The dual temperature process for isotopic separation

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Title:
The dual temperature process for isotopic separation
Series Title:
United States. Atomic Energy Commission. MDDC ;
Physical Description:
2 p. : ill. ; 27 cm.
Language:
English
Creator:
Columbia University
U.S. Atomic Energy Commission
Publisher:
Technical Information Division, Oak Ridge Operations
Place of Publication:
Oak Ridge, Tenn
Publication Date:

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federal government publication   ( marcgt )
non-fiction   ( marcgt )

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Bibliography:
Includes bibliography references.
Statement of Responsibility:
Columbia University.

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Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 005024256
oclc - 277230276
System ID:
AA00009349:00001


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MDDC 891


UNITED STATES ATOMIC ENERGY COMMISSION


THE DUAL TEMPERATURE PROCESS FOR ISOTOPIC SEPARATION


Columbia University


This document consists of 2 pages.
Date Declassified: February 26, 1947


This document is for official use.
Its issuance does not constitute authority
for declassification of classified copies
of the same or similar content and title
and by the same author (s).




Technical Information Division, Oak Ridge Directed Operations
Oak Ridge, Tennessee


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THE DUAL TEMPERATURE PROCESS FOR ISOTOPIC SEPARATION


The chemical exchange method for isotope separation, as developed by Urey and his co-workers
at Columbia University, has been successfully applied to the concentration of isotopes of several
elements. An important variation of this method was devised by J. S. Spevack at the Columbia Uni-
versity Laboratories in 1942. This procedure, known as the dual temperature process, is essentially
an engineering application of the well-known fact that the equilibrium constant for isotopic exchange
reactions varies with the temperature.


PRINCIPLE OF THE METHOD

The system uses two principal components, each of which can exist as a separate phase. These
components contain a common constituent (i.e., two isotopic forms of an element) capable of taking
part in a reversible exchange reaction. The desired constituent may concentrate in either phase,
depending on the equilibrium constant for the reaction.
Two exchange towers are required, one of which is maintained at a higher temperature than the
other. The phase in which the desired isotope tends to concentrate is fed into that tower, hot or cold,
in which the larger equilibrium constant for the exchange reaction prevails. This tower is known as
the concentrating tower. The other phase flows countercurrent to the feed stream in the so-called
stripping tower, where the smaller equilibrium constant applies. Here the countercurrent stream is
equilibrated with the feed. The desired isotope is removed from the stream leaving the concentrating
tower and swept back into the opposite phase. Essentially, this operation is a means of producing
reflux to the concentrating tower. As a result, the isotope-rich phase that has entered the stripping
tower from the concentrating tower is stripped of its high concentration of desired isotope while
flowing through the former tower, and approaches an equilibrium concentration with the stream
entering at the opposite end of the tower. The latter stream came from the top of the concentrating
tower where it was practically in equilibrium with the feed stream. Therefore, since the equilibrium
constant prevailing in the stripping tower is smaller than in the concentrating tower, the stripped
feed stream will leave the system poorer in the desired isotopic constituent than was present in the
original feed. Stated in an equivalent manner, the concentration of desired isotopic constituent in the
stripped feed stream under ideal conditions approaches a fraction of the initial feed concentration
that is equal to the ratio of the equilibrium constant in the stripping tower to that in the concentrating
tower. From this, it follows that operation of the above system is accompanied by an enrichment of
the desired isotopic constituent in the region between the two towers.
The tower heights required for any desired enrichment of product can be obtained by the methods
employed in distillation and absorption practice, i.e., by determination of the lines representing
equilibrium conditions in the tower and the material balance relationships. The heights will depend
on the rates of diffusion, rates of reaction, types of packing and flow rates used.


EFFICIENCY OF THE METHOD

When the concentrations of the desired isotope are small, the equilibrium line for the hot tower is
Y = X/Kh


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and for the cold tower
Y = X/Kc
where Y and X are mole fractions of the desired isotope in the gas and liquid phases, respectively;
Kh, Kc are equilibrium constants for exchange between the two phases in the hot and cold towers,
respectively.
In the system, here described, the equilibrium constant for the exchange reaction favors enrich-
ment of the desired isotope in the liquid phase, and the cold tower is the concentrating tower.
At the top of the cold tower, the exit gas approaches equilibrium with the feed liquid, whereas,
at the bottom of the hot tower the waste liquid approaches equilibrium with the entering gas. Since
the equilibrium constant prevailing in the hot tower is smaller than that in the cold tower, the waste
liquid leaving the system has a lower content of desired isotopic constituent than the original feed
stream.
When the product stream is much smaller than the feed stream, it follows that the fraction of
desired isotopic constituent actually extracted by this process is given by:

fe = 1 -Xw/Xf
where Xw and Xf are mole fractions in the waste and feed liquids, respectively.
The maximum efficiency of extraction in such processes may be obtained by securing equilibrium
conditions at the terminals of the two towers. Under these conditions, the fraction of the desired iso-
tope in the gas leaving the cold tower is Xf/Kc and the concentration of the liquid leaving the hot tower
is XfKh/Kc. Since the maximum amount of desired isotope extracted and concentrated in the product
is determined by the difference in concentration in the feed and in the waste liquid, the maximum frac-
tion of the constituent in the feed which is extracted is

fm= 1- Kh/Kc
The fraction extracted in actual practice is given by fe. Its numerical magnitude depends on the
degree of attainment of equilibrium at the ends of the two towers.






































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