Amine scrubbing captures CO₂ by a reversible chemical reaction between an aqueous amine (here monoethanolamine, MEA) and CO₂. Cold, dilute ("lean") solvent absorbs CO₂ from flue gas in the absorber column; hot solvent releases it again in the stripper/regenerator, driven by reboiler heat. The equilibrium loading follows a Van't Hoff / Langmuir-type isotherm:
K(T) = K₀ · exp[ −ΔH_abs/R · (1/T − 1/T₀) ]
α_eq(T,P) = α_max · K(T)·P / (1 + K(T)·P)
ΔH_abs ≈ −84 kJ/mol for MEA-CO₂ (exothermic), so K falls as temperature rises — the solvent holds less CO₂ when hot, which is exactly what makes the temperature-swing cycle work. α_max ≈ 0.5 mol CO₂/mol amine reflects the carbamate stoichiometric limit for a primary amine.
- Rich loading — α_eq evaluated at the absorber temperature and the flue-gas CO₂ partial pressure; this is the loaded solvent leaving the absorber bottom.
- Lean loading — α_eq evaluated at the hot stripper temperature and a low CO₂ partial pressure (diluted by stripping steam); this is the regenerated solvent recycled to the absorber top.
- Capture efficiency — how much of the incoming CO₂ the circulating solvent can actually absorb, set by circulation rate × loading swing (rich − lean) against the flue-gas CO₂ load.
- Reboiler duty — the dominant real-world operating cost: sensible heat to reheat the solvent plus the desorption heat, which is why a small loading swing (weak temperature separation, or a stripper barely hotter than the absorber) makes regeneration far more energy-hungry per tonne of CO₂ — real MEA plants run around 3–4 GJ/tonne CO₂.
This is the same absorption-stripping cycle used in commercial post-combustion capture plants (e.g. Boundary Dam, Petra Nova) — the mechanics scale up, the sliders here just make the trade-offs visible.