Investigation of phase transitions in the CO2 + bicyclohexyl system: Experimental and modeling study

This study explores the high-pressure phase behavior of the carbon dioxide (CO₂) + bicyclohexyl binary system over a temperature range of (303.15–373.15) K. Saturation pressures were measured using a constant composition expansion (CCE) method, covering pressures from (2.53–82.54) MPa. A total of 67 phase transitions were identified, including liquid (L) to liquid-vapor (LV), liquid-liquid (LL) to liquid-liquid-vapor (LLV), and vapor (V) to LV transitions, for CO₂ gas content ranging from (19.90–99.02) mol%. Notably, LL immiscibility was observed for mixtures with a global mole composition of (69.99, 80.05, 85.43, 90.03) mol% CO₂ at temperatures up to 323.15 K. These findings provide valuable insights about the CO₂ solubility in naphtenic hydrocarbons, which differs significantly from typical alkanes. The experimental data were modeled using the Peng–Robinson equation of state (PR EOS) with Modified Huron–Vidal non-random two-liquid (MHV-NRTL) mixing rules, agreeing with most conditions. This work contributes to the understanding of asymmetric mixture behavior and supports the development of improved thermodynamic models for industrial use.