Totally agree - I learnt new things and it is November 2019 - Nearly 5 years after the original question was posted, so please keep answering Necro Posts, saves starting a similar thread and utilises existing (although sometimes dated) information and data.
I have a similar conundrum but on a smaller scale. I hoped the vacuum distillation would go quicker, it doesn't and I also hoped the lower temperature required under vac would increase the quality, it doesn't.
The azeotrope issue does not bother me, 95% is all I'm after. Starting with a 80% ABV - this is the level obtained via a quick distillation I couldn't work out why it was so hard to get to the next level - this link explains why.
https://pubs.acs.org/doi/pdf/10.1021/i200028a029
Basically, the amount of energy required to distill above the 80% ABV increases exponentially for each %. (rough summary)
didn't know how to insert a link so copy and paste it.
