Simultaneous isolation of cellulose and lignin from wheat straw and catalytic conversion to valuable chemical products

Determination and calculation
The contents (purities) of cellulose, hemicellulose, lignin 
and ash were determined according to the previously 
reported procedures [
27
]. The determinations were based 
on the averages of three replicates. The yields of cellulose 
and lignin, theoretical yield of lignin and removal rates of 
components, such as hemicellulose, lignin and ash, were 
calculated as follows.
Componenet yield (% ) =
Mass of component isolated from wheat straw
Mass of EWS
× 100%,
Removal rate (% ) =

1 −
Amount of component in isolated cellulose
Total amount of component in EWS

× 100%,
Theoretical yield of lignin (% ) =
Removal rate of lignin × Lignin content in EWS × Mass of EWS
Mass of EWS
×100%,
Measurements
Infrared (IR) spectroscopy was performed on an EQUI-
NOX 55 spectrometer in the range of 500–4000 cm
−1
. 
Prior to analysis, the solid samples were grounded with 
dried KBr powder and compressed into a disk. X-ray dif-
fraction (XRD) was performed on a χ’Pert Pro diffrac-
tometer with CuKα radiation at 40 kV and 40 mA in the 
range from 10° to 80°, and the scanning rate was 5°/min. 
The surface morphologies of wheat straw and its deriva-
tives were observed using a scanning electron micros-
copy (SEM) microscope (Hitachi N-3000 apparatus), and 
a thin layer of gold was sputtered onto the sample prior 
to imaging. Elemental analysis (EA) was performed on 
a Vario EL III elemental analyzer. Specific surface areas 
were calculated using the BET model on a NOVA 2000e 
fully automatic specific surface and porosity analyzer. 
X-ray photoelectron spectroscopy (XPS) was recorded 
on a Kratos XSAM800 spectrometer with MgKα radia-
tion (1253.6 eV), which was operated at 12 kV and 
10 mA without a monochromator. The qualitative anal-
ysis of sugars was performed on a LC-100 PLUS HPLC 
equipped with a Rezex ROA column (Phenomenex) and a 
refractive index detector (Shimadzu Corp., Kyoto, Japan) 
at 63 °C using H
2
SO
4
(4 mM) as an eluent at a flow rate 
of 0.6 mL/min. HPLC–MS was performed on Waters 
Arc HPLC-2998 PDA-QDa equipped with YMC ODS-A 
(5 µm, 4.6 × 250 mm) using 85 wt% acetonitrile–water as 
the mobile phase at a flow rate of 1.0 mL/min. Nuclear 
magnetic resonance (NMR) including 
1
H NMR and 
13
C 
NMR spectra were acquired on a Unity-Inova 600 at 
50 °C using DMSO-d6 as solvent and tetramethylsilane 
as internal standard. The molecular weight of lignin was 
determined using Waters E2695 GPC (see Additional 
file 
1
).
Recovery rate (% ) =
Yield
Component content of EWS
× 100%.

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Page 4 of 13
Yu et al. Appl Biol Chem (2021) 64:15 
The quantitative analysis of HMF derived from wheat 
straw cellulose was determined by a GC2020 gas chro-
matography equipped with a HP-1 capillary column 
(30 m × 0.25 mm × 0.25 μm). The initial temperature 
was retained at 50 °C for 3 min, then ramped to 230 °C 
at 10 °C/min, and held at this final temperature for 5 min. 
The gasification and detector temperatures were 240 and 
260 °C, respectively. Glucose derived from cellulose was 
determined by DNS method using a UV measurement 
at 540 nm [
28
]. The quantitative analysis of the reaction 
product derived from lignin was performed on a LC-100 
PLUS HPLC equipped with reversed-phase Novapak-
C18-100 silica column (4.6 × 150 mm, 4 μm) and UV 
detector. The mixture of acetonitrile: 1 wt% phosphoric 
acid solution (12:88, v/v) was employed as mobile phase 
at the flow rate of 1.2 mL/min with column temperature 
at 32 °C.