Thermodynamics of hydrogen-bonding mixtures 4: GE, HE, SE and CPE and possible double azeotropy of water+ N-methylethylenediamine

• Published in: Fluid phase equilibria 2001-07, Vol.185 (1), p.209-218
• Main Author: Olson, James D.
• Format: Article
• Language: English
• Subjects: Azeotrope; Data; Excess properties; Heat capacity; N-methylethylenediamine; Vapor–liquid equilibria (VLE); Water
• ISSN: 0378-3812; 1879-0224
• DOI: 10.1016/S0378-3812(01)00471-X

An ebulliometer was used to measure total vapor-pressure ( PTx) data on nine mixtures of water+ N-methylethylenediamine (and the pure components) between 52 and 116°C. Bubble-point data were measured at six pressures from 13.33 to 101.325 kPa. These PTx data indicate the following azeotropic behavior: at pressures below 32.7 kPa there is a single maximum-boiling azeotrope, above 46.7 kPa there is no azeotrope, and between 32.7 and 46.7 kPa there is the possibility of a double azeotrope. This type of double azeotrope is rare because the pure component vapor pressures are considerably different ( P sat 1 / P sat 1 ≈1.6); it may be that the apparent extrema in the Tx data are due to artifacts related to the purity of the N-methylethylenediamine (≈95 mass%). A Redlich–Kister G E model was fitted to isotherms at 60, 85, 90 and 100°C via Barker’s method with an average standard error of 0.52% in pressure. The system exhibits large negative deviations from ideality (derived γ ∞=0.05–0.67) which decrease with increasing temperature. Equimolar G E/ T values thus derived increase with increasing temperature which predicts a negative H E. Equimolar C P E data, measured by differential scanning calorimetry (DSC), are positive and also increase with increasing temperature. These mixture thermodynamic data show that the system water+ N-methylethylenediamine belongs to the class of mixtures where G E