Sulfonic-acid-functionalized carbon fiber from waste newspaper as a recyclable carbon based solid acid catalyst for the hydrolysis of cellulose

Article abstract of DOI:10.1039/c9ra04568f

Waste newspaper is one of the most common cellulosic materials. Therefore, effective utilization of this commonly available biomass resource to prepare high-value carbon-based solid acid catalysts is an interesting and meaningful task. In this study we propose a new route for waste newspaper valorization, in which sulfonic-acid-functionalized carbon fiber can be directly produced from waste newspaper as a recyclable carbon based solid acid catalyst (WCSA) for the hydrolysis of cellulose. The as-prepared sulfonic-acid-functionalized carbon fiber contained -SO₃H, -COOH, and phenolic -OH groups and exhibited good catalytic activity for the hydrolysis of cellulose. WCSA prepared under sulfonation conditions at a temperature of 100 °C and for a duration of 10 h has a higher sulfonic acid content. A total reducing sugars (TRS) yield of 58.2% was obtained with a catalyst/microcrystalline cellulose (MCC) ratio of 4 at 150 °C using a reaction time of 6 h. The recycling performance of the WCSA catalyst indicated that the TRS remained almost stable for five cycles during the hydrolysis of cellulose.

Full text of DOI:10.1039/c9ra04568f

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Sulfonic-acid-functionalized carbon fiber from
waste newspaper as a recyclable carbon based solid
acid catalyst for the hydrolysis of cellulose
Cite this: RSC Adv., 2019, 9, 28902
a
a
ab
a
a
*
*
Yanzhu Guo,
Runming Gong, Zihao Ma, Xing Wang,
Guangwei Sun,a Yao Lia and Jinghui Zhou
Ying Han,
a
Waste newspaper is one of the most common cellulosic materials. Therefore, effective utilization of this
commonly available biomass resource to prepare high-value carbon-based solid acid catalysts is an
interesting and meaningful task. In this study we propose a new route for waste newspaper valorization,
in which sulfonic-acid-functionalized carbon fiber can be directly produced from waste newspaper as
a recyclable carbon based solid acid catalyst (WCSA) for the hydrolysis of cellulose. The as-prepared
sulfonic-acid-functionalized carbon fiber contained –SO3H, –COOH, and phenolic –OH groups and
exhibited good catalytic activity for the hydrolysis of cellulose. WCSA prepared under sulfonation
conditions at a temperature of 100 ꢀC and for a duration of 10 h has a higher sulfonic acid content. A
total reducing sugars (TRS) yield of 58.2% was obtained with a catalyst/microcrystalline cellulose (MCC)
ratio of 4 at 150 ꢀC using a reaction time of 6 h. The recycling performance of the WCSA catalyst
indicated that the TRS remained almost stable for five cycles during the hydrolysis of cellulose.
Received 18th June 2019
Accepted 30th August 2019
DOI: 10.1039/c9ra04568f
rsc.li/rsc-advances
OH, and COOH groups), have attracted a great deal of attention
owing to their favorable characteristics such as high acid
1 Introduction
densities, stability and recyclability, which are widely used in
the hydrolysis of cellulose and its derived polysaccharides.6
During CSA catalytic hydrolysis of cellulose, phenolic OH
groups bonded to CSA have the ability to absorb cellulose and
rich-phenolic hydroxyl CSA derived from phenolic residues have
improved this ability.7 The adsorption effect is affected by the
size and morphology of the catalyst owing to the solid/solid
interface effect between the CSA and the cellulose. Therefore,
it is imperative to change the size and morphology of the CSA in
order to enhance the interaction between the cellulose and
catalyst. Guo et al. prepared a sulfonated carbonaceous solid
acid catalyst with a spherical structure for catalytic hydrolysis of
cellulose and procured total reducing sugars (TRS) at a yield of
68.9%. Ma et al. hydrolyzed cellulose into glucose with yields of
40.2% using a porous morphology lignin carbon-based solid
acid.8 Pang et al. employed microcrystalline cellulose-derived
carbon fragments with an elongated structure for the catalytic
hydrolysis of cellulose and the glucose selectivity was found to
be 48.5%.9 The catalysts used by those authors can be easily
synthesized by the low temperature hydrothermal reaction of
renewable hydrocarbon feedstocks, for example cellulose,
lignin, and sugars.10
Efficient conversion of renewable biomass to useful chemicals
and biofuels is one of the most popular topics in green and
sustainable chemistry.1 Cellulose,
a linear homopolymer
composed of D-glucopyranose subunits linked by b-1,4-glyco-
sidic bonds, is the most abundant organic molecule on Earth,2
effective methods of hydrolysis or depolymerization of cellulose
seem to be an interesting entry point into the production of
biofuels and biochemicals.3 Homogeneous acid hydrolysis of
cellulose is a method that has been used for a long time;
however, the method has some shortcomings such as reactor
corrosion, poor catalyst recyclability, difficult product separa-
tion and treatment of the waste effluent.4 Enzymatic depoly-
merization of cellulose demonstrates a good selectively for the
hydrolysis of cellulose to glucose, but it is slow, expensive and
difficult to recover enzymes from the reaction mixture.5
In contrast to homogeneous acid catalysts (e.g., sulfuric acid)
and enzymes which are highly active and selective but cannot be
reused, solid acid catalysts are easy to handle on the large scale
and can be reused multiple times. Among solid acid catalysts,
carbon-based solid acids (CSA), such as amorphous carbons
consisting of aromatic carbon sheets bearing active sites (SO3H,
Waste newspaper is one of the most common cellulosic
materials, millions of tons of waste newspapers are generated
annually in China.11 Therefore, the effective utilization of this
commonly available biomass resource to prepare high-value
carbon-based solid acid catalysts is an interesting and
aLiaoning Key Laboratory of Pulp and Papermaking Engineering, Dalian Polytechnic
University, Dalian, Liaoning 116034, China. E-mail: wangxing@dlpu.edu.cn;
hanying@dlpu.edu.cn; Tel: +86 411 86323296
bState Key Laboratory of Pulp and Paper Engineering, South China University of
Technology, Guangzhou 510640, China
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meaningful task. In this work, we designed and synthesized isotherms were obtained using a 77 Kon Micromeritics ASAP
a carbon ber solid acid catalyst bearing –OH, –SO3H, and 2020 physisorption analyzer. Then the pore size distribution
–COOH groups from the hydrothermal carbonization of waste was obtained from the description branch using the Barrett–
newspaper under mild conditions and used it for the hydrolysis Joyner–Halenda (BJH) formula. The crystal phase of the as-
of cellulose in water. Cyclic experiments for the separated prepared products was characterized using an X-ray diffrac-
catalysts showed that the catalyst maintained its catalytic tometer (SHIMADZU XRD-7000S) with Cu-Ka radiation in the
properties and could be reused. These solid acid catalysts based range (10–60ꢀ). The density of the –SO3H, –COOH and –OH
on waste newspaper prepared using hydrothermal carboniza- groups of WCSA was determined using the Boehm titration with
tion provide a possible strategy for biomass conversion through
renewable materials.
a slight modication. The method used was previously
described in the literature by Lin et al.13
2.4. Catalytic activity of the hydrolysis of cellulose over
a sulfonated carbon catalyst
2 Materials and methods
2.1. Preparation of samples and reagents
For a typical run, the hydrolysis reaction was conducted by
adding the WCSA catalyst (0.3 g) and MCC (0.1 g) into water (10
mL) at a reaction temperature of 130–170 ꢀC and for a duration
of 2–10 h in a 20 mL polytetrauoroethylene tank with a stirring
rate of 400 rpm. Recycling experiments were performed to
determine the catalytic stability of the WCSA. At the end of each
hydrolysis of cellulose cycle, the WCSA samples were recovered
by centrifugation and ꢀwashed with water and ethanol several
times and dried at 80 C for 12 h in a vacuum oven. Aer the
hydrolysis of cellulose reaction, the TRS, such as glucose and
fructose, were measured using the dinitrosalicylic (DNS) acid
colorimetric method as described by Shimizu et al.14 Analysis of
glucose in hydrolysates was performed using an ion chro-
matograph (Dionex ICS-5000, USA), which was equipped with
a Capillary Reagent-Free IC System and a CarboPac 20 column.
Waste newspapers (WP) were obtained from Dalian Publishing
House (Dalian, China). The composition, based on the dry
substrate, was: 67.18 ꢁ 0.04% cellulose; 9.88 ꢁ 0.07% hemi-
celluloses; 5.36 ꢁ 0.06% lignin; 12.72 ꢁ 0.03% ash; 3.45 ꢁ
0.02% moisture; and 1.41 ꢁ 0.08% other additives. The
composition was determined using the standard method
described by National Renewable Energy Laboratory (NREL).12
Microcrystalline cellulose (MCC) was purchased from Merck. All
other chemical reagents and deionized water were of laboratory
grade and used as received.
2.2. Preparation of waste newspaper carbonaceous material
with sulfonic acid (–SO3H) groups
The carbonaceous material was prepared by the hydrothermal
carbonization of waste newspaper. Typically, the dried waste
newspaper (3 g) and deionized water were mixed at a ratio of
1 : 6 (w/w), and the slurry was then added to a 100 mL poly-
tetrauoroethylene hydrothermal reaction vessel. The samples
were carbonized at 240 ꢀC for 4 h. Aer the carbonization
treatment, the carbonized waste newspaper carbon ber was
ltered and then washed with 1 mol Lꢂ1 HCl for 1 h ve times to
remove the inorganic ller. Then the samples were vacuum
dried at 80 ꢀC overnight to produce the waste newspaper based
carbonaceous material (WCM). Then, 1 g WCM was treated with
3 Results and discussion
3.1. Structural characteristics of WCSA catalysts
Waste newspaper was prepared by hydrothermal carbonization
and sulfonated to generate a sulfonated carbon catalyst (WCSA).
A FT-IR spectrum (Fig. 1a) was used to determine the different
effects on various groups in the waste newspapers, before and
aer sulfonation. The absorption peaks of the C]C double
bonds (1608 cmꢂ1) and –CH2 (1431 cmꢂ1) were found on WCM
and WCSA. The absorption bands at close to 1180 cmꢂ1 (S]O
symmetric stretching vibration), 1030 cmꢂ1 (S–O stretching
vibration) and 645 cmꢂ1 (C–S stretching vibration) that were
also found on WCSA indicate that WCM was functionalized with
catalytic sites (–SO3H) on the surface.15 Similar characteristic
peaks for sulfonate groups have been reported by Peng et al. and
Li et al.15 The absorption peaks of the C]O double bonds
(1700 cmꢂ1), C–OH stretching and –OH bending vibrations
(1000–1300 cmꢂ1) were also found on WCSA, which conrm the
existence of the –COOH and phenolic –OH groups.16 As a result,
the adsorption peaks of the WCM and WCSA of the carbon were
ꢀ
concentrated sulfuric acid (ꢃ20 mL H2SO4, 98%) at 60–140 C
under nitrogen for 6–14 h. Deionized water was added under
stirring to remove the residual acids until the pH equaled 7 and
it was then dried in an oven at 110 ꢀC overnight. The func-
tionalized WCM samples were then obtained and denoted as
WCSA-sulfonation temperature (WCSA-60, -80, -100, -120, -140)
and WCSA-sulfonation time (WCSA-6, -8, -10, -12, -14),
respectively.
2.3. Catalyst characterization and analysis of the total
reducing sugars
Scanning electron microscopy (SEM) was performed using quite different. Again, this indicates that the WCM was
a JSM-7800F scanning electron microscope produced by JEOL successfully sulfonated by sulfuric acid which possessed
Co., Ltd. to characterize the apparent morphology of the hydroxyl groups for intermolecular dehydration.
sample. Fourier transform infrared spectrometry (FT-IR) anal-
The X-ray diffractometry (XRD) patterns of WP, WCM and
ysis was carried out in a PerkinElmer Spectrum 100 spectrom- WCSA are shown in Fig. 1b, the two weak and broad peaks at 2q
eter using KBr pellets. The wavenumber of the IR spectra was ¼ 20–30ꢀ and 40–50ꢀ are due to the carbon (002) and (100)
recorded from 4000 to 400 cmꢂ1. The N2 adsorption–desorption reections, respectively. These diffraction peaks indicate that
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3.2. Effect of sulfonation parameters on the yield and
structural characteristics of WCSA catalysts
The sulfonation temperature and time are important factors
affecting the structure and activity of the carbon-derived cata-
lyst.18 In this work, the effects of the sulfonation conditions on
the catalyst yield (Table 1), structure (Fig. 2 and 3) and catalyst
activity (Fig. 4) were investigated. The WCM yield obtained from
the hydrothermally carbonized WP was 48.7 wt% (see Table 1).
The yields of WCM aer sulfonation are also listed in Table 1. It
can be seen that, depending on the operational conditions, the
yields of WCSA-n were in the 71–93 wt% range. The sulfonation
conditions not only affect the yield of the products, but also
affect the composition of the functional groups on the surface
of the WCM. The amounts of –SO3H, –COOH and phenolic –OH
groups bonded to the WCSA with different sulfonation
temperatures and sulfonation times are also shown in Table 1.
As shown in Table 1, increasing the sulfonation temperature
has a positive effect on the –SO3H and phenolic –OH density for
the WCSA catalyst, however, WCSA-140 had lower amounts of
–SO3H and phenolic –OH than WCSA-100 because the high
sulfonation temperature resulted in increased acid dehydration
among the WCM, reducing the C–H and C–OH bonds which
could be replaced by –SO3H groups. Meanwhile, the total acid
density of all samples was slightly increased when the sulfo-
nation temperature was raised from 60 to 100 ꢀC, but they
decreased rapidly when the temperature was increased further.
Moreover, it was also found that the density of –SO3H groups
in the samples was slightly increased when the sulfonation time
was raised from 6 to 10 h, but this remained almost stable upon
increasing the time further, indicating that the –SO3H density
did not change signicantly with increasing sulfonation time.
The FT-IR and XRD patterns for WCSA prepared under
different temperatures and times are shown in Fig. 2. Fig. 2a
and c show that the absorption peak at 3600–3200 cmꢂ1 is the
OH stretching vibration absorption peak. The peak at
1600 cmꢂ1, which represents the C]C double bond stretching
Fig. 1 FT-IR spectra (a), XRD spectra (b), SEM images (c)–(e) and N2
adsorption–desorption isotherms and pore size distribution (f) for WP,
before (WCM) and after (WCSA) sulfonation.
WCSA is an amorphous carbon composed of aromatic carbon
sheets oriented in a considerably random fashion. Structurally,
the carbon framework of WCSA is approximately consistent
with others reported in the literature.17
Fig. 1c–e shows the differences between the SEM images on
the external surfaces of the WP, WCM and WCSA. SEM analysis
reveals that the surface of WP was quite compact and smooth.
Aer carbonization and sulfonic-acid-functionalization, the
obtained WCM and WCSA materials formed ber rods with
a rough and loose surface and a diameter around 10–30 mm.
There were no appreciable size and surface differences before
and aer sulfonation. During carbonization and sulfonic-acid-
functionalization, the chemical bonds between the cellulose
bers were broken, this caused the bers to become loose, and
form a ber rod structure. The rod-like structure provides the
catalyst with more contact points with cellulose than the sheet
structure. This rod-like structure may increase the adsorption
between the catalyst and the cellulose ber, thus improving the
yield of the TRS from cellulose hydrolysis. Fig. 1f shows that the
Brunauer–Emmett–Teller (BET) surface area of WCSA and WCM
were much higher than that of WP, and the isotherms exhibited
intermediate features between those of type I and II, which
indicates that the porous network was composed of micropores
and mesopores. In addition, the predominant pore size distri-
bution exhibited was below 10 nm, which is associated with
micropores with a narrow pore size distribution.
Table 1 Yield and acid density of WCM and sulfonated WCM prepared
at different carbonization and sulfonation temperatures and timesa
Acid density (mmol gꢂ1
)
Sample
T/ꢀC
t/h
Yield (%)
–OH
–COOH
–SO3H
WCM
—
60
80
—
10
10
10
10
10
10
6
48.7a
93.8b
91.2b
84.4b
80.5b
76.6b
71.2b
89.1a
87.2b
81.4b
80.8b
5.03
4.11
3.98
3.63
3.59
3.32
2.77
3.98
3.86
3.33
3.05
0.05
0.12
0.15
0.35
0.23
0.21
0.14
0.12
0.25
0.31
0.34
—
WCSA-60
WCSA-80
WCSA-100
WCSA-120
WCSA-140
WCSA-160
WCSA-6
WCSA-8
WCSA-12
WCSA-14
0.64
1.10
1.97
1.76
1.65
1.20
0.71
0.91
1.95
1.87
100
120
140
160
100
100
100
100
8
12
14
a
b
Yield is expressed as: g WCM/100 g WP. Yield is expressed as: g
WCSA-n/100 g WCM.
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orientation of the aromatic ring space is similar to that of
graphite. This indicates that WCSA is a type of polycyclic
aromatic hydrocarbon which is non-directionally arranged in
space and possesses a graphite-like amorphous carbon. The
sulfonation process has little effect on the crystal form of the
carbon materials.
The effects of the sulfonation conditions on the catalytic
activity were investigated, as shown in Fig. 3. The blank repre-
sents a catalyst which has not been subjected to sulfonation, it
is shown that the unsulfonated catalyst has a certain catalytic
effect on cellulose hydrolysis, and the sulfonated catalyst causes
a signicant increase in the yield of the reducing sugars. The
positive effects of the sulfonation process on the catalytic
activity are shown, while different sulfonation conditions have
different effects on the catalytic activity. As can be seen in
Fig. 3a, the yield of the TRS during the hydrolysis of cellulose
initially increased and then decreased with increasing sulfo-
nation temperatures. When the sulfonation temperature was
ꢀ
100 C (WCSA-100), the yield of TRS reached the highest value
Fig. 2 FTIR spectra and XRD patterns of sulfonated catalysts prepared
under different conditions. (a) and (b) FTIR spectra and XRD patterns
with sulfonation temperatures of 60–140 ꢀC; (c) and (d) FTIR spectra
and XRD patterns with sulfonation times of 6–14 h.
(56.7%). As shown in Fig. 3b, the yield of TRS remained almost
stable at about 54% over the sulfonation time from 10 to 14 h,
indicating that the catalytic activity did not change signicantly
with increasing sulfonation time. This was identical to the effect
of the sulfonation time on the –SO3H and phenolic –OH density
of the WCSA samples (Table 1). The hydrolysis of cellulose is the
process of destroying b-1,4-glycosides bonds. It is reported that
the OH groups in the CSA can adsorb cellulose through
hydrogen bonding between the OH groups in the CSA and
cellulose, so that the CSA can efficiently hydrolyze cellulose into
glucose as well as sulfuric acid.19
vibration peak of the aromatic ring, indicates that the above
described catalysts form a stable conjugated aromatic ring
system. The two bands at 1038 and 1180 cmꢂ1 in the WCSA
catalysts can be assigned to the O]S]O symmetric stretching
and –SO32ꢂ stretching modes in the –SO3H group of WCSA, this
indicates that WCSA successfully introduced the sulfonic acid
groups and that these groups were the active sites of WCSA.
WCSA prepared under sulfonation conditions at a temperature
of 100 ꢀC and a time of 10 h exhibits the largest peak area, and
we concluded that WCSA has a higher sulfonic acid content
under these conditions. Therefore, the groups supported on
WCSA mainly include –OH, –COOH and –SO3H.
Fig. 2b and d show the XRD test results for WCSA prepared
under different sulfonation temperatures and times. The results
obtained using the WCSA X-ray diffraction (XRD) pattern show
a broad peak located at 2q ¼ 23ꢀ, which could be attributed to
the characteristic peak of amorphous carbon (Fig. 2c). There are
two characteristic peaks around 2q ¼ 30ꢀ, which are attributed
to the carbon (002) peak, indicating that the degree of
As shown in Fig. 4, the effect of the sulfonation conditions on
the glucose selectivity in TRS was investigated. The blank
represents a catalyst which has not been subjected to sulfona-
tion, it plays a minor role in the hydrolysis of cellulose to
produce glucose. As can be seen from Fig. 4a, the yield of
glucose in the TRS initially increases with the increase in the
sulfonation temperature and then stabilizes. When the sulfo-
ꢀ
nation temperature was 120 C (WCSA-120), the glucose selec-
tivity reached the highest value (89.2%). When the sulfonation
temperature was 100 ꢀC (WCSA-100), glucose selectivity reached
89.1%. As shown in Fig. 4b, the glucose selectivity remained
almost stable at about 88% over the sulfonation time from 8 to
14 h, indicated that the catalytic activity did not change
Fig. 3 Effects of sulfonation (a) temperature and (b) time on the TRS Fig. 4 Effects of sulfonation (a) temperature and (b) time on glucose
yield from cellulose catalyzed using WCSA catalysts. Reaction condi- selectivity on the TRS yield. Reaction conditions: cellulose (0.1 g),
tions: cellulose (0.1 g), WCSA (0.3 g), and water (10 mL), 6 h, 150 ꢀC.
WCSA (0.3 g), and water (10 mL), 6 h, 150 ꢀC.
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signicantly with the increasing sulfonation time. This was
identical to the effect of the sulfonation time on the –SO3H and
phenolic –OH density of WCSA samples (Table 1).
3.3. Inuence of reaction conditions on catalytic activity in
the hydrolysis of cellulose
The effect of the hydrolysis reaction conditions on cellulose
hydrolysis using the WCSA-100 catalyst is shown in Fig. 5. The
different mass ratios of the catalyst and MCC employed were 2,
3, 4, 5 and 6 (Fig. 5A). When the mass ratio of the catalyst and
MCC (catalyst/MCC) was increased to 5, the TRS yield increased
to 58.2% at a temperature 150 ꢀC and a reaction time of 6 h. It
was proposed that a further increase in the ratio would probably
enhance the hydrolysis of MCC to produce TRS, however, the
TRS yield decreased slightly with a further increase in the
catalyst/MCC ratio. A large ratio of catalyst/MCC is likely to
provide excessive active sites in the reaction process, which not
only enhances the hydrolysis of cellulose into TRS, but also
enhances the depolymerization of TRS into small molecular
derivatives, such as 5-hydroxymethyfurfural (5-HMF) and for-
mic acid.20 The reaction temperature and time also had
a signicant effect on the TRS yield as shown in Fig. 5B and C.
When the reaction time was 6 h, the maximum TRS yield of
Fig. 6 Reusability of WCSA catalysts for the hydrolysis of cellulose.
Reaction conditions: cellulose (0.1 g), WCSA-100 (0.4 g), water (10
mL), reaction temperature 150 ꢀC, and time 6 h per cycle.
ratio was increased from 50 to 200, the TRS yield sharply
increased from 9% to 56.7%. When the ratio of the liquid and
MCC was higher than 200, the TRS yield quickly decreased. The
possible reason for this may be that too much water in the
reaction system could not only reduce the contact probability
between the active sites of the catalyst and MCC, but it may also
affect the activity of the WCSA catalyst owing to the hydration of
the –SO3H groups in the catalyst.22
ꢀ
56.7% was reached at 150 C. When the temperature and time
ꢀ
were increased to 170 C and 10 h, respectively, the TRS yield
was decreased to 29% and 46%, respectively. The possible
reason for this may be that the high reaction temperature led to
further side reactions, forming by-products such as formic acid
and 5-HMF.21 It is known that water is an indispensable reactant
in the cellulose hydrolysis reaction. Herein, the inuence of the
different mass ratios of water and MCC on the TRS yield was
investigated, as shown in Fig. 5D. The TRS yield was 9% when
the mass ratio of the liquid and MCC was 50. When the mass
3.4. Reusability of WCSA
The recycling performance of the waste newspaper-derived solid
acid catalyst was also investigated using the hydrolysis of MCC.
Between each cycle of the reaction, water was employed as
a washing solvent to recovery the catalyst. The effect of catalyst
recycling on cellulose hydrolysis using the WCSA-100 catalyst is
shown in Fig. 6. The TRS remained almost stable for ve cycles
for the hydrolysis of cellulose. When the catalyst (WCSA-100)
was used for the rst time, the yield of TRS reached the high-
est value (58.2%). The yield of TRS decreased to 55.2% in the
h catalyst cycle. The yield reduced further aer recycling ve
times, indicating that the catalyst displays a good stability in
terms of the catalytic activity. Moreover, as shown in Table 2, the
–SO3H, –COOH and phenolic –OH groups could still be identi-
ed. This illustrates that the groups chemically bonded onto
WCSA do not exhibit the leaching problems that occur in most
Table 2 Acid density of WCM and sulfonated WCM prepared using the
prescribed carbonization and sulfonation temperatures and times
Acid density (mmol gꢂ1
)
Fig. 5 Effects of reaction conditions on the yield of WCSA-100
catalyst hydrolyzed cellulose. (A) Effect of catalyst dosage on the yield
of reducing sugars; (B) effect of reaction temperature on the yield of
reducing sugars; (C) effect of reaction time on the yield of reducing
sugars; and (D) effect of solvent dosage on the yield of reducing
sugars.
Sample
–OH
–COOH
–SO3H
Fresh
5th run
3.63
3.33
0.35
0.29
1.97
1.94
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carbon based-solid catalysts. Thus, the catalyst has excellent
stability and good repeatability.
5 Z. Qiu, G. M. Aita and M. S. Walker, Bioresour. Technol., 2012,
117, 251–256.
6 S. Shen, B. Cai, C. Wang, H. Li, G. Dai and H. Qin, Appl.
Catal., A, 2014, 473, 70–74.
7 M. Hara, Top. Catal., 2010, 53, 805–810.
4 Conclusions
In this work we proposed a new route for waste newspaper
valorization, in which sulfonic-acid-functionalized carbon ber
can be directly produced from waste newspaper as a recyclable
carbon based solid acid catalyst for the hydrolysis of cellulose.
The prepared WCSA contained –SO3H, –COOH, and phenolic
–OH groups and exhibited good catalytic activity for the
hydrolysis of cellulose. WCSA prepared under sulfonation
conditions at a temperature of 100 ꢀC and with a reaction time
of 10 h has a higher sulfonic acid content. A TRS yield of 58.2%
was obtained with a catalyst/MCC ratio of 4 at 150 ꢀC with a 6 h
reaction time. Meanwhile, the recycling performance of the
WCSA catalyst indicated that the TRS remained almost stable
for ve cycles during the hydrolysis of cellulose.
8 Z. H. Ma, R. M. Gong, Y. Han, X. Wang, G. W. Sun, Y. Li and
J. H. Zhou, Tappi J., 2019, 18, 67–71.
9 Q. Pang, L. Wang, H. Yang, L. Jia, X. Pan and C. Qiu, RSC
Adv., 2014, 4, 41212–41218.
10 P. Asawaworarit, P. Daorattanachai, W. Laosiripojana,
C. Sakdaronnarong, A. Shotipruk and N. Laosiripojana,
Chem. Eng. J., 2019, 356, 461–471.
11 I. F. Nata, M. D. Putra, C. Irawan and C.-K. Lee, J. Environ.
Chem. Eng., 2017, 5, 2171–2175.
12 G. Xia, J. Wan, J. Zhang, X. Zhang, L. Xu, J. Wu, J. He and
J. Zhang, Carbohydr. Polym., 2016, 151, 223–229.
13 Q. Lin, C. Zhang, X. Wang, B. Cheng, N. Mai and J. Ren,
Catal. Today, 2019, 319, 31–40.
14 K.-i. Shimizu, H. Furukawa, N. Kobayashi, Y. Itaya and
A. Satsuma, Green Chem., 2009, 11, 1627–1632.
15 X. Peng, S. Shen, C. Wang, T. Li, Y. Li, S. Yuan and X. Wen,
Mol. Catal., 2017, 442, 133–139.
Conflicts of interest
There are no conicts to declare.
16 X. Li, Y. Jiang, L. Shuai, L. Wang, L. Meng and X. Mu, J.
Mater. Chem., 2012, 22, 1283–1289.
17 G. Chen and B. Fang, Bioresour. Technol., 2011, 102, 2635–
2640.
18 Q. Shu, J. Gao, Z. Nawaz, Y. Liao, D. Wang and J. Wang, Appl.
Energy, 2010, 87, 2589–2596.
19 M. Li, D. Chen and X. Zhu, Chin. J. Catal., 2013, 34, 1674–
1682.
Acknowledgements
This research was funded by the National Key Research and
Development Program of China (No. 2017YFB0307900), the
State Key Laboratory of Pulp and Paper Engineering (No.
201803), and the Liaoning Provincial Department of Education
science and technology research projects (No. 2017J002).
20 F. Shen, T. Guo, C. Bai, M. Qiu and X. Qi, Fuel Process.
Technol., 2018, 169, 244–247.
21 S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi,
H. Kato, S. Hayashi and M. Hara, J. Am. Chem. Soc., 2008,
130, 12787–12793.
22 A. Sluiter, B. Hames, R. Ruiz, C. Scarlata, J. Sluiter,
D. Templeton and D. Crocker, Laboratory Analytical
Procedure, 2008, 1617, 1–16.
References
1 H. Guo, Y. Lian, L. Yan, X. Qi and R. L. Smith, Green Chem.,
2013, 15, 2167–2168.
2 B. R. Caes, R. E. Teixeira, K. G. Knapp and R. T. Raines, ACS
Sustainable Chem. Eng., 2015, 3, 2591–2605.
3 R. Rinaldi and F. Schuth, ChemSusChem, 2009, 2, 1096–1107.
4 Y. B. Huang and Y. Fu, Green Chem., 2013, 15, 1095–1111.
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