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Author: Subject: Efficiency of a car’s catalytic converter
Elemental Phosphorus
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[*] posted on 5-3-2017 at 11:58
Efficiency of a car’s catalytic converter


There has been some interest in making sulfuric acid using sulfur and air, but decent catalysts to oxidize SO2 to sulfur trioxide seem to be few and far between. Vanadium pentoxide has been discussed and I happen to have a quarter pound of it. A catalytic converter would be ideal for me because I would have to find a way to bind the pentoxide to a proper membrane. What is the efficiency of a catalytic converter in oxidizing sulfur dioxide? Will it only oxidize >1% or will it work almost quantitatively? Does anyone know or will I just have to try to find drain cleaner or use vanadium pentoxide?

Vanadium Pentoxide:

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[*] posted on 24-4-2017 at 22:47


Looked up some patents and it looks pretty promising actually. This has a wealth of knowledge not just in itself but in references to other patents: https://patents.google.com/patent/US5175136A/en?q=sulfur+tri...

A few speak specifically of platinum doped "honeycomb bodies with a cell density of 100 cells per square inch" - i.e. pretty much exactly a catalytic converter.

I'd say cut one off your buddies car and give it a test. Kidding - they're plentiful in junkyards. A lot of what I read described relatively low temperatures - around the same temp the catalytic converter runs off hydrocarbons and CO.




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[*] posted on 10-5-2017 at 10:10


IIRC, the problem with platinum group metals as catalysts for the contact process is that they foul too easily, and sulfur is famous for its ability to foul catalysts. That's why V2O5 was such a huge breakthrough: it's very resistant to fouling.
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[*] posted on 11-5-2017 at 04:07


Well looks like vanadium pentoxide it is then. The plan is to deposit it on silica gel, and pack that in a glass tube with 2 openings at one side, one for air, the other for sulfur dioxide. I could try and fuse a ground glass joint to the end, or just absorb the product in sulfuric acid. I am leaning toward the second one, since I really wanted the sulfur trioxide for oleum anyway, but maybe I'll also end up making thionyl chloride.
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[*] posted on 11-5-2017 at 08:55


Fleaker did this with great success almost 10 years ago: https://www.sciencemadness.org/whisper/viewthread.php?tid=89...



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Elemental Phosphorus
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[*] posted on 11-5-2017 at 13:13


Thanks for showing me that thread. I will be replicating his design with a few changes. I started this one to ask if a car's catalytic converter could be used, but it's probably better for me just to use the pentoxide.
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[*] posted on 12-5-2017 at 04:49


Thanks, I hadn't seen that thread but thanks. I will try to replicate his setup (with some modifications). I created this thread to ask if a car's catalytic converter could be used, but looks like the pentoxide is the better choice.
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[*] posted on 12-5-2017 at 18:30


You could use the catalytic converter ceramic as the substrate for your catalyst, if you already have it. And after looking into it, I learned that arsenic, not sulfur was responsible for fouling catalysts when they tried to use platinum early on for the contact process. Sulfur does foul palladium catalysts, but perhaps not platinum.
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[*] posted on 12-5-2017 at 23:53


Could the converter be used for the Ostwald process? The platinum is there and I don't think there is a large amount of palladium and rhodium in there.
Of course the yields would be lower, pressurizing would be difficult, but it might be usable
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[*] posted on 9-6-2017 at 08:29
Catalytic converters in the Ostwald process


A catalytic converter should work well for the first step of Ostwald process (ammonia to nitric oxide), since according to the wikipedia page:

Ammonia is converted to nitric acid in 2 stages. It is oxidized by heating with oxygen in the presence of a catalyst such as platinum with 10% rhodium, to form nitric oxide and water. This reaction is strongly exothermic, making it a useful heat source once initiated:[3]

4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g) (ΔH = −905.2 kJ/mol)

But it may cause problems since one function of a standard, modern 3-way catalytic converter is to reduce nitrogen oxides to nitogen and oxygen. If you can get an older, 2-way catalytic converter, that should work without problems.
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[*] posted on 12-6-2017 at 13:44


Three-way catalytic converters can only reduce all three pollution classes when there's a constant feedback loop with the vehicle's engine, because the operating range is so narrow. If your goal was conversion of ammonia into nitric oxide, you'd just have to operate at different conditions that favor its formation. Keep in mind that at least in the case of PGMs, catalysts lower the activation energy of reactions in BOTH directions.



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[*] posted on 12-6-2017 at 14:15


Tidbit
http://www.mse.engr.uconn.edu/why-pt-survives-but-pd-suffers...
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[*] posted on 13-6-2017 at 04:17


Well, this isn't really the thread for discussion of the Ostwald process, and my question has already been resolved.

But, I found some more information that should certainly be interesting for those that wish to carry out the Ostwald process at a reasonable price on a small scale.

Manufacturing Nitrates: the Ostwald process

Once ammonia has been produced by the Haber process, it can be converted into nitric acid through a multi-step procedure known as the Ostwald process. In the first step in this reaction, ammonia and oxygen gas catalytically react to form nitrogen monoxide:

4NH3(g) + 5O2(g) 4NO(g) + 6H20(g) H = -906 kJ

(1)

The reaction is quite exothermic. In the commercial reaction, the catalyst used in a platinum-rhodium metal gauze that is heated to about 900 oC.

!! However, even a hot copper wire can catalyze the reaction in the laboratory.!!


Once the reaction has started, the energy it produces is enough to keep the catalyst hot enough to sustain reaction.


In the next step, the NO reacts with oxygen to produce NO2. No catalyst is required for this reaction, as it will occur in air at room temperature.
2NO(g) + O2(g) 2NO2(g)

Copper will catalyze the first reaction. This source refers to a 'hot copper wire', but a few copper wool scrubber pads in a quartz or stainless steel tube should work, provided the tube is well heated. If you don't have access to a catalytic converter, this could be very helpful.
There is already a thread for the Ostwald process though, so maybe it is best to continue this discussion there.

Edit: In the Ostwald process thread, it was said that copper did not work in practice. When I read that, I thought that the problem could be relatively easily circumvented by decreasing the surface area, increasing the flow rate, or decreasing the overall length of the catalyst tube. There, it was said that nickel oxide worked excellently, and nickel is not that hard to get either, so that is an option as well.
Chemetix did a lot of great work on this and if you are interested I highly recommend you check out his setup. My interest was in oleum, not nitric acid, since nitrate salts are readily available where I live.

[Edited on 13-6-2017 by Elemental Phosphorus]
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[*] posted on 13-6-2017 at 05:49



I remember reading somewhere on this forum that copper catalyzes it too well and turns the ammonia into N2 and H2O, too quick to form any NO2.
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