Research On Microscopic Mechanism Of Ionic Liquid In Gas Drying

Water mixed in industrial gases can adversely affect production and transportation equipment and applications.In order to ensure the safe and efficient operation of the entire production process,the removal of water in the gas is very significant.In this work,quantitative calculation and molecular dynamics simulation as well as experimental verification,were used to study the interaction between ionic liquids and water,gas.So that the mechanism of ionic liquid in gas drying can be revealed.(1)The structures of different anions and cations,H2O and N2 were optimized,and the binding energies between them were calculated.It was found that both anions and cations tend to combine with H2O.The similar conclusions can also be obtained by calculation of the surface charge distribution.The anions and cations were combined to form nine different ionic liquids,and the binding energies between ionic liquids and water,N2 were calculated.It was found that the ionic liquids tend to combine with H2O.When the anions are the same,the shorter the chain length of the cations are,the stronger the interaction between ionic liquids with water are.The order of interaction between ionic liquids with different anions and H20 is[BF4]-type>[PF6]-type>[Tf2N]-type.In addition,through the IGM analysis,the untouchable interaction between different ionic liquids,anions,cations and H2O,N2 were qualitatively and quantitatively demonstrated by an innovative form of graphic.And the conclusions are consistent with the previous results of quantitative calculations,which explains the mechanism of dehydration at the molecular level.(2)Molecular dynamics simulations were used to study the microstructure of different ionic liquids,as well as the microstructure between different anions/cations/ILs and water.It was found that water mainly tends to combine with anions,and they are also closely related in space,which also coincides with the previous quantitative calculation results.Moreover,by studying the microstructure of three ionic liquids[OMIM][BF4]/[OMIM][PF6]/[OMIM][Tf-2N]with different water contents,it is shown that the interaction between cation-anion,cation-water and anion-water decreases with the increase of water content,while water-water is the opposite.Finally,the interaction sites between cation/anions and water indicate that oxygen atom in water molecules tend to combine with C5 atom of cation,as well as fluorine atom of anions[BF4]-/[PF6]-and oxygen atom of[Tf2N]'.(3)The vapor pressure data between three different ionic liquids and water were measured and compared with the predicted values by the UNIFAC model.It can be seen from experimental results that the vapor pressure data of the binary system(water+[OMIM][BF4])is the smallest,(water+[OMIM][PF6])is second,(water+[OMIM][Tf2N])is the largest at the same temperature and mole fraction.Moreover,in a certain composition range,with the temperature increases,the vapor pressures for all the binary systems increase.This verifies the correctness of the quantitative calculation from a macroscopic perspective,and also provides a large amount of data for the gas drying with ionic liquid.