What Does Hydrogen Sulfide Mean?
Hydrogen sulfide is a chemical compound with the formula H2S, and is often a colorless gas with a rotten egg odor, commonly referred to as "sewer gas." H2S is:
- Heavier than air
- Very poisonous
Corrosion of metal and concrete is a major issue associated with the generation and oxidation of hydrogen sulfide. Hydrogen sulfide gas causes severe corrosion of equipment, in particular piping.
Corrosionpedia Explains Hydrogen Sulfide
Uses of hydrogen sulfide include:
- Metallurgy for the preparation of metallic sulfides
- Preparation of phosphors, oil additives and as an analytical reagent in chemical analysis
- Metals separation, removal of metallic impurities and for reaction with numerous functional organic compounds
- To form a layer of sulfide on the surface of steel wires or plates that are to be coated with paint or plastic
Hydrogen sulfide is most commonly obtained by its separation from sour gas, which is natural gas with high content of H2S. It can also be produced by reacting hydrogen gas with molten elemental sulfur at about 840°F (450°C). Hydrocarbons can replace hydrogen in this process. Hydrogen sulfide production can be costly because of the dangers involved in production.
Corrosion due to H2S is mainly electrochemical in nature. The hydrogen sulfide gas is biochemically oxidized in the presence of moisture to form sulfuric acid. The effect of sulfuric acid on concrete and steel surfaces exposed to severe wastewater environments can be devastating. High amounts of sulfuric acid lower the pH of wastewater, which contributes to concrete and pipe corrosion.
The rate of concrete corrosion depends on the permeability of concrete and the amount of hydrogen sulfide gas that is adsorbed to the moist sewer walls. Signs of prolonged exposure to mild acid attack include:
- Rust bleeding
Many wastewater facilities that experience sulfide problems generally use aeration or chemical oxidizers. These only mask the underlying problem and do not actually remove the sulfur/sulfide molecules from the system, because the reduction of sulfur into hydrogen sulfide or oxidation to sulfuric acid (H2SO4) causes the problem.
Metal parts are sometimes passivated with hydrogen sulfide. Catalysts used in hydrodesulfurization are routinely activated with hydrogen sulfide, and the behavior of metallic catalysts used in other parts of a refinery are also modified using hydrogen sulfide.