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PHYSICAL SCIENCES / SUSTAINABILITY SCIENCE
Sustainable fuel for the transportation sector

Rakesh Agrawal^*, Navneet R. Singh, Fabio H. Ribeiro, and W. Nicholas Delgass

School of Chemical Engineering and Energy Center at Discovery Park, Purdue University, West Lafayette, IN 47907

Edited by Hans Joachim Schellnhuber, Potsdam Institute for Climate Impact Research, Potsdam, Germany, and approved February 5, 2007 (received for review November 10, 2006)

A hybrid hydrogen-carbon (H₂CAR) process for the production of liquid hydrocarbon fuels is proposed wherein biomass is the carbon source and hydrogen is supplied from carbon-free energy. To implement this concept, a process has been designed to co-feed a biomass gasifier with H₂ and CO₂ recycled from the H₂-CO to liquid conversion reactor. Modeling of this biomass to liquids process has identified several major advantages of the H₂CAR process. (i) The land area needed to grow the biomass is <40% of that needed by other routes that solely use biomass to support the entire transportation sector. (ii) Whereas the literature estimates known processes to be able to produce 30% of the United States transportation fuel from the annual biomass of 1.366 billion tons, the H₂CAR process shows the potential to supply the entire United States transportation sector from that quantity of biomass. (iii) The synthesized liquid provides H₂ storage in an open loop system. (iv) Reduction to practice of the H₂CAR route has the potential to provide the transportation sector for the foreseeable future, using the existing infrastructure. The rationale of using H₂ in the H₂CAR process is explained by the significantly higher annualized average solar energy conversion efficiency for hydrogen generation versus that for biomass growth. For coal to liquids, the advantage of H₂CAR is that there is no additional CO₂ release to the atmosphere due to the replacement of petroleum with coal, thus eliminating the need to sequester CO₂.

biofuels | coal | hydrogen | oil

Author contributions: R.A. designed research; R.A. and N.R.S. performed research; R.A., N.R.S., F.H.R., and W.N.D. analyzed data; and R.A., N.R.S., F.H.R., and W.N.D. wrote the paper.

Conflict of interest statement: R.A. and N.R.S. are the co-inventors of the H₂CAR process, which is trademarked by Purdue University and covered under provisional U.S. patent application 60/843678.

This article is a PNAS direct submission.

This article contains supporting information online at www.pnas.org/cgi/content/full/0609921104/DC1.

*To whom correspondence should be addressed. E-mail: agrawalr{at}purdue.edu

© 2007 by The National Academy of Sciences of the USA

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