Figure 6. Overall biomass pretreatment mass balance of WT
sorghum stover by pretreatment (140°C for 3h) and enzymatic hydrolysis
(20 FPU/g of biomass, 72h) using (a) ChCl-DHBA-W DES and (b)
ChCl-DHBA-EG DES, and TG sorghum stover using (c) ChCl-DHBA-W DES and
(d) ChCl-DHBA-EG DES.
Compared to the binary DES, both ternary DESs (ChCl-DHBA-W and
ChCl-DHBA-EG) resulted in higher fermentable sugar production. For a
better understanding of the overall mass balance of both approaches with
WT and TG sorghum stover, process flow diagrams with the mass balance of
major biomass components were presented in Figure 6 . The mass
balance was calculated based on 100 g of sorghum stover as the starting
material. The average value of each treatment was used for the mass
balance calculation. Stream 1 describes the amount of major biomass
components in the untreated feedstock (i.e., sorghum stover), and Stream
4 shows the final products (fermentable sugars after enzymatic
hydrolysis). As shown in Figure 6 , both WT and TG sorghum
stovers have over 25 g of extractives with ~9 g of ash,
and the three main components (glucan, xylan, and lignin) accounted for
approximately 65 g per 100 g biomass. WT biomass had slightly higher
glucan and lignin content than TG biomass, with the TG biomass having
more extractives. Among four scenarios, water-incorporated DHBA DES
exhibited higher glucose production (26.0 g and 26.9 g with the
pretreated WT and TG biomass) than ethylene glycol-incorporated one
(25.0 g and 26.0 g with the pretreated WT and TG biomass). However,
ethylene glycol-incorporated DHBA DES resulted in higher xylose
production (5.2 g and 5.1 g with the pretreated WT and TG biomass) was
higher than water one (3.1 g and 3.7 g with the pretreated WT and TG
biomass) even though its xylan conversion was lower (Figure 3 ).
This is because ChCl-DHBA-EG pretreated biomass retained more xylan
during the pretreatment (Table 2) . For this reason,
ChCl-DHBA-EG pretreated sorghum stover produced the highest amount (31.1
g) of the total fermentable sugars (glucose + xylose) with the
pretreated TG biomass, shown in Figure 6d . However, a large
portion of the hemicellulose was solubilized in the liquid fraction
during the pretreatment; therefore, the separation and utilization of
these sugars after the recovery of lignin and DES should be considered
to complete the biorefinery strategy.