lahthffire
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Supercritical Methanol - mild steel compatibility?
Does anybody have any data for material compatibilities with supercritical methanol? We're talking temp. up to 350 deg. C, and pressure up to 4500
psi.
I'm mainly interested in the compatibility with mild steel.
Also, I would love to know of any online resources, or good books, covering the topic of engineering material compatibilities with common chemicals.
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Fleaker
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I imagine it would not react with it. If you have concerns, go with stainless 316, pretty much an industry standard, and cheaper than monel/inconel.
Make sure you have thickwalled tubing, even at 350C steel starts to lose some strength.
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neutrino
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If I may ask, what do you need supercritical methanol for? Supercritical CO<sub>2</sub> is much easier to work with, if all you need is a
supercritical solvent.
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lahthffire
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It's for the catalyst free methyl transesterification of vegetable oils : making biodiesel.
I already made a reactor out of 316L stainless which works fine. However, it is only a little thing, capable of ~20 ml batches. I would like to make a
bigger reactor, but stainless isn't exactly cheap (let alone inconel, hastelloy, etc!).
I had just assumed that if there were going to be a compatibility problem with regular mild steel, it would be the methanol, but the more I think
about it, the more I wonder about the effect super hot free fatty acids might have. Anybody have any thoughts?
Also, I really would like to find some good resources that cover this topic (chemical compatibilities of engineering materials) as it seems I am
frequently running into these questions.
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Magpie
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Perry's Chemical Engineers' Handbook covers this fairly well for common chemicals at ordinary pressure and temperatures ranging from 0-300F.
Included is a table titled "Detailed Corrosion Data on Construction Materials" to which I often refer.
Biodiesel is in commercial production. Is supercritical methanol being used there or is this a research area? I would look into the corrosivity of
the fatty acids. I saw a recent reference that indicated their surprising corrosivity. No wonder they refer to McDonald's hamburgers as "gut bombs."
The single most important condition for a successful synthesis is good mixing - Nicodem
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unionised
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I realise this isn't exactly a propper reference but I remember an engineer who worked on HPLC systems saying he didn't like supercritical fluid work
because
" supercritical CO2 strips the silanisation off the column packing; supercritical methanol disolves the silica support and supercritical water disolve
that stainless steel too."
I'd be wary of supercritical methanol in pipework, especially if there's any water present.
BTW, Supercritical N2O- great solvent- much better than CO2 for a lot of things.
Solution of organic matter in supercritical N2O - passable explosive.
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lahthffire
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As far as I know, the supercritical method is not yet being used by anybody commercially, although there is at least one group in Japan working on it.
And me and my two friends, I guess.
Thanks for the note about Perry's Chemical Engineers' Handbook; I actually do happen to have a copy of that which I haven't yet looked into!
That's interesting about the supercrit. water dissolving stainless steel. What could possibly be the mechanism behind that?
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unionised
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My best guess would be
Fe +H2O --> H2 +FeO.
(That was refreshingly easy to balance). That reaction takes place with red hot iron and steam so I can imagine supercritical water managing it. Of
course, the bloke may have been exaggerating.
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