Sciencemadness Discussion Board

Birkeland-Eyde reactor for making nitric acid.

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axehandle - 24-8-2004 at 17:38

Everything could go wrong. It's only a matter of how much you want to take the blame for. :)

New HomeTechnic for Nitric acid

SAM4CH - 30-11-2004 at 08:22

I'd like to make full mechanism for production my nitrci acid, I finished my nitric acid reactor for production NO2 by Electrical arc, it was good yeild of red-brown gas (NO2 and some N2O4), Now I search for small mechanism that let NO2 disslove exactly in water by puting some water in Empty Oxygen Jar and pump the gas by strong Compresser, I think I will get high pressure (around 50 bar) and this will make high dissloving rate for NO2 in water.
I would like to add safty valve which control the pressure but I am afraid of (explosion) So I ask all experienced in this field to advise me.Note: I will use stainless steel Jar.

Marvin - 1-12-2004 at 10:49

High pressure is needlessly dangerous. A series of bubblers will provide reasonable concentration of acid (50-60% from an arc chamber).

For more than this the easiest way is to concentrate the resulting acid. A process more suited to industrial work would first concentrate the NO2 from the output stream.

Long time for bad results!

SAM4CH - 4-12-2004 at 08:33

I bubbled my (air/NO2) mixture for about 36 hours but I did not get a hopeful result (I get in first flask 8-9% nitric acid of 200 mL and in the second 4% of 300mL water) and I run my Jacob's ladder constantly, so are these true results for using a 15KV 200mA NST or there are a problem with my work.:(

Marvin - 5-12-2004 at 05:29

Without a power meter on the input to the transformer its difficult to say. If those are the correct ratings for the transformer and it really was drawing 3 kW then upwards of 5Kg of nitric acid (as a dilute solution) could have been produced.

SAM4CH - 5-12-2004 at 08:28

Okay.. Really I am not sure about my NST but when I bought it the seller told me that, as you say the NST Ampere output is important as its voltage then its power increases producing NO2 gas (Is it right?).

What about the best transformer for producing NO2 and its power (V, A output KW), is it NST, OBITs or potential tranformer, please see http://www.kronjaeger.com/hv/index.html

Finally Can I get 1 Liter or more of (55-60%) HNO3 daily using some of high power transformer?

Marvin - 6-12-2004 at 06:10

The transformer you have is ideal, but if you arnt getting in the region of 50g nitric acid per kilowatt hour there is either something wrong with your power measuring system or something wrong with your spark gap.

Have you thought about the possibility of turning everything else off in the house and using your consumer box meter(Where power from the grid enters your house) to measure the power? I've not used it for this purpose but I was surprised how rapidly and accurately they repond to a 60W lightbulb being turned on and off. (This was a spinning disk mechanical one, yours may differ).

Is this effective?

SAM4CH - 21-1-2005 at 16:31

Is this effective design for producing HNO3 by using Brickland method?
I want to test it in my small laboratory!
Please advise me before!:(

New desgin.bmp - 645kB

Marvin - 22-1-2005 at 08:07

It is unclear if the first jacabs ladder is pressurised, if it is this is far from ideal, as would also be pressurising the nitrous gasses. The second ladder is being fed from the waste of the first one, this would be better fed with fresh air, ie cascading is not useful.

IrC - 13-3-2005 at 02:55

"The transformer you have is ideal"

I don't agree, it is far from ideal. There seems to be a misconception here about NST's and their short circuit protection. Or rather, about the duration of it. What you should use here is the oil ignition transformer from an oil furnace. An NST is not designed for the heat buildup of a steady short circuit for long periods of time. An arc has a very low impedance, probably drawing more than the 60 mA rating. I would remove the potting from the transformer and put it in a container full of Shell Diala-X, with radiating fins on it. Actually, this would be a good idea even if using an OFT (oil furnace transformer). You could also pump the oil through a transmission cooler with a fan cooling it, very good idea.

I once built a Tesla Coil with Extra Coil that stood 18 feet tall, powered with two 10 KVA pole pigs (pole transformers), and they were very happy with my transmission cooler(s), (even if my mains supply was not). I don't know if you have ever watched one of those PBS or Nova shows with Robert Golka and his coil at Wendover (so that you would know who he is), but I have a picture of him in my front yard playing with the coil I built, I got many good ideas back in the 80's from him about running transformers to the extreme, and the forced air cooling for the oil was one of the better ones we played with. While you may not need these extremes, at the very least oil would be better than the potting and an OFT would be the right choice instead of an NST for a continous arc over long timeframes.

I also am not so sure recycling the air is a bad idea, there is little chance that the arc is converting all of the air in the stream, and at the end of the chain the air has to go somewhere (hopefully outside). It would seem to me that the more efficient the conversion was the less air contaminated with NOx you would be dumping outside in your neighborhood, considering the fact that less air would be running through the system for a given amount of acid produced. The downside would be greater erosion of your electrodes, a problem I faced often with a 14,400 volt arc at 1.5 amps. Not even my tungsten carbide electrodes with cooling fins stood up to that very well.

I agree with a previous post that more bubbler cells would not only raise efficiency it would also make for less NOx in the enviornment at the output end of the airflow.

Have you ever thought about getting hold of some bricks that are used in kilnbuilding (firebrick)? It is very easy to drill or saw if you are careful, it seems you have problems finding things that would hold electrodes and take great heat for long periods, while providing little leakage for the high voltage. The only drawback I see is you would have to pay attention to any cracks that may occur, so as to eliminate possible leaks of O3 or NOx into your home. Just some ideas I had while reading this thread.

All I can say axehandle is that no matter what else goes on, I am far more impressed with a hands on Mad Scientist than a theoretical one. So keep up the good work, best if done in the safest possible way. I never do anything without a long period of research on not only what I am doing but also as much if not more on what can go wrong, and what every possible hazard may be involved in the process.

Marvin - 13-3-2005 at 18:56

The transformer is ideal. A neon sign is an arc, the pressure is lower than air which allows it to go a lot furthur on a given voltage/power but its essentially just an arc.

An NST is a magnetically limited system, which makes for a more reliable unit under experimentation and they are designed to run continuously.

The air arc should not drop a low voltage, and the NST should not exceed its normal ratings or very little of the power put in goes to nitric acid at the end. Repotting, often done anyway by shorting the secondary winding and letting it cook for a day should not be required.

The design of the arc chamber is as important as the electronics for good yeilds both for EE and chemical reasons.

Given a history of tesla coil building I understand why you would make those assumptions about the arc itself but its wrong and colouring your whole interpretation of the arc process.

The output gas post scrubbing is depleted in oxygen, though not by much, which is slightly bad, and it is wet, which is very bad. The ideal amount of oxygen is 50% and were oxygen added recyling this gas and drying would be worthwhile, but cascading would still not be the best way.

IrC - 13-3-2005 at 23:55

"Given a history of tesla coil building I understand why you would make those assumptions about the arc itself but its wrong and colouring your whole interpretation of the arc process."

You are assuming you know how much knowledge I have. In your defense I should have worded it better and said "make it want to draw more than 60 Ma" rather than sounding like it was going to do so. This does not change the fact that I am not in error about any processes going on in the arc as may have been gleaned from my post.

I can tell you this, a man with experience is never at the mercy of a man with an argument.

I took my first NST apart and repotted it with oil in 1965 and built my first Jacobs Ladder. In the last 40 years I have worked on many of them, I think I know quite well how the current is limited and this has nothing to do with my statement that the OFT is a better choice. This is based upon the NST's I have smoked in various and sundry mad scientist experiments in the last 4 decades.

Put quite simply the OFT is designed to withstand the transients from power arcing better than the NST, not surprising since industry does not put NST's in oil furnaces, they use OFT's and so should you. Myself I don't use either any longer, I have several pole pigs from 5 to 25 KVA to play with and a variable core Lincoln Arc Welder to use as a current limiter. I was just trying to teach axehandle from my years of experience a better way, seeing as how he wants to maintain arcs for periods of a day or longer while saving on his pocketbook.

To depot an NST you short it for 30 minutes not 20 hours, and even this has no bearing since it is the transients which the OFT is designed to withstand better than the NST, and these transients are worse for a power arc in air than they are in a rarified gas tube.

"An NST is a magnetically limited system"

So is the OFT.

"The air arc should not drop a low voltage"

The impedance of an arc in air can be as low as 50 milliohms to 2 ohms. This is how in a 2KW Tesla coil with a spark gap between the capacitor and primary there are still circulating currents in the hundred amp range, in the thousands of amps in the coils I have built. These hundreds or thousands of amps are flowing through the arc in the gap, and if the impedance was not extremely low such currents would not be possible. I can tell you this from direct hands on experience. This was in reference to your impedance statement.

In any case his transformer is not going to let over 60 Ma flow, but this does not reduce the possibility of arcs between turns, which would be the death of his expensive investment.

A transformer designed to handle a power arc is going to stand up longer to it than one not designed for such service, before shorts occur in the secondary turns, and I was just giving advise for the next time he buys one to look into OFT's, seeing as how he already has an NST now. Also, 100 or 120 Ma might make his conversion more efficient than 60, if he ever decides on finding another transformer. It does not take many volts to tear apart molecules, so even in the low voltage across the arc conversion occurs, and on a larger scale if there is more power in the arc to create greater heat. Higher currents are going to give greater conversion, all other things being equal, assuming a high enough voltage to create the arc in the first place. This is no mystery since current is merely a measure of the number of current carrying entities, whether electrons or ions.

"Repotting, often done anyway by shorting the secondary winding and letting it cook for a day should not be required."

Using oil would allow his transformer to self heal for minor arcs between turns, whereas one arc between turns in the secondary now will destroy his investment.

In any case the point is moot as so far his transformer is still alive and repotting is quite a job, but it may provide some good ideas for his next project for what it's worth.

It would also seem that adding O2 by powering an electrolysis cell would increase production, the hydrogen also produced could be burned separately or safely vented outside.

I need more effective method!

SAM4CH - 16-3-2005 at 01:18

I work with two transformer (12KV, 30mA) and I put two Jacob's ladder in a reactor then I allow air to enter and exit from a small open and put some of Al2O3 as a catalyst for converting NO to NO2 and it was do well, but I did not get a good amount of NO2 or not enough to reach 1% in exit air, I try to bubble it through water (I used two oxygen weter bottle) I reach a density of 1.02 in 24 hours?!! I belive I did not get a good yelid of HNO3 as it knows (1KW gives 50-62 pure HNO3 per hour), please advise me I really want to make 50-60% HNO3 and my dream is making 1Kilogram of HNO3 per day.
Now I think my main problem is not in absorption but in yeild of producing NO gas from Jacob's ladder.
please what do you say in this ARCs
http://www.kronjaeger.com/hv-old/hv/do/sparks/index.html

IrC - 16-3-2005 at 22:40

axehandle, I have been looking into patents on the subject, and two things which are going on in your setup serve to reduce the final product, by breaking up the NOx products just formed in the arc. The gasses must be cooled right after the arc and protected from the UV radiation coming from the arc. It would seem to me that one way to do this would be to have a quartz tube which the air passes through a small chamber which has a steady arc perpendicular to the flow, where the air passes rapidly out of the arc. In one design the air is cycled back and forth. Following are a list of the patent numbers I have found so far on the subject.

U.S. Patent Documents
----------------------------------
1388112
1547714
2898277
2992980
3049488
3117068
3421988
3453196
3832513
3983021
4039412
4125754
4267027
4324971
4451436
4833293

Just a thought.

neutrino - 17-3-2005 at 03:26

Why quartz? It is transparent to UV, so wouldn’t this be the opposite of what you’re trying to do?

Marvin - 17-3-2005 at 10:13

IrC,

"The impedance of an arc in air can be as low as 50 milliohms to 2 ohms. This is how in a 2KW Tesla coil with a spark gap between the capacitor and primary there are still circulating currents in the hundred amp range, in the thousands of amps in the coils I have built"

This is exactly my point. The design of tesla coils involves a set of design assumptions and rules of thumb that within this application work very well, matched impedences, resonant energy transfer, quarter wave radio engineering and so on. One of these is that the spark gap is used like a thyratron and has a very low dynamic impedence in the 'on' state, neerly a direct short. Transients caused by sparks degrade dielectrics and the faster the gap, eg rotary or forced air, the more this is the case. The obvious conclusion is that our nitric acid plant resembles a forced air quenched spark gap in a tesla coil.

For something as simple as two wire ends seperated by air this is about as far from the truth as its possible to get and still be EE. For a decently designed 'home' sized arc chamber the dynamic impedence can be (depending on many variables) in the 10's or even 100's of kOhm range. Yes, kOhm. This is not a direct short by any stretch of the imagination and ensures the majority of the energy drawn by the transformer is dumped into the air not into its windings. Tha arc is not sparking in any decent design, so transients are not a problem.

Now we have corrected the assumptions lets look at NST's versus OBITs as general classes of transformer.

NSTs, reasonable short circuit protection. 100% duty cycle.

OBITs, designed for sparking/arcing so better insulation. Higher current but designed for low duty cycle (amounts to poorer current limiting essentially), intended for ignition only.

Aside from the duty cycle advantage there is another consideration. A typical NST jolt is considerably less likley to kill someone than a typical OBIT, and since the majority of people building nitric acid arc systems are teenagers frustrated about being unable to buy nitric acid I consider this relavent to what constitutes an 'ideal' transformer for the job.

"Also, 100 or 120 Ma might make his conversion more efficient than 60, if he ever decides on finding another transformer. "

I can see why you would think that, but its wrong.

"It does not take many volts to tear apart molecules, so even in the low voltage across the arc conversion occurs,"

I can't see why you would think this, its garbage. For this specific case the production of NO is by thermal equilibrium.and Ive explained it in nausiating detail before, possibly not here. The rest of that paragraph isnt even worth quoting, its just wrong.

Adding oxygen is useful, but unless the full recyling system is setup most will be wasted for only a small increase in yeild.

You are correct about the length of time an NST needs to be shorted to depot, but it serves my point, it can be shorted for long enough for mishaps, arc ignition etc.


SAM4CH,

Try a better arc design, this has been discussed, read the whole thread. Is the volume of water the same as before? How rapid is the air flow? How strongly coloured is the gas exiting the arc chamber?

Why are you using a 'catalyst'? I'm unconvinced this is helping.

[Edited on 17-3-2005 by Marvin]

12AX7 - 17-3-2005 at 10:34

Would a corona discharge work better? It can cover a much greater volume than an arc.

BTW, low voltage high current arcs (say between carbon rods) also work nicely.

For arcs, voltage is length, current is thickness, voltage times current is power.

Tim

Twospoons - 17-3-2005 at 21:51

Since an arc has a negative resistance characteristic (i.e. resistance drops as current increases) Marvin and Irc are both correct in their respective contexts.

This PDF on Spark ignition is interesting

Marvin - 18-3-2005 at 00:22

Twospoons, not wishing to sound like I have a planitary sized ego, but I have been correct in both contexts of the arc from the start :P

12AX7,

Corona discharge is electrically active but not 'hot' so it produces ozone and nitric pentoxide in rather poor yeilds. As Ive said, production of nitric oxide is thermally driven.

"BTW, low voltage high current arcs (say between carbon rods) also work nicely. "

Nicely for what....

My understanding is that low voltage high current arcs deposit most of the energy in the electrodes, hense the use in welding. All of the highest yeilding benchtop processes for NO are high voltage low current for a whole bunch of reasons. Power is the ultimate limit of course.

"For arcs, voltage is length, current is thickness, voltage times current is power"

Voltage determines the spark breakdown distance but a combination of voltage and current and airflow determine the maximum length it can be pulled. Assuming the current is a measure of thickness is almost completely wrong. If you pass a very low current through a discharge tube the glow fills the tube. This is normal because the electrons/ions are accelerated by the field and scatter off the gas in the chamber randomly. As the current is increased the discharge starts to collapse to a single arc between the electrodes. This is due to a second force. When currents are sent through parrallel conductors they each produce a field, which overlaps. The overlap produces a force and if the current is in the oppasit direction the force is repulsive and if the same is attractive. Exactly the same is true of the current by the electrons and ions. They each have their own field and it attacts eachother, so the magnetic field the current produces has the tendency to make the discharge collapse into a tight straight arc.

More help!

SAM4CH - 18-3-2005 at 04:01

I tried to improve my arc but no chance to get more effective system, I used two arc with two NST and my first bottle contains 300mL water (100mL more than before) and I used a reactor which has a volume of (15000 cm3) and my air flow was around 20-30 bubbles per second, I noticed a slightly white gas flow through my silicon hose (I could see it clearly) and after I add few grams of Al2O3 I noticed a slightly red/brown gas flow through my hose.
Finally I got around 300mL of 10% HNO3 (1.05 g/cm3) within 24 hours (very very bad yield)
I want to ask about heating my entrance air to increase the efficiency of my system?!
Please help me to get 1 kg HNO3 per a day!

[Edited on 18-3-2005 by SAM4CH]

12AX7 - 18-3-2005 at 07:50

Quote:
Originally posted by Marvin
"BTW, low voltage high current arcs (say between carbon rods) also work nicely. "

Nicely for what....


Well, heating things and making fat arcs, at least.

Quote:
My understanding is that low voltage high current arcs deposit most of the energy in the electrodes, hense the use in welding.


Ah, true. HV arcs do go much longer, heating just air instead...

Quote:
Assuming the current is a measure of thickness is almost completely wrong.


To a very gross approximation, it is.

BTW, what is it with this forum and people going off on long paragraphs just to say someone is wrong? A quick "fuck no" is much more succinct.

Tim

IrC - 29-3-2005 at 00:07

Marvin the only thing you are proving here is that you are arrogant and full of yourself. To state someone is wrong without stating where and why is as useless as your ego, not to mention the fact that if you carefully read all 5 pages of this thread it is clear you contradict youself more than once. If long thin very high voltage arcs from toy transformers worked then everyone would be making acid instead of ending up in failure. The 2 million volts out of my Tesla coil produces lots of ozone and little NOx. But in the rotary gap with closely spaced electrodes, much lower voltages, and very high currents, the smell of NOx is overwhelming, and the interior of the box and components inside are constantly being attacked and corroded away. Rather than trying to impress people with your lack of people skills why don't you actually do something useful and tell how us all with carefully detailed plans how it should be built. Better yet, build a working one yourself rather than verbally abuse others who do while you merely talk about it.

The very purpose of a forum like this should be for others to give their ideas and best advise, without worrying about whether or not someone like you is going to tear into them seeing as how they are not as cool as you perceive yourself to be. If you were as smart as you want the world to believe you are you would be capable of making intelligent posts without the use of foul language and verbal abuse such as the remarks you made on previous pages of this thread. This I state not from your comments to me but to others in many threads as well. Seeing as how you are not paying them for their time and input I would assume they have a right to try and help with ideas without being abused by persons such as yourself, just because they do not meet your criteria. In short if you had people skills instead of the personality of a rope you would be able to artfully and cheerfully guide and help others in their efforts to learn and grow in the sciences. I had hoped this was a forum where ideas and scientific insights could be exchanged freely without the childish pissing contest antics of a reject from junior high school.

12AX7 - 29-3-2005 at 01:45

Quote:
Originally posted by IrCIn short if you had people skills instead of the personality of a rope you would be able to artfully and cheerfully guide and help others in their efforts to learn and grow in the sciences. I had hoped this was a forum where ideas and scientific insights could be exchanged freely without the childish pissing contest antics of a reject from junior high school.


:thumbsup:

Back to your regularly scheduled topic

fizzy - 29-3-2005 at 03:56

I found the following at a forum dedicated to discussing the book 1632 (SciFi: a small town in W. Virginia is sent back in time to a spot in Germany in the middle of the 30 years war) at Baen's Bar.

The process is from Nitrogen In Industry by Marshall Sittig.
In the Birkeland-Eyde process air was passed through a flaming electric
ark at about 3500 deg Whereupon a small percentage of the nitrogen in
the air was burned to nitric oxide (NO).The arc was distorted by a
magnetic field until it broke, a new ark formed and this cyclic process
was repeated at .02 sec intervals. Water cooled copper electrodes were used
to carry the 50 cycle current at 500 volts. The arc furnace was a narrow iron
chamber insulated with fire bricks. The gases leaving the furnace at 1000 deg
Contained about 1% nitric oxide. The product gases were cooled rapidly to quench
and retain the NO.It was then passed through the reaction chamber lined with
acid proof brick where the reaction NO+1/2O2 yields NO2 is completed at about
50 deg C. The NO2 was dissolved in water to give nitric acid. The yield was
62.5 grams of pure HNO3 per kilowatt hour.

So the people who actually had to make money at this used 500 V arcs.

[edit] By the way the first two books in the 1632 series (1632 and 1633) are available as FREE electronic books at the Baen website.

http://www.baen.com/library/

[Edited on 29-3-2005 by fizzy]

Twospoons - 29-3-2005 at 15:07

It occured to me that an HID lamp ballast and ignitor circuit might be the way to go. The ignitor provides the 5kV pulse (or so) to strike the arc, then the ballast maintains the arc current. Ballasts are available for a few watts up to multi-kilowatts.

Marvin - 5-4-2005 at 03:55

IrC,

"Marvin the only thing you are proving here is that you are arrogant and full of yourself. "

I think after 2 and a half years on this forum thats gone one way or another already.

"To state someone is wrong without stating where and why is as useless as your ego, not to mention the fact that if you carefully read all 5 pages of this thread it is clear you contradict youself more than once."

If someone states that nuclear power plants are elephants on treadmills is it really worth explaining the whole concept of nuclear power from scratch, and then using average dietary requirements to fix an upper limit for the work a single elephant can do, or is it more time effective and just as useful to just point out someone doesnt know what they are talking about?

When I contradict myself, feel free to point it out. Genuine changes I like to call 'learning'.

"If long thin very high voltage arcs from toy transformers worked then everyone would be making acid instead of ending up in failure."

Do you blame the pen for a bad test score? High voltage, low current can do very well for a given power.

"The 2 million volts out of my Tesla coil produces lots of ozone and little NOx. But in the rotary gap with closely spaced electrodes, much lower voltages, and very high currents, the smell of NOx is overwhelming"

The output of the tesla coil is high frequency large volume. A lot of ions, little heated air. As I said, its a thermal process. The spark gap is a very dense discharge and thus the primary producer of nitrogen oxides, its far from ideal for a number of reasons. Its too hot for a start and this is wasted energy. Mainly, if it used most of the power in the primary tank circuit it wouldnt be a very good tesla coil, its a switch, its not a load.

"why don't you actually do something useful and tell how us all with carefully detailed plans how it should be built. "

Detailed plans are pointless, everyone has different requirements and equipment. Knowing how something works is more important than any single example.

"Better yet, build a working one yourself rather than verbally abuse others who do while you merely talk about it."

Thats a great idea. I should go away and build another one, furthur to my work slightly over a decade ago and which matched the trends in the theory while you continue making overly defended wild guesses in a subject you know nothing about based on an unrelated area of electronics. But wait! Heres an even better idea. How about I stick around and try to do my part toward a better S/N ratio.

"The very purpose of a forum like this should be for others to give their ideas and best advise"

I'm sure it would all be very friendly if all points of view were valid, but then it wouldnt really be a science would it? In chemistry there are good methods, safe methods, right answers and dire consequences. For me a chemistry forum should be as accurate and safe as possible.

"without worrying about whether or not someone like you is going to tear into them"

If something is outright wrong, it needs correcting. If its defended forcefully it needs tearing apart forcefully.

"rather than verbally abuse others"
"useless as your ego...personality of a rope...childish pissing contest antics of a reject from junior high school..."

The only person currently throwing insults is you.

fizzy,

There is a zero missing, its 5000V.


SC Wack has scanned one of the better books covering this subject, its Mellor Volume 8, his link is in the books thread. The arc fixation of air section is essential reading.

Great Transformer!?

SAM4CH - 24-4-2005 at 15:25

I got a great high voltage transformer its output = 17KV,1A, it is italian trans., but its output is DC not AC I want to run it to produce HNO3 by (ARC furnace) but I need advice before running it like safty, design of reactor, arc .. etc.
Note: I am sure about it and its price is 6000$
Thanks

Marvin - 25-4-2005 at 13:15

You need more than just advice, you need a miricle.

It sounds like a bad power source. Transformers by themself cannot be DC, so you have additional electronics somewhere which will almost certainly hate what you have planned. Find out more about the device if you've allready got one, you will need to tap the AC output of the transformer stage directly, and disconnect the rest.

For the high current of 1 amp the voltage maybe a little high. I would expect to be able to climb into the arc chamber and you'll still have problems raising the impedence. I would also suggest spending an additional kilowatt or so running an electromagnet from mains in order to move to a magnetic field design. This will need water cooling even if nothing else does.

Read the sections on this process in Mellor 8. Right now Mellor is the best friend you have.

Above all I suggest going back to the low power transformer and chamber and not moving on until it works properly. If you cant make a decent design at a few hundred watts I think you'll crash and burn at 17KW. Even simple things become complicated, electrodes will probably need liquid cooling (spot any potential problems with water cooling both electrodes?) and you'll need to do a lot better than just bubbling the output gas through water, you'll need seperate stages for cooling and extraction.

SAM4CH - 8-5-2005 at 04:25

Marvin, how can I find Mellor8, I tried with rapidshare but no way.
"A Comprehensive Treatise on Inorganic and Theoretical Chemistry" its price is 240*2$!!
Can you help me in this please?!
I need only the section which talk about nitric acid and birkeland eyde process.

[Edited on 8-5-2005 by SAM4CH]

[Edited on 8-5-2005 by SAM4CH]

Duster - 16-5-2005 at 08:51

Sorry to jump in like this but I would like to share what I plan to make here shortly... Hopefully within the next couple of weeks (soon as I get home).

Just the other day I bought a 15kv NST from ebay No guarentee but for the price, as long as it works to prove itself thats fine with me. I can always buy another, better one...

For the reaction chamber itself, this is where I think I get a bit... Abitious...

I remember back home there was a rather large (we're talking 36" high, and at least a 20" diameter) crock pot or something. No holes in it, and at least an inch thick of clay.. I belive the outside was glazed but not the inside. In any case, I had an idea (of course). I could probably find a couple of these around where I live (I already called my brother and recruited him to find some), and I figure a nice big reaction vessel that like wouldnt have to worry about cooling as much as a smaller one. Also, the jacobs ladder could be about 48" tall (slightly protruding from the top of the bottom pot).

I have a couple fans at home... One of which is damn near a mega blower, but I also have a couple of smaller ones laying around. Im wondering how much airflow would be needed. I figure trial and error will decide...

Im also seeing at least 3 absorber tanks (aka glass jars).

Dont get me wrong, this could be FAR from ideal, but going by what I have seen in this thread (heat being an issue, absorbing being an issue, air pressure, etc etc) I would be led to belive that a large reaction chamber with multiple absorber tanks would be an ideal setup coupled with at least a moderate (but not violent) air inlet...

As for wanting to do this... Well for one its cheap (the NST cost me <$50), its simple, I just bought a glass distilling setup specfically for nitric acid, and if I could make large enough amounts of HNO3, I could produce H2SO4 (I think).

Well, thats it for my post... For now... If this thread isnt completly dead when I actually put all this together, I'll post a few pics... Im working on my own website (its comming along nicely so far) so I will probably have the pictures hosted there.

Lastly, if this setup does work, at least somewhat well... I figure I could buy a second NST and have them alternating 10 on 10 off (minutes that is) so they dont burn out... If I cant safely have them do this on the same jacobs ladder, I could also have a second reactor vessel but have it pump its output into the same absorber jars.

Hope 8 days doesnt count as bringing up a dead topic...

jpsmith123 - 29-6-2005 at 18:17

Although I'm not planning on trying to make any HNO3 in the near future, it is something I looked into once.

I found a few patents on the subject, most of which involved portable NO generation for medical use, and a few involved local fertilizer production for farms.

Most of the patents made use of an electric arc to produce the NO, but patent #5,692,495 was interesting because it employed a noble metal catalyst (e.g., platinum) at a temperature between 300 and 1200 degrees C, and "preferably" between 500 and 1200 degrees C.

Another method that might work and might be less troublesome than an electric arc is a dielectric barrier discharge.

12AX7 - 29-6-2005 at 18:44

Quote:
Originally posted by jpsmith123
Another method that might work and might be less troublesome than an electric arc is a dielectric barrier discharge.


Is that like pointing a Tesla coil at a piece of plate glass and drawing arcs off the opposite side? That just makes O3, IIRC.

Tim

jpsmith123 - 29-6-2005 at 20:31

It's similar in the sense that you've got a high AC voltage and an insulator...I guess that would be an example of a DBD, albeit not a technologically useful one.

Here's a paper that describes it:

http://sunsite.wits.ac.za/iupac/publications/pac/1999/71_10_...

I would guess that the major design issue to produce NO is to make sure that the average electron energy in the discharge is around 10 ev, i.e., enough to break the N2 molecule apart.


Quote:
Originally posted by 12AX7
Quote:
Originally posted by jpsmith123
Another method that might work and might be less troublesome than an electric arc is a dielectric barrier discharge.


Is that like pointing a Tesla coil at a piece of plate glass and drawing arcs off the opposite side? That just makes O3, IIRC.

Tim

Marvin - 29-6-2005 at 20:49

I hate to sound like a broken record but this idea comes up regulally and the answer is the same. NO is produced thermally. Silient electric discharges are useful becuase they produced broken molecules without the high temperatures that normally decomposes down to the most stable products. By the same point, any lower temperature process involving air cannot possible produce a higher concentration of NOx gasses than an arc furnace no matter what the catalyst. Even at 1200C the concenctration of NO will be small, getting strong nitric acid from the few percent of a 3000C arc is hard enough.

jpsmith123 - 29-6-2005 at 23:21

Hello Marvin,

I'm not sure I understand exactly what you're saying. Are you saying that it's impossible to produce any NO in a dielectric barrier discharge, or are you saying that it is possible to do so, but only at reduced efficiency, compared to an arc discharge (i.e., lower NO output per unit of input energy)?

I also cited a patent involving a method to produce NO using a catalyst at a temperature between 500 and 1200 degrees C. With regard to this, are you saying the catalyst won't help at all or that it will not be as energy efficient as an electric arc? Please elaborate.


Quote:
Originally posted by Marvin
I hate to sound like a broken record but this idea comes up regulally and the answer is the same. NO is produced thermally. Silient electric discharges are useful becuase they produced broken molecules without the high temperatures that normally decomposes down to the most stable products. By the same point, any lower temperature process involving air cannot possible produce a higher concentration of NOx gasses than an arc furnace no matter what the catalyst. Even at 1200C the concenctration of NO will be small, getting strong nitric acid from the few percent of a 3000C arc is hard enough.

Archimede - 3-7-2005 at 11:10

I just throw in the garbage a 10KV external transformer for neon signs thinking... there is no way I can find a way to use it at home... well, now I read this threat.

BTW guys... in this forum we have a chance to get insights from people with degrees and decades on the fields. Try to get criticism in a positive way instead of being defensive.

Commercial Plasma Cutting Torch As Birkeland-Eide Reactor?

jpsmith123 - 14-8-2005 at 12:33

I wonder if a plasma cutting torch (like the following one for sale on ebay) would produce lots of nitric oxide, and if not, why?

http://cgi.ebay.com/PLASMA-CUTTER-Cutting-torch-220v-Air-hoo...

uber luminal - 28-8-2005 at 06:49

the plasma cutter would be a far push.
In order for the device to work... you need to have an anode and cathode. (complete the path to the ground)

So you would place it near some conductive surface, initiate the plasma... and... ohhh the conductive surface is gone, spattered into millions of tiny particles. If you dry arc, you pit down your electrode really really fast and those are about $15/ a pop.

No, a commerical plasma cutter would not be of any use for making nitric acid. unless... maybe you did some modifications and used compressed N2 and O2 already mixed correctly.

You could just as well, spend a lot less to build something that uses compressed gasses fed through an arc.

jpsmith123 - 28-8-2005 at 07:49

Hello Uber luminal,

I realize that a plasma torch may not be a cheap way to go, but I don't see why it wouldn't work. The advantage would be high power, and almost ready to go out of the box; i.e., power supply, igniter, one electrode and gas input channel already set up.

If, in the ebay description, the "cutting gas" was air (the Birkeland-Eyde process uses air, no?), and the anode material and geometry were suitably chosen (say, a piece of graphite tubing), why wouldn't it be expected to make nitric oxide?

Regards,
Joe

Duster - 28-8-2005 at 15:03

I would say it would be because a plasma cutter... Well... Does just that, cut. I do belive his point is that any electrodes wouldnt last long enough to be of any value. I have no doubt it would work, but only to an extent. And only for a brief period.

I would see an ARC welder to be a better choice, just convert it so it runs on DC...

But even then, a NST seems just fine...

neutrino - 28-8-2005 at 17:56

AC/DC doesn't matter. You just have to get to a high enough temperature.

Duster - 28-8-2005 at 18:43

Ah true, got me there. I was thinking of something else...

uber luminal - 29-8-2005 at 10:54

with a plasma cutter, you need 3 things.

heres the thing with the plasma cutter...

You need about 90 psi at 5+ CFM. Constantly while in operation, plus the post flow cooling operation. So, you do some math, and figure out that you will need a pretty big tank, with a pretty big compressor to run for a period of time.

a typical plasma cutter needs a 30 or 40 gallon compressed air tank with a 6 CFM @ 90 psi compressor. This runs about $500-600. and takes up a large amount of space.

IF you go with the cylinders route, I have eaten a full tank of 255 Ft^3 N2 gas in about an hours worth of work. that was however at 70 psi, so you could go as low as say.. 55 psi. so Just calculate again, but either way, the tank wont last very long.

The biggest problem... Your powersupply and electrodes, which are made from copper cooled by compressed air. (duh). However you power supply is prone to overheating. a lot. You would need to buy a large power supply with a high duty cycle.(even for the lowest possible setting).

One of the plasma cutters I have, (Powermax 1000, costs about $2000 USD), could run, on the lowest settings, for about 4 min, constantly. Thats a long time. After 4 min, the controller unit says... no, thats enough, and stops the current to let everything cool down.

another plasma cutter I have, (no name, cheap POS, about $500) has a really crappy duty cylce even at the lowest settings. very annoying, while cutting 1/16 steel, it decides about 1 min is enough and stops to cool.

like I said, $500 spent on a cheap TIG welder, and build a compression chamber would be money better spent (plus you could use the TIG welder, to build the thing :)

AGAIN, you would need to create a small plasma cloud onto a conductive surface, which would go away, leaving your cloud elongated, and the machine would either stop the current, OR you would pit the crap out of the electrode inside the torch. Dryarc is not good for your torch. Those little electrodes are annoyingly expensive.

fuse123 - 27-10-2006 at 01:46

Oh MARVIN are you playing with us ?:(
please tell us how to make it (easy),
you know, we are amateurs
Thanks MARVIN :D

497 - 25-10-2007 at 22:13

so has anyone made any progress? sorry for disturbing the dead (thread)

497 - 25-10-2007 at 22:53

i had the idea (probably not new) of using a stationary arc and passing a stream of air through it at a relatively hight speed, ie. from a large hypodermic needle pointed at the arc. i realize the problem is the electrodes. i have access to TIG welding electrodes of all kinds (thoriated tungsten etc.) i was wondering if anyone has tried this or knows how well they hold up in air for extended period of time? i also have access to a TIG welder that may be able to be used as a power supply. being in Alaska the shipping cost for nitric is insane (even more so than everything else)... not to mention the initial price and all the government lists you get on. i suppose just being a member of this forum gets you on most of them anyway... :P

[Edited on 25-10-2007 by 497]

kilowatt - 26-10-2007 at 20:12

Hmm, if this works out I might have to try it as well. I had planned to use the Ostwald process once I run out of nitrate salts, but this could be a lot easier although less efficient. Maybe a watercooled glass chimney and an arc from my pole transformer. Plus it would give me an excuse to have a large multi-kW jacobs ladder running continously in my shop that is actually doing something. If they make a medication to treat polyprojectitus, I need it.:P

497 - 26-10-2007 at 23:51

well i did some testing with tungsten electrodes without shield gas. not pretty. they got crapped up (oxide i assume) in a few seconds to the point that the arc died. but not really a good test because its very low voltage high amp (~20) but soon i'll try it again with a furnace transformer. while i'm at it i think i'll try graphite rods out of D cells. i suspect these may be the best option. the contamination with carbon might be an issue though. i love the general idea of producing nitric from air though, best method ive seen yet, even with the low efficiency.

Antwain - 27-10-2007 at 00:46

I would have thought that the benefit of moving the arc along the electrode was that any given patch has a low duty-cycle and does not get ungodly hot and start to melt/evaporate...

497 - 28-10-2007 at 18:00

that was my logic too. but apparently its not a problem for an oil furnace transformer. apparently its not powerful enough to damage the electrodes even though the arc is stationary, ~1 mm steel welding rod had no visible damage after many minutes of running. a little less powerful than i had hoped (draws ~50 watts.) it makes an arc maybe 2 cm at most. i did make a jacobs ladder and after seeing how fast the arc travels (completes a full cycle quite a few times per second) i wonder whether it might be better because it seems like it might allow the air to cool faster and retain more NO2. with a stationary arc it takes about 8 minutes to fill a liter glass with red NO2 (running it longer doesn't help). i then set the NO2 filed jar upside down in a container with 50 ml or water in the bottom. the color in the gas is gone by 5 minutes. so i did that 5 times and got enough acid to make the pH read 2. then i distilled it down to about 1 ml of fairly concentrated acid. it got hot and fizzed quite alot when dropped on baking soda. so it works! now i just have to get it to work without constantly babysitting it. the transformer seems to fair pretty well, getting only a little warm after running for and hour. any ideas on a good way to diffuse the NO2 into water? i'm not confident that simply bubbling it would work very well.

[Edited on 28-10-2007 by 497]

densest - 28-10-2007 at 22:59

A random thought about some variant ways to get air enriched with oxygen up to 2000C or so. Electric arcs are a very intense heat source, but it's easy to overheat the electrodes and melt them. This has probably been tried and discarded, but.....

There are a few materials which remain solid in an oxidizing atmosphere above 2000C. Limiting the search to oxides for simplicity, there are CaO, TaO2, Ce2O3, La2O3... ThO2 is very nice at over 3000C. Would passing a N2/O2 mix through a lattice heated to 2000C be likely to produce NO in any significant quantity?

I tried producing a little fused La2O3 with a propane/oxygen torch. The flame is hot enough. At the required temperature, radiation carries away a lot of energy, so fusing the interior of a large blob of powdered oxide is much easier than working from the outside. If you try this, wear at least grade 5 welding eye protection. Grade 8 would be better. It's very bright and emits huge amounts of infrared and sufficient ultraviolet to be harmful.

A further variant to the solid phase reactor could be to heat the oxide blobs electrically once they're heated enough to be conductive. Tungsten or molybdenum electrodes protected from air with an oxide layer would be able to stand the heat.

Perhaps a set of Coleman lamp mantles would also serve... they used to be doped with thorium oxide. I forget what the generic term for the lamp is - it evaporates pressurized gasoline into a gas mantle lamp.

12AX7 - 29-10-2007 at 00:48

BTW, once you heat up ceramic enough, it conducts. How much depends on the ionic mobility. You might consider an Al2O3 or mullite matrix with some SiO2 and Na2O glass phase. Na ions of course become mobile at reasonable temperatures. Then a bit of noble or refractory metal or conductive oxide could be used to maintain continuity.

After oxidation, vaporization and sputtering are probably the next things to worry about. High-Z oxides, high binding energies and high boiling points would be preferred.

In fact, WC and SiC satisfy conductivity, Z, MP and oxidation resistance, variously. A composite containing W, C, Si and SiO2 might be very practical.

Tim

densest - 29-10-2007 at 15:43

Quote:
Originally posted by 12AX7
BTW, once you heat up ceramic enough, it conducts. How much depends on the ionic mobility. You might consider an Al2O3 or mullite matrix with some SiO2 and Na2O glass phase. Na ions of course become mobile at reasonable temperatures. Then a bit of noble or refractory metal or conductive oxide could be used to maintain continuity.

After oxidation, vaporization and sputtering are probably the next things to worry about. High-Z oxides, high binding energies and high boiling points would be preferred.

In fact, WC and SiC satisfy conductivity, Z, MP and oxidation resistance, variously. A composite containing W, C, Si and SiO2 might be very practical.

Tim


All good points. According to an ancient Chem Rubber Handbook, the carbides can't stand a hot oxidizing environment, and all the silicates I looked at melt below 2000C.

High-Z materials that look good: Zirconium oxide looks good (solid to 3000C) and there are companies which fabricate it :P:P Various lanthanide oxides are solid up to 2200-2400. Thorium oxide, of course, would be ideal.

By comparison, my oxygen/propane torch which makes enough NOx to require heavy forced ventilation is about 2800C, though it might generate enough free radicals to make that figure meaningless.

ZrO2 conducts electricity starting somewhere about red heat. If protected from air by (for instance) a coating of La2O3 or other convenient oxide (I have a kilo or so of it) melted onto them, tungsten and molybdenum can be used as electrodes and supports well into the 2000s. None of this equipment can stand getting wet; one must be careful about that.

Now to find the time and energy to actually try some of this :( It's fun to talk about though. Perhaps an extremely simplified version to do a quick test will come to mind.

Twospoons - 29-10-2007 at 16:46

If you are feeling really adventurous (and know what you are doing) you could try a microwave driven plasma.

Microwave plasma torch

Microwave coupled plasmas can achieve very high temperatures, with no electrodes to melt, or wear away. Neither simple nor cheap, unless you have access to some amazingly good surplus outlets.

497 - 29-10-2007 at 19:03

that is an interesting idea, using the oxides. but i really doubt it would easily achieve the temperatures needed for efficient conversion (i've read that the equilibrium is about 5% at 3000 C), and looks like it would be a considerable amount of effort to get a working setup. probably worth a try if you have the time and materials, but as far as i can see a plain old arc works pretty well. at least with a lower power one like i have, it seems to put very little heat into the electrodes at all, as i said before they have no signs of wear. the microwave plasma torch is very interesting, it looks like it could work very well indeed. unfortunately i lack the resources to experiment with it... one problem i've come to is how to get the very dilute NO2 to dissolve in water efficiently and yet make fairly concentrated acid. I had the idea of cooling the air-NO2 mixture causing it to form N2O4 which would then condense (or maybe freeze) and could be added to water in the needed proportions. would this work?

497 - 15-11-2007 at 12:10

so i've finnaly done some more testing. using a oil furnace transformer arc with an airpump pushing the gas through a bubbler, i've produced 600ml of water the reads 3500 microseimes (1750 ppm according to my meter) which gives me about a gram of HNO3 in theory. it only ran for maybe an hour. I think i'd be happy with 24 g HNO3 per day. and i can always find a bigger transformer. i am also happy the the NO2 is diffusing into the water effectively, i'm only getting a loss of maybe 5-10%. i'll run it some more later today and see how it does.

tentacles - 15-11-2007 at 21:57

497: Interesting results, can you post pictures of your setup? I'm also interested in any results you might have for the N2O4 production - where I live the winters are long and cold, it'd be nice to have a use for it being -30C outside!

I wonder if you could run a B-E reactor made of glass continuously here, outside in the winter? Would the external cold cool the plasma arc excessively? The output gasses could easily be run inside, or into heated (above freezing anyway) jars of water. The cold would also help the water retain the NO2.

12AX7 - 15-11-2007 at 22:10

I don't think outside air temperature will bother you in the least: with the plasma at circa 10kK (i.e., 10,000 K), the difference between 250 and 300K doesn't seem all that important. :)

N2O4 condensed in the environment reminds me of metal-melting friends in frigid locations... always a shame when your propane tank freezes up without even having drawn a drop of gas off it!

Tim

497 - 16-11-2007 at 17:54

so i've found that the added pressure from the second bubbler really increases the diffusion of NO2 into H2O. with my pathetic little setup i was getting about 40 microseimen increase per minute in 500 ml of water (ran for ~3.3 hours and ended at 8000 microseimens) i then boiled off most of the water and ended up with about 2 ml of pretty concentrated acid that reacted with copper fairly quickly. so i calculated that at about .5 g per hour. not bad. but i'm just a little too impatient for that so i'm going to see if i can find a good microwave transformer at the dump. i know i'll have to add a big resistor to keep the thing from melting but thats ok, power is cheap. and maybe i'll use
the heat to do something useful like concentrate the resulting acid...

with a microwave transformer i imagine the problem will become dissipating all that heat from the arc. so this is my idea for an arc chamber: stainless steel tube maybe 2 cm dia and about 15 cm long with a cap welded on the bottom end. then have one electrode welded to the center of the cap, the other one mounted on a movable insulator (to allow adjustment of the gap.) for electrodes i'm thinking stainless rod with 5mm balls the on the hot ends. the air would travel through linearly, i think this is more effective than just having an arc in a turbulent container of air. the steel tube would have a boiling water jacket to cool it. i think it'll work, any comments/improvements?

as far as freezing the N2O4 goes, i have yet to do a good test but it seems to diffuse into water quite well at room temp, so i don't see the need.

anyone know a good way to measure the concentration of nitric acid? i have a pH/conductivity meter, but i don't trust it's accuracy above very dilute acid.

i'll post pics of my little oil furnace transformer setup as soon as i have time.

[Edited on 16-11-2007 by 497]

497 - 18-11-2007 at 23:09

so ran it for ten hours today. the first diffuser is about 120 ml volume ended up with roughly 25000 ppm (25 grams per liter) not bad... 8 grams per kw

497 - 24-11-2007 at 01:27

i just got an old microwave. perfectly good as far as i can see. i ripped it apart, the transformer is nice, works good, amazingly powerful compared to my little OFT. also got a really nice fan out of it.

the problem now is how to ballast it. with no ballast it gets hot real fast as i expected, so i hooked up 8 10 ohm 25 watt resistors but i'd need quite a few more to get them to not overheat. i've heard i can use another MOT as an inductor to ballast it but i don't have one. i suppose it's more trips to the dump then...

another problem is how i'm going to make a chamber that can handle that much power. i'm thinking water cooling.

anyone know a good use for a magnetron? i'm not sure what to do with it.

12AX7 - 24-11-2007 at 03:41

Since you're probably not interested in the 10cm ameteur band, you might as well smash it. Inside, you will find a steel housing, aluminum cooling fins, copper anode, ceramic (probably pink alumina, unless it's an old one made with beryllia, in which case don't crack it!) and the cathode, which is probably "rare-earth" oxide coated tungsten.

Tim

497 - 24-11-2007 at 16:30

so if i wanted to wind an inductor to ballast the arc, can anyone tell me how i could figure out the number of turns, diameter of wire, etc.? i don't have another MOT to use.

12AX7 - 24-11-2007 at 20:39

If you don't have a laminated iron core, you'll be up in the 10,000 turns range, of some very substantial wire (heavier than rated, since the required length adds so much resistance). Better find another MOT methinks!

Tim

497 - 27-11-2007 at 15:57

hmm well i calculated that about 350 feet of 20 guage magnet wire in a coil with no core will produce an impedence of ~12 ohms (plus 3 resistance) at 60 hz. that should be enough to keep my current down to 8 amps, which is no more than it would use when running the magnetron, and i know it can handle that for an extended period of time. maybe i calculated wrong. but even if i didn't i'd rather use a MOT, much easier. still havn't found another one yet though..

12AX7 - 27-11-2007 at 23:42

Yeah, and 20 AWG is good for how much current?

Try 20 AWG nichrome...

Tim

497 - 28-11-2007 at 12:11

well i'm not sure exactly what current its said to handle but i figured that it would have about 120 watts of resistve heating. i figure that could be handled, maybe with a fan. i suppose you could just have it submerged in water... i hope i can get some soon.

Increasing NO2 Formation and Dissolving

UncleJoe1985 - 30-9-2008 at 21:44

I've attempted running a Birkeland Eyde reactor with a 9kv, 30mA NST, but got very poor results: ~3-4% acid max. I'm planning to resume after stopping for 5 months. Rather than increase my power supply, which I think is sufficient, I want to improve the efficiency. Here's what I think was wrong with my previous setup (I'm pretty confident my arc configuration is good).

1. Not enough time is given for NO2 to form before bubbling it through water. I just directly lead a tube from the top of my 1.5L reactor to the bottom of the 1st water jar. I heard from someone else who had better success put a second larger container in between to allow time for the conversion, which he claimed was noticeable based on the darker color in it. I then found out that NO2 has a much higher solubility than NO, which might explain the low yield. Can anyone confirm this or know the time it takes for NO to NO2 conversion?

2. Poor NO2 absorption. The absorption columns used in the Ostwald process are 5 stories high, so that says something about the rate of dissolution. I was thinking of adding something porous to increase the time the bubbles react with water, but I can't think of anything that's acid resistant. Also, does anyone know how important temperature is on absorption rate? I heard 50C is good, which seems
to trade off solubility for reaction speed.

Thanks to everyone who shared their experience above.

[Edited on 30-9-2008 by UncleJoe1985]

Magpie - 1-10-2008 at 13:13

Quote:

I was thinking of adding something porous to increase the time the bubbles react with water, but I can't think of anything that's acid resistant.


Adding inert mass (like small pieces of broken porcelain) to the absorption vessel will not increase residence time of the gas, but decrease it. It will, however, increase turbulence (and hence mixing), so might improve the absorption rate that way.

Edit 1: In fact all industrial size absorption columns have some kind of packing, sieve trays, or bubble-cap trays for just that reason: increase interfacial contact between liquid and gas, and thereby improve the absorbtion rate.

Edit 2: I just checked my "Chemical Process Industries" book by Shreeve for making 65% nitric acid. The absorption tower for commercial units is, as you say 40 feet high. It uses bubble-cap trays with cooling coils on each tray. Column pressure is 100 psig. Column feeds are cooled water, NO, and cold air. One paper states that in the authors' opinion the following reaction is the rate limiting step (not the oxidation of NO), and that "...this is an absorption phenomenon":

3NO2 + H2O <--> 2HNO3 + NO

I think I can see why this thread is so long. It would be quite a challenge for the home chemist to simulate those conditions.

Edit3: Upon further reading of Shreeve, he implies that 55% acid can be made at atmospheric pressure. The column diameter is 5.5 ft. Production rate is 55 tons/day. So, computing a rough value for the liquid residence time:

flow = (55 tons/day)(2000 lbs/ton)(day/24 hr)/[(8.34 lb/gal)(1.2)(7.5 gal/ft3)] = 61 ft3/hr

Column volume (disregarding internals) = (3.14/4)(5.5 ft)^2(40 ft) = 950 ft3

Therefore, residence time (roughly) = 950 ft3/(61 ft3/hr) = 15.5 hr

Edit4: The assumption of a column full of liquid is erroneous for a column using bubble-cap trays. I correct this in my next post.





[Edited on 2-10-2008 by Magpie]

UncleJoe1985 - 1-10-2008 at 17:47

"It uses bubble-cap trays"

http://www.jaeger.com/BubbleCap.jpg - Ingenious! The cup will trap the gas until it overflows. Now if I can only buy or build one myself, I definitely would.

Thanks for looking up Magpie, but I don't think your calculations are meaningful. 15 hours would be the time it takes for liquid on the bottom of the column to rise to the top, assuming the column was initially empty and that nothing mixes. The correct calculation should involve the volume of NO2 passing:

55 ton/day => 792 K Moles HNO3 /day

Assuming, the reaction path is, 3 HNO2 + H2O => 2HNO3 + NO, the gas flow is:

2.66 * 10^7 (L NO2 /day) => 308 L/s

Using your dimensions of the absorption column, the gas will travel at
308L/s / (bottom area of column) = 14.0 cm/s

column height / 14.0 cm/s = 87.4 s

Still, that's a long time for absorption. This probably explains why so many people before have complained about low yield. Any ideas on how to increase absorption compactly? I was thinking of using a rain forest mist generator, but am worried about it not being acid resistant, assuming it was a closed cycle (i.e. respray the acid in the jar).

I proposed earlier to use hot water to increase the absorption rate. Even though they said to use cold water, I think that's just to cool the entire setup, not what the equilibrium temperature is. My chemistry is mediocre, so does anyone know if increasing the temperature improves the absorption rate?

Also, I did try using several plastic mesh pot scrubbers as a filter, but it was hard to eliminate all gaps with the jar. Large bubbles would just go through the gaps.


[Edited on 1-10-2008 by UncleJoe1985]

Magpie - 1-10-2008 at 20:38

Quote:

Thanks for looking up Magpie, but I don't think your calculations are meaningful. 15 hours would be the time it takes for liquid on the bottom of the column to rise to the top, assuming the column was initially empty and that nothing mixes. The correct calculation should involve the volume of NO2 passing:


You are right about my calculation not really being meaningful. In thinking about how a bubble-cap tray really works, the tray (of which there are many) is the only place there is liquid holdup, ie, each tray holds up enough liquid to overflow its downcomer weir. The rest of the column is gas. The liquid flows in from the top then cascades down through the trays. The gas enters at the bottom and flows up through the bubble cap slits, sparging through the liquid held up on the tray. So a more reasonable estimate of the liquid volume in the column might be 1/10th of the column volume. This would reduce the residence time to 1.5 hrs. I will see if I can look this up, or maybe someone else can give a better estimate.

A bubble-cap tray is not practical for small scale work. I'm thinking that a packed column might be about the best a home chemist could make. Again, the residence time is going to be the problem. There's no way you are going to have a 40 ft column (right?).

The usual chemists' expedient to gas absorption is a sparge tube in a glass column, ie, a "gas absorber." Shown below is a picture of mine. Gas residence time is a problem here. You just have to keep sparging away until you get an acceptable concentration of acid.

The cold temperatures are necessary for efficient gas absorbtion. The colder the solvent, the more soluble the gas.

All this theory and technology of gas absorption can be found in Perry's Chemical Engineers' Handbook, available in any technical library.

gas absorber.jpg - 95kB

jarynth - 18-10-2008 at 04:58

What materials would be best suitable for the electrodes in an amateur setting?

US1462987 suggests a 50:50 mixture of O2/N2 for better yield... In a oxygen-poorer atmosphere (such as air), the equilibrium should be more strongly shifted towards the monoxide. What catalysts cold be used to reverse the disproportionation? Maybe V2O5 as in the lead chamber process could do the job.

[Edited on 18-10-2008 by jarynth]

watson.fawkes - 18-10-2008 at 09:20

Quote:
Originally posted by jarynth
What materials would be best suitable for the electrodes in an amateur setting?
I suggest tungsten electrodes for TIG (GTAW) welding. They're readily available, modestly priced, and have well-proved resistance against degrading in ordinary atmosphere. (The shielding gas protects the weld, not the electrode.)

12AX7 - 18-10-2008 at 09:37

I find that suspect. Tungsten filaments *burn* in air. In fact, they literally produce a flame!

Filaments are a whole lot thinner than rods, much like powders are pyrophoric when the bulk material isn't, but still...

Tim

Atomizer for absorbing NO, yea!!

dann2 - 18-10-2008 at 12:33

Hello Folks,

I am totally new in this thread.
Was just wondering about the problem (perhaps it's not a problem) of getting the NO to dissolve and not go to the atmosphere.
There are devices sold in stores that atomise water for to give a display somewhat like what you get with a bowl of liquid Nitrogen in humid conditions. (ie. a creeping mist flowing out of the bowl).
If this device were incorporated into the Birkeland-Eyde it would surely capture all the NO produced via the water mist.
The membrane of the atomizer would need to be acid resistant. Have they got ceramic membranes?, I think they have, or you could pipe in the mist from a seperate chamber.
Perhaps the whole idea is a bit too 'Heath Robinson' (ridicoulsy complicated) with the bubbling system doing the job.

Dann2

UncleJoe1985 - 18-10-2008 at 14:20

Quote:
US1462987 suggests a 50:50 mixture of O2/N2 for better yield


Actually, I was thinking of exploiting that since my 30mA current is relatively low. My idea was to electrolyze water and feed the oxygen to the aquarium pump. I tried calculating the benefits of increased O2 concentration, but there's little theoretical benefit:

Page 583 of A Dictionary of Applied Chemistry gives the equilibrium constant of NO formation (N2 + O2 => 2 NO) as

k = (10^(0.5441 - 4725.5 / temperature))^2

To solve for the concentration of NO (mols/L) after going through the arc, I used

k = [NO]^2 / (([N2] - [NO] / 2)([O2] - [NO] / 2))

[N2] and [O2] are the initial atmosphere concentrations of nitrogen and oxygen. For non-chemistry experts like me, this is just a rate equation where the numerator on the right is the reaction rate of NO decomposition and the denominator is the rate of NO formation. The subtraction accounts for the loss of 1/2 mole of O2 and N2 for each mole of NO produced in the equilibrium state.

At T = 3200K, the NO concentration will be 4.18% by molar fraction and volume as well, assuming gas is immediately cooled to STP.

Solving a similar equilibrium equation for 2 NO + O2 => 2 NO2, using the equilibrium of NO formation as the initial state and a very high equilibrium constant (couldn't find it, but I'm pretty sure it's very high because it's exothermic), the final NO2
concentration will be 3.8% by volume.

Increasing the O2 concentration to 50% by volume resulted in a NO and NO2 concentration of 5.27% and 5.11%, not a large improvement. Plus, the reported NO % in an industrial
setup is only reported as 1.5 - 2.0%, which is probably due to the NO decomposing as the gas is cooled. In that case, O2 becomes even less of a limiting factor.

Of course, the k and T I used might not be accurate, or maybe a higher [O2] will help speed up the rates of reaction or help with reconverting NO, created during NO2 absorption, to NO2. However, any improvement in [NO] will be canceled by NO decomposition when it cools, unless you can quench it very fast. I did remember reading from some turn of the century text on Google books saying some Rayleigh reporting large improvements in electrical efficiency from using a 50:50 N2, O2 mixture, which might not be from increased [NO], but couldn't find that source again.

I've also included a program for calculating my #s.


[Edited on 18-10-2008 by UncleJoe1985]

Attachment: NitricOxidesCalculator.java (4kB)
This file has been downloaded 1135 times


watson.fawkes - 18-10-2008 at 15:02

Quote:
Originally posted by 12AX7
I find that suspect. Tungsten filaments *burn* in air. In fact, they literally produce a flame!

Filaments are a whole lot thinner than rods, much like powders are pyrophoric when the bulk material isn't, but still...
That's because it's the tungsten itself that gets hot in filament form. With a tungsten electrode, only its point of contact with the arc is subject to significant heating, and the thermal mass of the electrode acts to dissipate even that heat. TIG torches come in both air- and water-cooled versions, since tip heating is, indeed, the limiting factor in electrode life.

UncleJoe1985 - 19-10-2008 at 22:19

I didn't bother reading the patent jarynth mentioned before I did my calculations, but on the 1st page, it says a 50:50 N2, O2 mixture improves the NO yield by 25%, exactly as I predicted. Damn, I feel smart!

UncleJoe1985 - 20-10-2008 at 19:11

Fellow experimenters,

I've put together some pictures, video, and explanations for my procedures. Enjoy:

Some of the pictures are blurry. That's because the room doesn't have a lot of lighting and I didn't want to use the unnatural looking flash, so I instead set the exposure to 1/80 s.

The video is separate because it's over the attachment size limit. Can any admin let me host it on this site?

A couple of notes:

1. The absorption column is just a 1.6L acrylic jar from Walmart that has grooves carved along the inner circumference with a Dremel tool to allow the DVD layer to fit.

2. I used the smallest volume aquarium pump I could find. I think anything over will decrease the concentration of NO2 formed, unless I add more delay between the arc and absorber. On the plus side, a higher air flow should quench the gas faster, allowing a higher concentration of NO to be locked in.

3. I'm not sure if the low climbing arcs are efficient. On one hand, they will reduce the amount of gas from re-entering the arc, but on the other hand, higher climbing arcs are wider and are exposed to more air and also dissipate more power since they have larger resistance, though not as intensely?

After running for probably 24 hours at least, I measured the HNO3 concentration by titration with 10% ammonia, using red cabbage indicator. I only had a medicine dropper that had tick marks every 0.5mL, so the results aren't too precise:

2.25 mL acid to neutralize 0.5mL ammonia means

0.5mL * 0.9605g/mL * 0.1 * (1 mol NH3 / 17g) = 2.825 * 10^-3 mols NH3 neutralized = mols HNO3 neutralized

2.825 * 10^-3 mols / 2.25mL = 1.26 mols HNO3 / L

ammonia specific gravity


After concentrating it by boiling ~500mL to < 30mL, I measure the molar concentration again
0.8 mL 10% ammonia to neutralize 0.5 mL acid

= 9.04 mols / L

The weight % is just
9.04 mols / L * (63 g HNO3 / mol) * (1 L HNO3 / 1400 g) ~ 0.4

I didn't have the exact specific gravity of HNO3, so I just approximated.

So I went through all that effort to get 40% acid, while relatively inefficient, it suits my needs.

Any information on improving efficiency will be greatly welcome.

Fixed: zip file got corrupted during upload, also use VLC or mplayer to view the video. It seems QuickTime stutters.

[Edited on 21-10-2008 by UncleJoe1985]

Attachment: nitric_acid_reactor.zip (684kB)
This file has been downloaded 1003 times


497 - 20-10-2008 at 20:41

If you have read "Absorption of Nitrous Gasses" then you should have everything you need.. It's a good book, I read it nearly cover to cover (which I don't do often). That 1% NO2 is sure hard to deal with...

My newest idea for easy concentrated nitric acid is directly from liquid N2O4 via the decomposition of calcium nitrate fertilizer (actually 5Ca(NO3)2*NH4NO3*10H2O). So far everything seems to look promising, I have tried the decomposition on a test tube scale and it worked nicely. At first it melts in its own water of hydration, then after boiling part of the water off it suddenly precipitated into a pasty mixture that continued to give off water. After some time the paste hardened a bit and the NH4NO3 decomposed. Then on further heating to about 550*C the mostly anhydrous Ca(NO3)2 melted again and gave off large quantities of 4NO2 + O2 until eventually only CaO was left. There are plenty of other nitrates out there that decompose at much lower temperatures, but I can't buy them in 50 pound sacks... meaning I have to synthesize them and that adds so much work that I find it easier just to use higher temperatures and Ca(NO3)2.

I think this could be done on a kilogram scale in a steel vessel heated with propane, or even wood, which I have tons of. Once substantial NO2 production starts you could attach a condenser cooled to -25*C or so and catch most of the N2O4. Once you have liquid N2O4 all you need to do is add it in excess to water and bubble some oxygen (could be the byproduct O2 from another batch of N2O4 :P) through it while stirring to get near 99% acid. N2O4 has many other wonderful uses including direct ozonization to produce N2O5. It makes lovely binary explosives too.

Of course if you don't have calcium nitrate this isn't very useful, but seeing as most people in the US can get it for cheap ($25 per 50lb for me) it seems like a useful method. Also it seems people are less suspicious of it compared to NH4NO3 or KNO3.

tentacles - 21-10-2008 at 15:02

497: It seems to me that Fe + molten Ca(NO3)2 is probably not going to work. Stainless steel might do the job, although I'd suggest 316 grade as it's far more resistant to nitrate salt corrosion.

497 - 21-10-2008 at 16:40

You are correct, 316 would be a much better material to use. But, it is also more expensive and harder to get. The mild steel crucible will surely corrode to some degree, but I suspect that it will be slow enough to allow it to be used at least a few times. Once it wears out I can just make another one, I have plenty of steel around. If the corrosion turns out to be extremely fast, then I'll just have to figure out an alternative, but I have a hunch it will be satisfactory. Of course before building a big crucible I'll test it on a smaller scale to find out.

[Edited on 21-10-2008 by 497]

chloric1 - 21-10-2008 at 17:52

IIRC you need 3 moles of NOx with 1 mole of water based on this reaction scheme:

3NO2 + H20> 2HNO3 + NO^

The NO can be used to make more NO2, metal nitrosyl complexes, nitrites etc etc.

UncleJoe1985 - 26-10-2008 at 11:36

I've built a slightly larger absorption tower using a 2.1L acrylic jar from Walmart with 10 polycarbonate DVD layer trays. Adjusting the electrodes to allow longer arcs, which are more efficient, I ran it for 28.6 hours.

The result is 1.5 L solution with a concentration of 1.28M = 8% by weight, which means I made ~4.1 g HNO3 / hour. Based on the efficiency of 65 g / Kwh reported for industrial setups, my efficiency would be 24%, assuming I was drawing 260W on average (don't know very accurately).

One possible explanation could be poor gas absorption. Based on my experience, the concentration seems to peak out at 1.3 M. I've read somewhere that it only takes ~5s for

3 NO2 + H2O => 2 HNO3 + NO

to reach completion, which I thought using 10 bubble layers would suffice. Of course 5s probably assumes the gas and water are very finely mixed, which might not be in my case.

Another explanation could be maybe the 65 g / Kwh efficiency only accounts for the energy dissipated in the arc. In that case, my arc probably only dissipates 135 W based on dann2's diagram (says ~1/2 voltage dropped across arc), which would raise the efficiency to ~50%. Anyone know the details?

I've included a new picture of the absorption column with bubbles evenly spread out. The sheet of paper is used to shield sunlight, which might decompose the acid.

[Edited on 27-10-2008 by chemoleo]
Please use reasonable image sizes next time! Attached a smaller version.

[Edited on 26-10-2008 by UncleJoe1985]

absorption_column.jpeg - 123kB

497 - 26-10-2008 at 15:32

Quote:

Based on my experience, the concentration seems to peak out at 1.3 M. I've read somewhere that it only takes ~5s for 3 NO2 + H2O => 2 HNO3 + NO to reach completion, which I thought using 10 bubble layers would suffice. Of course 5s probably assumes the gas and water are very finely mixed, which might not be in my case.


That may be, but it takes much longer to fully oxidize the resulting NO back to N2O4. So you are probably losing about a third of your yield..

Since your N2O4 is so dilute you're never going to get very concentrated acid straight from the absorber, you might as well not try, it will just make for more effort and loss of yield.

If I were going to make an efficient absorber I would use a cheap submersible aquarium pump with the output air from the arc plumbed into the venturi inlet (this would actually have enough suction to pull the air through the whole system). The pump would then be set in the bottom of a 5 gallon bucket and aimed so as to produce a spiral water movement. The bucket would be about 1/2 to 2/3 full and ideally would have a sealed lid that was then plumbed into a second venturi in a second bucket (that could be smaller). The air space will allow some residence time for things to get fully oxidized. This setup should handle quite a bit of N2O4. With your amount of N2O4, you could set it up to run for weeks at a time.

For reducing the absorber size and complexity and/or increasing your yield I would recommend using dilute H2O2 as your absorption media. It will work much faster and catch almost all the N2O4. Each gram of H2O2 will absorb 2.7g N2O4, so a liter of 2% will absorb about 54g (making 74g HNO3) at high efficiency. If you have ready access to more concentrated H2O2 then by all means use that, it will work even better.. Or you could run the (cold) output gas through an ozonizer, this is said to greatly improve absorption by forming N2O5 in situ.

UncleJoe1985 - 26-10-2008 at 16:25

Quote:
It takes much longer to fully oxidize the resulting NO back to N2O4 ...
The air space will allow some residence time for things to get fully oxidized.


Yeah, I found that too from the same publication (attached) that reported the NO2 + H2O equilibrium of ~5s (figure 2). I guess using an additional 5 bubble layers compared to my previous setup isn't worth much because most of the NO2 is already absorbed, while the NO still doesn't have enough time to react.

I imagine adding a delay space between a second absorption column will work well in the same way as I added a delay chamber in between the arc furnace and the 1st absorption column. However, I'm hesitant to do so yet because I'm using a relatively weak aquarium pump that probably will reduce its flow under higher load. I have a more powerful one, but it's probably too powerful - it breaks the arcs before they stretch to the max. Plus, the higher pressure might cause more leakage - the epoxy on top of my furnace gets soft when it's on and there's a funny smell, probably ozone.

Quote:

use a cheap submersible aquarium pump


I probably could use it and go up to 30% acid before the plastic gets attacked, but I'm worried that the moving parts (e.g. check valve) aren't acid resistant.

Quote:
I would recommend using dilute H2O2 as your absorption media


Looks promising, considering that 1L H2O2 is only 97 c.

[Edited on 26-10-2008 by UncleJoe1985]

Attachment: no2_equilibrium.pdf (835kB)
This file has been downloaded 961 times


497 - 26-10-2008 at 16:59

The kind of submersible pump I'm talking about has only one moving part: the impeller. Some have all plastic exposed surfaces, it depends on the brand.
Plastic being attacked by dilute HNO3 could be a problem, I don't know how fast it proceeds..
You can even bubble the gas into the intake of the pump and the impeller will chop the bubbles up extra fine, at the cost of some water flow.
The ultra fine bubbles will allow the absorption to be nearly instant, the oxidation of NO being the limiting factor.

According to Absorption of Nitrous Gasses it takes 180 seconds to oxidize 90% of the NO in a 1% NO-air mix.
To get 98% oxidized it takes 1014 seconds.. So you need to adjust your residence times accordingly.

Note the graph applies only to mixtures not in contact with water, which changes the whole dynamic.
When lots of water is present the NO gets oxidized to N2O3 (which takes much less time) and it then absorbed as HNO2.
Later over time this HNO2 will break down again releasing 2/3 of the nitrogen via

3HNO2 > 2NO + HNO3 + H2O

and causing some loss. So ideally your oxidation chamber is separate from the absorbers.

PS. Do you have affordable access to a nitrate fertilizer such as calcium nitrate, etc?

[Edited on 26-10-2008 by 497]

Attachment: NO oxidation.doc (75kB)
This file has been downloaded 829 times


UncleJoe1985 - 26-10-2008 at 17:04

OK, I've found the reference to higher [O2] => greater efficiency. It's on page 36 of this book. In general, the book is a very good survey and many of my experimental results are confirmed by it. Since the increase in efficiency is probably not due to higher [NO] created by the arcs, my guess would be that it is due to improved oxidation of [NO] after leaving the arc and after being produced during absorption (3NO2 + H2O => 2HNO3 + NO).

[Edited on 26-10-2008 by UncleJoe1985]

UncleJoe1985 - 26-10-2008 at 17:30

497:

Quote:

it takes 180 seconds to oxidize 90% of the NO


Wow, I never knew it was that long. The gas in my delay chamber is moderately dark, so I thought I gave it enough time. This explains the height of the absorption columns I calculated earlier. In light of this, I should make my first delay chamber even larger.

I probably can get nitrate fertilizer and make HNO3 cheaper the old school way, but haven't looked where to get it yet. I'm a M.S. in computer science / CSE at Georgia Tech and I'm mostly doing this out of curiosity and its minimal reliance on chemicals - only air, water, and electricity! I mostly frequent ACE hardware, Walmart, and Target and try to build everything from commodity parts, which takes ingenuity.

[Edited on 26-10-2008 by UncleJoe1985]

chemoleo - 26-10-2008 at 17:34

UncleJoe, in your picture (which I reduced in size), you could put in a magnetic stir bar at the bottom, and stir the whole thing at high speed. This will break up bubbles into many small ones, keeping them in suspension for a long time, and therefore should increase absorption drastically.

Also, if you are going to discuss thermal decomposition of nitrates, please do so in a separate thread - I'll happily move the existing posts in here...

497 - 26-10-2008 at 18:06

Quote:

you could put in a magnetic stir bar at the bottom, and stir the whole thing at high speed.


That's not a bad idea. Alternatively, if you don't have a magnetic stirrer set up, you might be able to rig up a mechanical stirrer with the shaft down the center. But really, with the small amounts of N2O4 he's dealing with, I don't think absorption area is the problem, residence time is the big issue. In Absorption of Nitrous Gasses the author puts much emphasis on the free space in the absorption tower packing. Ideally it is upwards of 80% free.

If someone wants to discuss decomposition of nitrates I'm all for it.. however the mods want to set it up.

[Edited on 26-10-2008 by 497]

OMG - 26-10-2008 at 18:59

If one was inclined, could you absorb the NOx into say a NaOH filled filter? Would that be a better way to capture and concentrate nitrates generated? Then maybe use sulfuric to make concentrated nitric after that.

kclo4 - 26-10-2008 at 19:08

You'd have the problem of Sodium Nitrite forming. Also, the NaOH might liquefy from the H2O produced, the H2O in the air, and also the Sodium Nitrite/Nitrate Mixture would prevent a lot of the NOx from reacting with the NaOH since it might coat the particles.

Another thing to consider is you'd also have to then react that with a strong acid, which might be though of as wasteful since reacting NOx with water doesn't use a strong acid, but it produces one.

If you were to just react a Nitrate with a strong acid, you'd be better off getting nitrates from the organic waist/dirt. there are a few references on the forum about this process.

But I think the purpose of this thread is more directed towards turning Air and Water directly into Nitric acid.

Formatik - 26-10-2008 at 20:46

Quote:
Originally posted by UncleJoe1985 The video is separate because it's over the attachment size limit. Can any admin let me host it on this site?


That's a creative idea how to have used those CD protectors to better facilitate gas absorption. I would have never thought of that.

kclo4 - 26-10-2008 at 21:29

I wish to watch your video, since it seems pretty interesting but it randomly starts speeding up.
Even after I downloaded it, it still does that! I wonder why?
Either way, I really like how your project is going.
You've inspired how I plan to absorb some gases from now on! :P

UncleJoe1985 - 26-10-2008 at 23:13

Formatik,

I didn't use CD protectors - didn't know they existed until now. I split DVDs in half and used the non-label polycarbonate layer. The top layer fractures too easily. HCl was used to dissolve any aluminum and organic dye.

My idea probably isn't too original. I was intentionally trying to build the bubble cap trays used in an industrial setup. What is original is using DVDs - finally, something useful to do with all those junk CDs and DVDs.

Earlier, I tried using plastic mesh pot scrubbers, but they failed miserably because they weren't held in place and large bubbles just went through any gaps. I think I'll try it again, now that I can secure them between the layers.

KCLO4,

Thanks for watching. Unfortunately, QuickTime has flaky H.264 high profile support or my encoder has a bug. I don't have the original source, so I can't reencode it. It plays fine in VLC player or if you don't want to install it, play it in Adobe Flash (wow, never knew Flash Player can play stand alone videos).

Also, what size power supply will you use? My power supply is relatively small and I would like to see how well things scale up. The pump will need to be more powerful and the delay chamber needs to be larger to compensate for the increased flow.

[Edited on 27-10-2008 by UncleJoe1985]

Formatik - 26-10-2008 at 23:31

I see. I was thinking of those colorless CD protectors that come with sets of empty CDs or DVDs. One could also puncture those wether by a tool or heat.

UncleJoe1985 - 27-10-2008 at 06:58

Here's some more data I measured after getting up today:

The concentration is now 1.61 M = 9.6% after running an additional 18.8 hours which means 1.6 g / hour HNO3 produced over that span and 3.1 g / hour if counting from the beginning. Moderately thick white fumes came out when I opened the top of the jar.

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

Also, I'm starting to doubt the accuracy of my concentration measurements using titration. I'm worried about how much HNO2 affects the measurement. If all the HNO2 eventually converts to HNO3, then the titration end point should accurately measure [HNO3]. It's tempting to think that the [H+] measured comes almost exclusively from HNO3 since very little HNO2 ionizes in water (k = 4.0 x 10-4), but as the acid is neutralized, any unionized HNO2 will ionize until all of it is gone. Anyone know the %s of HNO2 and HNO3 in a typical setup?

[Edited on 27-10-2008 by UncleJoe1985]

Magpie - 27-10-2008 at 12:06

Commercial towers are run at 100 psig and have interstage coolers. But I think you already know that.
Quote:

Anyone know the %s of HNO2 and HNO3 in a typical setup?


Is your product slightly blue in color? I think if there was any significant HNO2 it would be a faint clear blue. One job I worked on used a packed column (Intalox saddles IIRC) to absorb waste NOx from metal dissolution to prevent air pollution. The column was about 6" in diameter and a couple stories high. The product had a beautiful faint blue tint. Sorry I can't remember the molarity of the product or whether the column was pressurized. Maybe I can find out from one of my old colleagues.

Edit: I don't think the column was pressurized and we didn't care about the product molarity. It was just a waste product. What we cared about was the ppm NOx in the effluent gas. This had to meet state discharge requirements.

What you have constructed is a sieve tray tower. It is a clever use of Wal-Martian material. You might also try a packed column. Little saddles of some kind might be ideal. I don't know what the equivalent Wal-Mart stand-in would be, however.

[Edited on 27-10-2008 by Magpie]

[Edited on 27-10-2008 by Magpie]

UncleJoe1985 - 27-10-2008 at 13:36

No, the 1.6 M acid is very light yellow, too pale for my camera to capture.
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