Siegfried Peter

The rheological behavior of coexisting phases in systems containing fatty acids and dense gases

Abstract An experimental system consisting of an autoclave, a capillary viscometer, and a density measuring device was constructed. Phase equilibria, density, and rheological behavior of the coexisting phases are measured as a function of pressure, temperature, and composition. The following systems are investigated: pelargonic acid/CO2; pelargonic acid/C2H6; oleic acid/CO2; oleic acid/C2H6; linoleic acid/CO2; linoleic acid/C2H6; valeric acid/C2H6. At flow rates up to 1000 sec−1, the coexisting liquid phases of the systems pelargonic acid/CO2 and pelargonic acid/C2H6 show dilatant flow behavior. The others show Newtonian flow behavior. The viscosity of the coexisting gas phase increases with increasing pressure whereas the viscosity of the liquid phase decreases. The density of the liquid phase of systems containing ethane decreases with increasing pressure (i.e., increasing gas content) whereas that of systems containing CO2 increases.

Interfacial tension in binary systems containing a dense gas

Interfacial tension in binary mixtures consisting of a non-volatile solute (pelargonic acid or stearic acid) and a gaseous component (carbon dioxide, ethane, nitrogen, argon, helium, or hydrogen) has been measured as a function of pressure (up to 25 MPa) and temperature (in the range from 313 to 393 K) using the pendant-drop method. It is shown that the interfacial tension is affected by two factors, namely pressure and the amount of gas dissolved in the liquid phase. While interfacial tension increases with pressure, it decreases with increasing concentration of the gaseous component in the liquid phase which reduces the viscosity. It is further observed that, at a constant temperature and constant mass flow, when a certain pressure is exceeded, a falling film becomes unstable and disintegrates into droplets.

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

Abstract Density and viscosity of the coexisting phases and interfacial tension of the following binary systems were measured: pelargonic acid, linoleic 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 temperatures from 313 K to 393 K. With increasing pressure the concentration of the supercritical component in the liquid phase increases and viscosity and liquid interfacial tension decreases. At greater activities of the dense gases the interfacial tension decreases dramatically to values less than 2 mN/m. If the pressure exceeds a certain limit, a falling film disintegrates into small droplets. The surface excess passes through a maximum at these conditions. At first appearance of instabilities 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,...

Ash removal from viscous media by supercritical gas extraction

Abstract The separation of solid μ-sized particles from viscous media sometimes raises difficulties because sedimentation is too slow, so that use of a centrifuge is required. In the centrifuge, however, the particles may act as an abrasive material. Examples are finely dispersed solid ingredients in shale oil, in oils from tar sand, in hydrogenation process (slurries) suspensions etc. The media containing the finely dispersed particles are processed with a compressed gas at high density using an entrainer. The conditions are chosen so that the ternary (or pseudoternary) system composed of supercritical gas, entrainer and viscous substance (or mixture) is supercritical. In this way, high concentration of the viscous medium are obtained in the gas phase. As the viscosity of the supercritical gas phase is relatively low, the density of the gas phase can be adjusted by variation of pressure and temperature so that the difference between the solid and the gas phase is sufficiently high for rapid separation of the solid particles. The velocity of sedimentation at constant temperature and pressure depends on the concentration of the viscous substance in the gaseous phase. Even at concentrations of the viscous medium in the gaseous phase, of 30 to 35 % in weight the velocity of sedimentation is sufficiently rapid for the process to be of economical interest.

Separation of Low-Volatile Substances Using Compressed Gases

The solubility of components in compressed gases can be used to separate substances with low vapor pressures. Several authors have suggested making use of this effect [1]. The present investigations were concerned with the oleic acid/stearic acid system [2], with the glycerides of oleic acid [3,4] and with mixtures of fatty acids of different degrees of Saturation. For example, the Separation of monoglyceride from a mixture of glycerides of the oleic acid demonstrated that a Separation process using compressed gases is possible without expanding and recompressing the circulating gas. In these investigations we used a semi-commercial apparatus with plate columns.