Any chemists out there?

[JaXanim]

Yep. What's the problem?

JaX

[JaXanim]

Assuming your density/water content data are correct, I'd say you haven't got enough water out at the salting out step. The basic principle is that though water and IPA are miscible, adding a water soluble electrolyte (NaCl) reduces the proportion remaining in solution. A small residual water content will spoil the results when you distil the product. IPA and water form an azeotrope, which means the water will co-distil and dilute the product. The salt isn't soluble in IPA at all, but water will partition between the IPA and brine layers depending on how much salt is used. I suspect you didn't use enough. Alternatively, you didn't allow long enough for the salt to 'find' all the water at the shaking stage. You need to get this mixture really well shook up for quite a while to ensure the salt does its job.

JaX

[JaXanim]

@Hodgkinson

Heating won't help very much and you'll lose some IPA by evaporation. It's the contact that's important. I'm surprised that salting out will get the water down as low as suggested in the article. Making 99%+ IPA by this method is gonna be difficult I reckon. A better method for the final drying step is dehydration using something like anhydrous sodium sulphate or maybe silica gel. The IPA layer should be treated with this for a couple of days before distillation.

JaX

[JaXanim]

There needs to be excess salt undissolved in the mixture to ensure you get the maximum dehydration. Saturated brine is only around 27% salt so add enough to remain undissolved.
You may not need to add anything extra if you can get the last traces of water out using salt. Any sodium sulphate or silica gel is better added before distillation. It won't be affected by the salt.

JaX

[JaXanim]

Hodgkinson wrote:
- - - why add the silica gel before the distillation? To prevent contamination?

No, simply to avoid distilling the azeotrope. You can do a final dehydration on the distillate if you wish. What you use for that depends on what's available to you. I supposed you were doing this in the kitchen sink, but if you're working in a lab, there's other alternatives/techniques. Anhydrous sodium sulphate takes some beating.

Watch the videos.

JaX