Solubility and Liquid Density Measurement for CO₂ + Lubricant at High Pressures

抄録

Solubility of supercritical carbon dioxide (CO₂) and liquid density were measured for CO₂ + tetraethylene glycol (TEG), and four CO₂ + lubricant systems by using a recirculating type apparatus equipped with an oscillation U-tube densimeter at 344.3 K. The lubricant employed were two synthetic oils, polyolester (POE), and polyalphaolefin (PAO), and two mineral oil, naphthenes (NAP), and paraffins (PAR) for refrigerators. The experimental pressure range was set to be from 2.97 to 20.11 MPa. For all systems, two phases were maintained, and three phases, vapor-liquid-liquid equilibrium, was not observed. The mass fraction of CO₂ in the liquid phase was almost stayed with constant at high pressure, and the liquid density showed a concave shape, revealing minimum for CO₂ + TEG system. Though the same tendency was observed for PAO, NAP, and PAR, the liquid density was monotonically increased with pressure. These phase behaviors were similar to liquid-liquid equilibrium. On the contrary, the mass fraction of CO₂ was linearly increased with pressure, and the density was decreased for CO₂ + POE system. Then, supercritical CO₂ was seemed to be dissolved into POE like as gases.