Sciencemadness Discussion Board

Trouble Understanding

Arsole - 23-2-2013 at 03:25

I am having trouble understanding Patent 1,948,069 "Production of Paraformaldehyde" 1934 Otto Fuchs and Erich Naujoks.

www.google.com/patents/US1948069

I would like some help clarifying what is happening.

From what I understand:

1) A regular 37% formaldehyde solution is being added slowly midway into a fractionating column.

2) In a RBF below the column there is a liquid that is heated. The vapor is to travel up the column and come into contact with a small amount of the Formaldehyde solution. It is important that this liquid form a low boiling azeotrope with water.

This is where I get lost.

The patent says in the example given that after the mixture of formaldehyde, water, and ethyl acetate go through the condenser and are collected they separate into two layers and the ethyl acetate can be removed. (Do they only form the azeotrope in vapor phase?)

Is the Formaldehyde being dissolved into the Ethyl Acetate and after the concentration becomes high enough it starts to polymerize?

I am having a little trouble understanding the mechanics of this patent any help would be appreciated. :)


watson.fawkes - 23-2-2013 at 06:45

Quote: Originally posted by Arsole  
The patent says in the example given that after the mixture of formaldehyde, water, and ethyl acetate go through the condenser and are collected they separate into two layers and the ethyl acetate can be removed. (Do they only form the azeotrope in vapor phase?)
Yes, the mixture behaves differently between vapor phase and liquid phase. It's the nature of gas phases generally that all substances are miscible, irrespective of whether they are miscible in the liquid phase. Ethyl acetate is used to lower the boiling point of water; the azeotrope boils at 70.4 °C (see azeotrope data). After condensation, the solubility of water is ethyl acetate is about 3%, so after separating the ethyl acetate phase, it's dried before being returned to the still pot. Ethyl acetate is being used as a carrier to dehydrate the pot mixture. The initial formaldehyde solution is introduced into the column directly to avoid overloading the system at the start. Over time, water is removed, the concentration of formaldehyde increases, and it falls out of solution. The big trick in this patent to do this at a temperature lower than otherwise required, decreasing the amount of polymerization in the paraformaldehyde.

Arsole - 23-2-2013 at 14:31

Thank you that makes things clearer. Is it correct to think that the formaldehyde that is not carried over in the azeotrope mixture is returned to the pot as re-fluxing takes place.

As formalin has a bp of 101C it would be brought down the column where the water is continuously stripped away via the low bp azeotrope moving up the column.

I think that all the water could not be stripped out as formaldehyde itself has a very low bp (-19C) and would distill over. Does it start to polymerize as soon as the water begins to be stripped so that it does not come over? Or does it dissolve in the auxiliary liquid and return to the pot?