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Study suggests energy and GHG impacts of synthetic hydrocarbon fuels from CO2 are greater than impacts of existing hydrocarbon fuels

6 June 2014

Master.img-001
Synthetic fuel production from fuel-combustion-based energy and CO2 (top) and from atmospheric CO2 using solar electricity (bottom). Credit: ACS, van der Giesen et al. Click to enlarge.

Researchers at the Institute of Environmental Sciences at Leiden University, The Netherlands) have concluded that the energy demand and climate impacts of using CO2 to produce synthetic hydrocarbon fuels by using existing technologies can be greater than the impacts of existing hydrocarbon fuels. Their quantitative lifecycle assessment of the environmental merits of liquid hydrocarbon fuels produced from CO2, water and energy compared to alternative fuel production routes is published in the ACS journal Environmental Science & Technology.

In their study, the researchers evaluated five hypothetical production routes using different sources of CO2 and energy. The team undertook the work specifically to investigate four general arguments that have been proposed in support of such fuels:

  1. That such fuels are renewable and can be used in the existing energy infrastructure;

  2. That solar fuels—liquid hydrocarbon fuels produced from CO2, water and solar energy—provide a synergistic solution to the problem of overabundance of CO2 and the abundance of renewable energy on the one hand, and the scarcity of hydrocarbon fuels on the other.

  3. That solar fuels offer the promise of solar energy storage—a key challenge in a world predominantly relying on renewables.

  4. That the costs of carbon capture can be offset by producing valuable fuels or chemical products from CO2.

If we review these four broad claim areas, we observe that all of them have merit in principle, but all of them call forth immediate questions of utility. These questions often cannot be answered in abstracto but will require some form of (quantitative) life cycle assessment (LCA). Although the importance of a life cycle approach for these questions has been acknowledged, the authors are not aware of any existing LCA studies on CO2 utilization. It has been the observation of the authors that—in the absence of such evidence—the participants in the public and scientific discourse on solar fuels use any or all of the four claims above to substantiate their argument. In the absence of quantitative evidence for or against, four intuitively persuasive arguments make a very strong case indeed. This is the state of affairs as we perceive it to be. It is the purpose of this paper to hold the claims up to quantitative scrutiny and review the general merit of the idea of solar fuels, subject to the definition above.

—van der Giesen et al.

In the study, the team called fuels produced by the conversion of CO2 into liquid hydrocarbon fuels using proven technologies “synthetic fuels”, and fuels produced via a production route that uses solar energy “solar fuels”.

The team explored three different CO2 sources (from natural gas (NG) combustion; from biomass (BM) combustion; and from direct air capture (DAC)); and three sources of electricity (natural gas (NG) combustion; biomass combustion (BM); and solar (PV)). For the study, the hypothetical CO2 pathways were designated by the combination of abbreviations for CO2 source and power—for example, DACPV indicated direct air capture for CO2 and solar power.

Their lifecycle analysis of the fuel production routes put a main focus on the energy and material inputs, using fuel production from source-to-fuel expressed in 1 MJ of liquid fuel as the functional unit. CO2 emissions from combustion were also taken into account when calculating net GHG emissions.

They compared the outcomes to the performance of existing hydrocarbon fuels such as diesel; bioethanol; from sugar cane; GTL and BTL diesel.

Master.img-005-2
GHG emissions of different liquid fuel production routes related to a functional unit of 1 MJ. Data for diesel, GTL, ethanol, BTL and solar hydrogen cannot be divided into the uptake of CO2 and connected processes and are therefore aggregated. R indicates reference alternatives not explicitly modeled in this study. Credit: ACS, van der Giesen et al. Click to enlarge.


Master.img-006
Disaggregated cumulative energy demand (CED) scores of different liquid fuel production routes related to a functional unit of 1 MJ. CED data for diesel, GTL, ethanol, BTL, and solar hydrogen are presented in aggregated form since separate production steps for hydrogen and CO2 cannot be discerned. R indicates reference alternatives not explicitly modeled in this study. Credit: ACS, van der Giesen et al. Click to enlarge.

Overall, they found that an improvement in life cycle CO2 emissions is only found when solar energy and atmospheric CO2 are used. With respect to their analysis of “the four questions”, they found:

  1. Even the best performing fuel production route (DACPV), both now and in the near future depends on nonrenewable fuels and large amounts of renewable electricity.

  2. The showed that using CO2 from a fossil origin will not provide a carbon-neutral fuel. Carbon neutral fuels might be produced from CO2, but only in a future energy system completely based on renewable energy.

  3. The third claim, that producing fuels from CO2 presents a route to storing renewable energy could not be completely supported or countered from the results, they concluded. Producing fuels from CO2 by using solar electricity converts solar energy into easily stored chemical energy. To assess if this is a preferable route to store energy, additional research is needed in which the production and use of fuels from CO2 needs to be compared with battery and hydrogen storage and possibly others storage options, such as water reservoirs, they concluded.

  4. Producing a fuel from CO2 neglects the primary goal of carbon sequestration. In addition, more energy is needed to produce a fuel from CO2 than it will deliver when combusted. It would be more profitable to sell the required energy directly on the market than to lose a great deal of energy in the inefficient production of liquid fuels, the researchers found.

In conclusion, we state that the energy demand and climate impacts of using CO2 to produce synthetic hydrocarbon fuels by using existing technologies are higher than the impacts of existing hydrocarbon fuels. The intuitive claims in the public discourse cannot be supported by our quantitative assessment which shows that producing liquid fuels from CO2 is not the straightforward panacea as suggested. However, novel technologies (e.g., photocatalytic, solar thermal and enzyme based routes) might show a slightly improved system performance.

In a distant future, we foresee possible niches for hydrocarbon fuels produced from CO2. Since hydrocarbon fuels offer high energy to mass and volume ratios compared to alternatives like electricity and hydrogen, the application of fuels produced from CO2 in applications such as airplanes and heavy duty transport may prove to be a valuable but future niche. Another application could be as a storage medium for so-called stranded renewables. Because renewable energy technologies produce difficult-to-store electricity and renewable electricity supply increasingly exceeds demand, research has begun in leveling supply and demand using concepts such as smart grids. Even in smart grid systems it can be expected that some sort of energy storage will still be needed. For storing large amounts of renewable energy, the production of synthetic hydrocarbon fuels is one of the technologies that could be used. However, it would have to compete with other storage technologies such as batteries, hydrogen storage, water reservoirs, or compressed air storage.

—van der Giesen et al.

Resources

  • Coen van der Giesen, René Kleijn, and Gert Jan Kramer (2014) “Energy and Climate Impacts of Producing Synthetic Hydrocarbon Fuels from CO2,” Environmental Science & Technology doi: 10.1021/es500191g

June 6, 2014 in Biomass, Carbon Capture and Conversion (CCC), Carbon Capture and Storage (CCS), Fuels, Solar, Solar fuels | Permalink | Comments (22) | TrackBack (0)

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Comments

boulderdash

Are various types of fuel combustion and CO2 route safe and justified for future energy production and storage?

Isn't time to use clean (non combustion) energy sources and electrify?

This is a flawed study with predetermined outcomes, they mix a lot of factors to leave an impression. I don't think many people advocate this as a storage medium.

Use natural gas in a combined cycle power plant, oxygen blow the turbines, then you will get pure CO2. Use electricity from renewable sources, use the carbon twice to reduce emissions.

Better yet, get the hydrogen and carbon from the natural gas to make synthetic fuels using the waste heat from the combined cycle natural gas power plant.

Don't start with assumptions that this must all be sustainable, renewable, CO2 neutral and a storage method, that is easy to prove wrong.

"..hydrocarbon fuels by using existing technologies are higher than the impacts of existing hydrocarbon fuels."

Notice that they do not show an LCA for taking oil from the ground to make gasoline for your tank. Use gasified biomass to get the synthesis gas, use the waste heat from power plants. Don't burn biomass to make electricity, that is a waste.

Like I've said before: Go BEVs first, use BTL or solar-fuels only as a range extender.

We have 200 million engine driven cars in the U.S. and 800 million world wide. At present and projected adoption of EVs being maybe 1% in the next ten years, I think we need synthetic fuels.

The car companies have failing the Earth's society by not working diligently to perfect EVs when they've known for decades their engines cause pollution, climate change and health problems.
Think how much closer we would be to an all electric fleet and clean air, if they would spend their money on EV innovation instead of PR and Lawyers.

The only good combustion engine is a dead one. "Kill The ICE."

I don't see any conspiracy by the auto makers to render the EV non viable, it is a matter of a limit to the knowledge in electro chemistry.

Anyone with a sense for business knows that the first company to create a better EV battery will be rewarded with profits. If it were easy, anyone would do it.

Yes Lad. The auto industry has created a worldwide ecology and health problems and they should pay to clean it up including all secondary ill effects.

Somebody should start a HUGE class action against all ICE manufacturers to force they to pay for all damages (past, present and future) done. The penalties could be reduced by producing an equivalent number of BEVs.

The same should be done against CPPs facilities owners. The penalties could be reduced by producing an equivalent number of clean (solar, wind, nuke etc) kWh.

In our minds there are only 2 choices for massively scaleable carbon-free synthetic fuel: hydrogen and ammonia. All the otherwise attractive synthetic hydrocarbons are carbon intensive in the molecule.

Making hydrogen or ammonia from any feedstock allows full capture of process CO2 emissions for value added functions like CO2 Enhanced Oil Recovery.

There are many other methods to make these fuels, so the use of coal and natural gas in the immediate term (using sequestration) is just the first step. In the longer term, when fossil fuels are depleted or no longer cost competitive (50+ years from now) we will have perfected bio, renewables and nuclear methods of sythesizing hydrogen and ammonia.

This study is correct when it comes to the assessment of the inefficiency and economic non-viability of CO2 captured from either combusted exhausts or from the air. I've arrived at this assessment many times here in GCC.

There are vastly more efficient ways to produce synthetic fuels that are over 90% GHG-sparing and yet can produce gasoline and diesel fuels at cost competitive with petroleum.

One possibility is the process of adding renewable-energy H2 to the pyrolysis of waste biomass to produce bio-crude that is chemically comparable with crude petroleum oil. The renewable-energy H2 addition will double the energy yield of the waste biomass when it comes to the production of liquid synthetic fuels, or can triple the yield of waste biomass when it comes to the production of synthetic methane, since methane contains almost twice the amount of H2 in comparison to longer chains of hydrocarbons.

This, in addition to a growing percentage of BEV and PHEV, and FCV very soon to come, will means that we will have enough of waste biomass to entirely replace petroleum usage.

Hydrocarbon fuels are too valuable to be used for stationary use such as for electricity generation. For this, a combination of nuclear energy, solar, wind, hydro, leveled by energy storage of batteries, H2, etc...can do it much more efficiently and will be able to entirely displace fossil fuels such as coal and NG for power generation.

Furthermore, synthetic hydrocarbon fuels are too valuable for use in another stationary application: Living-space heating and water heating and process steam production. For this, the waste heat of power generation can be used, for example, from distributed power generation via H2-FC. Higher temperature PEM-FC can produce waste heat above the boiling point of water, and this heat can be used to produce process steam and hot water, as well as for living space heating. Cooking and baking requires higher temperature heat and can use electricity from FC, while hot water heating can use waste heat.

Thus, excess RE or nuclear energy in springs and falls can be used to produce H2 and stored in local pipeline and underground reservoirs to be used in winters for distributed co-generation of heat and power. Local personal transportation by FCV and short-haul trucking can use H2-FC utilizing the H2 stored from excess RE and nuclear energy. This will reduce the demands for hydrocarbon fuels to the point that we will have enough carbon in the biomass to produce all the hydrocarbon fuels that we will ever need!

If you want to make this sustainable and low carbon, gasify biomass and make more H2 and O2 with solar and wind. If you use solar, you can concentrate the IR and use the heat for an SOEC electrolyzer, more efficient.

@ Roger Pham:
To date, this is the best method yet that I've come across to store hydrogen.
http://phys.org/news/2014-06-hydrogen-liquid-fuel-atmospheric-co2.html

This is a flawed study with predetermined outcomes

I have to disagree with you, SJC.  The outcome was predetermined by thermodynamics, not any flaw.  I'd go so far to say it was a no-brainer.

Use natural gas in a combined cycle power plant, oxygen blow the turbines, then you will get pure CO2. Use electricity from renewable sources, use the carbon twice to reduce emissions.

Thereby putting in several times as much RE electricity to re-create fossil fuels than the first use got out of the natural gas.  And begs the question:  what energy do you use to capture and store the CO2, if you're only generating CO2 when you don't have RE available?  I see efficiency going into the toilet.

Some people will always give the "my opinion is the only opinion" response with the "no sense discussing it any further" arrogance. This is why this site does not attract good inputs.

If you can show errors in the analysis done by the authors or come back with numbers of your own that look good, you've got something.  Absent that, all you're doing is opining.

"This is a flawed study with predetermined outcomes"

?

They did the science right, but to what conclusion? They seem to want something sustainable, renewable with an efficient storage of energy...don't we all.

Their conclusions are that nothing is really acceptable, the same thinking some have on here. If it can not do everything, forget it.

"..impacts of using CO2 to produce synthetic hydrocarbon fuels by using existing technologies CAN be greater than the impacts of existing hydrocarbon fuels."

They have one column labeled "diesel" presumably that is made from oil at a refinery. They talk about LCA and list factors for CO2 to fuel, but NONE for going from the ground to the fuel tank.

Since all those numbers are missing, I would say it is a flawed study. Since they have mixed together a lot of factors and left out information, I would say they had a particular conclusion in mind from the beginning.

@yoatmon,
Thank you for bringing H2 + CO2 = formic acid into the discussion. Certainly, the ability of formic acid to store 3.5 x higher mass of H2 per liter at atmospheric pressure in comparison to compressed H2 at 350 bar is highly desirable. However, formic acid is heavy, such that formic acid only contain 4.5% H2 by weight, meaning lower gravimetric density than compressed H2 at 350-bar when using carbon fiber container at 6% wt of H2 and H2 at 700 bar at 5% wt of H2. Adding the considerable weight of the container for formic acid given its corrosiveness, and the weight % of H2 for formic acid will be even less.

Furthermore, the corrosiveness of formic acid makes it difficult to transport it via metal pipelines or stored in metal container, thus making it difficult to use formic acid as means of seasonal storage of H2. Over time, formic acid will spontaneously decompose to CO and H2O, presenting a double problem of CO toxicity as well as loss of stored energy, especially in hot climates.

Much more research will be needed before formic acid can be considered as a contender as H2 storage means, in comparison to molecular H2, which is already established.

When they say that they "can" be greater it's the same as saying that in some cases which may be most cases it is likely less. This is standard fear mongering technique people, and use of weasil words to imply the truth but not effectively communicate the real truth that they don't want people to know. If it can, then it mostly cannot. Remember that when they use "can". Besides why wouldn't they tell us when it cannot or more correctly does not? And, when are you business mopes going to get with it and stop trying to fake your ways to wealth? The people have been so dumbed down now that they aren't even worth fooling anymore, since they are too stupid to make any money to give you in your scams.

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