Heat of Dissolution Measurements for CO2 in Mixed Alkanolamine Solvents

Abstract

The main objective of this research was to measure heat of dissolution of CO 2 in carefully mixed alkanolamine solvent systems, and provide such directly measured data that might be used for efficient design of CO 2 capture process, and for better understanding of the thermodynamics of CO 2 -Alkanolamine systems. An experimental set-up has been designed using the Isothermal Micro Calorimeter for measuring the solubilities and enthalpies of CO 2 in mixed solvents made of MEA, MDEA, PZ, KF and water. All the measurements were done at temperatures 15, 40, and 75 ºC by maintaining a constant pressure of 100 psig. A detailed study has been done on the variation of solubilities and enthalpies over a wide range of temperatures, pressures and concentrations, by extracting the information from the literature. 3 EXECUTIVE SUMMARYThe main objective of this project was to measure heat of dissolution of CO 2 in carefully selected mixed alkanolamine solvent systems, and provide such directly measured data that might be used for efficient design of CO 2 capture processes, or for better understanding of thermodynamics of CO 2 -alkanolamine systems. Carbon dioxide is one of the major greenhouse gases, and the need for stabilization of its composition in earth's atmosphere is vital for the future of mankind. Although technologies are available for capture and storage of CO 2 , these technologies are far too expensive for economical commercialization. Reduction of cost would require research for refinement of the technology. For more economical CO 2 capture and regeneration, there is a need for development of more efficient solvent systems. In this project we have extended the thermodynamic database by measuring heat of solution data of CO 2 in mixed solvents made of MEA (monoethanolamine), MDEA (methyldiethanolamine), piperazine, and water. Mixed solvents of different compositions were selected and in each case data were measured at temperatures 15, 40 and 80C and a fixed pressure of 100 psig. Fairly good comparisons were observed for solubility and enthalpy data when compared with the available literature data.An apparatus was designed and built that uses an isothermal micro-calorimeter (made by Calorimetry Sciences Corp) to measure the heat of solution, and allows measurement of heat of solution as a function of carbon dioxide concentration. The solubility of CO 2 in the solvent can be estimated from the saturation point on the heat curve. In addition to aqueous MEA, MDEA, piperazine and their mixtures, data were also measured using aqueous MDEA solvent with potassium fluoride (KF.2H 2 O) as an additive. The goal of these measurements was to investigate whether potassium fluoride enhances the solvent properties of MDEA. Results did not show any obvious improvements. The data showed no appreciable improvements in solvent properties as a result of adding potassium fluoride.A thorough literature search was conducted for solubilites and enthalpies. More data are available for solubilites than for enthalpies. All the enthalp...