Preparation Of Sulfur-containing Ionic Liquid Adsorbents For Highly Selective Capture Of Sulfur Dioxide

The large amount of sulfur dioxide emission is one of the main reasons for the formation of acid rain and acid mist,which poses a huge threat to the environment and human health.The emission of sulfur dioxide mainly comes from the burning of coal fossil fuels.How to deal with the sulfur dioxide emission after combustion in a green and efficient way has become a research hotspot in the field of energy and environment.As a typical representative of green solvents,ionic liquids and deep eutectic solvents have the advantages of low volatility,high thermal stability,and structural designability,which provide a direction for the development of sulfur dioxide capture technologies.However,the exhaust gas from combustion contains carbon dioxide and sulfur dioxide.It is difficult for ionic liquids and deep eutectic solvents to capture and separate sulfur dioxide and carbon dioxide with high selectivity.Based on this,two types of sulfur-containing ionic liquid adsorbents were synthesized and used for the selective capture and separation of sulfur dioxide and carbon dioxide.The adsorption capacity,separation selectivity and cycle performance of sulfur dioxide at different temperatures and partial pressures were systematically investigated.At the same time,combined with nuclear magnetic resonance and infrared spectroscopy and other characterization methods,the mechanism of sulfur dioxide capture by sulfur-containing ionic liquid adsorbents was further studied.The main contents include:（1）Through a simple acid-base neutralization reaction,three bisulfate ionic liquids[N₂₂₂₂][HSO₄],[N₄₄₄₄][HSO₄],and[N₆₆₆₆][HSO₄]were prepared and used to capature and separate sulfur dioxide and carbon dioxide.The results show that the equilibrium capacity of[N₄₄₄₄][HSO₄]and[N₆₆₆₆][HSO₄]for sulfur dioxide is 2.4 mol·mol^-1(7.1 mmol·g^-1)and 2.6 mol·mol^-1(5.1 mmol·g^-1)at a temperature of 293 K and a pressure of 1.0 bar,the ideal separation selectivity between sulfur dioxide and carbon dioxide is as high as 887,and the―solid-liquid‖phase transition phenomenon of this type of ionic liquid adsorbed sulfur dioxide is observed.Nuclear magnetic resonance,infrared spectroscopy characterization and quantitative calculation results show that the intermolecular hydrogen bond formed by the anion bisulfate and sulfur dioxide reduces the melting point of the bisulfate ionic liquid,making the solid phase gradually liquefy into liquid phase,and finally achieving high selectivity and high capacity adsorption of sulfur dioxide.（2）Through a simple impregnation method to adjust the loading of diethyl sulfate ionic liquid（[TMEDA][DES]）,x[TMEDA][DES]@BN（x is the mass ratio of[TMEDA][DES]to BN,x=0.5,1.0,1.5,2.0）was prepared,and was used to capture and separate sulfur dioxide and carbon dioxide.The results show that the adsorption capacity of the composite absorbent 1.5[TMEDA][DES]@BN for sulfur dioxide reaches 7.6 mmol·g^-1 at a temperature of 293 K and a pressure of 1.0 bar,and the adsorption capacity of SO₂ is also as high as 3.0 mmol·g^-1 at a low pressure of 0.1 bar.Further,FT-IR,XRD,TG,SEM,TEM and other characterization results prove that the two-dimensional boron nitride nanosheets disperse the diethyl sulfate ionic liquid well,making the composite absorbent with a very low specific surface area.The capacity of adsorbing sulfur dioxide effectively inhibits the adsorption of carbon dioxide.The ideal separation selectivity of SO₂ and CO₂ at different partial pressures is as high as S（1/1）=109 and S（0.1/1）=431.Penetration experiment and circulation tests results show that the composite adsorbent also has excellent adsorption performance for 2000 ppm SO₂in simulated flue gas,and there is no significant decrease in adsorption performance for5 cycles.In summary,this article successfully prepared two types of sulfide ion-containing ionic liquid adsorbents to achieve high selective capture of sulfur dioxide from carbon dioxide,and has a good application prospect.