Study on hydroxylammonium-based ionic liquids. II. Computational analysis of CO2 absorption.

In the previous work of this series, we reported a wide experimental and computational analysis of the properties of hydroxylammonium-based ionic liquids. This family of ionic liquids shows very favorable economical, technological, and environmental properties in comparison with other ionic liquid types. We report in this work a computational study, using quantum chemistry and molecular dynamics methods, to analyze the absorption of carbon dioxide by hydroxylammonium ionic liquids. The selected compounds were 2-hydroxyethyl-trimethylammonium L-(+)-lactate and tris(2-hydroxyethyl)methylammonium methylsulfate. The main objective of this work is to study and analyze CO(2) absorption from the molecular point of view, therefore contributing to the knowledge and advancement on the absorption ability of ionic liquids. The computational study would lead to a deeper knowledge of factors controlling CO(2) absorption for this ionic liquid family in comparison with available information for other relevant types. The results were analyzed considering the effects of absorbed gas on the ionic liquid structuring from a molecular level viewpoint, interionic interactions, diffusion of the involved compounds, and interaction of CO(2) with anions and cations. The reported results show a strong effect of the presence of hydroxyl groups in the involved cations and anions through the interaction with CO(2) molecules, along with the effects rising from the size of cations on the fluid structure.