摘要 |
A process for the separation of a substance from a liquid feed mixture and for the purification of the substance by fractional layer crystallization, wherein the liquid feed mixture comprises the substance to be separated and purified in a concentration of less than 70 % by weight, which comprises the subsequent steps in the given order:
(a) feeding the liquid feed mixture into a crystallization zone, in which at least one surface is provided, so that at least a part of the surface contacts the liquid feed mixture,
(b) cooling the at least one surface of the crystallization zone to a temperature below the equilibrium freezing temperature of the liquid feed mixture so that a crystal layer enriched in the substance to be separated and purified is deposited on the at least one cooled surface, whereby a mother liquid having a lower concentration of the substance to be separated and purified than the liquid feed mixture is formed from the liquid feed mixture,
(c) removing at least a portion of the mother liquid from the crystallization zone,
(d) adding a further portion of liquid feed mixture into the crystallization zone,
(e) allowing further deposition of a crystal layer enriched in the substance to be separated and purified to take place on the at least one cooled surface,
(f) optionally carrying out a sweating stage and removing a sweating residue and
(g) melting the crystal layer to obtain the separated and purified substance. |