Available online at www.sciencedirect.com J. of Supercritical Fluids 43 (2008) 421–429 Phase behavior of 1,3,5-tri-tert-butylbenzene–carbon dioxide binary system Cerag Dilek, Charles W. Manke ∗ , Esin Gulari Department of Chemical Engineering and Material Science, Wayne State University, Detroit, MI 48202, USA Received 16 February 2007; received in revised form 13 July 2007; accepted 20 July 2007 Abstract 1,3,5-tri-tert-butylbenzene (TTBB) is solid at ambient conditions, and has substantial solubility in liquid and supercritical carbon dioxide. We present the phase behavior of TTBB–CO 2 binary system at temperatures between 298 and 328 K and at pressures up to 20 MPa. Phase diagrams showing the liquid–vapor, solid–liquid and solid–vapor equilibrium envelopes are constructed by pressure–volume–temperature measurements in a variable-volume sapphire cell. TTBB is highly soluble in CO 2 over a wide range of compositions. Single-phase states are achieved at moderate pressures, even with very high TTBB concentrations. For example, at 328 K, a binary system containing TTBB at a concentration of 95% by weight forms a single-phase above 2.04 MPa. TTBB exhibits a significant melting-point depression in the presence of CO 2 , 45 K at 3.11 MPa, where the normal melting point of 343 K is reduced to 298 K. With its high solubility in carbon dioxide, TTBB has potential uses as a binder or template in materials forming processes using dense carbon dioxide. © 2007 Elsevier B.V. All rights reserved. Keywords: Solid–liquid–vapor equilibrium; Liquid–vapor equilibrium; Pressure induced crystallization; Melting-point depression; Isothermal compressibility 1. Introduction In sand casting and powder injection molding of metal and ceramic parts, binders used in the molding processes are removed by methods such as solvent extraction, combustion, thermal and catalytic debinding. These binder removal methods produce significant amounts of solid and liquid wastes, as well as air pollutants [1]. Therefore innovations in material forming pro- cesses using dense gas and supercritical CO 2 (scCO 2 ) for binder extraction and recovery have great potential to improve envi- ronmental problems associated with traditional binder removal processes [2–6]. Compounds that are solid at ambient temperature and are soluble in dense carbon dioxide have potential uses in casting and molding processes as CO 2 -extractable binders and tem- plates. For designing a supercritical CO 2 extraction process, solubility and phase behavior studies are needed to determine the technical and economic feasibility of the process, and to define and optimize processing conditions. Solubility and phase ∗ Corresponding author. Tel.: +1 313 577 3849; fax: +1 313 577 3810. E-mail addresses: cdilek@chbe.gatech.edu (C. Dilek), cmanke@eng.wayne.edu (C.W. Manke), egulari@ces.clemson.edu (E. Gulari). behavior of various materials, including specially designed CO 2 - philic compounds, in near critical and supercritical CO 2 have been investigated extensively [7–14]. As a category of possible binder materials, sugar acetates are solids at room temperature, and have high solubilities in dense carbon dioxide, which is attributed to the Lewis acid–base interaction between CO 2 and the carbonyl group [15–18]. We recently investigated the phase behavior of -d-galactose pentaacetate with CO 2 at tempera- tures and pressures representative of possible binder extraction processes [19]. Here, we continue our investigation of carbon dioxide-soluble solids for possible binder candidates with a symmetrical tri- alkylbenzene, 1,3,5-tri-tert-butylbenzene (TTBB), the structure of which is shown in Fig. 1. In our preliminary studies, we observed high solubility of TTBB in carbon dioxide. In the literature, early studies on TTBB include its synthesis, spec- tral characteristics, physical properties and its reactions with other components yielding higher molecular weight hydrocar- bons and other derivatives [20–25]. Later studies investigate different methods of synthesis, its reactions with metal ions and its physical and thermochemical properties [26–30]. It is inter- esting to note that one of the TTBB synthesis methods involves palladium-catalyzed cyclotrimerization of tert-butylacteylene in supercritical carbon dioxide in the presence of MeOH [31]. 0896-8446/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2007.07.009