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Bacterial Formic Acid: The New Fuel

December 30, 2013

Formic-acid-3D-ball-stick

The most underreported science story of the year, in Ultraphyte’s opinion: Bacteria hydrogenate CO2 and CO to make formic acid, a pure storable fuel that is interconvertable with hydrogen gas.

Hydrogen gas, H2, has long been a dream for the world’s cleanest fuel. Hydrogen could power houses and autos, and propel lightcraft from Earth. But hydrogen is also the world’s lightest gas, easily escaping confinement. Storage requires high pressure and/or low temperature.

So how do bacteria manage? In natural environments, such as the soil or the human intestine, bacteria release hydrogen gas as a byproduct, while others consume it. Much of intestinal hydrogen seeps out through our tissues; our bodies are essentially hydrogen balloons. To fix hydrogen quickly, microbes attach it to CO2, making either methane (methanogens) or formic acid (bacteria such as E. coli; a metabolism important to our lab, interacting with cell pH).

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Now, German researchers report a new bacterial way to interconvert H2 and formic acid. The bacterium Acetobacterium woodii performs this reaction cleanly, with a single enzyme, hydrogen-dependent CO2 reductase (HDCR). The enzyme acts without requiring cofactors that complicate the reaction. When purified, its activity depends solely on reactant pressure and concentration; it can be adjusted to interconvert H2 and HCOOH readily.

But the bacterium itself turns out to be the cleanest interconverter. The researchers found a simple way to halt bacterial growth and direct all activity to making formic acid. Biomass growth is halted by removing sodium ion. So, bacterium added to H2 and CO2 makes formic acid–which can then fill a tank.

Within the bacterium, a second enzyme also hydrogenates carbon monoxide (CO), a dangerous component of syngas. Syngas is a mixture of H2, CO2 and CO that can be produced from solid waste, and may provide an alternative to petroleum. So the bacterial reaction can provide a cheap way to extract hydrogen from the syngas. Once again, bacteria offer partners for green chemistry.

9 Comments
  1. December 30, 2013 2:16 pm

    You might find this 2012 review paper useful too.

    The biggest problems I see are that formic acid has relatively low energy density, so transport is going to be more costly than methanol or other organic carbon compounds, plus the corrosive nature of the acid in handling. The diagram shown leaves out a very important step between the bacterial generation and transport – extraction and purification. Even if formic acid is viable, purely chemical synthesis may be more appropriate than biological.

    • December 30, 2013 7:27 pm

      Thanks for the interesting review. Actually, formic acid has high energy density, compared to hydrogen gas. Thus it would be of interest for long-term storage of hydrogen for vehicles where weight is a premium.

      For fuel cells, formate and microbial cells are a large, promising area. Here are examples:
      http://pubs.rsc.org/en/Content/ArticleLanding/2011/CC/c0cc05225f#!divAbstract
      http://www.sciencedaily.com/releases/2013/05/130527231802.htm

      • December 30, 2013 8:41 pm

        I should have been more precise. I was referring to energy density as energy/kg, not energy/volume. Hydrogen is clearly more energy dense in the former, but much lower in the latter.

        I see from one of your references that storage would be as formate, rather than the acid, which would certainly remove the corrosive issue, although I would think that reduces the energy density (by half?) with the loss of one of the 2 hydrogens.

        Always good to have different options for energy generation, as they may fill different niches.

        • December 30, 2013 9:28 pm

          You’re right, multiple options are the smart way to go. Small batteries are a different story from megawatt power plants. Hydrogen I still think will wind up as the choice for ground and air transport, because you’re paying to carry the weight of the fuel.

          But ultimately where do you get any kind of energy from? I don’t see how we can keep drawing energy from Earth, in any form. At our escalating rate of energy use, anything–solar, wind, geothermal–will end up harming the planet. That’s why I think we’ll end up with solar energy and factories out in space. Earth will be the bedroom planet.

  2. December 31, 2013 2:47 am

    The Bedroom planet, I like it. Very exciting stuff, not that I could it discuss it intelligently, but the way you put it, very exciting. Happy New Year, Joan.!

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