Contact process

The contact process is a process for producing sulfuric acid by passing a blend of sulfur dioxide and air over a solid catalyst, producing sulfur trioxide, which is then absorbed into water, producing sulfuric acid:

1. Burn sulfur producing sulfur dioxide

   {{#Chem: S + O2 { = 983-1150°C } SO2 dH=-70.94}}

2. Gas phase oxidation of sulfur dioxide ion air over a solid catalyst producing sulfur trioxide
3. Absorb sulfur trioxide into sub-saturated sulfuric acid

   {{#Chem: SO3 + H2O {H2SO4 = } H2SO4 }}

Catalysts

Vanadium pentoxide

A mixture of 8% sulfur dioxide in air is passed over vanadium pentoxide producing sulfur trioxide

{{#Chem: SO2 + ½O2 {V2O5=390-600°C, 1.2-1.4atm} SO3 dH=-23.64}}:

Platinum

See also Platinum

NB: Platinum catalysts can be rendered inert by gaseous arsenic in the feedstock gasses

1. Soak asbestos, glass wool, quartz, or another inert substance in chloroplatinic acid
2. Pyrolize the chloroplatinic acid, leaving finely divided platinum on the surface of the catalyst base

Pass a mixture of sulfur dioxide and air over the platinum catalyst

{{#Chem: SO2 + ½O2 {Pt =} SO3}}