. "8 Key Challenges to Commercial Deployment." Liquid Transportation Fuels from Coal and Biomass: Technological Status, Costs, and Environmental Impacts. Washington, DC: The National Academies Press, 2009.
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Liquid Transportation Fuels from Coal and Biomass: Technological Status, Costs, and Environmental Impacts
Cellulosic ethanol is in the early stages of commercial development; a few commercial demonstration plants are expected to begin operations in the next several years. Over the next decade, process improvements in this generation of technology are expected to come from evolutionary developments and knowledge gained through commercial experience and increases in scale of operation. Incremental improvements in biochemical conversion technologies can be expected to reduce nonfeedstock process costs by about 25 percent by 2020 and 40 percent by 2035. It will take focused and sustained industrial and government action to achieve those cost reductions.
The key technical issues to be resolved to achieve cost reductions are these:
More efficient pretreatment to free up celluloses and hemicelluloses and to enable more efficient downstream conversion. Improved pretreatment is not likely to reduce product cost substantially, because pretreatment cost is small relative to other costs.
Better enzymes that are not subject to end-product inhibition to improve the conversion process.
Maximizing of solids loading in the reactors.
Engineering of organisms that can ferment sugars in a toxic biomass hydrolysate and produce high concentrations of the final biofuel. Improving microorganism tolerance of toxicity is a key issue.
An expanded ethanol transportation and distribution infrastructure will be required if ethanol is to be used in much greater amounts than now in light-duty vehicles. Ethanol cannot be transported in pipelines that are used for petroleum transport. It is currently transported by rail or barges, not by pipelines, because it is corrosive in the existing infrastructure and can damage seals, gaskets, and other equipment and induce stress-corrosion cracking in high-stress areas. If ethanol is to be used in fuel at concentrations higher than 20 percent (for example, E85, which is a blend of 85 percent ethanol and 15 percent gasoline), the number of refueling stations offering these options to alternative-fuel vehicles will have to be increased. To enable widespread availability of ethanol in the fuel system, the