or adjacent to a contact sulfuric acid plant, is to pass the diluted acid itself through the acid plant absorption tower. This amounts to on-site addition of sulfur trioxide, and the increased acid inventory obtained can be sold to markets through the normal producer channels. 

The synthetic detergents industry originated in the 1940s, when it was found that a new anionic surfactant type—alkylbenzene sulfonate—had detergent characteristics superior to those of natural soaps. The first surfactant of this kind was sodium dodecylbenzene sulfonate (SDBS). This material was produced by the Friedel-Crafts alkylation reaction of benzene with propylene tetramer (a mixture of Co olefin isomers), followed by sulfonation with oleum or sulfur trioxide and then neutralization, usually with sodium hydroxide. The alkylation was typically performed using homogenous acid catalysts, such as HF or sulfuric acid. 

Sulfuric Acid.42 Sulfuric acid is prepared on an enormous scale by the lead chamber and contact processes.43 In the former, S02 oxidation is catalyzed by oxides of nitrogen (by intermediate formation of nitrosylsulfuric acid, HOS02ONO) in the latter, heterogeneous catalysts such as platinum are used for the oxidation. Pure sulfuric acid, H2S04, is a colorless liquid which is obtained from the commercial 98% acid by addition first of sulfur trioxide or oleum and then titration with water until the correct specific conductance or melting point is achieved. 

Sulfuric acid and oleum are often used in excess, thereby advantageously functioning as cheap, low-viscosity solvents for the product sulfonic acids which are often quite viscous in pure form. They are always used in liquid form, while sulfur trioxide, on the other hand, is usually employed as a vapor since it is easily vaporized (bp, 44.8°C) and the vapor form is considerably milder than the liquid. Liquid sulfur dioxide is an excellent sulfonation solvent for use with sulfur trioxide and with oleums, and it has been used industrially. Halogenated organic solvents (tetrachloroethylene, carbon tetrachloride, trichlorofluoromethane, etc.) are miscible with sulfur trioxide in all proportions, but not with its hydrates. 

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