For starters, may I note that other than proving the process and Lil Terp equipment, the balance of my R&D has been with active systems using a pump?
I've also never inline de-waxed with a passive system, but let's first talk about how they work and how to figure out pressures, so as to keep things in perspective.
Passive systems move the butane around using differential pressure created by differences in temperature. The Gay/Lussac law says that the pressure of a given amount of gas, held at constant volume, is directly proportional to it temperature Kelvin. P is a constant function of T, so P/T=C, and P1/T1 = P2/T2 = P3/T3........
That makes equipment sizing critical, and too many brothers try to run columns too large for the base. With a 10" X 12" collection pot and 3 X 18 column, you have about a 7.4:1 ration and should be more than adequate.
Kelvin is Celcius minus -273.15 degrees, so at 21C/70F ambient, we are at 294.15K, and the volume of your 10" X 12" pot is 942.5 in/3 at 29.92" Hg, and your columns 127 in/3 each.
29.92:294.15::1:X=19.5K or C /35F temperature differential in temperature needed per inch Hg of vacuum. As you can see, passive systems operate with relatively low pressure differentials, so they don't gracefully tolerate much resistance to flow.
You can also see why water ice and brine give little vacuum for inline filtration, so suggest using dry ice and alcohol.
Predistill your butane and have everything in the system connected and vacuumed to as close to -29.92" Hg as possible to remove all the atmospheric oxygen, and to eliminate any non-condensable gases in the system. After vacuuming, close the valve between the collection and recovery tank and open the recovery tank valve.
Note, if your injection and recovery tank are the same and you can't plumb it to do both without disconnecting it in the process, install a tee fitting in the line between the recovery port and the tank, that allows you to vacuum out the line again after re-connection.
I suggest packing and freezing the material column to ~-18C/0F, and wrapping insulation around it, but installing swiftly and not putting coolant and ice in the jacket.
If it is warmer than -.5C/31F, when the butane hits it, it will vaporize and impede further butane flooding the column, without a vapor vent.
Chill the pre-distilled n-butane to -30C and use an auxiliary hot vapor tank to provide tank head space pressure. You can also use N2 for this, but I prefer hot vapor, so as to not require subsequent burping.
I would put alcohol and dry ice in the de-wax column jacket, and set the collection tank in an alcohol dry ice bath, as well as the storage tank connected to the collection tank by hose.
I would use a screened gasket and a couple wadded up commercial sized coffee filters between the extraction column. You just have to keep the chunks out, as you will be filtering again. I would use a 1 micron 4" X 8" polyester felt sock filter between the dewaxing column and the collection tank. Face filters blind rapidly when filtering wax.
An alternative is a roughing filter, followed by finer face filters, but you need to get down to around 25 microns or below.
I would inject through the material column, into the de-wax column, and let it sit for 30 minutes to an hour, before opening the valve under the de-wax column, and pulling the butane through a 1 micron sock filter.
I would remove the insulation from the material column after injection and when I got ready to filter, I would add warm water into the material column to warm it up and drive off butane.
Open the dump valve and allow the 29.92" vacuum in the collection pot provide the initial boost for vacuum filtration.
Once that vacuum is lost, open valve to recovery tank.
Once the column is drained, I would set the collection pot in ~100/110F warm water, leaving the recovery tank in dry ice and alcohol for final recovery.
