3.1 Determination of the molar ratio between ChCl and DHBA
Among the tested molar ratios of ChCl and DHBA, the molar ratio of 2:1
and 3:2 with ChCl and DHBA formed a homogenous and transparent liquid,
as shown in Figure S1 . A previous study reported that the DESs
with the same components at different molar ratios showed different
properties and performances.32 In this study, prior to
investigating ternary DESs, two binary ChCl-DHBA DESs with different
molar ratios (3:2 and 2:1) were evaluated by applying them to pretreat
TG sorghum stover. The pretreatment was carried out at 120 ℃ for 3 h,
adapted from our previous study of DES pretreatment with sorghum
stover.33 The pretreatment efficiency was determined
based on xylan removal, delignification, and fermentable sugar
production, as shown in Table 1 . ChCl-DHBA 3:2 DES showed
higher xylan removal and delignification than its 2:1 counterpart.
Clearly, the composition of DES is an important factor affecting the
pretreatment performance. Since the removal of both xylan and lignin
could enhance the enzymatic digestibility of the biomass, both ChCl-DHBA
DES-pretreated biomass samples were tested for the release of
fermentable sugars using a cellulase mixture. The sorghum stover
pretreated with ChCl-DHBA 3:2 DES released a higher amount of glucose
(391 mg/g-biomass) than that pretreated with ChCl-DHBA 2:1 DES (341
mg/g-biomass); therefore, the 3:2 molar ratio of ChCl and DHBA was
selected for subsequent ternary DES testing.
Table 1. Xylan removal, delignification, and glucan production
after 72 h of enzymatic hydrolysis of the pretreated transgenic (TG)
sorghum stover with ChCl-DHBA at different molar ratios at 120 ℃ for 3
h.