Freezing Point Depressions of Phase Change CO2 Solvents

Freezing point depressions (FPD) in phase change solvents containing 2-(diethylamino)ethanol (DEEA) and 3-(methylamino)propylamine (MAPA) were measured using a modified Beckmann apparatus. The measurements were performed for the binary aqueous DEEA and MAPA solutions, respectively, in the concentration ranges of (0 to 55) mass percent and (0 to 32.5) mass percent of amine. For the ternary aqueous DEEA–MAPA solutions, freezing points were measured for 5:1, 3:1, 1:1, 1:3, and 1:5 molar ratios of DEEA/MAPA. The FPD method was extended for easy and accurate measurement of freezing points in the CO2 loaded systems. It is based on saturation of the solution by CO2 and then dilution by using a batch of the original unloaded solution in order to get the solutions with different CO2 loadings. Freezing point measurements were then carried out for (12, 20, 30, and 33) mass percent DEEA solutions and (10, 20, and 27) mass percent MAPA solutions at different CO2 loadings. The apparatus and the experimental method used showed good repeatability and accuracy. The measured freezing point data were compared with monoethanolamine (MEA) and methyl diethanolamine (MDEA) found in the literature. The experimental values indicate that the DEEA–water interaction is almost similar to that of MEA–water interaction. MAPA has shown a stronger nonideal behavior compared to DEEA. A correlation for the freezing points as a function of solution composition was formulated for the unloaded binary and ternary systems.