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Author: Subject: Ostwald style nitric production
violet sin
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[*] posted on 27-1-2017 at 22:19


This was the kind of thing I was suggesting:

https://www.google.com/patents/US2578674
Nitric oxide recovery system
US 2578674 A

"The optimum temperature has been calculated to be about 60 F.; at this temperature the silica gel adsorbs approximately 6.5% of its weight of nitrogen dioxide before becoming saturated by a stream of gas containing 1% NO2."

"if one passes 1.19% of NO: through a 3 foot bed of 10-14 mesh silica gel, at 15 C., at the rate of 100 fit/min.. the bed adsorbs with 100% emciency for 12 minutes. After 12 minutes, the adsorption efficiency begins to fall ofi' and after 31 minutes only 75% of the N02 is adsorbed and 25% is Wasted to the stack. "

"he nitrogen dioxide may be desorbed from the adsorption gel bed by means of heat introduced into the latter. It is impractical to desorb by heating the container of the gel bed, because the gel is too poor a conductor of heat. We have discovered that desorption by means of a current of hot gas consisting essentially of nitrogen dioxide not only is possible but also is much more advantageous than is desorption by steam or by hot air as sole means."

"have been heated to about 165 C. By means of this treatment the adsorption bed is caused to part from approximately 70% of its adsorbed NO2. If the adsorbent is heated to a higher temperature level a higher percentage of the NO2 will be released as nearly pure NO2"

You get the idea...

Man some of these patents had horrible translators or numerous deletions-> ". To effect this operation, we heat a supply of NO2, or, a gaseous mixture consisting largely of NO2, to a temperature of approximately C. " nice to see some of the numbers in things like this just gone... Deff not the first time I have noticed this in parts of the critical numbers on old patents. Probably crappy document scaning software or under paid staff. Either way it can be irritating




Sauce
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[*] posted on 28-1-2017 at 10:59


That's a good find, violet sin! Reading through this document, I can't help but feel impressed with how clever this whole patent is. The only thing I think could possibly be suboptimal would be the initial drying by water rinse, since this could produce some acidic waste water. It's not absolutely necessary anyway. I hadn't really thought of using saturated silica gel as a catalyst for NO oxidation, but it makes perfect sense as to why this works. In my own experiments, I passed the dry oxidized gas from the oxidation chamber, through the silica gel tube, and into a second oxidation chamber. I never saw any gas coloration in the second chamber, even after running the reaction for a while. I thought this was odd, as I'd expect some small amount of unoxidized NO to be getting through the silica gel. I suppose the leftover NO was getting catalytically oxidized in the silica by excess oxygen.



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Chemetix
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[*] posted on 28-1-2017 at 14:09


What would happen to the gel-NOx system if it sees ammonia? Can it discriminate? And would absorption be unaffected? I'd think the NO is still reactive whether or not it's stuck to silica gel. But the idea of using the silica as a oxidation catalyst could help a good deal. There has been left over NO2 sitting in the oxidation chamber for weeks now, there is acid condensate present and enough air to complete the reactions to nitric I would have thought, but there it is, a mild reddish colour. The reaction needs very large volumes to complete the reaction and long residence times.

I'm very busy atm with work, can't play with the plant, but have been contemplating the last few runs. One of which was done with (NH4)2SO4 /hydroxide generator.
The ammonium sulfate system gave good steady flows of ammonia at a full 6-7% of air, I made 20ml of condensate in about 3hrs. But This seems the upper limit of the catalyst system as it is. There has been ammonia getting through and I've had the silica absorption idea rolling around in my head.

The first modification is going to be catalyst bed geometry, long and skinny= high flow rate low reaction site time, vs. wide and short=large area slow flow rate high contact time.

It's a balancing act with the dynamic equillibria of all the reactions; NH3 can decompose, so can the NO. I guess the best I can do is make a small change and see if I can squeeze some more performance out of the system. Without rate studies, engineering is going to be a suck it and see approach.
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[*] posted on 2-3-2017 at 12:54


@Chemetix, any updates? :)
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[*] posted on 3-3-2017 at 01:16


'Fraid not...busy atm. Want to get to play with the catalyst geometry.
Watch this space as they say.

thnx!
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