The Chemistry of Carbon Capture
Carbon Capture and Storage (CCS) relies on chemical reactions to isolate Carbon Dioxide (CO2) from industrial emissions. The goal is to "trap" the gas in a liquid or solid form before it is compressed and stored underground. Carbon capture technologies aim to intercept CO2 before it enters the atmosphere (point-source capture) or remove it directly from ambient air (direct air capture – DAC).
1. Amine Scrubbing (Chemical Absorption)
This is the most mature technology. It uses aqueous amine solutions (like Monoethanolamine or MEA) to react with acidic CO2 molecules.
C2H4OHNH2 + CO2 + H2O ⇌ C2H4OHNH3+ + HCO2-
In the Absorber, the reaction happens at low temperatures (around 40-60°C). When the solution is moved to a Stripper and heated (to about 120-150°C), the reaction reverses, releasing pure CO2 and regenerating the amine for reuse.
Most common solvents in 2026:
- 30–35 wt% aqueous Monoethanolamine (MEA) – still #1 by installed capacity
- AMP + piperazine blends (advanced hindered amine + activator)
- PZEA (piperazine ethylamine) formulations
- KS-1 / KS-2-type proprietary solvents (Kansai Electric / Mitsubishi)
- EAB / EFG+ solvents (ExxonMobil / FuelCell Energy lineage)
2. Adsorption (Solid Sorbents)
Instead of a liquid, solid materials like Zeolites or Metal-Organic Frameworks (MOFs) act as molecular sponges. These materials have massive surface areas—one gram of a MOF can have the surface area of a football field.
- Physisorption: Weak Van der Waals forces hold the CO2.
- Chemisorption: Stronger chemical bonds are formed, often involving amine-functionalized surfaces.
3. Calcium Looping
This process uses the reversible carbonation of calcium oxide (lime). It is particularly useful for cement plants because the chemistry is already compatible with their raw materials.
Carbonation: CaO + CO2 → CaCO3 (Exothermic)
Calcination: CaCO3 → CaO + CO2 (Endothermic)
4. Oxy-Fuel Combustion
Rather than scrubbing the CO2 after the fact, this method burns fuel in pure oxygen instead of air. Since air is ~78% Nitrogen, burning in pure O2 results in a flue gas that is almost entirely water vapor and CO2. The water is simply condensed out, leaving a nearly pure stream of CO2.