Solid-Liquid Equilibrium and Binodal Curves for Aqueous Solutions of NH3, NH4HCO3, MDEA, and K2CO3

Solid-liquid equilibrium (SLE) data were obtained at 0.1 MPa for binary, ternary, and quaternary aqueous solutions containing ammonia (NH3), ammonium bicarbonate (NH4HCO3), methyl diethanolamine (MDEA), and potassium carbonate (K2CO3) using a modified Beckmann apparatus. The reproducibility of the experimental method was verified by measuring the SLE of aqueous solutions containing NH3, K2CO3, or MDEA in a temperature range between 237 and 273 K. A total of 120 new data points were measured for MDEA-NH3 and NH4HCO3-H2O mixtures (250 to 305 K), and 23 new data points were obtained for MDEA-K2CO3-H2O solutions (250 to 270 K). These measurements allow for an accurate estimation of water activity in such mixtures and provide insights on the limits of solid formation. The results indicate that the addition of MDEA increases the solubility of NH4HCO3, whereas a liquid-liquid split was observed when K2CO3 was added to aqueous MDEA. This opens the possibility of using it as a phase demixing solvent for carbon capture. Despite the extensive literature regarding mixed salt-amine solutions, liquid demixing in such systems has not been reported before. For this reason, the binodal curve for the MDEA-K2CO3-H2O solution was measured at 293.15 K using the method of cloud point titration. These results assist the selection of operation parameters that avoid a liquid-liquid split in the process.