Can you post a picture of your setup? I was thinking of building a refraction still myself. Not for cooking iso but for many other things hehehe. Just interested in seeing what you got cookin. How many runs do you plan on doing?
I did not know that 85C was the boiling point of iso as I had never bothered to look it up but you should end up with a more potent end product than doing a simple iso bath in open air as you need to heat THC to approximately 65-75 C in order to decarboxylate the inactive THC molecules in active THC molecules. It is the main reason I use a double boil procedure in my butane extractions.
If you have the time would you mind posting a detailed breakdown of your equipment and process and perhaps the final results? I'm sure many here would appreciate it, plus I love learning something new and (potentially) dangerous. Not that its dangerous so long as proper precautions are taken and all equipment is in good working order. I do have a strong understanding of using a refraction still to produce alcohol.
As far as the time required doesn't that directly depend on the volume of ISO being used? Do you have a temp gauge on the pressure cooker itself so that you can see how hot it is inside the device? If so I would imagine you would just set your elements temp to 100C (boiling point of water) and watch your temp gauge. It should maintain a steady temp of 84C give or take a couple degrees depending on your elevation until the ISO has boiled off, you would then notice the temp would begin to rise past the boiling point of ISO. As soon as you see the temp rise above the ISO's boiling point just remove the heat. I'm sure you know this already but I will say it for those out there that don't. This is the basic principle behind separation of distillates, the temp will only rise to the lowest boiling point of a single liquid in the solution until that liquid evaporates off, then it will rise to the next lowest boiling point of whichever liquid is in the solution.
Say you had an ISO solution but you weren't sure of the water content or if there were other liquids in the solution. You could seperate each by applying heat to the solution while it is contained in the device described above, when it hits 85 degrees you know that the iso will boil off and you can collect it. As soon as you see a temp variation, remove the collection vessel and swap in a clean one. Record the next stable temperature and find out which things boil at that temp. Repeat the process until no liquid remains. Toss the first few drops between each change in temp (this is called the tails in brewing) as it will be contaminated with more than just a single liquid. The point of the refraction still is to cause the distillate to re-condense in the column and flow back into the bath below slowing the process down to achieve better results.
Very cool stuff, I hope to see more on this.