Kontaktdprocessen

Kontaktdprocessen, commonly called the contact process in English, is the principal industrial method for the large-scale production of sulfuric acid (H2SO4). It converts sulfur-containing materials to sulfuric acid through a two-stage sequence: first, the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) over a catalyst, and second, the absorption and hydrolysis of SO3 to form concentrated sulfuric acid.

The oxidation step uses a vanadium(V) oxide–based catalyst (commonly V2O5 promoted with oxides such as WO3 on a solid support). The reaction is exothermic and occurs at around 400–600°C, typically near 450°C, and near atmospheric pressure. The main reaction is 2 SO2 + O2 ⇌ 2 SO3. Reaction conditions favor a balance between rate and equilibrium, and catalyst life is maintained by careful heat and impurity control.

In the second step, SO3 is absorbed in concentrated sulfuric acid to form oleum (H2SO4·SO3), which is then hydrolyzed by water to yield sulfuric acid. The simplified overall equation is 2 SO2 + O2 + H2O → 2 H2SO4. The process is continuous and designed for high per-pass conversion and large-scale output.

Historical note: the contact process supplanted the older lead chamber process in the late 19th to early 20th century due to higher yields and the ability to produce concentrated sulfuric acid more efficiently. It remains the dominant method for industrial sulfuric acid production, central to chemical manufacturing and fertilizer industries.

Safety and environmental aspects: SO3 is highly reactive and corrosive; cooling, gas handling, and corrosion-resistant equipment are essential. Sulfuric acid is a strong mineral acid requiring careful handling and containment.

See also: sulfuric acid, lead chamber process, vanadium oxide catalysts.