Saturday, April 27, 2013

The Methane Game

A few days ago, I became aware of a potentially game-changing development in fossil carbon energy: The successful prototype mining venture of methane hydrate, potentially "an energy source that could free not just Japan but much of the world from the dependence on Middle Eastern oil that has bedeviled politicians since Churchill’s day."

Added to the current developments in "fracking", "a technique used to release petroleum, natural gas (including shale gas, tight gas, and coal seam gas), or other substances for extraction", this spells potential access to huge amounts of fossil carbon for relatively cheap energy for a number of decades.

In a quick comment at Judith Curry's blog, I proposed that this would be "a game-changer" for issues of fossil carbon.

The question is, what plans for the future can be made under these new circumstances, and what enabling technology would be necessary to support them.

Let me start with a few assumptions. Given the behavior of virtually all major polities in the years since the Kyoto protocol was signed, there seems to be little chance of any long-term reduction in the use of energy based on fossil carbon. This is certainly a debated subject, but the efforts by the EU and Australia seem to me to be temporary, and in any event will have little effect without cooperation by the developing world, which doesn't seem forthcoming.

A good thing in my view, since the entire Industrial Revolution, and the widespread improvements in lifestyle and human happiness it entails, have been powered by energy from non-human, and essentially non-biological, sources. Starting with wind and water power, during the middle ages, the addition of steam, primarily enabled by innovations of James Watt, touched off a complete revamping of the lifestyle of common people.

As the exponential increase in fossil power during the 20th century brought the advantages of Western European style life to ever-larger parts of the world, the level of CO2 in the atmosphere also increased, in very roughly equivalent exponential fashion. This has been plausibly attributed to the increased burning of fossil carbon.

There is widespread concern regarding the risks of increasing CO2 levels, especially if they continue to a point well above anything the planet has experienced in millions of years. Access to fossil methane, as petroleum accessed by "fracking", and now the mining of methane hydrate clathrate from the ocean floors, totally changes the game.

Efforts so far have concentrated on raising the price of energy to the point that non-fossil alternatives can compete. However, given the general unworkability of that approach (IMO), a focus on increased research and development of, and perhaps subsidies for, processes that remove CO2 from the air are likely to be the best approach.

For the short term, reductions in production of CO2 can be achieved by building new power facilities to burn methane rather than coal (or oil). Combined with a host of possible energy-saving initiatives, this could provide a temporary reduction in the amount of CO2 entering the atmosphere, at least relative to what would happen with coal-fired power plants.

But what about the longer term? The current buzz-word today is "renewable" energy, with a vague meaning something like "not using up fossil reserves that can't be replaced". Technologies like windmills, solar power, and nuclear fission are all lumped into this category. So are "biofuels"[2], including fuels produced by agriculture or engineered algae (cyanobacteria).


Technically, of course, "bio-" anything means something produced by biological processes. Coal and oil only escape this definition because they have been modified by geological action from the biologically produced material that was laid down hundreds of millions of years ago. When it comes to methane hydrate from the sea floors, some comes from seepage from petroleum sources, but most is essentially unmodified from the form produced during anaerobic decay of sea-floor detritus.

Despite this, I can predict with total confidence that the term "biomethane" will be used from the start to denote methane produced biologically as a "renewable" fuel. And that's what I intend to discuss in the rest of this post.

While some petroleum methane may be produced by geological action on more complex precursors, most is produced through a complex process of decay of organic matter. This process involves an even more complex ecology, with a variety of different eubacteria and archaea working together[3]. Interestingly, though, the actual creation of methane often seems to be performed by a single archaeal species, Methanobacterium bryantii, e.g. strain M.O.H. This reaction is as follows:

4H2 + CO2 → CH4 + 2H2O with an energy yield of "−131 kJ (per mole of CH4)"[3]

We have to be aware that energy yields are heavily dependent on relative concentrations, however this reaction is very much downhill, and can draw down the hydrogen to trace levels, sufficient that the reactions that produce it are also functionally downhill[3].

Now, how can we produce an artificial version of this process powered by modern sunlight? Many people would probably jump immediately to using photosynthetic organisms, contained in easily manufactured vessels exposed to sunlight, in analogy to the system used by Audi (above). There has certainly been some interest in creating hydrogen directly using photosynthesis[4]. Perhaps, by combining this with a Hydrogen-eating methanogen, it would be possible to produce a sunlight-powered reactor to produce methane.

In my view, however, there is a much easier way. There is already a lot of work being done on mechanisms to convert sunlight to electrical energy, especially photovoltaic (PV) and concentrated solar power (CSV). These techniques get conversion efficiencies much higher than normal crop plants, probably as high as anything using photosynthesis, although that's certainly open to dispute. However, an important point is that hydrogen can be produced directly from electricity through electrolysis, at very high efficiencies.

This is important because oxygen photosynthesis creates reactive oxygen species (ROS), " chemically reactive molecules containing oxygen." This, in turn, creates a very destructive environment for all the various enzymes and other compounds involved in biosynthesis. These materials have to be replaced frequently, which is wasteful in terms of energy that could otherwise be used for synthesizing methane or whatever other materials are required for civilization. When hydrogen from external sources is fed into the reaction, and energy needed by the cell is provided by reducing CO2 to methane, neither of the processes that are the main creators of ROS need to take place.

So, do we use Methanobacterium bryantii to convert hydrogen to methane? Well, perhaps. There is a host of other methanogen species, many of them associated with sea-floor vulcanism, which may be able to perform the process much faster[1]. This seems to me to represent an opportunity for forward-looking biotech companies: Starting with the variety of natural species, engineer an artificial organism that can be "programmed" to reproduce to the limits of necessary nutrients, then settle down and convert hydrogen to methane at a rapid clip. The lack of ROS would make each non-reproducing bacterial body much more stable, with much lower replacement needs for important molecules. Because the process doesn't require sunlight, it could be carried out in self-contained reaction vessels, with a variety of possible designs.

This approach would leverage the ongoing investment in solar power technology, as well as allowing a long-term strategy based on methane-fired power plants, which would not need to go out of service during a shift to "renewable" energy, but simply use methane from a "renewable" source. It would avoid potential problems with using engineered organisms for oxygen photosynthesis, which is wasteful in terms of the rapid replacement rate required for many important enzymes. It would take advantage of over two centuries experience in creating manufactured technology, with probably much simpler bio-technology needed to create high-speed methanogens.

Space Solar Power (SSP)

For the long run, the most probable source of energy will be the Sun, from power stations in space. While this may be several decades down the road, it's important to recognize that the technology proposed here will fit right in. Electricity at the surface can be dedicated to electrolysis, producing hydrogen. Unlike systems based on photosynthesis, conversion of hydrogen and CO2 to methane can be performed in large, out-of-sight reaction chambers, perhaps floating underwater. If we assume that energy from space is converted to electricity (from microwaves) at a rectenna a few kilometers across, floating in the ocean, we can place the reaction chambers underwater, out of the way but easily accessible for hydrogen from electrolysis. CO2 can be transferred from ocean water, in the form of bicarbonate, or perhaps ocean water from which the oxygen has been removed can be fed right through the reaction. Or perhaps regenerative technologies can be developed that precipitate the carbonate from the ocean water, transfer it into the (topological) environment of the reaction chamber, and re-dissolve it.

While this last option might take some development, we should note that hydrolysis can produce substantial pressures of hydrogen, which means the reaction can be downhill even with extremely low CO2 pressures. This differential from the surrounding ocean could likely be used to create a good rate of diffusion or other transfer from the ocean. Key technological development would include artificial membrane materials with appropriate extreme levels of diffusivity. And, of course, the necessary bio-technology.

Overall, this seems like a very workable option, with enabling technologies that are all within our current level of technological development. Methane can be easily returned to the ocean floor as solar power finally replaces its use, although even with space solar power it might be more practical to convert the space power to methane and ship it to smaller local power stations for a while, at least in some locales.

The technology doesn't have to wait until space solar power is on-line, it will work fine with CSP or PV power, technology that is already on-line, although not self-supporting without subsidies.

And returning methane to the sea floor also doesn't have to wait. There's no reason why a proportion of the methane produced by this method can't be simply returned to the form of methane hydrate and deposited on the sea-floor. Moreover, it's quite possible that as future power technology develops, it will be feasible to capture the CO2 and return it to the ocean floor. The use of bio-technology to extract CO2 from sea water, and combine it with hydrogen from clean power, may end up being the most cost-effective way of capturing the output of carbon-burning power stations.

Finally, this technology isn't limited to creating "renewable" energy. It can not only capture and "put back" carbon from burning of fossil fuels while it's running, it can capture carbon that was already burned. That means that, as this technology comes on-line sufficiently, it can draw down the atmospheric pCO2 to the point it was at the beginning of the Industrial Revolution. If that turns out to be appropriate, once we have a better understanding of how changes to atmospheric pCO2 impacts the environment.

1.  Hydrogen-limited growth of hyperthermophilic methanogens at deep-sea hydrothermal vents by Helene C. Ver Eecke, David A. Butterfield, Julie A. Huber, Marvin D. Lilleyd, Eric J. Olson, Kevin K. Roe, Leigh J. Evans, Alexandr Y. Merkel, Holly V. Cantin, and James F. Holden PNAS August 21, 2012 vol. 109 no. 34 13674-13679

2.  Microalgae for biodiesel production and other applications: A review by Teresa M. Mata, Antonio A. Martins, Nidia. S. Caetano Renew Sustain Energy Rev (2009), doi:10.1016/j.rser.2009.07.020

3.  Physiology, Ecology, Phylogeny, and Genomics of Microorganisms Capable of Syntrophic Metabolism by Michael J. McInerney, Christopher G. Struchtemeyer, Jessica Sieber, Housna Mouttaki, Alfons J. M. Stams, Bernhard Schink, Lars Rohlin, Robert P. Gunsalus Annals of the New York Academy of Sciences (2008) DOI: 10.1196/annals.1419.005

4.  Energy biotechnology with cyanobacteria by S Andreas Angermayr, Klaas J Hellingwerf, Peter Lindblad, M Joost Teixeira de Mattos Current Opinion in Biotechnology Volume 20, Issue 3, June 2009, Pages 257–263 doi: 10.1016/j.copbio.2009.05.011

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