Assuming Passive. [edit: wish I could read! you explicitly state active. drop the warm side a bit and just make like you’re running product]
You’re not trying to boil off the longer chains. They have a HIGHER boiling point than your solvent of choice.
you need one bath slightly above the boiling point (-42C), and one well below.
Dry ice/Ispropanol should work well for the cold side.
For the warm side, there are a slew of options here…
Ice + NaCl will get you -20C, but I imagine a hair colder would be ideal.
Maybe ice & calcium chloride hexahydrate?
You vac your system down, load the solvent into your receiver, and use the column as a reflux head (so you want to chill the column to -40C too). You chill the hell out of the working tank, & it acts as the condenser.
All the bad players are left in the splatter platter where the good stuff usually appears.
Skunkpharm has a decent writeup of the process for n-butane. although you’ll need to translate things like valve numbers to match your rig
caveate: I haven’t performed this particular trick, as my rig is only certified for a 30/70 mix & I’ve only ever run n-butane in it.
Manual should have this in it too…