An Experimental and Theoretical Carbon Dioxide Capture-Based Investigation of Methyltrioctylammonium Trifluoromethanesulfonate Ionic Liquid

Abstract

An alarming elevation of anthropogenic carbon dioxide (CO₂), primarily responsible for global warming and its drastic effects on climatic conditions, must be challenged on a priority basis. Various types of absorbents capture as much CO₂ as possible to minimize the harsh effects of environmental and climatic changes. In this study, one such compound, methyltrioctylammonium trifluoromethanesulfonate $$ ionic liquid (IL), was analyzed experimentally and theoretically. The COSMO-RS, a type of conductor-like screening model, is an advanced fast method to predict the thermo-physical properties of IL. It depends upon unimolecular, statistical thermodynamics, molecular structure, and conformation, which provides the required information for estimating interactions in ILs. The COSMO-RS, not dependent on data, coefficients, or parameters, was used to calculate the sigma surface, profile, and potential. These parameters are crucial for predicting high-absorbing CO₂ materials, such as ILILs. Spectroscopic methods, such as Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), and carbon-13 NMR (¹³C NMR), verified the structure confirmation. In addition, spectrochemical characterization of the IL was performed using FTIR, NMR, ultraviolet–visible (UV–Vis) spectroscopy, and fluorescence. The thermal integrity of IL was measured by thermogravimetric–differential thermal analysis (TGA-DTA) over the temperature range of 323–773 K in an oxygen ambiance with a ramp rate of 283 K/min. Due to its high potential for gas absorption, as confirmed by COSMO-RS calculations, IL was investigated for CO₂ absorption and desorption studies at 298 K and 4.5 MPa. The maximum CO₂ absorption obtained was ~ 6.0 mmol/g, performed at similar experimental conditions. The high uptake of CO₂ might be due to fluorinated anions, as CO₂ has a high affinity for fluoroalkyl groups. According to a hysteresis-based classification, the hysteresis formation during CO₂ absorption and desorption follows type H3, indicating the presence of both microporous and mesoporous characteristics in the sample. A detailed study of the excess Gibbs energy of sorption and the activity coefficient of the IL indicates a strong sorption capacity under moderate conditions.