|Anthropogenic chemical carbon cycle. Click to enlarge.
In a Perspective published in the Journal of the American Chemical Society, researchers from the Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California describe their work on developing the feasible anthropogenic recycling of carbon dioxide.
Under their scheme, carbon dioxide is captured by absorption technologies from any natural or industrial source, from human activities, or even from the air itself. It can then be converted by feasible chemical transformations into fuels such as methanol, dimethyl ether, and varied products including synthetic hydrocarbons and even proteins for animal feed, thus supplementing the food chain. This broad concept the basis of what they call the Methanol Economy.
The required energy for the synthetic carbon cycle can come from any alternative energy source such as solar, wind, geothermal, and even nuclear energy. The anthropogenic carbon dioxide cycle offers a way of assuring a sustainable future for humankind when fossil fuels become scarce, they propose.
While biosources can play a limited role in supplementing future energy needs, they increasingly interfere with the essentials of the food chain. We have previously reviewed aspects of the chemical recycling of carbon dioxide to methanol and dimethyl ether. In the present Perspective, we extend the discussion of the innovative and feasible anthropogenic carbon cycle, which can be the basis of progressively liberating humankind from its dependence on diminishing fossil fuel reserves while also controlling harmful CO2 emissions to the atmosphere.
We also discuss in more detail the essential stages and the significant aspects of carbon capture and subsequent recycling. Our ability to develop a feasible anthropogenic chemical carbon cycle supplementing nature’s photosynthesis also offers a new solution to one of the major challenges facing humankind.
...The use of chemistry to supplement nature is indeed not new. The Haber-Bosch process provides ammonia by chemical synthesis using atmospheric nitrogen and hydrogen generated from any source, presently mostly natural gas but eventually by water electrolysis or splitting. The anthropogenic carbon cycle, which we have proposed and discuss here, eventually will vastly exceed the scope and significance of the synthetic ammonia cycle.—Olah et al.
In their paper, Olah et al. outline the major components of such a cycle, along with the current state of technology and possible future directions, including:
- CO2 capture from natural and anthropogenic sources;
- Capture and recycling of CO2 from the atmosphere;
- Chemical CO2 recycling to fuels;
- Production of hydrogen for CO2reduction;
- CO2 reduction to CO followed by hydrogenation;
- Electrochemical reduction of CO2;
- Methanol-based fuels, chemicals, synthetic materials and proteins.
In the past 15 years, we have developed the concept of the Methanol Economy and some of the underlying new chemistry for using methanol as an energy storage medium, transportation fuel, and raw material for producing synthetic hydrocarbons and their products. It is based on the chemical anthropogenic carbon cycle. Whereas methanol is currently produced from fossil fuels through syn-gas chemistry, these resources are finite and being rapidly depleted. The recycling of CO2 using hydrogen generated eventually from water with any source of energy offers a sustainable long-term solution to our energy challenge.
However, significant bottlenecks remain, such as the relatively high cost of electricity from renewable sources needed to produce methanol. Methanol can also be made sustainably from biomass, although the available amounts of biomass will be able to provide only a small portion of humankind’s energy needs. The amount of methanol needed to replace petroleum is staggering. With half the volumetric energy density compared to gasoline, about 60 billion barrels of methanol (7.6 billion tonnes) would be required to replace the 30 billion barrels of petroleum used globally each year. This represents about 160 times the current methanol production of 48 million tonnes per year!
The anthropogenic chemical carbon cycle constitutes humankind’s practical technological analogue of nature’s slow photosynthetic CO2 recycling, which eventually could give new fossil fuels. As CO2 is available everywhere on Earth, it could liberate humankind from the reliance on diminishing and limited fossil fuels and associated dependence on obtaining them from increasingly expensive, frequently far away and geopolitically unreliable sources. Eventually, it also offers the possibility to produce all hydrocarbon-based products and materials including single-cell proteins from the CO2 content in our atmosphere.—Olah et al.
George A. Olah, G. K. Surya Prakash, Alain Goeppert (2011) Anthropogenic Chemical Carbon Cycle for a Sustainable Future. Journal of the American Chemical Society Article ASAP doi: g/10.1021/ja202642