Perfectionnements aux procédés et aux appareils pour la purification des cristaux

摘要

A process for the purification of cystals such as for the separation and purification of at least one of the components of a mixture having at least one but not all of its components in crystalline form, comprises heating the crystals, introducing the heated crystals into an upstream portion (with respect to crystal movement) of an elongated purification zone, moving the crystals as a compact mass toward one end of the zone, melting at least a portion of the compact mass in the downstream end portion of the zone, displacing a portion of the resulting melt countercurrently through at least a portion of the length of the crystal mass to displace occluded impurities therefrom, removing displaced liquid from an upstream end portion (with respect to crystal movement) of the zone, and removing a purified product from the downstream end portion of the zone. A mixture of materials is fed by a conduit 11 (Fig. 1) to a heat exchanger such as a chiller 12 to obtain crystals of at least a portion of at least one constituent of the mixture. The slurry so obtained is fed to a filter 14 where uncrystallized material is removed. Crystals are then passed by a conduit 16 to a heating chamber 17 to melt a portion of the crystals to obtain a slurry, preferably containing 35 to 45 per cent by weight of solids, which is passed by a conduit 22 to a column 23. A piston 25 compacts the crystal mass and moves it downstream towards a heating element 28. A filter 29 removes liquid from the crystal mass, or the piston 25 may have a perforate lower face through which liquid may be removed. A portion of the material melted by heater 28 is displaced upstream through the compact crystal mass, thereby displacing occluded impurities from the crystals, the liquid being removed by filter 29, or through piston 25 when it is perforate. Purified material, which may be molten or partially solid, is removed through a conduit 32. In modifications conduits 16 and 22 may be heated and conduit 22 may be inclined. In a further modification material from heater 17 is passed through a chiller to cause further crystalliation before entering column 23. In examples para-xylene is separated from a mixture also containing ortho- and meta-xylenes, ethyl benzene and toluene. Lists are given of compounds which may be separated by the process.