About 10 min ago, I saw something on my extraction setup that really threw me for a loop. I use 100L kegs as intermediate vessels for mostly for recovered/fresh solvent. I transfer with about 5 psi of clean compressed air in the head space with the receiver vented to atmosphere to relieve any pressure. As a safety rule, I you are never allowed to walk away from a pressurized vessel or transfer in progress, if you’re going to leave, you have to vent the vessel/stop the transfer. So I go to vent the keg, everything goes fine, but once the pressure is released, a kind of fog spilled out.
The open you see is a vent plug for my air/vac fittings.
I gave it a whiff (don’t try that at home) and it smelled like really good terps (which I suppose worries me), but I really don’t know why that would happen. It is recovered ethanol, so their presence is not really surprising, but I’m not sure why they would do that. I would expect an increase in pressure would cause the vapor pressure of pretty much all compounds (including ethanol) to reduce. Maybe it did and it precipitated as droplets, but didn’t have time to condense so they travelled with the air? I’m really just grasping at straws.
a few questions to explore the setup:
how cold is the ethanol?
how cold is the air in the room? is the humidity particularly high?
what type of process/machine do you use for solvent recovery?
Room temp ethanol, 52% humidity, is about 75-80F in the room. I use a membrane system for solvent recovery. I did have some leaky membranes so my ethanol was a bit green and I would guess a touch terpy.
right on thanks. i ask because often a ‘foggy’ vapor can simply be cold air/ethanol vapor condensing tiny droplets of the water in humid air–or, the air in the room itself is cold and causes the same phenomenon. i realize that was likely obvious to you already but worth asking towards, as the ethanol and the room are room temp it looks like probably a no on that one.
does that vapor condense back to a liquid on a gloved hand placed in front of the vapor stream? if it does it might be ethanol vapor, which would be confirmed with a sniff of the glove. if it does not, likely terps as you suspect, they’re too volatile to recondense at room temp (at least in my experience).
CO2 was a suspect mentioned above, is this a gas that’s involved in your process? if you’re not putting any in, I wonder where it would arise on its own.
i would think if it was CO2, when you inhaled it you’d know, in that it gives a ‘tickley’ feeling to the nose (like when you drink a freshly cracked soda) and/or will briefly displace the O2 you’re breathing.
do you smell the vapor after transfers when you don’t see this foggy phenomenon too? just thinking about a comparative reference point on that one.
leaky membranes and greenish ethanol point to something in that area, even if that’s the end of the road and we can’t end up classifying what that vapor really is beyond a ‘best guess’, its fun to think through
Hmm, interesting. I don’t use CO2 in my process, however I do use compressed air, and CO2 (probably like most gasses) gains solubility with pressure, but I’m not sure that would be cloudy since it would be room temp. I haven’t had it happen again (it was with a fresh keg). I had a faint smell of ethanol, but it didn’t burn my nose. I haven’t smelled it sans vapor so I’ll give that a try.
I think I may have figured it out though. I had changed he regulator to 15 psi for a different vessel as opposed to 5 psi. I realize the gas is decompressing and therefore cooling the port it is escaping more than it normally does. This could have condensed some of the less volatile compounds (terps) which is why I was smelling it.
*And safety note, the kegs are rated for 40 psi, I keep it below 15psi so it isnt considered a pressure vessel. You really don’t need any more than that.
i think you’re right, that definitely tracks. and yeah that 15psi threshold for a pressure vessel is an extremely useful thing, it’s gotten some of my projects over the hump and into implementation (once again, big shoutout to PRVs lol)
did not know this! that’s interesting af thank you i’ll be looking into that more.
applying it to this though, do we consider ethanol a LPG? to my knowledge these are more propane/butane etc. unless you mean the terps themselves?
Fast moving air creates low pressure (Bernoulli’s principle), and a rapid change in pressure with the presence of particulate in the air can easily form a cloud.
