DarthCreepus
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Acid bath: redundant containment
Hello everyone! Been silently reading here for a while, but can't actually seem to find a thread with the info I need, and google has been relatively
fruitless D:
First some background:
I am currently a chem major, studying at a junior college. I am working on a project in school using EPA method 1694 to analyze local river water for
pharmaceuticals. The method calls for acid treatment of samples, followed by solid phase extraction of analytes of interest. After extraction,
samples are analyzed via HPLC/MS. To this point we have been able to clearly identify and distinguish several analytes in mixed standards, but there
is a high abundance of noise. This noise is also present in blanks. It seems that our mobile phase (MeOH) was contaminated, but I know that some of
the glassware we use has been through the ringer.
To ensure maximum 'cleanliness' we plan on utilizing an acid wash treatment of the glassware using Nochromix. The preparation of this solvent calls
for high concentration H2SO4. I have been able to square away all the PPE, but have been asked to find a non-glass container to place the container
holding the Nochromix in. Sort of a beaker in a pan, set up. This is meant to catch any spills and as such must be able to hold the entire volume (1
gallon) of Nochromix solution.
This is where I am having real problems. I'd prefer glass, but I have been asked to avoid this, since it can break. Stainless steel has been
suggested, and according to what I could dig up on google, 904L grade stainless is suitable for H2SO4. But I can't find anywhere to get a suitable
vessel.
I was hoping someone here might have some experience/insight/suggestions!
Thanks!
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MrHomeScientist
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For Christmas I asked for and received HDPE trays from McMasterCarr. These sound like they'd be perfect for your needs.
http://www.mcmaster.com/#parts-trays/=vclwh3
The ones I got are the HDPE pans - lightweight and chemical resistant. The polypropylene ones would also be a good choice.
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Praxichys
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I would recommend either a polyethylene tub or a galvanized steel tub, either of which would be filled with cat litter as the primary absorbent for
spills. Ideally the entire gallon could spill and the majority be absorbed before it even touches the tub. Either that, or get some lab cleanup
absorbent that is designed specifically for conc. sulfuric acid.
If you need to recover the spilled Nochromix, glass is really the best option. Maybe find a pan that can be plasti-dipped on the outside to reduce the
damage in the case of breakage.
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DarthCreepus
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Fantastic! I hadn't even considered using HDPE, kind of a 'duh' moment now :p
That link looks great as well, the trays there look to be exactly what we need.
The idea of absorbent material lining the tray hadn't occurred to me either, what a great suggestion.
Thanks so much!
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macckone
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From what I have been able to gather, NOCHROMIX is just sodium
persulfate with some additives. The decomp temp is similar. This is
effectively creating a piranha solution (aka caro's acid). This will attack
most plastics to one degree or another. PVC and PTFE would be the
plastics that are usable. PP and PE (both HD and LD) will be attacked
and are not recommended. Metal won't do it unless you use something
exotic like alloy Hastelloy C-276.
http://us.burkert.com/img_article/US_Chemical_Resistance.pdf
PVC containers are available. PTFE is going to cost an arm and a leg.
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Fulmen
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It can't be sodium persulfate as it is supposed to be free from metal ions. From www.http://godax.com/
NOCHROMIX® is a patented, white crystaline, inorganic oxidizer.
Ammonium persulfate perhaps?
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Praxichys
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It is indeed sodium persulfate.
From here, under "disposal": http://godax.com/NOCHROMIX_Directions_for_use.pdf
| Quote: | NOCHROMIX® solution may be neutralized with ammonium carbonate, yielding a mixture of sodium sulfate, carbon dioxide and water,
or with calcium carbonate, yielding a mixture of calcium sulfate, carbon dioxide and water. |
They probably
mean "no heavy or toxic metals." Sodium will leach from glass anyway.
As for the PE/steel tub, it is not designed to contain the solution - only the absorbent. A spill would warrant immediate action to replace the
absorbent. I am imagining something like a plastic litter box. Either way, the material need not be rated for continuous contact with the solution,
but only must survive for a few tens of minutes while a spill is cleaned up. The absorbent will help greatly in this case.
A PTFE or hastelloy container of that size would be very expensive for a simple drip tray.
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Fulmen
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Huh, why wouldn't they list sodium when neutralized with calcium carbonate? Nevertheless the lack of other species seems to suggest a persufate of
some sort, which should be enough to choose a suitable container.
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macckone
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If the absorbent contains starch or something similarly oxidizable
polypropylene would work very well. It can withstand concentrated
sulfuric acid but not the caro's acid/piranha solution. Polyethylene would
require more immediate action in any case.
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macckone
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It is most likely sodium persulfate with additives.
The decomposition temperature matches closely (175C v 180C).
Ammonium persulfate is considerably lower.
You could do a flame test to verify the actual composition.
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DarthCreepus
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Since its (hopefully) incidental contact only, the pan doesn't need to be completely resistant to the solution. We'll be keeping the calcium
carbonate in the fume hood with it, so we should be able to neutralize it quickly. But that resistance guide is pretty handy. Thanks for that link!
I really like the idea of a cheap litter pan, lined with absorbent material. This would be fantastically cheap. Maybe I'll mix up a small amount and
test it out on a few plastics, to be safe.
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