Oxford Team Outlines Progress and Potential in CO2 Capture and Conversion to Synthetic Transportation Fuels
In an open-access paper published in Philosophical Transactions of the Royal Society A, researchers from the University of Oxford, led by Dr. Peter Edwards, provide an overview of progress in the area of the conversion of carbon dioxide to synthetic transportation fuels (Carbon Capture and Conversion, CCC), its potential, and barriers to future progress.
The authors highlight three possible strategies for CO2 conversion by physico-chemical approaches: sustainable (or renewable) synthetic methanol; syngas production derived from flue gases from coal-, gas- or oil-fired electric power stations; and photochemical production of synthetic fuels.
Major reductions in emissions from the transportation sector will necessitate a change in vehicle fuels. The three leading alternatives generally advanced at present are electric (battery), hydrogen and biofuels; the first two options require fundamental large-scale changes in our energy infrastructure, while the latter will not meet the exceptionally high and ever-growing demand for transportation fuels.
...In order to take full advantage of the high ‘tank-to-wheel’ efficiency of electric vehicles, critical steps will also be needed to decarbonize the upstream energy (electricity) supply. In addition, batteries are fundamentally limited by their very low net gravimetric and volumetric energy densities...while the net on-board density of liquid hydrogen comfortably exceeds that of batteries, it is still extremely low when compared with carbonaceous liquid fuels such as diesel, gasoline, ethanol and methanol. In addition, the provision of hydrogen production, distribution and refuelling facilities will necessitate enormous investments for this completely new infrastructure base.
This same analysis (Pearson et al. 2009) concludes:A fourth option, the focus of this review, has emerged, namely, the idea of using captured, anthropogenically produced CO2 to synthesize liquid renewable or sustainable hydrocarbon and carbonaceous fuels. This approach offers the intriguing possibility of using primary energy from renewable, carbon-free sources (such as electricity derived from solar, wind, wave or nuclear) to convert CO2, in association with hydrogen (or indeed methane), into high-density vehicle fuels compatible with our current transportation infrastructure. Its real attraction is that this approach offers the prospect of decarbonizing transport without the paradigm shift in infrastructure required by electrification of the vehicle fleet or by conversion to a hydrogen economy.
The fundamentals of physics and electrochemistry dictate that the energy density of batteries and molecular hydrogen is unlikely ever to be competitive with liquid fuels for transport applications.
—Jiang et al.
The authors note that with carbon capture and storage becoming a key element in worldwide efforts to control/minimize emissions, large amounts of CO2 could likely become available as feedstock for innovative conversions to synthetic fuels. Whole process energy balances and economics remain a critical issue.
Realizing any or all of the approaches for CCC will require major advances in the science and engineering of materials, as well as significant socio-political commitments to CO2 capture and utilization, they note.
International collaborative research between developed, and developing countries is also absolutely critical in such a venture. Our hope is that this present summary helps to catalyse such a worthwhile development.
—Jiang et al.
Z. Jiang, T. Xiao, V. L. Kuznetsov and P. P. Edwards (2010) Turning carbon dioxide into fuel. Phil. Trans. R. Soc. A vol. 368 no. 1923 3343-3364 doi: 10.1098/rsta.2010.0119