Manufacture of sulphuric acid

1 Contact process. Sulphuric acid suffered a decline in production for a number of years, but 1983 showed a slight improvement over 1982 and this appeared to be continuing in 1984. 

The method of making sulphuric acid is now exclusively by the Contact process although the plant has been improved consistently in recent years because of energetic and environmental demands. These will be considered in 

Molten sulphur is sprayed into the furnace in a current of dry air at about 950 °C — 1000°C when about 10 to 10.5% of sulphur dioxide is formed. 

Sulphur trioxide is absorbed in the intermediate absorber and in the final absorber. The former absorbs SO 3 from the third catalyst bed and the latter from the first bed. If water is used for absorption a fine acid mist forms which is unacceptable in practical or environmental terms. In order to prevent this the vapour pressure above the acid must be made sufficiently low. This can only be achieved if the absorption medium is greater than 97% strength sulphuric acid—in practice 98% sulphuric acid is employed. The final product is about 98.5% sulphuric acid, which is then diluted to 98% with water in the pump tanks. The heat formed in the reaction 

Environmental emission of SO2 can be controlled by tail-gas scrubbing. This, although efficient, adds considerably to running costs. In this process SO2 is absorbed by lime or A,iV-dimethylaniline. 

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Sulphur is used in the manufacture of matches and fireworks, as a dust insecticide and for vulcanising rubber. Most of the world supply of sulphur, however, is used for the manufacture of sulphuric acid (p. 296). 

On the industrial scale it is produced in large quantities for the manufacture of sulphuric acid and the production methods are dealt with later. It was once estimated that more than 4 000 000 tons of sulphur dioxide a year entered the atmosphere of Britain from the burning of coal and oil. 

This is the basis of the industrial manufacture of sulphuric acid and is dealt with on p. 296.)... 

Figure 10.5. The Lead Chamber process for the manufacture of sulphuric acid...

Vanadium Pollution control, e.g. removal of hydrogen sulphide and in manufacture of sulphuric acid Respiratory irritation green-black tongue (transient)... 

In the contact plant for the manufacture of sulphuric acid, sulphuric acid is itself used for drying the air for the oxidation of the sulphur. When drying hydrocarbons such as benzene, it is sometimes convenient to pass the material through a bed of solid caustic soda, although, if the quantity is appreciable, this method is expensive. 

G. Lunge, The Manufacture of Sulphuric Acid and Alkali, London, 1. 679, 1911. 

J. F. Persoz, Traill thiorique et pratique de Vimpression dee tissue, Paris, 1846 G. Lunge, The Manufacture of Sulphuric Acid and Alkali, London, 3. 588, 1911. 

The preparation of sodium carbonate from impure natural soda, and from the ashes of soda plants, has been already described. Methods have also been suggested for transforming various sodium salts—sulphate, chloride, fluoride, cryolite, nitrate, and felspar—into the carbonate. Many of these are discussed in detail by R. von Wagner s Regesten der Soda/abrik (Leipzig, 1866) and by G. Lunge s A Theoretical and Practical Treatise on the Manufacture of Sulphuric Acid and Alkali (London, 1896). Much of what is said of the sodium salts applies also to the potassium salts, and conversely. 

The resulting sulphide of iron would be of value to tbe manufacturer of sulphuric acid. 

From a consideration of the details of the ordinary contact process it will readily be recognised that the catalytic method of manufacture of sulphuric acid is capable of yielding an acid of the highest degree of purity. 

Nitrosulphonic Acid, Nitrosylsulphuric Acid or Nitroso-sulphuric Acid, NQ2.S02.0H.—In 1806, Clement and Desormcs, during the manufacture of sulphuric acid by the lead chamber process, observed the formation of a crystalline solid, to which the names nitrosulphonic acid and nitrosylsulphuric acid were later given the term chamber crystals, however, is still commonly applied to this acid.6 The composition and nature of the acid were first investigated by Weber,7 and by Michaelis and Schumann.8... 

It is fairly generally believed that nitrosulphonic acid plays an important part in the lead chamber process for the manufacture of sulphuric acid (see p. 153). The vapour pressures of mixtures of sulphuric acid with nitrous or nitric acid or with both these acids, within the range occurring in the chambers, increase with the nitrogen acid content and with rise in temperature, and the total pressure is always higher than the sum of the individual pressures, especially when the sulphuric acid is concentrated, for nitric acid - sulphuric acid mixtures this may be explained 1 by the occurrence of the following... 

Extraction.—(1) From Pyrites.—In the oxidation of the pyrites (or other sulphur mineral) for the formation of sulphur dioxide in the manufacture of sulphuric acid, foreign elements like arsenic and selenium also undergo oxidation and pass ofC as vapours with the sulphur dioxide. The selenium dioxide produced in this manner their suffers more or less complete reduction by the sulphur dioxide, when finely divided selenium separates, mainly in the lead chambers, as a red, amorphous powder, accompanied possibly by some of the greyish-black form a portion of the dioxide is also found in the Glover tower acid. The amount of selenium in the chamber mud depends, of course, on the nature of the pyrites relatively large quantities of compounds of arsenic, zinc, tin, lead, iron, copper or mercury are always present, arising almost entirely from impurities in the pyrites. 

Miles, Manufacture of Sulphuric Acid (Contact Process), vol. iv. (London, 1925), p. 120. 

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