Design And Synthesis Of Amino-functionalized Ionic Liquids And Their SO₂ Absorption Performance

The pollution of SO₂ emitted by coal combustion becomes more serious.It is urgent to control and reduce the SO₂ emission.More attention has been paid on separation by ionic liquids.Ionic liquids are well known for gas absorption and separation without polluting the gas phase.The nitrogen atom on the amino group could interact with SO₂ as it has strong electronegativity,which could enhance the ability of absorbing SO₂.Thus,the amino-functionalized ionic liquid is an important researchdirectiononSO₂absorption.However,theinteractionof amino-functionalized ionic liquid and SO₂ is usually chemical absorption reaction.The strong binding energy as well as high absorption enthalpy can lead to the higher SO₂ desorption temperature.In order to solve this problem,functional groups,such as amino group,ether chain and active hydrogen,which have the ability of absorbing SO₂,are introduced into the amino-functionalized ionic liquid to increase the number of active sites with SO₂,thus decreasing the chemical absorption enthalpy of SO₂,reducing the desorption temperature and improving its engineering ability.In this paper,four kinds of amino-functionalized ionic liquids substituted by functional groups were designed and synthesized.The experimental results were discussed and analyzed by determining and characterizing the SO₂ absorption experiments and quantum chemical calculations.In this paper,amino acid ionic liquids with ether modified imidazolium cations were studied.Amino acid ionic liquids with ether modified imidazolium cations were prepared and its SO₂ absorption performances were studied.The results showed that,the introduction of ether decrease the density and viscosity of the prepared ionic liquids.But its SO₂ removal result indicated that neutral alanine precipitated in the alanine-based ionic liquid with or without water.In order to avoid the problem that the precipitation of neutral amino acid after SO₂absorption intheionicliquids leadto poor recyclability,threenew tetramethylguanidine dicarboxylate ionic liquids[TMG][SUC],[TMG][SUB]and[TMG][DOD]were designed and synthesized by introducing dicarboxylic acid into guanidine-based ionic liquid.The results showed that,these ionic liquids could chemically absorb SO₂ through amino group on the cation,as well as physically absorb SO₂ through the carboxyl group and the active hydrogen on the anion,so the ability of absorbing SO₂ was improved.However,these three ionic liquids have some drawbacks,such as high symmetry,large viscosity,low thermal stability and high absorption enthalpy.On the basis of guanidine-based ionic liquid,polyether group was introduced in the new amino-functionalized ionic liquids[TMG][PBE]and[TMG-MPEG][PTS]on the cation of[TMG-MPEG][PTS]or anion of[TMG][PBE]respectively.Ether group could interact with SO₂ with a moderate intensity.The results showed that,the introduction of ether groups increased the number of active sites between ionic liquids and SO₂.The more active sites increased the SO₂ absorption ability,decreased the binding energy of SO₂ with IL as well as reduced desorption temperature.This was further confirmed by quantum chemistry calculation.The different combinations of cation and anion in ionic liquids can adjust its viscosity,desorption performance,and thermal stability changed,thus resolving the bottlenecks such as high viscosity,difficult desorption,and easy decomposition in the industrial application.