Volatility of 2-(diethylamino)-ethanol and 2-((2-aminoethyl) amino) ethanol, a biphasic solvent for CO₂ capture

Amine volatility may be a critical problem with biphasic solvent for CO₂ capture such as the blend of 2-(diethylamino)-ethanol (DEEA) and 2-((2-aminoethyl) amino) ethanol (AEEA). The Henry's law constant (H_am) of DEEA and AEEA in water at 40 and 50 °C was measured using a hot gas FTIR. DEEA is 20–30 times more volatile than monoethanolamine (MEA) while AEEA is nearly non-volatile. At lean loading, the amine volatility is 327 ppm in 12 m DEEA and 1.1 ppm in 2.5 m AEEA at 40 °C. The NRTL model shows good consistency with the DEEA-H₂O data for amine and water activity coefficients. Amine volatility in 12 m DEEA with 0 to 0.4 mol CO₂/mol DEEA and in 2.5 m AEEA with 0 to 0.9 mol CO₂/mol AEEA at 40 and 50 °C was also measured. DEEA partial pressure (P_DEEA) increases with CO₂ loading even though there is less free DEEA in the loaded solutions. The ionic reaction products of DEEA and CO₂ increase the ionic strength and DEEA activity coefficient. The effect of ionic strength on the DEEA activity coefficient was confirmed with data for 12 m DEEA-H₂O-KNO₃ and 12 m DEEA-H₂O-H₂SO₄. AEEA partial pressure (P_AEEA) decreases with CO₂ loading as AEEA is converted by the reaction with CO₂ to other non-volatile species.