Study On Mechanism Of Formation And Absorption Of SO₂ By Caprolactam-Tetraalkylammonium Halide Ionic Liquid

Acid gases,especially sulfur dioxide?SO₂?,released from coal combustion,have made great contribution to environmental pollutions and human health.The preliminary study found that Caprolactam-Tetraalkylammonium halide?CPL-TAAX?had good SO₂absorption properties.While the formation mechanism and the interaction between TAAX and SO₂ in the process of absorbing SO₂ need further study.In the formation mechanism study of CPL-TAAX ionic liquid,the effects of raw material ratio,water content,halogen and alkyl chain length were investigated.The physical properties of thermal decomposition temperature,density,acidity,viscosity and conductivity were also measured.The chemical structure of CPL-TAAX was investigated by the RT-IR,¹H-NMR.The structure-property relationships for CPL-TAAX was deduced.The results showed that the CPL-TAAX structure had a great influence on the thermal stability.The optimal ratio of TAAX and CPL depended mainly on the acceptability of halogen anion in TAAX.With the increasing of temperature,the viscosity and density of CPL-TBAB?Caprolactam-Tetraalkylammonium bromide?decreased,the conductivity increased.The viscosity apparent activation energy of CPL-TBAB was 13.98 kJ·mol^-1.The NH bond of CPL reacted with Br^-of TBAB,and formed intermolecular hydrogen bonds C=O-NH...Br^-.With the addition of water,red-shift absorptions could be observed in the FT-IR spectroscopy.Molecular simulation showed that Br^-,Cl^-and CPL were more likely to form hydrogen bonds,and the order was Br^->Cl^->F^-.SO₂ absorption mechanism was investigated.The effects of temperature,pressure and moisture on the SO₂ solubility were investigated.The process of absorbing SO₂ of CPL-TBAB was examined by RT-IR.Comparing the changes of infrared and nuclear magnetic spectrum before and after absorption of SO₂,the absorption mechanism of SO₂and CPL-TBAB molecules was derived.The results showed that the solubility of SO₂decreased with the increasing of temperature and pressure.After 5 cycles of absorption-desorption,there was almost no loss for the absorption capacity.As the acidity of ionic liquids was higher,the polarity was greater,and the viscosity was smaller,the SO₂absorption efficiency was higher.New C=O vibration peak of CPL-TBAB occurred after SO₂ absorption(1146.4 cm^-1 and 1353.8 cm^-1).The NH-peak?7.89 ppm?of CPL disappeared in the NMR spectrum,and the CH₂ peak of CPL raised from the low field to the high field.All of these confirmed that there was a chemical change between SO₂ and CPL-TBAB.