Closed loop systems like the Terpenator also have the ability to vacuum distill the LPG used in the process, so as to reduce the PPM of components heavier than C-4 Butane and commonly referred to as Mystery Oil.
While start with a 99.5% Instrument Grade, we routinely distill regardless of LPG grade. As noted above, it can be significantly more important if you are unable to obtain reagent grades and must rely on less regulated lighter or refrigerant grades.
You can do distillation with the column in place and the dump valve closed, but I typically leave the column out of the system and clamp the column top end cap directly to the column base.
Mk VB set up for Mystery Oil removal
The fractional distillation procedure involves injecting liquid LPG directly into the collection pot, and recovering it as a vapor under controlled conditions, so as to leave behind the heavier constituents.
To do so requires that distillation temperature be above the boiling temperature of the LPG involved, but below the next fraction, which is Pentane at 36C/97F, with Hexane next at 68C/154F.
Propane boils at -42C/-43.6F and n-Butane at -1C/30.2F, so our margin with Butane is only 37C/ 67F delta T and the closer you get to Pentanes boiling point, the more will be transported along with the recovered butane, and the closer you get to the boiling point of Butane, the slower the process goes.
We run the hot water bath that the Terpenator collection pot is sitting in at 21C/70F, which is close to the middle, with 85F the process limits, and maintain positive pressure in the pot during recovery.
When the pressure reaches zero gauge, aka atmospheric pressure, we stop recovering, because Pentane's boiling point will drop under vacuum and it will be conveyed with the Butane.
The critical key point is that we are not adding heat to boil the LPG in the collection pot, we are simply replacing the BTU's lost through boiling. Regardless of how hot you get the water bath, the boiling pool of LPG in the collection pot will not rise above the boiling point of the liquid at the pressure inside the collection pot.
That is because when a liquid boils and converts to a gas, it liberates the latent heat of vaporization, cooling the liquid pool it was liberated from. Unless we replace that lost latent heat of vaporization, the pool of liquid chills and boiling slows to a crawl or stop.
I suggest turning one collection pot bath heaters first, so they are preheated and ready to go once your have your start up inspection and pressure checks done.
Connect your LPG supply tank to your Terpenator's injection port via a 1/4" Nylon/Kevlar lined refrigerant hose. Open injection port flood valve, but leave supply tank valves closed.
If you have a WolfWurx Mk IV or V, replace the collection pot thermocouple with the LPG loading attachment provided, which is held in place with a 1 1/2" triclamp. Otherwise attach your tank of LPG to be distilled and leave the tank valve closed, but open the flood valve on the Terpenator, so that everything gets vacuumed out.
The next step is to start up the system and conduct safety inspection and pressure checks, per the operators manual for your specific system. If you don't have an operators manual, check out the Generic Operators Manual at XXXin the index.
Either set the LPG supply tank on a scale to monitor how much LPG you are injecting, or if your have viewports in your lid you can simply monitor the level in the collection tank.
With successful safety checks, proceed to evacuate the complete system to -29.9" Hg, so as to remove all the oxygen.
Next close flood valve on collection pot and open both recovery tank valves.
Start recovery pump and open recovery pump isolation valve.
Open the flood valve and either transfer by weight or by sight, but you only want the Collection pot to reach the half full level, to minimize liquid pickup from popping bubbles and the higher velocity of a Terpenators intake port when the system is under pressure.
Monitor the process and transfer more LPG as the collection pot level drops and when it is all transferred, the internal pot pressure will start to fall as the pool of LPG is recovered. When it reaches zero (0) Gauge (atmospheric pressure), close the recovery valve and shut off the recovery pump.
Start the high vacuum pump and open the vacuum pump isolation valve. Insure that the pump exhaust is vented to the extraction booth ventilation system.
Continue to vacuum until the system reaches -29.9F, and close off the vacuum pump isolation valve, and then the vacuum pump.
Open the N2 backfill valve if your Terpenator is so equipped, or back fill with atmosphere if not.
Open the collection pot and remove the Mystery Oil left behind, using hot water and detergent. Because we ended up under vacuum, the lighter Alkanes will boiled away and been evacuated by the high vacuum pump, leaving behind the even heavier molecules.