Heat of absorption of CO 2 in phase change solvents containing 2-(diethylamino)ethanol (DEEA) and 3-(methylamino)propylamine (MAPA) were measured as a function of CO 2 loading at different temperatures using a commercially available reaction calorimeter. The tested systems were aqueous single amines (5M DEEA, 2M MAPA and 1M MAPA) and aqueous amine mixtures (5M DEEA + 2M MAPA and 5M DEEA + 1M MAPA) which give two liquid phases on reacting with CO 2 . All parallel experiments have shown good repeatability. The measurements were taken isothermally at three temperatures in the industrially important temperature range of 40-120 o C. The measured differential heat of absorption values were converted into integral values by integration. Heats of absorption of CO 2 in aqueous single amines were affected by changing the solvent composition (large difference in concentrations) and CO 2 feed pressure simultaneously. In addition to these two parameters, it also depends on temperature and the type of amine used. Tertiary alkanolamine (DEEA) has shown greater dependency on these parameters compared to the diamine (MAPA) containing both primary and secondary amine functional groups. In aqueous amine mixtures, heats of absorption depend on CO 2 loading, temperature and composition of the constituent amines in the mixture. All measured heat of absorption data were compared with 30 mass% MEA used as a base case.

In this work the solidÀliquid equilibrium (SLE) and freezing-point depression (FPD) in the electrolytic binary aqueous systems piperazine (PZ, and aqueous 2-amino-2-methyl-1-propanol (AMP, were measured. The FPD and solubility were also determined in the ternary AMPÀPZÀH 2 O system. A method was developed by which solubility can be determined at higher temperatures using the FPD setup. A total of 86 data points are listed in the full concentration range from (À35 to 90)°C. The solid phases piperazine hexahydrate (PZ 3 6H 2 O), piperazine hemihydrate (PZ 3 1/2H 2 O), and anhydrous PZ precipitated during the experiments. The data can be used in the formulation, prevention, or intentional formation of slurries in piperazine solvents for promoting CO 2 capture using absorption and desorption. INTRODUCTIONCO 2 capture is an openly debated topic for carbon emission reduction to reduce pollution by greenhouse gases. Process streams containing carbon dioxide can be cleaned by absorption in aqueous liquid solvents. Amines, strong bases, or combination of the two are typically used as active components. The low heats of absorption and desorption are design criteria that reduce the cost of energy in regeneration of the solvent. This is obtained by using sterically hindered amines. The result is often slow reaction kinetics between the solvent and CO 2 . Consequently piperazine (PZ) is being used in solution formulation to create an enhanced CO 2 capture solvent. PZ can be used with both amine and potash solutions (K 2 CO 3 ) to increase the rate of absorption and thereby promote the CO 2 capture.A lower PZ concentration was typically used in literature. Recently the scope has changed, and PZ is now being used at higher concentrations. On increasing the concentration, the solubility limit of PZ is being reached, especially during winter temperatures and even up to room temperature. The unexpected formation of slurries and solids downstream may create unforeseen process conditions, decrease efficiency, and create clogging which will result in unfortunate hazardous operations. In general it could be interesting to provoke the formation of CO 2 containing solids and thereby facilitate and increase the capacity of the capture solvent. CO 2 deprived solids are rarely preferable in terms of CO 2 capture.The aim of this work is to determine the solidÀliquid phase boundary in the two binary PZÀH 2 O and AMPÀH 2 O systems and also in the ternary AMPÀPZÀH 2 O system. 2-Amino-2-methyl-1-propanol (AMP) is a sterically hindered amine. CO 2 absorption in AMP solutions can be promoted by adding PZ.An additional goal of this work was to enhance the utilization of freezing-point depression (FPD) equipment developing a method for the purpose of studying solidÀliquid equilibrium (SLE) behavior in solutions precipitating solids other than ice.

Equilibrium total pressures were measured and equilibrium CO 2 partial pressures were calculated from the measured total pressure data in binary and ternary aqueous solutions of 2-(diethylamino)ethanol (DEEA) and 3-(methylamino)propylamine (MAPA). The measurements were carried out in a commercially available calorimeter used as an equilibrium cell. The examined systems were the binary aqueous solutions of 5 M DEEA, 2 M MAPA, and 1 M MAPA and the ternary aqueous mixtures of 5 M DEEA + 2 M MAPA (5D2M) and 5 M DEEA + 1 M MAPA (5D1M), which gave liquid−liquid phase split upon CO 2 absorption. The total pressures were measured and the CO 2 partial pressures were calculated as a function of CO 2 loading at three different temperatures 40 °C, 80 °C, and 120 °C. All experiments were reproduced with good repeatability. The measurements were carried out for 30 mass % MEA solutions to validate the experimental method. All the measured data were also compared with the results of 30 mass % MEA as a reference case. 5 M DEEA has shown high cyclic capacity. Both 2 M and 1 M MAPA showed high loading capacities at 40 °C and 120 °C. The aqueous amine mixtures, 5D2M and 5D1M, gave fairly good cyclic capacities and their results depend on the concentration of the promoter (MAPA) in the mixture. Approximate enthalpies of absorption of CO 2 in all the tested aqueous amine systems were estimated from the CO 2 solubility data. The measured total pressure and the estimated CO 2 solubility data can be useful in thermodynamic modeling of the capture systems when aqueous DEEA−MAPA solutions are used as capture solvents.

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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 CO 2 loaded systems. It is based on saturation of the solution by CO 2 and then dilution by using a batch of the original unloaded solution in order to get the solutions with different CO 2 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 CO 2 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.

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