Heat Capacity of Aqueous Mixtures of Monoethanolamine with N-Methyldiethanolamine

Heat capacities of aqueous mixtures of monoethanolamine with N -methyldiethanolamine were measured from 30 to 80 °C with a differential scanning calorimeter (DSC). The binary systems studied were N -methyldiethanolamine + water and monoethanolamine + N -methyldiethanolamine. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the monoethanolamine + N -methyldiethanolamine + water systems were studied. The estimated uncertainty of the measured heat capacities is ±2% including the effect of up to 1% impurities in a substance. An excess molar heat capacity expression using the Redlich−Kister equation for the composition dependence is used to represent the measured C p of aqueous alkanolamine solutions. The overall average absolute percentage deviation of the calculation of the molar heat capacity for a total of 176 data points for the monoethanolamine + N -methyldiethanolamine + water system is 0.5%. The heat capacities of aqueous mixtures of monoethanolamine with N -methyldiethanolamine presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.