Koaleszenzprobleme in chemischen Prozessen

Abstract

Das Trennen von Flussig/Flussig-Dispersionen gilt als Verfahrensschritt, der in vielen Fallen im technischen MaBstab erhebliche Schwierigkeiten bereitet. An einer Reihe von Beispielen aus chemischen Prozessen wird gezeigt, wo Phasentrennprobleme auftreten, welche Auswirkungen sie haben und welche industriell praktikablen Methoden fur ihre Losung zur Verfiigung stehen. Die vorgestellte Problemanalyse geht vom Entstehungsmechanismus der Dispersion aus und fuhrt zu einer qualitativen Charakterisierung der verschiedenen Koaleszenzprobleme, ohne daB die Kenntnis des Tropfenspektrums vorausgesetzt wird. Diese Vorgehensweise gewinnt wesentliche Erkenntnisse aus der Beurteilung vorangegangener Verfahrensschritte. Aus den Ursachen fur eine schlechte Phasentrennung werden MaBnahmen zu deren Verbesserung aufgezeigt: Modifikation der physikalischen Eigenschaften, h d e r u n g der Dispergierung, mechanische Trennhilfen (Packungen, Koalisierfilter), Anlegen eines elektrischen Feldes, Zentrifugen und Hydrozyklone, koaleszenzfordernde chemische Zusatze. Fur die Auslegung von Apparaten zur Durchfuhrung dieser Verfahrensweisen werden industriell anwendbare Methoden mitgeteilt.Coalescence problems in chemical processes. Separation of liquid/liquid dispersions is a process step which often gives rise to considerable difficulties on an industrial scale. A number of selected examples taken from chemical processes demonstrates where phase separations occur, the consequences they may have, and what industrially practicable methods are available for their solution. The problem analysis presented starts from the mechanism of generation of the dispersion and leads to a qualitative characterization of the various coalescence problems without presuming any knowledge of the droplet spectrum. This procedure acquires important knowledge from an assessment of prior process steps. Measures for improvement are deduced from the causes of poor phase separation: modification of physical properties, change of dispersion, use of mechanical separation aids (packings, coalescing filters), application of an electrical field, centrifuges and hydrocyclones, coalescence-promoting chemical additives. Industrially applicable methods are reported for design of equipment for implementation of these approaches.

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