Evaluation of a phase change solvent for CO2 capture: Absorption and desorption tests

A blend of a tertiary amine (DEEA) and a diamine (MAPA) was studied in a screening apparatus for preliminary absorption tests. Two immiscible liquid phases were formed upon CO2 loading and the system was shown to have large capacity for CO2. The two phases were analyzed individually for both amines and CO2. MAPA and water were found concentrated in the heavy CO2 rich phase whereas the CO2 lean phase contained mainly of DEEA. Volumetric phase ratio was measured as function of CO2 loading and together with the individual phase compositions this forms part of a basis for an equilibrium model. The CO2 rich phase was heated to desorption temperatures and shown to regenerate CO2 at higher pressures than normally used for 30 wt.% MEA. The data enabled understanding the system behavior as MAPA is first loaded in the heavy phase and subsequently DEEA reacts with CO2 and dissolves. The data show that the system has potential for significant reduction in regeneration heat through high cyclic capacity, very high CO2 stripping pressures, and for operating where the heat of reaction lies between primary and tertiary amines. The tests also give good estimates for the absorption rate at higher loadings.