Melt crystallization sweating

The final purity after the pressure sweating step is limited by the melt which adheres at the porous crystal layer. Therefore there is no significant difference between the experiments under 15 bar C02, 50 bar N2 and 175 bar N2 atmosphere which means that there is already enough gas solved at 15 bar CO2 respectively 50 bar N2 in the liquid impurities to transport them with the escaping gas to the crystal layer surface. 

The period of released pressure is used as sweating time (see the following section). After discharge of the created crystals the remaining highly conterminated melt must be separated before receiving the pure product. The equipment is used industrially, e.g., for the purification of p-cresol from p-/w-cresol mixtures. Successfully executed experiments on the laboratory level are described by Moritoki et al. (1989) for the purification of benzene from benzene-cyclohexane mixtures. 

Phase 2 partial melting (sweating Figures 2.3.S-7 and 2.3.5-8b). In the second phase, the crystal layer is tempered, so that impurities that adhere to it or are incorporated therein can drip off. The dripping liquid, also known as partial melt, is collected in the collecting tank, and when a certain quantity is reached is removed via the residue pipe or pumped to a stage tank. 

In practice, however, some amount of mother liquor remains between crystals. From this state, when the liquid pressure is decreased slightly, a small amount of crystals melts at their surfaces so as to dilute impurities in the remaining liquor. And then the diluted liquor is further separated. Such a partial melt and dilution is called sweating. The sweating and the liquid removal can be carried... 

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