Screening of ionic liquids for CO2 capture using the COSMO-SAC model

In this work, we develop a simple method that can be used to screen for the ionic liquid (IL) candidates for use in various CO2 capture processes. In particular, Henry׳s law constant, an important physical quantify determining the capacity and selectivity of CO2 absorption, is determined from the product of infinite dilution activity coefficient (IDAC) of a gas molecule in an IL and the fugacity of the gas in a hypothetical liquid state. The IDAC is calculated using the predictive COSMO-SAC activity coefficient model, where the interaction between the gas and the IL are determined through the screening charges on the molecular surfaces obtained from quantum mechanical solvation calculations. We have developed a simple model for the fugacity of 4 gas molecules, including CO2, CH4, N2 and H2, and examined the solubility, selectivity, and the temperature dependency of solubility. The predicted results for Henry׳s law constant of CO2 in ILs are in good agreement with experimental data (53 data points) over a wide range of temperatures (from 283 K to 303 K), with an average absolute relative deviation (ARD) of 17%. This method is used to screen for the best IL candidates for CO2 capture from a set of 2080 ILs combined from 65 cations and 32 anions. The computational time used for screening for this set of IL is less than 3 min on a personal computer. Our results show that the COSMO-SAC model can be a powerful method for the design and screening of new ILs as a medium for CO2 capture.