4. Conclusion
In this study, the effects of the constituent of ChCl-DHBA DES on WT and
TG sorghum stover with in planta accumulation of DHBA were
investigated. Binary DES and ternary DESs were synthesized with ChCl,
DHBA, and the solvent-based third constituents including water and
ethylene glycol. TG biomass had similar chemical composition to WT
biomass while becoming more susceptible to enzymatic hydrolysis after
the DHBA-based DES pretreatments, therefore, releasing higher amounts of
fermentable sugars than WT biomass. The third constituent led to
dramatically enhanced pretreatment performances. Binary ChCl-DHBA DES
removed over 70% of xylan with less than 20% of delignification.
EG-incorporated ternary DES doubled the delignification while having
20% less xylan removal compared to the binary DES. ChCl-DHBA-W DES also
increased both high xylan removal and delignification. The applied
ternary DESs resulted in a significant enhancement in the conversion of
glucan and xylan conversion compared to the binary DES, as expected from
the changes in chemical composition. However, the enhanced fermentable
sugar production after the pretreatments with ChCl-DHBA-EG and
ChCl-DHBA-W are not easily concluded with a single dominant factor,
either xylan removal or delignification, in this study. Investigation of
lignin structure after pretreatment indicates that using water as the
third constituent for ternary DES preserved the most β–O–4 linkage,
while binary ChCl-DHBA DES mostly only removed lignin from the low
molecular weight fraction. Taking fermentable sugar conversion and
lignin structure together, both water and ethylene glycol showed great
potential as the third constituent in developing a sustainable
biorefinery process for total biomass utilization. The results
demonstrated that synthesizing ternary DESs could enhance the
pretreatment performance of binary DESs.