CO2-binding organic liquids for high pressure CO2 absorption: Statistical mixture design approach and thermodynamic modeling of CO2 solubility using LJ-Global TPT2 EoS

Abstract

CO2-binding organic liquids (CO2-BOLs) or switchable ionic liquids (SILs) are switchable polarity solvents (SPS) that can be used as non-aqueous, energy efficient solvents for CO2 absorption. In this study, the three-component CO2-BOLs comprised of a single-component CO2-BOL (tertiary alkanolamine) and a two-component CO2-BOL (superbase/alcohol) are introduced. The most efficient equimolar combination of superbase (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)), alcohol (methanol, n-butanol, sec-butanol, tert-butanol and hexanol) and amine (Dimethylethanolamine (DMEA), Diethylethanolamine (DEEA) and N-methyldiethanolamine (MDEA)) are obtained using screening experiments considering CO2 loading (αeq) and absorption rate (αR). The mixture design technique is employed for modeling of αeq and αR as a function of mole fraction of components at 35.0 °C and initial pressure of 25.0 bar. The DBU/DMEA/n-butanol CO2-BOL represented the best performance for CO2 uptake. The experimental CO2 solubility data in DBU/n-butanol, DBU/DMEA and DBU/DMEA/n-butanol BOLs were obtained in the temperature range of 25.0–45.0 °C and the pressure range of 1.0–45.0 bar. The DBU mole fraction was selected to be 0.1 and 0.2 while the molar ratio of DMEA to n-butanol was kept constant at 2 in the three-component BOL. The simultaneous vapor–liquid and chemical equilibrium calculation algorithm using LJ-Global TPT2 equation of state was used for the thermodynamic modeling of CO2 solubility in BOLs. The average absolute relative deviation error (AAD%) for the calculation of total pressure of DBU/n-butanol, DBU/DMEA and DBU/DMEA/n-butanol BOLs were obtained to be 8.5%, 5.8% and 8.6%, respectively.