Sciencemadness Discussion Board - PTFE filters? What are they for?

PTFE filters? What are they for?

fusso - 30-8-2019 at 15:23

I saw PTFE filter "paper" on ebay, thin like paper. Anyone knows what they're for?

unionised - 30-8-2019 at 15:41

"What are they for?"
Anything you like; that's the point.
Want to filter sulphuric acid?- no problem. Strong solvents like ethyl acetate?- sure.
Weird stuff like concentrated solutions of zinc chloride or cuprammonium sulphate? go right ahead.

Don't try those with cellulose based filters, or nitrocellulose ones.

Dr.Bob - 21-10-2019 at 09:14

They are membrane filters, often used to micro filter a solution. They are ideal for removing almost any particle, even most bacteria, if the pore size is right. They work well for organic solvents, not so well for water, which does not wet them. There are other materials in membrane form for aqueous solutions. Most are used with Whatman type 47 mm filter apparati.

TheMrbunGee - 21-10-2019 at 11:44

I accidentally ordered MCE (mixed cellulose ester) filter papers, cut out and everything, sadly they dissolve in methanol, most used solvent in my lab. There are quite a lot of filter paper materials, as I researched after my "paper" filter dissolved away with everything, each better for some specific application.

RogueRose - 21-10-2019 at 14:50

Quote: Originally posted by fusso

I saw PTFE filter "paper" on ebay, thin like paper. Anyone knows what they're for?

Would you want to share the links? I'm looking for some PTFE filters, especially sheets that are cuttable to proper size if possible.

I'm looking at making a PTFE filter housing that can take square sheets of PTFE filter membrane where I can replace the filters. The only thing I'm wondering about is if there is a problem using a square filter. The filter would be held down very tightly (near 2500-5000 PSI holding down filter material using bolts/screws on outside of housing - it's amazing the pressure that can be obtained from bolts!).

The round filter papers are pretty expensive and I'm trying to find a place where I can buy uncut sheets. If you find anywhere, please let me know. I'm thinking maybe alibaba might be a place to find these.

Also, here is a PTFE chemical compatability chart and you will see why it is such a great material for filtration membrane! It even is great with things like aqua regia, fuming HCl or nitric acid and even 100% HF (scary!!)!

https://www.calpaclab.com/teflon-ptfe-compatibility/

I thought I'd look through and see what PTFE didn't have "A-Excellent" resistivity to and here's the list, which is less than 1% of the listed chemicals

"B - Good"
Fuel Oils
Gallic Acid
Gasoline (high-aromatic)
Lead Sulfamate
Mercuric Cyanide
Naphtha

"C - Fair"
Iodoform
Petrolatum

" D - Severe"
Diethylamine
Fluorine
Gold Monocyanide

[Edited on 10-21-2019 by RogueRose]

[Edited on 10-21-2019 by RogueRose]

Metacelsus - 21-10-2019 at 15:13

Quote: Originally posted by RogueRose

" D - Severe"
Diethylamine
Fluorine
Gold Monocyanide

Hmm, I've used PTFE-coated stir bars with diethylamine solutions and I've never had a problem.

BromicAcid - 21-10-2019 at 15:26

Pulling aqueous through a PTFE filter is very difficult. Just a voice of experience.

RogueRose - 21-10-2019 at 16:15

Quote: Originally posted by Metacelsus

Quote: Originally posted by RogueRose

" D - Severe"
Diethylamine
Fluorine
Gold Monocyanide

Hmm, I've used PTFE-coated stir bars with diethylamine solutions and I've never had a problem.

Well maybe pressure, time and temp can effect how reactive it is. Filters will probably be higher pressure and maybe higher temp. IDK though, I was just listing what was on the page - not personal experience. It's good to know your experience.

I'd be intersted to know the weight of the stirrer before and after the stirring. Maybe it dissolved some PTFE and it wasn't very noticeable?

Herr Haber - 22-10-2019 at 03:18

Quote: Originally posted by BromicAcid

Pulling aqueous through a PTFE filter is very difficult. Just a voice of experience.

You said it wrong:
IT IS VERY DIFFICULT !

You guys remember when you didnt have a vacuum pump and had to filter superfine particles clogging the filter and adding to the funnel every few hours ?
Well, it's almost that bad.

But hey, in my case I didnt think much before proceeding and chose the most inefficient solution so I'm the only one to blame.

RogueRose - 22-10-2019 at 13:47

Quote: Originally posted by Herr Haber

Quote: Originally posted by BromicAcid

Pulling aqueous through a PTFE filter is very difficult. Just a voice of experience.

I'm wondering if it was slow filtering b/c you used a really small pore size or is it b/c of PTFE is hydrophobic maybe?

I've used .45um and .22um filters but I used a 3ml syringe and about 50-70 syringes worth for the 200ml and it seemed pretty easy until the last ~10 or so and it got progressively harder until it was impossible. I started off with a 60ml syringe and it was near impossible after about 8ml worth, then tried 20ml, then moved to 3ml.

IDK if the smaller syringe allows for more pressure or what, but it made a huge difference.

fusso - 22-10-2019 at 15:26

Quote: Originally posted by RogueRose

I just searched ptfe filter on ebay.com. There are literally tons of it. Unfortunately the links I copied are monstrously long.

G-Coupled - 22-10-2019 at 20:56

You can shorten the links by using the 'URL Tool' on the formatting bar above the post box - it looks like a low rez blue/green globe with a paperclip (?) next to it.

Like this

[Edited on 23-10-2019 by G-Coupled]

Herr Haber - 23-10-2019 at 03:51

Quote: Originally posted by RogueRose

I'm wondering if it was slow filtering b/c you used a really small pore size or is it b/c of PTFE is hydrophobic maybe?

Maybe a bit of both but I'm certain I clogged the filter.

Also, since you are looking for sheets / plates be careful not to get fabric impregnated with PTFE. I'm not sure this would be useful as the distribution is uneven.

unionised - 23-10-2019 at 10:01

You can make life easier by pre-wetting the filter with a little methanol or acetone before trying to draw water through it.

DavidJR - 23-10-2019 at 14:49

I was just about to write that! Yes, pre-wetting PTFE membrane filters with organic solvent before trying to filter aqueous solutions helps a lot.

fusso - 23-10-2019 at 15:50

Must the wetting solvent be water-miscible?

Tellurium - 9-12-2019 at 08:13

Quote: Originally posted by fusso

Must the wetting solvent be water-miscible?

I tested it out a few minutes ago.
For comparison I took a unwetted filter, a acetone wetted filter and a DCM wetted filter. "Competitor" for the 0,45um syringe filter was a freshly prepared suspension of precipitated lead sulfate in water.

Through both the Acetone and DCM wetted filter the suspension was a lot more easy to filter, than with the unwetted filter. But I feel, like the acetone wetted filter was a little bit easier to push, but only a very minor difference

[Edited on 9-12-2019 by Tellurium]

DavidJR - 9-12-2019 at 15:27

Interesting, I would not have expected that.

glen - 4-12-2020 at 18:53

Normal PTFE membrane filters are generally used for either gas filtration or NP solvent filtration. In all cases to remove things such as bacteria or fungal spores if they are .2um pore size.
Non normal HYDROPHILIC PTFE membranes are used for things which might be polar but detrimental to other membrane materials.

Fyndium - 5-12-2020 at 15:09

Yep, they are used also in sterile 0.2um and 0.1um filtration, for example pharmaceutical injectable oil formulations. I've once accidentally seen them in use because my friend in the past decade used such filters to filter steroid stuff. I thought about the whole idea several years later and at that time I just though it was some random thing done to make it more clear. The idea of sterilizing solutions by filtering still fascinates me.