Claus process

The Claus process is a desulfurizing process, recovering elemental sulfur from gaseous mixtures containing hydrogen sulfide (H2S). First patented in 1883 by the chemist Carl Friedrich Claus, the Claus process remains the most important desulfurization process in the petrochemicals industry. It is standard at oil refineries, natural gas processing plants, and gasification or synthesis gas plants. In 2005, byproduct sulfur from hydrocarbon-processing facilities constituted the vast majority of the 64 teragrams of sulfur produced worldwide.

The overall Claus process reaction is described by the following equation:

2 H2S + O2 → 2 S + 2 H2O

However, the process occurs in two steps:

2 H2S + 3 O2 → 2 SO2 + 2 H2O
4 H2S + 2 SO2 → 3 S2 + 4 H2O

Moreover, the input feedstock is usually a mixture of gases, containing hydrogen cyanide, hydrocarbons, sulfur dioxide or ammonia. The mixture may begin as raw natural gas, or output from physical and chemical gas treatment units (Selexol, Rectisol, Purisol and amine scrubbers) when e.g. refining crude oil.

Gases containing over 25% H2S are suitable for the recovery of sulfur in straight-through Claus plants. Gases with less than 25% H2S can be processed through alternate configurations such as a split flow, or feed and air preheating.

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