Synthesis And Performance Of Functionalized Dicationic Ionic Liquids For Sulfur Dioxide Absorption

Sulfur dioxide（SO₂）released from fossil fuel combustion has serious harm to the ecological environment and human health,and the efficient capture and comprehensive utilization of sulfur dioxide has drawn the widespread attention.Ionic liquids（ILs）have outstanding physicochemical properties and excellent gas solubility,which make they are ideal alternatives to traditional flue gas desulfurizers in the future.In view of the shortcomings of low SO₂ absorption capacity,poor cycle stability and high desorption energy consumption of SO₂ capture by ILs,four kinds of polyethylene glycol chain-linked dicationic ionic liquids（DILs）and a conventional DILs with high thermal stability,high absorption efficiency and low energy consumption were prepared for highly efficient capture of SO₂ capture,and which were characterized by Fourier transform infrared（FT-IR）spectroscopy and nuclear magnetic resonance（NMR）spectroscopy.The physicochemical properties of polyethylene glycol（PEG）-linked DILs with thiocyanate anion,such as density,viscosity,conductivity and decomposition temperature,etc.,were measured,and the effects of temperatures and ionic group structures on their physicochemical properties were investigated.The effects of different conditions,such as ionic liquid structure,absorption temperature,SO₂ partial pressure,water content of ILs and oxidation environment on the SO₂absorption performance by the five DILs were also systematically investigated.The results showed that the decomposition temperatures of the as-prepared DILs were all above 255oC,the absorption rate was fast and the absorption capacities were much higher than those of monocationic ILs,especially,[E₃Eim₂][Cl]₂had the absorption capacity up to 6.779 mol SO₂/mol IL at 20°C and 1 bar and 3.298 mol SO₂/mol IL at 20℃and 0.1 bar,respectively.The mechanism of SO₂absorption by DILs was also studied with FT-IR and NMR,which revealed there just existed physical interaction between DILs and SO₂.PEG-linked DILs have a high selectivity between SO₂ and CO₂,good antioxidant stability and cyclic absorption/desorption performance.Overall,the DILs used in this study have good desulfurization performance,which can be used for reference in the research and selection of sulfur dioxide alternative absorbent.