I think you’ve already nailed this one, my friend. This is why I recommend just using a heavy helping of (Maybe Blue) Dyed PG with Corrosion Inhibitors an’ Stuff Init™ in precisely 4.2 decabloops of water as the heat exchange medium for closed systems. Maybe put a domed popcorn maker lid or something over your bath to keep any steam refluxing… or just seal the damned thing with the lid, a gasket and a brick or twelve… The water/PG vapor pressure is trivial, but sure, put the bricks in a bowl of ice if you don’t believe me!
I’m not sure that I expect passivation to get me all that far down the road, but it seems like one of the few actions that I can take that might move things in the right direction.
Tangentially: I frequently point out that “prove” and “proof” are philosophical concepts that exist outside the realm of hypothesis-driven scientific exploration. The Scientific Method is not set up to extract “proof,” nor can it ever get us there.
You know all this.
I am pretty sure that you meant “Next step is to convince myself that…”
Okay. I know you are already going down the rabbit hole on passivating the system (huzzah! great science coming out on that one). But I wanted to put out there that this is probably not formaldehyde. In my experience its always been hard to quantity… so I always look for its derivatives. I assume you are using some kind of solvent to mix with the heat transfer fluid when putting it to the GC. So you probably have it reacted with stuff already (acidified EtOH? MeOH? Something else?).
I’m pretty sure you are using FID… so you are not going to see formaldehyde, so you’ll need to look for a derivative.
Formaldehyde smells like pickles - so it smells like a lot of other stuff too. Sure you could be reacting stuff and creating things, but that peak that you have shouldn’t be formaldehyde. You could always try the USP method for formaldehyde impurities - that should get you prepped good and let you move forward.
Are you having any degradation of seals? That’s where I’ve seen this kind of contamination come from before. I’ve also seen weird reactions with siloxanes when exposed to EtOH - so that’s always possible. Most of these heat transfer fluids are designed with stabilizers and everything so that they don’t react with things.
I’d look at seals, gaskets, and any other adhesives in your rig before thinking about fluids. Its also possible it is now in the fluid but came from somewhere else.
While I can find a lot of literature about various forms of siloxanes becoming other things, I cannot find very much at all about siloxane itself having these issues.
Which again points me to looking at seals, gaskets, and other possibilities of contamination that is then leading to formaldehyde (if what you have is indeed that…)
It is a lot easier to get formaldehyde out of ethanol or silicone than it is to get it out of siloxane.
Nope. Pulling head space from the circulator. No solvent added. Trying to repeat that out of voc vials with new vs used fluid +/- plasma cutter slag and the hose we used. Incubating at ~100C for the weekend.
Yeah there are lots of things that smell like pickles, few that are quite as disabling as formaldehyde/ paraformaldehyde that I’ve run into.
why would I not expect to see H2C=O + O2 => CO2 + H2O as electrickery at the FID ?!?
Edit: As Roy so succinctly put it
formic acid represents a highly oxidized form of the tetravalent carbon, and formaldehyde represents the second oxidation degree of the tetravalent carbon /starting with methane/.
Oxidation of HCOOH in FID leads stright to CO2 and H2O without creation of an intermediate carbon-radical ion /reaction scheme: HCOOH + 1/2 O2 = CO2 + H2O/.
Oxidation of CH2O in FID yields stright CO2 and H2O, followind the reaction scheme CH2=O + O2 = H2O + CO2. As it can be seen from the above scheme, combustion of formaldehyde is not accompanied by any intermediate carbon-radical ion formation, either.
You can´t detect these compounds with FID/ flame ionization detector/.
The principle of FID detection is based on an inrease in electro conductivity betwen two electrodes in a detector in the moment of incineration of molecules leaving the chromatographic column. The condition for detection of any sample component is creation of temporary carbon-radical ions intermediates which are finally oxidized to CO2 and H2O.
The higher amount of the detectable compound is leaving the column, the proportionally higher the detector response /electroconductivity/ is.
Your compounds can be however, detected by TCD /thermal conductivity detector/
Note: the sharp and high peak in your chromatogram is most posibly a signal of CH3OH.
I don’t have a reading for when we were running the duratherm. The above is after flushing with Isopropanol, alcojet at 70C 2x, and water 2x also at 70C, ten replacing duratherm with 50:50 dowfrost.
The formaldehyde reading was up around 0.500 after the isopropanol, and has been falling steadily since.
Pretty convinced circulator was turning duratherm into formaldehyde…but I’ve still got no clue how…
I see nothing new on the GC after incubation of duratherm S with plasma-cutter slag at 100-110C for 48hrs (red is lab air, black is test sampke. Blue is calculated baseline)
Propane and butane signals are just a fact of life in a hydrocarbon lab…
Would you mind quantifying the oxidized materials inside the jacket for us? Are you seeing a lot of corrosion? I know you showed some photos of build-up. Can you do some tests on that to see exactly what it is?
How much air is getting into the system? And if air is not getting in - how is oxygen getting into the system (this would be needed for the siloxane reaction that might have a byproduct of formaldehyde). In any case - you’d need a lot of it, and that access to air would have to be there often, either that you are adding, or material that is already dissolved in the substance.
Any chance that you are getting Ethanol in there at all? That would make the formaldehyde generation process a bit easier from an energy activation standpoint (meaning it could happen at lower temps…)
Perhaps its under A LOT of pressure as well? Like 10 bar or more?
That picture was from the web. No clue what is in there. Don’t have a camera I can get in there. It would seem to be different in composition to the plasma cutter slag I substituted.
“Open bath” circulator, with lid. 10” drop from inlet to surface of fluid may have provided oxygenation.
Essentially no pressure (less than 1 bar). Pump probably has 20’ max head
OKay so not under a lot of pressure. But plenty of oxygen - is there any EtOH in the atmosphere that could get dissolved - if yes, there you go. Those things combined and you easily get formaldehyde even at low temperatures. It can happen at room temp with enough time even, very slowly.
Hope the cleaning method and swap out of fluid has helped. And hopefully it doesn’t happen again right away. If so - you might ask them about a oxygen stabilizer or something similar. Something that will scrub the O2 out before it has time to catalyze/oxidize anything.
duratherm got back to me, and said the fluid looked fine. even via FTIR. then noted that essentially nothing is miscible in the stuff so they probably wouldn’t see anything even if it was there.
Was gonna suggest a Harbor freight boroscope might help you out if you were curious as to the condition of your jacket. Having since gotten one it has come in handy many times.
