Methanol vapor compatibility with PTFE

[jmj5152]

I am building a prototype of an invention that reforms methanol to hydrogen at 120 Celsius, and would like to build (machine) it out of PTFE or PFA. Does anyone have any idea of the limits of PTFE and/or PFA for methanol:steam mixture (1:1.25 molar ratio) at 120-150 celcius?

 

[moltenmetal]

PTFE/PFA in what sort of service? As a lining, a seal material, or as a pressure boundary?

PTFE and PFA are definitely compatible with methanol vapour at these temperatures as seals and linings. But both materials have a tendency to "creep" or cold flow under these temperatures to a degree dependent on the mechanical design of the device in question. And neither is adequately strong for direct pressure-bearing service at these temperatures.

 

[jmj5152]

moltenmetal: Thanks. The design consists of plates machined out of PTFE or PFA, say 2" thick, and 1 square foot, almost like filter press plates, with channels for distribution of gas flow. So the gas would hit the entire plate during service. Do I have to cover the inside walls of the plates with something for long term exposure? The unit will run 24 hours/day.

 

[StoneCold]

JMJ5152
You would be better off to cut the the teflon thickness down to 1/4" or less and use steel or stainless steel to create the pressue boundry.
IMHO

StoneCold

 

[jsummerfield]

You can obtain lots of technical information from Dupont on each of their elastomers, etc.

John

 

[moltenmetal]

You'd better get some pricing on PTFE and PFA and THEN decide if this is an appropriate design. The material is very expensive- you may be shocked. A 2" plate 12"x12" will almost certainly be well over $1000 for the unmachined block, even at OEM prices. Lots of other materials will be cheaper unless you need the properties of Teflon in your device.

If your plates are retaining pressure and exposed to these temperatures, get the help of a mechanical engineer to design this. Use a metallic material as the pressure boundary for sure.

 

[jmj5152]

moltenmetal: Thanks. Yes, I am cognizant of the costs. The cost is more like $800 for the sq. ft., We have designed the unit with steel plates at the end. We have run a year long test on a 1 sq inch bench top, which worked well. I wanted to be sure before we ordered the machining on the 1 sq ft model. BTW, the conventional equipment for this process would be 10X the price due to the exotic materials required (conventional process works at 300 C and 20 atm).
Thanks again.