The contact process is the current method of producing sulfuric acid in the high concentrations needed for industrial processes. Platinum was initially 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.
The process can be divided into five stages:
Combining of sulfur and oxygen (O2) to form sulfur dioxide
Purifying 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.
As this process is an exothermic reaction so the temperature should be as low as possible. The yield has been found to be maximum at about 410 - 450° C.
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