The Physical Properties Of Caprolactam-Tetrabutyl Ammonium Halide And Its Aqueous Solution And The Absorption Mechanism Of The Solution Absorbing SO₂

The wet desulphurization technologies is a FGD technology widely used the most worldwide at present,and to research and development new higher efficient absorbents are becoming hotspots in air pollution control fields. Ionic liquids are considered as a kind of environmentally friendly absorbents due to their extremely low vapor pressure, high thermal and designable structure. Quaternary ammonium ionic liquids have been used to absorb SO₂; however, the viscosity of system should be reduced for industrial applications.Therefore, the system of caprolactam - tetrabutyl ammonium halide ionic liquids (CPL-TBAH ILs) and water has been studied to absorb pure SO₂. The experiments are carried out to study caprolactam - tetrabutyl ammonium halide ionic liquids (CPL-TBAH ILs) and water absorb pure SO₂. In this study, the physical properties, such as thermal stability, pH, viscosity, density, conductivity, of caprolactam-tetrabutyl ammonium ionic liquids(CPL-TBAB ILs), caprolactam-tetrabutyl ammonium chloride ionic liquid(CPL-TBAC ILs), caprolactam-tetrabutyl ammonium fluoride ionic liquids(CPL-TBAF ILs) and the binary system of ILs and water, have been measured. The Solubility of SO₂ in the system of ILs and water and the reuse of the binary system absorb SO₂ have been studied. The results showed the following conclusions: (1) The thermal decomposition temperature of CPL-TBAH ILs is 219℃to 231℃and the all ILs are prove to be acidity, and the viscosity decreases with an increase of temperature and the density increases with an increase of temperature. (2) The pH values of the binary system of CPL-TBAB ILs and water decreased with increasing temperature, and the pH values increased first, then decreased slightly as the concentration of ILs in the mixture increased. The pH values of the binary system of CPL-TBAC ILs and water increased with increasing temperature, and the pH values decreased first, then increased as the concentration of ILs in the mixture increased. The pH values of the binary system of CPL-TBAF ILs and water increased first, then decreased with increasing temperature, and the pH values increased as the concentration of ILs in the mixture increased. The viscosity values of the binary system of CPL-TBAH ILs and water decreased with increasing temperature, and the viscosity values increased as the concentration of ILs in the mixture increased. The density values of the binary system of CPL-TBAH ILs and water decreased with increasing temperature, and the density values increased as the concentration of ILs in the mixture increased. The conductivity values of the binary system of CPL-TBAH ILs and water decreased with increasing temperature, and the density values increased first, then decreased as the concentration of ILs in the mixture increased. (3) The solubility of the solution absorbed SO₂ increased with an increase of anion, the solubility of the binary system of CPL-TBAB ILs and water is largest. The efficiency of reusing the solution absorb SO₂ is high.At the same time, the content of each component in upper and lower levels has been measured and the mechanism of the interaction between SO₂ and the solution was also conducted from qualitative analysis of upper and lower levels which was been by the binary system of CPL-TBAB ILs and water absorb SO₂. The CPL/TBAB molecule interact forms the N-H…Br/C/F hydrogen bonds. When SO₂ was added into the aqueous CPL-TBAH ILs, the O in H₂O and the S in SO₂ forms the S-O bonds, so sulfurous acid was formed, N-H…Br hydrogen bonds was break. The aqueous CPL-TBAH ILs and SO₂ were divided into two layers (SO₂-TBAH-H₂O and SO₂-CPL-H₂O). The two levels by the binary system of CPL-TBAB ILs/CPL-TBAC ILs and water were immiscible, the lower level is SO₂-TBAB/TBAC-H₂O and the upper level is SO₂-CPL-H₂O. The two levels by the binary system of CPL-TBAF ILs and water were miscible. The pure ILs can be obtained by evaporating the absorbed solution, because the water and SO₂ was gone.The physical properties dates of CPL-TBAH ILs and the binary system of CPL-TBAH ILs and water, and the reusing study of the solution absorb SO₂, establishes technical foundation for the industrial application of this ILs. The study of the mechanism of the interaction between SO₂ and the solution, have offered the theoretical basic for interact of ILs+H₂O+SO₂ on the microcosmic level.