Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: curiouscat on January 13, 2013, 01:32:25 AM
-
What are good ways to wash off an occluded / adsorbed organic off an inorganic precipitate? A water wash didn't help at all. The organic is fairly oily and seems stuck on the ppt.
Ideas I have are:
- a hot / boiling water wash
- some solvent wash; probably a low boiling one to separate easily from my organic later. Acetone? Hexane?
- Surfactants / Detergent to get the organic to mix with water. Normally the organic is substantially insoluble with H2O
- Sonication?
Comments? Ideas?
-
Take a sample of the organic and see what it dissolves in.
-
That depends on what the inorganic and organic material are. The order I would try is surfactants, then solvents, then some form of reactive chemical treatment.
If the surfaces are accessible, just adding something like dishwashing detergent to the surface, rubbing it with a soft brush, and then washing it off with water will remove most tarry or sticky organic materials.
If the surface of the inorganic material is sensitive to brushing, dissolving the organic material in a solvent like toluene, hexane, or any of the various commercial oil paint brush cleaners usually works. Sonication may speed this process.
Finally, if nothing else works and the inorganic is inert, soaking the material in chromic acid cleaning solution or a concentrated sulfuric acid cleaning solution may degrade the organic material to the point where it will fall off. This was particularly useful for cleaning stubborn deposits on laboratory glassware, until it got so difficult to dispose of the extremely toxic and reactive waste.
-
Is this an industrial process?
How is the inorganic product isolated?
How much of the organic component is there compared with the inorganic?
How big a wash can you do?
Can you easily do a hot wash with solvent?
I've found that washing is not always effective in situations like this. I think you might be better doing a re-slurry in hot solvent.
-
Is this an industrial process?
Well, it's at the kg. scale right now. And the interest is in closing our material balance. The loss of organic is a problem on that front. Ultimately, yes, we'd like to scale it to industrial.
How is the inorganic product isolated?
Settling followed by filtration.
How much of the organic component is there compared with the inorganic?
I expect ~5-10% w/w. That's on the basis of how much our material balance is off.
How big a wash can you do?
I don't see an obvious limit right now. We have a few kilos of the ppt.
Can you easily do a hot wash with solvent?
Yes.
-
Finally, if nothing else works and the inorganic is inert, soaking the material in chromic acid cleaning solution or a concentrated sulfuric acid cleaning solution may degrade the organic material to the point where it will fall off. This was particularly useful for cleaning stubborn deposits on laboratory glassware, until it got so difficult to dispose of the extremely toxic and reactive waste.
Sorry, I should have clarified: I'm interested in recovering the organic. The ppt is not important to recover.
-
Lets see if I understand the problem fully:
You are making an organic product and during the process you get an inorganic precipitate that you aim to filter out and discard.
Your yield for the organic material is 90-95% and you assume the lost yield was lost with the inorganic precipitate.
If I have that right the questions I'd ask are:
Have you confirmed the inorganic filter cake does contain the "missing" organic fraction or it it actually lost elsewhere?
If it a coating on the precipitate you might get back with a solvent wash but if it is part of the precipitate it will be much harder to get back out.
Does the value of the organic product justify the extra processing steps required to recover the 5-10% yield?
-
Take a sample of the organic and see what it dissolves in.
Checked it. Dissolves in hexane, ethyl acetate, acetone, may be more.
Now will try washes.
-
Then just wash it with warm acetone.
-
Have you confirmed the inorganic filter cake does contain the "missing" organic fraction or it it actually lost elsewhere?
How else? It's not in in any of the other streams we looked for it in.
Does the value of the organic product justify the extra processing steps required to recover the 5-10% yield?
Yes, for reasonable steps. Not if it turns out to be unreasonably hard. Even if it is impractical later, would be nice to confirm the ppt is where we are losing it all.
-
Then just wash it with warm acetone.
Will do. Thanks.