The recalcitrant nature of lignocelluloses
requires a pretreatment
process before the fermentative butanol production. The commonly used
pretreatment processes, such as steam explosion, sulfuric acid, ammonia
fiber explosion, ionic liquid (IL), and biological, require different
quantities and types of process chemicals, and produce different quality
and quantity of fermentable sugars. This study determines life-cycle
greenhouse gas emissions (GHG) these pretreatment methods by developing
a system-level process model including corn stover feedstock supply
system and the downstream butanol production process. This study further
evaluates the uncertainty associated with energy use and GHG emissions
for each stage of the entire butanol production chain and provide
the future optimization opportunities. Probabilistic results of these
analyses describe a distribution of GHG emissions with an average
of 18.09–1056.12 gCO2e/MJ and a 95% certainty to
be less than 33.3–1888.3 gCO2e /MJ. The highest
GHG emissions of IL-pretreatment of 1056.12 gCO2e/MJ reaches
to 89.8 gCO2e/MJ by switching IL-recovery from 80 to 99
wt %, which is the most influential parameter for IL-pretreatment.
Additionally, credits from excess electricity, butanol yield, nitrogen
replacement, and diesel fuel for transportation and harvesting were
the most influential parameters. Based on the current state of technologies,
apart from ionic liquid and biological pretreatments, other pretreatment
processes have similar metrics of sustainability.
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