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Converting CO2 Back to Fuel

Elcat
ELCAT uses catalysts within carbon nanotubes for the photoelectrochemical conversion of CO2 to hydrocarbon fuels.

Most of the work on reducing the concentration of anthropogenic carbon dioxide in the atmosphere is focused on either reducing the emissions from fossil fuel combustion or capturing and sequestering the resulting carbon dioxide. There is, however, a third possible path: the conversion of CO2 back to a hydrocarbon fuel.

In an invited talk at this week’s National Meeting of the American Chemical Society, Professor Gabriele Centi from the University of Messina provided an overview of an ambitious EU-funded project to use solar energy to power the photoelectrochemical gas-phase conversion of CO2 back to hydrocarbon fuels.

It is feasible to convert CO2 to fuel. There is still a long way to go to practical application, but it is a good and interesting direction to go.

—Prof. Gabriele Centi, University of Messina

There have been a number of attempts over the past decades to use solar energy to reduce carbon dioxide (CO2) and water (H2O) into a variety of products, including hydrogen and carbon monoxide for use as a syngas for further processing (e.g., Fischer-Tropsch) as well as direct hydrocarbon products.

Past efforts have found that the rate of recombination is not very high and productivity is very low, according to Prof. Centi. The products formed were lower carbon hydrocarbons—CH4 (methane) and CH3OH (methanol) for example. No hydrocarbon greater than C3 was obtained.

These aqueous phase processes found that the photoreduction of carbon dioxide was in competition with the formation of other reaction products, the formation of which would need to be blocked to develop higher carbon hydrocarbons—i.e., hydrocarbons closer to the liquid fuels used in most engines.

There were also a number of other limits on the processes. But not much had been done in exploring a gas-phase conversion.

The EU provided €875,246 ((US$1.1 million) in funding for ELCAT—electrocatalytic gas-phase conversion of CO2 in confined catalysts—a three-year project under the Sixth Framework Program (6FP) to focus on the gas-phase electrocatalysis of CO2 to Fischer-Tropsch (FT)-like products (C1-C10 hydrocarbons and alcohols). Work began in 2004.

The project was born from the observation that with carbon dioxide confined inside carbon micropores, and electrons and protons allowed to flow to an active catalyst of noble metal nanoclusters, that gaseous carbon dioxide was reduced to a series of hydrocarbons and alcohols. The reaction products were remarkably similar to those of the Fischer-Tropsch (FT) process in which synthetic gas is converted to a series of hydrocarbons (alkanes, alkenes and so on) and water.

Three organizations are involved in addition to the University of Messina, Italy: Fritz-Haber-Institut der Max-Planck-Gesellschaft in Berlin, Germany; Université Louis Pasteur in Strasbourg, France; and University of Patras in Patras, Greece.

The ELCAT approach confines the catalyst particles within carbon nanotubes. The catalyst particles need to be quite small, due to the fact of the high number of electrons that must be transferred to generate the higher hydrocarbons. The number of electrons required is quite high—on the order of 24 for a butanol product, and an average of 46 for C8 to C9.

There is no evolution of hydrogen in this process.

The ELCAT team has found that it is possible to produce higher carbon hydrocarbons (C8 to C9), with productivity depending upon a number of factors such as catalyst, electrolyte and flow rates.

As a closing note, Prof. Centi observed that in addition to its utility on Earth, such a process would be of use for Mars missions that could use Martian resources (CO2 and water) to produce propellant for Earth return as well as life-support consumables.

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Comments

SJC

Why not gasify biomass and pipe the CO2 back to oil wells to get more oil out and then to old gas wells for storage. That way we turn plants into CO2 collectors and maybe take some of the ppm back out of the air.

Roger Pham

Welcome back, Rafael,
Thanks for eloquently posting what I was planning to post. This artificial photosynthesis will be the greatest achievement for our energy future, if it could be efficiently and cost-effectively reduced to practice as cost-competitively with fossil fuels as possible.

Who will pay for the cost? The same people who are paying for petroleum, natural gas, coal and nuclear energy right now, meaning all of us.

That ocean CO2 sequestration is also a very good idea, but again the question will be who will pay for all the cost of this non-economic endeavor? It would be far easier to get people to pay for renewable energy rather than paying for doing something without immediate benefit to themselves (CO2 sequestration without economic gain)

SJC

CO2 sequestration is estimated to cost 30% more than without. One of the people at NREL was quoted as saying that he would rather see all that money go to renewables.

Paul Dietz

CO2 sequestration is estimated to cost 30% more than without.

This statement is at best misleading, at worst meaningless. There are many ways to do sequestration, and some cost less than this. You are possibly refering to capture of coal-derived CO2 from flue gas using MEA. This is not the best approach. Precombustion removal of CO2 in IGCC, or flue gas extraction using the chilled ammonia process, should be much cheaper.

SJC

The statement was made at NREL and refered to IGCC plants. If people want EVs then they need electriity. If they don't want all nuclear then they may need clean coal. If you have a much cheaper way to sequester, then I suggest you contact the DOE and NREL.

Paul Dietz

If you have a much cheaper way to sequester, then I suggest you contact the DOE and NREL.

EPRI and Alsthom suggest the chilled ammonia process could separate 90% of the CO2 from flue gas for as little as $15/tonne. This should not increase the cost of power from a powdered coal plant by 30%.

SJC

From what I understand, the comment from NREL was based on not only the extra cost of the plant, but the increase in fuel usage. It stated that the increase in IGCC fuel usage could be as much as 17% over a non-IGCC plant producing the same power. There is a cost associated with not emitting CO2 to the atmosphere. The question is, do we have an accurate assesment of these costs and are we willing to pay them.

Stan Peterson

Whoa! Way too many of you unscientific technical illiterates assume that "Solar energy" is pollution free.

Well its not! that is pure nonsense.

In a discussion here one fellow complained of the cost of 1,000 000 km sq of Pv cells. But he didn't complain about the consequences. He just naively assumed as did the original proponent, that they were benign. Far from it.

Do any of you have any conception of the environmental damage done by the operation of 1,000,000 sq km of PVs. Aside from the aesthetics, you would immediately create a Saahra dessert of over 1,000,000, km sq as you raised the temperature there by 30-60 degrees Celsius by the massive alteration of the Albedo. The place would be hotter than the deepest Sahara by many degrees. That oven would roast the local flora and fauna and generate weather effects like tornadoes and massive precipitation and soon sandstorms over at least twice the area.

The supposedly bad thing about fossil Carbon fuel is that it alters the re-radiation to space of incident solar energy to the surface and atmosphere of the Earth. It does this by absorbing energy and reradiating it at a a different less transparent frequency.

Whatt is a PV cell if it is not an carefully engineered product that is expressely made to absorb as much a possible all the solar energy frequencies, convert some to other energy forms, and shift it and re-radaite the waste (which is around 89%!) at best. A PV cell essentially is a carefully made "Green House Gas" analogue but much more effective and powerful.


Why would you want to dump the equivalent of vast quantities of CO2 effect onto the Earth to generate phoney "clean" energy to make some fuel from realtively minicule amounts of atmospheric CO2?

There is an old proverb about the wisdom of "jumping out of the frying pan into the fire..."

Roger Pham

Stan the man, please spare us the inappropriate insult. Many forum members here are highly-credentialed scientists and engineers.

Now then, please recall that in one hour, the earth receives enough solar energy to equal all of human energy consumption world-wide in one year. One year has 8760 hours. At 30% solar-to-electricity efficiency of concentrated solar PV (demonstrated efficiency up to 40%), one will need 3.3 hours of total earth insolation to equal total human needs in one year. Since 30% of this solar radiation is already turned into electricity, only 65% of this will be turned into heat at a level reflection of 5%, since there are no perfect radiation absorber, nor are there perfect reflector. 65% heat production will amount to but 2 hours of total earth insolation. How good is desert sand at absorbing solar radiation into heat? At least over 50%, depending on the sand colors and composition. Dividing the 2hrs by 8760 hours and multiply this by 15% the heat production difference between sand and concentrated PV will give 0.003% the heat increase as the result of enough solar collectors to satisfy all human needs. Darker sands or dark ground will absorb heat at higher rate than 65% that of concentrated solar PV's, and will result in less net heat received. At night, the darker concentrated PV will irradiate heat faster into space to partially make up for the 15% increase in heat absorption during the day time, so, the net heat gain by concentrated PV will be even smaller, much smaller than the .003%, may be 0.0005% or so...Please do the math, if you are such a genius!

The .003%-.0005% in either direction is negligible heat gain or loss in comparison to the vast quantities of heat retention as the result of green house gas piling up as the result of consumption of fossil fuels.

SJC

Or, you could just turn the heat into electricity using solar thermal concentrating parabolic troughs, like they do in the Mojave desert at Kramer Junction in California. In more than a decade of operation, I have heard of no negative effects to the desert from their operations.

Noogums

A little left field here, but Roger and Stan's quarrel on solar pannels and hot sand gave me an idea perhaps useful for this discussion. Why use solar pannels?
If there are places with black sand around the place that can absorb so much heat, why not run long heat pipes with fins (to grab heat) along the desert floor slightly submerged under this black sand which gets so hot. You coud use the heat to drive some turbine. The cold end of the heat pipe can be burried some 10-20 m below ground level where the average temperature remains about the same all year round.

This would solve the issue with solar pannels being an eyesore, and lessen the environmental impact in fabricating the panels themselves (assume the copper/aluminium heat pipes are relatively ok to manufactureenvironmentally)
Plus the overall exercise would be much cheaper to implement then solar pannels.
The assumption is that sand storms don't gradualy raise the height of the sand at a noticeble rate such that the pipes end up too far below the ground. I've no idea what the drop in temperature with depth of sand is should this happen.

SJC

I am not sure there are a lot of black sand deserts. The temperature you get would have to be high enough to get an adequate efficiency out of something like an organic turbine used in geothermal. Those temperatures would be on the order of at least 200F just to get maybe 10% efficiency. I do not think you would get 200F temperatures with pipes and fins buried in a black sand desert. Not a bad idea using the earth to condense. You would be creating a sort of solar geothermal system. There are news groups like alt.solar.thermal and alt.energy.renewable that you can get on Outlook Express that discuss lots of these ideas, if you are interested.

Alex

Probably a much more effective but not very popular approach would be changing people's mind set about energy use. The US has over twice the ammount of carbon emissions per capita to the EU. There is a lot to be won there.

RichardH

My two cents' worth on PV as an energy source. First, I am bemused by those who talk about covering vast areas of the desert with arrays of PV (even here, in the Australia, where we're not short of deserts). Of all generation technologies, PV is the most distributed. It makes no sense whatsoever to build a vast array, convert the low as-generated DC voltage to transmission-level AC, send this power through the grid at several hundred thousand volts, and transform it back down to the domestic low voltages we all use. While the current generation of PV panels may be aesthetically challenging, a few years at most will see the availability of construction materials designed for outdoor use (roof tiles, sheeting, windows, awnings) that also generate electricity and perhaps (through thin-film Li batteries) store it as well. Work it out: your roof and mine (at least if you don't live in an apartment building) more than likely has more than enough area to meet the total energy needs of your house with PV cells that are around 10% efficient (you might have to look at your space-heating and cooling options more carefully).

Cost, you say? The cost of electricity from PV is falling in line with classic experience curve effects; with compound annual growth rates in installed capacity of 25%, the real cost of PV-based electricity halves every eight years. By the end of this decade it will be cheaper (at the household electricity meter) than grid electricity for most of us; give it another decade and it will be cheaper for the average punter to disconnect him/herself from the grid entirely--and run his electric/PHEV without recourse to the gas station, too.

This is not science fiction, just the extrapolation of long-term technological trends. Too often people (and not just those who have little or no technical education) see the future as being built on today's commercially available technology.

Jared

My thought and sure others as well, sounds like this is the breakthrough chemical process needed to almost finish an organic solar cell. I love the idea of this being able to recycle carbon, now nano carbon tubes may become inexpensive....

Finally

wolfgang barnbeck

converting co2, is the only chance humans have. uncountable plants are doing it since uncountable years.
quit quiet and without getting money :)
I think, something fails in the lot of methods.......
;)

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