March
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Can't figure out which molecular sieve I need
Recently I have been using military grade gas mask filters to filter Sulfur Dioxide out of Nitrous Oxide. I would like to switch to a reusable
molecular sieve as it would be a one time purchase and I would not have to keep buying filters I could just recharge the one I make. I think the type
of sieve I want is a 5a molecular sieve. But what I'm worried about is that this type of sieve may also adsorb the N2O. Does anyone know what type of
sieve would work best for this?
Thanks,
-March
[Edited on 18-9-2014 by March]
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Magpie
lab constructor
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From this website:
http://www.kayelaby.npl.co.uk/general_physics/2_2/2_2_4.html
the calculated molecular diameter for SO2 is 4.3 A (angstrom) and for N2O is 3.9 A. So these two are very close in size.
It would appear that a 5A sieve would catch them both.
A 4A sieve might provide some separation.
I have no data or experience here. This is just based on theory.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Dan Vizine
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Molecular sieves with 5 angstrom pores (i.e., 5A sieves) , particularly formulations of Ca, Na aluminosilicates, are used to remove H2S, small
mercaptans and carbonyl sulfide, somewhat preferentially, even from gasses that are similarly sized. After all, size is only one consideration with
zeolites. Some interactions are stronger than others because of the polarity, polarizability and other characteristics of a potential "sorbate" as
well as the natures of the cations present in the particular zeolite.
But, I'd scrub it out if I were you. Use a gas dispersion tube to bubble the gas through a dilute base like sodium bicarbonate. All of the SO2 will be
reacted and removed. If the gas is for human inhalation, a subsequent water scrubber may be nice, too. All you need by way of equipment is a few
flasks, rubber tubing, rubber stoppers, and some glass tubing. You can buy a lot of baking soda for the cost of a pound of zeolites. This frees you
from the task of regeneration of the sieves, too, which requires heating under a stream of purge gas or in vacuo. Additionally, with
sieves you need to seal the trap well to avoid partial deactivation by local atmospheric gasses during down times. It may not seem like much, because
the rate is low, but it never stops.
[Edited on 21-9-2014 by Dan Vizine]
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Dan Vizine
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This guide may be useful to anyone planning on using zeolites for a specific purpose.
Attachment: Which Zeolite To Use.pdf (120kB)
This file has been downloaded 2259 times
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Little_Ghost_again
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Sorry to chirp up but... isnt this the stuff they use to make cars go faster? Why would anyone inhale it??? Not being funny its just I thought it was a gas
used for cars not people, or have I got my gasses mixed up maybe?
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Mailinmypocket
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Nitrous oxide is indeed used in some cars... It is also known as laughing gas, used as an anesthetic and also recreationally by some. It is also the
gas in whipped cream.
Sometimes just searching for the name of a chemical will get you a quicker answer to your questions than waiting on an answer on here btw 
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Dan Vizine
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The main danger with recreational nitrous use is asphyxiation. Toxicity is very low and it's as near to harmless as get-highs get. This statement, of
course, means that someone, somewhere is probably furiously searching for contradicting facts, since we aren't supposed to acknowledge that getting
high can be innocuous, but, aside from people with so little foresight as to decide to fill their parked car with nitrous from a cylinder (they died,
simple O2 displacement), nitrous never harms anyone. When I was in grad school, nitrous parties (everybody had their balloons) were popular events
both in the dorms and in the surrounding student-dominated neighborhoods. Not that that means anything statistically or medically, but you know what I
mean. Nobody ever dropped out, got sick, etc. because of a nitrous habit. Well, I did know this rouge dentist... but that's another story.
That's not to entirely dismiss the asphyxiation danger, though. Do you know what gas kills more people working in industrial settings than any other
every year? Not chlorine, not HCN, not CO....it's Nitrogen. The usual scenario goes something like this...a worker enters a space which has been
inerted with N2. When you don't suspect, you breath naturally, the O2 is rapidly swept from your lungs and you lose consciousness in seconds,
literally. This is in no way related to how long you can hold your breath, you are purging your lungs of O2 in these accidents. Death occurs in
minutes. Then, in really unfortunate instances, someone tries to help and the tragedy compounds itself with another victim. The instinct to help often
overrides the training. This trend is finally starting to slow as awareness has built, but it has taken decades.
[Edited on 25-9-2014 by Dan Vizine]
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Praxichys
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Quote: Originally posted by Dan Vizine  | | This is in no way related to how long you can hold your breath, you are purging your lungs of O2 in these accidents. Death occurs in minutes.
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Quite correct. It's all about partial pressure. Many fail to realize that O2 ends up diffusing back out of your blood. One can be overcome in seconds.
The hypercapnic alarm response (the urge to breathe and the feeling that you cannot breathe) is triggered by the buildup of CO2 in the blood. Since
you can still eliminate CO2 an a hypoxic/anoxic environment, this response is not triggered. There is no feeling respiratory distress. One simply
becomes disoriented and loses consciousness.
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