The Naked Scientists

The Naked Scientists Forum

Author Topic: Why not break down excess carbon dioxide into carbon and oxygen?  (Read 14487 times)

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 511
  • Thanked: 12 times
    • View Profile
Nick Gassman  asked the Naked Scientists:
   
Hi Chris. I have a question that I'd love to hear on the show.

We do of course hear a lot about what to do with the build up of CO2, and there's much debate about storing it underground. I wonder though why we don't hear of plans to break it down into carbon (and then used for nanotubes and graphene), and oxygen. Is it that the energy cost of doing so isn't worth it, or some other issue?

Thanks

Nick Gassman

What do you think?
« Last Edit: 15/08/2012 01:30:01 by _system »


 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
The energy is the issue.

Oxidizing hydrocarbons is used to produce energy (which is why we use coal and natural gas, and gasoline, and etc).  It would take energy to reverse the process.

There have been proposals to essentially just burn the hydrogen, and leave a type of concentrated carbon/coke.  But, that would would essentially only utilize about half of the energy from the fuel.  It still might be worth considering.  The carbon could then be easily buried with the intention of keeping it away from biological organisms that might break it down and eventually create CO2.

Plants, of course, do just what you're proposing.  Using photosynthesis, they use solar energy to produce hydrocarbons from the carbon dioxide (and other nutrients).  The "and other nutrients" could potentially be a problem in the future.  If we utilize fossil fuels, then we overwhelm the natural ability to absorb CO2 by putting long sequestered carbon into the atmosphere. 

Biofuels are a cycle, of burning the biofuels, then having plants reabsorb the CO2, to be burnt again.  Unfortunately there is concern whether we truly have the capacity to grow all the biofuels we require as well as growing all the food we require.  There is also the concern about the environmental impact of fertilizers that are used to grow food and biofuels.

The USA is predicting a corn shortage this summer, and there are questions about reducing the corn derived alcohol that is being diverted into fuel.

A gradual reduction in global population would reduce the food/fuel pressure. 
 

Offline netwiz

  • First timers
  • *
  • Posts: 1
    • View Profile
Er, thanks, although I have to say I got a bit lost there. When you say 'proposals to just essentially burn the hydrogen', do you mean 'burn the oxygen' in the CO2?  Even if it only used half the energy, it would mean you're left with carbon (I assume), and not the 'dangerous' CO2. The other part is, isn't carbon useful? Carbon nanotubes? Graphene? Why does it have to be buried?

thanks
Nick
 

Offline schneebfloob

  • Jr. Member
  • **
  • Posts: 49
    • View Profile
CO2 consists of a carbon atom double-bonded to two oxygen atoms. Double bonds are extremely strong, and require a large amount of energy to break. You'd be inputting more energy into breaking down the CO2 than you'd have obtained from burning the fossil fuels in the first place.  So, in doing so you'd be burning even more fossil fuels, and thus releasing even more CO2, to provide the energy to do it. In the end you'd be making the problem worse, by adding to the CO2 and getting nothing really out of it. Plants can do it because they break down the process into a large number of steps, and make it energetically favourable. Plus they have the benefit of obtaining glucose at the end of it.

What CliffordK was saying is that the fossil fuels (hydrocarbons) can be utilised such that you effectively use up the hydrogen within them, without touching the carbon and so not releasing CO2. I've not heard of it before, and it sounds like a neat idea.
« Last Edit: 17/08/2012 00:19:38 by schneebfloob »
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
What CliffordK was saying is that the fossil fuels (hydrocarbons) can be utilised such that you effectively use up the hydrogen within them, without touching the carbon and so not releasing CO2. I've not heard of it before, and it sounds like a neat idea.
I'm sure I saw it somewhere, but I'm not seeing any more notes on it.  It didn't seem like a very efficient idea at the time.

Hmmm.
Maybe this from marcelo is what I was thinking of, about carbonizing wood and burying it.
http://www.thenakedscientists.com/forum/index.php?topic=40099.msg362039#msg362039

There are some notes about making syngas and biochar, which is then added to the soil.
http://www.renewableenergyworld.com/rea/news/article/2009/04/biochar-the-key-to-carbon-negative-biofuels
 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
mod note

William - Oxygen is consumed in the normal burning of hydrocarbons.  Clifford has correctly explained this a few times.  I am gonna have to ask you to stop propounding your own personal concepts of chemistry in the main forums. I have moved the discussion to New Theories. 
 

Offline TONY MANERA

  • First timers
  • *
  • Posts: 1
    • View Profile
I understand that it takes energy to break down carbon dioxide into carbon and oxygen and that, if such energy is derived from burning of fossil fuels, we just make the problem worse by generating further carbon dioxide emissions.
But who says that the energy required to break down carbon dioxide has to come from fossil fuels? Why can it not be derived from renewables, such as wind?
I know that wind energy is intermittent, but if the carbon dioxide can be temporarily stored, then it can be broken down during periods when wind energy is available.
Of course, there would be a cost (capital, depreciation and maintenance of the wind turbines). That cost could legitimately be charged to emitters of carbon dioxide. It would increase the cost of  energy produced from fossil fuels, discouraging such use in favor of non polluting sources. There could be negative economic consequences in the short term, but in the long term, benefits could be substantial.
Tony Manera
December 6, 2013
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
The amount of coal/gasoline/etc we're using is in the billions of tons a year.  It would take a lot of making and disposing of synthetic carbon compounds each year to offset that.  What are you doing with the carbon?  Feeding it back into the system as a fuel?  Making diamonds?  Consider how much more gasoline and heating oil you use than diamonds, graphite, carbon fiber, and etc.

At 50% or so efficiency burning carbon, then, say 50% efficiency at recovering the carbon, the energy losses would be greater than just using the electricity from the wind directly. 

In a sense, if one grows something like canola oil, one is using sunlight to convert CO2 to oil which can then be burnt in a renewable cycle.  If all our energy needs could come from Canola, then the CO2 problem would go away.  Unfortunately we've been too energy hungry to make much of a dent in our energy usage with renewable fuels.

Another option would be to grow trees.  If one can prevent the wood from decaying, indefinitely, then we are in effect taking the carbon out of the environment.  For example, use for framing in your house.  However, if that wood is ever allowed to rot, then the captured carbon is lost.
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Another option would be to grow trees.  If one can prevent the wood from decaying, indefinitely, then we are in effect taking the carbon out of the environment.  For example, use for framing in your house.  However, if that wood is ever allowed to rot, then the captured carbon is lost.

Another option, one which I believe could play a pretty big role is simple Algae. I am not that read up on Algae but I remember reading a paper about it, using iron sulfate to create "man made" Algae blooms in the southern sea where it would't bother anyone as it's pretty darn cold and uninhabited by humans pretty much. Then when the Algae eventually dies it sinks to the bottom and stores the CO2 for "at least several hundred years"

I am unsure why the Algae doesn't get decomposed by bacteria or other microbes when they sink like usual but it seems like a pretty good plan to try out.
Dumping Iron Sulfate into the sea, creating massive Algae blooms which takes CO2 out of the air and then stores it when the Algae blooms, seems simple enough.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
I am unsure why the Algae doesn't get decomposed by bacteria or other microbes when they sink like usual but it seems like a pretty good plan to try out.

It was tried last year... and apart from wondering what action was taken against this 'business man', I note that we are not all singing his praises and repeating this idea all over the oceans.

Simplicity is often very attractive when it comes to fixing a difficult problem eh!  And apart from the further acidification of the seas that is likely to occur, it seems somewhat premature to suppose that a little added iron is going to be the quick fix humanity wants.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
When it comes to the 'market' driving carbon mitigation efforts (all too slowly to be of any use IMO), I have to wonder about how the calculations are arrived at for some of this stuff. ... I can almost see some civil servant hitting on using electricity from wind or solar to 'crack' carbon dioxide indeed!

An example we have at the moment that seems especially lacking in 'full lifecycle analysis' is the import of torrefied (anaerobic 'cooked') wood, shipped from forests in Canada to the ageing Drax power plant here in the UK.  By doing this Drax's operators can merrily continue to burn large amounts of CO2-laiden coal, whilst keeping just inside the EU imposed emissions ceiling on greenhouse gases per MW.

A pragmatic (if still flawed environmentally) alternative it seems, would be to instead take the 'cooked' wood and stick it back in the ground close to where it was grown.  This is known as biochar (historically as Terra Preta) and is by far the oldest form of anthropogenic carbon sequestration.  The char can be produced in such a way that practically all the carbon locked into the wood during growth remains, but the cooked product becomes far more inert biologically than raw biomass ~ a web search on Terra Preta describes that soil and productivity is improved as well as locking in most of the carbon for centuries.

On this analysis, it would appear that ironically continuing to burn coal (the more 'local' the better) - with it's higher energy content than torrefied wood - and burying the very same biomass where it originated would mean less co2 is released. - No ships. - No lorries. - and better soils!

Or maybe I'm missing the obvious - ???
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4707
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
There have been proposals to essentially just burn the hydrogen, and leave a type of concentrated carbon/coke.

Like the bad old days of Town Gas, when we made all sorts of useful chemicals from coal tar, then used the coke to generate hydrogen from water.

Quote
A gradual reduction in global population would reduce the food/fuel pressure. 
The only sensible solution. zero cost + no new technology = global happiness. The problem is that "zero cost" and "no new technology" are anathema to economists and industrialists, and global happiness won't please politicians or religious professionals who rely on other people's misery to pay their salaries.
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
I am unsure why the Algae doesn't get decomposed by bacteria or other microbes when they sink like usual but it seems like a pretty good plan to try out.

It was tried last year... and apart from wondering what action was taken against this 'business man', I note that we are not all singing his praises and repeating this idea all over the oceans.

Simplicity is often very attractive when it comes to fixing a difficult problem eh!  And apart from the further acidification of the seas that is likely to occur, it seems somewhat premature to suppose that a little added iron is going to be the quick fix humanity wants.

What were the results of the attempt? Also, I believe the melting ice in the south sea releases iron on it's own so it's a natural phenomenon, but so is CO2 release, and we obviously cannot predict what all of the effects can be without testing.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
What were the results of the attempt? Also, I believe the melting ice in the south sea releases iron on it's own so it's a natural phenomenon, but so is CO2 release, and we obviously cannot predict what all of the effects can be without testing.

It did result in plumes of algae, but moral questions aside (about how and why this guy did this unilaterally), the 'ocean system' outcome seems anything but clear.  The simplistic concept that dead algae would reliably transport vast amounts of carbon to the seabed, or that if this did happen the sea's PH balance would remain unaffected - has not been verified.
« Last Edit: 13/12/2013 15:40:22 by peppercorn »
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4707
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
100 tonnes of FeSO4 in the Pacific? What on earth is the point of that? Every shipwreck deposits thousands of tons of iron in the sea (about 5,000,000 tonnes of Japanese merchant ships alone were sunk in the Pacific during WWII)  and every major river carries tons of the stuff into the sea every day. Probably 100 tons of meteoritic iron falls in the Pacific each day.

Or was the Press report several orders of magnitude too low?

Where's the science - or even common sense - in this?
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8661
  • Thanked: 42 times
    • View Profile
100 tonnes of FeSO4 in the Pacific? What on earth is the point of that? Every shipwreck deposits thousands of tons of iron in the sea (about 5,000,000 tonnes of Japanese merchant ships alone were sunk in the Pacific during WWII)  and every major river carries tons of the stuff into the sea every day. Probably 100 tons of meteoritic iron falls in the Pacific each day.

Or was the Press report several orders of magnitude too low?

Where's the science - or even common sense - in this?
A shipwreck deposits iron at the bottom of the sea where it is dark, and as a big insoluble lump.
Not ideal conditions for promoting algal growth.
So, the common sense is in doing something different, like "seeding" the surface with a soluble form of iron.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4707
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
A shipwreck deposits iron at the bottom of the sea where it is dark, and as a big insoluble lump.

Some ships sunk by gunfire or icebergs end up deep in the ocean, but the majority of wrecks and targets are in shallow coastal waters.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8661
  • Thanked: 42 times
    • View Profile
"A shipwreck deposits iron at the bottom of the sea where it is dark, and as a big insoluble lump"
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums