Undergraduate · 20 min

Carbon capture with an amine scrubbing loop

Follow flue gas through an absorber–stripper loop where cold amine grabs $\ce{CO2}$ and hot amine lets it go.

Goal

Understand how a reversible chemical absorbent lets one solvent loop capture $\ce{CO2}$ continuously.

Apparatus and reagents

Flow diagram of an absorber–stripper plant: flue gas inlet, absorber column, clean gas outlet, hot stripper and compression/storage stage.

Procedure

Read the five stages left to right: flue gas in, absorber, clean gas out, stripper, compression.
Vary the flow-rate slider and note which stages speed up: absorption and stripping must stay balanced.
Identify where the solvent circulates: rich amine leaves the absorber for the stripper; lean amine returns.

What to observe

In the cold absorber, $\ce{CO2}$ reacts reversibly with monoethanolamine: $\ce{2RNH2 + CO2 <=> RNHCOO^- + RNH3^+}$ (a carbamate).
Heating the rich solvent to ≈ 120 °C reverses the reaction, releasing concentrated $\ce{CO2}$ and regenerating the lean amine.

Explanation

Amine scrubbing exploits temperature-swing chemistry: the carbamate forms fast at 40–50 °C and decomposes near 120 °C, so one solvent loops endlessly between absorber and stripper. Roughly 90 % of flue-gas $\ce{CO2}$ can be captured; the energy penalty of the process is dominated by the stripper reboiler (≈ 3–4 GJ per tonne of $\ce{CO2}$ ). The pure $\ce{CO2}$ is then compressed for storage (CCS) or used as a feedstock for synthetic fuels and chemicals (CCU).

Chemists behind it

Carl Bosch