Chemistry C3 Part 8

Based on Edexcel textbook

pg 142-143 The Contact Process

Sulfuric acid is mainly manufactured using the Contact Process which is as efficient and safe as possible. It has four stages:

• the production of sulfur dioxide
• conversion of sulfur dioxide to sulfur trioxide
• absorbtion of sulfur trioxide to form oleum
• dilution of oleum to form sulfuric acid

I reccommend looking at a diagram to see how it is done.

Sulfur dioxide can be made by burning sulfur in air (S(s) + O2(g) -> SO2 (g) ) or by roasting minerals such as Iron sulphide.

Iron sulphide + Oxygen ---> Iron oxide + Sulfur dioxide

These reactions are strongly exothermic. The next stage of the contact process is most difficult when sulfur dioxide is turned into sulfur trioxide. The convertion is never 100%. At catalyst (vandium oxide) is used to speed the reaction up. A temperature of 450'C is used at a compromise because it is hot enough to speed up the reaction but not too hot to stop the reaction altogether. The sulfur dioxide is passed through three or four convertion chambers to get the best convertion rate. The reaction is again exothermic so the heat from the reaction can be used to keep the reactor at 450'C.

The reactor is operated at slightly above normal atmospheric pressure. Higher pressures would give an even better converstion rate but that would be very expensive and more dangerous to the workers. Finally excess air is added to reduce the amount of left over sulfur dioxide. A 99.5% convertion rate is required by law.

The last stage of the reaction requires sulphur trioxide to be dissolved in water.

SO3 + H2O ---> H2SO4 

The reaction is so exothermic that the sulfuric acid would boil so for safety reasons the sulfur trioxide is added to 98% sulfuric acid instead to make a liquid called oleum that can then be diluted with more control.

pg 144-145 Detergents

Detergents are something that cleans. Water will not mix with…