Sciencemadness Discussion Board

Removing graphite from glass frit filter

Lionel Spanner - 10-11-2022 at 18:05

Hello all,

In the course of my experiments I recently vacuum-filtered a water-based mixture with large amount of suspended graphite particles in it through a glass frit filter (rookie error, I know.)

Not only did this not stop graphite particles passing through - I filtered the grey filtrate again under gravity, which successfully clarified it - but now the frit has graphite particles embedded in it, and I have yet to find a way to shift or remove them.

Some solvents I have tried using to remove them, without success:
* Cold water
* Hot water
* Acetone
* White spirit
* Liquid paraffin BP
* A few drops of cold red fuming nitric acid

The last of these caused some gentle bubbling, but otherwise did nothing other than staining the underside of the frit a reddish-brown. I didn't dare use hot nitric acid.

Is there some other way of getting rid of the graphite, or is that filter stained for life?

Many thanks!

[Edited on 11-11-2022 by Lionel Spanner]

Piranha solution

Sulaiman - 10-11-2022 at 19:21

https://en.wikipedia.org/wiki/Piranha_solution

violet sin - 10-11-2022 at 22:04

I've never tried to clean such a filter, let alone something like graphite stuck in there. My best guess right off, maybe reverse flow. I have a small ultrasonic mister for an aquarium. If you fill above a certain height, it just shakes the water without kicking up mist. Set up a reverse flow water with aquarium pump, in a tub of water overfilled for the mister and let it run for a day pointed at one another? It would either be noticable or useless with minimal effort. But that's just with what I have on hand and my level of free time. Best of luck

j_sum1 - 11-11-2022 at 03:43

I have used pirhana on frit glass before. Came out looking brand new.
Not that I think it really matters too much in most situations. If something is discolouring the frit but not going through, but filtering still works, then it's mostly ocd and aesthetics that is causing stress.

Boffis - 11-11-2022 at 09:36

Have you tried reversing the flow of water through the frit. If this and Piranha solution don't move it I think you are stuck with it! On the other hand if these processes won't remove it then I don't think its going to be a long term problem. Graphite is very inert.

Texium - 11-11-2022 at 10:50

Piranha is the way to go. And in the future, if you have to filter such a mixture, a pad of celite pressed into the bottom of the funnel works wonders and keeps the frit clean.

Lionel Spanner - 11-11-2022 at 14:30

Thank you all, your advice is much appreciated!
I have some 25% and 50% hydrogen peroxide and I'm planning to make some conc. sulphuric acid before long. When I do, I'll be sure to give piranha solution a go.

Going forward, I'll be using a Buchner funnel for this particular procedure. The filter papers I have (Whatman grade 1 equivalent, medium speed) do an excellent job of filtering out even the tiniest particles.

[Edited on 11-11-2022 by Lionel Spanner]

Sulaiman - 12-11-2022 at 04:36

Just thought I'd mention that the common acid:peroxide ratio (varies from 3:1 to 7:1 according to wikipedia)
is not required if no tar/organics are present.

A 1:1 molar ratio is suitable for carbon,
in which case you would be making "Caro's acid".
https://en.wikipedia.org/wiki/Peroxymonosulfuric_acid

I think that it would be better (less hazardous) to use your 25% peroxide rather than the 50%

Lionel Spanner - 12-11-2022 at 16:28

Quote: Originally posted by Sulaiman  
Just thought I'd mention that the common acid:peroxide ratio (varies from 3:1 to 7:1 according to wikipedia)
is not required if no tar/organics are present.

A 1:1 molar ratio is suitable for carbon,
in which case you would be making "Caro's acid".
https://en.wikipedia.org/wiki/Peroxymonosulfuric_acid

I think that it would be better (less hazardous) to use your 25% peroxide rather than the 50%

Thank you!
This was actually my plan - because of the way I obtained it (azeotropic distillation) I have a lot more of the 25% peroxide to hand than the 50%.

Lionel Spanner - 14-1-2023 at 15:02

Update: The filter wound up being caked in burnt-on sugars following its use, insufficient washing, and subsequent oven-drying during the preparation of mucic acid.
Piranha solution, followed by hot alkaline peroxide, worked a treat and restored it to pristine condition - thank you again to all who suggested it!