Scientists Recycle CO2 with Sunlight to Make Fuel

An anonymous reader brings us this article from Wired about a new method to produce fuel with the help of concentrated sunlight and carbon dioxide. The process "reverses" combustion, breaking down the CO2 into carbon monoxide, which is then used as a building block for hydrocarbons. Quoting: "The Sandia team envisions a day when CR5s are installed in large numbers at coal-fired power plants. Each of them could reclaim 45 pounds of carbon dioxide from the air daily and produce enough carbon monoxide to make 2.5 gallons of fuel. Coupling the CR5 with CO2 reclamation and sequestration technology, which several scientists already are pursuing, could make liquid hydrocarbons a renewable fuel."

Doesn't make sense

[SiliconEntity]

It doesn't make sense to me: first you burn coal, which basically creates energy by oxidizing carbon and creating CO2; then you use solar energy to undo that and turn the CO2 back into CO. Wouldn't it make more sense to make electricity directly from the solar energy and not involve the coal at all? Besides which, if the CO is later used as fuel as they say, then eventually you're going to oxidize that anyway and create the same CO2 you would have in the first place. It seems like a very roundabout way to add solar energy into the mix.

Renewable not!

[bradbury]

So long as any of the carbon in the cycle is coming from sources currently in the ground or oceans (e.g. coal, oil, natural gas, or methane clathrates). I.e. we are harvesting energy by oxidizing previously reduced carbon -- it is NOT RENEWABLE or SUSTAINABLE!

The only cycles which potentially work over the long term are: (a) solar; (b) fusion reactors; (c) breeder reactors; (d) thorium fuel cycle reactors. That is probably in decreasing order of length of time we could sustain our civilization off of those sources (your opinions may differ).

The coal power plant output conversion of CO2 to liquid fuels simply shifts the problem from an CO2 source one can easily sequester (coal plant smokestacks) to one which is much less easy to sequester (automobile exhausts). You have a fundamental problem here which is when are we going to incorporate the cost of "full sustainability" into our energy costs? That means any carbon you put into the atmosphere you pay to take back out of the atmosphere. Ideally you do more than that to reduce atomospheric CO2 levels back to pre-industrial levels [1], i.e. you are taking more CO2 out of the atmosphere than you are putting into it. We are currently very far from being able to do that.

So long as we continue to live off of the reduced carbon sources (stored solar energy harvested by plants hundreds of millions of years ago) and don't fully pay for them we have a real problem.

Robert

1. Or humanity makes a decision to allow the glaciers and icecaps to melt, the sea levels rise a bit, some islands and low lying areas get flooded, weather patterns to change a bit *and* spends the money necessary to mitigate the negative effects of these processes.

Re:Doesn't make sense

[vakuona]

It enables people to not have to change everything overnight. We have a big investment in carbon based fuel processes, so having away to create hydrocarbons which we then burn, and create CO2, then use solar energy to repeat the process means that hydrocarbons are now just an intermediate step, and that we have a dynamic equilibrium, and can forgo the pain of trying to get rid of all our petrol engines and replace them with fuel cell engines. At least, this won't have to be done overnight, and we actually do stop the increase in greenhouse gases, because we recycle them.

If it works, it is a clever solution.

Re:Doesn't make sense

[Znork]

"Wouldn't it make more sense to make electricity directly from the solar energy and not involve the coal at all?"

To some extent, yes. The main problem is that electricity produced needs to be (almost) instantly consumed. Chemical storage of the energy avoids that problem. As such, there are various forms of chemical energy storage, ranging from batteries, through hydrogen, through ammonia to hydrocarbons, all with their own problems and advantages.

With batteries, the main trouble is they store too little and they (comparatively) rapidly break down.

Fuel cells can run on hydrogen or ammonia, with varying success. Hydrogen is a PITA to store, but perhaps ammonia is a simpler compromise.

Or hydrocarbons. Which have the advantage of being easy to store and fairly stable.

The thing about the energy crisis is there is no lack of energy (in fact, global warming is in essense an excess of it, and provides excesses of it in the form of weather). There's just a huge problem of extracting, transporting and, above all, storing that energy so you can use it when and where you need it.

Re:Not carbon neutral

[xaxa]

The caption for the picture in the article reads "Sandia researcher Rich Diver checks out the solar furnace which will be the initial source of concentrated solar heat for converting carbon dioxide to fuel. Eventually parabolic dishes will provide the thermal energy." so it seems he is concentrating the solar energy anyway.

More steps, more energy loss

[Veramocor]

Or you could use solar energy directly (photovoltaics or solar thermal) to generate electricity and not use as much coal decreasing Carbon dioxide emissions that way. Instead they generate electricity using coal, then use solar energy to convert the CO2 back, which is dumb because each processing step has inefficiencies associated with it and adds unneeded complexity to the system.

In the best case it takes as much energy to break the CO2 bonds as you get from generating the CO2, in reality it will take much more.

Re:Renewable not!

[bradbury]

I'm not saying it is impossible to use CO2 from the atmosphere as an input. Plants do it. But they have a *lot* of surface area to harvest CO2 which is only present at hundreds of ppm levels. We have the same problem with harvesting CO2 from the atmosphere that we have with harvesting solar power from the sun -- one has to produce relatively complex molecular structures, which are hopefully lightweight, at high surface area to mass (cost) ratios.

If we solve those problems for solar cells, we may be on the path to solving it for carbon sequestration -- but I expect it will be at costs significantly higher than we currently pay for energy from ancient reduced carbon sources. (Carbon sequestration fees are essentially a tax on our semi-sustainable use of ancient solar energy. We *will* eventually use up all of the ancient solar energy resources.)

I don't think we will solve either the inexpensive solar energy or inexpensive carbon sequestration problems without a far amount of bionanotechnology or "hard" nanotechnology (diamondoid and robust molecular manufacturing) being applied and I'd guess we are 10+ years away from the first and 25+ years away from the second.

Robert

Re:Doesn't make sense

[saundo]

The mising link is how to get the CO2 that is now emitted from the cars burning said converted fuel. I suspect that it might not be enough to offset that through simply removing CO2 from the atmosphere in equal amounts, but I digress.

The fact that this kind of secondary use of solar energy is starting to come about is a much more interesting development. Sure, you can generate electricity/heat water/etc from solar, but what else can we do with that energy that is also beneficial? THAT's interesting.

Re:underwhelming

[Jimithing DMB]

Interesting? Mods.. please. I really hope the poster was joking.

[...] the solar energy could be more profitably used to directly produce electricity

As if we have a limited supply of solar energy. Yes, we better not do this because we might drain the sun.

The sad thing is that I think there are far too many people on this forum who are completely uninterested in technologies like this. Yeah, sure, we'd love to be able to grab all the energy we need from the sun and we'd love to be able to store during dark periods or transmit it with relatively low loss from lit areas to unlit areas. And it'd be great if we could harvest energy from the winds (hey, I'm a sailboat racer.. I do it all the time) or from the natural water flows.

However, until we can get all of these technologies working, something we may never see in our lifetimes, wouldn't it be nice if we could reduce the amount of pollution we produce and start harvesting at least some amount of energy from the sun? It's basically free energy. Every little thing we can do to use it will greatly improve our ability to continue the lifestyles we enjoy while reducing our environmental footprint.

We've got at least a few generations and probably many more to work this out and come up with creative ways to both meet our demands for energy and reduce our environmental footprint.

Re:underwhelming

[evanbd]

And steam locomotives would seem easier than high-temperature turbines. "Seems easier" is not what I'd call a good metric for evaluating such a technology.

Re:OK, Let's Do the Math

[misleb]

Correction: I messed up the calculation, the actual number is 240,000 units - but stil, a ridiculous quantity.

Not to mention that even if you did convert all the CO2 from the coal plants... you'd just be burning it again in cars (or something else). The entire process would not be carbon neutral. You're merely reusing the carbon once. In the end, you're releasing the exact same net amount of CO2 into the atmosphere.

Might as well just use the solar energy to create electricity directly and reduce the amount of coal burned in the first place. That would reduce the net amount of CO2 (from coal plants, anyway)... not just delay its release.

-matthew

Re:Vaporware

[myc]

You may have missed the part about requiring sunlight. Also, a common misconception about photosynthesis is that plants need "nutrients" to synthesize glucose from CO2. In terms of the biochemical pathways, the only "nutrient" that are required are water and CO2; the free energy required for photosynthesis and de novo glucogenesis is provided by photons from sunlight. ATP and NADPH, energy intermediates that are consumed during the dark reactions of photosynthesis (the Calvin cycle), are generated during the light reactions of photosynthesis.

Re:Vaporware

[evanbd]

I suppose you neglected to read the whole "solar energy" part of the article? The point of all these things, be they this plan or biofuels, isn't some magic pixie dust source of free energy. It's that the easiest way of getting solar energy into a useful form might be to take a detour through plants or CO or steam or something else.

Fortunately, some people are actually trying to solve these problems rather than bitching on /.

Re:Recycling CO2

[x2A]

"this does not remove CO2 from the atmosphere"

Well technically it does, it's just that burning it puts it back into the atmosphere. Anybody who feels strongly enough could bury it instead.

Re:Doesn't make sense

[dvice_null]

> For example, in Norway we produce much of our power using hydroelectric powerplants that run water coming from large magazines in our high mountains

1. Get a high mountain
2. Build hydroelectric powerplants
3. Sell electricity
4. Profit

I never realized it was that easy. So now I only need a mountain...

Re:Grampa's biotech solution

[arivanov]

Neither.

I am referring to the massive subsidies received by the corn farmers in the USA and the sugar beet farmers in Europe.

Re:Doesn't make sense

[Anonymous Coward]

Norway may have an abundance of craggy valleys and the like, but the reservoir required in most places to generate hydroelectric power is a considerable cost. For example, the Hoover Dam, a large, but not monstrous project, covered 640 km. That is a significant cost, especially in populated regions where people have to be moved. Furthermore, river bottom land is usually the most agriculturally productive, so the cost of hydro power is fairly high, not to mention the environmental costs of damming a river, and then the costs of de-commission at the end, with all the toxic muck at the bottom of the dam. That is why hydro power has fallen out of favor.

Re:Recycling CO2

[homer_ca]

Oil is already too expensive to use for power plants. Liquid fuels sell at a premium because all our transport runs on internal combustion, and the fuel produced by this process goes into a completely different market from the one for grid electricity. Electricity is probably still more efficient for harnessing solar energy, but as long as we need liquid fuels for transport, we'll need to consider ways like this to reduce oil usage.

Personally, I'll worried more about the production rate of 2.5 gal of fuel per day from each unit. They better work on scaling it up to be useful.

Re:Doesn't make sense

[Brandano]

Not really, it is quite possible... they already do this in Brazil somewhat. Grow sugar cane, distill it in methanol and use it as fuel. You don't even need to alter the engine. The problem is that to do this you need to wipe out a rather large portion of amazon forest, and use it to produce fuel rather than food. And tearing down the forest is bad for the environment, NOT because it uses up CO2 to produce O2 (it doesn't really, uses up almost the same amount of O2 it produces, and puts out almost the same amount of CO2 it uses. The oceans are what gives us fresh air) but because it throws the equilibrium off. Growing plants for fuel is more efficient than creating a solar farm, but we don't really ave the space for it.

Re:Vaporware

[evanbd]

The energy content that comes from the solar input is renewable. Certainly the system isn't completely renewable energy, but improvement is a good thing. It would replace some of our oil use with reprocessed CO2 from coal. "It isn't perfect" is a really, really horrible reason to not do something that's far better than the current plan.

Re:OK, Let's Do the Math

[PReDiToR]

if you did convert all the CO2 from the coal plants... you'd just be burning it again in cars (or something else)

And what would the cars be burning otherwise?

Oil is a fossil fuel too, using coal twice saves on burning gasoline once.