Process and apparatus for the separation of two-or multicomponent mixtures by multi-stage fractional crystallization

摘要

1,229,022. Progressive purification. METALLWERK A.G. BUCHS. 16 April, 1968 [14 April, 1967], No. 17849/68. Heading B1G. A process for progressive purification of a constituent of a liquid mixture in a plurality of crystallization stages employs a crystallization and melting circuit comprising a crystallizer A and a heater B, the circuit being fed successively with liquid from each of a plurality of vessels (10 as shown) containing liquids of progressively increasing concentration with respect to the constituent. The circuit may also include a vessel E for washing liquid. The crystallizer A is an indirect heat exchanger having a separate coolant circuit and a crystal layer forms on the cooled surfaces of the heat exchanger. The liquid being treated may flow over the cooled surfaces as a film or stream. The crude liquid mixture is fed to vessel I, mother liquor is withdrawn from vessel F, and the desired purified constituent is finally withdrawn from vessel G. At an intermediate stage in the process, liquid from vessel n is circulated through crystallizer A to. form a crystal layer, the resulting mother liquor being discharged to vessel n-1. Further liquid of the same composition may then be passed from vessel E to crystallizer A after heating in heater B, thereby washing residual liquid from the crystal layer and dissolving a portion of the layer, and the wash liquid discharged to vessel n. Liquid from vessel n+I is then circulated through crystallizer A after heating in heater B, thereby dissolving the crystal layer, whereafter heating by heater B is discontinued and a further crystal layer is formed. A smooth layer may be built up by repeated alternate crystallization and partial redissolution. After completion of the stage, residual liquid on the surfaces of the heat exchanger may be cooled to form crystal nuclei before commencement of the next stage. The plurality of stages may be repeated to form a continuous process.