Preparation and investigation of highly selective solid acid catalysts with sodium lignosulfonate for hydrolysis of hemicellulose in corncob

Article abstract of DOI:10.1039/c7ra13362f

Saccharification of lignocellulose is a necessary procedure for deconstructing the complex structure for building a sugar platform that can be used for producing biofuel and high-value chemicals. In this study, a carbon-based solid acid catalyst derived f

Full text of DOI:10.1039/c7ra13362f

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Preparation and investigation of highly selective
solid acid catalysts with sodium lignosulfonate for
hydrolysis of hemicellulose in corncob†
Cite this: RSC Adv., 2018, 8, 10922
Xun Li,‡a Fengyao Shu,ab Chao He,b Shuna Liu,‡b Noppol Leksawasdi,c
b
b
Md. Asraful Alam,b Zhenhong Yuanbd and Yi Gaoe
*
*
Qiong Wang,
Wei Qi,
Saccharification of lignocellulose is a necessary procedure for deconstructing the complex structure for
building a sugar platform that can be used for producing biofuel and high-value chemicals. In this study,
a carbon-based solid acid catalyst derived from sodium lignosulfonate, a waste by-product from the
paper industry, was successfully prepared and used for the hydrolysis of hemicellulose in corncob. The
optimum preparation conditions for the catalyst were determined to be carbonization at 250 ꢀC for 6 h,
followed by sulfonation with concentrated H2SO4 (98%) and oxidation with 10% H2O2 (solid–liquid ratio
of 1 : 75 g mLꢁ1) at 50 ꢀC for 90 min. SEM, XRD, FT-IR, elemental analysis and acid–base titration were
used for the characterization of the catalysts. It was found that 0.68 mmol gꢁ1 SO3H and 4.78 mmol gꢁ1
total acid were loaded onto the catalyst. When corncob was hydrolyzed by this catalyst at 130 ꢀC for
12 h, the catalyst exhibited high selectivity and produced a relatively high xylose yield of up to 84.2% (w/
w) with a few by-products. Under these conditions, the retention rate of cellulose was 82.5%, and the
selectivity reached 86.75%. After 5 cycles of reuse, the catalyst still showed high catalytic activity, with
slightly decreased yields of xylose from 84.2% to 70.7%.
Received 15th December 2017
Accepted 25th February 2018
DOI: 10.1039/c7ra13362f
rsc.li/rsc-advances
Research on the preparation of solid acid catalysts and their
utilization in lignocellulose conversion has been carried out in
Introduction
recent years with the hope of solving the problems brought on
by liquid acid catalysis.9 At present, the commonly used solid
acids can be divided into the following categories: zeolite
molecular sieves,10 heteropoly acids,11 metal oxides and their
complexes,12 inorganic acid salts,13 strong acid cation exchange
resins14 and carbon-based solid acids.15
Due to the emergence of environmental and energy issues,
researchers and biofuel stockholders have devoted signicant
attention towards the conversion of lignocellulose into biofuels
and high-value compounds.1–3 Acid-catalyzed hydrolysis has
been considered as one of the most efficient pretreatment
approaches for delignication of lignocellulose by deconstruc-
tion of the complex structure to release the high yield of C5/C6
sugars for the preparation of important derivatives, such as
bioethanol and high-value-added chemicals.4,5 Liquid acid
catalysis is the commonly adopted method for the pretreatment
or hydrolysis of lignocellulose; however, this method is not only
corrosive and non-recyclable but also leads to the further
degradation of sugars.6–8
Research on carbon-based solid acids has received wide atten-
tion due to the relatively higher catalytic efficiency, good stability,
environmental friendliness, low price and renewability16 of these
catalysts. The carbon-based solid acid is a new type of solid acid
obtained by introducing sulfonic acid groups onto the carbon
material.17 Due to the rich presence of acidic functional groups
(–SO3H, –COOH, –OH), carbon-based solid acids can efficiently
adsorb the b-1,4 glycosidic bond and can subsequently depoly-
merize it effectively.18 This characteristic mitigated activation
energy greatly enhances the efficient hydrolysis of cellulose.16,19
Suganuma17 used sucrose and glucose as raw materials and sub-
jected them to carbonization at 300 ꢀC and subsequent sulfonation
to obtain a solid acid catalyst. Lian20 prepared a new catalyst via
hydrothermal carbonization of fructose and sulfosalicylic acid,
which resulted in aꢀreduced sugar yield of 60.7% for the hydrolysis
of cellulose at 130 C for 90 min in ionic liquid. Shen21 prepared
a solid acid by sulfonation of carbonized starch and polyvinyl
chloride. The corresponding yield of glucose was 44.76% for
cellobiose hydrolysis at 120 ꢀC for 6 h.
aChangsha University of Science and Technology, Changsha, 410004, China
bGuangzhou Institute of Energy Conversion, Chinese Academy of Sciences, CAS Key
Laboratory of Renewable Energy, Guangdong Key Laboratory of New and Renewable
Energy Research and Development, Guangzhou, 510640, China. E-mail: qiwei@ms.
giec.ac.cn; wangqiong@ms.giec.ac.cn
cFaculty of Agro-Industry Chiang Mai University, Chiang Mai, 50100, Thailand
dCollaborative Innovation Centre of Biomass Energy, Zhengzhou, 450002, China
eHenan Academy of Sciences Institute of Energy Co. Ltd., Zhengzhou 450000, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra13362f
‡ These authors contribute equally to this work.
10922 | RSC Adv., 2018, 8, 10922–10929
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
Due to the complicated structure of lignocellulosic biomass, powder was washed with deionized (DI) water until the ltrate
unsatisfactory results were oen obtained in the application of was colorless and then, the ltrate was dried at 105 ꢀC over-
carbon-based solid acids for lignocellulose saccharication or night. This black powder was denoted as Sl-C.
fractionation. Zhang prepared the solid acid catalyst Fe3O4/C–
One gram of Sl-C was mixed with 50 mL of 6 M hydrochloric
ꢀ
SO3H to catalyze corncob hydrolysis; 44.3% xylose yield was acid on a shaking table (QHZ-3B) at 150 ppm and at 30 C for
obtained at 160 C for 16 h.22 Xu23 used glucose and p-toluene- 4 h.27 It was then washed with a large amount of DI water until
ꢀ
sulfonic acid as raw materials to prepare solid acid (Gp–SO3H– the pH was neutral and then, it was dried at 105 ꢀC for 6 h. This
H2O2) for corncob hydrolysis and obtained a 77.5% xylose yield sample was denoted as Sl-C-H.
under the optimal condition. Zhong24 prepared the SO42ꢁ/Fe2O3
One gram of Sl-C and 20 mL of H2SO4 (98 wt%) were added to
solid acid catalyst and catalyzed the hydrolysis of wheat straw; a 75 mL thick-walled pressure bottle (Beijing Synthware Glass
63.5% of xylose was obtained aer the treatment of hydrolysate Co. Ltd.) and reacted at 130 ꢀC in an oil bath for 10 h. Then, the
ꢀ
with 1 M H2SO4 at 100 C for 1 h.
powder was washed with DI water until the pH was neutral. The
In this study, we used sodium lignosulfonate, a waste product was dried in an oven at 105 ꢀC for 6 h and was denoted
material from sulphite pulp, to prepare highly selective carbon- as Sl-C-S.
based solid acid catalysts, which can directly catalyze hemi-
One gram of Sl-C-S and H2O2 (0–30 wt%) were mixed in the
cellulose from biomass into xylose. Moreover, this study is solid/liquid ratio of 1 : 25–1 : 125 (m : v) and reacted for 30–
ꢀ
different from the reported studies on random acquisition of 150 min at 30–70 C in a 150 mL thick-walled pressure bottle
xylo-oligosaccharides during the hydrolysis of lignocellulose (Beijing Synthware Glass Co. Ltd.). Then, the powder was
catalysed by carbon-based solid catalysts. Recently, researchers treated via the procedures described above and denoted as Sl-C-
found that lignosulfonates were rich in aromatic ring structures S-H2O2.
and could be modied to produce an effective carbon-based
solid acid catalyst.25 Zhu26 approached cellulose hydrolysis by
Hydrolysis of corncob
lignosulfonate-based solid acid and obtained a total sugar yield
First, 0.3 g of catalyst, 0.3 g of corncob and 30 mL of DI water
of 44.2%. However, there are few publications regarding
were loaded into a 75 mL thick-walled pressure bottle, and this
lignosulfonate-derived carbon-based solid catalysts for ligno-
solution was maintained at 130 ꢀC in an oil bath for 12 h. Then,
cellulose hydrolysis.
the solution was centrifuged at 8000 rpm for 3 min. Part of the
We used sodium lignosulfonate as the carbon base and
supernatant was treated with 4 wt% H2SO4 to depolymerize the
prepared three kinds of solid acid catalysts. The solid acid
oligosaccharides. Next, 5 mL of the untreated supernatant and
catalysts were used for corncob hydrolysis, and a high yield
5 mL of the 4 wt% H2SO4-treated supernatant were neutralized
(84.2%) of xylose was directly obtained with a few by-products
with CaCO3, and they were then analyzed by high-performance
under mild reaction conditions. The retention rate of cellu-
liquid chromatography (HPLC).
lose in the residue was 82.5%. This process fully utilized
lignosulfonate by-products of sulte pulp to prepare a carbon-
based solid acid catalyst with high catalytic activity and selec-
Characterization of catalyst
tivity for the hydrolysis of hemicellulose to xylose. The high The functional groups of the catalysts were analyzed by Fourier-
retention of cellulose is also an important resource for ethanol transform infrared spectroscopy (FT-IR) using a TENSOR 27
and a platform for chemicals production.
spectrometer (Bruker) in the range of 400ꢁ4000 cmꢁ1. The
powder X-ray diffraction patterns were obtained in the 2q range
of 5–80ꢀ with a scanning step of 0.0167ꢀ using a PANalytical
X'Pert PRO (Cu Ka1 radiation), operating at 40 kV and 40 mA.
The surface morphology of the catalyst was observed by scan-
ning electron microscopy (SEM, S-4800, Hitachi, Japan). The C,
H, N, and S elemental contents were detected by an elemental
analyser (Vario EL cube, Germany). The acid functional groups
in the catalyst were determined by acid–base titration.23 First,
the total amount of acid in the catalyst was titrated as follows:
0.25 g catalyst was added to 40 mL of 0.05 M sodium hydroxide,
and this solution was put on a shaking table for 4 h at 50 ꢀC to
react HOꢁ and the acid group on the catalyst. Aer centrifuga-
tion at 8000 rpm for 3 min, 10 mL of the supernatant was
titrated with 0.05 M hydrochloric acid to evaluate the total
amount of acid in the catalyst. The catalyst (0.25 g) was also
added to 40 mL of 0.05 M sodium chloride under the same
conditions to fully exchange Na+ and H+ on the SO3H group.
Experimental
Materials
Sodium lignosulfonate (96%, 534.15 MW) was purchased from
Shanghai Macklin Biochemical Ltd (China). Sulfuric acid (AR),
hydrochloric acid and hydrogen peroxide (30 wt%, AR) were
obtained from Guangzhou Chemical Reagent Factory (China).
D-Xylose (AR) and calcium carbonate (AR) were purchased from
Tianjin Fuchen Chemical Reagent Factory (China). All reagents
were used without purication. Corncob powder was acquired
from a farm in Shandong Province, China. It was ground into
particles with a size of 40–60 mesh and then oven-dried at 80 ꢀC
for 12 h.
Preparation of catalyst
Under a nitrogen atmosphere, sodium lignosulfonate (denoted Aer centrifugation at 8000 rpm for 3 min, 10 mL of the
ꢀ
as Sl) was carbonized at 200–300 C for 2–8 h in a homemade supernatant was titrated with 0.05 M sodium hydroxide to
tube furnace (shown in Fig. S1†). Aer carbonization, the evaluate the concentration of SO3H groups on the catalyst.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 10922–10929 | 10923

View Article Online
RSC Advances
Paper
Analytical methods
The chemical composition of the raw material was analyzed
according to the standard laboratory analytical procedures
(LAP) for biomass analysis provided by the US National
Renewable Energy Laboratory (NREL).28 The analysis revealed
that the corncob was composed of 35.07% glucan, 34.54%
xylan, and 14.14% lignin (dry weight basis).
The xylose and by-products were identied by HPLC (Waters
2695) using a Shodex SH-1011 column, and 5 mM H2SO4 was
employed as the mobile phase with a ow rate of 0.5 mL minꢁ1
at 50 ꢀC. Calibration curves were established for quantitative
calculations.
Fig. 1 Xylose yields from corncob hydrolysis catalysed by three
catalysts.
The xylose yield (Yx), xylose conversion rate (Cx) and xylose
selectivity (Sx) were calculated by eqn (1), (2) and (3).
mass of xylose in the hydrolysate
Yxð%Þ ¼
ꢂ 100%
(1)
mass of xylose in corncob
xylose did not change much before and aer 4 wt% sulfuric acid
treatments, only changing from 78% to 84.2%, which indicated
the high selectivity of Sl-C-S-H2O2 for the hydrolysis of hemi-
cellulose to monosaccharides (xylose), and the selectivity
reached 86.75% aer calculation.
Small amounts of by-products such as glucose, arabinose,
furfural, glucuronic acid and acetic acid were also detected
(Fig. S2†) in hydrolysate. As reported, the presence of these by-
products was inevitable during the hydrolysis of lignocellu-
lose.4,24 Furfural was the degradation product of xylose or xylo-
oligosaccharide. According to the eqn (3), the selectivity of
xylose was calculated to be 86.75%. The selectivity of total
saccharides (xylose and xylo-oligosaccharide) was calculated to
be 93.65%, which also indicated the high selectivity of the
catalyst during the hydrolysis of corncob.
To identify the relationship between the components of the
three catalysts and the xylose yield, elemental and total acid
analyses were performed. As shown in Table 1, the solid acid Sl-
C-H revealed the weakest acidity, which accounted for the least
effective catalytic performance. Upon comparison of the
chemical formula of Sl-C-S (CH0.787O0.505S0.016) with that of Sl-C-
H (CH0.841O0.344S0.006), it was observed that the sulfur content of
Sl-C-S was signicantly higher than that of Sl-C, which was due
to the SO3H groups introduced by the reaction between Sl-C and
concentrated sulfuric acid. The sulfonic acid group was the
most effective group for corncob hydrolysis;18 thus, the catalytic
activity of Sl-C-S was higher than that of Sl-C-H, resulting in
a further increase in xylose yield. Aer the oxidation reaction,
Cxð%Þ ¼
mass of xylose in corncob ꢁ mass of xylose in the residue
mass of xylose in corncob
ꢂ 100%
(2)
(3)
Yx
Sxð%Þ ¼
ꢂ 100%
Cx
The crystallinity calculation equation is as follows:29
Icrystallineð002Þ ꢁ Iamorphousð101Þ
CrI ¼
ꢂ 100%
(4)
Iamorphousð002Þ
here, CrI is the crystallinity of cellulose, Icrystalline(002) is the
strength of the crystalline region (2q
22.5ꢀ) and
Iamorphous(101) is the strength of the amorphous region
(2q ¼ 17.5ꢀ).
¼
Results and discussion
Evaluation of catalyst activity
Comparative analyses of the catalytic activities of the three
catalysts (Sl-C-H, Sl-C-S, Sl-C-S-H2O2) were carried out. The
carbonization reaction using each of the three catalysts was
carried out at 250 ꢀC for 6 h, and the subsequent oxidation
process comprised 1 g of Sl-C-S reacted with 75 mL 10% H2O2 at
50 ꢀC for 90 min. To evaluate the catalytic activity of each
catalyst, the reaction conditions did not facilitate complete
reaction for any of the catalysts. As shown in Fig. 1, for Sl-C-H,
the direct xylose yield was 21%, and the xylose yield was 62%
aer 4 wt% sulfuric acid treatment, indicating that most of the
xylan in hemicellulose was hydrolyzed into xylo-
oligosaccharides. For Sl-C-S catalysis, the xylose yield
increased from 58.2% to 77% before and aer 4 wt% sulfuric
acid treatment, indicating that there was still a signicant
amount of xylo-oligosaccharides produced. From this, it could
be seen that both of these two catalysts were less selective for
the hydrolysis of hemicellulose to monosaccharides (xylose).
However, for the catalytic hydrolysis of Sl-C-S-H2O2, the yield of
the chemical formula of Sl-C-S-H2O2 was CH0.769O0.539S0.016
.
The oxygen content of Sl-C-S-H2O2 was the highest among the
Table 1 Elemental analyses and acid–base titration results of the three
solid acid catalysts
–SO3H
content
Total acid
content
Sulfur
Oxygen
Catalyst
content (%) content (%) (mmol gꢁ1
)
(mmol gꢁ1
)
Sl-C-H
Sl-C-S
Sl-C-S-H2O2 2.364
0.971
2.706
29.755
37.664
39.359
0.30
0.70
0.68
2.15
4.40
4.78
10924 | RSC Adv., 2018, 8, 10922–10929
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
three catalysts. This may be due to the introduction of carbox-
ylic acid groups and hydroxyl functional groups during the
oxidation reaction by hydrogen peroxide, which could also
account for its highest total acid content.
Characterization of catalysts
The surface morphologies of Sl, Sl-C-H, Sl-C-S and Sl-C-S-H2O2
are shown in Fig. 2. From the SEM micrographs, it could be
found that there were obvious changes through every step in the
syntheses of the catalysts. The smooth surface of Sl is shown in
Fig. 2(a). Aer carbonization at 250 ꢀC, surface cracks appeared
as shown in Fig. 2(b), which was attributed to the breakage of
chain structures such as ether linkages.27 Aer the sulfonation
reaction with concentrated sulfuric acid (Fig. 2(c)), the particle
size decreased and the particles tended to aggregate. Moreover,
many gullies and pores on the surface of the catalyst were
observed. However, the H2O2 oxidation did not signicantly
change the surface structure (Fig. 2(d)), indicating that this type
of oxidation process had less impact on the surface morphology
of the catalyst.
The XRD patterns of Sl-C-H, Sl-C-S and Sl-C-S-H2O2 are
shown in Fig. 3. It could be observed that there was no great
difference between the skeleton structures of these three cata-
lysts. The XRD patterns of all three catalysts had two diffraction
peaks. One broad diffraction peak was observed at a 2q angle of
10–30ꢀ, which was attributed to the (002) plane of the amor-
phous carbon framework. Another weak diffraction peak was
observed between 35ꢀ and 50ꢀ which was ascribed to the (101)
plane of the amorphous carbon framework corresponding to
the a-axis direction of the graphite structure.30 Aer the sulfo-
nation reaction, the peak at 10–30ꢀ became weaker, reecting
further dehydration by concentrated acid.26
Fig. 3 X-ray diffraction patterns of the catalysts.
1616 cmꢁ1 for the three catalysts was ascribed to the stretching
vibration absorption of the C]C double bond of the aromatic ring,
which indicated that the catalyst body still contained an aromatic
ring in its skeleton structure.15 In comparison to the absorption
peaks in the spectrum of Sl-C-H, the absorption peaks of Sl-C-S at
1169 cmꢁ1 and 1034 cmꢁ1 were different, and this was ascribed to
the corresponding asymmetric stretching vibration and symmet-
rical stretching vibration of –SO3H and O]S]O bonds, indicating
that the sulfonic acid groups were attached to the catalyst
successfully. The stretching vibration peak of C]O at 1705 cmꢁ1
indicated the presence of carboxyl groups. The broad absorption
band at approximately 3419 cmꢁ1 corresponded to the stretching
vibration of the hydroxyl groups.9,31 The FT-IR spectrum of Sl-C-S-
H2O2 showed clearer and stronger signals from acidic functional
groups (–COOH, –OH) than did the FT-IR spectrum of Sl-C-S.
From the results of SEM and XRD, it could be clearly
observed that the surface structures of sodium lignosulfonate-
based solid acids were severely damaged aer carbonization
and sulfonation, but the carbon skeletons of the three solid
acids were almost the same. The FT-IR results revealed the
difference regarding the functional groups among the three
solid acids: different acidic functional groups. Moreover, the
solid acid catalyst had a complex fused ring structure.32 Thus,
during the different preparation processes, the variation of the
functional groups of the three catalysts was exhibited in Fig. 5.
The FT-IR spectra of Sl and the three catalysts are shown in
Fig. 4. The peak at 1217 cmꢁ1 in the raw materials arose from the
stretching vibration of the ether bond (C–O–C). However, this peak
disappeared aer the carbonization process, which was due to the
high-temperature fracture of the ether bond and the correspond-
ing production of small molecules. The characteristic peak at
Fig. 2 Scanning electron microscopy images of the catalysts. (a) Sl, (b)
Sl-C-H, (c) Sl-C-S, (d) Sl-C-S-H2O2.
Fig. 4 FT-IR diffraction patterns of the catalysts and raw material.
RSC Adv., 2018, 8, 10922–10929 | 10925
This journal is © The Royal Society of Chemistry 2018

View Article Online
RSC Advances
Paper
It was reported that the phenolic hydroxyl groups and carboxyl lignosulfonate is a process that includes simultaneous thermal
groups in the carbon material, which were capable of adsorbing decomposition and polycondensation reactions.33 It was
cellulose and water molecules effectively, and the SO3H groups observed that when the temperature was below 250 ꢀC, the yield
bonded to the carbon material could decompose hydrogen bonds of xylose increased with the increasing temperature. This was
and hydrolyze the b-1,4-glycosidic bonds in the adsorbed cellulose due to the formation of carbonized amorphous structures,
molecules.18 Based on this report, it could be predicted that the which accommodated more acidic functional groups (–SO3H,
main catalysis effects of phenolic hydroxyl groups and carboxyl –COOH, –OH) for the hydrolysis reaction. A further increase in
groups in our carbon-based solid acids were absorbing hemi- the temperature resulted in the reduction of the xylose yield,
cellulose and water molecules, and the SO3H groups could which was due to the destruction of the optimum carbon
decompose the bonds in the adsorbed hemicellulose molecules structure, resulting in decreased availability of the active site. To
and released xylose or xylo-oligosaccharides.
further verify this result, acid–base titration experiments were
Through the results of Fig. 1 and 5, the relationship between conducted. In Table S1,† it can be observed that when the
the properties of the three solid acid functional groups and the temperature was lower than 250 ꢀC, the SO3H and total acid
xylose selectivity was analysed. The simplest solid acid Sl-C-H content were increased, and a further increase in the tempera-
could be obtained by direct carbonization of Sl and ion exchange ture resulted in a decreased acid content. It was found that the
with HCl. However, only a small amount of acidic functional effects of the carbonization temperatures were consistent with
groups (–SO3H, –OH, –COOH) were attached on the surface of the the results of the acid–base titration. The optimal carbonization
solid acid, resulting in the low xylose selectivity of corncob temperature and reaction time of the hydrolysis process were
hydrolysis showed in Fig. 1. To introduce more acidic functional determined to be 250 ꢀC and 6 h, producing the optimal xylose
groups, sulfuric acid was used to sulfonate the Sl-C, introducing yield of 83.5%.
more sulfonic acid groups (–SO3H) onto the catalyst. Furthermore,
The effects of H2O2 concentration, oxidation reaction time,
the oxidation of Sl-C-S by hydrogen peroxide was carried out to reaction temperature and the solid/liquid ratio on the catalytic
obtain more carboxyl and hydroxyl groups (–COOH, –OH). The activity of Sl-C-S-H2O2 were studied by a single factor control
results were consistent with the performances of Sl-C-S and Sl-C-S- method as shown in Fig. S3.† The xylose yield gradually
H2O2 in corncob hydrolysis (Fig. 1), and the results were also increased with the increasing H2O2 concentration and reached
consistent with those of FT-IR analysis (Fig. 4). The oxidation the highest level when 10% H2O2 was applied. This was attrib-
reaction by hydrogen peroxide was used to introduce more weakly uted to the improved availability of carboxylic acid and hydroxyl
acidic groups (such as –COOH and –OH) instead of –SO3H, which functional groups on the catalyst surface during the treatment
was conrmed by no change in the content of –SO3H before and process, which could enhance the catalytic activity for the
aer the hydrogen peroxide treatment (as shown in the elemental hydrolysis reaction. Further increasing the H2O2 concentration
analysis in Table 1). However, the weak acidic groups introduced beyond 10% did not result in enhancement of the xylose yield.
by the hydrogen peroxide treatment did not result in a remarkable According to Fig. S3(b),† the highest xylose yield was obtained
increase in the total xylose yield (84.2% with Sl-C-S-H2O2 vs. 78% when the reaction time was 90 min. The increase of oxidation
with Sl-C-S), but signicantly increased the xylose selectivity temperature could improve the catalytic activity when the
(86.75% for Sl-C-S-H2O2 vs. 68% for Sl-C-S); the xylose result for Sl- oxidation temperature was below 50 ꢀC. The change in this
C-S-H2O2 is shown in Fig. 1.
effect above 50 ꢀC was due to the rapid decomposition of H2O2
at higher temperature. The effect of the solid–liquid ratio was
similar to that of the reaction time, indicating that excessive
content of H2O2 was not necessary to promote the oxidation
process. Based on this analysis, the optimized reaction
Optimization of preparation conditions for Sl-C-S-H2O2
The effects of varying the carbonization temperature of the
corncob hydrolysis are shown in Fig. 6. The xylose yield ob-
tained was treated by 4% H2SO4. The carbonization of sodium
Fig. 6 Effect of carbonization temperature and time on the catalysis of
corncob hydrolysis. Oxidation condition: 1 g of Sl-C-S, 50 mL of 10%
H2O2 at 50 ꢀC for 90 min.
Fig. 5 Reaction formula for catalyst preparation.
10926 | RSC Adv., 2018, 8, 10922–10929
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
Table 2 Composition analysis of residues produced after corncob
hydrolysis with the three catalysts
conditions for ꢀthe catalyst Sl-C-S-H2O2 were determined to be
10% H2O2, 50 C temperature, and 90 min reaction time with
a solid–liquid ratio of 1 : 75 g mLꢁ1. The highest yield of xylose
obtained with these conditions was 84.2%.
Retention
rate of
In the study of hydrolysis of hemicellulose in biomass cata-
lyzed by carbon-based solid acid, Zhang prepared the solid acid
catalyst Fe3O4/C–SO3H to catalyze corncob hydrolysis; only
a 44.3% xylose yield was obtained when the hydrolysis was
Corncob
residue
Cellulose
(%)
Hemicellulose Lignin
cellulose
(%)
(%)
(%)
Sl-C-H
Sl-C-S
50.67 ꢃ 0.73 16.57 ꢃ 0.57
55.71 ꢃ 1.07 10.16 ꢃ 1.03
28.57 ꢃ 0.31
30.42 ꢃ 0.38
—
—
carried out at 160 C for 16 h.22 Xu used glucose and p-tolue-
ꢀ
Sl-C-S-H2O2 58.03 ꢃ 0.87
6.97 ꢃ 0.88
31.62 ꢃ 0.45 82.5
nesulfonic acid as raw materials to prepare a solid acid (Gp–
SO3H–H2O2),23 and a xylose yield of 78% (aer sulfuric acid
post-hydrolysis) was obtained when the hydrolysis of corncob
and sharper crystal peaks were both due to the hydrolysis of
hemicellulose, whereas the crystalline cellulose and lignin
remained in the corncob.
2ꢁ
ꢀ
was carried out at 140 C for 14 h. Zhong prepared the SO4
/
Fe2O3 solid acid catalyst and catalyzed the hydrolysis of wheat
straw at 140 ꢀC for 4 h; the yield of xylose was 63.5% (aer
sulfuric acid post-hydrolysis).24 In our study, the xylose selec-
tivity was signicantly improved, and the reaction condition
was mild.
When compared with those in the raw material, the relative
contents of cellulose and lignin in the residue increased aer
hydrolysis, whereas the content of hemicellulose decreased
(Table 2). This was because the degree of hydrolysis of hemi-
cellulose was greater than those of cellulose and lignin. As can
be seen in Table 2, the contents of cellulose and lignin in the
corncob residue subjected to catalysis by Sl-C-S-H2O2 were the
highest and reached 58.03% and 31.62%, respectively. These
were compared to the lowest hemicellulose content of 6.97%,
which suggested a greater hydrolysis degree for hemicellulose.
This was consistent with the result shown in Fig. 1, in which the
highest yield of hydrolyzed xylose was obtained using Sl-C-S-
H2O2. By calculation, the retention rate of cellulose was 82.5%,
which indicated that a large amount of cellulose was not
hydrolyzed into glucose.
Characterization of corncob feedstock and residue
The surface morphologies of the corncob raw material and the
corncob residue aer pretreatment are shown in Fig. 7. The
color of the corncob changed from light yellow to dark brown
aer the hydrolysis reaction. Meanwhile, the relatively smooth
and dense surface structure of the feedstock changed to
a structure having irregular gullies with loose holes. This was
mainly due to the decomposition of hemicellulose in the cell
walls to form water-soluble xylose during the catalytic
hydrolysis.
Both the corncob and residue produced a signicant XRD
peak at approximately 22.5ꢀ, which was attributed to the 002
plane crystal diffraction peak of cellulose as shown in Fig. S4.†
The diffraction intensity at 2q ¼ 17.5ꢀ corresponded to the 101
plane diffraction intensity peak associated with the amorphous
region of cellulose. The diffraction intensity at 2q ¼ 22.5ꢀ cor-
responded to the crystalline cellulose. According to eqn (2), the
crystallinity indices of the corncob and the hydrolysis residues
were 31.3% and 41.7%, respectively. The increased crystallinity
Reusability of the catalyst
The reusability of the catalyst is an important property for the
economical industrial application of solid acid catalysts.34 To
investigate the reusability of Sl-C-S-H2O2, which was prepared
under the optimum conditions, evaluation experiments were
carried out at 130 ꢀC for 12 h. Aer the hydrolysis reaction, the
catalyst was washed and ltered through a sand-core funnel
ꢀ
several times before drying at 105 C for 6 h and then, it was
separated by a 200-mesh sieve. It can be seen from Fig. 8 that
Fig. 7 The light and SEM images of corncob and residues: (a) corncob, Fig. 8 Xylose yields from corncob hydrolysis catalyzed by recycled Sl-
(b) SEM of corncob, (c) residue, (d) SEM of residue.
C-S-H2O2.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 10922–10929 | 10927

View Article Online
RSC Advances
Paper
the yield of xylose decreased gradually from 84.2% to 70.7%,
and the reduction in the catalytic ability was better than that in
the previous report by Xu,23 who reported that the yield of xylose
decreased from 77.5% to 65.0% aer 4 cycles of usage. The
elemental analysis and acid–base titration results for Sl-C-S-
H2O2 aer reuse are shown in Table S2.† It was found that the
total acid content aer 5 cycles of reuse was still very high, and it
was 90.79% of the initial total acid content.
4 D. Yamaguchi and M. Hara, Solid State Sci., 2010, 12, 1018–
1023.
5 X. Zhang, K. Wilson and A. F. Lee, Chem. Rev., 2016, 116,
12328–12368.
6 A. Esteghlalian, A. Hashimoto, J. Fenske and M. Penner,
Bioresour. Technol., 1997, 59, 129–136.
¨
¨
7 J. Soderstrom, L. Pilcher, M. Galbe and G. Zacchi, Appl.
Biochem. Biotechnol., 2003, 108, 127–140.
8 W. Qi, S. Zhang, Q. Xu, H. Li, Z. Ren, T. Li and Y. Yan, Chem.
Eng. Technol., 2009, 32, 534–540.
9 I. F. Nata, C. Irawan, P. Mardina and C.-K. Lee, J. Solid State
Chem., 2015, 230, 163–168.
Conclusions
A novel carbon-based solid acid catalyst with high catalytic
activity, high selectivity and reusability was synthesized from 10 L. D. Borges, N. N. Moura, A. A. Costa and P. R. S. Braga, Appl.
waste lignosulfonate. The solid acid catalyst synthesized Catal., A, 2013, 450, 114–119.
through the processes of carbonization, sulfonation by 11 S. A. Fernandes, A. L. Cardoso and M. J. da Silva, Fuel Process.
concentrated sulfonic acid and modication by H2O2 was rich Technol., 2012, 96, 98–103.
in acidic functional groups such as –COOH, –OH, and –SO3H. 12 H. Yan, Y. Yang, D. Tong, X. Xiang and C. Hu, Catal.
Under the optimized preparation conditions for the catalyst, the
Commun., 2009, 10, 1558–1563.
catalyst showed a high catalytic activity and selectivity for the 13 I. A. L. Bassan, D. R. Nascimento, R. A. S. San Gil, M. I. P. da
hydrolysis hemicellulose in corncob with an 84.2% yield of
xylose, 82.5% cellulose retention rate and only a few by-
Silva, C. R. Moreira, W. A. Gonzalez, A. C. Faro, T. Onfroy and
E. R. Lachter, Fuel Process. Technol., 2013, 106, 619–624.
products. Meanwhile, the catalyst showed good stability and 14 J. Y. Park, Z. M. Wang, D. K. Kim and J. S. Lee, Renewable
reusability, as it could be used four times with only a slight Energy, 2010, 35, 614–618.
decrease in the catalytic ability. Based on this research, we can 15 G. Chen and B. Fang, Bioresour. Technol., 2011, 102, 2635–
conclude that the synthesized catalyst is excellent for pretreat- 2640.
ment of lignocellulose, and it facilitates a new method for 16 S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi,
establishing a sugar platform.
H. Kato, S. Hayashi and M. Hara, Solid State Sci., 2010, 12,
1029–1034.
17 K. N. Satoshi Suganuma, M. Kitano, D. Yamaguchi,
S. H. Hideki Kato and M. Hara, Green Chem., 2005, 438, 178.
18 S. Suganuma, K. Nakajima, M. Kitano and D. Yamaguchi, J.
Am. Chem. Soc., 2008, 130, 12787–12793.
Conflicts of interest
There are no conicts to declare.
19 S. Li and X. J. Pan, Energy Environ. Sci., 2012, 5, 6889–6894.
20 Y. Lian, L. Yan, Y. Wang and X. Qi, Acta Chimica Sinica, 2014,
72, 502–507.
Acknowledgements
This study was supported nancially by the National Natural
Science Foundation of China (21376241, 51676193, 51506207, 21 S. G. Shen, B. Cai, C. Y. Wang, H. M. Li, G. Dai and H. F. Qin,
51561145015 and 21476233), the Youth Innovation Promotion Appl. Catal., A, 2014, 473, 70–74.
Association, CAS (No. 2017401) and the Key Project of Natural 22 X. Zhang, X. Tan, Y. Xu, W. Wang, L. Ma and W. Qi,
Science Foundation of Guangdong Province (No. BioResources, 2016, 11, 10014–10029.
2015A030311022). N. Leksawasdi gratefully acknowledges the 23 Y. Xu, X. Li and X. C. Zhang, BioResources, 2016, 11, 10469–
nancial support and/or in-kind assistance from the Sino-Thai 10482.
National Research Council of Thailand (NRCT). The authors 24 C. Zhong, C. Wang, F. Huang, F. Wang, H. Jia, H. Zhou and
further acknowledge support from the Project Funding of
P. Wei, Carbohydr. Polym., 2015, 131, 384–391.
National Research University-Chiang Mai University (NRU- 25 D. Lee, Molecules, 2013, 18, 8168–8180.
CMU) and the National Research University-Office of Higher 26 J. D. Zhu and L. H. Gan, Appl. Chem. Ind., 2016, 45, 1499–
Education Commission (NRU-OHEC), the Non-Food Agricul-
1502.
tural Research Cluster, and CMU Mid-Career Research Fellow- 27 F. Liang, Y. Song, C. Huang and B. Chen, New Chem. Mater.,
ship program (Grant Number: W566_21022560).
2014, 42, 86–89.
28 A. Sluiter, B. Hames, R. Ruiz, C. Scarlata and J. Sluiter,
Technical Report NREL/TP-510-42618, 2008.
29 L. Segal, J. Creely, A. Martin and C. Conrad, Text. Res. J.,
1959, 29, 786–794.
References
1 F. Isikgor and C. Becer, Polym. Chem., 2016, 6, 4497–4559.
2 H. S. Kambo and A. Dutta, Energy Convers. Manage., 2015, 30 B. Zhang, J. Ren, X. Liu, Y. Guo, Y. Guo, G. Lu and Y. Wang,
105, 746–755. Catal. Commun., 2010, 11, 629–632.
3 Y. J. Zhang, P. Y. Bi, J. C. Wang, P. W. Jiang, X. P. Wu, H. Xue, 31 X. Liang, H. Xiao, Y. Shen and C. Qi, Mater. Lett., 2010, 64,
J. X. Liu, X. G. Zhou and Q. X. Li, Appl. Energy, 2015, 150, 128–
953–955.
137.
10928 | RSC Adv., 2018, 8, 10922–10929
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
32 M. Hara, T. Yoshida, A. Takagaki, T. Takata, J. N. Kondo, 33 M. Brebu, G. Cazacu and O. Chirila, Cellul. Chem. Technol.,
S. Hayashi and K. Domen, Angew. Chem., 2004, 43, 2955–
2011, 45, 43–50.
2958.
34 J. Zhao, C. Zhou, C. He, Y. Dai, X. Jia and Y. Yang, Catal.
Today, 2016, 264, 123–130.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 10922–10929 | 10929