Performance And Mechanism Of Highly Efficient And Reversible SO₂ Capture By Novel Deep Eutectic Solvents

Efficient removal and recovery of SO₂ from flue gas is not only beneficial to the environment,but also has considerable economic benefits.The difficulty lies in the development of the highly efficient and reversible SO₂ capture agent.In recent years,ionic liquid（ILs）was considered as an ideal substitute for traditional desulfurization agent,due to its low vapor pressure,high stability and designability.However,the complex preparation process and high cost limited its large-scale application.Therefore,deep eutectic solvents（DESs）,which showed the similar properties with ILs,and presented the advantages of simple preparation and relatively low cost,had become a research hotspot in the field of SO₂ capture.In this work,a series of novel DESs with highly efficient and reversible capture properties were prepared by regulating the composition of DESs,and their absorption mechanisms were explained in depth through spectroscopy and quantum chemical calculations.This study will provide a new idea for the development of new FGD technology.Firstly,a new type of DESs for SO₂ capture were prepared by using symmetric ortho-bisamide derivatives as HBDs.The DESs presented good stabilities,relatively low viscosities and excellent absorption-desorption properties.Among them,the absorption capacities of EU/BmimCl（1:2）and DMU/BmimCl（1:2）were up to 1.18and 1.14 g_SO2/g_DES at 20℃and 1 atm,respectively,and the two DESs also presented excellent absorption selectivities and recycling performances.In addition,it was found that EU based DESs showed more excellent SO₂ desorption performance than DMU based DESs,and it could be used as the energy-saving FGD agent.The results of spectra analysis and quantum chemistry calculations indicated that the studied DESs captured SO₂ through physical action;the synergism of HBDs and HBAs was the reason why the studied DESs could absorb SO₂ efficiently;and the more excellent desorption performance of EU based DESs was due to the regulation of hydrogen bond interaction and charge transfer interaction between DESs and SO₂ by the cyclization strategy of HBD.Subsequently,the azole derivatives were introduced into EU/BmimCl based DESs as the second HBDs to improve the SO₂ capture performance at low partial pressure.The results showed that the prepared ternary DESs not only showed good stabilities,but also presented the lower viscosity than the binary DESs.In addition,the ternary DESs with 4-CH₃-Im as the second HBD could be used as the functional DESs to capture SO₂ from simulated flue gas.At 40℃,1 atm and SO₂ concentration of 2000ppm,the absorption capacities of EU/4-CH₃-Im/BmimCl（1:2:1）and EU/4-CH₃-Im/BmimCl（1:1:1）were up to 0.257 and 0.203 g_SO2/g_DES,respectively.The two DESs also showed good cycle performance and regeneration property.Under the given conditions,their available absorption capacities were as high as 0.169 and 0.120g_SO2/g_DES,respectively,far higher than the previously reported functional ILs or DESs.Spectral studies and quantum chemical calculations presented that the high-efficiency absorption performance of the ternary functionalized DESs was mainly due to the chemical interaction between 4-CH₃-Im and SO₂,and EU could improve the desorption performance by adjusting the activity of functional sites of DESs.