259322 Life Cycle Assessment of Bio-Jet Fuel From Hydrothermal Liquefaction of Microalgae
In 2011, ASTM standard D7566 was released for aviation fuel containing synthesized hydrocarbons such as those from algal feedstocks. Several flights on blends of conventional jet fuel and bio-jet fuel have been conducted on commercial airlines, including a Continental commercial flight on 40% algal bio-jet fuel. Government policy is also influencing the adoption of biofuels; the Energy Independence and Security Act of 2007 calls for the annual production of 36 billion gallons of renewable fuels by 2022. Twenty-one billion gallons of this target must be “advanced biofuel,” which is defined as a renewable fuel that produces 50% less greenhouse gas emissions on a life-cycle basis than petroleum-derived fuels. At these early stages in the production of algal bio-jet fuel, a life cycle assessment (LCA) is necessary to ensure that bio-jet fuel produced from algal feedstocks does not result in higher life-cycle greenhouse gas emissions than conventional jet fuel, and to determine whether algal bio-jet fuel would qualify as an “advanced biofuel” in energy policy.
A “well-to-wake” LCA was performed using SimaPro software and the ISO 14040 and 14044 guidelines to compare algal bio-jet fuel to conventional jet fuel. The functional unit is 1 gigajoule of jet fuel. The main algal bio-jet fuel production system analysed consists of algal production in open ponds of wastewater effluent, harvesting through flocculation and sedimentation, dewatering by solar drying, transport to a refinery, hydrothermal liquefaction, upgrading, distillation, transport to an airport, and combustion in a PT6A jet engine. Pilot-scale data collected from experiments at the Lawrence Wastewater Treatment Plant were utilized for the algal production process step and data from lab-scale hydrothermal liquefaction of microalgae was used in constructing the life cycle inventory. Average distances from United States wastewater treatment plants to petroleum refineries, and from petroleum refineries to public use airports, were determined using ArcGIS for the transportation steps. The life cycle impact assessment (LCIA) model was the EPA Tool for the Reduction and Assessment of Chemical and other environmental Impacts 2 (TRACI 2). Two additional algal bio-jet fuel production systems were modeled to compare to hydrothermal liquefaction of algal biomass: hydrotreatment of extracted algal lipids, and gasification and Fischer-Tropsch synthesis using the entire algal biomass. To the author's knowledge, this is the first LCA which involves hydrothermal liquefaction of algae to produce biofuels. The results of this LCA were also compared to other published LCAs for bio-jet fuel from camelina and Jatropha feedstocks.
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