Sciencemadness Discussion Board

Hydrogen from [bio]glycerine by electrolysis for fuel cells

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deltaH - 2-10-2013 at 00:32

This is another backyard open innovation project of mine, this time in sustainable energy.

As most you already know, one of the big challenges of working with/within a hydrogen economy and specifically running electric cars on hydrogen fuel cells, is how to store and transport the hydrogen.

My idea is for the onboard electrolysis of glycerine as it can be derived from renewable sources, for example, as a low cost byproduct of the biodiesel industry.

The straight forward reaction would be:

C3H8O3 + 3H2O + electricity => 3CO2 + 7H2

The hydrogen being generated at the cathode nice and pure.

BUT my idea takes this a step further... running the electrolysis like this would take a lot of energy because of the water on the left hand side of the equation, it's dGf is too low.

You want a more energetic source of oxygen that is also reactive and ideally can also contribute some hydrogen. I propose hydrogen peroxide as an excellent candidate since it is a 'green oxidant', so your new electrolysis becomes:

C3H8O3 + H2O2 + H2O + electricity => 3CO2 + 6H2

In fact you can create a new liquid fuel by preparing a solution of glycerine and the 'green oxidant' hydrogen peroxide. I think with the proper understanding and precautions, this is safe enough. I call such a mixture 'syrup of hydrogen' for fun :)

This equation would be the low temperature equivalent of what occurs with the high temperature steam reforming of hydrocarbons. In that case you would add a little oxygen to make the thermodynamics of the reaction more favorable.

You can read more about this on the open innovation site:
http://ideashack.org/category/energy/biofuel-hydrogen/

[Edited on 2-10-2013 by deltaH]

papaya - 2-10-2013 at 02:55

Quote: Originally posted by deltaH  

As most you already know, one of the big challenges of working with/within a hydrogen economy and specifically running electric cars on hydrogen fuel cells, is how to store and transport the hydrogen.
[Edited on 2-10-2013 by deltaH]


I've seen hydrogen tanks (looks like other gas tanks from appearance) myself which are used in undustry, so what is the problem?
Also why electrolyze glycerol instead of water?

deltaH - 2-10-2013 at 03:17

Hi Papaya

Quote:
I've seen hydrogen tanks (looks like other gas tanks from appearance) myself which are used in undustry, so what is the problem?
Also why electrolyze glycerol instead of water?

The problem as I explained here is that while hydrogen has a very high heat of combustion on a mass basis, it has a very poor heat of combustion on a volume basis... this is just another way of saying that compared to hydrocarbons, for example, it's a poor fuel because you need larger tanks to get the same job done... MUCH MUCH larger tanks.

In fact, even liquid hydrogen is an inferior fuel on a volume basis compared to hydrocarbons! (see above link) The only reason it's used in rockets for example is because there being light is of paramount importance to specific impulse!

In fact, as fuels go, one is hard pressed to beat hydrocarbons on energy density arguments alone, BUT the problem is that they are [generally] fossil fuel derived and thus generally not sustainable.

Also, hydrocarbons, as chemists know, are pretty inert at low temperature, so it's very hard to access their hydrogen content under mild conditions.

As for water electrolysis, this can't be used for on board hydrogen generation say in a car, because you have only the electricity being produced by the fuel cell available and that reacts hydrogen with oxygen to make water so what you would be proposing is a perpetual motion type system (not that I suggest this would be what you were thinking).

The difference with using a fuel instead of water is that now you can split off the hydrogen with much much less energy, so overall the system runs fine using that hydrogen to make water.

Some fuels like anhydrous ammonia stored in a tank as a liquid can also be electrolysed to produce a lot of hydrogen, BUT they in turn need a lot of electricity to do so, so it's not as good if you consider the entire system, however attractive on carbon arguments as your system would only be forming nitrogen and water vapours out of the exhaust... no CO2.

Glycerine with H2O2 and H2O is a compromise between chemical reactivity (how easy it is in terms of chemical kinetics to get access to the hydrogen at low temperature) and hydrogen generation capacity, while also being a sustainable fuel.

Hope that answers your questions?

[Edited on 2-10-2013 by deltaH]

kmno4 - 2-10-2013 at 03:23

Quote: Originally posted by deltaH  

As most you already know, one of the big challenges of working with/within a hydrogen economy and specifically running electric cars on hydrogen fuel cells, is how to store and transport the hydrogen.

My idea is for the onboard electrolysis of glycerine as it can be derived from renewable sources, for example, as a low cost byproduct of the biodiesel industry.

This is the most stupid idea I have read/heard recently.
No comment.

deltaH - 2-10-2013 at 03:27

Hi kmno4

Quote:
This is the most stupid idea I have read/heard recently.
No comment.

Care to share why?

papaya - 2-10-2013 at 04:11

Yes, thanks, but it worth to invest time in the development of new fuel cells that could use glycerol/whatever directly, as the cycle you proposed uses only H2 -H2O energy and C is just lost to CO2 during electrolysis (if I understand correctly), must be it's inferior to internal combustion engines fueled with the same glycerol (not an expert here).

deltaH - 2-10-2013 at 04:38

Quote:
Yes, thanks, but it worth to invest time in the development of new fuel cells that could use glycerol/whatever directly, as the cycle you proposed uses only H2 -H2O energy and C is just lost to CO2 during electrolysis (if I understand correctly), must be it's inferior to internal combustion engines fueled with the same glycerol (not an expert here).

Direct fuel cells may indeed someday offer better solutions if we can get them to perform better (currently they don't work nearly as well as hydrogen fuel cells).

On your second point, in theory a fuel cell should be able to operate at greater efficiency because of the lower temperature (if properly designed/functioning) on thermodynamic arguments alone. But at lower temperature comes chemical kinetic problems, hence the need to switch over to functionalised molecules. I am simply borrowing from nature here. Nature meets it's quick energy needs by using sugars. Sugars molecules are mostly a polyol, so hence I use the simplest cheapest liquid equivalent... glycerine (and some hydrogen peroxide as additional oxygen and hydrogen source).

It's a trade off / balance between reactivity and energy capacity and I think this beats many other technologies currently being considered.

Traveller - 2-10-2013 at 07:46

If you have enough onboard electricity to produce hydrogen through electrolysis, wouldn't it be somewhat (Canadian understatement for A WHOLE FRIGGIN' LOT!) more efficient to eliminate the electrolysis and apply the electrical current directly to the electrical motor that drives the wheels?

Or do you have some kind of brain wave like mounting a windmill atop the car to capture energy from the wind generated by driving down the road?

Metacelsus - 2-10-2013 at 07:57

Yes, just using an electric motor would be much more sensible.

Quote: Originally posted by Traveller  

a windmill atop the car to capture energy from the wind generated by driving down the road?


Assuming there is already a strong wind, mounting a windmill on top of a car is not a crazy idea, but using it when there is no pre-existing wind is (except maybe for regenerative braking?).

DeadHead - 2-10-2013 at 08:26

Even then an electric engine that would brake the car and run as a generator while applying brakes would be much more efficient than a windmill I would think.

Nicodem - 2-10-2013 at 09:07

Quote: Originally posted by deltaH  
Hi kmno4

Quote:
This is the most stupid idea I have read/heard recently.
No comment.

Care to share why?

I don't know, if the question was serious or not, but this must be one of the most entertaining posts on the forum. Nevertheless, facepalm threads like this one make the life of a moderator difficult: To detritus or not to detritus, that is the question.

http://www.youtube.com/watch?feature=player_embedded&v=v...

deltaH - 2-10-2013 at 09:44

Hi Traveler,

Quote:
If you have enough onboard electricity to produce hydrogen through electrolysis, wouldn't it be somewhat (Canadian understatement for A WHOLE FRIGGIN' LOT!) more efficient to eliminate the electrolysis and apply the electrical current directly to the electrical motor that drives the wheels?

Or do you have some kind of brain wave like mounting a windmill atop the car to capture energy from the wind generated by driving down the road?

I think when one hears the word electrolysis, we automatically think super energy drain, because we are all used to water electrolysis and that is about as energy intensive a process one may get. BUT that's because at the anode, during water electrolysis, you have to oxidise water to free oxygen. NOW put something there that wants to be oxidised, like a good fuel... like glycerine in this case, now THAT half reaction becomes considerably easier. Add a little peroxide there as well and you 'fix' the dG of reaction and can get it pretty close to zero.
So now the energy requirement to run the electrolysis is only a fraction of what the fuel cells puts out from the hydrogen that is generated by this.

Draw a big black box over the entire system and what you have is a car taking in a liquid fuel (glycerine+peroxide) and air and putting out water vapour and CO2. There's nothing fishy here, you have just broken an internal step into two because each one is easier to optimise and get working well with existing tech.

The reason we do this as opposed to a direct fuel cell running on this fuel is because alcohol based fuel cells don't as yet work very well. So we break the system into two internal halves that do work very well, a hydrogen fuel cell which works great and organic electrolysis on a reactive fuel system which should also work pretty great to generate the hydrogen at minimal energy cost (compared to what the fuel cells can put out).

One might ask, why do electrolysis and not a direct reaction? After all, this is the low temperature equivalent of steam reforming?

In principle, yes, there might be a catalyst that will work nicely for this reaction, but I like electrolysis better because it's simpler, robust and generates a pure hydrogen stream, i.e. I don't need to separate it out from a mixture of CO2 (or if in a reactor, likely small amounts of CO as well).

If I told you, build this at home, you are probably going to choose to do it by electrolysis rather than a complex reactor- separation beast no? I certainly also think an electrolysis system will be cheaper and easier to control.

I hope that shed's some light on the matter.

deltaH - 2-10-2013 at 09:50

Hi again Nicodem,

Quote:
To detritus or not to detritus, that is the question.

If you believe my idea is flawed, kindly prove it by logical argument on the forum.

[Edited on 2-10-2013 by deltaH]

Traveller - 2-10-2013 at 10:19

Quote: Originally posted by Cheddite Cheese  
Yes, just using an electric motor would be much more sensible.

Quote: Originally posted by Traveller  

a windmill atop the car to capture energy from the wind generated by driving down the road?


Assuming there is already a strong wind, mounting a windmill on top of a car is not a crazy idea, but using it when there is no pre-existing wind is (except maybe for regenerative braking?).


Uh, I was joking?? Don't you think a windmill mounted atop a car would sacrifice ten times more energy in DRAG than it could ever produce in electricity?

Traveller - 2-10-2013 at 10:23

Quote: Originally posted by deltaH  
Hi Traveler,

Quote:
If you have enough onboard electricity to produce hydrogen through electrolysis, wouldn't it be somewhat (Canadian understatement for A WHOLE FRIGGIN' LOT!) more efficient to eliminate the electrolysis and apply the electrical current directly to the electrical motor that drives the wheels?

Or do you have some kind of brain wave like mounting a windmill atop the car to capture energy from the wind generated by driving down the road?

I think when one hears the word electrolysis, we automatically think super energy drain, because we are all used to water electrolysis and that is about as energy intensive a process one may get. BUT that's because at the anode, during water electrolysis, you have to oxidise water to free oxygen. NOW put something there that wants to be oxidised, like a good fuel... like glycerine in this case, now THAT half reaction becomes considerably easier. Add a little peroxide there as well and you 'fix' the dG of reaction and can get it pretty close to zero.
So now the energy requirement to run the electrolysis is only a fraction of what the fuel cells puts out from the hydrogen that is generated by this.

Draw a big black box over the entire system and what you have is a car taking in a liquid fuel (glycerine+peroxide) and air and putting out water vapour and CO2. There's nothing fishy here, you have just broken an internal step into two because each one is easier to optimise and get working well with existing tech.

The reason we do this as opposed to a direct fuel cell running on this fuel is because alcohol based fuel cells don't as yet work very well. So we break the system into two internal halves that do work very well, a hydrogen fuel cell which works great and organic electrolysis on a reactive fuel system which should also work pretty great to generate the hydrogen at minimal energy cost (compared to what the fuel cells can put out).

One might ask, why do electrolysis and not a direct reaction? After all, this is the low temperature equivalent of steam reforming?

In principle, yes, there might be a catalyst that will work nicely for this reaction, but I like electrolysis better because it's simpler, robust and generates a pure hydrogen stream, i.e. I don't need to separate it out from a mixture of CO2 (or if in a reactor, likely small amounts of CO as well).

If I told you, build this at home, you are probably going to choose to do it by electrolysis rather than a complex reactor- separation beast no? I certainly also think an electrolysis system will be cheaper and easier to control.

I hope that shed's some light on the matter.


If you think you have a way to break a liquid fuel down to recover hydrogen, for your fuel cell, that will take only a fraction of the energy to make hydrogen out of the total energy available from that hydrogen, I suggest you get to the patent office post haste.

And then find a good place to hide. You will have solved the world's energy problems but, the big oil companies will have someone shoot you.

deltaH - 2-10-2013 at 10:31

Quote:
If you think you have a way to break a liquid fuel down to recover hydrogen, for your fuel cell, that will take only a fraction of the energy to make hydrogen out of the total energy available from that hydrogen, I suggest you get to the patent office post haste.

And then find a good place to hide. You will have solved the world's energy problems but, the big oil companies will have someone shoot you.

Guys, breaking fuel down to make hydrogen is done routinely in the chemical industry, this is called steam reforming. You can also make hydrogen from coal and water, this is called gasification. There's no voodoo here.
The only difference is finding a way to act on more reactive fuels so that you can do this at lower temperatures as opposed to what is required to do this with hydrocarbons or coal.

As for patenting, I have purposefully decided to release this tech into the public domain so it's free for all. My reasons for this are complex and I don't really want to go into that.

papaya - 2-10-2013 at 10:58

OK, how you render glycerol conductive ?

deltaH - 2-10-2013 at 11:10

Okay maybe we're jumping the gun here, lets take a big step back and consider a simpler example to get the principle across.

Consider formic acid, from wikipedia's table of standard electrode potentials, one can pull the following half reactions:

CO2(g) + 2 H+ + 2 e- <=> HCOOH(aq) E(std.) = −0.11V
and
2 H+ + 2 e− <=> H2(g) E(std.) = 0V

So for the overall reaction:

HCOOH(aq) => CO2(g) + H2(g) the dE = +0.11V

This is pretty close to 0V.

Now if you electrolyse formic acid, you can make quiet a lot of hydrogen pretty easily because that dE is close to zero. In reality, you have quite a overpotential if you don't use a suitable electrocatalytic anode (platinum black anode would probably work well but who has that lying around?

In reality, formic acid is not that great a fuel because you can only generate 4.4% hydrogen by mass and it's also freaking corrosive and smelly, so you don't want to be tanking that.

Glycerine with a the added peroxide has about 8% the hydrogen generating potential by mass. This is excellent as such systems go. Why so much higher? Because glycerine is more reduced than formic acid... you get more hydrogen capacity because of that, but you loose some reactivity (it's harder to free those hydrogen with glycerine) hence the need for the peroxide.

BTW make hydrogen from formic acid IS one of the technologies being HEAVILY studied for make hydrogen to power fuel cells, but I don't like it as much as mine, for one, because it's capacity is much lower and also because it's corrosive and extremely acrid!

watson.fawkes - 2-10-2013 at 11:16

Quote: Originally posted by deltaH  
If you believe my idea is flawed, kindly prove it by logical argument on the forum.
He's got no obligation to do that. Posting crappy information and expecting others to correct it is one of the oldest methods of trolling on the internet. It comes from an expectation that others will educate you. For example: "I've got perpetual motion! Prove me wrong!"

I've already stopped responding to you for this reason. I've got no time for someone who, when steered in the right direction, doesn't go off and do some work before asking another question.

deltaH - 2-10-2013 at 11:19

Quote:
OK, how you render glycerol conductive ?

I take it you mean ion conductive? The medium I'm proposing to carry out the electrolysis in is fairly concentrated sulfuric acid, probably starting around 70% or so (remainder being water). This solution would sit between the electrodes. One would then feed the glycerine/peroxide fuel slowly (dropwise) to this solution, probably in a stirred pot before it.

You would need to control the rate of adding the fuel to the rate at which gas is being evolved, but I would think this can be done by monitoring the solutions conductivity. When it goes down too much, slow down the feed of fuel.

Anyhow, a 70% H2SO4 solution comprises mostly of HSO4- and H3O+, thus it's darn ionically conductive.

When the fuel hits it, the glycerine would probably be converted to glyceryl sulfuric acid ester anions (migrating to the anode) and the peroxide would quickly form persulfuric acid anions also being drawn to the anode. There both would participate in a series of oxidation steps, ultimately yielding CO2. The H+ generated migrates to the cathode and is reduced to H2(g)

[Edited on 2-10-2013 by deltaH]

blogfast25 - 2-10-2013 at 12:26

Quote: Originally posted by deltaH  
So now the energy requirement to run the electrolysis is only a fraction of what the fuel cells puts out from the hydrogen that is generated by this.



That smacks decidedly of creation ex nihilo of energy. And thus impossible.

The information (if it proves to be worthy of that term) you're putting out here is decidedly bitty. You're going to have to do a lot better that this to get any serious attention.

Have you even remotely tried to electrolyse glycerol based conductive solutions, to see what you get? Add any magic powder you fancy, then get back us with your results.


[Edited on 2-10-2013 by blogfast25]

elementcollector1 - 2-10-2013 at 14:18

Quote: Originally posted by deltaH  
Quote:
OK, how you render glycerol conductive ?

I take it you mean ion conductive? The medium I'm proposing to carry out the electrolysis in is fairly concentrated sulfuric acid, probably starting around 70% or so (remainder being water). This solution would sit between the electrodes. One would then feed the glycerine/peroxide fuel slowly (dropwise) to this solution, probably in a stirred pot before it.
[Edited on 2-10-2013 by deltaH]


I see a major problem here.
If you use a 70% solution of H2SO4 with the balance being water, it's very true that the solution will now be very conductive. But now, the electrode potential will be much higher because - you guessed it! You are now electrolyzing sulfuric acid and water. So, any glycerine added will be both an insignificant source of hydrogen and an insignificant reactant to this mixture at the concentrations you're proposing.

You might want to read this - it might clear some things up. http://pubs.acs.org/doi/abs/10.1021/ie9016418

bfesser - 2-10-2013 at 14:56

Quote: Originally posted by Nicodem  
Nevertheless, facepalm threads like this one make the life of a moderator difficult: To detritus or not to detritus, that is the question.
Here, let me help you with that. [closed]

cut-off

Endimion17 - 2-10-2013 at 15:06

damn it, bfesser, I wrote a cold, rational smackdown of that water fueled car and you close the thread right in front my nose.

bfesser - 2-10-2013 at 15:12

Post it here and I'll split/merge it.

Endimion17 - 2-10-2013 at 16:04

Well if the moment has not passed, then it's ok, I guess. :)

I wrote:
"The moment I've read "onboard electrolysis" I knew this is doomed. It's the basic flaw I saw... around twenty times so far, on various places online.
Electrolysis consumes more energy than its products can yield when they recombine. That is the law and nobody can break it because that's how nature works.

Inserting electrolytical cell in the car is in fact widening the chain of energy transformations and thus creates more opportunity for wasting it. This is a huge waste of energy because electrolysis of water is a very consuming process.
If you're extracting energy from the gasoline+oxygen reaction in your car, you might as well use it directly to power your wheels and electric components. Why inserting anything more? To waste more gasoline? Because it will be wasted.

The only idea that could be feasible is the idea that hydrogen and oxygen might increase the efficiency of burning gasoline, but not only that doesn't happen (and yes, commercial exhaust gas detectors tend to derp and give false readings when people try that), but it would have to be a huge improvement of the efficiency to cover up for the huge waste in the first place.


Basically, when you strip this idea naked, you get a water fueled car, a known hoax. No amount of decorative bits can save it. It's wrong in its essence."


It's nothing I haven't said before. I'm actually surprised by the will of some people to go so far with these things, but in the same time ignore the basics.

Ammonia electrolysis

deltaH - 2-10-2013 at 22:44

Firstly, before I commence with this new thread, let me state for the record that I was very sad to see that my previous thread for the generation of hydrogen from glycerine electrolysis to power fuel cells shut down because moderators seem to believe I was proposing pseudo science... I'm going to resist the urge to lash out at them :)

Instead and in defense, I will now go down a more rigorous scientific approach and start with known science and work my way up back to where we previously left off and hopefully the powers that be will realize their error and merge the threads and reopen the previous one.

I'll start with research into the electrolysis of ammonia to generate hydrogen.

There is a ton of literature on this, but one research group specifically has done excellent work on the topic, namely Dr Botte of Ohio university, so for brevity I will refer readers to their site for their literature needs on this topic:

See http://www.ohio.edu/ceer/research/ammonia.cfm

Incidentally, it was their work that got me thinking about the topic in the first place.

Basically, the idea is quite simple. You electrolyse a solution of ammonia in strongly basic media. At the anode you oxidise the ammonia to form nitrogen gas, at the cathode you reduce water to form hydrogen. The half reactions are:

2NH3 + 6OH- -------> N2 + 6H2O + 6e-
2H2O + 2e- -------> H2 + 6OH-

The balanced net reaction is quite simple 2NH3 => N2 + 3H2

The theoretical standard potential of this process is 0.058V... practically very close to 0V (this is quoted from them, so don't argue with me about it).

In reality, you have a whole bunch of overpotentials creeping in that makes this far less efficient. The main challenge comes in reducing the activation energy overpotential at the anode, which is just a fancy way of saying you need a catalyst there to help ammonia dissociate into nitrogen and hydrogen, particularly when you are running this process at high rates. That way you don't end up wasting too much energy by heat production and you can come as close as possible to the minimum thermodynamic energy requirement for such a process of 1.55 W-h per gram of H2 produced (I assume they are referring to a minimum on their website where I get this number from).

This might seem quite good, it isn't really, why? Because ammonia isn't a particularly good fuel on energy density arguments compared to organic molecules. But it does have the up side of running very cleanly, producing only nitrogen gas as the co-product, i.e. no CO2 as the electrolytic oxidation of an organic molecule might.

But what people forget is where does the ammonia come from?

The best you can do is use the Haber process and surprise surprise, that needs hydrogen!

Unfortunately, most ammonia plants today use hydrogen derived from either coal gasification or steam reforming (fossil fuel hydrogen sources... not sustainable!). However, there's off course nothing preventing one from deriving it from more sustainable resources such as biomass gasification or steam reforming of natural gas derived from sewerage or biomass.

Anyhow, I trust people will agree there's no pseudo science in deriving hydrogen from ammonia by electrolysis and can accept those published numbers for starters?

Thanks

[Edited on 3-10-2013 by deltaH]

woelen - 2-10-2013 at 23:49

Ammonia resists oxidation amazingly well. I once was curious about what would happen if I electrolyse ammonia with some NaOH to make the solution conductive. The result is simple: hydrogen at the cathode, oxygen at the anode in a 2 : 1 volume ratio (the mix made a nice detonating gas). The ammonia was not (or hardly not) oxidized. I also needed severals volts before a decent current flowed through the cell. I used a metal cathode and a graphite anode.

Of course, this is not a proof of you being completely wrong, but it at least gives evidence that it is not easy at all to reduce the required potential to perform some electrolysis. Some compounds require a lot of activation energy to have them reacted and in the case of electrolysis this means that you lose a lot of energy in the form of heat.

deltaH - 3-10-2013 at 00:25

Hi Woelen,

Thank you for your civility. Yes the point is that graphite has the maximum overpotential possible and is probably completely electrocatalytically inactive for this system. The nitrogen hydrogen covalent bond is very hard to break without the right catalyst.

In fact, to emphasise this point, consider the reverse process, making ammonia from nitrogen and hydrogen is also extremely hard to accomplish without a catalyst!

While the researchers of Dr Botte's team propose their own electrocatalysts for this system, I would hazard that a simple platinum plated anode should give reasonable results at low current density, as platinum is very active for ammonia dissociation.

However, again let me emphasise that a simple platinum plated anode would only work well at low current because the surface area of a simple platinum coating is not high. If you want to operate at very high rates and current, you need to disperse the platinum on the anode, or even better and go the whole nine yards with the anodes proposed by the researches at Ohio.




[Edited on 3-10-2013 by deltaH]

deltaH - 3-10-2013 at 01:11

I think this brings us to an interesting junction that would bear merit to discuss. The propensity to get confused between thermodynamic arguments and chemical kinetic arguments.

Let consider two systems for example:

1. Water electrolysis under alkaline conditions.
2. Ammonia electrolysis under alkaline conditions.

This systems are similar on face value, but the standard cell potential for the water electrolysis is much higher than the ammonia one, compare for case 1: Ecell std. = -1.2V and for case 2: Ecell std. = 0.058V from the Ohio university website.

This means that it is thermodynamically much easier to electrolyse ammonia than water.

Now comes in the second part of to any chemistry story, chemical kinetics!

The nitrogen hydrogen bond needs to be dissociated in any mechanism that would oxidise ammonia on the surface of an anode. This would occur as a series of what in chemical kinetics is called elementary reaction steps.

for example, starting with NH3 => NH2* + H*
the star's simply denoting that this is a surface adsorbed species on the anode, not some radical, but bonded to the surface, usually as a surface hydride specie if a metal anode is used, for example.

After this point a whole bunch of things can happen but the point is it goes via simple steps that have an activation energy barrier to overcome.

The larger the activation energy barrier (the poorer you electrocatalyst) the larger the overpotential becomes and the lower you efficiency of electrolysis. There are other mechanism that lead to yet other types of overpotentials, but the activation energy overpotential is usually the most serious one that needs to be addressed when starting out.

Now back to the case of ammonia, since catalysts cannot alter chemical thermodynamics, only chemical kinetics, something that is catalytically a good catalyst for the forward reaction is by definition also a good catalyst for the reverse. So since we all know that platinum is a very active catalyst for the ammonia synthesis in the Haber process, it should work just as well in catalysing the split of ammonia into hydrogen and nitrogen by electrolysis, albeit it would be expensive!

Incidentally, I was told by the person who taught me catalysis that Haber, understanding this principle, screened materials as potential catalyst for his process not by trying to make ammonia with them (which required very high pressure), but in fact simply by trying to decompose ammonia back to nitrogen and hydrogen by applying heat at ambient pressures (much easier to carry out experimentally). He found that platinum was most active in ammonia decomposition, so therefor was also a good catalyst when he shifted conditions to favour a ammonia product in the chemical equilibrium by applying very high pressures.



Bezaleel - 3-10-2013 at 02:09

And do you have the list of catalysts haber tried before deciding for platinum? Maybe lead dioxide might be a cadidate as well. If it is only a little less effective, you might be a whole lot cheaper off.

deltaH - 3-10-2013 at 02:30

Hi Bezaleel,

I'm afraid I do have a list of what else Haber considered, though I know that modern ammonia synthesis catalysts use promoted iron. That said, I believe that ruthenium is king... a metal close to my heart as I worked on ruthenium catalysts during my PhD research.

I also know that pool chlorinator anodes are [usually] made of a ruthenium MMO coated titanium as this has the lowest activation over potentials for chlorine oxidation. So if one wants to experiment with ammonia electrolysis at home, maybe this is the way to go... sure beats having to work with platinum! :)

I don't know how stable the RuO2 on those chlorinator MMO electrodes may be in a caustic environment, I would suspect there is a very high chance that it would be oxidised to ruthenates and leach off.

So your choices are platinum (difficult but maybe best?) or RuO2 MMO from a pool chlorinator, easier but will probably leach out?

Talk about being between a rock and a hard place!

[Edited on 3-10-2013 by deltaH]

deltaH - 3-10-2013 at 02:56

Ha ha, just took a look at those Ohio guys' catalyst, turns out it is a tri-alloy of platinum, ruthenium and nickel...

No surprises there :)

Here's the link for lazy people like me:

https://www.google.com/patents/US7485211?dq=7485211&hl=e...

kmno4 - 3-10-2013 at 03:03

I do not understand - what do you want to discuss about ?
Did you bother to read (at least) literature (by Dr.Bottle) cited on your first post (ohio.edu link) ?

Varmint - 3-10-2013 at 03:05

The fact that hydrogen is needed to create ammonia is the singular most important thing to embrace.

The OP states hydrogen is currently derived from non-renewable energy sources is a point of interest certainly, but then goes on to assume it could be obtained using other methods. Either way, you start with hydrogen.

Frankly, all discussion should stop right there. If you have hydrogen, there is no real value in using it to create ammonia, only to disassociate that ammonia at a later time to recover the target hydrogen.

There might be some arguement that could be formed over safe storage or transportation where ammonia seems like a suitable "container" for hydrogen, but the bottom line is ANY process past the point of having hydrogen available to create ammonia begins a chain of losses.

Instead of hydrogen, the key thing to be researched is virgin sources of ammonia.

If you can't find a means of collecting or synthesizing raw stock ammonia, then no matter how efficient you can make the ammonia --> hydrogen process you are operating under the substantial losses required to create ammonia from HYDROGEN SOURCES.

The key is energy efficiency, start to finish. If you create an advanced fuel pellet that outgasses virtually unlimited supplies of hydrogen on demand, but it takes all of the available output from a typical nuclear electricity generating station for a year to create one pellet, you have created a scientific curiousity that has no practical application.

I suspect the original post was deleted for good reason, there is no compelling reason to discuss hydrogen synthesis from ammonia, when ammonia itself requires hydrogen for its synthesis.

Why is this not obvious?

DAS

deltaH - 3-10-2013 at 03:27

Hi Varmint

Thanks for your raising your points in a civil manner, though I beg to differ/expand thus:

Quote:
Frankly, all discussion should stop right there. If you have hydrogen, there is no real value in using it to create ammonia, only to disassociate that ammonia at a later time to recover the target hydrogen.

I also hold that ammonia isn't that great for this purpose, I proposed using glycerine in the thread that was closed because you can [indirectly] 'grow' glycerine, you can't 'grow' ammonia. My point here is that this isn't pseudoscience, you CAN generate hydrogen from fuels fairly easily by electrolysis and I was simply referencing the well researched topic of ammonia electrolysis as a case study.
However, that said, there is a BIG necessity to generate hydrogen for fuel cells on board, its an active topic of research for many scientists and inventors such as myself. This because you can only 'tank up' with comparatively little hydrogen in a car with existing technologies.

Quote:
Frankly, all discussion should stop right there. If you have hydrogen, there is no real value in using it to create ammonia, only to disassociate that ammonia at a later time to recover the target hydrogen.

In the chemical industry, converting a low density gas into something more dense for the sake of transport is routine! This is usually done by liquefaction, but liquefaction isn't very practical in the case of hydrogen, nor would you achieve nearly the same energy density as hydrocarbon fuels would even if you did.
Quote:
There might be some arguement that could be formed over safe storage or transportation where ammonia seems like a suitable "container" for hydrogen, but the bottom line is ANY process past the point of having hydrogen available to create ammonia begins a chain of losses.

Indeed, which is why I proposed glycerine in the first place on the thread that was closed.
Quote:
I suspect the original post was deleted for good reason, there is no compelling reason to discuss hydrogen synthesis from ammonia, when ammonia itself requires hydrogen for its synthesis.

It hasn't been deleted, it's been locked, so you're free to read it. I would suggest you read it before passing judgement. The post is called 'Hydrogen from [bio]glycerine by electrolysis for fuel cells' and it's just below this one in this forum.

Hope that clarifies why this is not obvious and thanks for reasoning and not just making inflammatory remarks.

Believe me I appreciate it!



Varmint - 3-10-2013 at 05:03

OK, I took a look at the other thread...

In situ electrolysis for automobiles?

Wow.

Interesting to note how you point out industry commonly uses liquifaction for transport, then go on to say it wouldn't really work here. Well, I already implied it wouldn't work here, I was giving you the opportunity to make a compelling case for the wasted energy for going from hydrogen ---> ammonia ---> hydrogen. Transport was a bone you could have picked up and run with, instead you chose to "educate" me.

In the other thread you discuss glycerin + H2O2 as a holy grail, but when challenged on making the combination conductive you easily flit off to discuss formic acid as an example of a conductive electrolyte, then you explain why formic acid presents problems. OK, now that we're back at glycerin/peroxide, where soes the conductivity to support electroyis come for?

Suddely the vision changes to having sulfuric acid as the electrolyte/catalyst, adding the "fuel" to be electrolysed "drop wise".

Aside from the obvious, it pays to consider the energy required to propel a vehicle down the road. 100HP = 74,5699 watts.

That's a lot of drops. That's a huge reaction, generating lots of heat which must be carried away, and presumably lots of H and O to combust. I can't begin to envision a reaction system capable of generating 10's or 100's of thousands of kilowatts that could handle being operated for minutes, let alone hours.

DAS


deltaH - 3-10-2013 at 05:20

Hi Varmint
Quote:
...instead you chose to "educate" me

My goodness, not at all, simple discussing.
Quote:
glycerin + H2O2 as a holy grail

Note at all, just a idea to be investigated / debated, instead most people just lobbed profanities, I try to engage with those who make / raise points, such as yourself
Quote:
but when challenged on making the combination conductive you easily flit off to discuss formic acid as an example of a conductive electrolyte, then you explain why formic acid presents problems.

No the formic acid post was an example to show (using data easily available on wiki's standard electrode potential table) how dE for the electrolysis of functionilised organic molecules is not that bad.

About the sulfuric acid, the thread was closed before I could respond (next day here in SA)
I def want to discuss that because it's a valid point, but I want to wait for the post to be reopened, this one is about ammonia electrolysis.

Quote:
Suddely the vision changes to having sulfuric acid as the electrolyte/catalyst, adding the "fuel" to be electrolysed "drop wise".

No that was always my vision, see the full details of that idea on my website as reference in that thread. It's just we got to the stage of starting to discuss that, then I got cut off.

As for the drop wise, that is only for test purposes and small scale operation, but again this discussion belongs there, not here.
Quote:
That's a huge reaction, generating lots of heat which must be carried away, and presumably lots of H and O to combust. I can't begin to envision a reaction system capable of generating 10's or 100's of thousands of kilowatts that could handle being operated for minutes, let alone hours.
Not so sure what you mean here, please clarify.

Sorry have to run now... but will respond later. Apologies!






Traveller - 3-10-2013 at 06:27

The scary thing is, someone will probably be foolish enough to give him a few million dollars in taxpayer money to continue his research.

Antiswat - 3-10-2013 at 07:50

Quote: Originally posted by woelen  
The result is simple: hydrogen at the cathode, oxygen at the anode in a 2 : 1 volume ratio (the mix made a nice detonating gas).


not trying to be too offtopic.. woelen if you ever considered it, stoichiometrical is not always the fastest of all, i recall 4000 m/s H2 + O2 in the ratio 75 + 25 STRAIGHT UP was the absolutely best ratio they could get, peaking at 4000 m/s

also, NH3 is made by N2 + 3H2 if im not entirely wrong, i dont see how you can make NH3 with hydrogen to make hydrogen..?
for efficiency i would say simple 316 steel with NaOH (aq) in which im trying to build a decent efficiency cell for a few gigs.. (=

deltaH - 3-10-2013 at 08:26

Quote:
also, NH3 is made by N2 + 3H2 if im not entirely wrong, i dont see how you can make NH3 with hydrogen to make hydrogen..?
I don't exactly understand your question, can you please rephrase it? Are you wondering why it's reversible?

deltaH - 3-10-2013 at 09:00

Sorry meant to also reply to this:

Quote:
for efficiency i would say simple 316 steel with NaOH (aq) in which im trying to build a decent efficiency cell for a few gigs.. (=
If you meant for the ammonia electrolysis, I doubt very much that it would have the necessary catalytic properties, you'd just end up with water electrolysis, but also highly inefficient at that.

You might have better luck with tracking down some special grades of titanium for the anode that contain small amounts of palladium, or ruthenium and nickel. I don't know if the amounts of PGM in them are enough to have a noticeable effect, but at worst you will have a longer lasting anode?

From the wikipedia article on titanium alloy I quote thus:

"Grade 7 contains 0.12 to 0.25% palladium. This grade is similar to Grade 2. The small quantity of palladium added gives it enhanced crevice corrosion resistance at low temperatures and high pH."

"Grade 11 contains 0.12 to 0.25% palladium. This grade has enhanced corrosion resistance."

"Grades 13, 14, and 15 all contain 0.5% nickel and 0.05% ruthenium."

If you track down a small sheet or tube of any of these, you might have an improved anode for electrocatalytic reasons.



deltaH - 3-10-2013 at 09:29

Out of interest, the spot price of ruthenium has dropped to some extreme lows of late, it's currently at $57/ounce. Pretty amazing as it was trading at over $840/ounce in 2007!!! Time to get your hands on ruthenium if you can... but good luck convincing Johnson Matthey to sell it to you!

I've always believed that ruthenium is WAY under rated for it's catalytic value and considering current prices compared to other PGMs...

blogfast25 - 3-10-2013 at 11:46

deltaH:

Can you answer a very simple question, please?

Is your purpose the onboard electrolysis of glycerol to CO2 and hydrogen with subsequent use of the generated hydrogen for the propulsion of the same vehicle?

deltaH - 3-10-2013 at 12:14

Quote:
Is your purpose the onboard electrolysis of glycerol to CO2 and hydrogen with subsequent use of the generated hydrogen for the propulsion of the same vehicle?
No, my purpose is electrolysis of glycerine + H2O2 + water to CO2 and hydrogen for propulsion of same vehicle where in a second step the hydrogen generated is oxidised to water using air in hydrogen fuel cells.

Nearly what you said, you omitted peroxide, this makes the difference between it potentially working and not. Sorry for having to say this, maybe you are not trying to catch me out, but I have to be exact with all the flack I'm taking on this.

Big black box around whole system (electrolysis + fuel cells) and overall equation becomes:

C3H8O3 + 3O2 + H2O2 => 3CO2 + 5H2O + Energy

deltaH - 3-10-2013 at 12:28

Guys it is very late here in SA and I need to sign off and go to sleep. Please I don't want to find tomorrow when I wake up, as I did this morning, that you post a bunch of challenge question but then close the thread without giving me a chance to respond... even worse, then accuse me the next thread that I avoided the challenge as was also posted today. So if I don't reply in the next few hours, I am SLEEPING.

The behaviour of some regular posters here has been poor in my opinion. PLEASE challenge me on my reasoning if you want to help me with this idea. If you don't simply don't, but all this nasty tone needs to stop (not saying you blogfast, nothing wrong with your question) and moderators please take care of that. I am trying my best to stay neutral and deal with points raised calmly, but my calm nerves can only take me so far.

I have raised this in the proper channels as I beleive is correct (u2u), hopefully people will consider. I am not angry with anyone, just tired of insults and want to continue doing what I love best, amateur science and innovation. Sigh.

blogfast25 - 3-10-2013 at 12:43

Quote: Originally posted by deltaH  
No, my purpose is electrolysis of glycerine + H2O2 + water to CO2 and hydrogen for propulsion of same vehicle where in a second step the hydrogen generated is oxidised to water using air in hydrogen fuel cells.

Nearly what you said, you omitted peroxide, this makes the difference between it potentially working and not. Sorry for having to say this, maybe you are not trying to catch me out, but I have to be exact with all the flack I'm taking on this.

Big black box around whole system (electrolysis + fuel cells) and overall equation becomes:

C3H8O3 + 3O2 + H2O2 => 3CO2 + 5H2O + Energy


I don’t think anyone here is trying to insult you. We’re deeply sceptical, as we SHOULD be.

My take on this is:

C3H8O3 + 3O2 + H2O2 + Energy1 => 3CO2 + 5H2O + Energy2

… with Energy1 > Energy2 (apart from the obvious problem of the electrolysis of glycerol to CO2 and H2)

No offense intended.

Sleep well (you’ll need it!)


[Edited on 3-10-2013 by blogfast25]

Traveller - 3-10-2013 at 16:25

Doesn't adding an oxidizer to glycerol just cause it to burn? I know this happens if you add potassium permanganate to glycerol.

bismuthate - 3-10-2013 at 16:38

depends on the concentration of H2O2

deltaH - 4-10-2013 at 00:05

Hi Blogfast,

Thanks for the consoling words, it helps and I understand, skepticism with reasoning is good! I want to have my idea picked apart, this might identify an important point/s going in to trying it out.

Parts of this is unchartered territory and I have doubts about certain aspects that I was hoping to get into a discussion about. This doubts might simple just remain until experimentation confirms or not, but sometimes someone might just point out something that's easy to see is a problem.

That said, the one thing I have very little doubt about is the overall thermodynamics, so lets get back to that for starters...

C3H8O3(l) + 3O2(g) + H2O2(l) => 3CO2(g) + 5H2O(g)

You can calculate a dG(reaction) for this overall equation. The answer is...

[(insert expletive here)... NIST chemistry web book site is closed on account of US gov shutdown... what a pain!

Ok, now I have to do it the long way and trawl for dHf and dSf anywhere else on the open literature...]

HOORAY, a paper online that had everything I needed and more (See attached).

NOTE though they made an error with their dGf CO2, so I recalculated dGf = dHf -T*dSf with T = 298.14K and correct dGf standard CO2 = -457kJ/mol)

Done... dGrx = -1663 kJ (per mole. C3H8O3 as per equation above)

OK, so the reason I've worked this out is because this is thermodynamically the maximum work that can be extracted from my system in the unlikely event of no other losses (see later points where I include these terms and consider the minimum work derivable).

Now, what I think some people are worried about is that inefficiencies will muck things up in the two internal steps.

BUT, this dGrxn must happen if you reacting those reagents overall.

that energy MUST be released in some way shape or form.

So dGrx = Work done (as generated electricity) + Heat generated (as losses)

My point is this can only be on the right hand side of the equation because dGrx < 0 and Heat losses can never exceed Work done as generated electricity or you will be claiming your reaction generated more heat than what is thermodynamically possible

Now that said, if you operate with your extreme best to maximise inefficiency, you will minimise the net electricity that can be generated by the system and maximise heat losses, but in reality this can only be some fraction of dGrx because this is thermodynamically the maximum energy change (in all forms that may be produced) that can occur!

Now, the best you can do in generating heat is to react those components directly with a heat sink at 25C.

This would be the dHrxn at 25C... I can work that out for you quickly, it's

dHrxn = -1532 kJ/mol (as per equation above on glycerine basis)

So Wmin = electricity min = dG(rxn) - dH(rxn) = -131kJ/mol

So you see, even if you extract absolutely the maximum heat thermodynamically possible from that reaction, your fuel cells minus electricity consumed by electrolysis will STILL have an electricity production of -131kJ/mol!

Why is this? Because electrochemistry can derive work from the entropic changes as well which a purely enthalpic change cannot (such as simple self heating).

Interestingly enough, I noticed that that published data had an error for dGf standard CO2 because when I first worked this out, dHrxn was larger than dGrxn and I knew that this is thermodynamically impossible which lead me to hunt for an error and I found it in the dGf of CO2!

Finally, that when considering the overall thermodynamics, this is path independent of what occurs internally! If you go from A to B, it doesn't matter thermodynamically overall if you went A to C to D then back to B. You still still consider overall change A to B as the net effect.

This is why it's easy to disprove free energy systems, for example in the case of some car claimed to be running on water:

The overall reaction is:

Water => Water

so dGrxn = 0
So maximum thermodynamic work derivable is when heat losses = 0 so dGrx = Work + heat losses =>>> dGrx = W =>>> W = 0 QED.

Nicodem, can you now understand why I was so insulted by your claims that I was proposing a free energy device?

Okay, that was a mouthful... sorry for the long text, but if we're going to do this properly, we need to do it properly lol

Blogfast25, are you happy with that bit now, can we close that portion off and move on to other technicality problems in this concept? If not then I can try and prove it from another angle, but please do state what you are unhappy with in my reasoning or I won't know where to start.

Thanks.





Attachment: thermodynamicdata.pdf (1004kB)
This file has been downloaded 1862 times



[Edited on 4-10-2013 by deltaH]

papaya - 4-10-2013 at 00:20

In computation you supposed that your reaction goes to completion, this may be not true in reality (thus lower yield of energy). And why would anyone mix glycerol with H2O2 if it's better to use separated cells in battery?

deltaH - 4-10-2013 at 00:32

Quote:
Doesn't adding an oxidizer to glycerol just cause it to burn? I know this happens if you add potassium permanganate to glycerol.
My worry too when I first thought about, so I tried it and the answer is no. As bismuthate pointed out, the amount is probably too little. That said, I was worried of partial oxidation, however, this appears slow in the absence of catalysts and dilution of peroxide. Remember the glycerine dilutes it as well!

As an aside, if I remember correctly, there may have been a very slight warming instantly upon mixing, but I believe that might be a simple heat of mixing because I was using pure glycerine (b.p. grade used on hair and bought from a pharmacy) and 50% H2O2 (200 volume) for swimming pools, presumably stabilized, but I was a bad scientist and didn't keep notes so I can't be sure of the warming, might just be confusing it with something else I may have mixed at the time! Lesson learned!

What is a worry is peroxide's self decomposition to oxygen and water, however, this is also slow and these days can be slowed to a crawl by the addition of small amounts of stabilisers and proper pH.

Anyhow, so long as you don't leave it in a closed container but use a vented one instead and use it within a reasonable time period (months?), then probably ok, but I don't know what the self partial oxidation (uncatalysed) would be over a long time, maybe not negligible.


deltaH - 4-10-2013 at 01:19

Quote:
In computation you supposed that your reaction goes to completion, this may be not true in reality (thus lower yield of energy). And why would anyone mix glycerol with H2O2 if it's better to use separated cells in battery?
Absolutely, if I cannot get glycerine to be oxidised fully to CO2, then it must decrease the amount of usable work I get overall. But this is just an inefficiency. Even a partial oxidation of glycerine is exothermic, it just wouldn't be good use of the fuel if I only partially oxidise it overall, but I will still get net work.

However, this is one of the reasons for using the hydrogen peroxide (strictly speaking on overall arguments it shouldn't be necessary).

Whether one oxidises the glycerine fully on the anode or not is a kinetic problem. The best you can do is employ a good electrocatalyst here to try and minimise barriers so that you don't have a large overpotential for complete oxidation. BUT there is one other thing you can do and I think this can really help, it's the peroxide. Normally on the anode you would be oxidising glycerine with water, this is energetically not favorable in intermediate steps but ok overall, when you get to making CO2 which really drives the whole thing home.

But now you have [some] peroxide instead of water, so you now are oxidising glycerine with peroxide and some water at the anode, this should be far easier to proceed on intermediate steps because of the low activation energy for peroxide as oxidant (compared to water).

What do you think?

deltaH - 4-10-2013 at 01:47

Quote:
And why would anyone mix glycerol with H2O2 if it's better to use separated cells in battery?
Appologies, but I want to specifically zero in on this point from another angle as well.

Consider steam reforming, say with methane and superheated steam, from wikipedia's article on it, I quote:

"At high temperatures (700 – 1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield carbon monoxide and hydrogen. These two reactions are reversible in nature.
CH4 + H2O ⇌ CO + 3 H2"

They then go on to say that you can use the water gas shift reactions at lower temperature to make even more hydrogen and convert the CO to CO2.

Okay, the point is that the first steam reforming step is very endothermic because it makes so much hydrogen.

Industrially, you have two choices to solve this problem. You either burn fuel on the outside in a furnace with these gases flowing in pipes on the inside OR as is often the case and simpler, you burn some of the methane internally with oxygen to make the heat for you!

How much? Just enough for this to tick over.

So you feed CH4, superheated H2O and some O2 and it works, you still get out CO and H2, but because of the oxygen, you change the CO to H2 ratio that you get. Sometimes having a lower CO:H2 ratio is imperative for the next down stream step (whatever you were making this mixture for), in that case, you have no choice but to run the reformer without co feeding oxygen and worry about the extreme heat transfer that is needed from the outside through the pipe walls in your furnace.

Anyway, as I've often said before, my system is similar, except that we go the low temperature equivalent and therefore have to use more reactive things for kinetic reasons. So instead of methane or hydrocarbons (too inert at low T), I propose glycerine as a compromise between hydrogen making capacity and reactivity (sacrifice some hydrogen making capacity compared to pure hydrocarbons but gain reactivity). However, just like steam reforming methane, the reaction:

C3H8O3 + 3H2O => CO2 + 7H2

is very endothermic, so you 'fix' this by the same trick as in steam reforming, you co feed an oxidant. However, you want your oxidant to also be nice and kinetically active (by the way oxygen is not as kinetically active as you might think, it has the slowest kinetics in a fuel cell even with platinum catalysts), so I propose using H2O2, which is in between H2O and O2 but has fantastic chemical kinetics on a catalyst.

deltaH - 4-10-2013 at 02:28

Quote:
You would get more energy, and the same waste products, if you burned glycerol with oxygen. An oxygen cylinder would be more practical to carry around with you than an electrolysis cell.
You would make more heat, but heat alone is useless, you need to convert it into useful work. You can do so by using an engine and this is where you end up only converting only a fraction of your heat into useful work because of the inherent thermodynamic inefficiency of an internal combustion engine or heat engine. Fuel cells convert chemical potential energy into electrical work and as they operate at low temperatures with catalysts, can theoretically do so in a far more efficient manner than what a heat engine can (albeit at a higher $ cost for now). Still not convinced, see this article on 'exergy'.

High efficiency electric motors are also a particularly efficient way to convert electrical work to mechanical work because they too do not need to operate at high temperatures.

Need any more proof that running at low temperature with catalysts is the best way to go? Consider how nature does it with lifeforms :)

There's a reason our bodies don't run on V8 engines, though it does make for entertaining snail racing movies!

papaya - 4-10-2013 at 02:47

Quote: Originally posted by deltaH  
Quote:
And why would anyone mix glycerol with H2O2 if it's better to use separated cells in battery?
Appologies, but I want to specifically zero in on this point from another angle as well.

Consider steam reforming, say with methane and superheated steam, from wikipedia's article on it, I quote:

"At high temperatures (700 – 1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield carbon monoxide and hydrogen. These two reactions are reversible in nature.
CH4 + H2O ⇌ CO + 3 H2"

They then go on to say that you can use the water gas shift reactions at lower temperature to make even more hydrogen and convert the CO to CO2.

Okay, the point is that the first steam reforming step is very endothermic because it makes so much hydrogen.

Industrially, you have two choices to solve this problem. You either burn fuel on the outside in a furnace with these gases flowing in pipes on the inside OR as is often the case and simpler, you burn some of the methane internally with oxygen to make the heat for you!

How much? Just enough for this to tick over.

So you feed CH4, superheated H2O and some O2 and it works, you still get out CO and H2, but because of the oxygen, you change the CO to H2 ratio that you get. Sometimes having a lower CO:H2 ratio is imperative for the next down stream step (whatever you were making this mixture for), in that case, you have no choice but to run the reformer without co feeding oxygen and worry about the extreme heat transfer that is needed from the outside through the pipe walls in your furnace.

Anyway, as I've often said before, my system is similar, except that we go the low temperature equivalent and therefore have to use more reactive things for kinetic reasons. So instead of methane or hydrocarbons (too inert at low T), I propose glycerine as a compromise between hydrogen making capacity and reactivity (sacrifice some hydrogen making capacity compared to pure hydrocarbons but gain reactivity). However, just like steam reforming methane, the reaction:

C3H8O3 + 3H2O => CO2 + 7H2

is very endothermic, so you 'fix' this by the same trick as in steam reforming, you co feed an oxidant. However, you want your oxidant to also be nice and kinetically active (by the way oxygen is not as kinetically active as you might think, it has the slowest kinetics in a fuel cell even with platinum catalysts), so I propose using H2O2, which is in between H2O and O2 but has fantastic chemical kinetics on a catalyst.


I don't understand your arguments here, I supposed you not to exclude peroxide or change your overall equation, but separate glycerol & H2O2 to anodic/cathodic cells - for the SAME amounts of reagents you get HIGHER concentrations => higher potential difference, isn't it?
But of course, the thing overall is too complex - peroxide needs to be produced in another plant (by electrolysis for example), H2O2/glycerol mixture looks like a rocket fuel (who knows if oxidation is auto-catalytic then it may go off some day, etc) and then you want to build a vehicle! If you were to build an electricity generation plant then maybe this would be accepted more calmly.

deltaH - 4-10-2013 at 03:43

Thanks Papaya, I love your questions, they really challenge me!
Quote:
I don't understand your arguments here, I supposed you not to exclude peroxide or change your overall equation, but separate glycerol & H2O2 to anodic/cathodic cells - for the SAME amounts of reagents you get HIGHER concentrations => higher potential difference, isn't it?
I see your point and frankly I'm not sure about this point at all, I think because we are using the peroxide in substoichiometric amounts to 'fix' the system, then it's placed on the anode side together with glycerine, in fact what would happen if you used a fairly concentrated sulfuric acid electrolyte as what I'm currently thinking of using (because the peroxide would quickly form persulfuric acid which as anions would concentrate at anode, and anions is exactly what nearly all would be at around 70% sulfuric acid strength!)

But maybe this is a big problem, I don't know, if at first I absolutely cannot get it to work one way, I will try the other.

As for your safety issues, ANY energetic fuel is dangerous... how many times do people die because gasoline catches fire in car accidents? To be honest though, I don't think such a sub stoichiometric mixture of glycerine would be as flammable as gasoline. In fact when I made it, I couldn't like it easily with a flame!!!

I say SAFER than gasoline and non toxic and non-volatile and non-smelly!!! In fact, probably have to purposefully make it smelly, bitter and coloured so that people don't accidentally drink it. Off course strong peroxide can still damage tissue on contact... certainly will make skin temporarily white but that's harmless. Never tried getting 30% H2O2 solutions on my skin though, maybe somebody can advise if this does major damage or just makes skin white temporarily.

I know that peroxidases in our bodies neutralise peroxide very quickly, but does high concentrations overwhelm it?

deltaH - 4-10-2013 at 04:05

Did some more simple thermo calculations in EXCEL using that data from before.

I was interested to find out how much peroxide to water was necessary to make the hydrogen generation dGrx = 0.

Turns out you need very little:

C3H8O3(l) + 0.2H2O2(l) + 2.6H2O(l) <=> 3CO2(g) + 6.8H2(g)

Has a dGrx standard = 0!

Ok in reality maybe you want a little more to help it alone, but this is the theoretical value, don't know if it is optimal though.

[Edited on 4-10-2013 by deltaH]

papaya - 4-10-2013 at 05:14

Discard my last posts, I thought about H2O2-glycerol "battery" when suggesting separated cells, not the electrolysis...

deltaH - 4-10-2013 at 05:27

Quote:
Discard my last posts, I thought about H2O2-glycerol "battery" when suggesting separated cells, not the electrolysis...
Might make a nice battery though, alkaline medium so no gases generated, microvent for peroxide... would need come catalyst on the anode though for the glycerine. What metal to use for cathode not to catalyse H2O2 decomposition, zirconium? Pricey... but oh so cool!

blogfast25 - 4-10-2013 at 05:31

Quote: Originally posted by deltaH  

Turns out you need very little:

C3H8O3(l) + 0.2H2O2(l) + 2.6H2O(l) <=> 3CO2(g) + 6.8H2(g)





Yeah, I worked out yesterday that the ΔGReaction for that reaction but using O2:

C3H8O3 + 3/2 O2 === > 3 CO2 + 4 H2

… is very close to 0. It's not a surprise: you lose a lot of bonding energy and gain relatively little of it in return. So those reactions are more or less 'energy neutral', at least on paper.

So your idea is to carry out this reaction (but with peroxide) by electrolysis, then use the H2 in a separate fuel cell to power the electrolysis of glycerol (plus some oxidant) AND power propulsion of the vehicle TOO? Is that the idea?

[Edited on 4-10-2013 by blogfast25]

papaya - 4-10-2013 at 05:37

Quote: Originally posted by papaya  
Discard my last posts, I thought about H2O2-glycerol "battery" when suggesting separated cells, not the electrolysis...


Hmm, but I thought a bit harder - I was right? Because if you plug that "battery" to external voltage REVERSED polarity then it certainly should help(hmm, you might generate hydrogen just shorting that battery?).
Also you have to separate H2O2 and glycerol, because if the oxidation and reduction takes place in the same compartment (on the same electrode) then you don't have opportunity to get that electrons flow to external circuit.
Now I feel totally lost, I must have had many errors here...

deltaH - 4-10-2013 at 05:37

@blogfast

Thanks for the confirmation on the calculation, always good to have a check or related check.

Yes that is correct, did you read my long thermodynamic calculations post I wrote in reply to you earlier (long post on page one)? It may have gotten lost in the wash of posts since.

[Edited on 4-10-2013 by deltaH]

deltaH - 4-10-2013 at 05:51

Quote:
Hmm, but I thought a bit harder - I was right? Because if you plug that "battery" to external voltage REVERSED polarity then it certainly should help(hmm, you might generate hydrogen just shorting that battery?).
Also you have to separate H2O2 and glycerol, because if the oxidation and reduction takes place in the same compartment (on the same electrode) then you don't have opportunity to get that electrons flow to external circuit.
Now I feel totally lost, I must have had many errors here...
Yeah this is a tough topic to grapple with, I struggling too if that makes you feel better.

Anyway, I am not exactly sure what you are trying to say here, but maybe this helps... at the moment with just a little peroxide, we have dG = 0, so it's neither battery nor electrolysis, but we can force it to be electrolysis. Add more peroxide, then dG drops dramatically the more you add and it becomes more and more a battery system but less and less hydrogen to produce, to the extreme where you add stoichiometric amounts of peroxide (separately off course) to maximise battery power and then your equation becomes:

C3H8O3 + 7H2O2 => 3CO2 + 11H2O + Huge energy

Hold on... I think I had a brainwave from that... maybe total nonsense, but isn't it that because we are targeting dG = 0 operation mode, it doesn't matter where the peroxide goes, annalyte or catholyte side. This is only a issue when targeting some distance away from dG, so if you want to minimise dG (i.e. make a battery) then you MUST put peroxide on cathode side and glycerine on anode side?

I declare that this topic is now officially causing me a critical mass in my brain lol

blogfast25 - 4-10-2013 at 08:19

deltaH:

Yes, I read your calculations w/o revising them in detail. At first glance they're sound.

Whatever oxidant you use, the real challenge will be to stop the oxidation from going all the way:

C3H8O3 + [oxidant] === > 3 CO2 + 4 H2O

... because the ΔG of that reaction really is strongly negative.

Adding whatever oxidant in drips and draps won't help: with an excess glycerol present the oxidation will always go to the end, i.e. water instead of hydrogen.

I no longer think you were peddling pseudo-science, only that extracting hydrogen from glycerol by whatever mechanism will be extremely challenging (and may cost more energy than paper calculations suggest).

You may want to consider 'something enzymatic'...

You chose glycerol because that way the idea is carbon-neutral, right? Glycerol is NOT very hydrogen-dense though...



[Edited on 4-10-2013 by blogfast25]

deltaH - 4-10-2013 at 09:20

Thanks blogfast, I appreciate it greatly.

You raise an interesting and problematic point about the complete oxidation of a small amount of glycerol that could mean bypassing the electrochemical mechanism altogether and thus just create heat and drop hydrogen generation capacity. I will need to give this more thought and consider exactly what could occur on the surface of the anode catalyst, as really this is where all the action will presumably be occurring. I'll have to get back to you on that!

I recall reading an article a while back about a proposed enzymatic route for glycerine oxidation electrochemically. Off the top of my head, that was for a partial oxidation. I think my worry there was that enzymes are too specific, we really want to take it all the way here and that's a very large number of reaction steps before you end up with CO2. Also, I don't like the very narrow operating range where you can use enzymes, I think it can be a problem with such brute force devices as I am considering, after all, I'm going to be driving these electrolysers crazy hard if I can ever get this to work, I just don't think enzymes will survive such operation. If I remember correctly, they were operating at very low current densities with those enzymes on the anodes.

As for your final point about why glycerol, yes you are correct, as organic fuels go, it's far from ideal. The point here is that for reactivity reasons you need at least every carbon functionalised to the very least to be an alcohol. So on the table are things like methanol, ethylene glycol, glycerine... etc. So some are out: methanol... too toxic and volatile for my liking, plus synthetic (mostly), ethylene glycol (toxic, synthetic), that leaves glycerine and sugars, bio glycerine prices have plummeted because of the surplus from biodiesel industry, so that's great, plus it's completely non-toxic and a liquid. If you're wondering why I didn't go for ethanol, that's because of the poor kinetic again of not having every carbon at least once functionalised, though I have read a while back that a research group has prepared a rhodium electrocatalyst that works well for direct ethanol fuel cells... well being VERY relative here or else we would all already be running our car on a direct ethanol fuel cell lol

In fact, I will put the open question to the SM community, can you suggest a better fuel than glycerine for generating hydrogen by electrolysis. Think of many factors, not just capacity. Think of capacity, sustainability, toxicity, cost, availability, chemical reactivity etc. Maybe I'm missing something better?





blogfast25 - 4-10-2013 at 09:25

deltaH:

Recalculating ΔG for:

C3H8O3 + 3/2 O2 === > 3 CO2 + 4H2

... using data from that *.pdf you linked too, I now got quite a negative value at 298 K (about - 400 kJ/mole) but in essence that doesn't change much.

[Edited on 4-10-2013 by blogfast25]

blogfast25 - 4-10-2013 at 09:43

I don't know of a better fuel than glycerol but something with the empirical formula CnO2nHm would have enough O to split it into n CO2 and m/2 H2. No oxidant needed. Totally hypothetical at this point of course...

[Edited on 4-10-2013 by blogfast25]

Threads Merged

bfesser - 4-10-2013 at 09:58

After getting a better perspective on this from another moderator, I've decided to re-open and merge the original topic. I get tired of saying this, but; <em>please keep the conversation civil</em>.

<strong>deltaH</strong>, I suggest that you learn to deal with criticism a little better. Stop imagining and/or complaining that you or your idea is being unfairly dismissed, insulted, or attacked. Someone can call your idea idiotic without calling you an idiot. I have idiotic ideas all the damn time, but that doesn't make me an idiot&mdash;other things do! :P

<strong><a href="viewthread.php?tid=19143">The ScienceMadness Guidelines</a></strong>

[Edited on 4.10.13 by bfesser]

deltaH - 4-10-2013 at 11:49

Yay, threads merged again... now I can refer to earlier posts and it doesn't all become a garbled mess. Thanks bfesser!

Anyhow, now back to more serious matters...

@blogfast25

Quote:
I don't know of a better fuel than glycerol but something with the empirical formula CnO2nHm would have enough O to split it into n CO2 and m/2 H2. No oxidant needed. Totally hypothetical at this point of course...
I love your thinking here, approach from the outside and then zeroing in. Starting with an empirical formula and the see what fits the bill is smart.

The classic case here is formic acid, H2CO2 BTW and I've touched on this earlier on in this thread.

You're right, kinetically, it's relatively 'easy' to get formic acid to decompose to H2 and CO2 because the carbon is so close to being fully oxidised. There's a VERY large body of literature on many different catalysts to do so... including my friend ruthenium!

I quote from wiki's article on formic acid thus:
"In the presence of platinum, it decomposes with a release of hydrogen and carbon dioxide. Soluble ruthenium catalysts are also effective.[22][23] Carbon monoxide free hydrogen has been generated in a very wide pressure range (1–600 bar).[22] Formic acid has even been considered as a material for hydrogen storage.[24] The co-product of this decomposition, carbon dioxide, can be rehydrogenated back to formic acid in a second step. Formic acid contains 53 g L−1 hydrogen at room temperature and atmospheric pressure, which is three and a half times as much as compressed hydrogen gas can attain at 350 bar pressure (14.7 g L−1). Pure formic acid is a liquid with a flash point of +69 °C, much higher than that of gasoline (–40 °C) or ethanol (+13 °C)."
Refs:

22. a b C. Fellay, P. J. Dyson, G. Laurenczy (2008). "A Viable Hydrogen-Storage System Based On Selective Formic Acid Decomposition with a Ruthenium Catalyst". Angew. Chem. Int. Ed. 47 (21): 3966–3970. doi:10.1002/anie.200800320. PMID 18393267.

23. G. Laurenczy, C. Fellay, P. J. Dyson, Hydrogen production from formic acid. PCT Int. Appl. (2008), 36pp. CODEN: PIXXD2 WO 2008047312 A1 20080424 AN 2008:502691

24. Joó, Ferenc (2008). "Breakthroughs in Hydrogen Storage-Formic Acid as a Sustainable Storage Material for Hydrogen". ChemSusChem 1 (10): 805–8. doi:10.1002/cssc.200800133. PMID 18781551.

This is just a snippet, a quick literature search on this topic turns out masses and masses of papers on the topic...

Now as I mentioned right back in the beginning of this thread, I think formic acid is no good...

It's corrosive, it's smelly as hell and you get a meager 4.4% hydrogen out of it by mass.

Guys, coming back to the big black box approach, you just have to look up the heat of combustion and get a quick idea whether you have a good fuel! This holds even for this kind of system!

Formic acid's heat of combustion is a meagre 5.5 MJ/kg

That's pathetic as fuels go, compare to
gasoline's heat of combustion is a wopping 47.3MJ/kg

So I would conclude that CnO2nHm types are over oxidised and can't perform well on energy density arguments.






blogfast25 - 4-10-2013 at 12:12

deltaH:

"It's corrosive, it's smelly as hell and you get a meager 4.4% hydrogen out of it by mass."

With hydrogen you're always going to get that: for glycerol it's only 8.7 %, not brilliant either. Even for water it's only 11 %. Try deuterium (just kiddin')

How about di or tri carboxylic acids: oxalic acid, citric acid? Just 'off the cuff' here... These have low hydrogen contents too of course but it might be easier to snip it off, vis-à-vis glycerol?



[Edited on 4-10-2013 by blogfast25]

deltaH - 4-10-2013 at 12:33

@blogfast25

I'll stick to my 8.7% thank you lol

By the way, before I considered polyols, I had the 'brainwave' of realising this was actually all about energetic materials, so I started thinking about along nitrogen containing lines...

One option was nitromethane in the don't-need-to-add-water-class-of-things:

2CH3NO2 => 2CO2 + 3H2 + N2!!!

But it's not a renewable, it's dangerous and and and... but you see how energetic materials can come into play

Hydrogen content of nitromethane is 5% and heat of combustion is 11.6MJ, so as liquid things that come prepackaged with their own required oxygen go, I don't think you can beat nitromethane...

Now calling all the energetic materials experts to run on over to this thread LOL







[Edited on 4-10-2013 by deltaH]

papaya - 4-10-2013 at 12:54

Urea ? (piss into car :P )

deltaH - 4-10-2013 at 13:17

Quote:
Urea ? (piss into car :P )
lol, yeah I actually looked into urea... urea for all intents and purposes is a clever non nasty form of ammonia, well that's what it behaves like in these kind of systems so since people thought ammonia was smart, certainly urea is smarter...

The corresponding reaction is (NH2)2CO + H2O => CO2 + 3H2 + N2

Pure urea is 6.7% H2 in theory, BUT it's not a liquid, though you can dissolve a lot in water. But it fails when it comes to energy content!!!

Incidentally, the urea as a source of hydrogen idea is commercially used in Diesel exhaust fluid exactly because it's pretty decent.

Germans... :)

Basically diesel engines run with a slight oxygen excess to minimise soot, but that means that there's not reducing agents in the fumes for the catalytic convert to reduce the NOX's with. So they use a solution of urea in water sprayed on the catalyst in the catalytic converter full of PGMs, off course the PGMS quickly decompose the urea which is 'desguided solid ammonia' into hydrogen and voila... pretty clever!

See this wiki: http://en.wikipedia.org/wiki/Diesel_exhaust_fluid

Anyhow, as for this threads topic, I think we can do better than urea...

BTW while we at it on solid nitrogens, I had also considered trimethylamine N-oxide as a safe 'disguised methanol' that would be easy and cheap to make, but also discarded by me.

[Edited on 4-10-2013 by deltaH]

papaya - 4-10-2013 at 13:36

urea + choline chloride = deep eutectic solvent (liquid at RT)
google finds many things http://www.erc.arizona.edu/seminar/Current-2011/DineshThanu_...

What is your final purpose? Do you intend to build such a cell, or convince some company to develop your ideas there or what? You seem to be more serious with it than just an amateur project (I find it impossible to build these hi-techs for someone alone).

deltaH - 4-10-2013 at 14:10

@papaya

Yeah, I've been playing with deep eutectic solvents... used it for another innovation of mine, choline soap, but that's another story. I'll open a thread about that soon, it won't save the world but it's fun chemistry :)

As for what I intend to with this, I have been desperately trying to get some funding for things which as you pointed out, was too hard to do without any money (I am a unemployed chemical engineer and can't find work here, been looking now for over a year in SA, but let's not get into that politically loaded issue on SM).

Anyhow, so I've released this idea into the public domain in the hopes that since I cannot do anything with it (believe me I've been trying with this and many others for two years now and still trying) others should be given a chance to start experimenting with it. This is the idea about open innovation. Not everybody in the world is greedy and no, contrary to what Traveller said, nobody is giving me a couple millions lol

I've also entered it into a big local innovation competition (along with my other ideas) that just closed... if I'm lucky and win something there, then I can get started properly!

But I fear that initial skepticism this idea caused when posted here would not be atypical, so I don't know if I will ever have it looked into as it deserves any time soon. Even scientists are likely to have the same initial reaction!

Otherwise if all else fails, I will still try to fiddle with this as best I can manage in my backyard...

I am very resourceful to doing science for cents :)

I'm also hoping that maybe people here on SM might show interest in the idea and those who can, would also start experimenting with it and we could discuss issues and results here. I might not have the means at the moment, but I have a lot of knowledge (going to waste) and the will to make this thing work and solve it's problems (if it is a sound idea... proof of the pudding is in the eating!)

Surely someone here has access to a platinum foil/gauze/wire and can start experimenting with beaker electrolysis of this stuff? I think the secret is going to lie in getting the anodes right and THAT is one thing I know amateur science is DAMN good at.

Maybe what we should do next is get serious about discussing the way shape and form of a simple proof of concept for this, if only the first electrolysis half for starters and later the fuel cell whole system.

I just want it to start with beaker type experiments, no need to go huge, plus... one can buy small toy fuel cells that drive a little fan or such, these days these things sell for minimal amounts of money... some people on SM may even have these!

Anyway, very late here now, will come back and we can get into serious planning of how this principle can be tested in a simple proof of concept home experiment and maybe SM community may start playing around with it then.

Otherwise, start thinking about it if you're interested in the concept and maybe you can help with it's investigation?

Unfortunately, you won't be able to patent it because I've released it now, but you can have kudos for being instrumental in its development (if successful that is).

Anyhow, it's super late again, catch you guys tomorrow!!!

Cheers for now.:)

blogfast25 - 5-10-2013 at 04:36

Quote: Originally posted by deltaH  
But I fear that initial skepticism this idea caused when posted here would not be atypical, so I don't know if I will ever have it looked into as it deserves any time soon. Even scientists are likely to have the same initial reaction!



It's about 'selling' the idea: good presentation makes all the difference to a naturally sceptical audience. I think you made a bit of a pig's ear of your presentation initially here. It would be worth spending quite a bit of time developing the right angle for pitching the idea.

Stripped bare, it comes down to extracting hydrogen from a plentiful renewable (glycerol) for use in hydrogen fuel cells. Put concisely like that, I think some ears would prick up already.

Traveller - 5-10-2013 at 09:13

Quote: Originally posted by blogfast25  
Quote: Originally posted by deltaH  
But I fear that initial skepticism this idea caused when posted here would not be atypical, so I don't know if I will ever have it looked into as it deserves any time soon. Even scientists are likely to have the same initial reaction!



It's about 'selling' the idea: good presentation makes all the difference to a naturally sceptical audience. I think you made a bit of a pig's ear of your presentation initially here. It would be worth spending quite a bit of time developing the right angle for pitching the idea.

Stripped bare, it comes down to extracting hydrogen from a plentiful renewable (glycerol) for use in hydrogen fuel cells. Put concisely like that, I think some ears would prick up already.


Electricity in, hydrogen out; followed by hydrogen in, electricity out. If the amount of electricity coming out of this is greater than the amount of electricity going in, I'll eat the darn thing.

There are no free lunches, at least not in this universe, anyways.

blogfast25 - 5-10-2013 at 10:27

Quote: Originally posted by Traveller  

Electricity in, hydrogen out; followed by hydrogen in, electricity out. If the amount of electricity coming out of this is greater than the amount of electricity going in, I'll eat the darn thing.

There are no free lunches, at least not in this universe, anyways.


The "electricity coming out won't be greater than the electricity going in", nor is it being claimed, nor does it have to be so to work.

If hydrogen can be extracted (by whatever means) from a renewable like glycerol, then it can be used to fuel hydrogen fuel cells. If the energy needed to extract that hydrogen is greater than the energy provided by the fuel cell then that difference plus the cost of the glycerol determines the running cost of the propulsion.

No free lunch is being chased here.

It's in essence no different from cracking water with cokes, producing water gas (CO + H2) and using that water gas as fuel. There's bills to be paid but your car runs.

The interest is in the fact that there's a lot of glycerol to be had and that it's carbon neutral.

deltaH - 5-10-2013 at 11:36

@blogfast26

I hear you and will try to do better in future

@traveller

Since my previous thermo calculation indicated that I only need 4.7% H2O2 to break even in the dG, I think WHEN you eat it, you may even find it quite palatable and sweet :P May even be an excellent tooth whitener lol.

@elementcollector1

Quote:
I see a major problem here.
If you use a 70% solution of H2SO4 with the balance being water, it's very true that the solution will now be very conductive. But now, the electrode potential will be much higher because - you guessed it! You are now electrolyzing sulfuric acid and water. So, any glycerine added will be both an insignificant source of hydrogen and an insignificant reactant to this mixture at the concentrations you're proposing.

You might want to read this - it might clear some things up. http://pubs.acs.org/doi/abs/10.1021/ie9016418
Sorry for the late commentary on this. You raised an interesting point here and believe me, I swore shortly after reading it and realising that the thread was temporarily closed, I didn't want to deal with it in my subsequent thread cause I didn't want to be accused of ignoring the closure. Instead I appealed it and thankfully the powers that be ruled in favour of unification.

Now I can come back and discuss this point. Firstly, this paper looks excellent (from the abstract). I cannot open it, so I will have to request it from whoever is kind enough to volunteer it. I believe there is a paper request option somewhere here... will look into that.

Now about your point that the solution would consist predominantly of H2SO4 and water and so this will be electrolysis of sulfuric acid or water (making either peroxydisulfuric acid or oxygen at the anode, respectively):

Consider the following oxidation half reactions (from wiki's table of standard electrode potentials):

2 SO4sup2- <=> S2O8sup2− + 2 e− E(std.) = -2.010V
2H2O <=> O2 + 4H+ + 4e- E(std.) = -1.229V

Now compare with that of formic acid (they didn't have glycerine, but you get the idea even with formic acid)

HCOOH(aq) <=> CO2(g) + 2H+ +2e- E(std.) = +0.11V

Now as you can see, the standard electrode potentials for either water oxidation or sulfuric acid oxidation are very unfavorable, while that of an oxidised simple organic is in fact favorable.

Now your argument is that dilution may alter this. It does slightly and we can use the Nernst equation to calculate by how much...

Let's say it was formic acid we were using at 0.1M and not 1M for which that standard potential is quoted at, we can use the Nernst equation to calculate the 'new' electrode potential under such dilution:

We need to flip the half reaction, so CO2(g) + 2H+ +2e- <=> HCOOH(aq) E(std.) = -0.11V

Then Eeff. = E(std.) - 0.05916V/z * log([HCOOH]actual) = -0.11V - 0.05916V/2 * log(0.1) = -0.08V

So you see the oxidation half reaction for formic acid only dropped it's electrode potential from +0.11V to +0.08V even when diluted to 0.1M

So as you can see, while dilution does change the half reaction potentials somewhat, the changes are small!

Now that said, thermodynamics is one thing, chemical kinetics are another.

If you have a completely catalytically inactive anode, say graphite or plain titanium, then you're glycerine cannot oxidise because you have a MASSIVE overpotential due to a large activation energy barrier. This WOULD make water electrolysis or even sulfuric acid favoured. In fact this is what @woelen refered to on the second page of this thread when he pointed out that when he tried to electrolyse ammonia with graphite anodes, he simply got water electrolysis and made oxygen at the anode!

This wasn't because of dilution, it was because the graphite was completely catalytically inactive towards ammonia dissociation into hydrogen and nitrogen and so THAT process faced a massive activation energy barrier. Had he used a platinum anode, he would would probably have made nitrogen gas at the anode because of platinum's ability to catalyse the dissociation/decomposition of ammonia.

Once again, this issue elligantly illustrates the importance of differentiating between thermodynamic and chemical kinetic effects / issues.

Please do tell me if you agree with my reasoning here.


[Edited on 5-10-2013 by deltaH]

kmno4 - 5-10-2013 at 12:59


Quote:

You might want to read this - it might clear some things up. http://pubs.acs.org/doi/abs/10.1021/ie9016418



Attachment: ie9016418.7z (351kB)
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blogfast25 - 5-10-2013 at 13:24

Thanks kmno4, I'm printing that attachment off.

deltaH - 5-10-2013 at 13:28

@kmno4 I second the thanks.

deltaH - 5-10-2013 at 13:55

Very interesting paper indeed... first time I hear of hydrothermal electrolysis (electrolysis at high pressure so that you can carry it out in water at very high temperatures). I would not want to do it this way... 10MPa electrolysers is not amateur science lol

Anyhow, these guys were trying to convert glycerine into partially oxidised products because they could possible be sold as more valuable chemicals. I actually think carrying out a partial oxidation by electrolysis is harder than a complete one because those products are easier to oxidise further than what the glycerine was in the first place.

Note they used non-catalytic titanium electrodes, but at 220C and 280C it appears catalysts are hardly necessary and since they didn't want to completely oxidise, it's hardly surprising either.

This gives me renewed confidence that electrocatalytic anodes such as platinum based ones could work at lower temperatures!

[Edited on 5-10-2013 by deltaH]

deltaH - 5-10-2013 at 14:06

@blogfast25

Quote:
The "electricity coming out won't be greater than the electricity going in", nor is it being claimed, nor does it have to be so to work.

If hydrogen can be extracted (by whatever means) from a renewable like glycerol, then it can be used to fuel hydrogen fuel cells. If the energy needed to extract that hydrogen is greater than the energy provided by the fuel cell then that difference plus the cost of the glycerol determines the running cost of the propulsion.

No free lunch is being chased here.

It's in essence no different from cracking water with cokes, producing water gas (CO + H2) and using that water gas as fuel. There's bills to be paid but your car runs.

The interest is in the fact that there's a lot of glycerol to be had and that it's carbon neutral.
Well said!

[Edited on 5-10-2013 by deltaH]

blogfast25 - 6-10-2013 at 06:02

deltaH:

I read the paper yesterday and for me the main relevant conclusion was that more hydrogen was being produced in the presence of glycerol than in its absence, showing a small degree of actual electrolytical decomposition of that substrate, in those specific conditions.

You're right that their goal is different: production of higher value, often shorter chain reaction products. Oxidising everything to CO2 and H2 would be counter productive to that goal.

There may be a wealth of information in some of the many papers referenced.

But I remain convinced that near-complete electrolysis of glycerol in the presence of an oxidiser in 'amateur science' attainable conditions is going to be a real hat trick. Maybe very specific, milder oxidisers should be looked at. But I'm just 'mouthing off' here because at present I've no idea what they could be...

[Edited on 6-10-2013 by blogfast25]

deltaH - 6-10-2013 at 06:30

Yeah it's going to be a real schlepp... SA speak for a pain in the... lol

Quote:
Maybe very specific, milder oxidisers should be looked at.
wow... THAT is a VERY interesting idea... I've been so focused on maximising energetic content that I've been concentrating my thoughts on super strong oxidisers (completely unwittingly). However, since we don't need much to 'fix' the dG, maybe there's leyway to play with gentler things.

In fact, in normal reforming/gasification, in many ways the water is the 'oxidant', okay granted, a very bad one, but between water and peroxide, maybe there's something in between... not as terrible as water, nor as aggressive as peroxide, but can provide both a source of oxygen and hydrogen so all the carbon in the glycerol can go to CO2.

What about hydroxylamine? The only problem is that it's not particularly green, but at least the glycerine is.

I'd need to work out how much hydroxylamine is needed to get a dGrx = 0.

The nice thing about hydroxyamine is that unlike glycerol peroxide mixtures, this should be stable indefinately without gas generation?

I know hydroxylamine can decompose energetically, but it only seems to be possible at very high concentrations and I don't think we would be anywhere near that.

Ok so lets say we go ape with this and use 50% hydroxyamine solution in water mixed with the appropriate amount of glycerine. Should make the dG of the reaction negative (will confirm shortly).

The electrolysis then yields:

C3H8O3(l) + NH2OH(l) + 2H2O(l) => 3CO2(g) + 1/2N2(g) + 7.5H2(g)

WOW Blogfast25... I think I like it a lot... you're a genius!

The hydrogen mass content of such a liquid mixture is 9.3% to boot! OMG

Okay... need to check the dG of that reaction...




deltaH - 6-10-2013 at 06:48

Okay before I get crucified by the pure chemists for referring to hydroxylamine as an 'oxidant' of sorts, I am well aware that it is a reducing agent, I simply need it as an inorganic source of oxygen for the carbon in glycerine.

The fact that it contributes hydrogens as well is a bonus :)

There is a problem though, peroxide would quickly form peroxysulfuric acid when mixed with strong H2SO4 electrolytes and so I don't have much doubt this would be attracted to the anode where we need it.

But wouldn't hydroxylamine simply form hydroxyammonium cations or could enough hydroxylamine-O-sulfonic acid form in sufficient amounts when the hydroxylamine hits the strong sulfuric acid solution? Can hydroxylamine-O-sulfonic acid even form in any amounts between strong H2SO4 and hydroxyamine? Fortunately the acid will be in excess here so that acts in its favour.

blogfast25 - 6-10-2013 at 09:23

Is there a particular reason for using sulphuric acid? Why do you think it's better than alkali? Personally I don't have the foggiest idea...

Rather than being a genius, I confess to being totally in the dark here. I'd really have to read up on much of the prior art first before being able to meaningfully contribute.

[Edited on 6-10-2013 by blogfast25]

deltaH - 6-10-2013 at 10:57

@blogfast

No its great and thanks for your thoughts, they are helping me a lot! The reason I would prefer acidic media is so that CO2 gas is produced at the anode, otherwise in caustic media carbonates would be formed... and then what. There are technologies for converting the carbonate to CO2 gas in a second step, but that's just too complicated for my liking.

There is, however, the big problem that for some reason, from what I've read in the literature... they never seem to get the acid version of organic electrolysis to work properly. This is puzzling to me and admittedly I need to dig deeper in the literature.

I don't think they are using concentrated enough acids though... let me explain my thinking here, I think for the organic molecule to be oxidised, it should be converted to an anion so that it can concentrate on the anode where oxidation is taking place. This is easy to do in basic media, so for example, formic acid forms formate anions that are drawn to the anode. Even anhydrous ammonia can have some sodium amide dissolved into it and you can carry out ammonia electrolysis with the amide ions being drawn to the anode.

Now as for acids, I think the mistake most researchers might have made was to not use sufficiently concentrated acids. For example, lets say you want to electrolyse methanol. You need methanol anions pulled to the anode but in acidic media?! This can only happen if the methanol forms an ester with sulfuric acid so you make methylsulfuric acid. If there is sufficient water present then you will have lots of methysufate anions and H3O+ present and the methylsufate anion can be pulled to the anode for oxidation and the H3O+ to the cathode for reduction.

The problem, come to think of it, is that not only do you need fairly concentrated acids to convert the organic molecule into an anion that can be drawn to the anode, but you also need your oxygen source to be converted to an anion in the acidic environment at the anode and I think this is why the conventional electrolysis of organic molecules in acid media haven't yielded good results. In the case people were carrying it out, using just acids in water, how was the water supposed to be anionically attracted to the anode under strongly acidic conditions, most of the water would be in the H3O+ form?!

This is were my idea for peroxide could make a big difference, because peroxide can form persulfuric acid and be pulled to the anode to act as my oxygen donor (in the form of persulfate anions) to the glycerol molecules (as glycerylsulfate anion esters).

In fact, I can form my first hypothesis to test this theory:

First hypothesis
The complete oxidation of glycerol to form carbon dioxide gas at the anode and hydrogen gas at the cathode in acidic sulfuric acid electrolyte requires an oxygen source that like the glycerol can also be esterified by the acid and drawn to the anode.

Sadly this would mean that just adding the minimum H2O2 required to break even on dG wouldn't be good enough, you would need stoichiometric amounts for the reaction, i.e.

2C3H8O3(l) + 3H2O2(l) => 6CO2 + 11H2

I don't like this large amounts of peroxide, this is maybe where hydroxylamine would maybe fair better:

C3H8O3(l) + 3NH2OH(l) => 3CO2 + 1.5N2 + 8.5H2

Anyhow, these are my thoughts on this point for now. I don't like the implications of having to use such concentrated mixtures... but how to make the water into an anionic intermediate to transport it to the anode under the acidic conditions?

I'll try to think up some possibilities...







[Edited on 6-10-2013 by deltaH]

[Edited on 6-10-2013 by deltaH]

kmno4 - 6-10-2013 at 13:05

deltaH, I think your idea became your obsession and leads directly to madness.
Do you know any premise that such a (quantitative) electrolityc glycerin decomposition (to H2 and CO2) is practically possible ?????
There is no analogy between NH3 and glycerin. These are completely different compounds.
Also formic acid is "special" case:
HCOOH→CO2+H2 , ΔH is >0 (but not very high) ΔG is <0.
With Rh catalysts reaction goes smoothly, without any additional reagents.
In glycerin case you must use some odditional oxidant, it is of course.
Electrochemical reduction/oxidation of glycerin must be very complicated and multi step reaction. You want only H2 and CO2 - wishful thinking.
You plan to add some unstable compounds (H2O2, NH2OH, who knows what else) to improve effect.
To one complicated reaction mechanism you add another reactant and you still want only CO2 and H2 (+N2 or whatewer you wish) - (wishful thinking)<sup>2</sup>
Have you made any estimation of cost of your H2 production ?
Have you done anything but pure chemical speculations ?
Do you realise, that low cost of glycerin is caused by governments forced production of "biofuels" ?

The best you can do is making glycerin-driven motor.
Overall reaction:
C3H8O3 + air →CO2 + H2O
Without electrolysers, precious electrodes, hydrogen cells... and dreams

Bonus: H2 from NH3




[Edited on 6-10-2013 by kmno4]

Attachment: NH3.7z (444kB)
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blogfast25 - 6-10-2013 at 13:13

Can't really find fault with that. I certainly hadn't thought of the formation of carbonates. But think of it as a form of carbon sequestration! ;) I mean, who really needs gaseous CO2: carbonates are more useful.

And in alkaline media, alcohols tend also to form anions: alkoxides (RO-). Hydrogen peroxide does too (it's a very weak acid). So still speaking mostly from darkness maybe don't exclude alkaline conditions just yet. There must be a pathway that explains part electrolysis of glycerol and H2 formation in kmno4's study.


[Edited on 6-10-2013 by blogfast25]

Traveller - 6-10-2013 at 14:31

Quote: Originally posted by deltaH  
@blogfast25

Quote:
The "electricity coming out won't be greater than the electricity going in", nor is it being claimed, nor does it have to be so to work.

If hydrogen can be extracted (by whatever means) from a renewable like glycerol, then it can be used to fuel hydrogen fuel cells. If the energy needed to extract that hydrogen is greater than the energy provided by the fuel cell then that difference plus the cost of the glycerol determines the running cost of the propulsion.

No free lunch is being chased here.

It's in essence no different from cracking water with cokes, producing water gas (CO + H2) and using that water gas as fuel. There's bills to be paid but your car runs.

The interest is in the fact that there's a lot of glycerol to be had and that it's carbon neutral.
Well said!

[Edited on 5-10-2013 by deltaH]


Yes, yes, lots of glycerol to be had (grows on trees, right?) and it is carbon neutral, of course. In actuality, coal is carbon neutral, if you don't mind being on a million year cycle.

I put these notions right up there with the pipe dreams from the proponents of the "hydrogen economy". It takes 1.2 times as much energy to dissociate water into hydrogen and oxygen than you could ever hope to recover IF your conversion of H2 and O2 back to water was 100% efficient which, we all know, is impossible; at least in this universe, anyways.

And when those of the "hydrogen economy" are asked where all the energy to dissociate water (or make glycerol) will come from, we are given a Utopian view of a world covered in windmills, solar panels and tidal generators.

"Dreamer....you know you are a dreamer...."

deltaH - 6-10-2013 at 22:49

@ traveller
Quote:
And when those of the "hydrogen economy" are asked where all the energy to dissociate water (or make glycerol) will come from, we are given a Utopian view of a world covered in windmills, solar panels and tidal generators.
I must admit that I am myself sceptical of the hydrogen economy. However, I am a big fan of the biomass economy. Forget solar panels, plants do a most excellent job of converting solar energy into chemical potential energy. So for example, we already have a thriving biodiesel industry (with much debate about running cars on food), but nevertheless, it's there already and as a result there's lot's of glycerine. On the other hand we also already have hydrogen fuel cell powered cars, so really what I'm proposing is the last link in already well established technologies.

I will be frank, while I know that what I am proposing can work... I've PROVEN the overall thermodynamics already on this thread, it's not going to be easy to get it to work in terms of getting the kinetics to behave and finding all the right conditions to get this to tick over in a practical way.

Time will tell if it's feasible, I'm waiting on some bits and pieces to start experimenting... for now and until then, I need to focus on designing this system as best I can and try to wrap my mind around many chemistry issues that I do not understand. As this is electrochemistry... there is A LOT I don't understand!

deltaH - 6-10-2013 at 23:30

@kmno4

Obsession... science madness? Maybe... guess I'm at the right place then :P

Quote:
Do you know any premise that such a (quantitative) electrolityc glycerin decomposition (to H2 and CO2) is practically possible ?????


Maybe this paper might, I don't have access to it myself but the abstract sounds promising, can you help out again please?

http://pubs.rsc.org/en/content/articlelanding/2013/cp/c3cp50...

What sounded very interesting from the abstract of this was:

"We propose that active oxygenated species are gradually formed on the glassy carbon by potential cycling (up to the saturation of the carbon area) and these oxygenated species are additional oxygen suppliers for the oxidation of glycerol residues adsorbed on the Au particles..."

First time I see some evidence that to have 'active oxygenated species' on the anode may be helpful... while these guys seem to be generating it in situ, adding it stoichiometrically by way of H2O2 might thus not be a bad idea?

froot - 7-10-2013 at 03:28

Ha! Another Safrican! :cool:

DeltaH I briefly skimmed over this topic and think I get the gist of your idea so what I say might not be of much use, but..
Let's say you've now got your hydrogen from your glycerol. If it's intended for fuel cells then wouln't simply feeding vaporized glycerol into a MCFC save you a lot of snot and trane?

That been said it seems to me that extracting hydrogen from organics comes down to catalyst efficiency. Keep going.

deltaH - 7-10-2013 at 03:56

Howzat froot/boet :cool:

Yeah it basically comes down to whether breaking a process into two potentially more optimisable steps results in sufficient an efficiency gain in each so that it beats the efficiency of existing one step versions, such as a MCFC.

At least I'll be making the local PGM guys happy!

Thanks for your support and encouragement!






watson.fawkes - 7-10-2013 at 04:15

Quote: Originally posted by deltaH  
I've PROVEN the overall thermodynamics already on this thread
No you haven't. You've presented a number of theoretical calculations with not even a nod to real-world inefficiencies of actual apparatus. Hint: Go learn what the third law of thermodynamics is about.

blogfast25 - 7-10-2013 at 04:48

Quote: Originally posted by Traveller  
[
And when those of the "hydrogen economy" are asked where all the energy to dissociate water (or make glycerol) will come from, we are given a Utopian view of a world covered in windmills, solar panels and tidal generators.

"Dreamer....you know you are a dreamer...."


Keep your political views out of it.

Nothing wrong with dreaming either.

You're still babbling as if this is water to hydrogen to water. It's not.

Glycerol? There's plenty of it.

[Edited on 7-10-2013 by blogfast25]

blogfast25 - 7-10-2013 at 04:57

Quote: Originally posted by watson.fawkes  
Hint: Go learn what the third law of thermodynamics is about.


Why don't you explain it here? Because I don't get what it's to do with this either.

If hydrogen could be extracted from glycerol why couldn't it be used as fuel for hydrogen cells? Of course it may prove to be impractically expensive or even technically undoable but right now we don't know this for sure.

Cryptic (and somewhat snobbish) remarks like yours don't really help, I feel.

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