Generation
of coproducts from nutrients is purported to improve
the sustainability of algae-derived transportation fuels by minimizing
life cycle impacts and improving economic sustainability. Although
algae cultivation produces lipids that is upgraded to drop-in transportation
fuel products, life cycle assessment and techno-economic analysis
have shown that without coproducts, energy/economic returns are diminishing
regardless of processing methods. This study utilizes a combined flash
hydrolysis (FH), hydrothermal liquefaction (HTL), and coproduct conversion
technology (atmospheric precipitation/AP; hydrothermal mineralization/HTM)
to conserve the most recyclable nutrients for coproduct marketability.
Six biofuel pathways were developed and compared in terms of “well-to-pump”
energy, life cycle greenhouse gas (LC-GHG) emissions, and economic
profitability: renewable diesel II (RDII), renewable gasoline (RG),
and hydroprocessed renewable jet (HRJ) fuel, each were modeled for
AP and HTM coproduct conversion. A functional unit of 1 MJ usable
energy was employed. RG showed a promising energy-return-on-investment
(EROI) due to multiple coproducts. All models demonstrated favorable
EROI (EROI > 1). LC-GHG emissions tie in with EROI such that RG
produced
the least emissions. HRJ-HTM was determined to be the most profitable
model with a profitability index (PI) of 0.75. Sensitivity analyses
revealed that dewatering affects EROI and PI significantly. To achieve
break-even, gasoline must sell at $4.10/gal, diesel at $5.64/gal,
and jet fuel at $3.43/gal.
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