Experimental measurement and assessment of equilibrium behaviour for phase change solvents used in CO2 capture

Phase change solvents are receiving increased attention in the effort to significantly reduce regeneration energy requirements in post combustion CO2 capture processes with chemical absorption. In this study, the phase behavior of various phase change, aqueous amine solutions, was experimentally investigated. A new experimental apparatus was developed and evaluated by determining the CO2 solubility in aqueous monoethanolamine (MEA) solutions at 40, 60 and 80 °C. Subsequently, new experimental data were obtained for aqueous solutions containing N,N-dimethylcyclohexylamine (DMCA), methylcyclohexylamine (MCA) and 2-amino-2-methyl-1-propanol (AMP) at 40, 60 and 90 °C that exhibit phase change behavior. It was observed that the investigated solutions present vapor – liquid equilibrium (VLE) at 40 °C and vapor–liquid-liquid equilibrium (VLLE) at 60 and 90 °C for CO2 partial pressures up to approximately 70 kPa. In addition, screening experiments were performed using sulfolane, which has been previously used for gas sweeting applications, instead of AMP in the DMCA-MCA mixture. However, such system presents relatively low CO2 solubility, compared to the aforementioned (DMCA-MCA-AMP) system and aqueous MEA solutions. Finally, additional screening experiments were performed for two aqueous DMCA – 3-methylaminopropylamine (MAPA) amine solutions at different concentrations.