Confused.
Are you calling your decarbed crude “distillate” here?
What is it you’re calling “terps”?
Or “crude” for that matter?
Not that semantics or terminology is gonna change the physics / chemistry, but it does make it harder to know exactly what’s going on and help.
If your “terps” are “all the liquid we get in our cold trap during decarb”, then yeah, that may be the source of your residual solvent.
15min at rm temp?!?
Maybe try 20min…and zero
Have you asked?
Perhaps the person that developed the SOP understood the possibility of residual butane at -50C ??
…and added this step to mitigate that possibility, as suggested by @Cassin
I’d suggest higher temps (than the -50C for three-five days)…rm temp isn’t horrible, but you might consider longer or under vac (15min, 15-20” Hg?).
Ref: Propane Butane Mixture - Evaporation Pressure
Suggests to me that yeah, you are catching some butane along with the volatiles you’re after, and you should perform a data informed purge (3rd party if you have no in house analytics).
$2k will get you a critter capable of informing your purge….