Phase Behavior of Liquid Crystal + CO 2 Mixtures

Liquid crystals are a potential new type of solvents for CO2 capture. For this purpose, it is important to study the phase behavior of mixtures of liquid crystals with CO2. P, T-isopleths of five binary mixtures of liquid crystals and CO2 were studied at a mole fraction of approximately x(CO2) = 0.06. The liquid crystals used in this study were 4-ethyl-4'-propyl bicyclohexyl and 4-propyl-4'-butyl bicyclohexyl, which have a smectic phase, and 4,4'-hexyloxy benzylidene aminobenzonitrile, 4-heptyloxy- 4'-cyanobiphenyl, and 4-pentyl-4'-cyanobiphenyl, which have a nematic phase. Phase equilibria measured for the systems were the bubble point curves nematic + gas to nematic, isotropic + gas to isotropic, the two-phase equilibria nematic + isotropic to isotropic, nematic to nematic + isotropic, smectic + isotropic to isotropic and solid + nematic to nematic. Three-phase equilibrium lines nematic + isotropic + gas and smectic + isotropic + gas were measured as well. Henry coefficients were calculated for the measured systems. It was found that 4-pentyl-4'-cyanobiphenyl and 4-heptyloxy-4'-cyanobiphenyl have the highest CO2 solubility.