Phase Equilibrium Measurements and Modeling for Alkanolamine Systems

CO2 capture was investigated in this work by measuring and modeling alkanolamine systems and by developing entirely new models for process design purposes. The Henry's law constant of CO2 in aqueous amine solutions is necessary when modeling CO2 capture processes. However, the physical solubility of CO2 in aqueous amine solutions cannot be measured directly and therefore it is derived from the Henry's law constant of N2O in the same solutions by employing the N2O - CO2 analogy. In this work a new model was developed for the Henry's law constant of N2O in aqueous binary and ternary amine solutions (monoethanolamine MEA, diethanolamine DEA, diisopropanolamine DIPA, N-methyldiethanolamine MDEA, and 2-amino-2-methyl-1-propanol AMP) as a function of temperature and amine concentration. The parameters of the new expression were fitted to 992 data points up to 393 K. The new model was also compared with the models found in the literature. The model developed in this work describes the experimental data better than the models found in the literature.Heat stable salts are formed in CO2 capture processes when oxygen is present in a system. Heat stable salts have not been studied much in the literature and thus this work was extended to cover amine degradation products. 2-hydroxyethylammonium acetate (2-HEAA), which is a heat stable salt but also a distillable protic ionic liquid, was prepared from MEA and acetic acid (HAc) and it was purified by distilling under vacuum. Vapor-liquid equilibrium was measured with a static total pressure apparatus. Solid-liquid equilibrium and the melting point of pure compounds were measured either with a visual method or with a Differential Scanning Calorimeter. Density was measured with a DMA HP connected to a DMA 5000 M densimeter. In addition, vapor pressure was measured using a Vigreaux type distillation column. The research of 2-HEAA indicated that the effect of heat stable salts on phase equilibria can be taken into consideration when modeling CO2 capture processes. A new model was also developed for the density of aqueous DIPA solution as a function of both temperature and composition since no general model for aqueous DIPA solution was found in the literature. In addition, vapor-liquid equilibrium data of thiol + hydrocarbon systems were modeled with the NRTL, Wilson and UNIQUAC activity coefficient models. Also predictive UNIFAC and COSMO SAC models were used.