Thursday, January 03, 2008

How to clean your sintered funnel

Lately when I have been cleaning my sintered funnels people have stopped and asked me what I was doing. To my surprise many chemists don't seem to know how to take a nasty, dirty sintered funnel and making it nice, white and shining again in about 15 minutes.
These days I'm doing lots of old school chemistry that involves heating the crap out of the components using for example conc. sulfuric acid as the solvent. Needless to say things are polymerising and decomposing left, right and centre and when you filter it through your nice white sinter it ends up looking nasty (see picture above). The stuff doesn't go anywhere with acetone, water, 2M sodium hydroxide or hydrochloric acid etc. so what should you do? Before I proceed please note that if you attempt any of the following you must:
(1) Wear a closed lab coat, safety glasses and plastic gloves
(2) Conduct the cleaning in a fume hood with the sash down at all times
(3) Ensure that all the glassware is clean and doesn't contain residual organic material such as acetone
Please take the above advice seriously. People have had nasty accidents doing the following because they weren't careful.
There are two common ways to get your sinter clean:
(1) Conc. nitric acid, or
(2) Conc. sulfuric acid and hydrogen peroxide
Nitric acid is the easy solution and more often than not it does the trick. However, occasionally it is necessary to use more vigorous conditions. I have never had a sinter that didn't become white after treatment with conc. sulfuric acid and hydrogen peroxide and this is generally the method that I use because I know it works every time.
(1) Fit the funnel to a Büchner flask attached to a vacuum that you can control easily
(2) Add a small amount of conc. sulfuric acid so that it covers the surface of the sinter
(3) Add a dash of hydrogen peroxide and stand back. Things get pretty hot, bubbly and exciting at this point (See picture above).

(4) When the ingredients have been cooking away for a minute or so apply a very gentle vacuum briefly. This should be sufficient to suck the sinter dry (See picture above),
(5) Allow the cocktail to settle down and cool off and clean all the equipment with lots of water taking care not to pour the contents all over yourself. Your sinter will now look like this.
Too easy but please do be careful guys. D!


Ψ*Ψ said...

I've always just used straight conc sulfuric and let it drip through overnight. Even gets rid of PTCDA brickdust.

david said...

thanks for the tip!! i assume you mean the usual 30-35% hydrogen peroxide?

milkshake said...

Ah, I have been saving a pile of sintered Buchner funnels after a particularly insoluble batch of kinase compounds since November since messing with piranha mix is no fun.

I usually mix it up and let it drip through overnight, next morning the expired mix is less risky to handle

A friend (who is now a chemistry professor) once poured piranha mix on a Buchner funnel that was stil wet with acetone. The resulting loud bang shattered the Buchner.

Oh, and it is very funny when one spills the mix in the hood and tries to wipe it out with a dry paper towel - only to see the paper towel go up in flames whith a nice puffing sound.

Pirnaha is once of very few things that actualy etches the black epoxy material used for hoods and benches.

Daniel Sejer said...

Yes David just use your standard hydrogenperoxide straight out of the fridge. Remember you only need to add a small amount of the stuff to make it take off.
Piranha mix? Didn't know that stuff had a name. And yes it is incredibly potent and will chew up your hood if you just splash it around. D!

Thomas said...

Daniel Sejer said...

The link in the previous comment contains excellent safety information for anyone considering using piranha for cleaning their glassware. Thanks for the link Thomas. D!

GlowingApple said...

What about aqua regia? I've found that when typical strong acids, like sulfuric acid, HCl, etc don't clean it up, aqua regia does a nice job. Neat nitric acid usually does the job, but I've run into cases where it's not good enough.

I always have problems after I filter out sieves that have been pulverized by stirring. I found that drying the funnel in an oven and blowing nitrogen up through the funnel works well for that.

milo said...

I have found that aqua regia does a great job at cleaning frits. More recently though, I have moved to the annealing oven. We clean a lot of our glassware by heating it to 550C over night. Works like a charm.

Ken said...

Have you tried using a KOH/ethanol bath? I've used that with a great deal of success on sintered glass frits. Of course, since it works by slowly dissolving the glass, eventually it will wear out the frit.

Henrik T Simonsen said...

In general Sulphuric acid is neat for cleaning any kind of glassware and also frits. But Daniel maybe you should make a book
"The Tricks that are never taught in Chemistry Classes"

wepplo said...

Looks like another reason that I always used porcelain Buchner funnels with filter paper. I never liked cleaning those frits. I just toss the used filter paper out.

Anonymous said...

hey hey, can someone send me the distributors/vendors/manufacturers contact for this sintered glass funnel? asap plz. thankss so much

Anonymous said...

Come on you lazy bugger. You are even to lazy to write real words. Look in any catalogue with lab equipment and you'll find the stuff.

João said...

I'm aware this is a very old post but nevertheless I would like to add that you could use, instead of the H2O2 some (NH4)2S2O8 (CAS 7727-54-0). If you want it to work faster just leave the glassware in the oven before adding the powder and conc. H2SO4. It's a lot safer the piranas concoction.

dioica said...

what about using DMSO? it always worked with my stuff.

Anonymous said...

After aqua regia failed to clean my sintered funnel, I tried pirana, and it works!!! Thanks!!!

Raison d'être said...

Thank you for the tip!