Fun With Carbon Dioxide

New materials can selectively capture CO2, scientists say:

Scientists have created metal-organic crystals capable of soaking up carbon dioxide gas like a sponge, which could be used to keep industrial emissions of the gas out of the atmosphere.

Chemists at the University of California Los Angeles said the crystals — which go by the name zeolitic imidazolate frameworks, or ZIFs — can be tailored to absorb and trap specific molecules.

[Prof. Omar] Yaghi and his colleagues describe their findings in the Friday issue of the journal Science.

He said the crystals are non-toxic and would require little extra energy from a power plant, making them an ideal alternative to current methods of CO2 filtering. The porous structures can be heated to high temperatures without decomposing and can be boiled in water or solvents for a week and remain stable, making them suitable for use in hot, energy-producing environments like power plants.

The team of scientists created 25 ZIF crystal structures in a laboratory, three of which showed a particular affinity for capturing carbon dioxide. The highly porous crystals also had what the researchers called “extraordinary capacity for storing CO2”: one litre of the crystals could store about 83 litres of CO2.

How much of this stuff do we need to stop adding carbon dioxide to the atmosphere?

According to Gary W. Harding, How Much of Atmospheric Carbon Dioxide Accumulation Is Anthropogenic?

Today, the atmosphere contains about 720 Gtons of carbon. The concentration of carbon dioxide is about 360 ppm. Regardless of its source, one billion tons of carbon released into the atmosphere as carbon dioxide would increase its concentration by 0.5 ppm (360 / 720) if all of it stayed there. However, scientists estimate that about half of present human carbon emissions are absorbed by the environment. Of the half absorbed, scientists have accounted for where half of that goes. Where the other half goes is the “mystery of the missing carbon” (about 1.8 Gton per year).

A gigaton, by the way, is a thousand million tons. And that's 1998 data on stocks not flows.

According to Table 3.2 on page 30 of Global Warming: The Complete Briefing we're up well past 7.5 GT added annually to the atmosphere due to fossil fuel burning and deforestation.

So to make humans carbon-neutral at present rates of emissions, we need what exactly? Let's fire up the calculator.

One liter of carbon dioxide at standard atmosphere and pressure weighs 1.965 grams. So 1 GT approximately equals a petagram (10 to the 15th power).

Divide 7.5 of those petagram by 1.965 grams and we get a measly 3.82 GT of these crystals. Per year. Assuming fossil fuel use stays flat.

How does this compare to this zany idea?

…a concept … for removing carbon dioxide from the air and turning it back into gasoline.

The idea is simple. Air would be blown over a liquid solution of potassium carbonate, which would absorb the carbon dioxide. The carbon dioxide would then be extracted and subjected to chemical reactions that would turn it into fuel: methanol, gasoline or jet fuel.

Even with those improvements, providing the energy to produce gasoline on a commercial scale — say, 750,000 gallons a day — would require a dedicated power plant, preferably a nuclear one, the scientists say.

According to their analysis, their concept, which would cost about $5 billion to build, could produce gasoline at an operating cost of $1.40 a gallon and would turn economically viable when the price at the pump hits $4.60 a gallon, taking into account construction costs and other expenses in getting the gas to the consumer. With some additional technological advances, the break-even price would drop to $3.40 a gallon, they said.

A nuclear reactor is not required technologically. The same chemical processes could also be powered by solar panels, for instance, but the economics become far less favorable.

This is not a small problem.

[erroneous timestamp corrected] [& spelling corrected too – thanks to Earl Killian]

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12 Responses to Fun With Carbon Dioxide

  1. Your calculation assumes that the crystals are single use, which is absurd in the extreme. In practice, any given kilo of the crystals would be saturated and purged many times a day, being used as a way to create a purified CO2 stream to go into some other process for recycling or sequestration.

    In short, it’s a more effective substitute for the potassium carbonate solution used in that “zany” idea. Didn’t you pick up on that?

  2. Michael says:

    Nope, didn’t pick up on that. How does one purge the crystals? What’s the energy cost?

  3. Chuck says:

    What’s the energy cost of creating the crystals?
    a. extracting the material from the ground.
    b. the energy to create the plant to create the crystals.
    c. the energy to run the plant.
    d. the energy to load the crystals with carbon dioxide.
    e. the energy to store the crystals.
    how long do they stay stable?
    do they break down after x number of years?
    are they effected by light, heat, chemicals in the air, oxygen, ozone?
    IMHO it’s not gonna be easy or cheap.

  4. Well, you’re talking about a fractal structure with voids of the right size and ionic environment to preferentially capture CO2 over other constituents of flue gas. It’s not holding on to that CO2 very tightly, there’s no chemical bond. Normally you’d purge such a material by either heating it to the point where the CO2 disassociates from it, or flushing it with an excess of some gas you don’t mind having go through your later processes. Probably a combination of the two.

    The minimum energy cost is going to relate to the fact that you’re performing a counter-entropic process, separating two mixed substances. Not a large number, in this instance. The heat can be largely recycled by using counter-flow techniques. I’d *guess* that most of the energy consumption will be due to the fact that you have to pump the gases through the medium.

    VERY dependent on the exact properties of the material, I wouldn’t hazard a guess at the KWH per ton of CO2 concentrated. Only note that physical law doesn’t require it to be very much.

  5. Earl Killian says:

    Here is some help with units:
    You wrote “pentagram” and “penagram”. It is “petagram”.
    Harding is using metric tons (also called tonnes). 1 GT is exactly (not approximately) 1 Pg (petagram).
    One metric ton is 1.10 short tons, and a short ton is 2000 pounds, so a metric ton is approximately 2200 pounds (actually 2204.6226).

  6. Earl Killian says:

    The CO2 to gasoline technology proposed by Martin looks feasible, but it is a really bad idea. You start with a high-grade energy source: electricity. You then waste much of that electricity turning the energy into a low-grade energy source: gasoline. I call gasoline a low-grade energy source because the most practical way to extract energy is to burn it in a heat engine (e.g. an internal combustion engine, or ICE), and the efficiency of that is limited by thermodynamics (the Carnot limit). Your average gasoline ICE is about 21% efficient. I call electricity a high-grade energy source because it can be turned into work at very high efficiency (electric motors are routinely over 90% efficiency).

    The end result is that to drive on the gasoline from this process you would need 500 nuclear reactors for our current consumption rate, but if you drove directly on electricity you would need only 100. (Alternatively, you need 3,000 sq.mi. of solar power vs. 15,000 sq.mi.) Which do you think is more practical?

    U235 reserves are not infinite, though some in the nuclear industry act as if they are. If one counts what the IEA Red Book lists as “speculative” and “prognosticated” and with no price limit, then there is U235 to fuel the existing 449 reactors plus about 1100 new reactors in the world for at most 50 more years (note to future generation: replacing them with renewable energy when the U235 runs out is your problem, oh, and please dispose of them too). Building 500 just for U.S. gasoline consumption is folly.

  7. We agree, at least in part: Given sufficiently good battery technology, (Which we don’t have now, but probably will have before we could get 500 nuclear plants built.) it’s sheer madness to use electricity to make gasoline, instead of charging batteries. I imagine there are some niche markets where it would make sense, but not on a large scale. Might want to use it for creating industrial feedstocks, though, instead of digging up our carbon.

    On U235 running out as a result of this scheme, please. We’d have to run the economy on synthesized petroleum for millennia before that would begin to be a consideration. Fissile and fertile elements aren’t infinite, but they represent many orders of magnitude more stored energy than fossil fuels.

  8. Dui says:

    I like the second idea of creating fuel from the carbob in the air. Very interesting! I would predict that we will be within the price level to make this viable in about a year (sigh…). It sounds like a very clever way to create fuel, and the source of it is almost unlimited. Cool story. :O)

  9. Earl Killian says:

    @Brett Bellmore
    Why do you say we don’t have sufficiently good battery technology now? We have a 2002 Toyota RAV4-EV which is a real workhorse for us. It has 76,000 miles on it and it is still performing great. Other RAV4-EV drivers have over 100,000 miles on their cars without problem, and Southern California Edison’s data suggests 150,000 miles is not unreasonable to expect. That is using 1990s battery technology (NiMH). 2007 battery technology is much better than NiMH. A123Systems batteries (LiFePO4 technology) should last as long as our NiMH batteries and deliver more range and power. They are inherently safe and long lifetime, unlike LiCo batteries found in laptops and cell phones. Cost is around $500/kWh for a battery pack. Range is seldom an issue, because one leaves the garage with a full “tank” every morning. One nice thing about battery electric vehicles is that they lack engines, spark plugs, radiators, belts, air filters, oil filters, oil, transmissions, catalytic converters, mufflers, alternators, belts, hoses, and most of the other things that are such maintenance chores on cars. Plus our fuel costs 2.7 cents a mile (try that with gasoline). With a plug-in hybrid electric vehicles you unfortunately get all of that maintenance, and you occasionally have to buy gas, but range becomes a non-issue. It doesn’t take many batteries to make a plug-in hybird (e.g. 5kWh).

    On U235, don’t take my word for it, check out the International Atomic Energy Agencies Red Book data:
    http://www.nea.fr/html/general/press/2006/redbook/red_book_questions_and_answers.pdf
    To fuel 1500 GW of nuclear takes 306,000 metric tons of uranium ore per year. See http://web.mit.edu/nuclearpower/ for details.
    Now divide 14,798,000 by 306,000. Answer 48.4. Note I used the largest number in the IAEA report. You get fewer years with the other numbers.

    If you think you know more than the IAEA on the subject of uranimum, e.g. perhaps you believe in extracting it from granite or seawater? Then you’d better read http://www.stormsmith.nl/ It can be done, but at greenhouse gas costs too great to be practical.

  10. We clearly have good enough battery technology for MY daily commute, and for a lot of people. Though the grid would require a LOT of upgrading if a significant fraction of the population were using electric cars; It’s just not sized to provide that much juice to residential areas.

    And, frankly, I think a lot of the problem with charging could be dealt with by developing a standard for quick change of batteries. With some standardization of physical dimensions and interface, swapping batteries in the space of a minute would be a lot easier than charging them in a minute.

    What we don’t have is good enough battery technology to totally supplant the use of petroleum for a fuel. The energy density of batteries is still far below the energy density of fuel, and electric vehicles make up the difference by being highly energy efficient, and carrying a much greater mass of battery than they would fuel, and still fall short on range. Short of switching to air based primary batteries, we’re unlikely to see a battery that can match fuel for energy density. We may be able to get close enough for practical purposes, though.

    Regarding U235 availability, the key point was made in your first link: “Further, deployment of advanced reactor and fuel cycle technologies could multiply all these numbers by a factor of at least 30.” 30*48.8 = 1464, which is more than a millennium. And, “In addition, thorium, which is more geologically abundant than uranium in the earth’s crust, is also a potential source of nuclear fuel, if alternative fuel cycles are introduced.” 1464* times X = ???

    You assume no ‘waste’ reprocessing, no breeder reactors, and no alternative fuel cycles. All dubious assumptions, were we to commit to a nuclear powered economy. Which I do not propose. Solar is making such great strides of late, it will be more cost effective than nuclear long before those plants could be built. Perhaps within a few years, if Nanosolar’s hype is to be believed.

  11. Earl Killian says:

    @Brett Billmore
    The grid could handle a lot of electric vehicles without upgrade. Why do you make up such statements? Check out the Electric Power Research Institutes’s (EPRI) work on the subject. They do analysis for the utilities; this sort of thing is their specialty. To see why instantly in a single picture, check out the graphic “Using off-peak power” on PDF page 9 of
    http://mydocs.epri.com/docs/CorporateDocuments/EPRI_Journal/2005-Fall/1012885_PHEV.pdf
    5 million plug-ins is 15% of the vehicles in California. From the graph, much higher percentages appear possible. For gory details, see
    http://www.epri-reports.org/

    Second, you seem to have simply ignored the data I posted about batteries and just reiterated your opinion that batteries aren’t good enough based upon assumptions that are wrong. First, batteries don’t have to totally supplant liquid fuels. A reasonable goal might be 50% electricity in the short-term, and in the long-term 95% electricity, 5% biofuels/renewableH2. Second, The energy density of batteries does not need to be equal to the energy density of gasoline for electric vehicles to be useful. (1) EVs are about 5 times the efficiency of ICEs (3 times the efficiency of HEVs); (2) EVs leave the garage fully charged every morning; the energy does not need to last 1-2 weeks as in a ICE; (3) plug-in hybrids offer the ability to use electricity for most of ones driving, switching to backup liquid fuel only when the battery range is insufficient; (4) a 10 minute charge of a BEV was demonstrated in 2007.

    On nuclear, one of my textbooks gives the energy available as
    U235 2,600 EJ
    Th232 11,000 EJ
    U238 320,000 EJ
    The 30x figure from the IAEA is for using U238 in breeder reactors, making Pu239, and then burning that Pu239. Proliferation concerns have so far limited the desirability of this option. I don’t intend to get into a discussion of the tradeoffs of breeder reactors other than it seems like a distinctly inferior option to me due to cost, safety, and proliferation risk. The 30x cannot be applied to the Th232 fuel cycle, so don’t make the mistake you made above. The U235 number is roughly compatible with the 1500GW for 50 years calculated before by different means.

    Note that world energy use is projected to be 900EJ/year in 2050. If nuclear supplied 50% of that (much more than the 1500GW I used in my first example), and both U235 and Th232 were used, reserves would last only 30 years. However, if you read the stormsmith.nl material, you would see that we would have a greenhouse gas problem trying to extract U235 from marginal ores. Again, you ignored that issue from the first post.

    For comparison, the earth’s winds represent 6,000 EJ of wind energy each year, and the sunlight it receives on its land masses represents 1,000,000 EJ of energy each year. These look like far better places to look for energy. We don’t need to wait for Nanosolar; large solar farms are being built today using mirrors and heat engines. This is also cheaper than Nanosolar, and it has the potential to generate during nighttime through thermal energy storage. Unlike nuclear, wind and solar will last for billions of years. In addition, extractable geothermal energy is estimated by MIT at 200,000 EJ each year.

    Denmark is targeting 50% wind power by 2025.

  12. Huey says:

    First off, Who IN THEIR RIGHT MIND thinks it’s a great idea to unleash some sort of atmospheric changer on our atmosphere because you don’t like how it’s been changed prviously!? Are you NUTS!? Do you really believe we understand how all of the atmospheric gasses work together? Are you confident that if we create some huge quantity of magic pixie dust, large enough to have a noticable effect on something that is a huge as a planetary atmosphere, that we will be able to also control it, or stop it when it reaches our goal? We can’t even stop a pile of tires from burning, do you really think we’d be able to stop millions of cubic yards of pixie dust, scattered around all over the planet, doing different tasks? “OK now everybody – well stop it on three, two, one…” Yeah right.

    Do you even think that if we confine it to filtering systems on smokestacks (for example) that that’s where it will stay and as far as it will go? Anybody noticed how well THAT always works?

    And more frighteningly: Do you REALLY, REALLY, think it would be a wise idea to create something that can purge itself (which just puts all the CO2 back), or which can rejuvinate it’s ability to scrub even more CO2?! Have you thought about this for even a second?!

    The biggest danger from global warming is that we won’t be able to live in certain places any more. Big frigging deal. The world has been a lot hotter than now in the past and life goes on. It’ll be a change, but it won’t end anything important. That’s assuming it even happens.

    Whereas the biggest danger from the alarming efforts to stop it is that we go to far and KILL EVERYONE! Are you THAT confident that science is sophisticated enough to do just the right thing in just the right amount? Is that typically what happens when science reacts to “problems?”

    I really hope nobody ever convinces the right people that he is smarter than everyone else and really embarks on one of these scary projects.

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