It is now well accepted that for several reasons, corn ethanol will have a rather limited role as a renewable substitute for petroleum-derived liquid transportation fuels. The shortcomings of corn ethanol have sparked interest in the production of other types of fuels--such as higher alcohols, oils, and hydrocarbons--from renewable biomass feedstocks (see "The Price of Biofuels"). While the potential economic, environmental, and security benefits of such cellulosic biofuels are clear, many hurdles need to be cleared before they can begin to make a difference in the overall supply of liquid fuels for transportation.

There are three major challenges in the economical conversion of biomass to biofuels. The first is to optimize the yield and quality of the biomass, as well as to work out the logistics of securing, transporting, and processing the large volumes that will be required to support the operation of future biorefineries. New ways of harvesting, preprocessing, and transporting biomass will be necessary before it's cost-effective for biorefineries to import biomass from more than 15 or 20 miles away. One scheme is to establish satellite collection and pretreatment facilities from which slurry biomass is transported by pipelines to the main biorefinery. One can envision pipelines where cellulose hydrolysis, the slow process by which cellulose is broken down into usable sugars, takes place while a slurry is transported from the satellites to the main biorefinery.