Production of Sulfur Trioxide

Though the multistage converters in the plant are generally able to convert more than 99.5% SO2 to SO3, it is practically difficult to condense it as such due to the low 

A controlled stream of the oleum is then heated (boiled) to release the vapors which contain almost 100% SO3 with only traces of SO2. The vapors are then condensed to obtain liquid SO3 or are absorbed in oleum to produce 60-65% oleum. 

For SO3 condensers, the falling film type condenser (SO3 vapors on the shell side and a trickling stream of water on the inside of tubes) is generally found to be safer as compared to a shell and tube type unit wherein water is circulated under pressure. 

However, the latter has a higher heat transfer coefficient due to greater water velocities and needs a lower area for heat transfer. It should be fitted with a pressure release valve with a vent line connected to a scrubber. 

Depleted oleum having a strength of about 20-22% is returned to the oleum tower to increase its strength again by absorption of SO3. 

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ILLUSTRATION 12.8 PRODUCTION OF SULFUR TRIOXIDE IN AN ADIABATIC FIXED BED REACTOR... 

ILLUSTRATION 12.9 PRODUCTION OF SULFUR TRIOXIDE IN A FIXED BED REACTOR WITH THERMAL LOSSES... 

For SO2, pure sulfides have to be reacted with an oxidizing agent, like CuO, CU2O, V2O5 or O2. It is important to minimize the production of sulfur trioxide since there is an isotope fractionation between SO2 and SO3. Special chemical treatment is necessary if pyrite is to be analyzed separately from other sulfides. 

This equation describes only the overall stoichiometry of the process many different oxidants actually participate in the oxidation of sulfur dioxide (see Chapter 15 for a further discussion). The production of sulfur trioxide is significant because it can combine with droplets of water in the air to form sulfuric acid ... 

The contact process for the production of sulfur trioxide in the manufacture of sulfuric acid (Section 24-11). 

The production of sulfur trIoxIde Is significant because it can combine with droplets of water in the air to form sulfuric acid ... 

Jiang, S.H.-K. Addition reactions of sulfur trioxide to carbon-carbon double bonds. I. Addition products of sulfur trioxide and some perfluoro oleflns. Huaxue Xuehao 1957,23, 330-339. 

ILLUSTRATION 12.8 Production of Sulfur Trioxide in an Adiabatic Fixed Bed Reactor... 

ILLUSTRATION 12.9 Production of Sulfur Trioxide in a Fixed Bed Reactor with Thermal Losses... 

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 ... 

IS reversible but can be driven to completion by several techniques Removing the water formed m the reaction for example allows benzene sulfonic acid to be obtained m vir tually quantitative yield When a solution of sulfur trioxide m sulfuric acid is used as the sulfonatmg agent the rate of sulfonation is much faster and the equilibrium is dis placed entirely to the side of products according to the equation... 

Benzene. The reaction of sulfur trioxide and ben2ene in an inert solvent is very fast at low temperatures. Yields of 90% ben2enesulfonic acid can be expected. Increased yields of about 95% can be reali2ed when the solvent is sulfur dioxide. In contrast, the use of concentrated sulfuric acid causes the sulfonation reaction to reach reflux equiUbrium after almost 30 hours at only an 80% yield. The by-product is water, which dilutes the sulfuric acid estabhshing an equiUbrium. 

Pan and cascade burners are generally more limited ia flexibiHty and are useful only where low sulfur dioxide concentrations are desired. Gases from sulfur burners also contain small amounts of sulfur trioxide, hence the moisture content of the air used can be important ia achieving a corrosion-free operation. Continuous operation at temperatures above the condensation poiat of the product gases is advisable where exposure to steel (qv) surfaces is iavolved. Pressure atomiziag-spray burners, which are particularly suitable when high capacities are needed, are offered by the designers of sulfuric acid plants. 

A basic research study on combustion of sulfur led to the postulation that sulfur trioxide may actually be the primary combustion product and that sulfur dioxide may then be produced by the further reaction of sulfur trioxide with sulfur vapor ki the oxygen-deficient region of the flame (261). 

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. 

Sulfur (qv) is among the most widely used chemicals and often considered to be one of the four basic raw materials of the chemical iadustry. In 1993, worldwide production of sulfur reached 55 million metric tons (1). Production of sulfuric acid consumes the vast majority (- 90%) of sulfur (2) (see Sulfuric acid and sulfur trioxide). This acid is a steppiag stone ia the production of other sulfur-containing compounds, most notably ammonium sulfate fertilizer which accounts for 60% of the total worldwide sulfur consumption (2) (see Ammonium compounds Fertilizers). 

Other chlorinated solvents such as tetrachloroethylene or chloroform may be used in place of carbon tetrachloride. Caution The reaction of sulfur trioxide with chlorinated solvents has been reported to give phosgene and other toxic products. Adequate venting of all by-product gases is essential. 

The use of dimethyl sulfoxide-acetic anhydride as a reagent for the oxidation of unhindered steroidal alcohols does not appear to be as promising due to extensive formation of by-products. However, the reagent is sufficiently reactive to oxidize the hindered 11 j -hydroxyl group to the 11-ketone in moderate yield. The use of sulfur trioxide-pyridine complex in dimethyl sulfoxide has also been reported. The results parallel those using DCC-DMSO but reaction times are much shorter and the work-up is more facile since the separation of dicyclohexylurea is not necessary. Allylic alcohols can be oxidized by this procedure without significant side reactions. 

Perfluoro-y-butyrolactone can be prepared from 1,4 diiodoperfluorobutane by reaction with turning sulfuric acid (oleum) [7S] (equation 19) The yield depends on the concentration of sulfur trioxide One of the by-products, 4-iodoperfluo-robutyryl fluoride, can be recycled to increase the overall yield of the lactone Pure sulfur trioxide generates only perfluorotetrahydrofuran, the lodo acyl fluoride, and perfluorosuccmyl fluoride... 

Another improvement (less by-products) has been made over the fuming sulfuric acid process operated commercially for the hydrolysis of 2-perfluoroal-kylethyl iodides. It entails the use of sulfur trioxide in liquid sulfur dioxide [52, 5J (equation 52). 

The advance of sulfur trioxide as sulfating agent largely depended on advances in sulfonation/sulfation reactor development and changes in raw material quality. Undiluted sulfur trioxide cannot be used as a sulfating agent except in special cases where suitable equipment is used because of its violent nature. Sulfur trioxide diluted in an inert gas, usually air, when used in batch processes can cause excessive dehydration and dark-colored products. However, batch processes were used years ago and inert liquid solvents were often suggested or used to moderate the reaction. Inadequate reaction conditions lead to a finished product that can contain dialkyl sulfate, dialkyl ether, isomeric alcohols, and olefins whereas inadequate neutralization conditions can increase the content of the parent alcohol due to hydrolysis of the unstable acid sulfate accompanied by an increase of mineral sulfate. 

Industrial scale production of sulfuric acid is dependent on the oxidation of sulfur dioxide to sulfur trioxide in fixed bed catalytic reactors. 

The acid is prepared by sulfonation of nitrobenzene with oleum, and the reaction product consists essentially of a hot solution of the acid in sulfuric acid. A completed 270 1 batch exploded violently after hot storage at 150C for several hours. An exotherm develops at 145°C, and the acid is known to decompose at 200 C [ 1], A similar incident arose from water leaking from a cooling coil into the fuming sulfuric acid reaction medium, which caused an exotherm to over 150°C and subsequent violent decomposition [2], Detailed examination of the thermal decomposition of the acid shows that it is much slower for the isolated acid than for the reaction mass, and that the concentration of sulfur trioxide in the oleum used for sulfonation bears... 

The only other X=Y bond involved in additions to MCP derivatives is the S=0 double bond of sulfur trioxide. Actually, the reactions of MCP (1) and BCP (3) with S03 afford exclusively the y-sultones 608 and 609 (Scheme 85) [160], formal products of [3 + 2] additions of TMM species to S=0 double bond. However, by analogy with larger methylene- and cycloalkylidenecycloalkane derivatives which give stable P-sultones at low temperature, it is presumed that... 

When elemental sulfur or a sulfur-bearing compound is present in any combustion system, the predominant product is sulfur dioxide. The concentration of sulfur trioxide found in combustion systems is most interesting. Even under very lean conditions, the amount of sulfur trioxide formed is only a few percent of that of sulfur dioxide. Generally, however, the sulfur trioxide concentration is higher than its equilibrium value, as would be expected from the relation... 

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