Sulphuric acid contact process

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

Sulphur trioxide, SO3, m.p. 17 C, b.p. 49 C. Formed SO2 plus O2 over a catalyst (contact process - see sulphuric acid). The solid exists... 

The conversion of sulphur trioxide to sulphuric acid arises as a separate reaction only in the Contact process. 

Separations of materials occur at several points in the typical chlorine gas processing system. Usually, cell gas first is cooled, removing much of the water evaporated from the cells. As suggested in Fig. 7.1, this may be completed in two stages, using chilled water in the second to enhance the condensation of water [2]. Cooling is followed by contact with concentrated sulphuric acid, giving a gas with less than 50 ppm of water and so considered dry . 

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. 

Liquid absorbents. If the partial pressure of the water in the gas is greater than the equilibrium partial pressure at the surface of a liquid, condensation will take place as a result of contact between the gas and liquid. Thus, water vapour is frequently removed from a gas by bringing it into contact with concentrated sulphuric acid, phosphoric acid, or glycerol. Concentrated solutions of salts, such as calcium chloride, are also effective. The process may be carried out either in a packed column or in a spray chamber. Regeneration of the liquid is an essential part of the process, and this is usually effected by evaporation. 

Processes 4, 5 and 6 are all essentially one step oxidations of SO2 to SO3 and hence sulphuric acid. The first pair are modified versions of the traditional Contact and Chamber processes for sulphuric acid manufacture, with the principal change being in their ability to accept dilute SO2 gas streams as the feedstock. The use of Activated Carbon as an air oxidation catalyst has clearly received international attention, with success or failure depending to a large extent on subtle modifications in catalyst preparation and catalyst presentation to the reactant gases. Virtually every type of catalyst bed configuration has been explored. 

Preparation of Sulphuric Acid by the Contact Process. Assemble an apparatus as shown in Fig. 72. Fill gas meter 1 with oxygen and... 

Fig. 72. Apparatus for preparing sulphuric acid by the contact process...

---