GB734754A - Improvements in or relating to continuous fractional crystallization process and apparatus therefor - Google Patents

Abstract

<PICT:0734754/III/1> <PICT:0734754/III/2> <PICT:0734754/III/3> A multi-component liquid mixture is cooled to crystallize at least a portion of one component, the resulting crystals are moved, without change in chemical constitution, from a zone of lower temperature to a zone of higher temperature containing a body of liquid so as to melt or dissolve at least a portion of the crystals, the movement of crystals being through at least one such body of liquid and resulting in displacement of liquid formed by the melting or dissolving of the crystals countercurrent to the movement of crystals, a first product is removed from the zone of higher temperature and material from which said product has been removed is removed from the zone of lower temperature. In Fig. 1 a two-component mixture is introduced at 1 and 2 into crystallizer 3 where crystals may form. Crystals are discharged at 13 and taken to crystallizer 15 which is at a higher temperature, while liquid is discharged by line 4 to crystallizer 5 at a lower temperature, and similarly for crystallizers 15, 18, 5 and 7 except that substantially pure crystals are finally withdrawn from crystallizer 18 and liquid is withdrawn from crystallizer 7 at 8. In the apparatus of Fig. II feed enters a trough 52 at 51, liquid is withdrawn at 58 at the lower temperature end and crystals at 60 at the higher temperature end of the trough. Crystals are moved to the outlet 60 by paddles 57 on an endless band 56. In the apparatus of Fig. 3 the heavier crystals sink through the lighter mother liquor and are removed at 80 at the higher temperature end of the vertical vessel 72. Feed is introduced at 71 and liquid removed at 75 from the lower temperature end of the vessel. Part of the liquid is recirculated after cooling at 73. The Specification lists mixtures of hydrocarbons which can be separated by the process of the invention and also states that the process is applicable to the sodium carbonate-sodium sulphate-water, sodium nitrate - sodium chloride - water and sodium hydroxide-sodium chloride-water systems.