Study On Absorption Of DMF With Imidazolium-Based Ionic Liquids

In order to solve the problems on low purification efficiency, recovery difficult andhigh energy consumption that exist in the technology of governance and recovery of DMFexhaust in the industry. The technology of absorption of DMF waste gas andthermodynamics and phase equilibrium properties for [bmim][BF₄] and [bmim][PF₆] ionicliquids as absorbent was studied.The density, pH and viscosity data of the binary systems of [bmim][BF₄] and[bmim][PF₆] ionic liquids with DMF at different temperatures and concentrations weredetermined. The temperature and mole fraction of DMF dependency of the value ofdensity, pH and viscosity were fitted and correlated using empirical equations, respectively.Excess molar volumes, viscosity deviations, and flow activation free energy have beenobtained from density and viscosity data. In the experimental conditions，excess molarvolumes and viscosity deviations were negative and it has been interpreted in terms ofion-dipole interactions and structural factors of the ionic liquid and DMF molecular. Flowactivation free energy were positive and the effect of temperature on them was very small.The liquid-liquid equilibrium data of the DMF-H₂O-[bmim][PF₆] ionic liquid ternarysystem were determined in283.15K～323.15K at atmospheric pressure, and theperformance of DMF and water extraction using [bmim][PF₆] ionic liquid was discussed.The results showed that the selectivity coefficients of [bmim][PF₆] ionic liquid decreasedwith the increase of the initial content of DMF and temperature and increased with theincrease of the amount of ionic liquid. The changes of selectivity coefficients withtemperature were small when the content of DMF was more than10%. The selectivitycoefficients increased after5%～25%of the mass fraction of NaCl, KCl, KBr solutionwere added and the effects of them on selectivity coefficient in sequence: NaCl>KCl>KBr.The changes of selectivity coefficients were small aftre the ionic liquid was reused for sixtimes. The extraction efficiency of [bmim][PF₆] ionic liquid could up to60%for the lowconcentration of DMF waste water at298.15K. The distribution coefficient and selectivitycoefficient data were fitted by empirical equations and the correlation models wereobtained.The [bmim][BF₄] and [bmim][PF₆] ionic liquids were used as absorbent for theexperimental study of absorption of DMF wast gas. The effect of reaction temperature,DMF waste gas concentration, gas flow rate on removal efficiency was investigated and the optimum absorption conditions were determined The ionic liquids were desorpted afterthe absorption of DMF at-0.1MPa, The effect of desorption time and temperature ondesorption efficiency was studied and the optimum desorption conditions were determined.The absorption-desorption cycle experiment was studied in the best operating conditionsand the results showed that the removal efficiency of DMF waste gas in the ionic liquidscould up to90%, the desorption efficiency could up to98%, and the ionic liquid has agood performance of regeneration and reuse. It is showed that the weak hydrogen bondswere formed between DMF and ionic liquids by IR spectra and proton nuclear magneticresonance spectral analysis, and when solution heated, the hydrogen bond wasbreaken andthe DMF was desorpted. There was no changes for the structure and properties of thefunctional groups of the ionic liquids in the desorption process.