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."

underwhelming

[macurmudgeon]

2.5 gallons of fuel produced per plant, per day? It's nice that it might scrub pollutants but it seems the solar energy could be more profitably used to directly produce electricity.

Re:Doesn't make sense

[Martin Foster]

If you are going to burn the coal in order to produce the large quantities of energy required to warm and light homes. Then you can alleviate its impact to the environment and reuse some of that waste to make the system more efficient overall.

Solar power as of yet, is not effective enough to produce the energy of a major coal plant (with the same density of land area used). Coal plants however, pollute en-masse and this addition makes them more efficient and less hazardous to the environment as a whole.

Now if solar was as efficient, then there would be no point to it.

Re:underwhelming

[xaxa]

It would seem easier to pipe the CO2 into a greenhouse and grow some food.

Govt science at work

[cinnamon colbert]

NASA wanted a pen that would work in zero G; spent millions on RnD
The russians used a pencil

much more productive to focus on using less energy in the 1st place, in terms of energy saved/research dollar

these tech fixes are really obscuring the problem: our basic life style is not good. the govt should stop building highways, put money and tax incentives to get homes and jobs at mass transit accessible sites; just getting one or two million people out of suburbs into nyc lifesytles would do more for the enviroment then a million years of Rnd

Re:underwhelming

[pla]

It's nice that it might scrub pollutants but it seems the solar energy could be more profitably used to directly produce electricity.

Great idea in the equatorial region, but solar really doesn't count as an option in the polar two-thirds of the planet (at least not until we have near-100% efficient PV panels that cost a pittance).

I would also point out that very few companies seem to want to build solar power plants, even in ideal places such as the vast tracts of desert wasteland in the US SouthWest. I presume this results because the long term costs might look great, but the books would take a big hit up front, and most companies (or at least, their current boards) couldn't care less beyond next quarter.

Given those two facts, we can either talk endlessly about why we don't use cool-tech-X, or we can deal with the reality we have now: We use a LOT of cheap and dirty coal power plants. And it costs considerably less to retrofit them with spiffy scrubbers such as TFA mentions than it does to rebuild new clean plants.

Also, who says only power plants can use this? Why couln't I (and everyone else who might care enough to give something like this a try) buy one (probably a scaled-down version to make it affordable) and toss it in my backyard? Five or ten tons a year, times a few hundred thousand people who want a free gallon or two of gasoline per day, could really make a difference.

No one renewable energy source will solve all our problems. Between them all, however, perhaps we can at least keep the planet habitable for a few more generations of humans.

Same process as wood gasification?

[bear_phillips]

Is this basically the same process used in wood gasification? In a wood gasifier, wood turns to charcoal, to CO2 then to CO. This seems to be the same thing but using the sun as the heat source instead of hot burning charcoal.

Re:Doesn't make sense

[Eivind]

Some natural energy-sources (all energy-sources are "natural" by the way, why don't you use the standard terminology and refer to them as "renewable" energy-sources?) are very well able to accomodate fluctuations in demand and produce when we need the power, infact better than nuclear. (most of the cost in nuclear is constructing, safety and decommision, fuel is a pittance, which mean if you throttle down a nuclear powerplant you save essentially nothing. Yes you can do it, but the cost of producing at 25% is going to be 95% of the cost of producing at full-throttle)

For example, in Norway we produce much of our power using hydroelectric powerplants that run water coming from large magazines in our high mountains trough turbines attached to generators. Very nice:

• The magazines are re-filled automagically by a process known as "rain" (solar-powered!)
  
• The magazines store enough energy for like half a YEAR of use, so even longish periods of drougth are no problem.
  
• The powerplants can be ramped up or down according to need inside of less than a minute. Significantly faster than most fossil-fuel-burning powerplants.
  
• Efficiency is high, about 90% in a modern powerplant.
  
• Low impact: some lakes have water-levels that vary more than is natural, a few dams, some rivers have less water in them then they would naturally have. That's about it, the powerplant itself is typically in a mountain-cave and neither visible nor hearable.
  

It's an excellent thing for combining with other renewables: When the sun shines, use that. When the wind blows, use that. When tides are strong, use those. When neither produces much, dial up a hydroelectric or two.

Better still:

With modest investment, the things can be used as batteries: If you've at any time got to -much- power from other sources, use excess power to pump water uphill to one of the magazines, where it can be stored safely for months until needed. (yeah, this pump-turbine cycle will waste like 40% of your power, but that's true for most other kinds of batteries too)

Sucks if you live somewhere -flat- with no or little rainfall, I guess.

This vs biofuels, sustainability & how to do i

[cgraves]

I am working [columbia.edu] on a similar process that synthesizes hydrocarbon fuels from carbon dioxide, water, and non-fossil energy (could be solar) and should eventually have some publications out about this. There are several ways to go about this. But first, let me comment on some of the comments:

Regarding the "They're leaving the production of actual liquid fuel to other people ... all this thing does right now is produce carbon monoxide." comment [slashdot.org], reducing CO2 to CO is the hardest part of the process. Once you have concentrated CO, you can follow the coal-to-liquids processes and water-gas shift (CO + H2O => CO2 + H2) to get hydrogen and run the syngas (CO + H2 mixture) into Fischer-Tropsch [wikipedia.org] reactors. They've been doing this for 50 years in South Africa to produce synthetic diesel.

Regarding the "Renewable not!" comment [slashdot.org] and using power-plant flue gas CO2 as the input to this process, this would indeed not be sustainable. However, if industrial capture of CO2 from the air [columbia.edu] is available, one can fully close the loop and have a sustainable hydrocarbon fuel cycle. Flue gas CO2 could be a good option in the short term, however. For instance, if solar and other nearly-carbon-free energy sources begin to rapidly take over, coal plants will not immediately be shut down. Other CO2-emitting industrial plants such as aluminum smelters, etc, will also have CO2 emissions to deal with, and this form of using it to store non-fossil energy by recycling it once as a liquid fuel would be worthwhile. One comment [slashdot.org] discussed this transition well.

Related, other comments [slashdot.org] say "why not just use the solar energy to produce electricity". These intermittent resources need storage, and liquid fuel storage is not a bad method (and very versatile). Others responded [slashdot.org] about storage.

So, processes like this are a way to store non-fossil energy as a convenient energy-dense fuel which can be used in our existing petroleum fuel infrastructure and vehicles (as opposed to hydrogen and batteries). Biofuels can do the same, and there are many comments above ("I saw something like this... it's called a tree") mentioning biofuels and how this process replicates it with much more complexity; indeed you could call this whole process including the Fischer-Tropsch fuel synthesis "artificial photosynthesis". However, this process cuts out the middle-man of the plant in biofuels processes, which has much lower sunlight-to-fuel efficiency than industrial solar collectors (PV or thermal) and requires a lot of fertilizers and pesticides to boost growth rate. Such land- and resource-intensive agriculture is not sustainable [sciencemag.org] in its current form and may not ever be on the scale we will need it.

TFA discusses a solar-heat-driven thermochemical process that has potential. A somewhat similar solar-heat thermolytic process splits CO2 directly [www.lare.us] at higher temperatures. There are many other methods of accomplishing this that are at different levels of development and being researched, including electrochemical (pdf link1 [risoe.dk], pdf link2 [confex.com]), photoelectrochemical, photo(bio)chemical...

Re:Doesn't make sense

[ignavus]

Why not use the solar energy to compress air?

Then you use the compressed air to drive compressed air engines - even small cars for urban use (http://en.wikipedia.org/wiki/Air_car).

If compressed air leaks out of its storage, you get ... plain old air in the air. No pollution problems.

Homes could compress air during the day and consume it at night - or during the next day in their cars.

Compressed air is energy stored in a readily available, non-polluting medium. When it is used, it just returns into the atmosphere to become part of the great big reservoir of uncompressed air. No battery acid leaks or disposal problems.

Re:Doesn't make sense

[maxume]

Cane is fermented into ethanol, not methanol. The product of the fermentation is then purified by distillation.

And rainforest destruction isn't really driven all that much by Cane production(I would suggest asking a Brazilian if you don't believe me). It is driven by logging and small farming.