Preparation of a novel carbon-based solid acid from cocarbonized starch and polyvinyl chloride for cellulose hydrolysis

Article abstract of DOI:10.1016/j.apcata.2013.12.037

A novel carbon-based solid acid was successfully prepared by sulfonation of cocarbonized starch and polyvinyl chloride (PVC). The characterization results show that this catalyst possesses all characteristics of traditional carbon-based solid acids (CSAs). The differences are that chlorine from PVC is covalently bonded to edges of aromatic carbon sheets as new active groups, and ether (C-O-C) and aliphatic (-CH₂-) bridges are formed during the cocarbonization process which are derived from oxygen in starch and alkyl in PVC, respectively. Chlorine groups can adsorb cellulose hydroxyl groups strongly and bridge bonds make the carbon framework fully stretch, which reduces hindrance between SO₃H groups and glycosidic bonds to promote the catalytic performance in cellulose hydrolysis experiments. Furthermore, the durability results indicate that this catalyst has good stability.

Full text of DOI:10.1016/j.apcata.2013.12.037

Applied Catalysis A: General 473 (2014) 70–74
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Preparation of a novel carbon-based solid acid from cocarbonized
starch and polyvinyl chloride for cellulose hydrolysis
Shuguang Shen∗, Bei Cai, Chunyan Wang, Huanmei Li, Guang Dai, Haifeng Qin
College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel carbon-based solid acid was successfully prepared by sulfonation of cocarbonized starch and
polyvinyl chloride (PVC). The characterization results show that this catalyst possesses all characteristics
of traditional carbon-based solid acids (CSAs). The differences are that chlorine from PVC is covalently
bonded to edges of aromatic carbon sheets as new active groups, and ether (C–O–C) and aliphatic (–CH2–)
bridges are formed during the cocarbonization process which are derived from oxygen in starch and
alkyl in PVC, respectively. Chlorine groups can adsorb cellulose hydroxyl groups strongly and bridge
bonds make the carbon framework fully stretch, which reduces hindrance between SO3H groups and
glycosidic bonds to promote the catalytic performance in cellulose hydrolysis experiments. Furthermore,
the durability results indicate that this catalyst has good stability.
Received 26 July 2013
Received in revised form
21 December 2013
Accepted 29 December 2013
Available online 7 January 2014
Keywords:
Carbon-based solid acid
Cellulose
Cocarbonization
Chlorine
© 2014 Elsevier B.V. All rights reserved.
Heterogeneous hydrolysis
1. Introduction
(–SO3H), to design to hydrolyze microcrystalline cellulose into
glucose, and the degradation of this catalyst was observed in exper-
Carbon-based solid acids (CSAs), the amorphous carbons con-
sisting of aromatic carbon sheets bearing active sites such as SO3H,
OH, and COOH groups [1–4], have attracted a great deal of attention
due to their favorable characteristics such as high acid densi-
ties, stability and recyclability [3,5], which are widely used in
biodiesel synthesis and cellulose hydrolysis. However, compared
with the esterification for biodiesel production, the efficiency of
cellulose hydrolysis is unsatisfactory mainly because the interac-
tion between CSA and cellulose is not strong enough. Although
phenolic OH groups bonded to CSA have the ability to adsorb cel-
lulose [6,7] and rich-phenolic hydroxyl CSA derived from phenolic
residue has improved this ability [8], the adsorption effect is not
efficient for breaking the hydrogen bonds in cellulose. Therefore,
it is imperative to introduce the high affinity group for cellulose
onto CSA in order to enhance the interaction between cellulose and
catalyst.
iment of Yabushita et al. [13]. From the standpoint of polymer
chemistry, this is due to the thermal stability of resins is rela-
tively poor, and it cannot be used at a higher temperature for a
long time. The electronegativity of chlorine is strong enough to
form hydrogen bonds with OH in cellulose, which should be advan-
tageous to cellulose hydrolysis. As a chlorine-containing resin,
Polyvinyl chloride (PVC) can be carbonized through the liquid
phase during heat treatment with elimination of massive amounts
of HCl [14], causing an obvious weight loss at higher tempera-
ture [15]. The residual amount of Cl is negligibly small due to
the complete dehydrochlorination of PVC during carbonization
[16]. If an appropriate method is adopted, chlorine-rich PVC can
be served as a relatively cheap and widely available source of
chlorine.
In this paper, a novel CSA was prepared by sulfonation of cocar-
bonized starch and PVC, aiming to introduce chlorine onto the
robust supporter and improve the yield of CSAs. In order to eval-
uate the impact of Cl on CSA, PVC was cocarbonized with starch
by adjusting the percentage of PVC in the feedstock. This chlo-
rine functionalized carbon-based solid acids (CCSAs) prepared at
different PVC ratio (10%, 20%, 30%, and 40%) are denoted as x-
CCSA, where x is the PVC ratio. With pretreated microcrystalline
cellulose [17] as the substrate, the hydrolytic activity of the cat-
alysts was evaluated by the yield of reducing sugar, and the
interaction between cellulose and Cl bonded to the CCSA was inves-
tigated.
Although many efforts have been devoted to the depolymer-
ization of cellulose [2,7,9–11], little attention has been paid to
strengthen the interaction between catalyst and cellulose. Recently,
Li and Pan [12] synthesized a sulfonated chloromethyl polystyrene
resin, containing cellulose binding sites (–Cl) and catalytic sites
∗
Corresponding author. Tel.: +8603516010588; fax: +8603516010588.
E-mail addresses: shenshuguang@tyut.edu.cn, sgshen@sina.com (S. Shen).
0926-860X/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.12.037

S. Shen et al. / Applied Catalysis A: General 473 (2014) 70–74
71
Fig. 1. Preparation of CCSA.
2. Experimental
(HPLC) system equipped with Hypersil NH2 column (250 × 4.6 nm)
and RI detector (Shodex RI-201H) under the following conditions:
flow rate, 1 ml min−1; mobile phase, acetonitrile/water (4:1, V/V);
column temperature, 40 ◦C. The amount of SO3H groups was esti-
mated through neutralization titration [19].
2.1. Materials
Potato starch was analytical grade from Xi’an Guowei Starch
Limited Company; Microcrystalline cellulose, trade name is
AVICEL®PH-101; PVC was industrial grade from Taiyuan Chem-
ical Plant; Glucose, cellobiose, hydrogen peroxide, concentrated
sulfuric acid (98%), concentrated phosphoric acid (≥85%) and 3,5-
dinitrosalicylic acid were of analytical grade.
2.6. Evaluation of hydrolysis performance
The catalytic performance of various catalysts was demon-
strated through the hydrolysis of cellulose and cellobiose. For
hydrolysis of cellulose, pretreated microcrystalline cellulose and
CCSA with the mass ratio of 1:2 were added into a high pressure
reactor in the presence of deionized water (10 ml), and then reacted
at 150 ◦C for 6 h under magnetic stirring. After reaction, the yield of
reducing sugar was estimated by the means of 3,5-dinitrosalicylic
acid (DNS method) [20]. For hydrolysis of cellobiose, CCSA and
10 ml aqueous solution containing cellobiose (10 mg ml−1) were
heated at 120 ◦C for 6 h. Samples were drawn from the reaction
mixtures and analyzed by HPLC.
2.2. Cellulose pretreatment
Prior to hydrolysis, microcrystalline cellulose was pretreated by
concentrated phosphoric acid according to the method by Wei and
Kumar [17].
2.3. Preparation of CCSA
Typically, starch and PVC, mixed uniformly with predetermined
proportion, were cocarbonized for 10 h at 450 ◦C under N2 to
produce black solid precursors, which were then heated in concen-
trated sulfuric acid (98%) at 150 ◦C under N2 for 6 h. Subsequently,
the black slurry was cooled to room temperature and filtered. The
residue was washed repeatedly in boiling deionized water until the
filtrate was neutral and free from sulfate and chloride ions, and then
dried in the oven at 80 ◦C overnight. The synthesis process of CCSA
is shown in Fig. 1.
3. Results and discussion
3.1. Characterization of catalyst
Fig. 2 shows the XRD pattern of CCSA. Two broad and diffuse
peaks at 2Â angles of 20–30◦ and 40–50◦ are due to carbon (0 0 2)
and (1 0 0) reflections, respectively. These diffraction patterns
reflect that CCSA is an amorphous carbon composed of aromatic
carbon sheets oriented in a considerably random fashion. Struc-
turally, the carbon framework of CCSA is approximately consistent
with the others reported in the literatures [5,21,22]. Nevertheless,
the peaks of the 0 0 2 and 1 0 0 reflections are changed slightly in
their position and shape. This may be due to the differences in
2.4. Determination of chlorine content
An analytical procedure, oxygen bomb combustion [18], has
been developed for the dissolution of total chlorine in CCSA and
then the chlorine contents were evaluated by turbidimetry.
2.5. Characterization
The X-ray diffraction (XRD) analysis of the CCSA was conducted
on a Shimadzu XRD-6000 diffractometer using Cu K␣ radiation
(ꢀ = 0.15405 nm) at 40 kV and 30 mA in the scanning angle (2Â) of
5–65◦ at a scanning speed of 8◦/min. The Fourier transform infrared
(FT-IR) spectrum was obtained by using a Shimadzu 8400 Fourier
transform infrared spectrometer in the range of 400–4000 cm−1
with a 4 cm−1 resolution. The Carbon nuclear magnetic resonance
(
13C NMR) spectrum was measured at room temperature using a
Bruker 600 MHz AV-III spectrometer with magic-angle-spinning
(MAS) at 4.5 kHz and the pulse length was 3.91 ␮S. X-ray photo-
electron spectroscopy (XPS) was performed using ESCALAB250
spectrometer employing an Al K␣ X-ray source operating at 200 W.
The photoelectron pass energies for wide and narrow scans were
150 eV and 60 eV, respectively. The base pressure of the XPS cham-
ber was 10−7 Pa. All binding energies were referenced to the carbon
C–H photopeak at 284.8 eV. The amount of produced glucose in fil-
trate was analyzed by a high performance liquid chromatography
Fig. 2. XRD pattern of 40-CCSA.

72
S. Shen et al. / Applied Catalysis A: General 473 (2014) 70–74
Fig. 3. FT-IR pattern of 40-CCSA.
Fig. 4. 13C NMR pattern of 40-CCSA.
carbonization mechanisms of starch and PVC, which impact the
size and orientation degree of graphite crystallite.
2.1 eV is clearly observed in the spectrum of CCSA, assigned to SO3H
groups. It means that sulfonation of amorphous carbon is success-
fully achieved to form sulfonic groups in concentrated sulfuric acid,
and all S atoms in the CCSA are contained in SO3H groups [3,27].
The Cl 2p peak is resolved into two individual photopeaks in
Fig. 5C, which are attributable to C–Cl (Cl 2p 3/2 binding energy
of 200.0 0.2 eV) [28], and C–Cl (Cl 2p 1/2 binding energy of
201.8 0.2 eV) [29] separately, indicating that the new generated
Cl groups are covalently bonded to sp2-carbons of CCSA.
The FT-IR pattern of CCSA is depicted in Fig. 3. The absorp-
tion bands at around 1134 cm−1 (O=S=O symmetric stretching) and
1030 cm−1 (SO3 stretching modes in SO3H) [23] are evidence that
the as-prepared carbon materials were functionalized with cat-
alytic sites (–SO3H) on the surface. The peaks at around 3410 cm−1
,
1700 cm−1 and 1600 cm−1 are ascribed to stretching vibrations of
O–H from phenols [21], C=O [24], and C=C, respectively, and these
demonstrate that a large number of hydroxyl and carboxyl groups
exist on amorphous carbons, which constitute its hydrophilic sur-
face. In addition, ether bridges (C–O–C) between aromatic rings at
the band of 1225 cm−1 [25] are observed in the FT-IR spectra stand-
ing for the cross-linking of condensed aromatic sheets. Clearly, a
signal of C–Cl stretching vibration, which is never reported on CSAs,
appears at around 673 cm−1, implying that Cl atoms have been suc-
cessfully introduced on carbon precursors during cocarbonization
and still remain after sulfonation.
3.2. Catalytic performance for cellulose hydrolysis
The differences of catalysts performance are closely related to
not only the structure of catalysts but also the pretreatment meth-
ods and conditions of cellulose, which together determine the yield
of reducing sugar. For this reason, we employed two commonly
used CSAs to compare with CCSA. As shown in Fig. 6, reducing
sugar yields from conventional glucose-derived CSA (GCSA) and
starch-derived CSA (SCSA) are 37.2% and 36.8%, respectively, and
their efficiency of cellulose hydrolysis is relatively low. Guo et al.
[11,30] also recognized the same problems, consequently they used
a combination of CSA and ionic liquids to obtain a higher reducing
sugar yield. This method leads cellulose to dissolve in chloride ionic
liquids, allowing it fully contact with acid sites on catalysts. To avoid
the difficulties in products separation and recovery of ionic liquids,
we attempted to immobilize chlorine on CSAs.
As shown in Table 1, when PVC was added in feedstock, the
amount of Cl on catalysts increases with the increase of PVC ratio,
and the amount of SO3H groups is roughly the same among dif-
ferent catalysts. This means that the acidity of catalysts is little
affected by the Cl content. However, from Fig. 6, it can be seen that
the yield of reducing sugar increases remarkably with the increase
of PVC content and the highest can reach 94.2%, revealing that the
The 13C NMR spectra (Fig. 4) of CCSA exhibits the resonance
peaks at 129 ppm [26], 160 ppm and 200 ppm attributable to
polycyclic aromatic carbon, phenolic OH, and COOH, respectively.
Besides, a signal for sp3-derived carbon at 20 ppm indicates that
part of sp3-carbons in starch and PVC are converted into aliphatic
side chains (–CH3) during the carbonization treatment. The sig-
nals at 73 ppm and 30 ppm are attributed to C–O–C and –CH2–
respectively, meaning that the carbon sheets are tethered via ether
bridges or short aliphatic bridges. The peaks assigned to aromatic
carbon bonded to Cl (ca. 135.1 ppm) or SO3H (ca. 139.2 ppm) are
obscured by the two broad peaks due to polycyclic aromatic carbon
and phenolic OH.
The elements of C, S, O, and Cl are observed in the full-scan XPS
spectrum (Fig. 5A) of CCSA, and the narrow-scans of S 2p and Cl 2p
are conducted by using the XPS peak separation technique.
The narrow-scan XPS photopeak for S 2p of the CCSA is displayed
in Fig. 5B. A single S 2p peak at 168 eV with a half-peak width of
Table 1
Catalytic performance for the hydrolysis of cellobiose over catalysts at 120 ◦Ca.
Amount of SO3H/mmol g−1
Amount of Cl in fresh catalysts/mg g−1
Hydrolysis of cellobiose
Catalysts
Yield of glucose (%)
TOF
GCSA
SCSA
10-CCSA
20-CCSA
30-CCSA
40-CCSA
0.855
0.853
0.858
0.862
0.863
0.832
–
–
2.73
3.80
5.51
6.55
44.06
44.01
44.21
42.01
44.52
44.76
0.241
0.240
0.240
0.227
0.241
0.250
a
Reagents and conditions: 0.2 g of catalyst, 0.1 g of cellobiose, 10 ml of water, 120 ◦C, 6 h.

S. Shen et al. / Applied Catalysis A: General 473 (2014) 70–74
73
Fig. 5. (A) XPS pattern of 40-CCSA; (B) S 2p XPS pattern of 40-CCSA; (C) Cl 2p XPS pattern of 40-CCSA.
participation of Cl on CCSA significantly accelerates the cellulose
hydrolysis.
which can make the CCSA more stable. The durability of CCSA was
examined by recycling the catalyst three times in cellulose hydrol-
ysis. After each reaction run, CCSAs were recovered by decantation,
washing, drying at 80 ◦C overnight with 99.0–99.5% recovery, and
then reused in the next batch of hydrolysis at identical conditions.
About 10–25% of Cl on CCSAs is leached after recycling three times.
In order to further verify the role of Cl, the hydrolysis of cel-
lobiose over different catalysts was studied in aqueous solution
and the results are shown in Table 1. Unexpectedly, there are neg-
ligible differences of glucose yield for various catalysts, suggesting
that Cl groups fail to work on cellobiose hydrolysis. One reason-
able explanation for this phenomenon is that cellobiose is a simple
and water soluble molecule consisting of two glucose linked by a ␤-
1,4-glycosidic bond, which has minimal problems in the interaction
with catalysts.
The process (Fig. 7) of cellulose hydrolysis over CCSA is
attributed to the strong electronegativity and small size of the Cl
atom, which has high hydrogen bonds basicity. As electron donors,
Cl atoms attack the cellulose hydroxyl protons, tending to form
hydrogen bonds with cellulose. Upon interaction between cellulose
and CCSA, the oxygen and hydrogen atoms from different hydroxyl
groups are separated, leading to opening of the intra- and inter-
molecular hydrogen bonds of cellulose and finally exposing the
glycosidic bonds within cellulose. On the other hand, these bridge
bonds in CCSA can make the carbon framework fully stretch to
reduce steric hindrance among SO3H groups and glycosidic bonds.
Consequently, SO3H groups and glycosidic bonds are located close
enough in space to permit the hydrolysis of cellulose.
At present, some studies have confirmed the good stability of
conventional CSAs [19,31]. After Cl, a new functional group, is
introduced onto CSA, the resonance effect exists in CCSA with the
consequent delocalization of electrons through the aromatic rings,
Fig. 6. Reducing sugar yield from different carbon-based solid acids.

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S. Shen et al. / Applied Catalysis A: General 473 (2014) 70–74
Fig. 7. The process of cellulose hydrolysis over CCSA.
As a result, the yield of reducing sugar from 40-CCSA is decreased
from 94.2% to 90%, indicating the stability of CCSAs is needed to be
further improved.
[8] S. Shen, C. Wang, B. Cai, H. Li, Y. Han, T. Wang, H. Qin, Fuel 113 (2013)
644–649.
[9] M. Kitano, D. Yamaguchi, S. Suganuma, K. Nakajima, H. Kato, S. Hayashi, M.
Hara, Langmuir 25 (2009) 5068–5075.
[10] A. Onda, T. Ochi, K. Yanagisawa, Green Chem. 10 (2008) 1033–1037.
[11] H.-X. Guo, X.-H. Qi, L.-Y. Li, R.L. Smith Jr., Bioresour. Technol. 116 (2012)
355–359.
4. Conclusions
[12] S. Li, X. Pan, Energy Environ. Sci. 5 (2012) 6889–6894.
[13] M. Yabushita, H. Kobayashi, A. Fukuoka, Appl. Catal., B 145 (2014) 1–9.
[14] A.N. Ainscough, D. Dollimore, G.R. Heal, Carbon 11 (1973) 189–197.
[15] M. Inagaki, Y. Okada, H. Miura, H. Konno, Carbon 37 (1999) 329–334.
[16] S. Suganuma, K. Nakajima, M. Kitano, S. Hayashi, M. Hara, ChemSusChem 5
(2012) 1841–1846.
[17] S. Wei, V. Kumar, G. Banker, Int. J. Pharm. 142 (1996) 175–181.
[18] M.A. Cortes-Pena, L.V. Perez-Arribas, M.E. Leon-Gonzalez, L.M. Polo-Diez, Waste
Manage. Res. 20 (2002) 302–307.
[19] Z. Fu, H. Wan, X. Hu, Q. Cui, G. Guan, React. Kinet. Mech. Catal. 107 (2012)
203–213.
[20] G.L. Miller, Anal. Chem. 31 (1959) 426–428.
[21] K. Nakajima, M. Hara, ACS Catal. 2 (2012) 1296–1304.
[22] A.M. Dehkhoda, A.H. West, N. Ellis, Appl. Catal., A 382 (2010) 197–204.
[23] R. Ormsby, J.R. Kastner, J. Miller, Catal. Today 190 (2012) 89–97.
[24] J.R. Kastner, J. Miller, D.P. Geller, J. Locklin, L.H. Keith, T. Johnson, Catal. Today
190 (2012) 122–132.
A novel carbon-based solid acid was successfully prepared
by cocarbonization of starch and PVC followed by sulfonation,
exhibiting strong potential for use as a replacement for conven-
tional CSAs. The chlorine groups and bridge bonds derived from
PVC and starch emerge as new parts of CSAs, which can form
hydrogen bonds with cellulose and make the carbon sheets fully
stretch, respectively. As a result, the accessibility of hydrolysis site
(SO3H) to glycosidic bonds is enhanced to stimulate the hydrolysis
of cellulose. Furthermore, the durability experiments indicate that
the CCSAs have good stability.
References
[25] N. Krishnan, H.-J. Kim, M. Prasanna, E. Cho, E.-M. Shin, S.-Y. Lee, I.-H. Oh, S.-A.
Hong, T.-H. Lim, J. Power Sources 158 (2006) 1246–1250.
[26] K. Fukuhara, K. Nakajima, M. Kitano, H. Kato, S. Hayashi, M. Hara, ChemSusChem
4 (2011) 778–784.
[27] T. Liu, Z. Li, W. Li, C. Shi, Y. Wang, Bioresour. Technol. 133 (2013) 618–621.
[28] P. Licence, Angew. Chem. Int. Ed. 51 (2012) 4789–4791.
[29] A.F. Pérez-Cadenas, F.J. Maldonado-Hodar, C. Moreno-Castilla, Carbon 41
(2003) 473–478.
[30] H.-X. Guo, Y.-F. Lian, L.-L. Yan, X.-H. Qi, R.L. Smith Jr., Green Chem. 15 (2013)
2167–2174.
[31] X. Song, X. Fu, C. Zhang, W. Huang, Y. Zhu, J. Yang, Y. Zhang, Catal. Lett. 142
(2012) 869–874.
[1] S. Dora, T. Bhaskar, R. Singh, D.V. Naik, D.K. Adhikari, Bioresour. Technol. 120
(2012) 318–321.
[2] T. Onda, K. Ochi, Yanagisawa, Top. Catal. 52 (2009) 801–807.
[3] S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi, H. Kato, S. Hayashi, M.
Hara, Solid State Sci. 12 (2010) 1029–1034.
[4] M. Toda, A. Takagaki, M. Okamura, J.N. Kondo, S. Hayashi, K. Domen, M. Hara,
Nature 438 (2005) 178.
[5] Q. Shu, J. Gao, Z. Nawaz, Y. Liao, D. Wang, J. Wang, Appl. Energy 87 (2010)
2589–2596.
[6] M. Hara, Energy Environ. Sci. 3 (2010) 601–607.
[7] S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi, H. Kato, S. Hayashi, J. Am.
Chem. Soc. 130 (2008) 12787–12793.