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RedDwarf
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Quote: Originally posted by rockyit98  | it not the size that matter its the molecular weight!
why most one people trying to concentrate alcohol ? they must be reading between the lines of "Concentrating H2SO4 without distillation (with flask
and some PTFE) ".which means they must be drunk already.
[Edited on 29-7-2019 by rockyit98] |
My assumption is that molecular size vs pore size in the membrane that is the mechanism here, but I'm happy for you to prove me wrong In the meantime I'll continue to work on seeing if the membrane can be used to
prevent passage of larger molecules.
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RedDwarf
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My isopropanol / water mixture test didn't turn out as hoped. I left the mixture in the flask at room temperature for over 12 hours without any loss,
but within 15 minutes of heating I'd got a strong smell of alcohol outside the flask (confirmed by reduction of K permanganate solution on a strip of
filter paper held over the membrane). Analysis of the starting and finishing densities (using a density bottle) showed that what had been lost was
mostly alcohol.
During this heating stage I noticed that the membrane was very bowed (so even more stretched than previously) and it appeared as if this was just the
outermost layer separated from the other 3 so there may have been a leak in one or more layers.
I'm going to try a number of different membranes/supports to try and avoid over stretching the membrane (and consequentially the pore size):
- I've ordered some gas (yellow) tape that should be thicker and thus more resistant to stretching.
- I've cut a few pieces of an old goretex coat to see if this membrane (supported on a permeable nylon mesh) might also work.
- I'm going to use some lightweight permeable nylon above white ptfe layers to prevent stretching, so that pore size should be more constant with
temperature and pressure.
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Abromination
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| Quote: Originally posted by RedDwarf | | Quote: Originally posted by rockyit98 | it not the size that matter its the molecular weight!
why most one people trying to concentrate alcohol ? they must be reading between the lines of "Concentrating H2SO4 without distillation (with flask
and some PTFE) ".which means they must be drunk already.
[Edited on 29-7-2019 by rockyit98] |
My assumption is that molecular size vs pore size in the membrane that is the mechanism here, but I'm happy for you to prove me wrong In the meantime I'll continue to work on seeing if the membrane can be used to
prevent passage of larger molecules.
|
I don't think I can! Molecular size is the main factor here as larger molecules diffuse slower, although weight matters as well because heavier
molecules move more slowly.
I am sorry that the isopropanol run did not work, but it is still good information. It would be nice to know the pore size of teflon also. The problem
is as we stretch it, the pores change size.
You would be surprised how little I have found in permeation of vapors, Fick’s law does not help to much as we know little of the variables in this
circumstance.
List of materials made by ScienceMadness.org users:
https://docs.google.com/spreadsheets/d/1nmJ8uq-h4IkXPxD5svnT...
--------------------------------
Elements Collected: H, Li, B, C, N, O, Mg, Al, Si, P, S, Fe, Ni, Cu, Zn, Ag, I, Au, Pb, Bi, Am
Last Acquired: B
Next: Na
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RedDwarf
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Just to be clear, I'm not suggesting that Graham's law (and hence molecular mass) isn't part of the effect here, but I believe there is also a pore
size issue, with pore size varying according to the delta P on the membrane. Out of interest does anyone know if membrane separation/effusion has ever
been used for isomer separation (same mass different shape), I know it has been used for isotope separation (same shape, (slightly!)different mass) ?
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Abromination
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According to Wikipedia, “When a diffusion process does not follow Fick's laws (which happens in cases of diffusion through porous media and
diffusion of swelling penetrants, among others),[3][4] it is referred to as non-Fickian.”
Fick’s law refers to diffusion without a membrane. If you you were to fill a container with a gate in the middle that nothing could pass through
with a solution on one side and pure water on the other, the diffusion of the ions across the container when the gate is removed is what Fick’s law
describes.
I guess that leaves it to being covered by Grahm’s law, although I hate to say it.
[Edited on 7-30-19 by Abromination]
List of materials made by ScienceMadness.org users:
https://docs.google.com/spreadsheets/d/1nmJ8uq-h4IkXPxD5svnT...
--------------------------------
Elements Collected: H, Li, B, C, N, O, Mg, Al, Si, P, S, Fe, Ni, Cu, Zn, Ag, I, Au, Pb, Bi, Am
Last Acquired: B
Next: Na
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Johnny Cappone
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I would really love to try this procedure.
One of the problems I have when concentrating battery acid, perhaps the biggest one, is that big cloud of whitish mist produced in the final moments
of the process. However, I confess that I am a little confused. Okay, normally just heating the acid, without using any membrane, works well. The heat
leaves the molecules agitated and the water, having a lower boiling point, escapes. The temperature gradually rises to 290-320 degrees, where we
finally reach the 98% azeotrope.
What is being said is that, with the membrane, I could perform this whole process at 95 degrees, is that it?
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