Schmelzkristallisation – theoretische Voraussetzungen und technische Grenzen

Abstract

Die Grundlagen zur Auslegung von Schichtkristallisationsverfahren werden mitgeteilt. Ein besonderer Schwerpunkt ist hierbei die Ermittlung des erforderlichen Energiebedarfs. Wahrend des Ausfrierens der Kristallschichten muB ein Vielfaches der Kristallisationswarme ab-und beim anschlieflenden Aufschmelzen wieder zugefuhrt werden. Daher sind diese -taktweise durchgefiihrten -Verfahren nur bei sorgfaltiger apparativer Gestaltung und ProzeBfiihrung konkurrenzfahig zu anderen thermischen Trennverfahren, bei denen eine kontinuierliche Gegenstromfahrweise realisiert werden kann.Melt crystallization -Theoretical presumptions and technical limitations. The fundamentals of the design of melt crystallization processes on cooled surfaces are presented. Determination of the energy requirement is the essential point. During each freezing step a multiple of the heat of solidification must be removed and must be re-introduced during the subsequent melting step. Consequently, discontinuous processes of this nature can only compete with other thermal separation techniques -in which a continuous countercurrent operation can be realised -if the plant is well designed and the process is precisely controlled. I Einleitung

Design of hybrid distillation/melt crystallisation processes for separation of close boiling mixtures

“…For a known differential distribution coefficient, the mean impurity concentration in the melt can be calculated by introducing an integral distribution coefficient, k int , as shown in Eq. (12) [18].…”

“…Therefore, it cannot be described by thermodynamic equations. To calculate the crystal purity, the differential distribution coefficient k diff is used [18], which is defined as the ratio of the concentration of the impurities in the crystal and the melt at the solid-liquid interface, as shown in Eq. (9).…”

“…The total energy demand is calculated implicitly by using the Wellinghof and Wintermantel [18] correlation, as shown in Eq. (13)…”

Global optimization of multistage binary separation networks

“…Furthermore, similar objective functions are used in the literature. The crystallization eort dened in [2,40]…”

“…Countercurrent cascades are deployed for a range of industrially relevant separation processes [1], including cooling crystallization cascades [2,3,4,5], evaporative crystallization cascades [6,7,8,9], organic solvent nanoltration cascades [10,11], and reverse osmosis cascades [12,13,14,15].…”