cryogenic azeotropes
cryogenic azeotropes
(OP)
A "discussion" at work centered around the presence or azeotropes in cryogenic separations. Does anyone know of such an animal?
Dave Hasse
Dave Hasse
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RE: cryogenic azeotropes
The only thing that I can think of is that the boiling points of oxygen and argon are very close together.
The composition profile in the low-pressure oxygen column is interesting. In this column, waste nitrogen comes off the top and your product oxygen comes off the bottom. Argon tends to concentration about 2/3 of the way down the column. This is commonly referred to as the "argon cloud" or "argon bubble". At this point, the argon-rich gas is taken into the crude argon column to separate the argon from the oxygen.
I hope this helps.
RE: cryogenic azeotropes
RE: cryogenic azeotropes
I have two questions.
One, what is NF3 used for?
Two, have you ever considered breaking the azeotrope with a membrane? At first glance, this would seem to be a workable membrane separation.
Dave
RE: cryogenic azeotropes
2. Is the membrane question in reference to Ar/O2 or NF3/CF4? In both cases I believe you face the same problem: The boiling points and molecular sizes are almost identical. In the case of NF3/CF4 they are -129/-128C and they differ by about 0.1 Angstrom is size. The NF3 has a dipole (0.235 debye), but is of little help in trying to remove CF4 from NF3, (data from Matheson 6th ed.). [The problem with electronics is everybody wants higher purity; 99.995+% purity or less than 50ppm total contaminants, and preferably less than 10 ppm CF4.]
RE: cryogenic azeotropes
My interest in the separation is professional curiosity, I work in gas separation membranes (usually at 35-50° C) but know little about cryogenics.
Gas separations are done by two mechanisms, solubility and diffusion. Clearly a diffusion controlled membrane would not work well and that is where I do most of my work. Solubility driven membranes are usually tracked with critical temperature.
I am also not sure how much separation is necessary, as the goal is not to do the separation but to replace a stripping column, but I looked up the critical temperatures, and they are pretty close (6 °C) so this is probably a dead horse.
Dave