GB784520A - Improvements in purification of crystals and concentration of solutions - Google Patents

Abstract

In processes for purifying crystals formed by cooling crystal-forming liquids in which a mass of crystals is moved towards a melting zone and the resultant liquid is in part refluxed countercurrent to the crystals and in part removed, the crystals are stirred during their movement towards the melting zone to prevent channelling by the reflux stream and to ensure more efficient mixing of the reflux and crystals. <PICT:0784520/III/1> The stirring is such as to impart no downstream force to the crystals. The process may be used to obtain concentrates by freezing out solvent from solutions. Fig. 2 shows a suitable apparatus in which crystals formed in a scraped surface chiller 13 are fed by gravity through a filter section 14 into the purifying column 16 at the end of which they are melted by a heater 34 and the melt partly withdrawn at 48, the remainder passing back to the filter section 14. This may comprise a single filter, mother liquor and reflux being withdrawn together or, as shown, two filter sections divided by a partition 56 from which mother liquor and reflux may be withdrawn separately. The mother liquor and reflux may be recycled in part to chiller 13. An extension of the scraper shaft 22 in the chiller carries scrapers to prevent clogging of the filter screen 52, and a further extension carries stirring arms 33 to stir the mass of crystals in the purification column 16. The wall of the column may carry stationary arms 66 to prevent the crystals rotating as a solid mass. The Specification also describes apparatus (Figs. 3 and 4, not shown), in which a scraped surface chiller feeds crystal slurry to a pair of inclined arms meeting at the top of the purifying column and fitted with pistons which feed the slurry to the purifying column. In a further embodiment a single arm fitted with a piston is used. The process may be used for the separation of close-boiling hydrocarbons and other organic compounds as set forth in Specification 734,756 and for the concentration of fruit juices and beverages by freezing out water and purifying the ice crystals. In an example high purity cyclohexane is obtained from a commercial product containing 85 per cent cyclohexane.