Phase Behavior of Liquid Crystal + CO2 Mixtures

Abstract

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 xCO2 = 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.