Im talking about if you bleed it from the recovery pot before recovery
I could never tell when the nitrogen was all out it was always guess work
I’m not planning on using a recovery pump though
Just an injection pump and pumps for the color remediation and solvent recovery membranes
I’ll run passive with giant 3" tubing
With my membranes and a big heater on the falling film a recovery pump would never keep up
You need to check out what I’m building 
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I used to recover residual hydrocarbon from seven five pound tubes in parallel overnight into a recovery cylinder.
The following morning, recovery cylinder pressure could be as high as 90 psi, indicating air in the system.
What you can do is gently relieving pressure by opening the gas valve for a few seconds, preferably outside. Then you wait for a little while, allowing the “new” partial pressure of the air in the headspace to be established.
Repeat a couple of times and you will soon arrive at a cylinder pressure that corresponds perfectly with the butane phase diagram, ie, all air/nitrogen has been removed from the cylinder.
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When the butane starts boiling again, as the nitrogen will usually keep it down. But, one shouldn’t vent from the collection where there excessive gasses present
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You should definitely pressure check your system. And have that pump looked at. That shouldn’t happen
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… but it easily can, particularly if the biomass tubes aren’t evacuated before a set of extractions. Or if the system allows air to enter the low pressure side during extended recovery.
It’s a temperature and pressure dependent phenomenon driven by mass transfer.
So the difference is bound to be significant at different temperatures, I will look for more information.
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Is it also a time related phenomenon, or does this happen in the short amount of time that nitrogen is present in the solvent tank?
I’d venture to say that these processes are essentially diffusion controlled, ie, happens without any discernible activation energy barrier.
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I would still like to know the pressure and temperature that I operate at, and how much it’s dissolving into my butane, and when it goes into gas phase does it let go
In the gas phase, it’s just a homogeneous mixture of molecules. It’s not as if there’s an “upper layer” of nitrogen and a “lower layer” of butane as in a separation funnel.
I cannot see any reason why it would be much different in the liquid phase; there are really no favorable solvation effects between butane and nitrogen. I see it as the nitrogen being “pushed into” liquid butane, rather than being “sucked up” by the liquid butane.
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Let me explain further on what I was implying. Yes, I completely understand that they are both in the vapor phase and will quite happily be one homogeneous gaseous mixture. When the butane condenses @0c (nitrogen BP is -195.8°C) back into a liquid, under no pressure, is the nitrogen still in the liquid, or did it stay a vapor? I want to say that it remained a vapor.
Sorta does. Have you ever put more nitrogen pressure in your evaporator than the butane is emitting? The nitrogen will prevent the butane from boiling and keeping it from from evaporating. When the excess nitrogen leaves, allowing the butane to boil and the gasses rise. I also could be seeing this in the wrong way, too.
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It depends on the partial pressure of the more volatile component. Butane’s vapor pressure at 0C is about 15 psi so that would be about its partial pressure in the “head space”.
I think you would need quite a high partial pressure of nitrogen to force appreciable amounts of it into a liquid hydrocarbon phase.
What happens is that presence of the nitrogen adds to the “total pressure” and it is that pressure that the expanding/“boiling” butane has to overcome.
Butane boils at 0C because it is at that temperature its vapor pressure is able to overcome the atmosphere’s 15 psi pressure.
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I was implying in the headspace (gas phase) as a whole.
In a cylinder containing a mixture of butane and nitrogen under high enough pressure so that a liquid phase is obtained, obviously the liquid phase will be heavily enriched in butane and the gas phase heavily enriched in the much more “volatile” component nitrogen.
Butane condenses @0c. My tank is under vacuum @ beyond -60c and only has positive pressure when nitrogen is added.
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As a whole they will be mixed. But the bottom will be mostly butane vapors and the top being nitrogen. You can even put a meter over the vent and it’ll tell you when the butane is escaping, after nitrogen has at first.
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Yes. That was exactly the point I was making in one of my earlier comments about how to vent a cylinder that has too much surplus atmosphere in it.
There’s also a discernible change in the sound of the volatiles being released. You can actually hear when all air molecules has escaped.
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The bottom will be mostly butane liquid with a tiny bit of nitrogen “dissolved” in it. The top will be a mixture of butane and nitrogen molecules banging into each other at such a rate so I would be very surprised if there is any discernible “stratification” in the gas phase.
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It condenses at 0C because at that temperature its vapor pressure is lower than that of the surrounding atmosphere.
The air we all breathe is at 15 psi, at least at sea level. We don’t “feel” that pressure because that is the pressure we have evolved in.
But any gas/liquid most definitely will, and behave accordingly.