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charley1957
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[*] posted on 13-6-2019 at 16:26
Vacuum filtration media


I have been using Cynmar qualitative cellulose filter paper, their grade CFP3. I have more trouble than I care to remember while using this paper. I spend more time filtering than I do anything else, due to the slow nature of the paper. I thought when I bought it it would be a good general purpose filter paper. I'd like to know what others here are using.

Specifically, I've had three go-arounds with black battery paste and all the manipulations to get purified manganese dioxide. Seems every step that requires filtration takes me at least a whole evening, sometimes two, to get through. I'm not finding anything specific at vendors' websites, just endless offerings of different grades and sizes with no explanations. I've been to other sites including different university sites and labsociety.com, among others, and filtration in most cases is treated lightly with no real meat.

I know this is really basic stuff, but sometimes I reinvent the wheel, thus the request for what others are doing. Thanks for your responses!




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XeonTheMGPony
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[*] posted on 13-6-2019 at 16:32


filtering any fine past is an excise of masochism. I use Glass frits at the #3 range with a vacuum aspirator, for moderately inert things and I want it fast I use my rotary vacuum pump.
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charley1957
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[*] posted on 13-6-2019 at 16:54


I use a HVAC vacuum pump but I've got the vacuum dialed back to 10 or 12 in. Hg. I was using it full bore but I got scared of maybe blowing something up, or in, as it may be. A huge mess at any rate. So it's not just me. Well I feel a little better knowing I'm not the only one. Thanks for the reply!



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charley1957
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[*] posted on 13-6-2019 at 17:56


I could still use some more suggestions of what others are doing. Thanks!



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[*] posted on 13-6-2019 at 20:39


A not-too-thick and well-packed layer of celite works, you can lightly scrape the top with the flat end of a spatula if it gets clogged.

Filtration is one of the most common tasks in the lab, and presents many difficulties. The science of filtration is far more complex most people assume, and there is never a simple answer such as "use this filter media or use that filter media."

Factors such as liquid temperature/composition/viscosity, volume of liquid, pH, reactivity (many things attach to cellulose/paper), position of the paper, intensity of vacuum, atmospheric pressure (you can filter with pressure, too, just not with paper, really), and we haven't even gotten into the plethora of solid molecules that are your real problem. Even tapping the side of the funnel, or putting a small vibrating module in the right position could be your solution.

Basically, welcome to chemistry! and if you really hate waiting for a filtration, now might be a good time to think about quitting this hobby.

The only easy and fool-proof way to get your filtration to finish earlier is the one I use ALL THE TIME: start your filtration earlier. ;)
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[*] posted on 14-6-2019 at 00:58


I use a #3 sintered glass Buchner funnel. Had to buy it for chromium VI compounds filtering. It works really well with a simple water aspirator (so well that the first time I used it, the rubber cone which fits in the neck of the Erlenmeyer flask to render the whole setup airtight almost got sucked in!).

[Edited on 14-6-2019 by Keras]
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[*] posted on 14-6-2019 at 01:42


I too found that filtering takes a lot more of my time than expected,

sometimes I've had to partially filter through a fast/coarse paper to catch the bulk of the material,
then a slow/fine paper to catch most of the remaining small particles,
then back through the same, used, undisturbed, fine filter - to catch the smallest particles.
I use a small dc vacuum pump and filter at about 25kPa/190mm.Hg absolute (-75kPa relative to atmospheric pressure)
Often I start a filtration then go for a snack, drink or toilet break.
If I use my rotary HVAC vacuum pump (<1Pa), liquids boil/froth-up/rapidly evaporate.

Where practical (e.g. battery paste, and especially PGM precipitates) I now prefer to let gravity and patience do the work:-
. leave the fluid in a tall sealed container (e.g. measuring cylinder with rubber bung)
. wait for the particles to settle (could be days)
. siphon or decant off the clear liquid




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[*] posted on 14-6-2019 at 02:13


Speaking of, what would you use to catch and recycle Pd/C?
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charley1957
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[*] posted on 14-6-2019 at 03:49


Sulaiman, I've about decided to start doing these difficult filterings in stages, as you mentioned. Happyfooddance, I've been at this since I was 12, and I'm now 62, so no, too late to quit. But it's always an option to see what others are doing. Time changes things and one might get left behind if he doesn't ask questions

I really appreciate all the replies, and after some more searching I found a decent guide to filter media and their uses. I searched for over an hour last night, couldn't find much. Should have searched for an hour and five minutes, I guess. Y'all take care!




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XeonTheMGPony
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[*] posted on 14-6-2019 at 04:18


When possible I like to use alcohol solvents, the lower viscosity allows it to flow easier.

Smaller batches help indeed, and procedure is based off what you want as well, if your after the solid, or the salut,, Glass frits are the best IMO make life way easier, for friction sensitive energetics I use high density synthetic fiber filter pads on the frit and a dental pick to lift it off.

Big thing is good cleaning after the work is don. So I plan things in batches so I don't have to do tons of cleaning! ATM it is Hydrazine sulfate synth, so once the batch is don filter will be cleaned thoroughly.

So play with some different solvents/transport media

Can you share the link, I all ways like reading more on the topic as well.

[Edited on 14-6-2019 by XeonTheMGPony]
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Herr Haber
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[*] posted on 14-6-2019 at 04:18


I dont find that filtering takes that much time :P

But that's because I didnt have vacuum for years. Now I almost giggle when I pour something in the funnel.
Also, what I filtered most these last years was silver cement. Probably not the worst.

I used for a time a porcelain buchner funnel with the rubber cone Keras mentions. Of course it needs a special Erlenmeyer.
I just dont like it anymore. Too many manipulations if you need to empty the Erlenmeyer and porcelain stains.

I now have a 90mm fritted funnel, a 90mm perforated disc and a 47mm.
All from Deschem. None of them need a special Erlenmeyer nor the rubber seal. Only thing that worries me is that the flask could implode.

For these funnels I simply got Dechem's paper and some PTFE, mixed cellulose esthers filters.
I havent used the 1 micron PTFE filters but I'm pretty sure they'll get my vacuum pump hot.

For gravity filtrations I have different grades of paper but I only really notice a difference when I use coffee filters.
They are also the only filters I have that regulartly let something through. Usually when I see that the particle size wont go through and need to use gravity then I simply use coffee filters.

I also found out that I sometime prefer to have some material going through the filter (then lost or maybe filtered a second time) rather than use a less porous filter and wait for ages.
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charley1957
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[*] posted on 14-6-2019 at 09:17


Xeon, I should have done this last night. Here ya go!

https://www.gelifesciences.com/en/us/solutions/lab-filtratio...

There are some other guides in this link that may be helpful to some. Enjoy!

[Edited on Jun06-14-2019 by charley1957]




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[*] posted on 14-6-2019 at 09:28


Herr Haber, I agree. When I first used vacuum filtration I danced a little jig and clapped my hands! When it works well it is a joy to behold. And I once tried coffee filters with vacuum.......pfffft!! Right away they perforated and let all the good stuff out. Lesson learned! But they're still great for gravity filtration, and I have at least two sizes for different jobs. Small household ones for use in a Buchner funnel, WITHOUT vacuum, and then I have a plastic strainer that a 1.5 gallon coffee filter fits nicely in, and the plastic strainer has little arms that let it sit nicely on a stainless steel pan that I use for most things except HCl. Never too old to learn!



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[*] posted on 14-6-2019 at 09:40


I love cut up old cotton bed sheets to use as a filter, they work fine for both gravity and vacuum filtering.
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[*] posted on 15-6-2019 at 04:05


Another thought on filtering, whether you are using gravity or vacuum the funnel also plays an important role.

The diameter of the column is very important as the liquid inside will also create a pull if long and narrow enough.
A wider column will not excert such a pull if it cant fill the diameter but will prevent clogging (after the filter if / when the temperature drops enough) if you are using a hot solvent filtration.

Finally another obvious observation is that good quality funnels designed especially for gravity filtrations will also have texturing outside the funnel to let air out of your collecting container !
Otherwise pressure builds up, filtering slows then stop and your funnel might tilt emptying its content... Unpleasant !
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charley1957
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[*] posted on 15-6-2019 at 05:01


Sulaiman, I've about decided to start doing these difficult filterings in stages, as you mentioned. Happyfooddance, I've been at this since I was 12, and I'm now 62, so no, too late to quit. But it's always an option to see what others are doing. Time changes things and one might get left behind if he doesn't ask questions

I really appreciate all the replies, and after some more searching I found a decent guide to filter media and their uses. I searched for over an hour last night, couldn't find much. Should have searched for an hour and five minutes, I guess. Y'all take care!




...it has often proved true that the dream of yesterday is the hope of today and the reality of tomorrow.

Robert H. Goddard
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