I have been fumbling with a system to extract cannabis oil using butane, where the butane is recovered and recycled, instead of simply evaporating to atmosphere. Here is my prototype test sled, generally based on the original work done by Foaf, and whom was kind enough to provide me with useful support in this endeavor.
He sagely observed that N-Butane is also known as R-600 refrigerant, which is used places where toxic refrigerants are unsuitable, such as a food propellant in pressurized cans.
I will post my progress in stages, because I am still shaking out the operational portion of it, but here is skunk pharm's vacuum botanical oil extraction unit assembled and ready to roll, though I run it on the patio instead of my kitchen.
The system consists of a Schedule 10 304SS stainless column with plumbed blanking flanges, in which the prepared material is placed. A 130 micron stainless filter at both ends, faced with a paper filter, contains the material.
The column sits over an electro-less nickel plated pressure pot, connected by a 3/4" stainless Swagelok tube and controlled by a stainless ball valve.
The top flange has a stainless ball valve and a 3/16" stainless vent tube running from the top of the column, to the pressure vessel below.
The pressure pot has a port for a refrigeration vacuum pump, an oil less refrigerate recovery machine, and a vacuum gauge rated in microns.
To operate the system, after loading the material into the column, the whole system is pulled down below 1000 microns vacuum using the vacuum pump, which also helps boil off any residual water in the material being processed.
When vacuum is achieved, the lower column valve is closed and the vacuum pump shut off.
A valve is opened that allows liquid butane to flow from a 50# butane recovery tank into the column and out through the top vent valve, back down into the collection vessel below. The top valve can be closed if soaking the material is desired.
The refrigerant recovery system is then switched on, which creates a push pull that circulates butane from the storage tank, through the material, and then again pulls it off as a gas and recompresses it back as a liquid in the original refrigerant recovery storage tank.
The extracted cannabis is left behind in the lower pressure vessel.
The lower pressure vessel and column are heated to speed up the process, which will otherwise grind to a halt as the butane temperature plummets from boiling under vacuum.
For system shakedown, I didn't bother to heat the column, and simply set the pressure pot in a larger pot of flowing water to supply heat.
My initial attempts at pulling a vacuum were scattered on the column, so I machined .210" O-ring seals into the blanking flanges, which solved the problem.
Here are the equipment shake out photos. More on process later.
