Evaluation of the potential of phosphonium-based ionic liquids for co2 absortion through soft-SAFT

RODRIGUEZ REARTES, SABRINA BELÉN; OUEDGHIRI BEN OTMANE, FÁTIMA; LLOVELL, FÈLIX

Valladolid

Conferencia; 2nd Greenering International Conference; 2023

BioEcoUVA - COST Action 18224 GREENERING

Even though amines (i.e., MEA and MDEA) are commonly used for CO2 absorption from flue gas streams, it is well known that they evaporate and degrade during process operation, with environmental and economic consequences. In the search for alternative solvents, the capture of CO2 with Ionic Liquids (ILs) is a technology that has gained a lot of interest mainly due to their low vapor pressure and the possibility to “design” them by combining different cations and anions for each particular case, considering the flue stream composition and specific conditions. Particularly, some phosphonium cation/anion combinations have been studied in literature with promising results.Nonetheless, restricted and limited laboratory data are available and a complete characterization of these compounds is still required to select the most appropriate CO2 absorber.In this work, the potential of phosphonium based ILs as CO2 absorbers at different operating conditions for industrial application is assessed through the use of an accurate statistical mechanics-based equation of state (EoS). Particularly, the soft-Statistical Association Fluid Theory (soft-SAFT) is found to provide a suitable description of ILs and their behavior in mixtures, and will be applied here, in combination with quantum-chemical approaches, such as Turbomole-COSMO, to obtain the charge distribution profiles and describe the key interactions in these compounds. The work departs from the trihexyltetradecylphosphonium cation [P66614]+, which is combined with different anions. The resulting ILs are characterized by a complete description of their pressure-temperature-density diagrams, and derivative properties. Transport properties, such as the viscosity, are also modeled using the Free-Volume theory coupled to soft-SAFT EoS. Then, CO2 absorption isotherms are described and compared to experimental data when available. The CO2 absorption capacity of the different ILs, considering both diluted and concentrated mixtures in CO2, is assessed through the calculation of Henry’s law constants and the solvation enthalpies and entropies at different conditions, proposing a preliminary list of potential compounds for different types of flue gases.