INFLUENCE OF INTERFACIAL-TENSION AND VISCOSITY ON THE BEHAVIOR OF A PACKED-COLUMN IN NEAR-CRITICAL FLUID EXTRACTION

Density and viscosity of the coexisting phases and interfacial tension of the following binary systems were measured: pelargonic acid, linol eic acid, oleic acid or stearic acid as subcritical and carbon dioxide as superecritical components. Also the corresponding phase equilibria were investigated at pressures ranging from 2 to 20 MPa and temperatu res from 313 K to 393 K. With increasing pressure the concentration of the supercritical component in the liquid phase increases and viscosi ty and liquid interfacial tension decreases. At greater activities of the dense gases the interfacial tension decreases dramatically to valu es less than 2 mN/m if the pressure exceeds a certain limit, a falling film disintegrates into small droplets. The surface excess passes thr ough a maximum at these conditions. At first appearance of instabiliti es on a falling film, the logarithm of the Reynolds number is a linear function of the logarithm of the film number. Independent of the type of the investigated packings, the number of theoretical stages per me ter versus Bodenstein number fall all on the same curve when an extrac tion is carried out in the droplet regime. Also the logarithm of the c apacity of a column at the flooding point versus the logarithm of the density difference between the coexisting phases is a linear function when an extraction is carried out in the droplet regime.