When scaling up, greater effort and time should be spent on salting out the KCl it's been discovered.
Another important note is viscosity, when the viscosity of the solution of H3PO3, KCl, H2O and ALky is viscuous, KCl will actually precipitate, a) but much of it will not be able to be filtered out, and b) it won't sink to the bottom as a white layer.
Signs of an overly viscuous solution are a cloudy solution, and perhaps not even any sign at all of a bottom layer (KCl, always KCl, this isn't H3PO3 that has sunk).
The cure if your in this situation is more alcohol, and even a splash of HCl solution if it's on hand. This is followed by a good shake, and generous amount of time to settle at room temp.
As you add more alky to a cloudy one-layer solution (overly viscuous, KCl suspended in H3PO3 solution) you'll gradually see a formation of two layers, KCl on the bottom, and a liquid layer of you-no-what with a slight yellow tinge.
Another thing that works really nicely is sitting the wine bottle in a bath of hot water for a few minutes and then sitting it at room temp to settle...this acheives a formation of layers without addition of further alcohol.
When you've got two layers, this is the time when the solution can bee filtered without clogging.
When it's all cloudy, filtration is primarilly a No-go. two layers good, one layer bad - remember that.
After a filtration session, let it settle and you may see even more KCl precipitate out of the filtrate. So it's not a one-go-show! But don't worry, the H3PO3 is out of harms way so you can take as much time as you like.
If you are desperate for some H3PO3 for a RXN or to put on the garden, just pour a little of the motherload being worked on in to a small bottle and work on it separately OK?
Good.
You can make it ultra pure really quickly when working with small amounts too...A splash of alkly and a splash of HCl, a dip in a bath of hot water, then time to settle will crash out everything when working with small amounts.
For ghetto drying, I think it's best to use the fan and or an air-con to remove the majority of the free-water, harming the H3PO3 none.
Then use the fan forced for a few minutes..preheat it, because if it isn't pre-heated it will tend to absorb water on the way up to temperature.
OK, finally isopropyl alcohol, TRY it. The story is that during testing, iso was used in one instance and I've got the sneaking suspicion it worked really nicely to salt out KCl. Someone upthread said that he'd been told to use iso, so those people may have had better information there, but I could only be sure on the metho tests, and so this is what I included in the write-up.
I would say that greater molecule sizes would work better,
Ill try to get more information here on alcohol molecule diametres etc.
To some up:
viscosity=bad for filtration & KCl settling out. Cure: more alcohol, a dip in a hot water bath.
10x
halfkast