Phase behavior of multicomponent mixtures of complex molecules in supercritical fluids

Supercritical fluid (SCF) technology is an attractive approach for impregnation of solid wood and wood composites with biocides for protection against fungal attack. Pure or modified carbon dioxide can be used to dissolve and deposit biocides within the wood structure. The phases formed by such mixtures at subcritical as well as supercritical conditions must be known for reliable scale-up of SCF impregnation of wood.; Experimental equipment was designed and used for the measurement of critical temperatures and pressures of multicomponent systems. The critical loci of binary {dollar}rm (COsb2/Propiconazole){dollar} and ternary {dollar}rm (COsb2/acetone/TCMTB{dollar} (2-(thiocyanomethylthio) benzothiazole) or {dollar}rm COsb2/methanol/tebuconazole){dollar} mixtures were determined experimentally for biocide and cosolvent concentrations up to 2 and 5 wt%, respectively. The effect of cosolvent and biocide levels on critical temperature and pressure of binary and ternary mixtures were determined. Compositions of the coexisting phases in two and three fluid phase equilibria were measured using a stoichiometric technique from measured volumes. The {dollar}rm COsb2/acetone/TCMTB{dollar} system was studied at three {dollar}(T, P){dollar} sets using TCMTB at two levels of purity. For the phase equilibria studies, overall biocide concentrations ranged up to 45 wt% and cosolvent concentrations up to 30 wt%.; Mathematical models were used to predict high-pressure phase equilibria of multicomponent systems. Models were first examined for liquid-liquid equilibria (LLE) of three binary systems (n-butane/water, propylene/water, n-butyl alcohol/water), vapor-liquid equilibria (VLE) of one binary system {dollar}rm (COsb2/methanol),{dollar} and vapor-liquid-liquid equilibria (VLLE) of four ternary systems {dollar}rm (COsb2{dollar}/isopropanol/water, {dollar}rm COsb2{dollar}/water/{dollar}rm Csb4Esb1{dollar}(2-butoxyethanol), {dollar}rm COsb2{dollar}/water/{dollar}rm Csb8Esb3{dollar} (n-octyl tri(oxyethylene) mono ether), {dollar}rm COsb2{dollar}/acetone/TCMTB). Two different equations of state (Peng-Robinson and Redlich-Kwong) and three different mixing rules (van der Waals, Panagiotopoulos and Reid (1987), Kwak and Mansoori (1986)) were used. The critical temperature of one component for each of the three complex ternary systems was not known. The unknown critical temperature was either estimated using a group contribution method based on normal boiling point or fitted to the experimental phase composition data. Agreement between experimental and calculated phase compositions was better at lower pressures when the system was farther from the critical region. The {dollar}rm COsb2{dollar}/acetone/TCMTB system was the most difficult to model, but the fitting improved when the Peng-Robinson equation of state with Panagiotopoulos and Reid's mixing rules (instead of van der Waals mixing rules) were used.