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Author: Subject: Purifying a formaldehyde solution w/ blue dye
DrIronic101
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[*] posted on 13-3-2020 at 07:39
Purifying a formaldehyde solution w/ blue dye


I have a cleaning chemical (left-over) which contains formaldehyde and methanol that I would like to use in an up-coming experiment. However, it contains a blue dye which would probably interfere with this. What would be the best way of purifying this product for use in experiments? Thanks!



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njl
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[*] posted on 13-3-2020 at 09:14


distillation sound reasonable. do you want just formaldehyde or a solution in methanol?
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clearly_not_atara
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[*] posted on 13-3-2020 at 17:31


You may be able to just convert it to hexamine and filter out the precipitate. The resulting hexamine will be reasonably pure.

https://www.nrcresearchpress.com/doi/abs/10.1139/cjr47b-062?...

However, I am not aware of good methods for recovering formaldehyde from hexamine, but sometimes you just want hexamine :p

EDIT: if there is a way, it should be in this thesis

https://ecommons.luc.edu/cgi/viewcontent.cgi?article=4186&am...

[Edited on 14-3-2020 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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Sulaiman
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[*] posted on 13-3-2020 at 19:51


Quote: Originally posted by DrIronic101  
However, it contains a blue dye which would probably interfere with this.

The blue dye will probably be in trace ammounts only. (e.g. 1ppm)
(I can turn the water of an entire swimming pool blue by adding 5g crystal violet
- if clorine/bromine levels are low as crystal violet bleaches easily)

so, would the blue dye really interfere significantly ?

and, I'd try one drop of chlorine bleach or hydrogen peroxide on a small sample,
the blue may vanish before the methanol or formaldehyde are significantly oxidised,
if it is just the colour that you do not like.
(I suspect that the methanol/formaldehyde may slowly reduce the dye back to blue)

maybe activated carbon would absorb the dye ?




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anti
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[*] posted on 14-3-2020 at 10:21


You could try oxidising the dye or distillation. Try using a bit of H2O2. However, the dye SHOULD be present in trace amounts, as pointed out by Sulaiman.
Maybe potassium permanganate. But then you would have to reduce it with a bit of sugar to get rid of the purple colour.
Please give us more information about the dye.
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DrIronic101
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[*] posted on 14-3-2020 at 20:59


Quote: Originally posted by Sulaiman  
Quote: Originally posted by DrIronic101  
However, it contains a blue dye which would probably interfere with this.

The blue dye will probably be in trace ammounts only. (e.g. 1ppm)
(I can turn the water of an entire swimming pool blue by adding 5g crystal violet
- if clorine/bromine levels are low as crystal violet bleaches easily)

so, would the blue dye really interfere significantly ?

and, I'd try one drop of chlorine bleach or hydrogen peroxide on a small sample,
the blue may vanish before the methanol or formaldehyde are significantly oxidised,
if it is just the colour that you do not like.
(I suspect that the methanol/formaldehyde may slowly reduce the dye back to blue)

maybe activated carbon would absorb the dye ?


I suppose I'll try a bit of h2o2. I'll report back on what happens.
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Corrosive Joeseph
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[*] posted on 14-3-2020 at 21:03


It would probably help some if you post your MSDS


/CJ




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draculic acid69
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[*] posted on 14-3-2020 at 21:08


Can formaldehyde solution be distilled like a liiquid with out it boiling the gas out of solution?
I'm doubting it.
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anti
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[*] posted on 15-3-2020 at 00:14


Quote: Originally posted by draculic acid69  
Can formaldehyde solution be distilled like a liiquid with out it boiling the gas out of solution?
I'm doubting it.

Actually, I think you're right. For the most part.
Formaldehyde tends to polymerise.
"Aqueous solutions of formaldehyde cannot always be concentrated satisfactorily by methods heretofore generally employed for such purpose for the reason that such methods involve the fractional distillation of an aqueous formaldehyde solution with the recovery of a distillate which in some cases may have a concentration of formaldehyde not substantially greater than the concentration of formaldehyde in the solution originally treated. Depending upon the formaldehyde concentration of the solution originally treated, such prior methods may yield a vapor which has a high concentration of anhydrous formaldehyde, part of which undergoes polymerization to paraformaldehyde at the temperatures employed, producing sufficient quantities of solid paraformaldehyde to clog the condensers and vapor and distillate lines, making operations difficult and uncertain, while unpolymerized anhydrous formaldehyde is difficult to recover because of its very low boiling point and high vapor pressure."

http://www.freepatentsonline.com/2153526.html
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S.C. Wack
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[*] posted on 15-3-2020 at 05:41


Distilling aq. solutions isn't a problem. Something like an azeotrope of 10% comes over on simple distillation if you have at least 90% water. This on vacuum distillation gives a distillate with barely an odor up to the point where the residue solidifies on cooling.

The problem is methanol which is not at all unreactive. The reactions are I think reversible hot, for sure if mixed with a lot of water, but maybe not at vacuum temperatures.

[Edited on 15-3-2020 by S.C. Wack]




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