Quantitative analysis of the interaction of ammonia with 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ionic liquid. Understanding the volumetric and transport properties of their mixtures

We used near infrared spectroscopy (NIR) and nuclear magnetic resonance, H-1 NMR and F-19 NMR to analyze the structural changes of 1-(2-hydroxyethyl)-3-methylimidazolium tetra fluoroborate ionic liquid (IL) when it interacted with ammonia. The NIR spectra of the ionic liquid recorded after it had interacted with ammonia gas at different pressures (between 1 and 6 bar) are resolved using multivariate curve resolution (MCR-ALS) to quantitatively evaluate the interaction. The analysis was done at 20 degrees C, 40 degrees C and 60 degrees C. The results show that the interaction of the ammonia with the ionic liquid is governed by the temperature. The interaction preferentially occurs through the hydroxyl group in the cation of the ionic liquid. The interaction through the anion is favored only at lower temperatures. The MCR-ALS results have shown that at 20 degrees C, when the ammonia mole fraction in the mixture is higher than 0.564, ammonia molecules not associated with the ions are also present. The diffusion coefficients of the ions in NH3 + IL mixtures prepared at 2.5 bar and 6.0 bar and in neat IL have been calculated from pulsed gradient spin echo (PGSE)-NMR experiments. The differences between them are discussed from the perspective of the quantitative analysis of the interaction between the NH3 and the IL The results discussed throughout the study shed light on the trends of the excess molar volume and viscosity data reported in the literature for the mixture of ammonia and the ionic liquid studied. (C) 2020 Elsevier B.V. All rights reserved.