Teflon - not so inert!

[d&tm]

doh.

that should have read , I find zero ethanol in non teflon lined cylinders of
ethylene.
terry

Using teflon lined stainless steel cylinders to sample high purity
ethylene I was surprised to find that the ethylene is reacting to produce
ethanol in ppm levels. If I sample the same ethylene gas with a non
teflon lined cylinder I find zero ethylene. Can anyone out there explain
this phenomena? I am quite certain the ethanol is not in the ethylene or
that the teflon lined cyclinders are contaminated.
terry

[d***@hotmail.com]

Using teflon lined stainless steel cylinders to sample high purity ethylene
I was surprised to find that the ethylene is reacting to produce ethanol in
ppm levels. If I sample the same ethylene gas with a non teflon lined
cylinder I find zero ethanol. Can anyone out there explain this phenomena?
I am quite certain the ethanol is not in the ethylene or that the teflon
lined cyclinders are contaminated.
terry

In order to help prove your theory that teflon catalyzes the hydration
of ethylene you would need to demonstrate the presence of water in
your "high purity ethylene". Have you done that? Teflon is known to
bleed substances that it absorbs. A perfectly reasonable alternative
hypothesis is that the teflon is outgassing ethanol, perhaps present
from the time of manufacture. You could make an attempt to disprove
your hypothesis regarding teflon catalysis by filling the teflon lined
stainless steel cylinders with an inert gas and then try to detect
ethanol.

[d&tm]

Post by d***@hotmail.com

Using teflon lined stainless steel cylinders to sample high purity ethylene
I was surprised to find that the ethylene is reacting to produce ethanol in
ppm levels. If I sample the same ethylene gas with a non teflon lined
cylinder I find zero ethanol. Can anyone out there explain this phenomena?
I am quite certain the ethanol is not in the ethylene or that the teflon
lined cyclinders are contaminated.
terry

In order to help prove your theory that teflon catalyzes the hydration
of ethylene you would need to demonstrate the presence of water in
your "high purity ethylene". Have you done that? Teflon is known to
bleed substances that it absorbs. A perfectly reasonable alternative
hypothesis is that the teflon is outgassing ethanol, perhaps present
from the time of manufacture. You could make an attempt to disprove
your hypothesis regarding teflon catalysis by filling the teflon lined
stainless steel cylinders with an inert gas and then try to detect
ethanol.

there is definately no water in the ethylene. The cylinders themselves had
been filled and emptied many times before with ethylene gas, so I would be
surprised if the ethanol was still there from manufacture. The teflon
coating by the way is green which seemed unusual in itself to me.
terry.

[David Stone]

In article <466401e6$***@news.iprimus.com.au>,
"d&tm" <***@iprimus.com.au> wrote:

[snip]

Post by d&tm
there is definately no water in the ethylene. The cylinders themselves had
been filled and emptied many times before with ethylene gas, so I would be
surprised if the ethanol was still there from manufacture. The teflon
coating by the way is green which seemed unusual in itself to me.
terry.

Then it's obviously not pure PTFE, but has a pigment in it. If it's
a problem, I'd take it up with the manufacturer of your cylinders.
Either that, or find an alternative supplier.

Don't forget, too, that PTFE can be chemically oxidized under
sufficiently aggressive conditions...

[r***@gmail.com]

There are all different grades of "Teflon" that have varying levels of
fluorination to improve manufacturability. For example, Teflon FEP is
a "fluorinated ethylene propylene resin", as opposed to Teflon PTFE
which is well..PTFE.

But anyway, I've observed that pure PTFE absorbs significant
quantities of water...and who knows what's in the pigment.

[Gregg]

Post by r***@gmail.com
There are all different grades of "Teflon" that have varying levels of
fluorination to improve manufacturability. For example, Teflon FEP is
a "fluorinated ethylene propylene resin", as opposed to Teflon PTFE
which is well..PTFE.
But anyway, I've observed that pure PTFE absorbs significant
quantities of water...and who knows what's in the pigment.

It's been a while since I worked with Teflon coatings, but a coating is
typically 3 layers,
A bond coat, a pigment or black coat and then a translucent top coat for
the majority of the protection.
Each layer was a different grade to optimize the bonding or chemical
resistance.
The bond coat I saw was green when fired. If no intermediate coat was
applied before the top coat, the finished coating was green.

Just an FYI, We also had jigs that were made by plasma spraying a base
coat ceramic on AL and then the "mostly" PTFE coating impregnated the
porous ceramic. This made a very abrasion and chemical resistant coating.

Gregg