Alkaline Pretreatment of Corn Stover: Bench-Scale
Fractionation and Stream Characterization
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Abstract
Biomass pretreatment generally aims to increase accessibility to
plant cell wall polysaccharides for carbohydrate-active enzymes to
produce sugars for biological or catalytic upgrading to ethanol or
advanced biofuels. Significant research has been conducted on a suite
of pretreatment processes for bioethanol processes. An alternative
option, which has received less attention in the biofuels community,
is the use of alkaline pretreatment for the partial depolymerization
of lignin from intact biomass. A known issue with alkaline pretreatment
is the loss of polysaccharides from peeling reactions, but this loss
can be mitigated with anthraquinone, as commonly practiced in pulping.
Here, we conduct a comprehensive bench-scale evaluation of alkaline
pretreatment using corn stover at temperatures of 100, 130, and 160
°C and sodium hydroxide loadings from 35 to 660 mg NaOH/g dry
biomass with anthraquinone. Compositional analysis is conducted on
the starting material and residual solids after pretreatment, and
mass balance is inferred in the liquor by difference. The residual
solids after alkaline pretreatment are characterized for crystallinity
and imaged by scanning and transmission electron microscopy to reveal
the physical changes in the carbohydrate portions of the biomass remaining
after pretreatment, which demonstrate dramatic modifications to biomass
cell wall architecture with lignin removal but rather insignificant
changes in cellulose crystallinity. Our results show that alkaline
pretreatment at relatively mild conditions is able to remove substantial
amounts of lignin from biomass. Going forward, to be an economically
feasibile process, technologies will be required to upgrade the resulting
lignin-rich liquor stream