[curiouscat]

I was browsing through the literature that came with some of our glass lined reactors and came across this warning:

"Hydrofluoric acid and fluoridated acid solutions are exceptional substances, for even in extremely low concentrations and at low temperatures they react with silicate based materials. A concentration [of Fluorine] as low as 0.001 % can render a glass lining matt and rough after long exposure. Such concentrations can arise simply through sulphuric acid being piped through PTFE tubing at 160 °C, for instance."

Now I know we use Teflon pipes at several places, in fact one of the feed nozzles itself is teflon lined. How can I measure if I have a 0.001 or higher conc. of Fluorine? Any recommended protocols?

Luckily we don't use H2SO4 nor 160 C temperatures, but we do have other acids and solvents. Would any of those leach out F from Teflon too?

Also, how real are these worries? Teflon seems ubiquitous especially in corrosive duties (even our agitator bushings are Teflon). But I've never heard this caveat before so am wondering.

[DrCMS]

If your glass reactor is nice and shiny then you've not had any HF in there.  The only thing I've seen attack PTFE are organometallic compounds.  During my PhD all my stirrers ended up dark brown/bronze after being attacked by silyllithium reagents.

[Corribus]

HF won't corrode Teflon to any appreciable extent. Telfon parts are specifically used (instead of glass) for ICP analysis of HF-containing matrices - for example, for geological samples that require HF-assisted digestions.

I suppose if you wanted to see if fluorine is leeching from Teflon you could do an ICP-MS or ICP-OES analysis.  I'm not sure what kinds of backgrounds you get for fluorine, though.

[DrCMS]

@Corribus  I think you've got the wrong end of the stick, either that or I have.  I assume curiouscat is using a glass lined steel reactor which has PTFE lined steel pipes connected to it for feed lines/services etc.  That is the set up I've seen before.  His concern is that some of the things fed through the PTFE pipework will 'leach' F into the glass lined reactor which would destroy it very quickly and easily.

[curiouscat]

Sorry, maybe I wasn't clear: The worry isn't HF corroding teflon. The worry is other fluids leaching the "F" (in some form) from teflon and then that F attcking the glass lining in the reactor downstream.

Looking at the low F conc. that seem to suffice to damage the glass lining, the teflon may not even show obvious signs of "attack". This looks like just trace leaching.

[curiouscat]

@Corribus  I think you've got the wrong end of the stick, either that or I have.  I assume curiouscat is using a glass lined steel reactor which has PTFE lined steel pipes connected to it for feed lines/services etc.  That is the set up I've seen before.  His concern is that some of the things fed through the PTFE pipework will 'leach' F into the glass lined reactor which would destroy it very quickly and easily.

Yes. Exactly!

[DrCMS]

Like I said just have a look in the reactor if it's the usual blue cobalt glass it's easy to see if the surface is still nice and shiny just using a torch looking in the manway.  Check down the sides near where the feed pipes are located and if you have and dull streaks you may have a problem.

[curiouscat]

Like I said just have a look in the reactor if it's the usual blue cobalt glass it's easy to see if the surface is still nice and shiny just using a torch looking in the manway.  Check down the sides near where the feed pipes are located and if you have and dull streaks you may have a problem.

Good idea. Thanks, I will. I hadn't realized that the damage is so obvious.

The larger story was, I'm trying to decide if teflon is or isn't a good choice for static mixers, dip-tubes etc. on the next Glass Lined Reactor we are going to order. Frankly, I don't know what else to use, though.

[DrCMS]

The larger story was, I'm trying to decide if teflon is or isn't a good choice for static mixers, dip-tubes etc. on the next Glass Lined Reactor we are going to order. Frankly, I don't know what else to use, though.

I think you answer your own question here.  Will the new reactor be doing the same duty as a current reactor?  If it is and the current one looks OK with PTFE pipework I'd stick with it.  If not then you might be into a much more expensive set up and need hastelloy titanium etc. or maybe you accept the corrosion to the glass as a cheaper option?

[Corribus]

Ah, got you. Sorry I misunderstood your problem.