Biofuels from Lignocellulosic Biomass - Sustainable Biotechnology: Sources of Renewable Energy - page 43

addressed in this chapter but are the focus of research in many projects. Ultimately,
the real cost of feedstock delivered to the conversion facility will be a major factor
determining the magnitude of success for lignocellulosic biomass. Potential out-
put products could include ethanol, butanol, biogasoline, FT liquids, and a range of
chemical intermediates. Reaching this potential in an economically acceptable man-
ner is a challenge, and requires an improved ability to convert the lignocellulosic
feedstock to a useable fuel.
After more than two decades of intensive R&D, several technologies have been
evaluated for biofuel production at the laboratory level. A few are now at the stage of
advanced testing and pilot-scale evaluations. Presently, the challenges facing com-
mercial conversion are such that no one technology has an absolute advantage over
the others. The approach of thermochemical pretreatment and enzymatic hydroly-
sis followed by microbial fermentation has been the most extensively studied. The
remaining challenges for this approach include further lowering pretreatment cost,
improving hydrolysis efficiency and cost of cellulases (and hemicellulases), and
improving the performance of fermentation organisms. The approach of thermo-
chemical gasification combined with FT catalytic conversion has also been widely
explored and may be promising under the appropriate conditions. The gasifica-
tion approach would benefit from improved gasification efficiency, easier syngas
cleanup, and better FT factors such as catalyst selectivity and longevity.
In some projects, various combinations (thermochemical front + biochemical,
biochemical front + thermochemical) have been evaluated. For economic operation
in an integrated biorefinery, it may be that such combinations of approaches will be
required and that the combination utilized will depend on the feedstock, the location,
the desired product stream, the degree of environmental impact, and the level of
investment available. It is expected that the best technologies for specific challenges
will be selected and implemented over the next 5-10 years and that the definitive
answer on the size of the contribution from lignocellulosic biomass will become
evident during that time.
References
1. USCB (2008) World Population Clock. United States Census Bureau.
2. EIA (2008) Annual Energy Outlook: with Projections to 2030. DOE/EIA-0383.
3. Kharecha PA, Hansen JE (2008) Implications of “peak oil” for atmospheric CO 2 and climate.
Global Biogeochem Cycles 22:GB3012.
4. Johnson JM-F, Coleman MD, Gesch R, et al. (2007) Biomass-bioenergy crops in the United
States: a changing paradigm. Am J Plant Sci Biotechnol 1:1-28.
5. Tilman D, Hill J, Lehman C (2006) Carbon-negative biofuels from low-input high-diversity
grassland biomass. Science 314:1598-600.
6. Hansen JS, Kharecha P, Beerling D, et al. (2008) Target atmospheric CO 2 : where should
humanity aim? Open Atmos Sci J 2: 217-31.
7. Klass DL, Cutler JC (2004) Biomass for renewable energy and fuels. In: Cutler JC (ed)
Encyclopedia of Energy. Elsevier, New York.
8. Petrus L, Noordermeer MA (2006) Biomass to biofuels, a chemical perspective. Green Chem
8:861-7.