Sciencemadness Discussion Board - Ostwald style nitric production

Ostwald style nitric production

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violet sin - 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

WGTR - 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.

Chemetix - 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.

ecos - 2-3-2017 at 12:54

@Chemetix, any updates?

Chemetix - 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!

BaFuxa - 8-7-2018 at 04:05

Hi everyone,

I have been playing around with the catalytic oxidation of ammonia as well.

I did change a few things to the process that was designed by Chemetix, I used copper (II) oxide and manganese dioxide as the catalyst. If comparisons are anything to go by, it works just as well as platinum. It does not need constant heating nor insulation, you just heat it up once and it generates its own heat, as long as the reactants are supplied it keeps going on its own.

As for the products I got either ammonium nitrate or nitric acid straight in the reaction tube ( photo 3 is some copper nitrate that was collected from it). So it works in fact so well that the NO that is generated upon first oxidation is oxidized a second time and then reacts with the water to HNO3 which, if ammonia passes unoxidized, makes ammonium nitrate. So I am onto maximizing the surface area in the minimum volume possible.

It is no suprize that industry uses platinum/rhodium gauzes. I need to make a gauze like catalyst bed. Any suggestions on how to do that are welcome.

I tried glass wool as a support but it melts like butter, borosilicate wool partially melts and packs up and ceramic wool tends to glue itself together as well, but that could be due to catalyst overloading and sintering. Pure quartz wool is about 140$ on ebay so I have to find another way.

As for the ammonia generator I was inspired by the Astral Chemistry process (https://www.youtube.com/watch?v=dMV4-CxCyL0&t=339s) and I put an ammonia solution with a bubbler and a vent port to regulate the gas feed. I had another pump feeding air as well but its pressure is so high it blocks the ammonia flow and snuffes out the reaction, will have to solve that problem as well.

I did also try to hook up the urea to ammonia generator to the apparatus but I let go of that idea as I found it just complexified the set up too much and the gas that is generated does not have a constant rate, you have to monitor it and adjust it to keep things going.

I also tried the electrochemical synthesis of ammonia from urea, it works but you need an electrolytic cell that 1) efficiently keeps the cathodic and anodic gases separated as this process generates N2 NH3 and H2, which is not desirable since it will favor a recomposition to NH3 and 2 ) should also be fairly large. I find it easier to make an ammonia solution from urea first but I keep an eye on these methods.

Anyway, long write up but I have been on this on and off from some months now and I thought I should give you guys a progress report of some sort. Thanks for reading.

[Edited on 8-7-2018 by BaFuxa]

[Edited on 8-7-2018 by BaFuxa]

[Edited on 8-7-2018 by BaFuxa]

Chemetix - 8-7-2018 at 16:29

Great set up! Congratulations on getting it working! The catalyst temps are a bit of a challenge. The crushed tile or bricks seemed to have a good surface area with porosity and allow the catalyst to soak into and onto the surface. They took the temperature well. You have noticed that ammonium nitrate forms when there is too much ammonia to air, I found 6% or thereabouts seems to work best with my cobalt catalyst at not producing ammonia. Playing with the geometry of the catalyst bed was going to be my next area of inquiry, wide and short or skinny and longer, to play with residence times and balancing the heat of reaction with subsequent reaction NO -> N2+ O2 that occurs when the nitrogen oxide is still in contact with the catalyst.

But controlled release of ammonia is probably the most valuable technological innovation at this stage.

Best wishes and keep us posted

XeonTheMGPony - 8-7-2018 at 17:33

I started to make a reactore tube, will be a while yet but look forward to it. BTY Any reason no one has don a small scale haberbosh plant?

Texium - 8-7-2018 at 18:30

Wow. How did I manage to never see this thread before? Unbelievable!

It shall be stickied posthaste!

Herr Haber - 9-7-2018 at 04:59

Quote: Originally posted by XeonTheMGPony

I started to make a reactore tube, will be a while yet but look forward to it. BTY Any reason no one has don a small scale haberbosh plant?

Because the fablab / hackerspace is more than 30km from home !!!

Otherwise, that would be my number 1 goal given a place and the resources of a fully equipped workshop.

VSEPR_VOID - 9-7-2018 at 09:35

What keeps the nitric acid from reacting with the copper oxide catalyst?

Ubya - 9-7-2018 at 12:11

Quote: Originally posted by VSEPR_VOID

What keeps the nitric acid from reacting with the copper oxide catalyst?

the catalyst should only be in contact with ammonia, air, and their products, nitrogen monoxide and dioxide (and or dinitrogen tetroxide), nitric acid is formed later in the absorbtion tower, so if there is a positive pressure (as it should be) no nitric acid will ever be in contact with the catalyst

BaFuxa - 5-8-2018 at 03:31

Success

Quick update, I have made HNO3 from my set up. Same catalyst was used except it was unsupported and required external heating ( wanted to try unsupported just to see), I made sure the air : ammonia ratio was correct by going over the tube fittings. This is the most important thing here with the catalyst, the (molar ) ratio of NH3 to O2 should be 4 : 5, less than that and you are making either N2O or N2. You check this by eye, if you see NO2 gas you are doing it right. It is a matter of knobs adjustment. No sintering of the catalyst was observed.

Oxidation tower was made with a gas washing bottle with an air inlet.

After about 3 minutes of running time I had some HNO3 in the receiving flask. Strong smell of nitric acid, PH 2.13. My dependency on ( very costly) nitrate salts is now over

. Now next challenge is to make 99% HNO3 from this mu ha ha ha.

[Edited on 5-8-2018 by BaFuxa]

j_sum1 - 5-8-2018 at 04:24

Woohoo!

Congratulations. Nicely done.

Now I need to go back over this thread carefully to see how it was done. Getting HNO3 from easy-to-get reagents is quite an accomplishment.

Deathunter88 - 5-8-2018 at 06:22

Congrats! But I have to ask, are you able to produce a feasible amount of acid with this method? A pH of 2.13 indicates very little actual nitric acid. (A few drops of nitric acid in 500ml of water is easily able to bring the pH to 1 or lower.) It seems to me at this point this is more of a proof of concept than a feasible route to usable quantities of nitric acid. Feel free to prove me wrong though, that would be even better.

WGTR - 5-8-2018 at 12:04

Quote: Originally posted by BaFuxa

It is no suprize that industry uses platinum/rhodium gauzes. I need to make a gauze like catalyst bed. Any suggestions on how to do that are welcome.

I tried glass wool as a support but it melts like butter, borosilicate wool partially melts and packs up and ceramic wool tends to glue itself together as well, but that could be due to catalyst overloading and sintering. Pure quartz wool is about 140$ on ebay so I have to find another way.

I'm planning to get some of this 1mm silica wick from eBay:
https://www.ebay.com/itm/3mm-High-Quality-Silica-Rope-Wick-T...
It looks like it has multiple strands in the cord, so it may be possible to make the thread even thinner than 1mm.

One option would be to try weaving a small piece of mesh from the material, and then impregnating the mesh with the catalyst. Another option would be to calcine the catalyst into beads around the silica thread, making a string of beads on the thread.

http://www.sciencemadness.org/talk/viewthread.php?tid=55&...

BaFuxa - 6-8-2018 at 03:26

Quote: Originally posted by Deathunter88

Congrats! But I have to ask, are you able to produce a feasible amount of acid with this method? A pH of 2.13 indicates very little actual nitric acid. (A few drops of nitric acid in 500ml of water is easily able to bring the pH to 1 or lower.) It seems to me at this point this is more of a proof of concept than a feasible route to usable quantities of nitric acid. Feel free to prove me wrong though, that would be even better.

Indeed I just wanted to see if it worked but there is no reason this should not produce very large amounts at very high concentrations. One step at a time.

WGTR - 6-8-2018 at 03:44

At least you're getting more acid than unconverted ammonia. That is an accomplishment. Are you able to test the product for ammonia to see how much got through? If yield is ever low because the ammonia is getting over oxidized to nitrogen, this is less of a problem I think, than if unconverted ammonia is getting past the catalyst. In any case, welcome to the brown gas club!

Alkoholvergiftung - 6-8-2018 at 13:25

If you Need an carrier material you could use Zeolithe Stones. You could excange the sodium inons with your catalaytic heavy metal Ions. Than you have an Catalyst with an very big survace erea. I recommend Ammoniumdichromate solution. Let it few days dry heat it and Ready to go.

Furnace development

Chemetix - 3-1-2019 at 01:26

My long absence is not an indication that I've abandoned the project, still thinking of some better ways to do things. A recent experiment has made the need for quartz reaction tubes a little redundant.

I was given a tube of what I think is an alumino silicate refractory which is used as a kiln element support so they are going to be structurally sound above 1200C. They should be chemically inert to steam at these temperatures; even quartz fails this test. This should be a fantastic material for a tube furnace. But connecting it to labware is a bit of a pain.

Would it join to borosilicate? If it did then putting joints on it would be very convenient for all sorts of furnace work. The result is- Yes it can be joined to borosilicate!

If anyone would like to try one with joints I can do them very economically . HMU if you have an experiment that can use 20mm dia tubing.

IMG_20190103_152130 (1024x768).jpg - 402kB

j_sum1 - 3-1-2019 at 02:07

Chemetix, that looks like a wonderful innovation you have there. Could be useful for CaC2 and CS2 synthesis amongst other things.

I want one. Sending you a U2U.

WGTR - 3-1-2019 at 07:27

Quote: Originally posted by Chemetix

Would it join to borosilicate? If it did then putting joints on it would be very convenient for all sorts of furnace work. The result is- Yes it can be joined to borosilicate!

If anyone would like to try one with joints I can do them very economically . HMU if you have an experiment that can use 20mm dia tubing.

That’s interesting. Do the materials have the same expansion coefficients? It would be interesting to know what the material is. I’m assuming you fused them together with a torch.

Chemetix - 3-1-2019 at 12:26

[/rquote]

That’s interesting. Do the materials have the same expansion coefficients? It would be interesting to know what the material is. I’m assuming you fused them together with a torch.[/rquote]

Borosilicate can be joined to similar coefficients of thermal expansion, with the right technique it can be quite forgiving sometimes. It was one of those suck it and see moments. Fortune favours the brave. I'll try to find out what the material is exactly.

And the join was done on my glass lathe with a torch, I don't think it would be very easy to do by hand.

geffmov - 22-1-2019 at 10:58

Hi, i like what youre doing.

Have you considered a tilly lamp mantle to support catalyst?
Its designed specifically to do what youre after doing, and youll have minimum residence time. Importantly each replacement will be same as the last, giving you more consistancy.
Also if you look carefully different types of mantles are already impregnated with various rare metal oxides. Barium, cerium etc. Some may be no good, some i feel will work very well.
you can spread the mantles for maximum gas exchange and complete oxidation by clamping over a feeder pipe

I think from my own experience of metal catalysts in other areas youll find they vary in activation temperature dramatically, and selectiveness. Some are too harsh.
some can be regenerated in a hydrogen atmosphere heated for an hour or two.

Id feel platinum would give you most stable results. It was the original catalyst on tilly mantles too.
thanks for the informative thread

Edit- i did some researching myself. chapter 10 - 744page, Industrial chemistry book.. 'Oxidation of Ammonia' is a great read.
Platinums favoured because of its selectivity over a wider range of temperatures. It appears a simple platinum gauze 80mesh 1foot diameter is used in the industrial preparation. Temperatures are kept on the low side of the 1924 patent so catalyst lasts longer.
800-900c tops although upto 1300c will give the desired result nitrogen formation from competing side reactions come more noticable as temperature is raised.
They suggest 11parts ammonia 89parts air is optimal
It appears they preheat the gases too 700c then the exothermic reaction on the gauze itself to 800-850c
will give a 90% yield
Ammonia can form an explosive mix over 16%
Your flowrate over the gauze will be dictated by its temperature.

If youre looking for an alternative catalyst ive a suggestion over a recent innovation, thats copper been treated with argon. Apparently the copper behaves like a noble metal. It may not be possible to do this in a clandestine laboratory. I dont have references to hand sorry.

I also like the idea of the heating element sleeve been impregnated with catalyst.
The tilly mantle i suggested would be ideal but its drawback is once set and burned in, its brittle

[Edited on 23-1-2019 by geffmov]

BaFuxa - 28-1-2019 at 09:49

Did not know about tilly lamp mantles. Interesting but the fixed bed design did word well enough.

I have left the HNO3 for now, other projects at hand. I may revisit this synthesis if time allows. You are free to pick it up.

vanBassum - 30-1-2020 at 13:00

Its been a while since the last post but, I am happy to report that I have re-created your process with success. I had a bit of difficulty with the adhesion of the NiO to the support (a broken ceramic plate) so I used a bit of Mg(OH)2 witch seems to work well. My setup isn't quite as fancy as yours, just some pieces thrown together. I ran the setup for about 30 min and I could clearly smell the dioxide. There was about 2 drops of acid witch turned a piece of PH paper red and fizzed when dropped on some carbonate. Now I know that I am able to get this working I will try to build a better setup. I may switch to platinum since only a very little amount is needed to create a catalyst so its possible to do for a few bucks. The most difficult part would be the steady generation of ammonia, I have been playing around with the electrolytic process posted previously on this topic but had little success. The smell of ammonia was somewhat present after a while but the main problem for me would be the production of hydrogen. This is something I rather not have mixed with air flowing over a hot catalyst...

Alkoholvergiftung - 30-1-2020 at 14:07

Try ammoniumdichromat on Zeolithe or Chromchloride and waterglass. After few secounds you see an Brown Cloud.

[Edited on 30-1-2020 by Alkoholvergiftung]

MarkRob - 20-4-2020 at 05:20

I do quite a lot of work with diesel emissions control hardware and might be able to help out - I think possibly diesel SCR hardware might be useful. The SCR catalyst pack can be salvaged from a euro 6 and some euro 5 diesels, so they might be a few in scrap yards at this point. Adblue is also a very widely available urea source.

I've been trying to design the ideal system... I'm thinking an atmospheric pressure system, something like:

adblue fluid -> controlled flow via drip -> one end of tube heated to 250C

then inside the tube, from one end there is:

adblue inlet -> some unreactive granules to ensure stable evaporation/decomposition -> crushed SCR catalyst -> air inlet via flow control system -> some objects to create turbulence and ensure mixing (e.g. some blocks of smashed china clay pottery?) -> second catalyst -> outlet to air cooling tube coil -> cooling/condenser coil in fridge -> water drain and gas outlet

The idea would be for the first catalyst to break down the urea into ammonia, SCR catalyst is designed to do this using the water vapour from the adblue. The the oxidation takes place on the second catalyst as normal.

As use of air results in lots of excess nitrogen, and the urea decomposition produces CO2, there is going to be a large buildup of unreactive gasses in the system. I was trying to come up with a way to avoid silica gel packs, but they do seem to solve a lot of problems.

Attachment: Chemical_and_mechanistic_aspects_of_the-SCR-catalysts.pdf (675kB)
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MarkRob - 21-4-2020 at 06:56

Okay after a bit more of a think... It looks to me like fairly high conversion efficiency of around 30% of max theoretical could be achieved using only SCR catalyst in two stages followed by a one through system - very simple and easy to construct.

If I've done the maths right then only about 1 minute gas residence time is required for 90% NO->NO2 oxidation in the product gas from the dual catalyst design I described in the last post. There would be some acid in the condensed water, so the condenser output could be used to feed the absorption column, giving a maximum ~30% concentration product assuming the second catalyst is 100% efficient, or ~15% if its 50% efficient like SCR catalyst would appear to be. There is then some NO loss in the absorber off-gas. Overall conversion of adblue to acid by mass would be something around 20%.

So, whole system would be:

adblue tank -> controlled flow via drip system -> reaction vessel heated to 250C, and comprising of:

adblue inlet -> vapourisation region (inert granules) ->crushed SCR catalyst -> carefully metered air inlet -> turbulator/mixer region -> second catalyst pack (probably finely crushed and thin, to make the exchange with the surface diffusion limited and the flow laminar) -> exhaust gas to condenser, comprising of:

air cooled coil, then fridge cooled coil at 4C, then condensate collector.

The gas then passes through a further coil designed to give a 1 minute residence time for oxidation of the NO.

Then a once through absorption column fed by the gas at bottom and the collected condensate at top. Acid product collected from a tray at the bottom.
From scaling the sizes of industrical atmospheric pressure acid plants, the absorption column needs to be quite large, perhaps 100l per kg/day of product.

Attachment: kineticsofnitricoxideozonation.pdf (307kB)
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[Edited on 21-4-2020 by MarkRob]

MarkRob - 22-4-2020 at 14:06

Okay after a bit more research, maybe a single stage catalyst using Al2O3 powder (as a support/packing) with added Mn2O3 (from exhausted alkaline cells) and TiO2 (from pigment suppliers) would work fine with Urea (no SCR salvage required!).

I'd be a little worried that the TiO2 might cause N2 formation, but it seems undoped TiO2 has little effect on NH3, but does decompose and hydrolise Urea to form ammonia. Mn2O3 looks to have a ~55% conversion efficiency for NO at 550K, and likely higher at higher temperatures, 60 or 70% might be practically feasible.

Some useful links here (I can't download the full papers)

https://www.cheric.org/research/tech/periodicals/view.php?se...

https://www.cheric.org/research/tech/periodicals/view.php?se...

So the system would then look like:

Urea tank ->
Drip system (for highly controlled flow) ->
Tube heated to 250C at inlet end, possible with Al2O3 granules or similar to aid stable boiling/decomposition of the adblue (sudden bursts in the flow would be bad).->
Then an air inlet from the metered air supply (possibly from air compressor to allow unattended operation?). ->
Catalyst. It might also be a good idea to have some length of tube before the catalyst to minimize flow variations from drips of adblue entering the tube. ->
Air cooled tube, spiralling down to allow condensate to flow ->
Minifridge cooled tube at ~5C, spiralling down through holes in top and bottom of the minifridge->
Condensate/gas separator, this might be really easily made via some sort of wick going from tube into top of absorption chamber.->
Extra tube to ensure ~1 minute or more of gas residence time->
Gas flows into bottom of absorption chamber.
Then the gas flows upwards in a serpentine path through the absorption chamber whilst the condensate flows downwards, before dripping out of the bottom as ~5molar acid (hopefully)...

Couple of useful papers attached, from the Lee et al publication, it looks to me like aqueous phase reactions forming HNO3 are very rapid (seconds), so the rate of acid formation in the absorption chamber is limited by dissolution of the NO2 into the acid solution. Therefore a high surface area is important.
Commercial systems tend to use trays and dripping showers, these result in high uptake of NO2 due to constant droplet/tray surface renewal. In the case of a small scale system, this is probably impractical, but a very thin layer of fluid with high surface area can be created by wicking it into an acid resistant porous polymer fabric. Uptake will then be limited by the aqueous diffusivity of NO2, which is really low, of order 10^-5cm^2/s. The good news is a really thin cloth (<1mm) makes the timescales manageable.
Assuming a serpentine cloth with 10mm air cavity between each layer of fabric, I calculated of order 1L absorption chamber volume per L/day of produced product. This should be manageable!

Attachment: LeeJGR81EvaluationNO2.pdf (1.6MB)
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Attachment: Mn2O3_ammonia_catalyst.pdf (2.4MB)
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MarkRob - 25-4-2020 at 05:40

I'm talking to myself here but...
I was wondering if N2O4 production would be much more useful.
This allows concentrated nitric to be produced and is a useful reagent itself.
The problem is that producing dehydrated NO2 is hard without a large drop in yield. I think it could be done with very rapid cooling following the catalyst chamber (gas stream cooled to ~30C or lower in a few seconds, to prevent significant oxidation and acidification of the condensate).
This should be possible using a ~8m long coil of ~3mm ID stainless steel tube in a ~5C water bath inside a fridge. Problem is the fridge will be taking up all the heat from the condensing water, so its going to be hard to stop it overheating.
The condensate from the tube will be mildly acidic and could be harvested as a dilute acid product.
Due to the rapid cooling, there will be considerable suspended condensate mist, so a non woven filter will be needed to clean that up.
Finally a standard freezer at -15C could be used to clean out the residual water as ice, the inside of the tube will be coated with ice, so it'd be best to remove as much water as liquid before this stage or it will ice up rapidly.
At standard domestic freezer temperatures, partial pressure of water is under 200Pa, so the gas stream will be quite well dehydrated after the freezer stage.
The final stage to get solid N2O4 would use an industrial chest freezer, these are widely available with -45C setpoint temp, which would freeze out almost all of the NO2 as solid N2O4.

MarkRob - 28-4-2020 at 14:00

Some more interesting papers attached
It looks like (from Sadykov) Fe2O3 is a very effective catalyst, with >90% selectivity, but it needs to be formed into ~1mm size "prills" to enable gas flow. Also it's not clear how important the Fe2O3 preparation is, and how much preparation from solution of Fe nitrate or chloride increases the conversion efficiency. There are lots of papers on Fe2O3 nanoparticle preparation from FeCl3, but the particles tend to have very regular sides, and Sadykov seems to be implying that irregular atomic layers at the surface of the particles improves performance, so a spray pyrolysis of FeCl3 solution is best

A method is described here:
https://www.researchgate.net/profile/Burcak_Ebin/publication...

I'm wondering if it could be as simple as FeCl3 solution sprayed into a flame.

Attachment: Structure_and_Morphology_Evolution_of_Fe.pdf (1.7MB)
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Attachment: Oxide_catalysts_for_ammonia_oxidation_in.pdf (1011kB)
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symboom - 21-10-2020 at 14:37

I hope I condensed this info correctly

Calculating ratio of ammonia to air
Slowly draw back 10ml, disconnect the syringe and put a finger over the end quickly, then put the tip into some water. The ammonia dissolves into the water and the water fills the syringe to replace the volume. You now know what ratio of ammonia to air is being fed to the reactor..

Observation
The pulsing glow happens due to the concentrated ammonia solution in the condenser falling back into the flask as drops, the cold concentrated solution emits gas as it hits the hot solution of urea.

means you should need to add air as well. The ammonia air mixture was quite oxygen rich and so the unreacted O2 formed the needed O2 in the sep funnel. diluting the reaction with more air and slowing the next reaction down

Optimization
did the NiO work, it worked well. The reaction zone glowed much hotter and pulsed hotter with the higher flow rates from the air/ ammonia generator. I'd bet that this would self sustain once it has got to this temperature. Will try next run.

I'd say if you get fairly anhydrous NH3 without the CO2 at an optimum air mix, the reaction might just self sustain the heating. Nickle oxide I strongly suspect to be more active than the cobalt, but that's a hunch at this stage.

side note about the air/ammonia ratio: In my experimentation and research I found out that if too much ammonia is present one would only get nitrogen and water because ammonium nitrite would be formed _in situe_. On the other side, if too much oxygen is present, the nitrogen oxides tend to decompose back into oxygen and nitrogen. One should try to maintain a slight oxygen excess for better yield of the nitrogen oxides and put another air inlet after the catalyst tube.

ammonia generator could have a few improvements made, I did a literature search for anything that can catalyze the urea decomposition reaction

For optimal absorption in an amateur setting, 3 column in a row can be used. A strong cooling of the exit gases and the tower is recommended for superior efficiency

maintain a slight oxygen excess for better yield of the nitrogen oxides and put another air inlet after the catalyst tube.
For optimal absorption in an amateur setting, 3 column in a row can be used. A strong cooling of the exit gases and the tower is recommended for superior efficiency

last few runs the catalyst was heated, then the air was started and at the same time the ammonia generator switched on. The rate of ammonia slowly increasing up to about 6% the total volume. The slow introduction of ammonia be critical to how the oxide performs as a catalyst.

The tube - how many other options are there?
I'd say the reaction can be lowered to 500C, which is borosilicate range of working temps, just pack more catalyst into a longer tube to allow for the slower rate of reaction. I have eyed off a piece of tubing used for thermocouples, a pyro-ceramic of some sorts. A suitable alternative would be something like a copper tube with some glass tape wound around it( automotive exhaust shop), make a paint with sodium silicate and some silica flour(inhalation hazard) from a ceramics supply. Then some nichrome wire around that and more insulation over the top.

The dried air/ammonia "burns" hotter than with the water rich vapour I was using. 1- it meant the high temperatures could have caused contaminants in the expanded clay balls to react with the catalyst or fuse with the catalyst, killing it.
2- it makes more concentrated acid without the introduction of water into the stream.

mysteriusbhoice - 20-4-2021 at 00:17

I finally got around to doing this and yes it is Mn2O3-CuO onto sand then packed into the quartz tube then the manganese acetate - copper acetate mix is blasted to infinity and beyond with a torch to bake the mixed metal oxide catalyst in the tube itself which also binds the sand together to form a porous catalyst block.

https://www.youtube.com/watch?v=mnItD3juQyE

BauArf56 - 20-4-2021 at 00:35

Quote: Originally posted by Chemetix

Here is the pilot plant.

It's a photo shoot of the unit in operation.

In a converted TV stand you can see the urea decomposer in the mantle front left. The black lump in the middle is the air compressor. The reactor tube runs into the converted 2L sep. funnel which admits air via the custom condenser fitting. The condensate runs into a reservoir where excess gasses run to an absorption tower.

This shot shows where the ammonia air mixture is fed into the reaction zone, the nice red glow is transmitted up the quartz.

Red fumes; condensation forms on the walls and the condenser. That's nitric, baby! You can see the tower behind it and the take off tap to collect the tower absorption.

The condensate ends up in this collection flask and you can see the splash head type design to let the outlet gasses pass into the tower. There is still a lot of fumes, enough to be visibly red, but once they go to the tower there is no evidence of anything leaving the tower. Kind of important not filling the room with NOx.

Does it fizz with bicarb? You betcha!

This Christmas. Give the gift of nitric!

[Edited on 24-12-2016 by Chemetix]

[Edited on 24-12-2016 by Chemetix]

urea decomposer? Urea should decompose into cyanuric acid, right? Does it give off NOx when heated?

Belowzero - 20-4-2021 at 01:47

It produces NH3 which is then catalysed to produce NOx.

Urea being a relatively cheap bulk source.

mysteriusbhoice - 23-4-2021 at 09:55

New video on this setup.
https://www.youtube.com/watch?v=7OAMSBFL36s
The ammonia is regulated by solution and raising and lifting a straw to regulate the ammonia level with a NaOH trap which also prevents ammonia from being absorbed then the actual reactor with Mn2O3-CuO catalyst on sand.

below is a pic of my new venturi absorber.

symboom - 11-5-2021 at 09:51

Materials
quarts tube
Fish bubbler
Ammonia solution
Copper acetate, manganese acetate
Catalysis bed (sand) maybe activated silica or silica gel works
Sodium hydroxide

Would an aluminum tube work due to nitric acid passivation effect also instead of the quarts tube but the catalysis would have to be unable to attack the aluminum.

As pipes go
Copper would be attacked
And so would stainless steel.

[Edited on 12-5-2021 by symboom]

Chemetix - 11-5-2021 at 19:15

Quote: Originally posted by symboom

Materials
Would an aluminum tube work due to nitric acid passivation effect also instead of the quarts tube but the catalysis would have to be unable to attack the aluminum.

As pipes go
Copper would be attacked
And so would stainless steel.

Are you asking if aluminium can be used for the catalyst chamber? If so then, no, the temperatures that are reached will melt aluminium. Borosilicate will melt which is around the 600-700 degree mark.

mysteriusbhoice - 15-9-2022 at 02:48

I have finally made a NO2 generator thats better than a birkeland eiyde using the ostwald process scaled down.
It uses urea and NaOH ammonia generator controlled by stirring rate and air inlet in the generator stage itself.
https://www.youtube.com/watch?v=b9mjbTU7sFc

mysteriusbhoice - 16-9-2022 at 12:43

I used a nichrome preheater in my lastest version so the catalyst doesnt wink out because getting it to run self sustaining is annoying...
I then also added a 1st ammonia cleanup stage because excess ammonia is mixed with NO2 and this stage contains oxalic acid or citric acid just to pull ammonia out.
ultimately you lose some HNO3 but the 1st stage is a simple bubbler which is shallow since NH3 is super soluble.

The 2nd stage is where the air diffuser which absorbs majority of the nitric and after a 3rd recovery stage then 4th venturi scrubber with alkaline solution to ease presure drop and scrub any remaining gases.

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