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Calculation For Vapor Ppm Of Formaldehyde In Batch

chemicals thermodynamics

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#1 ahumza94


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Posted 15 August 2020 - 09:30 PM

Have a batch with a 3 lb curative package. The curative package contains .1 weight percent formaldehyde. Its a butyl rubber based batch mixed in a banbury mixer so a lot of heat is generated from the rubber masticating. The batch mixes until it reaches 350F and then we dump the batch.
Question: We are trying to calculate how much formaldehyde is generated in ppm during the batch to see if our respirators can handle it and to also get an LEL %. Now the picture attached is our industrial hygienist way of calculating ppm. She calculated that we were generating a concentration of formaldehyde by taking the mass of formaldehyde in the batch (solid/liquid mass) of .3 lbs and dividing it by a rough estimate of the volume of the mixer. This is incorrect right? We need to take into account the vapor pressure of formaldehyde at the elevated batch temperatures using clausius clapeyron eq or antoine's parameters right ??? Am I missing something here? Please look at picture and I can provide more info as well.


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#2 breizh


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Posted 15 August 2020 - 11:17 PM




You need more data like the total pressure on the sky of the reactor, the other components  if any like (water ,etc)

The link above is about vapor pressure of formaldehyde.

Note :don't mix up PPM mol and PPM mass .

Hope this is helping you 

Good luck


Edited by breizh, 15 August 2020 - 11:18 PM.

#3 ahumza94


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Posted 16 August 2020 - 12:41 AM

Thank you very much for your reply Breizh!


I have attached the SDS of the curative, but I do not know exact composition because it is proprietary. 


When you say total pressure in the "sky" of the reactor, do you mean headspace--in other words the space above the liquid? I am not sure how to obtain that info as there is very little head space in a banbury mixer. Typically its 90-100% full in order to generate more shear with the blades. 


Am I correct in determining to use vapor pressure to calculate vapor generated in ppm, rather than the hand calculation shown in the picture?




Humza AhmadAttached File  sds.PDF   121.22KB   2 downloads

Edited by ahumza94, 16 August 2020 - 12:42 AM.

#4 breizh


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Posted 16 August 2020 - 01:00 AM


Yes I think so !

Sky =  head space

note :3*0.1 %= 0.003 lb not 0.3 lb .

In the worst case ( lack of data) you may consider that all the formalin is passed to the vapor phase (head space) 

Good luck.


Edited by breizh, 16 August 2020 - 03:17 AM.

#5 ahumza94


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Posted 16 August 2020 - 03:18 PM

Oh boy, I can't believe I missed that. Thanks Mr. Breizh. that would bring our concentration down to around 15ppm which makes a ton of more sense. 

Humza A

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