I have again a situation where I don't have exhaust outlet for my workspace, but I might still wanna do some experiments and I've got a few where some
gaseous stuff like NO2 or H2 is formed, stuff that is either toxic, highly flammable or disgustingly malodorous. It is totally out of question letting
it to my workspace, so while I was thinking how I could pull a duct outdoors, I thought if I could instead use a long hose with 15-20mm ID and lead it
out and attach it gas-tight to my apparatus. If the hose is 10-15 meters long, would there be too much backpressure to cause issues, or should the
gases evolved exit through it safely?
An improvement could be to actually put a miniature duct fan to the end of the hose so it creates a slight suction which would help extract the gases,
especially if and when the apparatus can bleed into? A more safer method would be to use small air pump, do a 90 kink to the hose and install a
smaller tube to turn it into low power gas aspirator.
[Edited on 19-7-2021 by Fyndium]teodor - 19-7-2021 at 08:51
This is a nice topic which I did a really lot experiments with.
So, my road was:
Step 1. Use all-glass aspirator to suck all gases from a closed system, mix them with water and allow them go to a drain, spray bottle to clear air
from NO2, gas mask and a pair of sneakers.
Step 2. Get a construction fan, put it on a window. If you have to generate curious amount of NO2 like reacting Fe and HNO3 for your pleasure do it in
front of the fan. There is no troubles for you, only for your neighbors.
Step 3. Get a hose for your fan. See my picture here: https://www.sciencemadness.org/whisper/files.php?pid=650686&...
Step 4. Build a fume cabinet: https://www.sciencemadness.org/whisper/viewthread.php?tid=67...
Step 5. The solution 4 doesn't work really well for gases which are denser than air, so there is a space for improvements.
[Edited on 19-7-2021 by teodor]
[Edited on 19-7-2021 by teodor]Fyndium - 19-7-2021 at 09:21
1) It would consume dozens of cubic M3 of water. NO also is not absorbed into water, it must first be oxidized to NO2, so it will leach through like
nothing. I know, because I tried and trued it with a hard lesson. The odor treshold is also so low that it will annoy you in short time even if there
are residues of it presisting. The toxicity and long-term effects are also not to be trifled with, it is actually really, really dangerous.
2) The structure is such that I cannot add any sort of fan or outlet duct. Also, the neighbors will call the police at once if they see or smell
anything.
3) If it was, I would have already installed an exhaust outlet to the roof with some reach by a chimney tubing so it all goes directly up to
atmosphere, pulled an air duct down, put a 1000m3 duct fan between and led it to my fume hood. I have a lot of experience installing these systems,
both hobby and commercial, and installing one is not an option for this space, hence the topic. I am already in possession of 3 of these large duct
fans, and also 3 activated carbon filters. The filters do actually little to remove some gases and odors, while they are highly efficient for others.
4) Fume hood is only useful if you can make large negative pressure inside it. It blocks pretty much zero anything if it is ambient, unless you can
really seal it and it is made out of impermeable materials. The main use for it is laminar flow direction of gases and odors, actually. I also built
one to my prior place where it worked perfectly with exactly the setup I described above. I could handle freely some really nasty smelling stuff there
and sleep next to it smelling nothing.
The hose idea arises from the fact that I do all my stuff in closed, ground glassware apparatus, hence the generated gases and stuff are easy to
direct if necessary. When I had the hood, I simply took a plug off the other end when a reaction was finished, and the apparatus was flushed by
suctive action of that outlet tube placed into the exhaust duct and it cleared all gases and crap before I took it apart. I never handled
oxygen-sensitive stuff, for that I had a bottle of argon on hand.
This is not a permanent but a temporary solution. It might take a year or so to find a new place, but I rather figure out a working solution than lay
off.Oxy - 19-7-2021 at 09:22
A hose attached to apparatus is a good idea. If the gases are really toxic or smelly it might be a small problem during disassembling. As gases
produced during reaction will go through the hose then after reaction is done they will stay in it. So you will have to pump some air through
apparatus and blow it away.
You can also buy elastic (PCV/ PP ?) ventillation duct like this one https://www.stevensonplumbing.co.uk/ducting.html and attach air blower on the end in a way that it sucks air. Then this pipe can be placed nearby
apparatus outlet. Any fumes should be taken away. This can be even enhanced by wrapping a thick foil around and making "disposable fume hood".
But just the hose, preferrebly with some gas washers will be enough if used with caution.teodor - 19-7-2021 at 09:47
I think hoses without suction/air blowing is not a good solution because a lot of compounds (I recall just alkyl halides or H2S when I attached a
silicon hose to the reflux condenser) can easily go through it into your room either through connections or through the material itself (pores?)
making the working conditions not quite comfortable. Also acids will attack them badly. So, if you have success with some particular materials it
would be interesting to know. I used either silicon or FEP.
For disassembling I always used aspirator, I have impression than even gases which are not absorbed by water will be mechanically removed as bubbles
directly to the sink.
Also having negative pressure inside apparatus is better than creating pressure like in the case of usage of long hose without suction.Fyndium - 19-7-2021 at 11:35
I consider silicon an unsuitable material nowadays. It's expensive, and it degrades very quickly on contact with at least HCl, ammonia and it's not
suitable with solvents neither. Ammonia and at least something that smelled horrible came through it like nothing, and after use the tube quickly
turned very fragile and crumbled upon touching. PVC/PU transparent tubes are very cheap, less than € per meter and while they corrode eventually,
they are easy to replace as needed. Fluoropolymers would withstand anything, but they will also crank up the cost to a huge degree. I can get 25
meters of 15mm PVC hose for less than 10€ and rather replace it now and then than invest 100€ for 5 meter piece of FPM.
I would likely use large caliber garden hose for the purpose. It's made out of PVC, which is not that resistant itself, but it will work for the hours
needed.
Blowing/sucking air through has been represented, yeah, and it works. The hose would be led to roof, so I can get at least 5-6 meters of elevation to
the other end, so if any thermal or gravitational gradient is to occur, it should be to my favor. No bother scrubbing anything, to the skies the trace
amounts shall disappear. I wouldn't think a small positive pressure inside would provide a big issue, but of course if a reaction quickly releases
large amount of gas, like mixing vinegar with bicarb, it will likely pop up a joint, but some kecks would prevent a bigger disaster.
When leading outdoors is not an option, putting hose through water lock of a toilet or a sink can be an option. Someone opted for that, even drew a
schematic for his intentions, and I've personally tested this, and while it works, NO2 reeked through the waterlock to my kitchen sink anyway.
Obviously we're not really dealing with HCN or H2S or stuff like that here. The measures for them would warrant a negative pressure fume hood in my
safety standards, no shortcuts.
[Edited on 19-7-2021 by Fyndium]teodor - 19-7-2021 at 15:14
Fluoropolymers would withstand anything, but they will also crank up the cost to a huge degree. I can get 25 meters of 15mm PVC hose for less than
10€ and rather replace it now and then than invest 100€ for 5 meter piece of FPM.
I bought FEP MUCH cheaper on ebay. They are definitely good at room temperature for virtually anything. BUT they are not so inert above 100C and when
they start to decompose by action of temperature & chemicals they emit very nasty fumes which can make very unpleasant burning sensation in your
throat and lungs. So be careful with them when they are hot, especially in a closed space.
I didn't find a source for PVC hoses yet, never saw them anywhere (I mean of small diameter) didn't try them but I suppose at least for HCL they
should be OK.
I wouldn't think a small positive pressure inside would provide a big issue, but of course if a reaction quickly releases large amount of gas, like
mixing vinegar with bicarb, it will likely pop up a joint, but some kecks would prevent a bigger disaster.
The problem here is not only pressure but also the speed of pressure change (the first derivative). Like during boiling when you have bumping the long
hose will not mitigate it well.
[Edited on 19-7-2021 by teodor]Fyndium - 19-7-2021 at 22:07
Perhaps the most simple method to test backpressure is to simply try to blow into the tube. If there is little to no resistance, it should be good to
go. When there is a reaction that produces for example 5 mol of H2 gas (=about 5 liters?) during several hours, the speed of pressure change will
remain very conservative.
One issue that might arise is condensation. If the reaction is run at hydrous conditions, water vapor can accumulate to the tube, pooling and blocking
it eventually. Effective condenser can reduce this, but the faster the flow rate, the more vapor will carry over. This would warrant the use of
desiccant vessel between.Oxy - 19-7-2021 at 22:28
When there is a reaction that produces for example 5 mol of H2 gas (=about 5 liters?) during several hours, the speed of pressure change will remain
very conservative.
5 moles of H2 (and for every other gas) in standard conditions will be 112 dm3, not 5. If a gas is hot then it's volume can be much greater, can be
easily calculated.
But in course of several hours it should be easy to remove it through a hose.
[Edited on 20-7-2021 by Oxy]teodor - 19-7-2021 at 22:56
I think the 1 1/2'' PVC hose for above ground pools is the way to go ("pool vacuum hose"). You can buy it of any length in steps of 1.5 meters - good
shops can cut it to your length as a single peace. Also there are PVC connectors. It's very resistant to jams, you can stay on it and it doesn't
deform.
If you can find suitable motor (a vacuum cleaner?) you probably can even build a mini-compartment from polystyrene sheets and duct tape (or some
aluminium corners) which you can assemble around you apparatus - using sheets of different size you can change the shape for different cases.
I wouldn't bother about 5L H2 in a laboratory - they always go up and diffuse through anything like crazy, it's very hard to even intentionally put H2
inside something having any pores and try to burn there. (I suppose we are talking about 5 dm3, not 5m3).
NO/NO2 is a nasty thing, but we as children played with it in home or at school not realising that. But it is very suffocating indeed. Nobody was dead
after dissolving a copper coin in HNO3 but some of us doing such experiments had bronchitis.
By the way does ammonia react with NO? If so, keeping open bottle of 25% NH3 close to any source of a possible leak can make the atmosphere healthier
[Edited on 20-7-2021 by teodor]
I think it should react well. See what happened to my bottle of an unnamed acid in the health atmosphere of my laboratory cabinet. I have no idea what
the salt is but suppose it has ammonium cation)
[Edited on 20-7-2021 by teodor]
[Edited on 20-7-2021 by teodor]
Also keep in mind that dissolving any real alloy in some acids (except HNO3) produce not only H2 (which I am not bothering about) but also different
pnictogen hidrides as well as different compounds of sulfur group and hydrogen. They are much more dangerous even in tiny quantities, such experiments
in a closed space can make me a bit ill for 1-2 days. That's why HNO3 is much healthier acid for dissolving most alloys from my point of view.
[Edited on 20-7-2021 by teodor]
[Edited on 20-7-2021 by teodor]
[Edited on 20-7-2021 by teodor]
[Edited on 20-7-2021 by teodor]Herr Haber - 20-7-2021 at 07:59
Obviously we're not really dealing with HCN or H2S or stuff like that here. The measures for them would warrant a negative pressure
fume hood in my safety standards, no shortcuts.
[Edited on 19-7-2021 by Fyndium]
Negative pressure does not exist. Partial vacuum is between 0 and 1
Garden hose is good, but what about getting your tube *past* the syphon of the sink or the toilet ?
You'd have to deal with a much shorter hoseFyndium - 20-7-2021 at 08:14
Relative negative pressure. Pun intended here.
The airlock siphon passage only works for some. I rather went it outdoors as there is unlimited space. I wrote earlier that my kitchen reeked of NO2
when I tried that last time.teodor - 3-8-2021 at 10:57
I've just accidentally discovered today, browsing some literature, that NO gas (which is not possible to absorbe by water) could be absorbed with
aqueous solution of acidic FeSO4. It forms Fe(NO)SO4 complex.
See, for example, here: https://doi.org/10.1021/i260067a019 .
[Edited on 3-8-2021 by teodor]Fyndium - 12-8-2021 at 10:24
They sell cheap 40mm vacuum tubing for around 2€/m, which looks perfect for the purpose. I was planning on getting a simple bucket, pulling the tube
through from side, and making a hole for 100mm 150m3/h duct fan to the bucket lid, and placing a pvc tube 2m long to push the fumes upwards with
effective velocity. This duct fan creates a good vacuum inside the bucket, which creates good suction to the 40mm tube. This is not enough to clean a
fume hood, perhaps fairs if the hood is fully enclosed during operation to allow for only minor leaks to create negative pressure inside, but perfect
as an outlet for smaller tube coming directly from closed reaction vessel. High velocities also keep the concentration much below LEL, preventing any
potential ignition, although the fan is brushless.BromicAcid - 13-8-2021 at 06:39
Here is the scrubber that I designed for use in the lab:
