Study On The Properties Of Ionic Liquids And The Mechanism Of Their Interaction With SO₂

As a new type of green solvent, ionic liquid attracts more and moreattention due to its unique properties, and shows great potential in theapplication of SO₂absorption. However, there are still two main problems:(1) most works focus on the ionic liquids that have chemical absorptioninteraction with SO₂. Chemical absorption has strong interaction betweenionic liquids and SO₂, but requires strict regeneration conditions for ionicliquids;(2) ionic liquids have large viscosity values. Therefore, I proposethe ionic liquids with multiple physical absorption points for absorptionof SO₂. The increase of physical absorption points can greatly improvethe absorption ability of ionic liquids, and also improve the strictdesorption conditions for chemical absorption. As absorbents, ionicliquids have the common problem of large viscosity. However, theviscosity value of ionic liquids can be recuced sharply by addingmolecular solvent. In this work, experiments and MD simulations arecombined to study the properties of ionic liquids with multiple physicalabsorption points for SO₂and their binary mixtures with molecularsolvents. Their characteristics and mechanism of absorption for SO₂, and the relation between micro-structures and macro-properties are alsoinvestigated.Therefore, at first, the density and surface tension of pure ionicliquids [bmim][L-lactate] which has3physical absorption points for SO₂,and its binary mixture with molecular solvents (methanol, ethanol,1-butanol, and H₂O) are measured at different temperatures andatmosphere pressure. The volumetric and surface properties are alsoinvestigated for ionic liquid [ocpy][NO₃] and its binary mixtures withalcohol (methanol, ethanol and1-butanol) to enrich the property data ofbinary mixture of ionic liquid and molecular solvent, and guide theirfurther applications.Then the UA force field for [L-lactate]-anion which was built in ourprevious work is improved. MD simulations are performed for a series ofimidazolium-based ionic liquids ([dmim]⁺,[emim]⁺,[bmim]⁺, and[hmim]⁺) with [L-lactate]-anion and binary mixture of [bmim][L-lactate]+molecular solvent. Their properties and micro-structures are studied.According to simulation results, the electrostatic interactions in ionicliquids dominate, and decrease with the increase of C atoms of alkyl incation. Strong interactions exist between cation and anion of ionic liquid,which is the cause of low vapor pressure and high viscosity. In the binarymixtures, solvent molecules prefer to gather around anions of ionic liquid,and there is no strong interaction between cation and solvent molecules. The absorption and desorption abilities of pure ionic liquids[bmim][BF₄],[emim][L-lactate],[bmim][L-lactate], and binary mixture[bmim][L-lactate]+H₂O for SO₂are discussed by experiments, QMcalculations, and MD simulations. Results indicate ionic liquid[bmim][L-lactate] shows the most excellent absorption ability for SO₂,and the absorption mechanism of ionic liquids with multiple physicalabsorption points for SO₂is also revealed.In this work, experiments, QM calculations, and MD simulations arecombined to investigate the properties of ionic liquids and the mechanismof their interaction with SO₂from micro to macro level. The data ofproperties of ionic liquids are enriched. The theoretical basis for theapplications of ionic liquids, especially as the SO₂adsorbent, is provided.