In comparison with natural gas-based FT syntheses, biomass requires more inten­sive engineering, and gas-cleaning technology has been slow to evolve for indus­trial purposes — although for the successful use of biomass, it is essential because of the sensitivity of FT catalysts to contaminants. In year 2000 U. S. doller terms, investment costs of $200-340 million would be required for an industrial facility, offering conversion efficiencies of 33-40% for atmospheric gasification systems and 42-50% for pressured systems, but the estimated production costs for FT die­sel were high, more than 10 times those of conventional diesel.89 Two years later,

Biomass Air, O2

Syngas

the same research group from the Netherlands was predicting the same produc­tion costs and concluded that, unless the environmental benefits of FT diesel were valued in economic terms, the technology would only become viable if crude oil prices rose substantially.90 This did, in the event, occur (figure 5.1), and the cost differential has undoubtedly narrowed — although with no signs of a surge in investor confidence.

If it could be produced economically, using an energy crop such as switchgrass as the substrate, FT diesel rates better than E85 (from corn-derived ethanol) as a biofuel in assessments performed by the Argonne National Laboratory (figure 6.9).9192 FT diesel greatly outperformed E85 for total fossil fuels savings and also exhibited much reduced emissions of total particulates, sulfur oxides, and nitric oxides — although it fared worse than E85 using the criterion of total CO. Compared with conventional diesel fuel, FT diesel had higher total emissions of volatile organic carbon, CO, and nitric oxides (figure 6.9).

An experimental biofuel conversion technology, presently explored only in the Netherlands, is that for HydroThermalUpgrading diesel.93 At high temperature (300-350°C) and pressure, wet biomass feedstocks such as beet pulp, sludge, and bagasse can be converted to a hydrocarbon-containing liquid that, after suitable refining, can be blended with conventional diesel in any proportion without engine adjustments. A pilot plant remains the focus for further process optimization and development.