Chromatography with Dynamically Created Liquid "Stationary" Phases: Methanol and Carbon Dioxide

Liquid films composed of binary mixtures of carbon dioxide and methanol were created in empty capillary columns to produce effective stationary phases for chromatography. Under certain conditions of temperature, pressure, and stoichiometric composition, a binary mobile phase composed of CO2 and an organic liquid, such as methanol, can form two immiscible (gas and liquid) phases within a chromatographic column. The two phases can coexist in dynamic equilibrium with the liquid phase migrating through the column at a slower velocity than the gas phase. The liquid phase, composed of methanol saturated with carbon dioxide, acted as a chromatographic stationary phase while the gas phase, composed of carbon dioxide saturated with methanol, acted as a chromatographic mobile phase. The exact conditions necessary for the formation of two phase systems were determined from three-dimensional (P, T, XY) phase diagrams calculated from the Peng-Robinson cubic equation-ofstate using one-parameter mixing rules. Separations of simple hydrocarbon mixtures are illustrated under various experimental conditions.