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

Abstract

Solid−liquid equilibrium (SLE) data were obtained at 0.1 MPa for binary, ternary, and quaternary aqueous solutions containing ammonia (NH 3 ), ammonium bicarbonate (NH 4 HCO 3 ), methyl diethanolamine (MDEA), and potassium carbonate (K 2 CO 3 ) using a modified Beckmann apparatus. The reproducibility of the experimental method was verified by measuring the SLE of aqueous solutions containing NH 3 , K 2 CO 3 , or MDEA in a temperature range between 237 and 273 K. A total of 120 new data points were measured for MDEA−NH 3 and NH 4 HCO 3 −H 2 O mixtures (250 to 305 K), and 23 new data points were obtained for MDEA−K 2 CO 3 −H 2 O 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 NH 4 HCO 3 , whereas a liquid−liquid split was observed when K 2 CO 3 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−K 2 CO 3 −H 2 O 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.

Vapor–Liquid Equilibrium Measurements for Aqueous Mixtures of NH3+ MDEA + CO2and KOH + MDEA

“…In addition to the listed species, potassium and mixed potassium–ammonium salts may precipitate in the solution . Solid formation in aqueous MDEA solutions has been the topic of investigation in an earlier study . Additionally, several authors have indicated the precipitation of ammonium carbamate (NH 2 COONH 4 ) due to a gas-phase reaction between CO 2 and ammonia. − The information regarding SLE in these systems was used to ensure that no solids were present in the system during the VLE experiments.…”