Could a catalytic converter turning CO into CO2 work in reverse?

No. It would take more energy to reduce the CO₂ back to CO than can be recovered from burning the CO. Net result: energy loss.

I know. But what if the energy is otherwise being thrown away?

But what if the energy is otherwise being thrown away?

those are pretty loose terms, how much energy and at what rate, ..........how do you throw energy away anyways?

Or do you mean utilize?

I do mean utilised, yes. I would have thought that was obvious!

if you added enough energy into the system, the reaction might reverse at sa 2000 F

It won't reverse. You Chemistry 101.

Sorry for the typo. I meant you need Chemistry 101.

Thanks. Is 2000degF a real ball-park figure?

Could it be somewhat lower in reality?

Impossible, Catalytic converter reaction chamber is designed for converting hazardus efflents gases into environmentally friendly green gases. It is forced reation, in the chamber where effelents are heated and burnt out later by feeding excess of oxygen.

???

Yes, the Catalytic converter reaction chamber IS going to convert one way only, but catalysts are effective at speeding up reactions in either direction if the 'geometry' of the converter is right.

Hi, Sheps!

No. Exhaust gases pass through the catalytic converter to be converted into the gases exiting at its outport. Pass 'em back through again (back to front this time), and the only thing that might occur of any difference is that the exhaust gases, now several degrees 'cleaner' than they began, are even cleaner than before.

Mark

Thanks Mark.

I am maybe being misleading. As I understand it a catalyst material that accelerates a reactions in one direction will equally do so in reverse. In a vehicle cat' it is the geometry & temperature of the device that makes CO + O2 become CO2. Hence I assume cats' that convert CO to CO2 don't need a lot of heat to get them going.

My original question should have been:

If we have a stream of high temp CO2 can a specially designed catylic convertor turn it into a cool CO + O2 gas stream?

Cheers, Tom

Hi, Sheps!

"As I understand it a catalyst material that accelerates a reactions in one direction will equally do so in reverse."

Assuming that there is some usefulness in recovering the CO, it will still be necessary to break the valence of the CO_² in order to accomplish that. Once that has been accomplished, a standard plutonium surface might adsorb the O radical. High heat is readily available in the form of electric sparking, and is used to create the pre-catalyst separation of all kinds of gases in order to arrive at CO₂ from CO, NO_x, etc. etc. in automobile exhausts (a useful direction in terms of air pollution). (uspto Ben Masters 1995).

Mark

Plutonium ! - really!! Scary!!

There must other less exotic chemicals that will do the same thing!

What sort of activaion temperatures are we talking about here (to get CO2 to split to CO in the presence of a catalyst) ?

Hi, Sheps!

Oops!

Did I say "plutonium"?

I meant "Platinum".

I was distracted during the piece by a telephone call about chocolate bars....waddya gonna do??

Er, sorry for the scare!

Mark

Sheps

As I understand it a catalyst material that accelerates a reactions in one direction will equally do so in reverse.

No, I looked at your bio, so I'm giving and an example without going into the chemistry and reactions.

your comment would be more like un-baking a cake and separated it back into flour, eggs and milk.

but catalyst incorporate the bonding of atoms with heat, pressure and dwell time

http://en.wikipedia.org/wiki/Catalysis gives a very good explanation

phoenix911

PS

or did I read your comment wrong with your meaning it doesn't matter which direction it travels in a catalyst. that true but not quite as efficient, there are different stages in a catalyst.

But separating the atoms, hope they don't mean splitting the atom. I better put my goggles on just in case.

Thanks phoenix911.

http://en.wikipedia.org/wiki/Catalysis - it's a good article.

I noticed it says:

"Catalysts do not change the favorableness of a reaction: they have no effect on the chemical equilibrium of a reaction because the rate of both the forward and the reverse reaction are both affected"

this is what I meant when I said:

a catalyst material that accelerates a reactions in one direction will equally do so in reverse

I think I've understood his right!!!

Tom

CO conversion to CO2 is a highly exothermic reaction and there are equilibrium effects. However, the Gibbs Free Energy is so high the equilibrium effects are negligible and the reaction essentially goes to completion given enough time. Reversing the reaction to make CO and Oxygen is not possible, much less practical under any plausible circumstances. Not only would all the heat of oxidation have to be 'added back', significantly more is required because the thermodynamics of the oxidation are not 100% efficient.

Thanks Keith,

I have to take umbrage with "Reversing the reaction to make CO and Oxygen is not possible" part of your answer. It is definitely possible under the right conditions (not least a high temp).

I agree with your statement that "[more than] all the heat of oxidation [would] have to be 'added back' ", but getting to CO is not all the way back, is it?

One of the basic problems with heat engines is part of the maximum efficiency has to be sacrificed to give a usable rev-range (for reciprocating engines). This equates to losing energy as heat in the exhaust to maintain high gas velocities. Many bolt-on devices have been used & suggested to recover some of this lost energy, but as far as I know there is no system that uses said heat to activate chemical reactions resulting in enhancing the engine's fuel stock.

I'm sure I am missing something here - maybe just that the temps available are too low for CO formation. But being wrong is part of the learning process, eh!

Cheers, Tom

The original purpose of the cat converter is to enable CO below the lower flammability limit to be oxidised. Because of the time available for combustion, even a perfectly tuned motor will usually have a small amount of CO and unburnt hydrocarbons in the exhaust. The concentration of these is too low to burn, so a catalyst is used to shift the equilibrium so that they can be burnt.

To reverse the process, you would not only need to provide energy (and exhaust gases contain a lot), you would need to shift the equilibrium of the reaction in a different direction. This would probably need a different catalyst.

If sucessful, the CO would be a small percentage in a stream of other gases (mainly nitrogen) so would need concentration before it could be usefully burnt.

Sceptic,

I'm sure you're right that a different catalyst would need to be found to shift the equilibrium in the opposite direction. I would have though separating some portion of the CO2 from the exhaust gas stream, before running it over the hot catalyst (the cat can still be activated by the exhaust via a heat exchanger) would be simpler - then you have some CO and oxygen to be fed back to engine (not the total CO2 equivalent you understand).

Based on the principle that the CO2 to CO reaction is highly endothermic the exhaust gas after this catalyst stage would be noticeably cooler - lower exhaust temp should equate to increased efficiency (for a heat engine).

Sheps,

I agree, separation of CO2 before reversal of the reaction would be a good idea. This could be done by cooling the stream then using a suitable adsorber (activated carbon, silica gel or activated alumina would be likely candidates) to adsorb the CO2. Heating would then desorb the CO2, which could be returned to the engine.

This whole "thought experiment" is looking more likely to be applicable to a large stationary engine than anything else.

For a catalyst, I suspect some of the alumino-silicates (clays) would be a good starting point. These, at about 300C) can convert vegetable matter to coal or oil in a matter of hours. (I can't give a reference immediately but read it in, I think, New Scientist in the late 1980's, I may have it around somewhere if needed).

Why?

An efficiently running vehicle with the perfect stochiometric ratio produces one gallon of water for every gallon of gas burned- you would have to consider this factor in your design.

I am intersted in converting CO2 to CO and burning for BTU value. Idea is to recover CO2 from gas wells with amine then either convert to CO and use as fuel, or turn into liquid and pump back down to displace hydrocarbons, or into liquid and dry ice as a saleable porduct. Thoughts?

"Idea is to recover CO2 from gas wells with amine then either convert to CO and use as fuel, or turn into liquid and pump back down to displace hydrocarbons, or into liquid and dry ice as a saleable product." Energy required in this application would exceed energy recovered.

Hi, Akuyu!

First of all, a very large Welcome! to the CR4 blog site. I hope you have a very rewarding time sharing your views, ideas and comments in here with us. It's nice to have you here!

The problem as I see it with pumping anything at all down into gas wells as a displacement for the contents is that we have not properly investigated the environmental impact of that process. Just like, for example, geothermal engineers attempting to change the permeability of the rock strata a depth by chemical or sonic/explosive means in order to better facilitate that method of energy harvesting have no clue about what that process will do to the below-ground environment. Nor, apparently, do they care about it, since geothermal's ability to produce a tidy profit with a fairly uncomplicated energy reclamation system is well-understood. The point is that thorough below-ground environmental impact studies are not being made before action is undertaken in most aspects of the well-production industry.

You may ask, "what can anything at that depth do to affect life on earth's surface?" But the smallest reflection on the subject leads to the inevitable conclusion that both are unalterably interconnected. Take for example the activity at the well head of oil producing operations. Below-ground cavities have collapsed, or siphoned away the surface water in nearby rivers and streams, or allowed the seepage of oil being mined into cavities that are met in the sunken pipeline to the oil/gas reservoir. Lately, the oil companies have tried to prevent these calamities by pouring cement pipe casings through the wells' tubing. In addition to well impact on both surface water and aquifers, life forms ranging from unusual bacteria and algae to complex animal life have been discovered living in both the hot and cool subterranean and sub-sea worlds; and even where life is not supposed to be able to exist.

Below-grade food chains extend from the surface tillers (worms, ants, burrowing animals) and detritus eaters down through the nitrogen-fixing bacteria, down through the methanogenic bacteria down through who knows how many eco-layers for who knows how deep a distance. We have already discovered that life in the oceans extends to the bottom of even the deepest depths. Interactively, all life forms lead eventually to a survival of the species at the top of the food chains, including us.

Pumping CO back into the wells, especially in liquid form, may have far-reaching impacts on the environment that you have not considered. So, before attempting anything of that nature, it might be a good idea to team up with some below-surface ecology experts to determine the safest way to go about displacement with the least amount of below-surface negative environmental impact.

And it might be a good idea for those already in like pursuits to do the same. Let's not wait until later to find out that we made some huge mistakes in order to sacrifice planetary safety on the altar of the profit.

Mark