Phase behavior of the vanillin–CO2 system at high pressures

The high-pressure phase behavior of the vanillin–CO2 is experimentally determined with emphasis on the determination of the two solid–liquid–gas (SLG) boundaries for this system. The SLG line starting at the melting point of vanillin exhibits a temperature minimum of ∼65 °C at 150 bar and ends at the upper critical end point at 73.6 °C, 1347 bar, at a vanillin concentration of 15.8 mol%. The low-temperature branch of the SLG line virtually superposes onto the vapor pressure curve of CO2 and ends at the lower critical end point at 31.6 °C, 74.5 bar, at a vanillin concentration of 0.72 mol%. Solid–fluid phase behavior exists at pressure–temperature (P–T) conditions located between the two SLG lines. The P–T trace of low-pressure region of the SLG line starting at the melting point of vanillin differs from that reported previously in the literature probably due to the differences in the experimental techniques used to determine the SLG line.