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Author: Subject: Filtration Problems
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[*] posted on 8-7-2021 at 05:45
Filtration Problems


This feels like an incredibly noobish question to be asking here, but I can't figure it out. I've been using the same vacuum pump (Across International EasyVac-2, 2.0cfm) for years now and have never had any problems filtering through Whatman 40 or Whatman 42 ashless paper. I've used it with Buchner funnels, gooch crucibles, and regular glass funnels...no problems.

Starting about a month ago, I started blowing out filter paper during filtrations; the Whatman 40 holds up a little better than the 42 ashless I've noticed. This hasn't occurred on the gooch crucibles, but happens almost every time now with regular glass funnels and even one or two pores will blow out when using the Buchner regularly...did the quality of filter paper suddenly go to shit? Is my vacuum pump suddenly pulling more suction for some reason? Anyone got any ideas?

[Edited on 8-7-2021 by ShotBored]
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Chemgineer
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[*] posted on 10-7-2021 at 07:54


My guess is your paper is clogging, either the paper now has finer pores or are you trying to filter something different than you normally do...something that might be clogging up?
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[*] posted on 12-7-2021 at 05:20


It does seem to occur with one compound in particular: Zirconium Oxide in an acidic media. The ZrO2 does seem to be quite clumpy compared to the other salts i filter out...but the original method I developed for this never had an issue until the last year. It's obvious something has changed, I just don't know what. But I'd agree, the ZrO2 precipitate is the main culprit. I'll be doing this filtration with a 75mL porcelain Gooch and the same filter paper next I swear once Whatman became Cytiva, the quality of these papers fell though.
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[*] posted on 12-7-2021 at 05:29


If the liquid is very strongly acidic, it may also weaken the paper.

Had this problem making paratoluenesulfonic acid.




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[*] posted on 12-7-2021 at 06:07


Quote: Originally posted by SWIM  
If the liquid is very strongly acidic, it may also weaken the paper.

Had this problem making paratoluenesulfonic acid.


This is definitely a contributor to the problem as well, however due to the nature of the method, which is an acid digestion (conc. HCl, HNO3, and H2SO4) of Zr into ZrO2 and precipitation using N-nitroso-N-phenylhydroxylamine (Kupferron), I'm not sure I can neutralize the solution without adverse recovery effect prior to filtration?
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[*] posted on 14-7-2021 at 07:09


If you are using an electric vacuum pump its probably too vicious and with fine precipitates the vacuum rapidly falls below 100 mbars, that's why I use a water venturi type pump for filtration; by controlling the water flow I can get very gentle suction which much reduces filter collapse. If you are using an electric vacuum pump try installing a "T" piece with a bleed value and maybe get yourself a pressure gauge between the value and the Buchner flask.

For filtering strongly acid or alkaline solutions try getting some fibre glass papers, they pop up on ebay from time to time. I use them a lot for certain procedures particularly in strongly alkaline procedures since cellulose filter papers are more susceptible to alkalis then acid. Incidently alkalis cause the cellulose fiber to swell and therefor seal the pores were as acids weaken the fibres by hydrolysis more quickly.

Have you tried adding kieselguhr and /or charcoal if the filtered solids are the waste product?
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[*] posted on 14-7-2021 at 07:15


I haven't bought any filter paper recently, but I never had the problem that the paper is destroyed when vacuum filtering. Neither on my Buchner nor on my frittes. I can confirm that hydrochloric and other strong acids do attack my filter paper and make it weak and spongy. I never vacuum filtered such degraded filters.

You may try to filter some ZrO2 suspended in water to double check.

As I said, I never had a problem with filter paper not withstanding the pressure, neither when it got clogged up with ZrO2, TiO2, Al2O3, Nd2O3 and the like. (My pressure goes down to 1mBar.)
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[*] posted on 14-7-2021 at 07:19


Quote: Originally posted by Boffis  
(...)
Have you tried adding kieselguhr and /or charcoal if the filtered solids are the waste product?

Our replies came in at more or less the same time.

Speaking about kieselguhr, I tried to obtain it, but where can you get it at a good price?
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