obtained do not uphold Equation 3 suggested by Massoth for chemical reaction controlling. O n the contrary, there is evidence to show that Massoth’s Equation 2 or Equation 18 developed by the authors ( 7 ) would be the more correct one, thus validating the mass transfer model suggested. Massoth’s Equation 2 can be more confidently used for a simpler system like carbonation of phenols. This work is expected to take several months before any conclusions can be drawn. For the present, however, on the basis of the estimated values of A , and k , and other considerations listed above, we feel that mass transfer would be the controlling step and
SEPARATION
literature Cited
(1) Phadtare, P. G., Doraiswamy, L. K., IND.ENC. CHEM. DESIGN DEVELOP. 4, 274 (1965).
L. K. Doraiswamy National Chemical Laboratory Poona, India
OF L I Q U I D METALS BY HIGH VACUUM SINGLE-STAGE DISTILLATION
SIR: Recent studies have revealed additional information dealing with the work of Westerheide and Burnet ( 2 ) . Using the same equipment, with minor modifications, it has been discovered that the degree of separation of cadmium from the leadbismuth eutectic is limited by short-circuiting of the distilland in the distillation chamber, from the distribution plate to the condensate receiver. Cadmium concentration in the distillate varied from 12 to 47 mass a t distillation temperatures of 450’ to 5 5 O O C . The concentrations predicted from relative volatilities exceeded 99%. The mode of contamination was studied by removing the distillation chamber from the circulation loop and installing it on a stand where the slope of the nearly vertical distribution plate could be varied. Because of similarity of physical properties, mercury was used a t room temperature and atmospheric pressure to simulate the lead-bismuth eutectic-cadmium mixture. Mercury from a constant head tank was allowed to flow through the chamber a t various flow rates and different distillation plate angles. The effects of flow rate and plate angle were correlated with the amount of metal collected in the distillate receiver. The per cent of total distilland (mercury) short-circuiting was directly related to the distilland flow rate and ranged from 2.0 to 2.8% for the flow rates used. The closer the distribution plate was to the vertical the greater the amount of short-circuiting. Almost none occurred at a n angle of 8’ from the vertical. Other tests conducted with mercury flowing down a full-size plastic model of the distribution plate disclosed that the shortcircuiting was due to globules of liquid metal spilling over the edges of the guide vanes on the distribution plate and falling into the distillate receiver.
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not chemical reaction. We hope that when more data become available, we will be in a position to delineate the reaction model unequivocally.
l & E C PROCESS DESIGN A N D D E V E L O P M E N T
The answer to the short-circuiting problem does not lie in merely increasing the slant of the distribution plate, since this complicates at least one other feature of the chamber. The metal molecules of distilland must be able to “see” the condenser-that is, have a straight-line path to the condenser. If the plate angle were significantly increased, the metal would be in a trough formed by the guide vanes and distribution plate and very little distilling metal would reach the condenser surface. The guide vanes are required for agitation and distribution of the metal, features which must be retained in any redesign. Several alternatives are now being considered and a t present it appears that the answer can be found in using a greater plate angle and redesigned guide vanes. As was found in the previous study, distillation temperature and distilland composition had a strong effect upon the distillation rate. A more complete account of this work is available (7). literature Cited
(1) Murdoch, L. B., “Separation of Cadmium from the LeadBismuth Eutectic by High Vacuum Single-State Distillation. Chamber Design and Distillate Purity,” unpublished M. S.
thesis, Library, Iowa State University, Xmes, Iowa, 1965.
(2) it‘esterheide, D. E., Burnet, George, IND.ENG.CHEY.PROCESS DESIGN DEVELOP. 4 , 4 3 (1965).
Work done at the Ames Laboratory, U. S. Atomic Energy Commission, Contribution No. 1865. L. B. Murdoch George Burnet
Ioreqa State University of Science and Technology Ames, Io%a
