Sciencemadness Discussion Board

"Expired" Formalin - Help

AndrewOfWallachia - 25-8-2025 at 04:42

I got a bottle of Formalin a while ago because I wanted to make some Hexamine but I never got around to it. I left the bottle of Formalin sitting in the garage and now I noticed that it became cloudy, and some white precipitate covers the clear walls of the plastic bottle - *this is worrying*.
Thankfully, the bottle was never unsealed. What actually happened here? And how should I dispose of it if necessary?
Thanks in advance! o7

Radiums Lab - 25-8-2025 at 05:53

2 posts? Ok what you see there is polymer of formaldehyde called Paraformaldehyde.

Radiums Lab - 25-8-2025 at 05:57

It is formed when formaldehyde is evporated slowly. Id recommend to filter it and add some H2O.

Radiums Lab - 25-8-2025 at 06:01

The H2O should be added to the remaining soln to prevent further polymerisation. Dont add too much.

bnull - 25-8-2025 at 07:12

It was stored in a cool pace, wasn't it?

Actually, methanol is used to limit polymerization. Adding more water just helps to dissolve some of the polymer.

You can depolymerize it by heating in the presence of an acid or base.

@Radiums Lab, what browser are you using?

Radiums Lab - 25-8-2025 at 07:48

Quote: Originally posted by bnull  
It was stored in a cool pace, wasn't it?

Actually, methanol is used to limit polymerization. Adding more water just helps to dissolve some of the polymer.

You can depolymerize it by heating in the presence of an acid or base.

@Radiums Lab, what browser are you using?


Oh, hi bnull. I meant that you need to add water to the filtered solution, since this polymerisation happens because of the formalin solution loosing water.
If we add a bit of water to the filtered solution then we can limit the remaining solutions polymerisation for couple of days.

If you are performing acid or base sensitive experiment then the water method is perfect.

Oh and I used this phone to post the previous 3 messages, It has an inbuilt opera browser in it. I cannot post more than 1 line in a single post so I did multiple posts.



image.jpg - 2.7MB


[Edited on 25-8-2025 by Radiums Lab]

bnull - 25-8-2025 at 08:34

Quote:
Oh and I used this phone to post the previous 3 messages, It has an inbuilt opera browser in it. I cannot post more than 1 line in a single post so I did multiple posts.

That's odd. Is it running a KaiOS or Jio's own OS?

Heating alone should do. If there is enough precipitate, save it. Paraformaldehyde takes much less space to store than formalin. I'm still considering which one to buy, as my needs are not so urgent.

Radiums Lab - 25-8-2025 at 08:51

Heating formalin, I would not do that, a soln. is good for me. And Bnull this runs on Jio's OS.

AndrewOfWallachia - 27-8-2025 at 11:36

Quote: Originally posted by bnull  
It was stored in a cool pace, wasn't it?

Actually, methanol is used to limit polymerization. Adding more water just helps to dissolve some of the polymer.

You can depolymerize it by heating in the presence of an acid or base.

@Radiums Lab, what browser are you using?

...Yep. It was. I know full well Formalin shouldn't be exposed to cold, and I did not intend to expose it, my garage was fine in temperature when I got it, but since I didn't get around to using it, it got cold over the winter.

So. You're saying, filter the paraformaldehyde out of the formalin, and then add water to the filtered formalin? (If I had some halfway decently pure methanol I'd use it to prevent polymerization as you said, but I don't.)
In that case, what is there to be done with the separated paraformaldehyde, since I don't feel confident depolymerizing it into gaseous formaldehyde like you suggested.
Thanks for the answer! o7

[Edited on 27-8-2025 by AndrewOfWallachia]

bnull - 27-8-2025 at 14:33

My reading skills aren't what they used to be. @Radiums Lab suggested adding water to formalin after filtering the polymer out, which I interpreted as adding water to the unfiltered solution.

Polymerization in formalin happens because of traces of formic acid that come either from the manufacturing process or from oxidation of formaldehyde by dissolved oxygen, although how likely the latter is I don't know. Adding water would dilute the acid and slow polymerization for some time, that much is certain. If you add a small amount of sodium hydroxide and leave the solution alone for a few weeks, I'm pretty sure, as long as the garage is not arse-freezing cold, that it will all depolymerize and go back to solution.

Heating (not boiling, that is) the solution will speed up the process but, as it seems you don't need all of the formalin right now, just filter out the polymer and store it still wet (no need to dry it) in a well-sealed flask. It will come in handy someday. Or put it in a bottle, add sodium hydroxide and water and leave it alone. When your first bottle is over, there will be this one.

Radiums Lab - 28-8-2025 at 11:55

Adding a base to formalin would lead to slow Aldol reaction. Polymer does not form due to HCOOH.

bnull - 29-8-2025 at 06:22

Are you sure? J. C. Bevington, The Polymerisation of aldehydes, p.145:
Quote:
Polymerisation in Solution at Normal Temperatures. Formaldehyde dissolves readily in water, polymerisation occurring to give polyoxymethylene glycols of general formula HO.[CH2.O]n.CH2.OH where n probably can have values up to 12; if n exceeds this value the polymer is insoluble in water. Cryoscopic measurements have shown that the degree of polymerisation decreases as the concentration of the solution is decreased or as the temperature is raised, and that the process is reversible. The velocities of the polymerisation and depolymerisation reactions have been measured by cryoscopic, interferometric, and dilatometric methods (the results have been summarised by Mark and Raff) and have been found to be comparatively small.
In aqueous solution formaldehyde is believed to form the hydrate CH2(OH)2 very readily; evidence for the existence of this hydrate is that the corresponding hydrate of chloral is stable, and that by using the isotope 18O it has been shown that oxygen is exchanged quite readily at 20° between acetaldehyde and water, probably by means of the equilibrium

CH3.CHO + H2O <=> CH3.CH(OH)2

The growth of the formaldehyde polymer may result from a polycondensation; the simplest type of reaction is represented as

HO.CH2.OH + HO.CH2.OH => HO.[CH2.O]2.CH2.OH + H2O

and the general reaction as

HO.[CH2.O]p.CH2.OH + HO.[CH2.O]qCH2.OH => HO.[CH2.O]p+q+1.CH2.OH + H2O

Both polymerisation and depolymerisation are catalysed by hydrogen ions and the former may occur by the following mechanism:

HO.[CH2.O]p.CH2.OH + H3O+ => HO.[CH2.O]p.CH2+ + 2H2O
HO.[CH2.O]qCH2.OH + H2O => HO[CH2.O]q.CH2.O- + H3O+
HO.[CH2.O]p.CH2+ + HO.[CH2.O]q.CH2.O- => HO.[CH2.O]p.CH2.O.CH2.[O.CH2]q.OH

The net reaction clearly can be represented by the general equation above. The mechanism of the depolymerisation is discussed in a later section.


Also, from Walker's Formaldehyde, p.75:
Quote:
Dilute alkalies and acids markedly accelerate the rate of paraformaldehyde solution, which varies with pH in the same manner as the solution reactions studied by Wadano, Trogus, and Hess (pages 34-36). The rate of solution as found by Löbering goes through a minimum between the pH values 2-5, increasing rapidly on either side of these limits, as illustrated in Figures 13 and 14.


Adding a small (we're not talking of grams here) quantity of hydroxide to the formalin solution in the presence of paraformaldehyde (the solution as it is in the bottle) will help dissolve the polymer and slow down polymerisation. The rate of aldol condensation under such circumstances will not be so high as to inutilize formalin.

A suggestion: test the pH of the solution.

J. C. Bevington, The Polymerisation of aldehydes, Q. Rev. Chem. Soc, 1952, 6, 141 (http://doi.o/10.1039/QR9520600141).

Radiums Lab - 29-8-2025 at 09:17

Yea after bnull said like for example previous post, I did a bit of digging and asked my chemistry professor too, according to many sources and my professor( he has a PHD in polymer chemistry) formic acid does not affect the polymerization but some sources say it helps the formalin to not polymerize and some sources say it catalyzes the polymerization. He said heating is enough to depolymerize it. He even stated that aldol condensation will take place but in a very slow manner, often taking 2 to 3 years to notice a significant effect. Some sources even stated that formalin oxidizes into formic acid and methanol. Now I'm going to wait for bnull's research about these facts.

bnull - 29-8-2025 at 10:33

Quote:
Now I'm going to wait for bnull's research about these facts.

Hold your horses. As far as my curiosity goes, with two reliable sources (that include other sources as well) and a plausible mechanism for polymerisation in acidic media, I'm satisfied. You may want to provide sources for these other facts.

Edit: I see now how methanol inhibits polymerization. There are only two places in a polymer chain that the monomer can attach to and, if both are protected by a methyl ether group, the monomer does nothing to it. It's like those caps one puts at the end of a pipe; there's no way to attach another pipe to it if the two ends are capped. Maybe even ethanol works as inhibitor.

[Edited on 29-8-2025 by bnull]

angrygiraffe - 8-9-2025 at 17:50

You'll see cloudiness and sediment because it wasn't stored properly‌.
I wouldn't recommend using it anymore—those chunks mean some formaldehyde has turned into paraformaldehyde, which really cuts down its germ-killing and preserving power‌.