The contact process is the current method of producing sulfuric acid in the high concentrations needed for industrial processes. Platinum was originally used as the catalyst for this reaction; however, as it is susceptible to reacting with arsenic impurities in the sulfur feedstock, vanadium(V) oxide (V2O5) is now preferred. History This process was patented in 1831 by British vinegar merchant Peregrine Phillips. In addition to being a far more economical process for producing concentrated sulfuric acid than the previous lead chamber process, the contact process also produces sulfur trioxide and oleum. In 1901 Eugen de Haën patented the basic process involving combining sulfur dioxide and oxygen in the presence of vanadium oxides, producing sulfur trioxide which was easily absorbed into water, producing sulfuric acid. This process was improved remarkably by shrinking the particle size of the catalyst (e.g. :le 5000 microns), a process discovered by two chemists of BASF in 1914. Process The process can be divided into four stages: Combining of sulfur and oxygen (O2) to form sulfur dioxide, then purify the sulfur dioxide in a purification unit Adding an excess of oxygen to sulfur dioxide in the presence of the catalyst vanadium pentoxide at 450 °C and 1-2 atm The sulfur trioxide formed is added to sulfuric acid which gives rise to oleum (disulfuric acid) The oleum is then added to water to form sulfuric acid which is very concentrated. Since this process is an exothermic reaction, the reaction temperature should be as low as possible. Purification of the air and sulfur dioxide (SO2) is necessary to avoid catalyst poisoning (i.e. removing catalytic activities). The gas is then washed with water and dried with sulfuric acid. To conserve energy, the mixture is heated by exhaust gases from the catalytic converter by heat exchangers. Sulfur dioxide and dioxygen then react as follows: 2 SO2(g) + O2(g) ⇌ 2 SO3(g) : ΔH = -197 kJ·mol−1 According to the Le Chatelier's principle, a lower temperature should be used to shift the chemical equilibrium towards the right, hence increasing the percentage yield. However too low of a temperature will lower the formation rate to an uneconomical level. Hence to increase the reaction rate, high temperatures (450 °C), medium pressures (1-2 atm), and vanadium(V) oxide (V2O5) are used to ensure an adequate (>95%) conversion. The catalyst only serves to increase the rate of reaction as it does not change the position of the