| Unfortunately The Paper [1] is closed source. I can't find much information; no comparison with existing, chemical synfuels processes (like methanol via syngas [CO]). There's a serious problem with the general idea: "clean" CO2 is hard to get. You can get concentrated (>10%) CO2 streams from a power plant, which could work for synfuels, but ultimately that's still transferring fossil carbon into the air (if more efficiently). The "nice" idea is to capture CO2 from the atmosphere (I think they are implying this?); this gives you a carbon-neutral cycle (CO2 => fuel => CO2). This is difficult because CO2 in the air is so dilute -- 0.04% vol., or 0.8 grams/meter^3. Can you get CO2 from the air? There's research in this; the APS assessment [2] thinks it could be done at around $600-800/tCO2, which translates to e.g. $7/gallon gas equivalent of methanol, just for the carbon. The process uses an inorganic base (NaOH) to scrub CO2, so maybe you'd think you could genetically-engineer superbacteria to do better. But the absorbent is not the bottleneck -- it's the extreme volume and flow of air that needs to be brought to the absorbent, over an insanely large surface area. The scale is visualized in [2] figure 1.2 (http://i.imgur.com/Y0D2f.png): a very small, 10^6 ton CO2/year capture plant is designed as a 1km * 1km grid of rows of giant, sucking fans. And the NaOH process isn't particularly inefficient -- it captures 50% of the CO2 in air. Some more about atmosperic CO2 capture from David Keith [3] and his startup [4]; this was featured in the Economist this month [5]. Wikipedia is a starting point for synfuels in general [6]; George Olah advocates a methanol/dimethyl ether economy using CO2 recycled from air [7]. [1] http://www.sciencemag.org/content/335/6076/1596.abstract [2] http://www.aps.org/about/pressreleases/dac11.cfm [3] http://www.keith.seas.harvard.edu/AirCapture.html [4] http://www.carbonengineering.com/ [5] http://www.economist.com/node/21550241 [6] http://en.wikipedia.org/wiki/Synthetic_fuel [7] http://wiki.ornl.gov/sites/carboncapture/Shared%20Documents/... |
My understanding is that using algae to do this via photosynthesis is limited by the fact that with wild strains you need to harvest and extract the biomass before you can get at the fuel, and you need to spread things out in a very thin film to get enough sunlight. Using modified strains helps solve the first problem, using (more efficient) synthetic photovoltaics, or another power source, with a process like this potentially helps solve the second.
To respond to another reply to this post, I don't think complex structures that maximise surface area would be necessary - you could just bubble air through the tank. As mentioned above, bubbling CO2 rich waste gasses from a power plant would likely be even more efficient.