What purity of Nitrogen required for the Haber Bosch process? 1

[sasa000]

Specifically concerned about oxygen contamination.

From what I've read it doesn't appear to be that critical, but even a rough rule of thumb (with a reference) would be helpful.

 

[georgeverghese]

The Wiki page on the Haber process says there are details in Ref 3 - the Ullman's Encyclopedia of Industrial Chemistry in a chapter dedicated to Ammonia production about the temporary catalyst poison O2. Dont know if the permissible concentration of O2 is dependent on the type of catalyst used. From some other article, it appears N2 of 98% v/v N2, 1.1% O2 and the rest being Ar is acceptable for the HB process, so the O2 permissible limit would be somewhat higher. This is easily achieved in N2 produced from cryogenic distillation plants.

 

[pierreick]

Hi,
Nowadays PSA unit can supply very good quality N2 with low O2 content .
My 2 cents
Pierre

 

[EdStainless]

Swing absorption units will easily make this purity level.

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P.E. Metallurgy, consulting work welcomed

 

[georgeverghese]

This article says 10ppm O2 in the feed to the reactor is the upper limit. O2 poisoning is by sintering of the catalyst by H20 due to the almost instant conversion of O2 to H20 on the catalyst surface. H2O is the actual catalyst deactivator. Hence 10ppm O2 or 10ppm H20 in the feed have the same effect on catalyst deactivation.

https://www.mdpi.com/2073-4344/10/11/1225/htm

I havent read the entire document - this is what I gleaned from the first few sections

 

[shvet]

One might say that N2 is not used in Haber-Bosch process as air is used instead. O2 level is referred to feed (N2+H2) mixture. See a process flow diagram from wikipedia for details.

https://en.wikipedia.org/wiki/Haber_process

 

[georgeverghese]

Typical pass conversion is 15%, so you can work out what the O2 in fresh N2 has to be in order to keep within the upper limit of 10ppm O2 in feed to the reactor.
O2 level in feed to the reactor would be a concern when H2 is derived from solar powered electrolysis of water and not by the typical 2step steam reforming / air reforming of methane, since any O2 in air introduced into the secondary reformer not taking part in the partial oxidation of methane slipping out the primary reformer would be completely converted to H20.