The Salting-out Effect in Some Physical Absorbents for CO₂ Capture

Abstract

The solubility of CO2 in organic solvents N-methyl-2-pyrrolidone (NMP), methanol and monoethylene glycol (MEG) at 30 °C was measured together with its heat of absorption. The salts lithium nitrate (LiNO3), lithium chloride (LiCl) and tetraethylammonium bromide (TEABr) were then dissolved in different proportions to these solvents to analyze their salting-out/salting-in effects. Results from pure and salt containing solvents were compared to those found for CO2 solubility in fully loaded hybrid solvents of each diluent plus monoethanolamine (MEA), wherein carbamate and protonated amine coexist, presumably causing similar salting-out/salting-in effects. Interestingly, an unexpected persistent enhancement in CO2 capacity was observed through all of the latter solutions, suggesting that physical absorption is not the only mechanism through which CO2 is absorbed after full theoretical amine loading. Vapour-liquid equilibrium (VLE) curves and heat of absorption data are provided for these hybrid solvents at 30 °C as well.