Claus process
Desulfurization process recovering elemental sulfur from hydrogen sulfide.
The Claus process is a method for removing sulfur from gas mixtures that contain hydrogen sulfide (H2S), producing elemental sulfur. Invented by German chemist Carl Friedrich Claus and patented in 1883, it is still the leading desulfurization technique in the petrochemical industry. It is commonly used at oil refineries, natural gas processing plants, and facilities that produce synthesis gas or handle gasification. In 2005, sulfur recovered as a byproduct from hydrocarbon processing made up nearly all of the 64 teragrams (64 million metric tons) of sulfur produced worldwide.
The overall chemical reaction for the Claus process is: 2 H2S + O2 → 2 S + 2 H2O. However, the process occurs in two steps: first, 2 H2S + 3 O2 → 2 SO2 + 2 H2O, and then 2 H2S + SO2 → 3 S + 2 H2O (or 16 H2S + 8 SO2 → 3 S8 + 16 H2O). The input feedstock is usually a mix of gases that may include hydrogen cyanide, hydrocarbons, sulfur dioxide, or ammonia. This mixture can come from raw natural gas or from the output of physical and chemical gas treatment units (such as Selexol, Rectisol, Purisol, and amine scrubbers) used during crude oil refining. Gases with more than 25% H2S can be processed in straight-through Claus plants, while gases with less than 25% H2S require alternative configurations like split flow or feed and air preheating.
**History** Carl Friedrich Claus, a German chemist working in England, invented the process and received a British patent for it in 1883. The process was later significantly modified by IG Farben.
**Process Description** A basic 2+1-reactor (converter) SuperClaus unit follows a schematic process flow diagram. The Claus technology is divided into two steps: thermal and catalytic.
**Thermal Step** In the thermal step, gas containing hydrogen sulfide is burned in a substoichiometric combustion at temperatures above 850 °C. The fuel-air ratio must be carefully controlled so that only one-third of the H2S converts to SO2, ensuring the correct stoichiometry for the catalytic step. A Claus facility typically uses several separate fires in lances around a central muffle to handle different gas sources. How the feed gas is burned depends on the concentration of H2S and other combustible components like hydrocarbons or ammonia.
- Inventor
- Carl Friedrich Claus
- Patent year
- 1883
- Field
- Industrial chemistry, desulfurization
- Nationality
- German (working in England)
- Known for
- Claus process for sulfur recovery
- Global sulfur production 2005
- 64 teragrams (64 million metric tons)
- Typical steam generated per ton sulfur
- Over 2.6 tons
Lore & Background
The process was invented by Carl Friedrich Claus, a German chemist working in England, who received a British patent in 1883. It was later significantly modified by IG Farben. The overall reaction is 2 H2S + O2 → 2 S + 2 H2O, occurring in two steps: first, 2 H2S + 3 O2 → 2 SO2 + 2 H2O, then 2 H2S + SO2 → 3 S + 2 H2O (or 16 H2S + 8 SO2 → 3 S8 + 16 H2O). Input feedstock is usually a mixture of gases, which may contain hydrogen cyanide, hydrocarbons, sulfur dioxide, or ammonia, and can originate from raw natural gas or output from gas treatment units such as Selexol, Rectisol, Purisol, and amine scrubbers.
The Claus technology divides into thermal and catalytic steps.
Reader's Guide
The Claus process is the dominant method for recovering elemental sulfur from hydrogen sulfide in the petrochemical industry, essential for environmental compliance and sulfur production. In 2005, byproduct sulfur from hydrocarbon-processing facilities constituted the vast majority of the 64 teragrams of sulfur produced worldwide. The process is standard at oil refineries, natural gas processing plants, and gasification or synthesis gas plants. Its significance lies in converting toxic hydrogen sulfide into valuable elemental sulfur, used in sulfuric acid production, fertilizers, and sulfur concrete. The process generates over 2.6 tons of steam per ton of sulfur yield, contributing to energy efficiency. However, careful temperature control is required to avoid catalyst fouling and to manage the anomalous solubility of H2S in liquid sulfur, which can lead to toxic gas buildup. The sub dew point Claus process addresses equilibrium limitations by using parallel reactors. Millions of tons of elemental sulfur are produced annually, with large stockpiles in Alberta, Canada, from Athabasca Oil Sands processing.
Did You Know?
- The Claus process was first patented in 1883 by German chemist Carl Friedrich Claus, working in England.
- The thermal step of the Claus process produces 60 to 70% of the total elemental sulfur.
- Over 2.6 tons of steam are generated for each ton of sulfur yield in the Claus process.
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