Recycling/Repurposing extra propane from propane heavy 70/30 Butane/Propane Blends

So I have been using a 70/30 butane/propane solvent blend because I’ve always had the best results with this blend, it seems to pull a decent combo of terps and cannabanoids from a wide range of materials, and due to the higher pressure of the propane I have not needed a nitro push to achieve decent flow rates thru my crc.

I also refuse to scrape so I always leave a small amount behind to be able to pour without too much loss on the sides of the platter.

I have been using the same 50# solvent tank (24lb capacity) to inject and recover into, and as most of you know when using blends and pouring, you lose some butane each time because the propane boils off first, making your solvent tank become more propane rich each time.

Well, this is becoming a pain in the ass because I have to adjust my ratios every 3-4 runs, and right now my tank is around 80/20 propane/butane…. Planning on getting a 100lb jacketed solvent tank to use as my injection solvent tank, and use this smaller tank to recover into, so I don’t have to adjust ratios and can just run the same blend from the main tank until it’s gone, as long as the ratio in that tank will remain the same even when its not full.

But I’ve been sitting here thinking about the best way to go about removing the propane from this tank without just off-gassing it so I can do another run, and I had a few ideas, but I don’t want to attempt anything without hearing some feedback on them first.

So, first question, if I were to want to just remove the propane from a blended tank that was say, 50/50 propane butane, could I theoretically take an empty tank, vaccum it down and place it in a DI slurry, and then connect that to the vapor port of the tank with 50/50 in it, place that tank in ice and let it condense the butane to the bottom(not sure how long this would take, maybe someone knows or has a formula?), then open the valves and transfer just the propane to the receiving tank? Since the propane will still be a gas and sit on top of the liquid butane? Or would that still transfer butane also? Would it help to have a condensing coil in DI between the tanks? Maybe use a Recovery pump to aid the transfer?

Second question. If this does work, would I also be able to transfer the extra propane to a regular propane tank from the gas station this way and then use it to grill with?

If that’s a stupid idea, tell me, but I’m just spitballing for ways to recycle and repurpose this extra propane. Could also store it and use it for warm solvent pushes thru my injection coil, or mixing with straight butane to create a blend when I refill my main tank…. trying not to waste it if possible.

Just wondering if anyone has done something like this or not, and if this is a stupid idea because of A, B and/or C, or if I stumbled on something that we could potentially use to improve efficiency

And I have looked all over the forum and the internet for a week trying to figure this out but I have not found a clear answer on the topic yet, so I decided to start one.

Why wouldn’t you just add butane to the 50/50 tank to bring it to 70/30?

Butane and propane are miscible and you cannot condense only butane to a liquid while the propane stays a vapor. your vapors will be heavier in propane but will still have butane in it.


Ok that’s the answer I was looking for. Just wanted to clarify if it was or was not possible to separate them that way when blended. And yeah adding butane is probably the best way to do it, I knew that but I guess I was thinking of a scenario where the tank is almost full and the ratio is off, and was thinking I could try to siphon the propane off and use it for something else, but it seems like the only way to fix the ratio if you have a full tank is to just vent it off to make room for the butane.


Just replace what you loose every run with pure butane until you hit your desired ratio. That’s how I brought mine down and made great hash the whole way (assuming you can safely handle the high propane ratio pressure in your system).


I refill with 100lbs 70/30 every couple days and usually end up at a stable ratio of 60/40ish. Verified by GC-fid


I have to disagree with this a bit. You can definitely preferentially condense LPG mixtures.

If at a given pressure the condensing point of butane is higher than the condensing point of propane, you will “preferentially” condense butane.

In theory, if you can maintain the entire environment (thermodynamic “system”) at or near the condensing point of butane while staying above the condensing point of propane—more butane will condense.

You can see this in the following T-X-Y diagram for a propane butane mixture:

I’ll have to draw something out to expand on this diagram…

If I start with a 50/50 mixture at temperature X and slowly increase to temperature Y, the composition of the liquid phase becomes point C and the vapor phase composition becomes point D.

This is the concept behind distillation:

Condense to C, the reboil that liquid at temperature Z1 up to temp Z2, condense to C1, reboil at Z2 up to temp Z3, condense to C2

Etc, etc.

This is why crude oil (like the kind from the ground) distillation columns fucking TALL (the tallest is almost 370ft tall) :melting_face:


Damn, hand drawn illustrations and graphs :bar_chart:




I was about to go down the rabbit hole for a second.

If anyone feels like taking this concept even further look up McCabe-Thiele method.

That test in separations almost ended my college career :rofl:


I have a few…lol

He gets his point across fairly quickly.


I love the result of the disagreement and I totally agree with you. Great drawings and information too!


I’m glad you commented what you did.

A lot of people I’ve come across are under the misconception in the opposite direction—I.e. that you can simply jump to the left or right side of that graph just by changing temperature.

Suffice to say that your previous assertion was more correct than the misconception i just typed in this comment

Until you can show someone this graphical explanation it’s hard to explain why that’s not the case.