It may be the one magic trick that can save the entire planet from global warming, and a couple of research scientists at the University of Southern California are close to figuring it out. This not-so-mysterious trick is a process known as “air capture”, and it is exactly what it sounds like – capturing air from the atmosphere and chemically converting it into a fuel source. Scientists George Olah and Surya Prakash have developed a method of converting carbon dioxide (CO2) from the atmosphere to methanol (CH3OH), which can be used as an alternative fuel source.1 This method has been of great interest to many environmental scientists because it tackles the issue of global warming on two fronts: not only does the process generate a potent fuel source that is renewable and more sustainable, but it also effectively removes a harmful greenhouse gas that is essentially the by-product of everyday fuel consumption from the atmosphere.
The process of converting carbon dioxide to methanol is actually not a completely new idea. In fact, there’s a giant manufacturing plant in Iceland that produces 4,000 tons of methanol from carbon dioxide every year. However, there’s a big downside to this process. The plant uses copper oxide and zinc oxide as catalysts, which require relatively high carbon dioxide concentrations that can only be found in geothermal steam instead of from the atmosphere. Consequently, the current catalyst system prevents direct conversion of atmospheric carbon dioxide to methanol. Furthermore, the reaction runs at 250 oC and 100 atmospheres of pressure - conditions that are rather expensive to maintain.2
In contrast, Olah’s and Prakash’s research3 seeks to improve this rather ineffective process by identifying and testing a ruthenium metal catalyst that speeds up the reaction yet enables it to run at milder conditions. In fact, the entire reaction simply consists of bubbling air at 155 oC and 50 atmospheres of pressure through an aqueous solution of pentaethylenehexamine (PEHA, a polyamine solvent) with some ruthenium-metal catalyst. After 55 hours, the research team produced dissolved methanol from CO2 with 79% yield, the highest achieved from their report. What’s cool about this reaction is that unlike the plant in Iceland, this new reaction allows CO2 capture directly from the air while the methanol produced can easily be extracted via simple distillation. So, with a little bit of system engineering, one can get a continuous production of methanol. Also, with careful handling, the catalyst and solvent can be reused again, making this a rather sustainable process.
“What’s cool about this reaction is that unlike the plant in Iceland, this new reaction allows CO2 capture directly from the air...”
Nevertheless, this reaction is far from perfect especially when considering expanding it to an industrial scale. Atmospheric scientist David Keith from Harvard University is skeptical that the process is really effective, citing how PEHA could easily evaporate when reacting with carbon dioxide of such low concentrations, making the overall reaction less effective.2 Also, these evaporated amines are air pollutants themselves. In addition, the very notion of CO2 capture itself presents some ethical concerns. Because the research essentially introduces a practical use for atmospheric CO2, many scientists are concerned that people will interpret the research as permission to continue burning fossil fuels.4
Despite these drawbacks, scientists continue to stress the importance of moving away from conventional energy production methods towards more sustainable processes. Methanol is a desirable candidate in mending the Earth’s currently damaged carbon cycle, especially when the chemical has been used to develop alternative automobile fuels such as biodiesel. Although their research is still in its primitive stages, Olah and Prakash are optimistic that they will be able to refine the process in the next five to ten years to the point where it can be effectively scaled up for industrial use.
James Siriwongsup is a sophomore from McMurtry College at Rice University.
Resources
1. Perkins, R. Turning air into fuel: USC scientists convert carbon dioxide into methanol. https://news.usc.edu/91297/turning-air-into-fuel-usc-scientists-turn-carbon-dioxide-into-methanol/
(accessed 2/8/2016), part of USC News
2. Extance, A. Carbon dioxide-to-methanol catalyst ignites ‘fuel from air’ debate. http://www.rsc.org/chemistryworld/2016/01/fuel-air-carbon-dioxide-capture-methanol-renewable-energy (accessed 2/8/2016), part of Chemistry World
3. Kothandaraman, J. et. al. Conversion of CO2 from air into methanol using a polyamine and a homogeneous ruthenium catalyst. Journal of the American Chemical Society 2016, 138, 778-781.
4. MacDonald, F. Researchers can now convert CO2 from the air directly into methanol fuel. http://www.sciencealert.com/researchers-can-now-convert-captured-co2-directly-into-methanol-fuel (accessed 2/8/2016), part of Science Alert