Measurement of equilibrium dissociation pressures for phenol and p-Cresol clathrate with methane and carbon dioxide

Abstract

Clathrate compounds are crystalline molecules formed by a physical reaction host molecules and low molecular weight gases. This compounds are divided into two categories depending on host molecules. Overwhelming research papers concerned to gas hydrates have been published in the literature. On the contrary, for nonaqueous clathrates there were reported only a few clathrate-solid host-vapor equilibrium curves in the range of low temperatures and pressures. In this study, another three phase equilibrium dissociation pressures were measured. A new equilibrium apparatus was built to measure dissociation pressures of the phenol-methane, phenol-carbon dioxide, $p$-cresol-methane, and $p$-cresol- carbon dioxide systems. The disappearance method by visual observation through sapphire windows was adopted in this study. Three phase (clathrate- organic-rich liquid-vapor) dissociation pressures of the systems over normal melting points of their host components (phenol and p-cresol) were carefully measured. An abrupt increase of the dissociation pressures appeared near 319 K for the phenol-carbon dioxide system. Comparing the experimental clathrate -phenol-rich liquid-vapor data with previously reported clathrate-solid phenol-vapor data, a quadruple point was found to be 313 K and 19 bar. The phenol-methane and $p$-cresol-methane clathrate equilibrium dissociation pressure curves were monotously increasing along the elevation of temperature. On the basis of the previously reported $p$-cresol-carbon dioxide equilibrium data, phase diagram of the system was constructed over vapor pressure line of guest component, carbon dioxide. In order to show the feasibility of separating cresol isomer mixture into pure state, $m$-cresol- methane system was also investigated and it was appeared that $m$-cresol did not form clathrate with methane. Therefore, it can be capable of saying that using clathration phenomenon becomes a separation technique of cresol isomers mixture into pure ones...