Purification of organic solid solutions by melt crystallization: Comparison between layer and suspension crystallization

In order to compare the degrees and rates of purification achieved by layer and suspension melt crystallization operations, purification by ''sweating'' of naphthalene-benzothiophene solid solution crystals was carried out after they were formed either on a cold surface (layer crystallization) or in supercooled melts (suspension crystallization). The purification rate coefficients obtained for the suspension system crystals were found to always be larger than those for the layer system, furthermore, the amount of impurities unable to be removed by ''sweating'' from the layer was higher than that from the particles. These two facts lead to the conclusion that the overall efficiency for the purification by sweating is higher for the suspension crystallization than the layer one.