THE SEPARATION OF EUTECTIC FORMING ORGANIC MIXTURES BY NORMAL FREEZING

Abstract

Normal freezing of the simple eutectic-forming system naphthalene-benzoic acid was carried out to investigate nonequilibrium separation phenomena. The growing interface was found to be concave under various conditions. The impurity concentration was found to be distributed not only axially but also radially in the ingot with noticeable concentration at the center. This fact was explained by assuming a distribution of temperature and impurity concentration of the melt on the growing interface. That is, solidification at the center must proceed at a lower temperature from a less pure melt which results in more trapping of the melt; thus the impurityrich solid will be formed at the center.
On the basis of the experimental results, an effective scheme for separation by normal freezing was demonstrated to provide a purer product in a short operating time.