Research On SO₂ Capture By New Deep Eutectic Solvents

Sulfur dioxide?SO₂?,which is one of the most important air pollutions,causes serious damage tothe environment and human health,so SO₂ emissions must be strictly controlled.Industrial flue gas desulfurization technologies often have problems such as inefficiency,waste water,and unwanted by-products of calcium sulfate.In order to overcome these problems,ionic liquids with low vapor pressure,high thermal stability,and adjustable characteristics have been used as a new method to capture SO₂ in recent years,but the current complex preparation method of ionic liquids,the expensive price restricts its application in SO₂ capture.Therefore,deep eutectic solvents?DESs?,which have the advantage of ionic liquid,become a new and green SO₂ absorbent because of its simple and inexpensive preparation compared to ionic liquid.As an emerging field,the current deep eutectic solvents mostly capture SO₂ through physical processes,which is not conducive to the capture of low concentration of SO₂ in the flue gas.Therefore,it is very important to design and synthesize new deep eutectic solvents with high efficiency to capture SO₂.Based on the information above,eight functional deep eutectic solvents were designed andprepared in this study.Their basic properties,such as melting point,density,viscosity and thermal stability were determined.The solubility of SO₂ in the eight deep eutectic solvents was investigated at different temperatures and SO₂ concentrations.Regeneration experiments of deep eutectic solvents were also conducted.Moreover,the absorption mechanism of SO₂ in the eight deep eutectic solvents was discussed based on ¹H NMR,¹³C NMR and FTIR.Details are as follows:1.Based on the strategy that the absorption capacity of deep eutectic solvents for SO₂ can be promoted through introducing amino,carbonyl group and so on,a variety of deep eutectic solvents were prepared based on some organic substances containing the above functional groups as hydrogen bond donor,and tetrabutylammonium bromide as a hydrogen bond acceptor.2.The absorption properties of these prepared deep eutectic solvents for SO₂ were investigated.The influence of the structure of the hydrogen bond donor and the type of functional group on the SO₂capture efficiency was studied.It was found that in the absence of negative ions,such as oxygen anion,nitrogen anion,the substance containing an amino group and a nitrogen atom with a lone pair of electrons can be used as a hydrogen bond donor,which is helpful for designing a deep eutectic solvent having a higher trapping ability for SO₂.3.Based on the above studies,imidazole and its four analogues were chosen as hydrogen bond donors and tetrabutylammonium bromide as a hydrogen bond acceptor,five other deep eutectic solvents were prepared.Physical properties of these deep eutectic solvents,such as,melting point,density and viscosity were investigated through multiple experiments.Furthermore,the effect of temperature and pressure on the capture of SO₂ was also investigated.Results show that these kinds of deep eutectic solvents have high capture capacity for SO₂ under low concentration.Besides,desorption and cycle performance of these deep eutectic solvents were also improved.Among them,tetrabutylammonium bromide:4-methylimidazole?1:9?could absorb 1.33g SO₂/g DES at 293.15K and 1.0 atm,which is much higher than other deep eutectic solvents reported up to date under same conditions.4.The absorption mechanism of SO₂ by deep eutectic solvents was studied through multiple methods such as ¹H NMR,¹³C NMR and FTIR.It was indicated that highly efficient capture of deep eutectic solvents for SO₂ were mainly affected by acid–base interaction between SO₂ and amino group on the hydrogen bond donor.The above research conclusions provide theoretical support and basic data support for the preparation of a deep eutectic solvent that efficiently captures SO₂,and provide a new way for controlling and reducing the source of SO₂ pollution.