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Biomass-derived jet (biojet) fuel has become a key element in the aviation industry's strategy to reduce operating costs and environmental impacts. Researchers from the oil-refining industry, the aviation industry, government, biofuel companies, agricultural organizations, and academia are working toward developing commercially viable and sustainable processes that produce long-lasting renewable jet fuels with low production costs and low greenhouse gas emissions. Additionally, jet fuels must meet ASTM International specifications and potentially be a 100% drop-in replacement for the current petroleum jet fuel. The combustion characteristics and engine tests demonstrate the benefits of running the aviation gas turbine with biojet fuels. In this study, the current technologies for producing renewable jet fuels, categorized by alcoholsto-jet, oil-to-jet, syngas-to-jet, and sugar-to-jet pathways, are reviewed. The main challenges for each technology pathway, including feedstock availability, conceptual process design, process economics, life-cycle assessment of greenhouse gas emissions, and commercial readiness, are discussed. Although the feedstock price and availability and energy intensity of the process are significant barriers, biomass-derived jet fuel has the potential to replace a significant portion of conventional jet fuel required to meet commercial and military demand. 3 Conclusion .

Biomass and bioproduct composition critical improvements are a priority for the nascent algae-based bioeconomy.

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. U.S. Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.NREL prints on paper that contains recycled content. ErrataThis report, originally published in August 2018, has been revised in September 2021 to correct life cycle assessment calculations applied to the biomass conversion via combined algae processing pathway analyses. The amended calculations and associated results were used to update Figures 22-28 and Tables 14 and A-1-A-4 in the Appendix. The changes to the results were not significant enough to impact any of the overall conclusions or trends outlined in the report, and did not impact resource assessment or techno-economic analysis metrics, nor life cycle assessment metrics for the hydrothermal liquefaction conversion pathway.iii This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. NomenclatureAD anaerobic digestion AFDW ash-free dry weight ANL Argonne National Laboratory BAT Biomass Assessment Tool BETO Bioenergy Technologies Office BGY billion gallons per year BGGE/yr billion gallons gasoline equivalent per year BT16 2016 Billion-Ton Report CAP combined algae processing CC carbon capture CHP combined heat and power CONUS conterminous United States DAP diammonium phosphate DOE U.S. Department of Energy FAME fatty acid methyl ester FFA free fatty acid FY fiscal year GAI Global Algae Innovations GHG greenhouse gas GREET Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation HCSD high-carbohydrate Scenedesmus

Modeling efforts to understand the financial implications of microalgal biofuels often assume a static basis for microalgae biomass composition and cost, which has constrained cultivation and downstream conversion process design and limited in-depth understanding of their interdependencies. For this work, a dynamic biological cultivation model was integrated with thermo-chemical/biological unit process models for downstream biorefineries to increase modeling fidelity, to provide mechanistic links among unit operations, and to quantify minimum product selling prices of biofuels via techno-economic analysis. Variability in design, cultivation, and conversion parameters were characterized through Monte Carlo simulation, and sensitivity analyses were conducted to identify key cost and fuel yield drivers. Cultivating biomass to achieve the minimum biomass selling price or to achieve maximum lipid content were shown to lead to suboptimal fuel production costs. Depending on biomass composition, both hydrothermal liquefaction and a biochemical fractionation process (combined algal processing) were shown to have advantageous minimum product selling prices, which supports continued investment in multiple conversion pathways. Ultimately, this work demonstrates a clear need to leverage integrated modeling platforms to advance microalgae biofuel systems as a whole, and specific recommendations are made for the prioritization of research and development pathways to achieve economical biofuel production from microalgae.

This study summarizes the detailed techno-economic analysis of the ethanol-to-jet (ETJ) process based on two different feedstocks (corn grain and corn stover) at the plant scale of 2000 dry metric tons per day.