MWB crystallization

FIG. 22-16 Siilzer MWB-crystallization process, a) Stepwise operation of the process, (h) System flow sheet. (Sulzer Chemtecli)... 

A.B. Miitzenberg and K. Saxer, The MWB crystallizer, Dechema Mono-graphien 66, 313-320 (1971). 

Fig. 7-6. "[ vo-stage purification process according to the Sulzer-MWB crystallization process. 

One drawback of static crystallization is that crystal layer growth rates are very slow. In the Sulzer MWB process, growth rates are gready improved by allowing a film to dow down vertical tubes (83). 

In the Sulser-MWB process the naphthalene fractions produced by the crystallisation process are stored in tanks and fed alternately into the crystalliser. The crystalliser contains around 1100 cooling tubes of 25-mm diameter, through which the naphthalene fraction passes downward in turbulent flow and pardy crystallises out on the tube walls. The residual melt is recycled and pumped into a storage tank at the end of the crystallisation process. The crystals that have been deposited on the tube walls are then pardy melted for further purification. Following the removal of the drained Hquid, the purified naphthalene is melted. Four to six crystallisation stages are required to obtain refined naphthalene with a crystallisation point of 80°C, depending on the quaHty of the feedstock. The yield is typically between 88 and 94%, depending on the concentration of the feedstock fraction. 

Commercial Equipment and Applications The falling-film crystallization process was invented by the MWB company in Switzerland. The process is now marketed by Sulzer Chemtech. Products successfully processed in the falling-film crystallizer are listed on Table 20-9. The falling-film crystallization process is available from the Chemtech Div. of Sulzer Canada Inc., 60 Worcester Rd., Rexdale, Ontario N9W 5X2 Canada. 

Sulzer-MWB [Metalwerk A. G. Buchs] An obsolete process for recovering naphthalene from a coal tar fraction by multi-stage fractional crystallization from the melt. Formerly operated by Rutgerswerke at Castrop-Rauxel, Germany. 

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).

The preferred route to higher punty naphthalene, either coal-tar or petroleum, is crystallization. This process has demonstrated significant energy cost savings and yield improvements. There are several commercial processes available Sulzer-MWB, Brodie type, Betz, and Recochem. 

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... 

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