Synthesis Of Nitrogen-containing Heterocyclic Binary Deep Eutectic Solvent Absorbents And Explore On Its Sulfur Dioxide Capture Performance

With the continuous development of society and the acceleration of global industrialization,the consumption of fossil energy such as coal,oil and natural gas is increasing,and the sulfides contained in fossil fuel are converted into sulfur dioxide（SO₂）at the same time as fossil fuel is burned,so that the content of SO₂ in the atmosphere is constantly increasing.Excessive SO₂ in the atmosphere will not only cause great harm to animals and plants,but also cause different degrees of pollution to the atmosphere,water and soil.In addition,it will seriously endanger the quality of human life,health and greatly hinder the sustainable development of the environment.Air pollution has the characteristics of rapid diffusion and wide scope of pollution,so effectively curbing and eradicating air pollution are important parts of environmental pollution control.With the improvement of global environmental protection awareness,higher requirements are put forward by countries around the world for flue gas desulfurization technology（FGD）,and the selection of an absorbent with high efficiency and absorption performance is the key element of this technology.Traditional absorbents include limestone/gypsum,organic amine solutions,and so on.Traditional solvents have disadvantages such as high toxicity and easy corrosion of equipment.Compared with traditional absorbents,ionic liquids（ILs）improve gas absorption performance,but they have the disadvantages such as difficult purification,high cost and long reaction cycle,and these advantages in gas absorption are not significant.As ILs-like materials,deep eutectic solvents（DESs）have already overcome some limitations of ILs,and DESs not only have similar physical and chemical properties to ILs,but also have the advantages like low cost,no purification,short synthesis cycle and environmental friendliness.Therefore,DESs are considered to be a promising SO₂ absorbents.In this work,a series of binary nitrogen-containing heterocyclic DESs absorbents were prepared,and the SO₂ absorption performance of the absorbents was systematically explored:（1）A series of pyrazole-based DESs were prepared with chlorinated 1-ethyl-3-methylimidazole（Emim Cl）as hydrogen bond acceptors（HBAs）and pyrazole or pyrazole derivatives as hydrogen bond donors（HBDs）.Experiments have shown that the optimal molar ratio of Emim Cl:Pyz is 7:1;at 293.15 K and 1.0 bar,the SO₂absorption capacity of Emim Cl:Pyz（7:1）can reach 1.466 g/g,under the same pressure,when the temperature rises to 298.15 K,the absorption capacity is 1.233 g/g,and the absorption equilibrium can be reached within 60 s;and there is still a good absorption capacity after 40 absorption-desorption times.The characteristics of DESs before and after SO₂ absorption by FT-IR and ¹H NMR showed that the absorption of SO₂ gas by pyrazole-based DESs was mainly based on Lewis acid-base action,supplemented by the strong charge interaction between chloride ions and SO₂ and the physical absorption between DESs and SO₂.（2）In order to further explore the absorption performance close to room temperature,the experimental temperature was increased from 293.15 K to 298.15 K,and in order to further promote the acid-base reaction between the DESs absorbents and SO₂,a more basic pyridine was used,and some basic groups were introduced to the pyridine to increase the absorption capacity.A series of pyridine-based DESs were synthesized by using Emim Cl as HBAs and aminopyridine or hydroxypyridine as HBDs,respectively.The experiment results showed that the optimal molar ratio of Emim Cl（HBAs）and 2-NH₂Py（HBDs）was 7:1.The effect of introducing basic groups into different sites of HBDs on their SO₂ absorption performance was investigated.Under the conditions of 298.15 K and 1.0 bar,the SO₂ gas absorption capacity of Emim Cl:2-NH₂Py（7:1）can reach 1.247 g/g,and the absorption capacity of SO₂ gas is improved under the same conditions,compared with the previous chapter,the absorption rate is faster,the absorption equilibrium can be reached within50 s,and there is still a good absorption capacity after 40 absorption-desorption times.The characterization of DESs materials before and after SO₂ absorption by FT-IR and¹H NMR was mainly based on Lewis acid-base action,supplemented by strong charge interaction between chloride ions and SO₂ and physical absorption between DESs and SO₂.（3）In order to further increase the absorption capacity and reduce the Emim Cl content to reduce costs.Emim Cl was selected as HBAs,and 1-aminopiperidine（1-NH₂Pi）or a series of piperidine derivatives were selected as HBDs to synthesize a series of different piperidine-based DESs absorbents.Experiments have shown that the optimal molar ratio of this DESs absorbents is HBAs:HBDs=6:1;the effects of HBDs containing different groups on their SO₂ absorption performance were investigated.At 298.15 K and 1.0 bar,the SO₂ gas absorption capacity of Emim Cl:1-NH₂Pi（6:1）can reach 1.326 g/g.The absorption capacity of SO₂ is higher than that of the previous two chapters.The absorption rate is faster than that of the previous two chapters,and the absorption equilibrium can be reached within 40 s,and the selectivity coefficient of SO₂/CO₂ gas is 916.4,which means that the selective absorption performance is excellent.Emim Cl:1-NH₂Pi（6:1）has basically no decrease in absorption capacity after 40 recycling experiments,and can still remain at1.230 g/g,indicating its good recycling performance.The characteristics of DESs before and after SO₂ absorption by FT-IR and ¹H NMR showed that the absorption of SO₂ gas by piperidine-based DESs was mainly based on Lewis acid-base action,supplemented by the strong charge interaction between chloride ions and SO₂ and the physical absorption between DESs and SO₂.