Tri-tert-butylphenol: A highly CO2-soluble sand binder

Tri-tert-butylphenol (TTBP) holds great promise as a CO2-recyclable sand binder. TTBP powder can be easily combined with sand, heated to at least its melting point (400 K) and then cooled to form rigid molds for metal forming operations. Further, TTBP exhibits significant melting point depression in the presence of dense CO2 and very high solubility in liquid and supercritical CO2. These properties facilitate the separation of TTBP from used molds via dissolution into dense CO2 and its subsequent recovery – via depressurization – for reuse. Pressure-composition diagrams at 301, 328 and 343 K indicate that TTBP is about 18, 50 and 70 wt% soluble in dense CO2, at pressures above 8, 14 and 16 MPa, respectively. At each temperature, the solubility of TTBP decreased slightly when pressure was increased above roughly 50 MPa. The TTBP-rich liquid phase composition at three-phase VFS equilibrium pressures of 6.76, 9.76 and 9.24 MPa at 301, 328 and 343 K is 8.5, 52 and 70 wt% TTBP, respectively. A pressure–temperature projection of this system has been proposed as the fluid-phase features of a Scott and Van Konynenburg type I system.