CO2 & H2S Removal (Amine Solvent)

The CO₂ & H₂S Removal process using Amine Solvent is one of the main techniques in the oil and gas industry to purify natural gas or produced gas. Here's the full explanation:

1. Process Objective

Natural gas coming out of production wells usually contains acidic gases such as:

• CO₂ (carbon dioxide)

• H₂S (hydrogen sulfide)

Both of these components must be removed because:

• CO₂ can reduce the heating value of the gas and cause corrosion.

• H₂S is toxic and corrosive, and produces sulfuric acid (H₂SO₄) when mixed with water.

Therefore, a "gas sweetening" process is carried out - removing the acid gas content so that the gas becomes safe and valuable for use or export.

2. Working Principle of Amine Solvent Process

This process uses an amine solution, which is an organic compound containing the -NH₂ group. The amine acts as a chemical solvent that selectively absorbs the acid gas.

Main stages:

1. Absorber (absorption tower)

   • Dirty gas (containing CO₂/H₂S) flows into the absorber column.

   • In it, the gas contacts an amine solution such as:

     • MEA (Monoethanolamine)

     • DEA (Diethanolamine)

     • MDEA (Methyldiethanolamine)

     • DGA, DIPA, and others.

   • Amines react chemically with CO₂ and H₂S, forming bound compounds.

2. Regenerator (Regeneration Tower or Stripper)

   • The saturated amine solution (rich amine) is heated to separate the acid gas.

   • CO₂ and H₂S are released to the top of the tower, while the pure amine (lean amine) is cooled and returned to the absorber for reuse.

3. Major Chemical Reactions

Examples of reactions that occur:

• With CO₂:

  RNH2+CO2+H2O→RNH3++HCO3-RNH₂+CO₂+H₂O\rightarrow RNH₃^++HCO₃^-RNH2+CO2+H2O→RNH3++HCO3-.

• With H₂S:

  RNH2+H2S→RNH3++HS-RNH₂ + H₂S \rightarrow RNH₃^++HS^-RNH2+H2S→RNH3++HS-

This reaction is reversible - that's why the solvent can be regenerated and used repeatedly.

4. Oil and Gas Field Applications

In oilfield operations, this system is used for:

• Gas sweetening units before the gas is sent to the transmission pipeline.

• Enhanced Oil Recovery (EOR) - maintaining the quality of injection gas.

• Offshore & onshore gas processing facilities.

• Amine treatment skids provided by chemical vendors (e.g. Nalco, Baker Hughes, Clariant, etc.).

5. Amine Type Selection

Selection depends on the requirement:

6. Operational Challenges

• Foaming → causes amine carry-over.

• Amine degradation → due to heat or oxidation.

• Corrosion → due to the presence of H₂S, CO₂, and water.

• Heat balance & reboiler duty → affects energy efficiency.

7. Conclusion

CO₂ & H₂S Removal (Amine Solvent) is a key process in gas treatment in the oil and gas industry to:

• Produce safe gas that meets sales specifications.

• Protect equipment from corrosion.

• Reduce the environmental impact of sour gas.