Equilibrium Measurement For Water Working Medium Systems Containing Imidazolium Ionic Liquids

The absorption cycle is an important energy saving and environmental protection technology which can be driven by low grade heat and not use ozone depleting substances as working fluids. It also can cut down the peak power and use renewable resources. Working pairs of absorption cycle are the most important and based factor, especially its thermodynamic properties which related to the improvement of existing working fluids or the new ones.The ionic liquids have been proposed as working pairs of absorption cycle. They have several special characters, such as low vapor pressure, high boiling point and can been designed. The absorption cycle need not distillation if ionic liquids be used as working fluids. This paper proposed water and the ionic liquids as new working fluids, and studyed the thermodynamic properties. Based on the relationship between refrigerator and absorbent in absorption cycle and the properties of the ionic liquid, two kinds of ionic liquids were chosen to synthesize.1,3-dimethylimidazolium chloride ([DMIm]Cl) was synthesized by gas-liquid phase reaction, starting from N-methylimidazole and methyl chloride. And 1,3-dimethylimidazolium Tetrafluoroborate ([DMIm]BF4) was synthesized by two steps reaction, starting from [DMIm]Cl and sodium tetrafluoroborate. The structural characterization and purity measurement had done to the refined samples.A new apparatus which was based on the boiling point method was designed and constructed to measure the saturated vapor pressure of solution. The vapor pressure of pure water and NaCl aqueous solution with 0.25 mass fraction were measured to verify the reliability of the apparatus. The data measured in this work agreed with those from the literature very well, and the average pressure relative diviations are 0.41% and 0.57% respectively.The vapor pressure of H2O (1)/[DMIm]BF4 (2) system was measured, with the mass fraction 0.90,0.85,0.75 and 0.65 of [DMIm]BF4 and the temperature from 310 K to 410 K. The correlated equations with vapor pressure, temperature and concentration had been built by Antoine and NRTL equation respectively. The average pressure relative diviations between experimental and calculated values are 1.06% and 1.15%. The ion dipole interaction between ionic liquid and water evokes negative deviation with Raoult's law, which is required for absorption pairs. And the higher concentration of ionic liquid had, the greater deviation with Raoult's Law.The vapor pressure of H2O(1)/LiBr+[DMIm]Cl(2)system was measured, with the mass fraction 0.69,0.60,0.50,0.40,0.30 of LiBr+[DMIm]Cl and the temperature from 300 K to 440 K, LiBr:[DMIm]Cl=3:1(mass ratio). Then, the correlated equation with vapor pressure, temperature and concentration had been built by Antoine equation. The average pressure relative diviation between experimental and calculated values is 1.18%.The advantage of [DMIm]Cl additive in this work is the reduction of the vapour pressure of the solution with respect to the traditional H2O/LiBr, and the solubility also be enhanced Simultaneously. H2O/LiBr+[DMIm]Cl as working pairs of absorption cycle has better thermodynamic properties.