I’ve been running propane for a few years and I’ve read a lot of great posts on here as well. This forum is a valuable resource and I appreciate anyone who takes the time to respond here.
As far as I can tell the general consensus is that a collection vessel under pressure will hold the extract in solution and the terpenes will be protected in the liquid solvent. During recovery if pressure is maintained there is little worry of terpene/volatile loss and everyone has their opinion on collection temps from 70-120 °f is typical depending on solvent
Here’s the thing. I am not convinced that terpenes stay in solution and are NOT carried out when recovering propane. I have burped the collection before and it smells amazing (despite the pressure being 50-75-100-125psi) - the terpenes must be co-vaporizing with the propane and lost to the molseive.
Please convince me that I am wrong, or provide some specific temps and pressures that should keep propane and terpenes from co-vaporizing during recovery. If it is impossible to keep them seperate, do I need to configure a terp condenser between collection vessel and molsieve? Im happy to hear peoples experiences even if they dont know the hard science behind it. Any other insights?
There’s a bunch of thermodynamics shit in play that I don’t understand, but the theory with pressure as it relates to terp preservation is that pressure is not preventing evaporation 100%, it’s just inhibiting it by increasing the bp of the volatile terps. Some small portion of the terps will be lost but you’re only trying to preserve as much as you can
You’re not wrong at all. Terps are most definitely still volatile in that solution and are recondensing everywhere from inside the collection vessel, compression pump, and back into your stock tank.
There is a ton of work to be done regarding azeotropic studies on terpenes with propane at these temps are pressures. I think there will always be some mol fraction of monoterpenes (much lighter than sesquiterpenes) that end up traveling with propane into the compression pump. You could definitely try to recapture them, but it might end up being a negligible amount unless you’re operating at a fairly large scale already. If you’re so inclined, a cold trap that is set at a temp from -20C to 0C could recollect. Or you could possibly use a solid phase column and wash them out later once it is saturated. Sounds like a lot more work though.
My only advice is to recover at as low a temperature as possible if time isn’t a factor, and if you’ve got the right coolant/water ratio to prevent freezing. Propane recovery is already insanely fast if you’ve got a jacketed collection vessel anyways.
If there are volatile compounds in a vessel under pressure; the content of the headspace will be determined by Raoults law. The partial pressure of each compound is proportional to; the mole fraction of the compound in the liquid phase and the compounds pure component vapor pressure at system temperature.
the total pressure of the vessel is defined by Daltons law; which is the sum of the partial pressures of all volatile components within the vessel.
it gets pretty complex; you can get deviations from things like activity coefficents; and at high enough pressures gas behaviors can deviate from ideal gas laws.
I specialized in thermo in school, mainly looking at hydrocarbon adsorption to carbon surfaces. We did away with gas laws and instead looked at NIST databases integration into excel for modeling. Most solvents folks work with (propane, butane, etc.) have real world data to use, which makes answering complex questions like this MUCH easier.
Yep this is the best option
I recover at -18C and that still leaves plenty of pressure for the recovery unit a coldtrap won t work
I run -18 but think that anywhere around -5 should be enough
If a cold trap could work, alternately what if I have the top section of my collection at -10c, would that attract volatiles and prevent them from escaping with propane? This is a 6x48 collection with 2 separate jacket sections. Is 6" too wide to capture passing volatiles? Could I have the top cold and the bottom set to 90f and get better speed while still condensing up top?
What temp would I need to recover only propane and no terpenes, and at what pressure? If I recover at -10c but my pressure goes below 5psi would that allow volatiles to vaporize or would they remain in solution due to low temp? I’m imagining the “pulling” of the pump yanking volatiles out of solution despite the cold temp.
Thank you for detailing the laws, I get the gist but am not great at complex thermodynamics. Is there a standard I could focus on as a guideline to make this more easily digestible?
What’s better for terpene retention:
A. High heat collection 90-100f, pressure 100 psi, recovery valve cracked minimally, possible recondensing inside collection.
B. Cold collection 20f -7c, low pressure 5-15psi, pump pulling on solution.
In my trails I found B to work best
But I have all solvent I wish on the ground so at night I recover with ease
Except for vapor pressure laws I think that co distillation deu to H bonds is also a thingy
Think like steam distillation compounds with a higher bp come along with the steam
Beta carofylene etc etc
Come to think of it maybe implementing a Head either vigreu
Or plated may be a solution for having a better separation of compounds guess a scrubie filled
Spool could function
Never tried
3a Molecular sieve doesn’t absorb hydrocarbons just water… and molecules of the right physical size which the hydrocarbons are too small.
No matter what you’re going to lose a little bit of terpenes whenever you open your vat.
Adding butane doesn’t actually help with keeping them in solution because when you recover the butane you pull vacuum on it and the vacuum pulls the terpenes out with the butane. It’s been known that running pure butane you can end up with terpenes in your tank and that is simply because you’re pulling a hard vacuum on it and there’s no pressure to keep things in solution. The upside to butane though does give you a liquid pour out so you can keep the pressure above it higher with the propane in the blend.
We highly suggest a 70-30 propane heavy blend to be used in our systems to maximize efficiency. It keeps it a nice liquid pour out at the end while also you’re not watching paint dry waiting for the butane to boil.
High propane runs definitely helps to keep it there, you might have your basin temperature a little hot. We don’t ever go above 40 c but that’s also because I’m using compressor exhaust to heat and we’re boiling the liquid from top down. When we do the final pour out we typically recover down to positive 10-20 or so PSI and then pour out wet and cold.
Nonetheless I have new terpene tech to isolate the terpenes in the extraction system. Adding a cold trap to your system before the molsieve will just collect solvent because the condensing temperature & pressure will co-condense both solvent and terpenes together.
You are saying a cold trap before molsieve will not collect terpenes and volatiles, why?
If I am running 100% propane and I set the cold trap to 20-30°f isn’t that warm enough for propane to stay a vapor, but volatiles would condense out of the recovery vapor?
it will; youll condense both your solvent and your volatiles though.
you would have to tune your system such the enthalpy of condensation is ideal for the condensation of your terps or whatever; yet there is still enough energy to keep your solvent in the vapor phase. this is easier said than done; and if there are any overlaps of various attributes; then you wont get away from co-condensing multiple volatiles.
Very true it is a fine line and requires tuning. But isn’t that similar to what we do when choosing recovery temps? So it would be doubling the chance of terp retention.
Does anyone know of a filter that allows propane through but blocks other volatiles? Or is re-condensing the best route…