Fluid-phase behavior of the guaiacol + CO2 system at high pressures

• Fluid-phase behavior of CO2 + guaiacol at high pressures was determined.
• Type III phase behavior per classification of Scott and Van Konynenburg.
• Critical curve has pressure minimum at 15 °C and 500 bar.
• V-L upper critical end point is just above the critical point of pure CO2.

The binary phase behavior of supercritical CO2 with guaiacol, a model lignin monomer that is a liquid at near-ambient conditions, has been determined. A variable-volume, high-pressure view cell was used to observe both liquid–liquid cloud points as well as bubble points along the liquid–liquid–vapor (LLV) three-phase line for this system. CO2 + guaiacol was found to exhibit Type III phase behavior according to the classification system of Scott and Van Konynenburg, indicating that even at high pressures the mutual solubility of the two components is relatively low. However, the system does exhibit a pressure minimum in the liquid–liquid critical curve at 15 °C and pressures just under 500 bar. The upper critical end point U for the CO2-rich liquid phase extends to temperatures and pressures 2.1 °C and 2.2 bar above the critical point of CO2.

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