Methane Oxidation Catalysts?

I've been helping to come up with a small engine that runs on methane extracted from compost. One issue that I've run into is the fact that completely utilizing the gas isn't very easy, and some can escape the exhaust. I've heard of catalysts that help to completely burn the stuff, but I'm completely unsure of how to get them for such a small project, what price they'd be, or how to make them. Does anybody have any tips?

sort by: active | newest | oldest
I do not think you need a catalyst to help speed up the combustion of methane with air.  That should be a reaction that is pretty fast already, and I would expect a carburated internal combustion engine (ICE) to run well on a mix of methane and air.

I mean that's using real methane.  I don't know what gasses come off from a compost digester.  It might be methane, and co2, and air, and water vapor, and who knows what?  I am guessing your real problem is going to be separating the good gasses (i.e. those that will burn, like methane, hydrogen, hydrogen sulfide?) from the junk that is not going to burn easily ( like co2 and water vapor)

Anyway, going back to this catalyst idea, there are some obvious questions, like:  Where is the catalyst located?  Is it inside the cylinder? That might make sense, since that's where the combustion reaction happens. 

Or were you thinking of some sort of reactor-converter located upstream of the engine, and in that case,  what reaction are you thinking will happen there?  Methane and air and stuff go in.  Then a reaction happens.   Then what comes out to feed into the engine?  Some gasses that will burn better, right?

Going back the idea of catalyst inside the cylinders.  Is it a homogenous catalyst (i.e a gas, same phase as the reactants)? Or is it a heterogeneous catalyst (like a solid surface painted to the cylinder walls, or attached to some other solid support)?

In a cylinder in an engine, gasses blow in, and also blow out. So you cannot have a gas phase catalyst inside a cylinder, or else it just blows out with the exhaust gasses. I think that leaves heterogeneous, solid catalyst, inside the cylinder, somehow...

Unless of course what you're using is not a true catalyst...  For combustion reactions there is this related thing, not a catalyst, but something else called an "accelerant".  That is a chemical that can speed up a combustion reaction, but that gets consumed in the process. 

For example there is a trick called "hydrogen boosting",
and that is pretty much just what it sounds like; i.e mixing some significant amount of hydrogen in with the fuel-air mixture for to make it burn better. 

The usual analogy used to explain hydrogen boosting is adding hydrogen to your fuel-air mix is like adding gasoline(petrol) to a pile of firewood.  It (the accelerant) quickly spreads itself through all the little nooks and crannies, then with just one little spark the whole thing goes FOOM!

That's the story. By the way, I have not actually tried any of this, mostly I have just read a lot about it.

But I mean if making engine fuel at home was easy... then everyone would be doing it, right?

Back to what I said at the beginning: I don't think you need a catalyst (or an accelerant either) for to improve the burning of methane with air.  You just need a good honest fuel air mix to start with.
DIY Emilio (author)  Jack A Lopez4 years ago
Thanks for the info. My idea (simple version) involves a light-duty compressor that is between two water-based flashback arrestors. They serve the dual purpose of preventing fires/explosions and scrubbing some of the waste and engine-unfriendly compounds. It'd then go through some dessicants to dry the gas out. After that, it'd be mixed with air for the engine. The burning is fine without the catalyst, so it's more of an efficiency/eco-friendly thing. I've forgotten the proper numbers, but the temperature has to be really high up to burn 100% of the methane, and a piston ICE can't take that amount of heat. As a consequence of the heat, there are also more bad byproducts. I heard about a new catalyst in an article that was supposed to take all of the methane in at a lower temperature: http://www.sciencedaily.com/releases/2012/08/120809141619.htm
I'm just wondering if there's some sort of chemical that I can use to improve my process a bit.
I mentioned the trick of mixing natural gas with hydrogen.  I have heard legends of buses for public transit that run on such mixtures, and in an attempt to confirm this legend I found some new acronyms:

HCNG (hydrogen compressed natural gas)

HENG (hydrogen enriched natural gas)

and I think HCNG and HENG are actually the same thing: natural gas mixed with some amount of hydrogen, usually something like 5% to 30% hydrogen, by heating value.

Also I found this,
A Review of Hydrogen-Natural Gas Blend Fuels in Internal Combustion Engines

So where do you get hydrogen from? Well if you actually have something resembling natural gas, you can steam reform it, into hydrogen and carbon monoxide. 

Although I wonder if this is worth the trouble. 

I read the article at ScienceDaily you linked to, and it seems to have a lot of the usual fearmongering about anthropogenic global warming.  Oh no! co2 is bad! The sky is falling! The sky is falling!

But seriously, if you can manage to make engine fuel from freaking compost (!), then your process is already very green.  In fact it's what they call "carbon neutral",
since the co2 emitted contains carbon that only recently left the atmosphere, and the net increase in atmospheric co2 is zero (compared to the heinous and unpardonable sin of burning fossil carbon).

Anyway, the steam reforming might be fun, if you can get that to work, and who knows? Maybe the added hydrogen will make your engine run more efficiently.  Although I think it would be impressive enough just to have an engine that runs.

DIY Emilio (author)  Jack A Lopez4 years ago
I've considered reforming, but it seems like it requires skills and resources that I don't have. I've already got some HHO generating stuff made, so I'll look into the HCNG/HENG stuff. Thanks for all of the help. I'm unfortunately incapable of building a fusion reactor, especially one that worked well enough to produce in the gigawatts of power. As for the lack of necessity, I've probably got OCD for efficiency. ;D
rickharris4 years ago
All cats will be expensive they contain plutonium and need yo run at high trmps
Is that what they used in Mr. Fusion?
I think Mr. Fusion runs on light elements, although I'm not totally sure which ones. This thinking is based on the conventional definition of nuclear fusion,
i.e. fusing light elements into heavier ones, and also that scene in the movie where Doc rummages through Marty's trash, and the nuclear fuel he chooses for Mr Fusion includes:
  • a banana peel
  • beer
  • an aluminum can (that formerly contained old beer)
See: http://backtothefuture.wikia.com/wiki/Mr._Fusion

Sort of the intriguing thing here is that if Mr Fusion is actually using elements as heavy as carbon and aluminum, then its inventors have somehow figured out a way to mimic stellar nucleosynthesis,
in an appliance small enough to fit on the kitchen counter.

And, you know, that'd be a neat trick.
For compactness, I assume that Mr. Fusion uses neutron-accelerated fusion to avoid the large magnets and pressure vessel. The plutonium is simply used as a neutron source :-)
...and since the plutonium is regenerated by a separate reaction, and thus it never needs to be replaced, its role in the Mr Fusion reactor is essentially catalytic.   That makes perfect sense. ;-)
I THINK you may mean "platinum" or "Palladium"......
Darn predictive text! At least the exhaust will be clean.... Oh, maybe not!

...happen'd to be plutonium in the flux capacitor,
And now I'm headed back to '55 with no passenger.
I wish that I packed myself a travel kit,
cause Doc was right!  I hit 88 and saw some serious...


Futuristic Sex Robots - Back to the Future
If you can smell it, it ain't methane.
DIY Emilio (author)  steveastrouk4 years ago
That's the hydrogen sulfide.
H2S burns actually, and over quite a wide range of concentrations. , If you smell too much of it ( VERY low doses) its poison BTW
DIY Emilio (author)  steveastrouk4 years ago
Yeah. I remember a story that some guy was telling when I was in a discussion about compost power. I don't know if it was BS, but he said that some little kids were playing in a really nasty smelling compost pile, and they died because of H2S inhalation. Could have been some sort of biological thing too. I don't think a pile of decaying material is a good substitute for a sandbox anyway. Thanks for telling any prospective compost gas makers a safety concern though. We're actually trying to work out a scrubber to try and minimize the release of H2S.
Industrially, you aren't allowed to linger in concentrations much above 10 PPM.