Design And Synthesis Of Ternary Amine-based Deep Eutectic Solvents And Study On Its Absorption Performance Of Sulfur Dioxide

With the development of society and the continuous improvement of people’s living standards,human demand for fossil fuels in industrial production and daily life has been gradually increasing as well.However,the burning of fossil fuels would produce a large amount of sulfur-containing gas,and the direct emission of sulfur-containing flue gas without any treatment would pollute the environment and would even cause great harm to people’s health.Therefore,achieving deep desulfurization of harmful gases is in a great of significance,as it would help for the protection of human being and nature.Traditional desulfurization methods for flue gas mainly include limestone method,gypsum method and ammonia–water absorption method.However,these traditional desulfurization methods have some obvious shortcomings such as strong volatility of the absorbent,poor cycle performance,and secondary pollution.These problems greatly limit their application in industrial production.Thus,in order to actively respond to the country’s policy of"green chemical industry",green,pollution-free and renewable deep eutectic solvents（DESs）were designed and used for the deep removal of sulfur dioxide（SO₂）.Firstly,a series of diamine ternary DESs were prepared by regulating the combination of amine substances and the carbon chain length of polyols to test their absorption ability of acidic SO₂ gas.The experimental result demonstrate that as the length of the polyol carbon chain increases,the absorption performance of SO₂decreases accordingly.For the absorption environment of 298.15 K,1.0 bar,and the molar ratio of diethylenetriamine（DETA）:acetamide（AA）:ethylene glycol（EG）equals to 1:1:2,the absorption of SO₂ reaches to 0.82 g SO₂/g DESs（g/g）.Diamine ternary DESs can be regenerated at least 6 times while on the basis of maintaining the highest absorption capacity（0.82 g/g）.According to Fourier-transform infrared spectroscopy（FT-IR）and proton nuclear magnetic resonance（¹H-NMR）,the mainly interaction between diamine ternary DESs and SO₂ is acid-base neutralization.The hydrogen bond formed by ethylene glycol（EG）,acetamide（AA）and SO₂ plays as an auxiliary absorption method.Choline chloride（ChCl）with lower alkalinity and lower toxicity was selected to replace AA to synthesize a series of choline ternary DESs.The relationship between temperature and physical properties（such as density,viscosity,thermal weight loss）,were studied systematically.Then,the required temperature range of the cycle experiment were evaluated through thermodynamics analysis.Under the conditions of298.15 K,1.0 bar,absorption of 0.87 g/g would be achieved for DESs with mole ratio of DETA:ChCl:EG=1:1:2.The absorption balance of choline ternary DESs can be achieved around 50 s.After the absorption,the choline ternary DESs can be regenerated,and it can be reused for at least 5 times,maintaining a high absorption capacity.FT-IR and ¹H-NMR characterizations prove that the nucleophilic Cl^-and SO₂ in the choline ternary DESs forms a strong charge interaction,which would help to promote absorption capacity.Less toxic and soluble imidazole with different alkyl chain length were selected to synthesize imidazole based ternary DESs.The relationship between the alkyl chain length of imidazole ternary DESs and absorption performance for SO₂ was investigated,and it concludes that for DESs with shorter the alkyl chain length,higher absorption capacity would be received.When the molar ratio of DETA:EG:[Emim]Cl equals to2:1:2,the absorption capacity can overtake to 1.02 g/g.The DESs can be regenerated for at least 6 times under 343.15 K,indicating its excellent regeneration performance.FT-IR,¹H-NMR,¹³C-NMR characterization and density functional theory（DFT）calculation indicate that the main reason for the higher absorption capacity of imidazole-based ternary DESs might be ascribed to the existence of multiple absorption sites.