Sulfuric acid is a product of the chemical industry produced in the largest quantities. Over 40 million tones are produced every year. The two main ways of producing sulfuric acid are the lead chamber process and contact process. The contact process is used more today and is much more efficient, cheaper and faster. The contact process yields pure sulfuric acid. The contact process was patented by Peregrine Philips in 1831. 
The contact process is divided into several stages in which sulfur dioxide is produced and then converted into sulfur trioxide. Sulfur trioxide is then converted into concentrated sulfuric acid.
Sulfur dioxide can be obtained by several ways. One of them is by burning sulfur in the burner in the contact process machine. Liquid sulfur is added to the burner were it its reaction with dry air happens and produces sulfur dioxide.
S(s) + O2(g) SO2(g)
Another way of preparing the sulfuric dioxide is by roasting pyrite (iron sulfide) in a pyrite burner,
4 FeS(s) + 7 O2(g) 2 Fe2O3(s) + 4 SO2(g)
…or by burning hydrogen sulfide.
2 H2S(g) + 3 O2(g) 2 SO2(g) + 2 H2O(g)
It is very important to avoid catalyst poisoning (stopping catalytic activities) by purifying the air and sulfuric dioxide. Sulfuric dioxide is purified by going through a dust chamber where dust particles are removed. After that it is sprayed with water, which helps with removing soluble impurities and in the end, the sulfuric dioxide is dried by using H2SO4.
SO3(g) + H2O(l) | H2SO4 | H2SO4(l) |
| | |
In all cases the excess of air is used in a way that the produced sulfur dioxide is already mixed with oxygen for the next stage of the contact process. This happens catalytically. In other words, a catalyst is used to speed up the chemical reaction, but it does not change the position of the equilibrium and it does not produce any greater percentage of sulfur trioxide. The catalyst used is Vanadium (V) oxide (V2O5). Platinum would be a more effective catalyst, but it...