Heat Capacities Of Aqueous Mixtures Research Articles

Physical properties of aqueous mixtures of N-methyldiethanolamine (MDEA) and ionic liquids

In the present study, experiments have been conducted to measure the surface tension and heat capacity of aqueous mixtures of N-methyldiethanolamine (MDEA) and ionic liquids (ILs) at atmospheric pressure. Two types of ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4] and 1-butyl-3-methyl-imidazolium dicyanamide [bmim][DCA]) were used in these experiments. The surface tension was found to decrease with increasing temperature and ionic liquid concentration. Furthermore, the heat capacity of the mixtures increases with decreasing ionic-liquid concentration and increasing temperature. Linear equations were used to correlate the measured surface tension values, quadratic equations were applied to correlate the heat capacity at different compositions and temperatures.

Liquid heat capacity of the solvent system (piperazine + n-methyldiethanolamine + water)

A new set of values for the heat capacity of aqueous mixtures of piperazine (PZ) and n-methyldiethanolamine (MDEA) at different concentrations and temperatures are reported in this paper. The differential scanning calorimetry technique was used to measure the property over the range T = 303.2 K to T = 353.2 K for mixtures containing 0.60 to 0.90 mole fraction water with 15 different concentrations of the system (PZ + MDEA + H 2O). Heat capacity for four concentrations of the binary system (PZ + MDEA) was also measured. A Redlich–Kister-type equation was adopted to estimate the excess molar heat capacity, which was used to predict the value of the molar heat capacity at a particular concentration and temperature, which would then be compared against the measured value. A total of 165 data points fit into the model resulted in a low overall average absolute deviation of 4.6% and 0.3% for the excess molar heat capacity and molar heat capacity, respectively. Thus, the results presented here are of acceptable accuracy for use in engineering process design.

Heat capacities of aqueous solutions containing diethanolamine and N-methyldiethanolamine

In this work, we present new results for heat capacities of aqueous mixtures of diethanolamine with N-methyldiethanolamine over the temperature range (303.2 to 353.2) K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the (DEA + MDEA + water) systems were investigated. For the binary system, (DEA + MDEA), heat capacities of nine concentrations were also measured. A Redlich–Kister-type equation for representing excess molar heat capacity was applied to correlate the measured C p of aqueous alkanolamine solutions. For a total of 176 data points for the (DEA + MDEA + water) system, the overall average absolute percentage deviation of the calculations are 16.5% and 0.2% for the excess molar heat capacity and the molar heat capacity, respectively. The heat capacities presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.

Liquid Heat Capacity of Aqueous Solutions Containing Diethanolamine and 2-Piperidineethanol

Liquid heat capacities of aqueous mixtures of diethanolamine (DEA) with 2-piperidineethanol (2-PE) were measured over the temperature range of 303.2 to 353.2 K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the DEA + 2-PE + water systems were studied. For binary systems, heat capacities of the nine concentrations of DEA + 2-PE were also studied. A Redlich–Kister-type equation for representing excess molar heat capacity was applied to correlate the measured Cp of aqueous alkanolamine solutions. For a total of 176 data points for the DEA + 2-PE + water system, the overall average absolute percent deviation of the calculations were 10.6% and 0.1% for the excess molar heat capacity and the molar heat capacity, respectively. The heat capacities of aqueous mixtures of DEA with 2-PE presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.

Liquid heat capacity of aqueous sulfolane + 2-amino-2-methyl-1-propanol solutions

Heat capacities of aqueous solutions of sulfolane with 2-amino-2-methyl-1-propanol (AMP) were measured over the temperature range from 303.15 to 353.15 K with a differential scanning calorimeter. Twelve solutions of sulfolane + AMP + water that cover the mole fractions of water from 0.6 to 0.8 were studied. The liquid heat capacities of sulfolane alone and of binary mixtures such as sulfolane + water and sulfolane + AMP were also studied. The heat capacities of sulfolane and sulfolane + water were found to be in good agreement with those values reported in the literature. A Redlich-Kister type equation was applied to represent the composition dependence of the heat capacities of binary and ternary systems. For 132 data points of sulfolane + AMP + water, the fitted results of heat capacity calculations (overall average absolute percentage deviation (AAD%)) were 0.3 and 7.7% for the molar heat capacity and the excess molar heat capacity, respectively. The heat capacities of aqueous mixtures of sulfolane with AMP presented in this study can be used to estimate the head load of absorbents in acid gas capture process when using sulfolane + AMP + water as the absorbent.

Heat capacity of aqueous mixtures of diethanolamine with 2-amino-2-methyl-l-propanol

Heat capacities of aqueous mixtures of diethanolamine (DEA) with 2-amino-2-methyl-1-propanol (AMP) were measured over the temperature from 30 to 80 °C with a differential scanning calorimeter (DSC). For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the DEA + AMP + water systems were studied. The binary system DEA + AMP with nine various concentrations were also studied. The heat capacities of aqueous mixtures of DEA with AMP presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.

Heat capacity of aqueous mixtures of monoethanolamine with 2-piperidineethanol

The binary system studied was monoethanolamine(MEA)+2-piperidineethanol (2-PE). Heat capacities of aqueous mixtures of MEA with 2-PE were measured from 30 to 80 °C with a differential scanning calorimeter (DSC). For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the MEA+2-PE+water systems were studied. An excess molar heat capacity expression, using the Redlich–Kister equation for the composition dependence, is used to represent the measured C p of alkanolamine aqueous solutions. The results of heat capacity calculation (overall average absolute percentage deviation) for a total of 176 data points for MEA+2-PE+water system are 0.2 and 7.4% for molar heat capacity and excess molar heat capacity, respectively. The heat capacity values of aqueous mixtures of MEA with 2-PE presented in this study are, in general, of sufficient accuracy for most engineering-design calculations when using MEA+2-PE+water as absorbent for acid gas removal process.

Heat Capacity of Aqueous Mixtures of Monoethanolamine with 2-Amino-2-methyl-l-propanol

Heat capacities of aqueous mixtures of monoethanolamine with 2-amino-2-methyl-l-propanol were measured from 30 °C to 80 °C with a differential scanning calorimeter (DSC). The heat capacities of 2-amino-2-methyl-l-propanol, 2-amino-2-methyl-l-propanol + water, and monoethanolamine + 2-amino-2-methyl-l-propanol were also studied. Eight binary systems and sixteen ternary systems were studied. The estimated uncertainty of the measured heat capacities is ±2%. An excess molar heat capacity expression using the Redlich−Kister equation for the composition dependence is used to represent the measured Cp of aqueous alkanolamine solutions. The results (AAD %, the average absolute percentage deviation) for the calculation of the excess molar heat capacities are 3.6% and 13.2% for the binary and ternary systems, respectively. The heat capacities of aqueous mixtures of monoethanolamine with 2-amino-2-methyl-l-propanol presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.

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 Cp 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 prese...

Thermodynamic properties of aqueous organic mixtures near the critical demixing: Cases of 2,6-dimethylpyridine and of 2-isobutoxyethanol

Phase diagrams, volumes and heat capacities of aqueous mixtures of 2,6-dimethylpyridine (2,6-L) and 2-isobutoxyethanol (iBE) and activities of 2,6-L in aqueous mixtures were measured in the monophasic region near the lower critical solution temperature (LCST). With 2,6-L some measurement were also made just above the LCST. From the temperature dependence of these data, partial molar relative enthalpies (2,6-L), expansibilities and the temperature derivative of heat capacities were calculated and show that iBE undergoes a microphase transition at low concentration which is not related to the phase separation. On the other hand, the properties of 2,6-L in the water-rich region at temperatures well below the LCST indicates that this solute has only a slight tendency to associate. The heat capacities of 2,6-L show an important increase near the LCST. Such changes are not observed for iBE and other alkoxyethanols and amines since these systems already exist in the form of microphases; the partial molar properties of iBE near the LCST are nearly equal to the molar values of the pure liquid, and the changes in thermodynamic properties corresponding to the macroscopic phase transition, are therefore too small to be measured by the present techniques.

A calorimetric investigation of interactions in aqueous solutions of poly(oxyethylene), 2. Determination of excess heat capacities and application of association theory

AbstractExcess heat capacities are given as functions of composition and temperature for non‐dilute aqueous solutions of poly(oxyethylene) and its oligomeric models, i. e. from the glycol monomer to tetramer and dimethyl ethers of these compounds. A theoretical model based on the concept of association equilibria was used to predict the excess heat capacities of aqueous mixtures of dimethyl ethers at 298K and 350K. Numerical values of parameters of the model were obtained by treatment of the heats of mixing reported in the first part of this study. It was sufficient to adjust two parameters of self‐association of water, and for each system also the parameter characterizing hydration of ether groups in oligomers. The agreement between theory and experiment was very good for both enthalpy and heat‐capacity data, with the exception of the concentration range rich in water, where the interaction scheme is probably more complicated.

Heat capacities and volumes in aqueous polymer and polymer–surfactant solutions

The apparent molar volumes and heat capacities of aqueous mixtures of neutral polymers and ionic surfactants were measured at 25 °C. The polymers chosen were poly(vinylpyrrolidone) (PVP) and poly(ethyleneoxide) (PEO) and the surfactants were the C8, C10, and C12 homologs of sodium alkylsulfates and the C10, C12, and C16 homologs of alkyltrimethylammonium bromides. The polymer–surfactant interactions depend on the nature of both components and on the chain length of the surfactant. The thermodynamic properties of the cationic surfactants are essentially the same in the absence and presence of polymer indicating little surfactant–polymer interaction. On the other hand, the thermodynamic properties of anionic surfactants are shifted, upon the addition of polymers, in the direction of enhanced hydrophobic association. The effect increases with the surfactant chain length and with the polymer concentration. The effect is larger with PVP than with PEO.