Melt crystallization multistage

Brodie crystallizer-purifier, 545, 547 Kureha purifier, 545,547 multistage, 543 MWB process, 543,545 Phillips process, 544-546 Schilaknecnt column, 543,544,546 TNO bouncing ball process 545.547 Melt purification. See Melt crystallization Membranes, 631,632,641 applications, 632 cellulose acetate, 635 equipment configurations, 632 gas permeation,633,644 hollow fiber, 632,633,641,643 performance, 646 Permasep, 641 olate and frame, 638 Prism, 633,643 properties, 635,636 structures, 632 tubular, 638,639 types, 635, 636... 

In those cases in which complete solid solution with no eutectic formation cecurs, it is possible to separate completely a binary mixture into its components via countercurrent multistage melt crystallization. However, such systems are the rare exception, whereas eutectic formation is the general rule in solid-liquid equilibria. Therefore, in tbe overwhelming majority of cases, the degree of separation attainable by crystallization is limited by the entectic composition. To accomplish a complete separation, it is necessary to couple an auxiliaty separation step to the crystallization process to break the eotectic,... 

The Sulzer MWB process (Fischer, Jancic and Saxer, 1984) is a melt crystallizer that operates basically by crystallization on a cold surface, but with features which allow it to operate effectively as a multistage separation device. Consequently, it can be used to purify solid solution as well as eutectic systems. 

For an earlier introduction to column crystallization vis-a-vis the variety of equipment and patents, see Albertins et al. (1967). Ulrich (1993) provides a more modern version of melt crystallization devices, plants and processes. For mathematical modeling and optimization of multistage crystallization processes, see Gilbert (1991). A more Involved model of continuous countercurrent contacting with axial dispersion in melt crystallization has been illustrated in Hemy and Moyers (1984). 

As an alternative to multistage batch crystallization processes with their attendant problems of material handling and losses, several types of continuous column crystallizers have been developed, in which the product crystals are washed with their own melts in countercurrent flow. Those illustrated in Figures 16.14-16.17 will be described. Capacities of column purifiers as high as 500gal/(hr) (sqft) have been reported but they can be less than one-tenth as much. Lengths of laboratory size purifiers usually are less than three feet. 

Figure 16.13. MWB (Metallwerk Buchs) batch recirculating crystallizer, with freezing on and melting off insides of thin film heat exchanger tubes adaptable to multistage processing without external solids handling [Miitzenberg and Saxer, 1971).

Sulzer-MWB [MetalWerk AG Buchs] An obsolete process for recovering naphthalene from a coal-tar fraction by multistage fractional crystallization from the melt. Formerly operated by Rutgerswerke at Castrop-Rauxel, Germany. 

Figure 8.23. The Sulzer MWB process a) multistage flow diagram (C = crystal, L = liquor) b) plant layout (A = crystallizer, B = melt collection tank, C = residue melt storage tank, D = heat exchanger, E = pump)...

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