Deciphering the conditional enhancement of CO₂ chemisorption by foaming

Foaming is traditionally regarded as detrimental in solution-based gas capture processes; however, its deliberate use as a gas–liquid contacting medium has recently emerged as a promising strategy for CO₂ capture due to the substantial increase in gas–liquid interfacial area it provides. A key unresolved question is whether this benefit can outweigh the additional mass transfer resistance introduced by the interfacial surfactant adsorption. Here, we systematically investigated CO₂ chemisorption in foaming solvents to elucidate the role of foaming in absorption enhancement. The study spans solvents with a wide range of intrinsic reaction kinetics, including slow-reacting (MDEA, Na₂CO₃), fast-reacting (MEA, PZ), and intermediate (AMP) systems, as well as diverse surfactant chemistries. Combined experimental measurements and mass-transfer analyses show that foaming significantly enhances CO₂ absorption in slow-reacting solvents, yielding higher volumetric mass transfer coefficients than conventional bubbling at optimal foam heights. In contrast, for fast-reacting solvents, surfactant-induced interfacial resistance limits performance gains, although foaming remains advantageous under high gas–liquid ratios or elevated CO₂ loadings, where solvent reactivity decreases. AMP exhibits transitional behavior between kinetically slow and fast regimes. CO₂ capture efficiency is further governed by foam volume and microstructure, which evolve during absorption and influence foam stability. These findings provide mechanistic insight into foam-assisted CO₂ capture and inform the design of foam-based contactors for flue gas treatment and direct air capture, with broader implications for interfacial transport–controlled gas–liquid separation processes.