Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: peppercorn on 06/11/2009 13:06:02
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The question is aimed more specifically toward high temperatures application (450-700degC).
There have suggestions that aluminium could be reacted with water to release hydrogen gas for fuel cells, etc.
Clearly producing aluminium has a very high energy requirement & therefore this is not an efficient means.
My question is:
Giving the availability of higher temperatures are there metals with a lower energy cost that will cause hydrogen release in the presence of water?
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Aluminium by itself does not react with water, perhaps it is an aluminium-gallium alloy you are thinking of.. http://www.physorg.com/news98556080.html (http://www.physorg.com/news98556080.html)
Well to be technical aluminium will react with water, but aluminium will usually form a layer of aluminium oxide which prevents it from reacting with water.
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perhaps it is an aluminium-gallium alloy you are thinking of.
Thanks MS. Interesting article! Also, odd that this work is from a Electrical and Computer Engineering dept!
Now, how about other metals?
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Many metals will do this if they are hot- iron is an example.
However the general problem is that, whatever metal you use it would be more efficient to make the hydrogen directly than to produce the metal and make hydrogen from it.
Incidentally, hot aluminium reacts with water. Under the right conditions the reaction is dangerously fast.
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whatever metal you use it would be more efficient to make the hydrogen directly than to produce the metal and make hydrogen from it.
Thanks!
I am under no delusion that making the metal isn't going to use more energy than straight hydrogen.
But, just as it isn't practical to drive around with a coal-fired power station under the bonnet to run an electric vehicle, there might be a handy 'battery' solution for making hydrogen on-board for an IC engine.
Aluminium could provide such a battery, but by picking a less reactive metal that will nonetheless grab oxygen from water at higher temps, there might be a way to cut the energy needed for the charging cycle of such a 'battery'. The extra energy is found from the waste heat of the IC engine.
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Hydrogen is actually quite light to carry about- the problem is the damned great metal tank.
There are other ways of carrying hydrogen- yuo can convert it into ammonia as one way (though this clearly has problems too).
What's so great about H2 anyway- what about methanol?
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Methanol is not a bad fuel also (apart from its low kJ/Kg).
Thing is I'm not really looking for a fuel in the strictest sense. I'm looking to recuperate some of the lost exhaust heat and at the same time make lean-burn engines more flexible by increasing the flame-front speed.
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You could run a steam engine from the exhaust and run a generator from that to produce H2 electrolytically.
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You could run a steam engine from the exhaust and run a generator from that to produce H2 electrolytically.
Yes, but this sounds more complicated than heating up some metal & water.
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You can skip the hydrogen production and go straight to electricity.
http://www.exo.net/~pauld/activities/AlAirBattery/alairbattery.html
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You can skip the hydrogen production and go straight to electricity.
Cheers Geez!
Can't use me waste heat though...
I'm convinced it'll work - the ol' metal & water & heat thang!
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You can skip the hydrogen production and go straight to electricity.
Cheers Geez!
Can't use me waste heat though...
I'm convinced it'll work - the ol' metal & water & heat thang!
OK - see your point! I suppose some of the heat could be used to speed up the reaction of the AlAir battery, but it might not help much. I'm no chemist!
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OK - see your point! I suppose some of the heat could be used to speed up the reaction of the AlAir battery, but it might not help much. I'm no chemist!
Still, as always, I appreciate your thoughts, Geez! [;)]
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Zinc looks like a good contender...
Production of hydrogen from zinc in steam atmosphere (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V3F-4NSPVV0-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1104809567&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=11e78354139b496c8aa3784e8779a156)
and the recycling looks route looks promising also
http://www.greencarcongress.com/2005/06/solzinc_storing.html
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Are you totally dedicated to using a metal?
Carbon reacts with hot steam to produce H2 and CO both of which can be used as fuels.
Of course, this does use up carbon, but then so does that scheme for "recyling" zinc.
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Here's an interesting application for SynGas
http://www.sae.org/mags/TBE/7195
BTW, I suppose it's not so bad if the carbon comes from a rapidly renewable source.
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Are you totally dedicated to using a metal?
Carbon reacts with hot steam to produce H2 and CO both of which can be used as fuels.
Of course, this does use up carbon, but then so does that scheme for "recyling" zinc.
Not at all. It's just that metals appear to have high energy density - compared with carbon. Also part of my original idea was to accelerate the flame front in the cylinder for very weak petrol/air mixtures. I have also read somewhere that adding H2 makes improves the overall octane value, so higher compressions can be used.
Only being a lowly 'sparks' engineer my chemistry is a bit rough and I've no idea what a syngas mixture addition does under these circumstances.
Also I might try storing some of the gas (at only a couple of Bar) for gas-from-cold running. I believe that syngas has a compunction to re-combine in certain conditions (?).
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How about....
Manifold hydrogen generator units for automotive I. C. engines (http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6422710)
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That's Brill
oiant! [;D]
(Sorry - I could not resist it. Stay tuned!)
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Manifold hydrogen generator units for automotive I. C. engines
"The hydrogen is produced in a three stage process starting with the conversion of water to steam by means of multiple coils of copper tubing closely fitted to the exhaust manifold(s) of the I. C. engine. The steam is directed into one or two reactor cylinders containing rotating wire brushes axially disposed within the reactor cylinder(s) which remove a portion of the oxygen through progressive oxidation of the iron wire brushes. Periodic forced purging of the wire brushes is provided by combined aeration and vibrating of the rotating brushes. A final reforming stage of the partially reformed steam/hydrogen flow is obtained by steel wool packs which are periodically replaced."
Your opinions, please.
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Are you totally dedicated to using a metal?
Carbon reacts with hot steam to produce H2 and CO both of which can be used as fuels.
Of course, this does use up carbon, but then so does that scheme for "recyling" zinc.
How hot does the steam have to be to react with carbon? And does O2 need to be present (as with making town gas)? Also what ratio of the gases are likely?
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Using the hot exhaust to provide power via a turbine would be a better use, and use the leftover power to provide steam to add to the inlet. Google steam cycle for more info, although the steam has a bad tendency to cause cylinder bore wear.
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Using the hot exhaust to provide power via a turbine would be a better use, and use the leftover power to provide steam to add to the inlet. Google steam cycle for more info, although the steam has a bad tendency to cause cylinder bore wear.
Cars already recover power by gas turbines aka turbos.
Further, steam into the inlet manifold is going to decrease engine efficiency & power.
I'm not interested in steam directly. I'm interested in hydrogen enrichment (from water/metal reaction) of the fuel/air mix - so avoiding the electrolysis route (or other energy intensive methods) to H2.
It was suggested that syngas (produced from steam/carbon reaction) might offer similar advantages in allowing a fast lean-burn combustion.
Hence, I was asking those out there with a wider knowledge of chemistry:
How hot does the steam have to be to react with carbon? And does O2 need to be present (as with making town gas)? Also what ratio of the gases are likely?
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Hi,
I am studying Wate4Gas projects for Cars and need some advise, if any thing dangerous or technically missing,
Use of Stainless Steel 316L grade wire as electrodes, to be spiral not straight rods. As it is said that it creates magnetic field with this installation to better ionize electrolyte.
Use Baking Soda, Sodium Citrate or KOH and NaOH for electrolysis. I think with one of "OH" KOH/NaOH it should be better as KOH + HOH, K should not do extra reaction but ionize ??? (comments)
Use Inverter to convert Car's 12V DC to 120V AC.
Result is HOH also called Brown's gas.
It's added to Air intakes and Vacuum of engine, to burn with fuel.
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Hi fas17,
As I'm sure you're aware splitting water to release hydrogen & O2 is always going to use plenty more energy than can be recovered by using it in a heat engine. That said there is a wealth of rhetorical evidence that claims advantages for using small quantities of H2 as an additive to accelerate the flame front in the cylinder (especially for lean mixtures).
Having not looked into the electrolysis method in any depth I can't tell you what set-up is most effective. I think you might find some better info for this on
http://ecomodder.com/forum/
For my inquiries into onboard production & use of hydrogen in vehicles I am considering the following prerequisites:
- There is a large source of waste thermal energy emitted from an engine.
- chemical reactions that won't occur at lower temperatures, can be activated by using waste heat - so allowing a type of recuperation.
- large-scale 'recharging' of any type of 'battery' off a vehicle should generally be more efficient than on-board (another reason electrolysis for H2 is highly questionable). The 'battery' I am considering is iron or carbon.
- replacing the total petrochemical fuels with biomass or other renewable energy sources is likely to cause damage in many other ways.
- liquid fuels as the primary energy giver suit our current transport systems.
- current petrochemical extraction & processing is by no means a free energy path (from mine to tank).
- a sizeable proportion of combusted petrol will become water vapour (although acids will condense out too) & may be recirculated.
Taking these issues together I can't help wondering if, with rather a simple modification to the hardy piston engine, a reasonable increase in efficiency can't be realised.