Oxidation of Ammoni

I made search and found that cars has Catalytic Converters : https://www.youtube.com/watch?v=DZdHUZTdi68
this part is plated with Pt.
Did anyone think to use this part as a catalyst to produce Nitric acid ?! I have some feeling that it will work.

@Jstufyzand, Birkeland–Eyde process has a yield of 4% and consume much power !

@PHILOU , I found a patent on google that use bacteria to make nitric acid. as far as i remember it take 10 days to get max 4000 mg/L of nitric acid





[Edited on 23-8-2016 by ecos]

Quote: Originally posted by PHILOU Zrealone

Catalytic converters also convert NxOy exhaust gases into inoccuous N2(g) and O2(g).

Quote: Originally posted by PHILOU Zrealone

A catalytic converter would also need a very good deep study of optimum T°, flow and reactant ratio (exept if you can only work with air then it is N2/O2= 4/1)...a good deal of engineering techniques.

Quote: Originally posted by ecos

Quote: Originally posted by PHILOU Zrealone   A catalytic converter would also need a very good deep study of optimum T°, flow and reactant ratio (exept if you can only work with air then it is N2/O2= 4/1)...a good deal of engineering techniques. why you search for optimum values ? if you can get a yield of 40% is still a perfect thing.

Quote: Originally posted by PHILOU Zrealone

It is just the way a catalytic reactor works...too hot it won't work correctly and too cool it won't work at all. Usually the working area of temperature can be as narrow as 50-100°C (sometimes best working into a 5-10°C range). The main problem is that the catalyst may produce heat so you have to cool it down or it may consume heat so you have to heat it up...if wrong temperature and flow control...then the reactor doesn't work long (maybe a minute) ... so even if your yield is 40% for 1 minute it is peanuts! The second "problem" is that the flow of material may furnish heat if preheated or freshness if not preheated and it has to be taken into account. So one working with this kind of reactors needs control loops (retro or feedforward loops) usually from T° probes at the input, into the catalyst, at the exhaust and flow meter.

Quote: Originally posted by ecos

Quote: Originally posted by PHILOU Zrealone   It is just the way a catalytic reactor works...too hot it won't work correctly and too cool it won't work at all. Usually the working area of temperature can be as narrow as 50-100°C (sometimes best working into a 5-10°C range). The main problem is that the catalyst may produce heat so you have to cool it down or it may consume heat so you have to heat it up...if wrong temperature and flow control...then the reactor doesn't work long (maybe a minute) ... so even if your yield is 40% for 1 minute it is peanuts! The second "problem" is that the flow of material may furnish heat if preheated or freshness if not preheated and it has to be taken into account. So one working with this kind of reactors needs control loops (retro or feedforward loops) usually from T° probes at the input, into the catalyst, at the exhaust and flow meter. Oh my god. I thought the temperature is just related to the catalyst material only! do you know how this temperature is defined ? Control loop means you need some sensors and control circuits to make sure everything has the right values ! [Edited on 24-8-2016 by ecos]

Welcome to the real world!

"Do you know how this temperature is defined ?"
Like usual...by trial-error tests and optimisation of yield by slight modifications of the parameters 1 by 1 (simplex method or other methods).

That elusive nitric

I don't know why I would torture myself with giving this a go, but I did, and I'll explain the results of my findings. And it wasn't terrible.

The holy grail, per se, is to find a non PGM catalyst for Ostwald style nitric.

I wish to report that from an un-optimised study there is a catalyst that may fit the requirements of both activity and availability.
Cobalt carbonate on a silica fibre matrix at red heat seems to be a viable catalyst for NO production via NH3 air oxidation.

My initial study sought to control the copper catalysed oxidation of ammonia.
The apparatus:
Urea decomposition flask
50ml heating mantle
Condenser
Quartz reaction tube 10mm dia.
Electrolysis O2 generator
Copper scourer
Aquarium pump
flowmeter (from a gas chromatograph flow units unknown)
A propane/ air burner
Copper Carbonate (pottery grade)
Silica fibre

The experimental setup:
A heating mantle with a 50 ml flask was charged with about half it's volume of urea and 2ml of distilled water.
A quartz reaction tube designed to fit the ammonia generator and consist of an inlet venturi.
An oxygen source, ie. an aquarium air pump and an electrolytic source of O2.




The Technique:
A flask with urea and an amount of water is heated via mantle to provide a stream of ammonia and CO2. A condenser is used to trap water vapour and small amounts of ammonium carbamate. A source of oxygen from either air or pure oxygen was used. A flowmeter with unknown units of delivery was used to control the amount of oxidiser delivered to the reactor.
A quartz tube with a venturi for air (oxygen) was set up on top of the ammonia generator, with a catalyst inserted far enough away from the inlet to allow heating from an air propane torch, without damaging the
coupling to the ammonia generator.


Experiment 1
Copper metal catalyst/ air



The ammonia generator was started by heating the urea/water in the flask. The aquarium pump started and set to a low flow on the meter. Catalyst is a piece of copper scourer and heating is applied to the catalyst region via a propane/air torch. At dull red heat the ammonia being generated should be enough to show an exothermic reaction when in contact with the copper. There was no reaction with the copper using air, at any flow rate.

Experiment 2
Copper metal catalyst/ oxygen
The same arrangement was used except oxygen from the electrolysis cell was used.
At dull red heat the catalyst began to show incandescence at low flow rates of oxygen. There was no ability for the reaction to be maintained without the application of heating.
At a high flow rate on the meter the reation became more pronounced even though it was pulsing regularly, the reaction was now self sustaining. Water vapour was developing furthur down the reactor at a considerable rate.

Experiment 3
Cobalt carbonate /air
The same arrangement was used as experiment 1, except a catalyst of silica fibre soaked in a cobalt carbonate/water mixture then dried, was used. Heating was applied at red heat and maintained, at no flow rate did the reaction show any exothermic reaction. At no point did the reaction become self sustaining.


Results.

In experiments 1&2 the there was no brown NO2 developing from the end of the tube.

In experiment 3 there was no obvious NO2 but a distinct whiff of Nitric and then white fumes.

Conclusions:
The copper catalyst, although very active was too active, there was no evidence of any oxides of nitrogen, the quantity of water suggested there was complete oxidation of the ammonia to nitrogen.
The cobalt carbonate required constant heating, but there was a waft of nitric vapours, until the ammonia generator started generating more ammonia than the air flow can keep up, then white vapours began to appear at the end of the tube. Clearly there was nitric acid being formed in the condensation water at the end of the tube and the excess ammonia began to fume with either ammonium nitrite or nitrate.

Discussion
Copper metal is a proficient catalyst for oxidation of ammonia in oxygen. Although air would probably work as well if the CO2 from the urea decomposition reaction was removed. The reaction runs to completion with nitrogen and water seemingly the only products formed.
Cobalt carbonate shows activity as a catalyst, with evidence of nitric oxide/ nitrogen dioxide being formed. Controlling the rate at which ammonia is formed is (not surprisingly) the limitation of how the reaction tube functions as a method of controlled oxididation of ammonia. A reservoir tank or bladder with a pump, to collect, then deliver a constant ratio of ammonia to air into the reactor could create a viable means of benchtop Ostwald style nitric acid.








[Edited on 9-11-2016 by Chemetix]

Benchtop Nitric

Here is an updated and improved method of production of nitric acid via air oxidation of ammonia. Notably, the process relies on cobalt carbonate on a sand matrix as a catalyst. Unfortunately I'm not able to spend the time on doing an awesome write up, but a quick and dirty explanation with some pics should be enough for now.

The experimental setup:

Urea is charged to a 50ml flask and some water added, this is placed on a heating mantle as a source of NH3. A 1L flask with a 19/26 cone on the bottom is fitted to the 50ml flask. The top of the one liter flask is fitted with a screw fitting,24/29 adapter. This adapter is modified to have a gas outlet on the side. An 8mm piece of borosilicate tubing is inserted through the screw fitting and extends some way into the 1L flask. The NH3 filling the 1L flask is mixed with air from an aquarium pump which enters through the glass tube. The mixed gas leaves from the side spigot on the modified adapter.

A quartz tube 250mm long, 10mm dia. is fitted with an inlet made of 3mm tube at one end, the other remains open but fitted with large screw thread adapter. At a point closer to the inlet tube, the reactor is plugged loosely with glass wool. This is filled with enough catalyst to make a zone 3cm long and then loosely plugged with glass wool. This zone sits roughly half way along the quartz tube.

A kanthal element is made from 0.6mm Kanthal wire wound onto a TIG welding filler rod 1.0mm dia. using a hand drill. The coil is then wound around the catalyst zone and held in place with cellotape. Glass wool is packed between the coils and then the whole element is given a layer of Fibrofrax and then a final layer of woven glass mat over the Firbrofrax. This is held in place with refractory string. The ends of the Kanthal element are joined with a crimp to a thick copper wire and then connected with a terminal block to a variac.


The catalyst is a 1:6 mixture of cobalt carbonate and builders sand.
No preparation other than add a spatulas worth and stir.



The method

The ammonia generator is started on a low setting and the aquarium pump turned on.
Ammonia from the generator is mixed with air in the 1L flask over the urea decomposition reaction. A larger mixing volume is needed to prevent the slightly erratic generation of NH3 caused by concentrated solutions of NH3 returning to the flask. Pulses of NH3 would overwhelm the reaction zone and allow ammonia to pass otherwise.
The catalyst heater is operated to provide red heat to the sand catalyst
About 23V AC and 2.0A was required.

The generator was slowly given more power until red fumed appear in the collection tube, a measuring cylinder was used in this instance. The cylinder was loosely connected to the fitting to allow air to enter the cylinder and unreacted CO2 to escape.


Results:

After running for about 10mins the red fumes had become quite concentrated. A spray of water was delivered into the cylinder and then returned to the outlet of the reactor adapter. The red fumes dissolved in the water and collected on the bottom. The reactor was run for another 10 minutes and then shut down. The picture was taken shortly after turning off all pieces of equipment. The liquid in the cylinder smelled distinctly of nitric and fizzed when a small amount of sodium bicarbonate was added.

Discussion:

I do believe I have achieved benchtop nitric without platinum. I deliberately ran this apparatus without any cleanup of the raw materials and kept the whole procedure as lean as possible with the required technology. Cobalt carbonate might need a constant source of heating and a large surface area to be effective, and as such is not going to compete as an industrial catalyst. But it does seem to be effective at a small pilot plant level, capable of generating molar amounts in a run.

Mods! - Should this post get a sticky in technochem? I think this is going to be of interest to a few of us

[Edited on 12-12-2016 by Chemetix]

Quote: Originally posted by awlb2

copper (II) oxide, when heated, can catalyse reaction between ammonia and oxygen from air to NO and then further oxidation to NO2

Ostwald Process

The oxidation of ammonia by those catalysts is often used as a demonstration:

http://www.rsc.org/Education/EiC/issues/2009May/ExhibitionCh...



This link shows info on using copper catalyst and further oxidation of NO to NO2 by air


Here's an old publication on it also:
http://pubs.acs.org/doi/abs/10.1021/ed011p575?journalCode=jc...

I might actually try the process in the above publication myself!
It sounds like an interesting and easy way to make nitric acid but expensive platinum appears to be the most effective catalyst. I presume this is why the Pakistani Government has not only banned NH₄NO₃ but also urea and other non-oxidising ammonia salts to prevent manufacture of explosives!


[Edited on 12-12-2016 by awlb2]