Abstract
BackgroundThe objective of this study was to evaluate the environmental impact of the production of a range of liquid biofuels produced from the combination of fermenting sorghum stalk juice (bioethanol) and the pyrolysis/hydrotreatment of residual bagasse (renewable gasoline and diesel). Life cycle impact assessment (LCIA) was performed on a farm-to-wheels system that included: (i) sorghum farming, (ii) juice extraction, (iii) juice fermenting, (iv) bagasse pretreatment, (v) bagasse thermochemical treatment (pyrolysis, hydroprocessing, and steam reforming), and (vi) typical passenger vehicle operation. LCIA results were compared to those of petroleum fuels providing the equivalent functional unit—cumulative kilometers driven by spark ignition direct injection (SIDI) vehicles utilizing either renewable gasoline or ‘bioE85—a blend of bioethanol and renewable gasoline,’ and a compression ignition direct injection (CIDI) vehicle utilizing renewable diesel produced from 76 tons of harvested sweet sorghum (1 ha).ResultsSweet sorghum biofuels resulted in a 48% reduction climate change impact and a 52% reduction in fossil fuel depletion. Additionally, reduced impacts in ozone depletion and eutrophication were found (67% and 47%, respectively). Petroleum fuels had lower impacts for the categories of non-carcinogenic health impact, smog, respiratory effects, and ecotoxicity, showing tradeoffs between sorghum and petroleum fuels.ConclusionOverall, sorghum biofuels provide advantages in environmental impact categories including global warming potential, fossil fuel depletion and eutrophication, showing potential for sorghum as a promising second-generation feedstock for fuel.
Highlights
IntroductionThe objective of this study was to evaluate the environmental impact of the production of a range of liquid biofuels produced from the combination of fermenting sorghum stalk juice (bioethanol) and the pyrolysis/ hydrotreatment of residual bagasse (renewable gasoline and diesel)
The objective of this study was to evaluate the environmental impact of the production of a range of liquid biofuels produced from the combination of fermenting sorghum stalk juice and the pyrolysis/ hydrotreatment of residual bagasse
Previous life cycle assessment (LCA) studies that focus on sweet sorghum fuels have evaluated primarily biochemical pathways that deal with grain-based or sugar-based feedstock [4, 17, 27, 39] and residual bagasse conversion into cellulosic ethanol via batch, continuous or advanced solid-state fermentation [9, 10, 37]
Summary
The objective of this study was to evaluate the environmental impact of the production of a range of liquid biofuels produced from the combination of fermenting sorghum stalk juice (bioethanol) and the pyrolysis/ hydrotreatment of residual bagasse (renewable gasoline and diesel). The advantages of sweet sorghum as a second-generation biofuel feedstock has sparked research on the various genotypes of this crop and their fermentable sugar content [24, 28, 33], sugar extraction methods and fuel conversion pathways [21, 22], and the economic and environmental feasibility of various biofuel processing pathways from either its grain, stem juice, or bagasse [6, 9, 21, 30].). Previous life cycle assessment (LCA) studies that focus on sweet sorghum fuels have evaluated primarily biochemical pathways that deal with grain-based or sugar-based feedstock [4, 17, 27, 39] and residual bagasse conversion into cellulosic ethanol via batch, continuous or advanced solid-state fermentation [9, 10, 37].
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