As a part of a research project on the mass transfer in liquid pulsed sieve-tray extraction columns (PSE), the diameters and hold-ups of the drops were measured: the drop size using a suction technique, with photoelectric detection, which was adapted to the special boundary conditions of the PSE; the integral hold-up by the pressure difference between the lower and upper parts of the column. Since experimental results cannot be described by known calculation formulae for the Sauter mean diameter and the hold-up, a new method of calculation was developed. It is phenomenologically based on high-speed photographs of the drop motion on a sieve tray. The mathematical-physical model allows the prediction of drop size and hold-up within certain limits, while the possible different operating regimes of the PSE, i.e. the mixer-settler and dispersion regimes can also be estimated.

Progress in liquid/liquid extraction. Liquid/liquid extraction continues to increase in importance. Classical areas of application, such as aromatic chemistry, hydrometallurgy, and reprocessing of spent nuclear fuels are being supplemented by new uses in biotechnology, in pharmaceutical production, and in water treatment. This upswing would be unthinkable without intensified R & D in chemistry and process engineering. Deeper knowledge of the physical chemistry of solvents permits purposeful choice of solvents for special separation tasks, advances in engineering elucidation of flow and mass transfer in proven and in newly designed extractors creates a basis for calculation or at least assessment criteria for the choice and operating behaviour of equipment. Yet much remains to be clarified. This article describes the current state of the art in the analysis of flow and mass transfer in countercurrent gravity feed columns with and without pulsation or agitator energy and in centrifugal extractors. A brief look at new designs demonstrates that scientific knowledge gave birth to the new ideas expressed therein.

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