文摘
The use of carbon dioxide in the synthesis of ionic liquids (ILs) has many advantages over conventional solvents. Here, the high-pressure phase equilibria (including CO2 solubility, volume expansion, and mixture critical points) are measured and modeled for the system involved in the synthesis of a model imidazolium ionic liquid 1-hexyl-3-methylimidazolium bromide ([HMIm][Br]) from 1-bromohexane and 1-methylimidazole. The global phase behavior of 1-methylimidazole was investigated and found to be a Type V system (or potentially IV) from the classification of Scott and van Konynenburg with regions of vapor 13;liquid equilibrium, vapor 13;liquid 13;liquid equilibrium, liquid 13;liquid equilibrium, an upper and lower critical endpoint and mixture critical points. The solubility and volume expansion of CO2 in 1-methylimidazole, 1-bromohexane, a 1:1 mixture of 1-methylimidazole and 1-bromohexane and [HMIm][Br] was determined at 313.15 K and 333.15 K for pressures ranging from 10 to 160 bar. The solubility of CO2 and the volume expansion increases in the order of [HMIm][Br] 1-methylimidazole < 1:1 mixture of reactants < 1-bromohexane. The Peng 13;Robinson equation of state with van der Waals 2-parameter mixing rules was used with estimated critical properties to well correlate the vapor 13;liquid equilibrium. The results have important ramifications on the kinetics and process constraints of an actual IL synthesis with CO2.
