Calorimetric measurement of heat capacity and heat of mixing for aqueous organic solvents of importance in gas sweetening

Natural and refinery gas streams usually contain gases such as carbon dioxide and hydrogen sulphide that must be removed. Removal of these components is crucial for the marketability of the gas. The existing methods of removing these gases are by physical, chemical, or mixed (hybrid) solvent systems. In order to understand the molecular behavior, it is necessary to have a better understanding of the solute-solvent interactions. The measurements of heat capacity and heat of mixing are also important for the design of absorbers and regenerators. To achieve this, analysis of the heat capacity and heat of mixing data of four widely used aqueous physical solvents were studied in terms of excess molar heat capacity and excess enthalpy. The first aspect of this research work is the experimental determination of heat capacity for four physical solvents systems: Triethylene glycol dimethyl ether (TEGDME), 1-Methyl-2-pyrrolidinone (NMP), 4-Formylmorpholine (NFM), and Tetramethylene Sulfone (Sulfolane) aqueous solutions from 30°C to 80°C. The mole fractions cover the whole range of concentration. An excess molar heat capacity expression using the Redlich-Kister (RK) equation for the composition dependence is used to represent the derived excess Cp of the systems. For a total of close to 5000 data points, fitting by RK equation gives an overall average absolute deviation of 0.2% in the case of the excess molar heat capacity. The heat capacities presented in this study are, in general, of sufficient accuracy for most engineering-design calculations. The second aspect of this research work is, the experimental determination of heat of mixing H E for the previously mentioned aqueous systems. The regression by the Non-Random Two-Liquid (NRTL) model gives an overall absolute average deviation of 5%. The results show that water has the weakest interaction with Sulfolane followed by NFM but forms complexes in the case of TEGDME and NMP.