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The financial and environmental performance of the National Renewable Energy Lab's (NREL) thermochemical and biochemical biofuel conversion processes are examined herein with pine, eucalyptus, unmanaged hardwood, switchgrass, and sweet sorghum. The environmental impacts of the process scenarios were determined by quantifying greenhouse gas (GHG) emissions and TRACI impacts. Integrated financial and environmental performance metrics were introduced and used to examine the biofuel production scenarios. The thermochemical and biochemical conversion processes produced the highest financial performance and lowest environmental impacts when paired with pine and sweet sorghum, respectively. The high ash content of switchgrass and high lignin content of loblolly pine lowered conversion yields, resulting in the highest environmental impacts and lowest financial performance for the thermochemical and biochemical conversion processes, respectively. Biofuel produced using the thermochemical conversion process resulted in lower TRACI single score impacts and somewhat lower GHG emissions per megajoule (MJ) of fuel than using the biochemical conversion pathway. The cost of carbon mitigation resulting from biofuel production and corresponding government subsidies was determined to be higher than the expected market carbon price. In some scenarios, the cost of carbon mitigation was several times higher than the market carbon price, indicating that there may be other more cost-effective methods of reducing carbon emissions. [ABSTRACT FROM AUTHOR]

The production of six regionally important cellulosic biomass feedstocks, including pine, eucalyptus, unmanaged hardwoods, forest residues, switchgrass, and sweet sorghum, was analyzed using consistent life cycle methodologies and system boundaries to identify feedstocks with the lowest cost and environmental impacts. Supply chain analysis was performed for each feedstock, calculating costs and supply requirements for the production of 453,592 dry tonnes of biomass per year. Cradle-togate environmental impacts from these modeled supply systems were quantified for nine mid-point indicators using SimaPro 7.2 LCA software. Conversion of grassland to managed forest for bioenergy resulted in large reductions in GHG emissions due to carbon uptake associated with direct land use change. By contrast, converting forests to cropland resulted in large increases in GHG emissions. Production of forest-based feedstocks for biofuels resulted in lower delivered cost, lower greenhouse gas (GHG) emissions, and lower overall environmental impacts than the agricultural feedstocks studied. Forest residues had the lowest environmental impact and delivered cost per dry tonne. Using forest-based biomass feedstocks instead of agricultural feedstocks would result in lower cradle-to-gate environmental impacts and delivered biomass costs for biofuel production in the southern U.S. [ABSTRACT FROM AUTHOR]

Biomass pretreatment by autohydrolysis uses hot-water to extract soluble components from wood prior to converting the woody residuals into paper, wood products, or fuel, etc. Mixed hardwood chips were autohydrolyzed in hot-water at 150, 160, 170, and 180 ºC, for 1 and 2 h. The tradeoff between fermentable sugar yield and caloric value of the residual solids was studied for a process that will be referred to as "value prior to combustion". The extracted liquid was treated with dilute sulfuric acid to break down sugar oligomers into fermentable monomers. Material balances were performed around autohydrolysis to evaluate the role of temperature and residence time on sugar production and residual solid heating value. The composition (sugars and byproducts) of the extracted liquid was determined. As the autohydrolysis temperature increased, the material balance became less precise, presumably due to more volatile byproducts being formed that were not quantified. More hemicelluloses were extracted from the wood by the hot water extraction process under higher temperature and longer residence time, but a greater degree of sugar degradation was also observed. After hot-water extraction the heating value of the solid residues was higher than the original wood. The total energy content of the residual solid after extraction ranged from 74 to 95% of the original energy content of the feed. [ABSTRACT FROM AUTHOR]

Green liquor pretreatment, a technology presently used worldwide in hundreds of kraft pulp mills, is proposed in this work as a potential pretreatment pathway for the efficient conversion of lignocellulosic biomass into ethanol. Mixed southern hardwood, eucalyptus, and loblolly pine were evaluated through process simulations in two investment scenarios: a greenfield mill scenario and a repurposing scenario, using existing kraft pulp mill assets for cellulosic ethanol production. Several advantages come with this concept: i) proven technology (both process and equipment), ii) chemical and energy recovery in place, iii) existing fiber supply chain, and iv) experienced labor force around the mill. Ethanol yields through enzymatic hydrolysis of pretreated fibers were highest in natural mixed hardwood and eucalyptus (280-285 liters of ethanol per dry ton of biomass) and lowest in loblolly pine (273 liters per dry ton of biomass). Natural hardwood and eucalyptus in the repurposing scenario form the most profitable combinations with an IRR of about 19%, mainly due to low capital expenditure (CAPEX) (per liter of ethanol), low enzyme costs, and higher ethanol yield (compared to loblolly pine). Production cost (in the repurposing scenario) was estimated at $2.51 per gallon of ethanol (or $0.66 per liter), cash cost at $2.14 gallon-1 (or $0.57 per liter), and CAPEX at $3.15 gallon-1 (or $0.83 per liter). Repurposing existing closed mills creates a potential alternative to ramp up in the task of producing alternative lignocellulosic biofuels. [ABSTRACT FROM AUTHOR]