Clathrate phase equilibria and its application to the selective separation of phenolic compounds

Abstract

Clathrate phase equilibria for the ternary water-phenol-carbon dioxide system containing two host and one guest components were studied. Three four-phase equilibrium loci for this ternary system were determined over the wide temperature and pressure ranges. A quintuple point, thermodynamically unique and invariant condition appeared in this type of ternary system, was carefully measured and found to be 293.7 K and 57.2 bar. At this quintuple point, five individual phases of water-rich liquid, phenol-rich liquid, carbon dioxide-rich liquid, phenol clathrate, and vapor could coexist in equilibrium. A new experimental technique was used to determine the liquid phase compositions coexisting with phenol clathrates at the isobaric conditions of 30.0 bar and six temperatures ranging from 278.2 to 303.2 K. A potential applicability of the clathration process to phenol separation from aqueous solutions was demonstrated in terms of phenol concentrations on the basis of carbon dioxide-free concentration. In particular, phenol separation by using the high-pressure carbon dioxide as a clathrate-inducing agent could be applied even to multi-phase aqueous solutions over an entire range of phenol concentrations. A schematic pressure-temperature diagram for this ternary and three corresponding binary systems was constructed, and its thermodynamic validity was deeply investigated. Clathrate phase equilibria for two ternary water-deuterium oxide-carbon dioxide and water-deuterium oxide-chlorodifluoromethane (R22) systems were measured at several different mass % of water and deuterium oxide mixtures. Equilibrium dissociation pressures of these two ternary systems at the three-phase (clathrate-liquid-vapor) boundaries range from (1.43 to 4.86) MPa and (0.141 to 0.886) MPa, respectively. The temperature range occupied by the three phase boundary of the water-deuterium oxide-R22 system is a little larger than that of the water-deuterium oxide-carbon dioxide system. The dissociation ...