Sulfur trioxide equilibrium reaction

Sulfur dioxide, SOj, reacts with oxygen in the presence of a catalyst (vanadium(v) oxide) to form sulfur trioxide. This reaction is carried out in a sealed container of volume S.Odm by mixing 2.0mol of sulfur dioxide and 1.4 mol of oxygen and allowing equilibrium to be established. A conversion rate of 15% is achieved at 700 K. Calculate the equilibrium constant at this temperature for this reaction. 

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... 

In the first step an S03 molecule is inserted into the ester binding and a mixed anhydride of the sulfuric acid (I) is formed. The anhydride is in a very fast equilibrium with its cyclic enol form (II), whose double bonding is attacked by a second molecule of sulfur trioxide in a fast electrophilic addition (III and IV). In the second slower step, the a-sulfonated anhydride is rearranged into the ester sulfonate and releases one molecule of S03, which in turn sulfonates a new molecule of the fatty acid ester. The real sulfonation agent of the acid ester is not the sulfur trioxide but the initially formed sulfonated anhydride. In their detailed analysis of the different steps and intermediates of the sulfonation reaction, Schmid et al. showed that the mechanism presented by Smith and Stirton [31] is the correct one. 

One stage in the manufacture of sulfuric acid is the formation of sulfur trioxide by the reaction of S02 with 02 in the presence of a vanadium(V) oxide catalyst. Predict how the equilibrium composition for the sulfur trioxide synthesis will tend to change when the temperature is raised. 

This reaction can be forced to effective complete conversion by first carrying out the reaction to approach equilibrium. The sulfur trioxide is then separated (by absorption). Removal of sulfur trioxide shifts the equilibrium, and further reaction of the remaining sulfur dioxide and oxygen allows effective complete conversion of the sulfur dioxide, Figure 6.6. 

Sulfur trioxide gas dissociates into sulfur dioxide gas and oxygen gas at 1250°C. In an experiment, 3.60 moles of sulfur trioxide were placed into an evacuated 3.0-liter flask. The concentration of sulfur dioxide gas measured at equilibrium was found to be 0.20 M. What is the equilibrium constant, Kc, for the reaction ... 

The only stable 1,3,2-dioxathietanes known are fluorinated sulfate derivatives formed by addition of sulfur trioxide to bis(trifluoromethyl)ketene. These structures are fairly well characterized from spectral data and from reactions with nucleophiles. Hexafluoroisopropy-lidene-l,3,2-dioxathietane 2,2-dioxide acts as a sulfur trioxide transfer agent to alkenes and is in equilibrium with a dimeric form as indicated by 19F NMR (Scheme 138) (71KGS1645, 72KGS306, 73KGS178, 132l). 

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

A mixture consisting of 1.1 mmol S02 and 2.2 mmol 02 in a 250-mL container was heated to 500 K and allowed to reach equilibrium. Will more sulfur trioxide be formed if that equilibrium mixture is cooled to 25°C For the reaction 2 S02(g) +... 

PROBLEM 13.1 The oxidation of sulfur dioxide to give sulfur trioxide is an important step in the industrial process for synthesis of sulfuric acid. Write the equilibrium equation for each of the following reactions ... 

This reaction is reversible and so the ideas of Le Chatelier (Chapter 11, p. 178) can be used to increase the proportion of sulfur trioxide in the equilibrium mixture. The forward reaction is exothermic and so would be favoured by low temperatures. The temperature of 450 °C used is an optimum temperature which produces sufficient sulfur trioxide at an economical rate. Since the reaction from left to right is also accompanied by a decrease in the number... 

The successful operation of the contact process became possible only through a knowledge of chemical equilibrium and the factors that influence such equilibria. Since the reaction is exothermal, the temperature must be controlled carefully in order to avoid favoring the reverse reaction—that is, the decomposition of the desired sulfur trioxide. 

An excellent example of an optimum operation design is the determination of operating conditions for the catalytic oxidation of sulfur dioxide to sulfur trioxide. Suppose that all the variables, such as converter size, gas rate, catalyst activity, and entering-gas concentration, are fixed and the only possible variable is the temperature at which the oxidation occurs. If the temperature is too high, the yield of SO, will be low because the equilibrium between SO, SO, and 0, is shifted in the direction of SO, and 0,. On the other hand, if the temperature is too low, the yield will be poor because the reaction rate between SO, and 0, will be low. Thus, there must be one temperature where he amount of sulfur trioxide formed will be a maximum. This particular temperature would give the... 

Exothermic reactions with a decrease in entropy reach equilibrium (AG = 0) at some temperature and reverse beyond this point. This is evident from Eq. (4.2) where the negative term AH will cancel with the positive term TAS when T gets sufficiently large. Since we already noted that such reactions are common in the chemical industry, should we expect most reactions to be reversible In principle, yes, but in practice we operate many reactors at a temperature far below the equilibrium point and therefore never notice any influence of the reverse reaction. There are, however, industrially important exceptions to this rule. The manufacture of ammonia from nitrogen and hydrogen and the formation of sulfur trioxide from sulfur dioxide and oxygen are two prominent cases. 

Ammonia and sulfur trioxide reactors must be designed and operated such that the heat of reaction does not raise the reactor temperature enough to cause the reaction to reach equilibrium and therefore stop. The same applies to the reversible isomerization reaction studied in Chap, 9. 

However, this reaction is very slow in the absence of a catalyst. One of the mysteries during early research on air pollution was how the sulfur dioxide produced from the combustion of sulfur-containing fuels is so rapidly converted to sulfur trioxide in the atmosphere. It is now known that dust and other particles can act as heterogeneous catalysts for this process (see Section 15.9). In the preparation of sulfur trioxide for the manufacture of sulfuric acid, either platinum metal or vanadium(V) oxide (V205) is used as a catalyst, and the reaction is carried out at approximately 500°C, even though this temperature decreases the value of the equilibrium constant for this exothermic reaction. 

The solution to this problem was the discovery of certain catalysis (platinum, vanadium pentoxide), which speed up the reaction without affecting the equilibrium. The catalyzed reaction proceeds not in the gaseous mixture, but on the surface of the catalyst, as the gas molecules strike it. In practice sulfur dioxide, made by burning sulfur or pyrite, is mixed with air and passed over the catalyst at a temperature of 400° to 450° C. About 99% of the sulfur dioxide is converted into sulfur trioxide under these conditions. It is used mainly in the manufacture of sulfuric acid. 

Bis-trifluoromethylmethylene)-1,2,4-thiadioxetane 1,1-dioxide (hexafluoro-isobutenylidene sulfate) (499) is a stable, colorless liquid obtained by treatment of bis(trifluoromethyl) ketene, 3,3,3-trifluoro-2-trifluoromethylpropanoic acid, or the anhydride of the latter with sulfur trioxide. It is said, on the basis of F nmr data, to be in equilibrium with a cyclic, eight-membered dimer (/Teq = 0.1321iter/mole at 34.5°C), analogous to the structure of the above-mentioned methylene sulfate . Hydrolysis of 499 gives 3,3,3-trifluoro-2-trifluoromethyl-propanoic acid. The cyclic sulfate is a powerful donor of sulfur trioxide, as exemplified by its reactions with fluoride, bromide, and iodide ions (but not chloride ions), triethylamine, dioxane, sulfolane, and alkenes (See... 

Both the rate and tire equilibrium conversion of a chemical reaction depend on the tem-peraUire, pressure, and compositionof reactants. Consider,for example, the oxidation of sulfur dioxide to sulfur trioxide. A catalyst is required if a reasonable reaction rate is to be attained. Witli a vanadium pentoxide catalyst the rate becomes appreciable at about 573.15 K (300°C) and continues to mcrease at higher temperatures. On the basis of rate alone, one would operate tire reactorat the highest practical temperature. However, the equilibrium conversion to sulfur trioxide falls as temperature rises, decreasing from about 90% at 793.15 K (520°C) to 50% at about 953.15 K (680°C). These values represent maximum possible conversions regardless of catalyst or reaction rate. The evident conclusion is that both equilibrium and rate must be considered in the exploitation of chemical reactions for commercial purposes. Although reaction rates are not susceptible to thermodynamic treatment, equilibrium conversions are. Therefore, the purpose of this chapter is to detennine the effect of temperature, pressure, and initial composition on the equilibrium conversions of chemical reactions. 

A reaction between gaseous sulfur dioxide and oxygen gas to produce gaseous sulfur trioxide takes place at 600°C. At that temperature, the concentration of SO2 is found to be 1.50 mol/L, the concentration of O2 is 1.25 mol/L, and the concentration of SO3 is 3.50 mol/L. Using the balanced chemical equation, calculate the equilibrium constant for this system. 

The orientation of phenylsulfamic acid would be expected to be orthopara, since there is an unshared electron pair on the nitrogen atom adjacent to the benzene ring. Dimethylaniline forms no complex with sulfur trioxide 48 and consequently the formation of the para isomer may be interpreted as a reaction proceeding through the small amount of dimethylaniline in equilibrium with the substituted ammonium salt ... 

The second reaction, oxidation of sulfur dioxide to sulfur trioxide with air, is a somewhat less exothermic, equilibrium reaction (Eq. 9.24). 

A catalyst is a substance, which speeds up a chemical reaction but is not itself consumed in the reaction. However, it cannot alter the equilibrium position of a chemical reaction (i.e., the relative proportions of sulfur dioxide and sulfur trioxide present after the reaction). Thus, the reaction rate for an equilibrium reaction, such as that represented by Eq. 9.24, is the speed with which equilibrium is reached not the speed to complete conversion). 

At 500°C the rate of reaction is about 100 times as fast as at 400°C, requiring a much smaller reactor volume for the same sulfuric acid throughput, but the equilibrium constant, Kp, drops to about 50. Hence, at this temperature only about 85% of the sulfur is present as sulfur trioxide. 

At 600°C, the rate of reaction is some 30 to 50 times faster again, requiring an even smaller reactor for the same throughput, but the rate of dissociation of sulfur trioxide to sulfur dioxide becomes appreciable. The value of Kp drops to about 10, giving only about 60-65% of the sulfur as sulfur trioxide at this temperature, and the remainder as sulfur dioxide. For process purposes there is no point in considering the sulfur oxide equilibrium situation for any higher temperatures than this. With a promoted vanadium pentoxide catalyst bed at 600°C a 2-4 sec contact time is already sufficient to obtain essentially equilibrium concentrations at this temperature. 

The air pollutant sulfur dioxide can be partially removed from stack gases in industrial processes and converted to sulfur trioxide, the acid anhydride of commercially important sulfuric acid. Write the equation for the reaction, using the smallest whole-number coefficients. Calculate the value of the equilibrium constant for this reaction at 25°C, from values of AGf in Appendix K. 

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