Zonenschmelzen und Kolonnenkristallisieren, neue Trenn- und Reinigungsverfahren für kristallisierende Substanzen

Abstract

The methods of operation of normal freezing, zonemelting and column crystallization are described as means of purifying crystallizable substances and their performances are illustrated by examples.
The simple and relatively fast method of normal freezing is especially suitable for the separation of eutectics. Its application provides an especially good possibility for the careful concentration of active substances from plant extracts.
Zonemelting is a very good method for preparing materials in high purity. The theory and practical application of this method are presented, i. e. the influence of the zone length on the separation effect, work with horizontal, inclined and vertical apparatus, repeated zonemelting and the determination of purity are discussed. Of special interest is the separation of cis- and trans-isomers, the separation of pyridin and piperidin which form an azeotrop and are thus difficult to separate by distillation and finally the identification of three components from the bladder content of the waterbeetles.
The disadvantage of the long time required for purification by zonemelting is avoided in column crystallization. In applying this method a temperature gradient is maintained along the column length and melting and recrystallization is carried out in a continuous manner. As a result the low melting substances are enriched at one end of the column and the high melting substances concentrated at the other. The process is especially interesting because it can be operated in a continuous manner, i. e. raw material is fed into the middle of the column in an uninterrupted stream and lower and higher melting products are taken off continuously. The operation of the apparatus is illustrated by the purification of diphenyl and the separation of a mixture of the three terphenyl isomers.