Measurements of the Molar Heat Capacity and the Molar Excess Enthalpy for Various Alkanolamines in Aqueous Solutions
MetadataShow full item record
The purpose of this study is to determine the molar heat capacity (Cp) and molar excess enthalpy for 4-Ethylmorpholine, 2-(Isopropylamino)ethanol, 2-(Diisopropylamino)ethanol, 3-Dimethylamino-1-propanol(3-DEAP), and1-Dimethylamino-2-propanol (1-DEAP) in aqueous solutions by means of a C80 heat flow calorimeter over the entire range of mole fractions at different temperatures. The heat capacity measurements were carried out from 303.15K to 353.15K, whereas the excess enthalpies were measured at 298.15, 313.15, and 333.15K. An estimated uncertainty of 1% was found in the measured amount of the molar excess enthalpy as well as heat capacity. Among the five selected alkanolamines, 2-DPAE possessed the highest value in terms of molar heat capacity whereas 4-EMP had the lowest value. The values of heat capacities are dominated by –CH3. In this study, the experimental values of molar heat capacities were correlated using the Redlich-Kister Equation. Solution theory and group contribution modelslike NRTL (Non-random Two-liquid), UNIQUAC (Universal-Quasi chemical), and UNIFAC (Universal Functional activity coefficient) were used to model the experimental values of the molar excess enthalpies. Among the three above-mentioned models, the modified UNIFAC (Dortmund) was the most accurate for predicting and representing the values of molar excess enthalpies. The present study shows the value of molar excess enthalpies for the five selected amines are dominated by –CH3 group contribution and most importantly by the steric hindrance of the amine. The molar excess enthalpy increases in the negative side with more access of water molecules to the nitrogen atom. The negative value of molar excess enthalpies decreases as the temperature increases. This study has shown that the interaction between the hydrogen of water and amine group plays a significant role in the magnitude of the molar excess enthalpies of the five selected alkanolamines.