1 Fluid-Phase Behavior of the Guaiacol + CO 2 System at High Pressures Jesse R. Richards a , JulianG. Velez a , Ladawan Songtipya a,b , Amporn Sane b , Mark C. Thies a * a Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, SC 29634-0909, USA b Department of Packaging and Materials Technology, Faculty of Agro-Industry, Kasetsart University, Bangkok 10900, Thailand __________________________________ * Corresponding author. Tel.: +1-864-656-5424; fax: +1-864-656-0784 E-mail address: mcths@clemson.edu (M. Thies). Abstract. The binary phase behavior of supercritical CO 2 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.CO 2 + 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 CO 2 -rich liquid phase extends to temperatures and pressures 2.1 °C and 2.2 bar above the critical point of CO 2 . Keywords: guaiacol, carbon dioxide, lignin, phase behavior, liquid–liquid, supercritical fluid © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/