3.2 Impact of the third constituent in ChCl-DHBA DES system on
the chemical compositions of sorghum stover
One of the challenges in the application of several binary DESs is its
relatively high viscosity, limiting the processibility. Ternary DESs
were synthesized with the selected 3:2 molar ratio of ChCl and DHBA
mixture and an additional third constituent, either water (W) or
ethylene glycol (EG). The molar ratio between ChCl, DHBA, and the third
constituent was 3:2:5, according to our previous
study.33 The prepared ternary DESs were applied to the
pretreatment of two different biomass, WT and TG sorghum stover at 140 ℃
for 3 h. The contents of glucan and xylan in intrinsic WT and TG sorghum
stover were similar. Although TG sorghum stover showed slightly lower
lignin content (12.8%) than WT biomass did (14.4%), the values are
comparable (Table 2 ), which is in accordance with the previous
study.34 All the applied DES pretreatments removed
over 50% of the initial mass of biomass regardless of the DES
composition, resulting in solid recovery yields ranging from 43% to
46%. For the further evaluation of the performance of DHBA-based
ternary DESs, the changes in the chemical composition of the pretreated
biomass were measured with cellulose retention, xylan removal, and
delignification, as shown in Figure 1 . The preservation of
cellulose in the solid is a critical factor affecting the yield of
glucose in the following enzymatic hydrolysis step. As depicted inFigure 1a , after pretreatment, over 90% of cellulose remained
in the solid fraction, regardless of the biomass type and DES
composition. This result indicated that ChCl in the DESs could actively
bind and stabilize the cellulose fractions while the HBD facilitates the
removal of hemicellulose and lignin,35 which aligns
well with the current results. On the other hand, the DESs having
different compositions resulted in varied xylan removal and
delignification, as the xylan removal ranged from 54% to 77% and
delignification ranged from 9% to 40% (Figure 1b and1c ). Detailed information on solid recovery after different
pretreatment and chemical compositions of untreated and pretreated
biomass are in Table 2 .
Table 2. Solid recovery and chemical compositions of WT and TG sorghum
stover before and after binary & ternary DES pretreatments with
different compositions.