Ebulliometric Determination of Vapor-Liquid Equilibria for Pure Water, Monoethanolamine, N-Methyldiethanolamine, 3-(Methylamino)-propylamine, and Their Binary and Ternary Solutions Inna Kim, † Hallvard F. Svendsen,* ,† and Eli Børresen ‡ Department of Chemical Engineering, Norwegian University of Science and Technology, N-7491 Trondheim, Norway, and SINTEF Materials and Chemistry, N-7465 Trondheim, Norway Vapor-liquid equilibria (VLE) for binary and ternary aqueous solutions of water, monoethanolamine (MEA), N-methyldiethanolamine (MDEA), and 3-(methylamino)propylamine (MAPA) were measured in a modified Swietoslawski ebulliometer at (40, 60, 80, and 100) °C. Experimental temperature (T) and total pressure (P) were measured, and the compositions of both the liquid (x) and vapor (y) phases were analyzed. Boiling temperatures (T b ) of pure water and amines were measured over the pressure range of P ) (2.5 to 101.3) kPa. Experimental activity coefficients (γ) were calculated from the experimental P, T, x, and y data and were fit to the Wilson and NRTL equations. Introduction Vapor-liquid equilibria (VLE) are fundamental properties, and a knowledge of them is essential for the design and operation of separation processes. Many experiments are neces- sary for obtaining such equilibrium data, at least for binary systems, where nonidealities in both phases must be deter- mined. 1 Ebulliometry enables very fast and accurate determi- nation of the vapor-liquid equilibrium. The accuracy of the results is limited by only the purity of the substances used and the precision of the analytical methods used for the sample analyses. An advantage of the method is that degassing is not required. It also involves a simple apparatus, and straightforward procedures are used. 2 Aqueous alkanolamine solutions are widely used for the removal of the acid gases (CO 2 and H 2 S) from gas mixtures. In addition to the well-established industrial uses of experimental data for these completely miscible (water + alkanolamine) systems, there is a general scientific interest in using such experimental data in combination with theories or mathematical models to improve our understanding of molecular interactions in nonideal liquid systems. 3 For proper thermodynamic modeling, accurate equilibrium data for the amine + water binary system over a wide range of temperatures, pressures, and amine concentrations are essential. Values of the limiting activity coefficients (γ ∞ ) are important for the development of new thermodynamic models as well as for the adjustment of reliable model parameters or the choice of selective solvents for the absorption. VLE data for alkanolamine + water systems are rarely available in the literature. Binary VLE data are often reported as the composition of the liquid phase either at constant pressure as a function of temperature or at constant temper- ature as a function of pressure (P, T, x data). Total pressure over MEA + H 2 O solutions was measured by Nath and Bender 4 at (60, 78, and 91.7) °C and by Touhara 5 at (25 and 35) °C. Hilliard 6 measured vapor pressure over (3.5, 7.0, 11.0, and 23.8) molal MEA + H 2 O solutions over the temperature range of (39.8 to 72.7) °C. Vapor-phase composition and activity coefficients were then calculated from the total pressure data on the basis of the Gibbs-Duhem equation. However, total vapor pressure data do not allow direct * Corresponding author. E-mail: hallvard.svendsen@chemeng.ntnu.no. † Norwegian University of Science and Technology. ‡ SINTEF Materials and Chemistry. Table 1. Equlibrium Vapor Pressures of Pure H 2 O with Relative Deviations from Riedel Equation 27 T P T P T P °C kPa % dev °C kPa % dev °C kPa % dev 38.48 6.78 -0.74 75.65 39.83 0.37 89.74 69.83 0.53 40.09 7.38 -0.86 75.69 39.83 0.21 89.78 69.83 0.38 41.84 8.11 -0.71 76.76 41.40 -0.35 94.33 82.79 0.36 49.96 12.28 -0.62 76.79 41.39 -0.51 94.34 82.79 0.32 49.99 12.28 -0.78 76.82 41.40 -0.57 94.52 82.79 -0.35 50.00 12.27 -0.89 79.99 47.18 -0.48 94.54 82.79 -0.40 52.32 13.78 -0.70 80.00 47.18 -0.50 94.54 82.78 -0.44 52.46 13.80 -1.24 83.87 55.17 -0.32 98.52 96.51 0.42 59.61 19.84 1.12 83.92 55.18 -0.49 98.55 96.51 0.31 59.70 19.84 0.70 83.93 55.17 -0.54 98.75 96.47 -0.43 60.02 19.88 -0.58 85.72 59.88 0.64 98.76 96.58 -0.36 60.02 19.88 -0.58 85.77 59.88 0.42 98.76 96.58 -0.38 60.03 19.88 -0.62 89.40 68.92 0.49 99.54 99.28 -0.39 60.04 19.87 -0.72 89.44 68.92 0.36 99.71 100.59 0.31 67.26 27.60 -0.41 89.65 69.00 -0.34 99.74 100.59 0.20 67.29 27.58 -0.60 89.68 69.00 -0.43 100.01 100.98 -0.39 67.32 27.60 -0.69 89.68 68.98 -0.46 Table 2. Vapor Pressures of Monoethanolamine (MEA) P/kPa P / kPa T b / °C meas corr % dev a % dev b T b / °C meas corr % dev a % dev b 84.31 2.98 2.98 0.13 4.62 130.28 24.97 24.87 0.39 0.96 89.84 3.98 3.98 -0.01 3.91 135.04 29.97 29.98 -0.02 0.32 96.18 5.48 5.48 -0.02 3.25 142.66 39.95 39.99 -0.10 -0.08 101.14 6.98 6.98 0.03 2.82 142.63 39.98 39.95 0.09 0.12 105.26 8.47 8.47 -0.06 2.36 151.46 54.95 54.93 0.03 -0.17 110.92 10.97 10.97 -0.02 1.90 156.29 64.95 64.96 -0.02 -0.28 117.99 14.96 14.96 -0.03 1.34 158.46 69.95 69.94 0.02 -0.27 124.86 19.97 19.98 -0.03 0.87 162.46 79.95 79.95 0.00 -0.30 a Deviation from the correlation using Antoine parameters fitted in this work. b Deviation from the correlation using Riedel parameters from ref 28. J. Chem. Eng. Data 2008, 53, 2521–2531 2521 10.1021/je800290k CCC: $40.75  2008 American Chemical Society Published on Web 10/24/2008