My understanding is as follows:

The glycerol layer created during the biodiesel reaction stage is about 40% pure. You can then remove the methanol and acidify it in order to bring the purity to 80%. Finally, by passing the glycerin through an "ion exchange resin bed" (which can be obtained for a few hundred dollars, apparently) you can reach a purity of 95%. Any purity beyond that is only economical at industrial scales.

This is according to a post I've read by Girl Mark (scroll down 75%), which is already five years old.

Has anything changed? If you could reliably get to 97 or 98% purity, that would be technical grade.

I've read about coalescers, such as the Pall PhaseSep, and other systems such as the AmberSep BD50, but I'm not getting information about final product purity from the former, or pricing from the latter.

Does anyone have pearls of wisdom to share with me?

Thanks in advance!

I have been experimenting with separating the impurities from the glycerol and although I have made some progress it wouldn't be fit for human consumption.

I know nothing about ion exchange resins but I hope this helps.

So far I have acidulated with sulfuric acid and added water to help with the separation.
I then evaporated to 60% glycerol and then chilled in the freezer to precipitate the sodium sulfate in solution.
It was still almost jet black at this stage so I used activated bentonite to remove the color. After three goes with the bentonite it is about the color of new vegetable oil.

I tried heating some to get rid of the rest of the water but it was obviously to hot because it started to turn black again.

I am beginning to think that vacuum distillation might be the way to go.

quote:

Originally posted by sinbad:
So far I have acidulated with sulfuric acid and added water to help with the separation.
I then evaporated to 60% glycerol

Wait a sec, I'm already confused!

I thought that the glycerin byproduct after the reaction was about 45% pure, and that the glycerol layer created after acidifying the bi-product the glycerin layer is supposed to be 80% pure.

Are you saying that after separating AND evaporating you are still only at 60% purity?

The lye is very soluble in glycerin which is why the glycerin goes solid when cooled.
To remove the lye I convert it to sodium sulfate which is pretty harmless.

I added water to the mix to separate the remaining oils from the glycerol.
The 60% is the amount of glycerol relative to the amount of water.

Purity is another matter many things are soluble in or miscible with glycerol (methanol salts food preservatives) so without a lab to test the purity I really have no idea.

Which is why I am leaning towards vacuum distillation as it would remove the acid stage and remove any other salts that might be there. A commercial process I read about used triple distillation with steam.

quote:

Originally posted by sinbad:
I added water to the mix to separate the remaining oils from the glycerol.
The 60% is the amount of glycerol relative to the amount of water.

My bad. You said that you were adding water, and I should have caught that.

quote:

Originally posted by sinbad:
Purity is another matter many things are soluble in or miscible with glycerol (methanol salts food preservatives) so without a lab to test the purity I really have no idea.

Can you take a stab at the Glycerin/Water/Other Breakdown?

quote:

Originally posted by sinbad:
Which is why I am leaning towards vacuum distillation as it would remove the acid stage and remove any other salts that might be there.

Forgive my ignorance, but I thought I remembered reading that acidifying the byproduct was the most cost effective way to achieve ~80% purity, with the added benefit of getting a fertilizer as a byproduct if you use Phosphoric Acid.

Why do you wish to forgo the acidification?

I have evaporated salts from water before and it never ceases to amaze me how much salt can exist in such a small amount of water but hear goes
Apart from the water I am guessing 1-2% and 5% max.

The water is not really a problem as it is easily removed from the glycerol due to difference between the boiling points.

Phosphoric acid is good if you use potassium hydroxide as the catalyst because the pottassium phosphate is insoluble in alcohol and I think glycerol.

Sodium phospate is used as an emulsifier in batters etc so you might already have some in the mix but more importantly it will prevent separation of any oil remaining trapped in the glycerol.

I picked sulfuric because I use NaOH, and sodium sulfate solubility drops with temperature.

Also Phosphoric acid is quite expensive compared to the other acids.

quote:

Originally posted by sinbad:
I have evaporated salts from water before and it never ceases to amaze me how much salt can exist in such a small amount of water but hear goes
Apart from the water I am guessing 1-2% and 5% max.

Sorry, I'm new to this... "1-2% and 5% max" of what? 'Other' and Methanol?

quote:

Originally posted by sinbad:
The water is not really a problem as it is easily removed from the glycerol due to difference between the boiling points.

Phosphoric acid is good if you use potassium hydroxide as the catalyst because the pottassium phosphate is insoluble in alcohol and I think glycerol.

Sodium phospate is used as an emulsifier in batters etc so you might already have some in the mix but more importantly it will prevent separation of any oil remaining trapped in the glycerol.

Sorry again: I feel stupid already for asking, but why don't you want to separate the oil from the glycerol? Aren't we discussing cost effective ways of purifying glycerol?

quote:

Originally posted by sinbad:
I picked sulfuric because I use NaOH, and sodium sulfate solubility drops with temperature.

Also Phosphoric acid is quite expensive compared to the other acids.

I get this part. Since your catalyst is NaOH, there is no benefit for using Phosphoric Acid as a coalescer. Your tertiary byproduct is sodium sulfate or potassium sulfate.

quote:

"1-2% and 5% max" of what? 'Other' and Methanol?

That would depend on your oil source there are lots of chemicals in fast food and you may even get cleaning products in the mix. The most obvious contaminant would be sodium chloride.

And yes I do want to separate the oil that is why Sodium phosphate is a problem. Sorry I didn't write that very well.