Based on my research, it's probably best to avoid isopropyl alcohol for use in extractions since it is a LOT harder to purge than butane and it's toxic (unlike ethanol or butane; see the MSDS).
Boiling point Butane: -1 C
Boiling point Isopropyl: 82.5 C
Vapor pressure Butane: 1520 mmHg
Vapor pressure Isopropyl: 40 mmHg
Copy/pastes from posts at other forums found while doing my research:
"Purging butane is much easier and able to be completed to a higher level of purity than iso. Boiling point, vapor pressure etc. are all much more favorable for butane than iso as far as performing an extraction. Butane is also much less harmful to humans than iso. Inhaling butane has more or less no adverse effects (check the msds), iso is much worse."
One guy concluded: "Double the terps retained by bho on average browsing test results, MUCH lower and well below safe limits when butane is used as oppose to alcohol and butane is a much safer (for your body) substance (see: msds). Can't find many reports for ISO, the only 3 residual for alcohol showed 12,000-18,000ppm (out of a safe 5,000ppm daily) which is more than alarming."
Residual solvent test results isopropyl (>12,000 ppm): http://analytical360...archived/127456(again, it's only one test, but a lack of data for iso in general isn't reassuring)
Residual for ethanol: (>18,000 ppm): http://analytical360...archived/139817(while higher than iso, ethanol is far less problematic. Heck, I even drink the stuff on occasion...).
Even butane cannot be completely purged from the oil, but at least butane isn't bad for you unless it's concentrated enough to explode (or asphyxiate you by displacing oxygen). Residual for BHO (~1000 ppm, and that was the highest residual amount for BHO the poster had found; also note the higher terpene retention than alcohol extracts): http://analytical360...archived/138217
So while using butane is generally is the most dangerous way to make an extract, using alcohol appears to result in having the highest potential for leaving behind high levels of residual solvent. Given a choice, I'd definitely prefer to consume an ethanol-based extract over an iso-based (assuming there's no CO2 oil around, of course).
As far as vaping it, VG is problematic with extracts due to being very difficult to keep mixed for very long and unless the mixer juice has PEG (polyethylene glycol) in it, it will eventually separate from the extract (even from a 100% PG juice, though it might take a while). The mixes sold specifically for extracts like "EJ Mix" and "DB Mix" are both blends of two weights of PG and some PEG, which emulsifies hash oil best (and results in a mix that doesn't separate). I went with DB Mix based on prices and many reviews.
I'm on my fourth mini test-batch of experiments and have pretty much nailed it down (the one I'm working on today will hopefully be the winner).
From what I've done so far, I'd have to say that Winterizing your extract is critical to making a good vape-able hash oil mix that doesn't clog up or make you cough your lungs out. I've made a straight extract/DB Mix blend, an isomerized and decarboxylated extract/DB Mix blend, and an isomerized, decarboxylated, and winterized extract/DB Mix blend (which was beautiful, almost too potent, and no-cough smooth even with monster hits). By the end I'd lost ~16% of the starting weight of the extract after all the processing, but the potency boosts more than made up for it.
It's taken me a while to get to this point since I had to wait on a new heavy, ceramic Buchner funnel setup to arrive to make Winterizing a lot easier (a thick ceramic funnel like a CoorsTek brand is ideal since the high thermal mass keeps the alcohol cold during filtration so long as you remember to chill the funnel in the freezer ~24 hours before using it).
For my next test I'm going to boost the ratio of DB Mix to extract up to 4:1 since 3:1 was still a bit too potent for my purpose, which is vaping in public when I generally only want incremental boosts in my buzz or to sustain a comfortable level all day (when I just want to get totally blasted in one hit I'll break out my new ceramic temp-controlled Kiln vaporizer and vape a dab of straight extract processed as above but not mixed with any DB Mix, which is awesome).
I'll probably never hit another titanium dab-nail again now that I'm becoming familiar with ceramic-coil vapes; a dab the size of a grain of rice makes one enormous hit off a hot nail (with most of it exhaled into the air, not absorbed in our lungs!) but I get 4 or 5 great hits from the same amount vaped in a Kiln and each one is as good as the one big hit off the traditional nail.
Thanks to good post-harvest processing and recent technological developments I'm stretching my hash/weed-budget farther than I ever thought possible, while actually "smoking" very little plant material anymore (I definitely still enjoy smoking top-shelf, well-cured bud on occasion but the times they are a changin' and now the best time of day IMO is 7:10, not 4:20!).
Edited by TVCasualty, 12 March 2016 - 12:27 PM.