Phase equilibrium measurements and thermodynamic modeling of CO2 + guaiacol, CO2 + guaiacol and ethanol, and CO2 + guaiacol, ethanol, and water

This work reports phase equilibrium measurements for the systems CO₂ + guaiacol, CO₂ + guaiacol + ethanol, and CO₂ + guaiacol + ethanol + water, which are related to the lignocellulosic biomass processing with supercritical CO₂ as solvent. Measurements at constant compositions were carried out in a high-pressure variable-volume view cell at temperatures ranging from 303 to 343 K. CO₂ molar fraction ranged from 0.3989 to 0.9695 in the CO₂ + guaiacol system, from 0.5024 to 0.8492 for the CO₂ + guaiacol + ethanol system, at three different ethanol to guaiacol molar ratios (1:1, 2:1 and 3:1), and from 0.4084 to 0.8997 for CO₂ + guaiacol + ethanol + water, at a fixed ratio guaiacol:ethanol:water (1:3:1). Under these conditions, vapor-liquid (VL), liquid-liquid (LL), and vapor-liquid-liquid (VLL) phase transitions were detected depending on the system and composition evaluated, where bubble point (BP) and dew point (DP) transitions were observed. In the ternary system, the presence of ethanol as a cosolvent led to a decrease in the phase transition pressure compared to the binary system. Conversely, in the quaternary system, the inclusion of water resulted in an increase in the transition pressures compared to the ternary system due to the hydrophobic interaction between CO₂ and water. The experimental data were modeled using Peng-Robinson equation of state and the quadratic van der Waals mixing rule (vdW2), and this applied thermodynamic model was capable of correlating and describing the phase behavior of these systems satisfactorily. The findings of this study are crucial for understanding and determining the phase behavior of systems involving CO₂, guaiacol, ethanol, and water and can be helpful in the development of new processes for producing valuable compounds from lignocellulosic biomass.