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Author: Subject: Birkeland-Eyde reactor for making nitric acid.
chemoleo
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[*] posted on 27-10-2008 at 17:48


Well the analytical proof for NO2- (nitrite ions, so you need to neutralise first) is with an H2SO4-acidified solution of FeSO4. Brown solution indicates nitrite.
Otherwise, couldn't you bubble the acid solution just with plain air for a while (with a condenser above), to oxidise all the nitrite to nitrate?




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[*] posted on 27-10-2008 at 20:47


Quote:

Any ideas on why the absorption goes down so much? An industrial setup can achieve 40% acid before diminishing gains.


I would hazard a guess that this is happening because your N2O4 concentration is extremely low. Probably much lower than any commercially used process. The best concentration made (with any efficiency) by an electrical process was less than 2%, and on a very large scale. I bet you've got more like 0.6-0.2%... not surprising it is beginning to not be absorbed effectively, as the HNO3 conc goes up I think the equalibrium of

3HNO2 <-> HNO3 + 2NO + H2O

gets pushed to the left, and the resulting higher conc of HNO2 pushes

N2O3 + H2O <-> 2HNO2

to the left resulting in lower absorption, and when your partial pressure of N2O3 is so extremely low, it apparently doesn't take a very high conc of HNO3 to affect it. Plus when the NO fraction is so low, it takes so long for the NO to oxidize, I bet a fraction of it never even gets to N2O3 and results in an even lower partial pressure.

In my opinion, for this particular set up it would be more effective to simply absorb the gasses in a suspension of CaCO3. This will give you a mixture of Ca(NO3)2 and Ca(NO2)2 (if CaCO3 is excess) at high yield that will be relatively easy to decompose at into a concentrated N2O3 + N2O4 gas that can be easily absorbed, liquefied, etc. Either that or build a better arc system.. That is unless you're happy with 10 or 15% acid.

[Edited on 27-10-2008 by 497]
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[*] posted on 29-10-2008 at 00:10


Quote:

bubble the acid solution just with plain air for a while (with a condenser above), to oxidize all the nitrite to nitrate


I've let the solution sit for a day and the new concentration is 1.48 M = 8.9%, down from the original 1.61 M. I'm not sure about the exact decomposition path for HNO2, but a lower bound for [HNO2] when the reactor is running would be 0.127 M based on this drop.
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[*] posted on 16-6-2009 at 07:45


hi :)
This is a very interesting topic, I'm also planning to build my own reactor to make HNO3.
lately i was using a fly back to make NO2, well it did make a bit, but it take so long.

I'm wondering in a microwave transformer will do the job of making NO2 gas? i can't seem to find a neon sign transformer.
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[*] posted on 16-6-2009 at 08:10


I haven't read all posts but even with an NST the process is very inefficient and this is the reason the B-E process was discontinued in Norway all those years ago. . .
It's also an involved process with lethal voltages which makes HNO3 distillation from KNO3/H2SO4 look like a walk in the park by comparison!
I made a Jacob's Ladder many years ago using two NSTs in parallel; unfortunately I had to use a fridge compressor, the output of which contained oil droplets.
The absorbing solution became acidic over time and developed a yellow colour.
The colour was caused presumably by partly nitrated paraffins. . .
Distillation is easier and produces the strong acid I need!
Welcome to SciMad. . .


[Edited on 16-6-2009 by hissingnoise]
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[*] posted on 16-6-2009 at 17:23


thanks, yes but i can't obtain KNO3 or nitrate salts for such reaction to make nitric acid.
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[*] posted on 17-6-2009 at 03:55


KNO3 is a popular fertiliser---it's a matter of knowing where to look. . .
I got mine online because it works out cheaper than getting it locally.
It's 96% KNO3, so I have to crystallise to get usable purity.
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[*] posted on 23-11-2009 at 20:02


hi im back, ok i just want share what i came up with. a few months ago i was successful in building a birkeland eyde reactor (prototype reactor) here the video link http://www.youtube.com/watch?v=smKX36mvBiQ BTW im building a better and more efficient version. thanks to this forum, helps alot thanks again. :)
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hissingnoise
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[*] posted on 24-11-2009 at 02:04


Nice work kencbk! It's vaguely similar to what I put together all those years ago!
I had the jar upside down (its lid was bakelite) and the electrodes were straight thin aluminium (welding) rods.
The arc had a longer travel and moved more slowly.
Airfeed was such that the amber colour was much darker (higher concentrations of NO2 dissolve and react more readily) and my delivery tube was much thinner than yours.
Also, I used a tall cylinder for absorption and had intended going on to a flint-packed PVC sink-waste tube down which water would have been sprayed for better absorption, but I lost interest around that point.
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[*] posted on 24-11-2009 at 04:07


thanks hissingnoise, well... i have to stick with this method of making nitric acid; i can't buy chemicals here because license is required. btw nice design, more NO2 gas. i appreciate your help. :D
i'll post the new video of the reactor when it works well and i'll try to titrate the solution to find the concentration.
thanks again.
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[*] posted on 24-11-2009 at 04:33


Don't expect great results initially, kencbk. . .
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[*] posted on 24-11-2009 at 11:55


Weighing or measuring the specific gravity of the product may assist in determining the product.
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[*] posted on 29-11-2009 at 05:59


Has anyone thought of using a dessicator (otherwise there would be some vaporous nitric acid, which would eat away at the copper pipe), and using copper tubing, which is submersed in a superchilled ice bath, and out of the pre-cooler, have N2O4 solidify on a small peltier stack? The N2O4 could have a temperature regulated, dilute nitric acid drip on it, so that the N2O4 woudln't vaporize. I have never handled N2O4, but it may be one way of decreasing the time that it takes for the NO2 to disolve in water.

If this worked out good, even with the ice bath, and thermoelectric cooler, less NO2 would be wasted by the somewhat long periods that it takes for NO2 to disolve in water, which may result in a net increase in efficiency.

[Edited on 29-11-2009 by PolarSmokes]
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[*] posted on 29-11-2009 at 06:53


Dessicator? . .Peltier stack?
I don't know what you're talking about, PolarSmokes, and neither, I suspect, do you. . .
It should be obvious that copper tubing should never be used to carry substances that will readily attack it!
And NO2 dissolves in H2O to form HNO3 and HNO2.
Nitrous acid may oxidise by reaction with O, or it may be lost as NO.
If sufficient oxygen is present in the water and absorption-time is lengthy, all the NO may oxidise and react, forming HNO3.
But it's not as cut-and-dried as you seem to think.
Reading up on this subject might be useful. . .
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[*] posted on 29-11-2009 at 07:45


I was under the impression that nitrogen dioxide did not react with copper, but nitric acid did. I know that nitrogen dioxide and water do disproportionate, so there will be some nitric oxide. However, it is a quite likely that nitric oxide would be more soluble in cooler water, versus warmer water, and may allow a larger portion of the nitric oxide to form nitrogen dioxide. However, without a peltier stack (stack of thermo-electric coolers), the nitrogen dioxide would not remain frozen.

My idea would not work with copper tubing if nitrogen dioxide DOES react with copper tubing. I am sure that over time, the copper will form a small, somewhat passivating layer of copper II oxide, however, this should be somewhat stable, as long as the pH remains above seven.

With the dessicator, functioning as a dehumidifier, there will only be very, very little [H+], so the copper should not be attacked by the nitrogen dioxide.

And FYI, I have used, and operated both dessicators, as well as peltier units. However, I have not stacked them, but I know people who have, and have achieved near dry-ice temperatures.


[Edited on 29-11-2009 by PolarSmokes]

[Edited on 29-11-2009 by PolarSmokes]

[Edited on 29-11-2009 by PolarSmokes]
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[*] posted on 29-11-2009 at 13:54


Quote: Originally posted by PolarSmokes  
I know that nitrogen dioxide and water do disproportionate, so there will be some nitric oxide. However, it is a quite likely that nitric oxide would be more soluble in cooler water, versus warmer water, and may allow a larger portion of the nitric oxide to form nitrogen dioxide. However, without a peltier stack (stack of thermo-electric coolers), the nitrogen dioxide would not remain frozen.

My idea would not work with copper tubing if nitrogen dioxide DOES react with copper tubing.
Your thesis is that you can keep enough moisture out so that the lifetime of the copper is reasonable. I find this barely plausible, but with enough engineering effort it could be done. That's because with enough money you could attain the right states of matter, not because it would be easy to do so. So that's one question I've got about this idea, is whether or not it's feasible and/or economical (compared to other mechanisms). So if dissolution of the nitrogen oxides in water is the rate-limiting step, then you can assume that all the water present in the system is a catalyst for the reaction between nitrogen oxides and copper.

On the other hand, you're also making the assumption that the reaction in completely dry atmosphere has a low enough rate. This requires a whole separate kind of justification by experiment, be it yours or someone else's.
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[*] posted on 29-11-2009 at 17:12


I might be confusing people by mixing my ideas up- the copper coil merely acts as a “near” “solidifier”, bringing the temperature within a few degrees of freezing for NO2/N2O4. After the exit, it will come into contact with a freezing unit, where N2O4 will solidify on the surface. After that, a solution of nitric acid (nitric acid to depress the freezing point, so the N2O4 may remain frozen within the HNO3), where it will disproportionate into NO + HNO3. The solution of nitric acid could be diluted after.

Thank you for pointing that out, even the smallest amount of moisture will increase the rate of corrosion, because 4 HNO3 + Cu → Cu(NO3)2 + 2NO2 + 2 H2O, so the rate of nitrate produced would accelerate as it proceeds down the tube. Longer sections of tubing could be used, though, even if they don't have the heat conductivity of copper. It would add up to quite a bit, though, as I had planned to use 100 ft. of copper tubing, which I thought was overkill, but using FEP would work for transferring the heat, just not as well, nor as cheap (as you have pointed out, watson). Other than that, there are really no problems. The Nitrogen Dioxide will still solidify, and the nitric acid will condense.

The main idea of this is to allow the NO2 and H2O to have sufficient time to react. Peltier units don't cost that much to buy, but I will admit that they do take a bit of money to operate, and to properly stack them. Actually, I hardly have enough power to use them all! A good stack would use about 1000 W, and I only have two power supplies good for that. All of the cooling would be about the same as the electric arc input! However, ALL of the NO2 will react with the water. But most of the NO will still be wasted.
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[*] posted on 30-11-2009 at 17:21


I've considered trying to make H2O4 in the winter (thermal decomp of nitrate salt) here, it can be -45C actual temp outside at night, no problem condensing the NO2. Alternative option would be to use the 12kV transformer I got this summer.
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[*] posted on 30-11-2009 at 17:27


Quote: Originally posted by tentacles  
I've considered trying to make H2O4 in the winter (thermal decomp of nitrate salt) here, it can be -45C actual temp outside at night, no problem condensing the NO2. Alternative option would be to use the 12kV transformer I got this summer.


What is it you would do with the N2O4?

Also.. are you saying you are interested in making a reactor?




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[*] posted on 30-11-2009 at 19:57


Because production of NO (which is the main stage) is thermally dependant, a Microwave Oven transformer would be much more likely to produce higher amounts of NO. A trigger would need to be used to ionize the air, so the microwave oven transformer would arc, and it would need to be initiated each cycle of the jacob's ladder.

A microwave oven transformer running unballasted will get hot, and require cooling. If it keeps flipping a breaker, it will need to be ballasted.

It will also be a lot more dangerous- a kilovolt or two, at about an amp. It is very dangerous.
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[*] posted on 30-11-2009 at 20:02


and Kclo4, I'm guessing he would add it to water, to make nitric acid and nitric oxide, with the nitric acid being what he is after. I'm just taking clues from the context of the general idea of this thread! I could be wrong, though!
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[*] posted on 1-12-2009 at 02:03


Forget MOTs!
10kV NSTs are ideal for powering Jacob's Ladders. . .
And they don't run hot!
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[*] posted on 1-12-2009 at 06:02


If you were going to use a microwave oven transformer, you'd be better off using it as part of the microwave it came with, and trying to generate a plasma within the microwave rather than electrical arcs directly.
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[*] posted on 1-12-2009 at 06:20


Do you know of any attempts at modifying a Microwave oven to make a Birkeland-Eyde reactor? This seems like it could be a pretty efficient means of producing given the large area of the plasma.

I have a question perhaps some can answer. When I use to play with HV alot one of the ways to tell the amount of power was to look at the spark. Its lenght gave alot of information of the Voltage present and its color gave info about its current. It was said that if the color was blue then that was from it fixing nitrogen in the air. Now I don't remember what exact numbers these where suppose to denote but wouldn't a blue spark instead of the hot yellow plasma yeild a higher concentration of NOx gas? I do know that I would encase the spark gap of my Tesla coil and only after a few seconds of running the who inside would be coated brown from Nitrogen oxides.

The Plasma can be increased in power by simply making a salt water capacitor from some old wine bottles.





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[*] posted on 1-12-2009 at 10:42


the microwave oven plasma will burn through the glass in no time. I have used both a high current zvs flyback driver, as well as a 15 kv/60 mA transformer. None compare to the amount of Nitrogen Dioxide (estimated by rate of change of color) formation of a microwave oven transformer with it drawing about 3,000-4000 watts. This isn't fair, as the ZVS driver is pulling about 500 watts, and the NST, which is drawing 900 W.

Again, while using the microwave oven transformer, one of the main problems I have is a suitable container. The arc can get to over six inches long (unballasted), and actually longer than that, if you could "uncurl" it.
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