Evolution of formaldehyde from Heat transfer fluid?!?!

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Not a chemist, need an assist figuring this one out…

Our decarb reactor appears to have become homicidal. Near as I can tell it’s emitting formaldehyde!

Duratherm swears that’s just not possible. I’ve got no other explanation. They’re happy to test our fluid, but their testing consists of “flash point, viscosity, and total acids”, which doesn’t seem like it’s likely to solve this.

I could use some help setting up a testable hypothesis or three to figure this out.

Here’s what I have so far:

I asked the all Gnowing One about the production of formaldehyde because I was pretty sure I caught a whiff of it. when ASKED to associate the thermal degradation of siloxanes to the production of formaldehyde I got the following

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Pretty clear that aldehydes are a KNOWN degradation pathway for poly-siloxanes….just no obvious explanations for why it might happen at low temperature….(until I ASKED)

When I drop the requirement for formaldehyde, and ask about low temp decomposition, I get

Which, although it doesn’t mention Form-aldehyde explicitly, definitely lists it as a possibility.
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Assuming you’re behind a paywall on that one, you can obtain the full text via

Here is the rig in question

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And here is my first attempt at analysis. Head space sample taken from the circulator.

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Two unidentified peaks between water and propane. Which is where I imagine H2C=O would likely elute.

I’ve got a brand new 5gal pail of duratherm, and was planning on new vs used +/- some welding slag to see what I can find.

My best guess is that the insides of those jacketed vessels resembles this nonsense, and that chromium oxide or nickel oxide make great catalysts (they do!).

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Edit: formaldehyde “standard” incoming.

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Actual picture of their engineers conferring on how to fix this

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There are inexpensive formaldehyde test kits that people use when buying new homes. I don’t know if they would offer any insight to the endless list of other VOC’s that could be forming but it’s surely an affordable place to start.

It might help to remove the whole rig from the room temporarily, run an AC air scrubber, and wait a bit to establish a baseline. There may already be detectable amounts in the air from paint, sealant, adhesives, new plastic totes, etc.

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what brand/type of fluid are you using specifically? I know one of the silicone oils we’ve used as a heating fluid (SIL180 by ThermoFisher Scientific) states on the SDS: ‘At a temperature of approx. 150 °C a small amount of formaldehyde can be released by oxidative degradation.’
It does not state it as a significant danger, though it doesn’t quantify past ‘a small amount’. All other info on the SDS gives the impression of it being generally safe to handle and work around. I contacted ThermoFisher Scientific about this degradation point specifically, I can let you know what they say

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Duratherm S.
Rated to 300C open bath.
We are at 100C

OEM confirms their standard test battery it not likely to get us very far, they do however have all the toys to do this right, so I’m gonna lay off the poor kid who is fielding my query for a bit :shushing_face:

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I wanna say if SIL180 (Polydimethylsiloxane) can degrade into formaldehyde from heat/oxidization alone (even without metal oxides involved) it stands to reason Duratherm S (Siloxane) could as well? unless i’m oversimplifying (I’m not a chemist either)
then it’s a question of concentration and danger of exposure, again once I hear back from ThermoFisher I’ll let you know. very curious myself

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They’ve also suggested Duratherm G as a work around.

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I’d think so, if not for the low temp he’s decarbing at.

“Duratherm S - ideally suited for high oxidation applications or completely exposed systems. Duratherm S is virtually impervious to oxidation at temperatures under 204°C (400°F) and offers superior protection from fluid degradation”

@cyclopath I think your jacketed vessel theory is a strong one. Also, check the circulator plumbing.

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Testable hypothesis…

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Just a spoon full of sugar helps the duratherm break down…in the most delightful way

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You could probably drain the fluid out and snake a flexible inspection camera into the fluid path to see if you can spot some of the “sugars” (I.E. oxides) that form when stainless is heated without sufficient inert gas backing, flux or other very necessary things to keep oxygen from reacting (poorly) with the weld pool. Milwaukee makes a very nice one but I haven’t convinced myself to upgrade from my cheap auto parts store one that runs on AA batteries instead of the M12 packs.

Passivation helps clear out free iron particles and prevent future rusting but I doubt the short exposure duration would entirely get rid of the oxides and sugars from a poor weld job.

I’d love to believe that all manufacturers have the decency to do real QC, and to hold their employees accountable for sending poorly made products out into the hands of their customers, but I worked for a crappy one and I know full well that they don’t.

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@SubstituteCreature that one and Sniper Business are my favs. Rip Trevor Moore.

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I mean you’ve met me and seen how fuckin nuts I am - my favorite is obviously the tattoo :grin:

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Relevant cuz pot leaf

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This is a classic. I remember watching this with my brothers, laughing hysterically. You just took me back to simpler times. Thank you

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Looks like my ghetto heat bath can manage the appropriate temp.

Just need to get my “catalyst” into smaller pieces.

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Yeah trying to sort this out before expanding capacity.

Switching fluids AND passivating the jackets on all the new parts are certainly on my list.

I’d still like to KNOW what’s going on.

Formaldehyde (/fərˈmældəhaɪd/ (listen) fər-MAL-də-hide, also /fɔːrˈ-/ (listen) for-) (systematic name methanal ) is a naturally occurring organic compound with the formulaCH2O (H−CHO). The pure compound is a pungent-smelling colourless gas that polymerises spontaneously into paraformaldehyde (refer to section Formsbelow), hence it is stored as an aqueous solution (formalin ), which is also used to store animal specimens.

Which might mean the ugly looking blob on the GC was actually data….and certainly means I’ll need more than just a headspace pull from a buddies wet tissue specimen to confirm the ID.

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Closed bath?

Regardless of whatever duratherm you are using, the formaldehyde is in theory a result of the products oxidation. So, how can we minimize or prevent this from happening?

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I got some ive been using for yrs if you wanna test that, only been in a roto bath for the last handful of yrs. No noticeable corrosion on the heating element, maybe it actually stainless. Side note, took a few 100 lbs to the scrap yard and many of the top sellers “stainless” was not stainless

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I have Duratherm S in the cheap china heater circulator’s for my 50L glass and SS reactors and have not noticed anything kinky (I decarb at 155c tho) but it cant hurt to get a test from my lab … just wonder about the poor lab tech who has to clean the column lol Duratherm is slippery chit

Thx for raising awareness @cyclopath

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This is very interesting and confirms my fears about expensive transfer fluid and open baths. We just use a mixture of PG and water in our decarb vessels, but we also don’t go much past the BP of water @ 107C

Breaking down expensive HT fluid was a big reason why we just went with the PG/H2O mixture and run at minimum decarb temps. We still get complete decarb (usually less than 1%THCa remaining) and can still turn out about 12 kilos/day if all 6 of our chambers are running.

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Yeah, we are also running pretty close to 100C…which is why the folks answering the phone at Duratherm don’t believe me.

I’d like the ability to go warmer, but first I need the ability to run what I’ve got safely.

Given that PG & water will get the job done, the first order of business is probably to clean these critters out and swap fluids. That will get us back in production today.

Next trick is to prove that testable hypothesis regarding unpurged welds. So I can justify an attempt at passivating the jackets.

Will keep y’all posted on the lady with the umbrella

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