Sciencemadness Discussion Board

Buchner funnel: glass or ceramic?

fusso - 6-5-2018 at 14:45

As stated in the title. Thx!

Yes

Sulaiman - 6-5-2018 at 14:49

DavidJR - 6-5-2018 at 15:19

Don't forget to consider polypropylene!

I have three Buchner funnels - one of each glass (sintered), polypropylene, and porcelain.

Honestly I probably use the polypropylene one most often because it's the easiest to clean as it comes apart into two halves so you can clean the inside. I'm too lazy to clean sintered filters unless I really have to.

zed - 6-5-2018 at 15:52

Umm. I know folks are now calling Sintered Glass Funnels.... Buchners.

But to me, the Buchner is a ceramic funnel. Plenty expensive nowadays, and for no really good reason.

Polypropylene! Now, that's the ticket! Much more affordable. At least, I hope so.

I'm off to e-bay.

DavidJR - 6-5-2018 at 16:02

Quote: Originally posted by zed  
Umm. I know folks are now calling Sintered Glass Funnels.... Buchners.

But to me, the Buchner is a ceramic funnel. Plenty expensive nowadays, and for no really good reason.

Polypropylene! Now, that's the ticket! Much more affordable. At least, I hope so.

I'm off to e-bay.


My polypropylene buchner funnel cost just £1.78 (edit: excl.VAT, but still, cheap).

You can also get glass Buchners which just have holes and must be used with filter paper (the search term you need to find them is "pore plate"), but for some reason they seem to be more expensive than equivalent sintered filters (at least in terms of cheap eBay/Aliexpress Chinese glassware).

[Edited on 7-5-2018 by DavidJR]

fusso - 6-5-2018 at 17:13

I prefer funnel with holes to put filter paper, not sintered glass cuz they're nightmare to clean.

fusso - 6-5-2018 at 17:42

Quote: Originally posted by Sulaiman  


What

S.C. Wack - 6-5-2018 at 18:38

It depends on what kind of stem I want to use. No option with porcelain. Sometimes its really convenient to put one of these on a RBF on a cork ring and suck on it.
https://www.ebay.com/itm/350ml-24-40-Glass-Buchner-funnel-3-...

JJay - 6-5-2018 at 19:11

I have a 1 L 24/40 pore plate funnel that I got from Yee Chen for a very low price. There are some bubbles in the glass, but it functions just fine. I really don't think that ceramic Buchners have a dog in this fight.

fusso - 6-5-2018 at 20:01

Quote: Originally posted by DavidJR  
Don't forget to consider polypropylene!

I have three Buchner funnels - one of each glass (sintered), polypropylene, and porcelain.

Honestly I probably use the polypropylene one most often because it's the easiest to clean as it comes apart into two halves so you can clean the inside. I'm too lazy to clean sintered filters unless I really have to.


but will polypropene be destroyed by certain solvents?

unionised - 7-5-2018 at 02:51

With glass, you can tell if it's clean

DavidJR - 7-5-2018 at 04:06

Quote: Originally posted by fusso  

but will polypropene be destroyed by certain solvents?


Probably yes, but it's good for a lot of things.

See: https://www.industrialspec.com/images/files/polypropylene-ch...

Reboot - 7-5-2018 at 04:12

I assume the real question is 'sintered glass vs filter paper'. For me, the answer is mostly about material compatibility and cleanup. A funnel with a pore plate (as noted, you can get them in plastic and glass, not just ceramic) is easier to fully clean, while sintered glass can require aggressive oxidizers (such as piranha mix) to get clean. The good news is that sintered glass is also immune to all solvents and most of those powerful oxidizers, so you can filter some crazy things (like hot sulfuric acid, etc.) that would eat filter paper.

Which to get? If possible, both. A traditional Buchner funnel (with holes in the plate and discs of filter paper to actually do the filtering) for general purpose use, and a sintered glass filter funnel for things that are too aggressive for filter paper. If you had to pick, for most hobbyists I'd say the Buchner design is the better option.

unionised - 7-5-2018 at 04:18

Quote: Originally posted by Reboot  
I assume the real question is 'sintered glass vs filter paper'.

Why?

If sintered glass, what pore size is 'best' ?

Sulaiman - 7-5-2018 at 04:36

I use 90mm filter papers and a porcelain Buchner funnel, overall I am pleased with performance BUT
I am considering a sintered glass filter funnel for hot and/or corrosive liquids,
but I do not know what pore size to buy,
the cheapest commonly available seem to be 2-4, 4-7, 16-30, 30-50 and 50-70 microns.

Anyone have experience with different pore size fritted filters ?
or
fibreglass round filters for Buchner funnels, e.g. https://www.ebay.co.uk/itm/Glass-Fibre-filter-pack-of-80-rou...


[Edited on 7-5-2018 by Sulaiman]

fusso - 7-5-2018 at 09:37

Quote: Originally posted by unionised  
Quote: Originally posted by Reboot  
I assume the real question is 'sintered glass vs filter paper'.

Why?


No, I mean whether glass or ceramic "pore plate" funnels.

Which filter diameter should I use?

fusso - 7-5-2018 at 10:09

For the pore plate filter, which diameter should I use?

Dr.Bob - 7-5-2018 at 10:26

Quote: Originally posted by Sulaiman  
I use 90mm filter papers and a porcelain Buchner funnel, overall I am pleased with performance BUT I am considering a sintered glass filter funnel for hot and/or corrosive liquids, but I do not know what pore size to buy, the cheapest commonly available seem to be 2-4, 4-7, 16-30, 30-50 and 50-70 microns.


The medium porosity is an ideal starting point. Course ones are hard to clean, fine are slow. That is about 10-15 microns from Ace or pyrex, Chemglass would be "M", and some are 10-20 micron.

To answer the original question, Buchner filters in porcelain and filter paper are great for collecting and drying solids that you want to keep. It is easy to let the solids dry air dry and remove them. Glass frits are idea for collecting larger amounts of solids, or for removing large amounts of solids when you want to keep the filtrate (liquid). Buchners are cheap to buy, especially used, frits are expensive to buy new, and often dirty when bought used. Glass frits clog easily, and are hard to clean. If I want to collect solids, I will often put a piece of filter paper on top of the frit to keep it clean, then try to scrape out any solids that bypass the filter paper. One big advantage of frits is that solids cannot bypass the filter paper and leak through.

The PP Buchners will handle most organic solvents and many aqueous solutions, but are not good for oxidants, hot corrosives, and a few esoteric solvents. They are cheap and easy to clean, so not a bad idea. I use them some, but use PP powder funnels all of the time, and they handle most every normal solvent.

fusso - 7-5-2018 at 10:53

Quote: Originally posted by Dr.Bob  
Quote: Originally posted by Sulaiman  
I use 90mm filter papers and a porcelain Buchner funnel, overall I am pleased with performance BUT I am considering a sintered glass filter funnel for hot and/or corrosive liquids, but I do not know what pore size to buy, the cheapest commonly available seem to be 2-4, 4-7, 16-30, 30-50 and 50-70 microns.


The medium porosity is an ideal starting point. Course ones are hard to clean, fine are slow. That is about 10-15 microns from Ace or pyrex, Chemglass would be "M", and some are 10-20 micron.

To answer the original question, Buchner filters in porcelain and filter paper are great for collecting and drying solids that you want to keep. It is easy to let the solids dry air dry and remove them. Glass frits are idea for collecting larger amounts of solids, or for removing large amounts of solids when you want to keep the filtrate (liquid). Buchners are cheap to buy, especially used, frits are expensive to buy new, and often dirty when bought used. Glass frits clog easily, and are hard to clean. If I want to collect solids, I will often put a piece of filter paper on top of the frit to keep it clean, then try to scrape out any solids that bypass the filter paper. One big advantage of frits is that solids cannot bypass the filter paper and leak through.

The PP Buchners will handle most organic solvents and many aqueous solutions, but are not good for oxidants, hot corrosives, and a few esoteric solvents. They are cheap and easy to clean, so not a bad idea. I use them some, but use PP powder funnels all of the time, and they handle most every normal solvent.

What's a esoteric solvent?

Diachrynic - 7-5-2018 at 11:58

Quote: Originally posted by fusso  

What's a esoteric solvent?

He is probably referring to unusual or exotic solvents.
In this case xylene, tetrahydronaphtaline and decahydronaphtalene will dissolve PP at elevated temperatures.

alking - 13-5-2018 at 08:36

I MUCH prefer my glass sintered funnel over my buchner, I cannot see ever getting another buchner again. Sure it's harder to clean, but I don't need to buy filter paper, don't need to worry about things interacting with the filter paper or it slipping/losing a vacuum and leaking, and most importantly it is FAR FAR more efficient. There are many things that would clog a buchner/filter paper really quickly yet have no issues at all with the sintered funnel, it just has so much more surface area and is not absorbent.

Cleaning wise I really do not have an issue with it either. Sure some things call for piranha solution, but generally I just scrub it, run some hot water through, some cold water, and finally some acetone and it's just like new. Often times even if there are some debri left behind if they're not soluble in acetone or water then they're also not going to dissolve in 99% of what will go through them, if it's a concern then I'll run some acid or in the worst case some piranha solution through it. So yeah, it is more work to clean however you break it down, but imo it makes up for it by being so much less work to actually use.

DavidJR - 13-5-2018 at 20:00

Quote: Originally posted by alking  
I MUCH prefer my glass sintered funnel over my buchner, I cannot see ever getting another buchner again. Sure it's harder to clean, but I don't need to buy filter paper, don't need to worry about things interacting with the filter paper or it slipping/losing a vacuum and leaking, and most importantly it is FAR FAR more efficient. There are many things that would clog a buchner/filter paper really quickly yet have no issues at all with the sintered funnel, it just has so much more surface area and is not absorbent.

Cleaning wise I really do not have an issue with it either. Sure some things call for piranha solution, but generally I just scrub it, run some hot water through, some cold water, and finally some acetone and it's just like new. Often times even if there are some debri left behind if they're not soluble in acetone or water then they're also not going to dissolve in 99% of what will go through them, if it's a concern then I'll run some acid or in the worst case some piranha solution through it. So yeah, it is more work to clean however you break it down, but imo it makes up for it by being so much less work to actually use.


Re clogging of sintered glass vs filter paper, that depends entirely on the combination of the particle sizes and the filter porosity. And of course you could buy a few different types of filter paper and use them as appropriate.

I don't really see the cost of filter paper as a problem because it's just not that expensive. I value not spending ages cleaning sintered filters over saving a few pence on filter paper. Actually, that may be a false economy if you have to use acetone, piranha solution etc anyway.

I like my glassware to be spotless. For most things I routinely soak in a base bath to get rid of organic residues, which usually works very well and leaves a hydrophilic surface. But base baths are a no-go for sintered filters.

Acid baths are much less effective for stubborn organic crud, so to get a sinter perfectly clean you end up needing to use piranha solution (which is dangerously reactive, and also must be prepared fresh so can't be reused many times like a base bath) or chromic acid (which is toxic/carcinogenic and an environmental nightmare).

Or: pick out the bit of filter paper, rinse the funnel, and plop into a base bath. Much easier IMO. Only time I use the sintered filter now is for things that are incompatible with paper.

[Edited on 14-5-2018 by DavidJR]

PirateDocBrown - 14-5-2018 at 02:56

If you are filtering a material that might clog the sinter, there's no rule that says you can't lay filter paper on top of it. Just cut it to size.

Sulaiman - 14-5-2018 at 04:08

I moved from folding/pleating filter papers to a ceramic Buchner funnel
mainly because I got tired of folding/pleating,
so cutting filter papers to fit fritted funnels is a non-starter for me :P
The phenomenal increase in filtration speed using vacuum was a very welcome bonus :D

I wish that there were more holes per unit area, maybe only 1% of the paper is actually used.
I'm considering using glass fibre filter disks for my ceramic Buchner funnel
they are not cheap, but not terribly expensive - anyone have experience ?

Very important in the Buchner is the smooth non-perforated periphery of the plate,
where the paper seals against the ceramic.
Can anyone comment on how well filter papers seal to fritted filters ?

Doped-Al2O3-fusion - 14-5-2018 at 06:46

Quote: Originally posted by fusso  
I prefer funnel with holes to put filter paper, not sintered glass cuz they're nightmare to clean.


This is exactly the type I have. It uses 47mm diameter glass fiber filter papers. I'm currently using 1.6μm rated. You can get any pore size you want which is what prompted me to get this as my first Buchner funnel. So far I've had no issues with it and it's easy to clean.

Doped-Al2O3-fusion - 14-5-2018 at 06:49

Quote: Originally posted by Doped-Al2O3-fusion  
Quote: Originally posted by fusso  
I prefer funnel with holes to put filter paper, not sintered glass cuz they're nightmare to clean.


This is exactly the type I have. It uses 47mm diameter glass fiber filter papers. I'm currently using 1.6μm rated. You can get any pore size you want which is what prompted me to get this as my first Buchner funnel. So far I've had no issues with it and it's easy to clean.


Mine work great. I got mine from eBay as Omicron Scientific brand. Glass fiber filters GF/1F, 47mm diameter, rated at 1.6μm. Qty 100 per pack. It wasn't too expensive for this pack, but I know some of the others are really expensive. I like it and think it's very easy to clean.