Sulphur and its Compounds:Large scale (industrial) manufacture of sulphuric (VI) acid

5.0 Sulphur and its Compounds

5.3 Large scale (industrial) manufacture of sulphuric (VI) acid

Generally, an acid is made by dissolving the corresponding acidic gas (or solid) in water.

Questions 5.3(a)

1. State the formula and name of the gas that, when combined directly with water, would form sulphuric (VI) acid, H₂SO₄.
2. Write two equations to represent the two stages through which the gas identified in Question 1 can be prepared. Indicate at least one required condition where necessary.
3. Suggest suitable raw materials for the manufacture of sulphuric (VI) acid.
4. Manufacturing processes require pure substances. Suggest how the raw materials can be purified before reacting them.
5. Some of the reactions are highly exothermic (produce a lot of heat) and require high pressure. Suggest how you would cater for these in the design of sulphuric (VI) acid manufacturing plant.

NB: Dissolving SO₃(g) directly in water is so highly exothermic and explosive and therefore avoided. Instead, SO₃(g) is first dissolved in concentrated sulphuric (VI) acid to form oleum (H₂S₂O₇), which is then diluted back to sulphuric (VI) acid.

Figure 5.3 is a flow diagram showing the industrial manufacture of sulphuric (VI) acid by the contact process.

Figure 5.3: Large scale manufacture of sulphuric (VI) acid (the Contact Process)

Questions 5.3(b)

1. The drying process in Step I makes use of a liquid. Suggest the identity of the liquid.
2. Name the two elements that react with each other in Step II.
3. Write an equation for the direct combination of (a) sulphur (VI) oxide with concentrated sulphuric (VI) acid in Step V to form oleum (b) dilution of oleum using water, in Step VI to form concentrated (VI) sulphuric acid.
4. Identify two reactive components of the gaseous mixture, R, and explain why the mixture is recycled rather than allowing all of it to flow into the absorption tower.
5. Explain why use of elemental sulphur (S), where it is available, is preferred to metal sulphide ores in the sulphuric (VI) acid manufacturing process.
6. The catalyst often employed is vanadium (V) oxide (V₂O₅) rather than platinum (Pt). Give a reason for this (Search in other sources).
7. A student argued that "dissolving sulphur (VI) oxide in concentrated sulphuric acid, then diluting the product to give back the acid" does not make sense, because it assumes that the acid is already manufactured.
   1. Suggest a possible source of the sulphuric (VI) acid used to dissolve sulphur (VI) oxide.
   2. Why might this possible source be unsuitable for large scale production of the acid?
8. Identify any four factors you would consider before constructing a sulphuric (VI) acid manufacturing plant.
9. Like in other industrial plants, it is difficult to completely convert the two oxides of sulphur into sulphuric (VI) acid; yet they are harmful to the environment. Suggest what can be done to the residual gases.