Volatile compounds formed from the pyrolysis of chitosan

Article abstract of DOI:10.1016/j.carbpol.2010.10.007

Chitosan is a renewable resource for the production of nitrogen-containing aromatic heterocyclics. It was found that chitosan started to decompose and produce some volatile compounds at around 525 K in a nitrogen atmosphere, the volatiles were characterized by Fourier transform infrared spectrometer. The apparent activation energy for the thermal degradation of chitosan was determined. To further investigate the degradation, chitosan was pyrolyzed under vacuum at 553 K for 1 h, and the volatile compounds were analyzed by gas chromatography/mass spectrometry. The volatile compounds included aromatic heterocyclics such as pyrazines, pyridines, pyrroles and furans, and the pyrazines were the major products. The pyrolysis mechanism of chitosan was also proposed.

Full text of DOI:10.1016/j.carbpol.2010.10.007

Carbohydrate Polymers 83 (2011) 1553–1557
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Volatile compounds formed from the pyrolysis of chitosan
Lintao Zeng, Caiqin Qin∗, Liansheng Wang, Wei Li
Hubei Key Laboratory of Biomass-Resource Chemistry and Environmental Biotechnology, Xiaogan University, Xiaogan 432000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 August 2010
Received in revised form 3 October 2010
Accepted 6 October 2010
Available online 12 October 2010
Chitosan is a renewable resource for the production of nitrogen-containing aromatic heterocyclics. It was
found that chitosan started to decompose and produce some volatile compounds at around 525 K in a
nitrogen atmosphere, the volatiles were characterized by Fourier transform infrared spectrometer. The
apparent activation energy for the thermal degradation of chitosan was determined. To further investigate
the degradation, chitosan was pyrolyzed under vacuum at 553 K for 1 h, and the volatile compounds were
analyzed by gas chromatography/mass spectrometry. The volatile compounds included aromatic hete-
rocyclics such as pyrazines, pyridines, pyrroles and furans, and the pyrazines were the major products.
The pyrolysis mechanism of chitosan was also proposed.
Keywords:
Chitosan
Pyrolysis
Volatile compound
Aromatic heterocyclics
© 2010 Elsevier Ltd. All rights reserved.
1. Introduction
to produce aromatic heterocyclics. To utilize this widely avail-
able biomass to produce some fine chemicals, it is very necessary
Chitosan, a widely available polysaccharide, is mainly composed
of 2-amino-2-deoxy-d-glucopyranose (d-glucosamine, GlcN) units
with some degree of 2-acetamido-2-deoxy-d-glucopyranose. Due
to their special chemical and biological properties, chitosan and
their derivatives have been widely used in food industry, agri-
culture, pharmacy, medicine and waste water treatment (Kumar,
Muzzarelli, Muzzarelli, Sashiwa, & Domb, 2004).
As an environmental-friendly and renewable resource, chitosan
and its degradation behavior in environment have been extensively
investigated. The degradation of chitosan in various environmen-
tal conditions leads to breaking of chains and release of volatile
products (Nieto, Peniche-Covas, & Padrón, 1991; Peniche-Covas,
Argüelles-Monal, & Román, 1993). At high temperature, chitosan
usually produces char and some volatile compounds (López, Mercê,
Alguacil, López-Delgado, 2008; Zawadzki & Kaczmarek, 2010).
Although kinetics of thermal degradation of chitosan is largely
explored (Britto & Campana-Filho, 2007; Sato et al., 2002; Tang,
Wang, & Chen, 2005), there is still very limited knowledge of the
pyrolysis of chitosan for production of fine chemicals. It has been
reported previously that the monomer of chitosan, glucosamine,
was pyrolyzed to produce aromatic volatile compounds such as
pyrazines, pyridines, pyrroles and furans (Chen & Ho, 1998). Thus,
it is reasonably assumed that chitosan would be an abundant source
to investigate the pyrolysis behavior of chitosan and the formed
volatiles.
The main aim of this work is to investigate the pyrolysis of chi-
tosan for production of fine chemicals. Thermal analysis methods,
such as thermogravimetry analysis (TGA) and differential scan-
ning calorimetry (DSC), have been well established in monitoring
the pyrolysis of natural polymers. For characterization of species
evolved from the pyrolysis of polymers, Fourier transform infrared
spectroscopy (FT-IR) has turned out to be an important technique.
So, in this work, we employed TGA equipped with DSC to inves-
tigate the pyrolysis behavior of chitosan in nitrogen atmosphere.
The volatiles evolved from the pyrolysis of chitosan were online
identified by FT-IR connected to a thermal analyzer via a heated
line. To further identify the volatiles from the pyrolysis of chitosan
in vacuum, gas chromatography coupled with mass spectrometer
(GC/MS) was employed. It was found that the volatiles evolved
from the pyrolysis of chitosan were aromatic heterocyclics such
as pyrazines, pyridines, pyrroles and furans.
2. Experimental
2.1. Materials
Chitosan with degree of deacetylation (DD = 85.5%) and Mw
7.60 × 105, was supplied by Golden-shell Biochemical Co., Ltd.,
China, and used directly without any further purification. Other
chemicals were purchased from Sigma Chemical Co.
∗
Corresponding author at: Laboratory of Natural Polysaccharides, Xiaogan Uni-
versity, Xiaogan 432000, Hubei, China. Tel.: +86 712 2345697; fax: +86 712 2345265.
E-mail address: qincaiqin@yahoo.com (C. Qin).
0144-8617/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbpol.2010.10.007

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L. Zeng et al. / Carbohydrate Polymers 83 (2011) 1553–1557
40
100
90
80
70
60
50
40
TG
DSC
30
20
10
0
-10
-20
-30
300
400
500
600
700
T/ K
Fig. 1. TG and DSC curves of chitosan.
2.2. Non-isothermal pyrolysis of chitosan and FT-IR
characterization of gas products
Simultaneous TG-DSC coupled with FT-IR was performed on
a thermal analyzer (SDT-Q600) and a Fourier transform infrared
spectrometer (Thermo Nicolet 380).
5.0 mg chitosan was loaded into an open alumina crucible.
The heating rate of TG furnace was 10.0 K/min and nitrogen gas
(purity > 99.999%) with a flow rate of 100 mL/min was used as car-
rier gas. The transfer line used to connect TG and FTIR was a 1.0 m
long stainless steel tube with internal diameter of 2 mm, and the
temperature was maintained at 473 K. Accessory of the IR spec-
trometer was used, which has a 45 mL gas cell with 200 mm path
length and was also kept at 473 K. The IR spectra were collected at
8 cm−1 resolution, co-adding 32 scans per spectrum. This resulted
in a temporal resolution of 4.32 s. Lag time that the gas products
went from furnace to gas cell was about 7 s.
Fig. 3. FT-IR spectra of the gas products from thermal degradation of chitosan. (a)
26.8 min; (b) 35.4 min.
553 K for 1 h. After cooling to 283 K, 3 × 10 mL CH2Cl2 was added
to the flask to extract the products generated from chitosan. The
organic phase was dried over anhydrous magnesium sulfate, then
filtered and concentrated to approximately 0.5 mL under a gen-
tle stream of nitrogen gas. The concentrated sample was ready for
GC–MS analysis.
The pyrolysis of chitosan was also studied by using simultaneous
TG and DSC in nitrogen atmosphere when the heating rate of TG
furnace was 2.5, 5.0 and 20.0 K/min, respectively.
The gas chromatograph was performed on a Varian Model 3400
equipped with a flame ionization detector (FID) and a non-polar
fused silica capillary column (DB-1, 30 m × 0.25 mm (i.d.), 0.25 ␮m
film thickness: J&W Scientific, Folsom, CA). The column tempera-
ture was programmed from room temperature to 543 K at heating
rate of 3 K/min. The injector and detector temperature were main-
tained at 543 K. The flow rate of helium carrier gas was 1 mL/min.
The volume of the injected sample was 1 ␮L, and the spilt ratio
was 25:1. GC/MS analysis was performed using an HP Model 5790
GC coupled with an HP 5970A mass-selective detector. The cap-
illary column and temperature program were the same as in the
GC analysis. Mass spectra were obtained by electron ionization at
70 eV and a mass scan from 33 to 500. Quantification was based on
GC/FID data, and compound identification was based on mass spec-
tra obtained from the GC/MS. Identification of compounds referred
to Wiley mass spectra library.
2.3. Isothermal pyrolysis of chitosan and gas
chromatography/mass spectrometry (GC/MS) analysis
1.0 g dry chitosan was loaded into a 100 mL stainless flask and
the inner atmosphere was reduced to vacuum by oil-pump, then
the flask was sealed. The flask was put in an oil bath and heated at
2.5K/min
5.0K/min
10.0K/min
20.0K/min
100
80
60
3. Results and discussion
3.1. Non-isothermal pyrolysis of chitosan
40
3.1.1. TG and DSC analysis of chitosan
To investigate the pyrolysis behavior of chitosan, it was heated
from room temperature to 823 K in dynamic nitrogen atmosphere,
and the corresponding TG and DSC curves were showed in Fig. 1.
The first thermal event was a wide endothermic peak in the range of
320–385 K coupled with weight-loss about 7%. This thermal event
300
400
500
600
700
800
T/K
Fig. 2. The TG curves of chitosan at different heating rates.

L. Zeng et al. / Carbohydrate Polymers 83 (2011) 1553–1557
1555
Fig. 4. Gas chromatography of volatile compounds generated from pyrolysis of chitosan.
was associated with evaporation of water absorbed in the sam-
ples (Qin, Du, Zong, Zeng, & Liu 2003). The second thermal event
for chitosan was a wide exothermic peak coupled with a weight-
loss about 48% between 525 and 650 K, suggesting that chitosan
started to decompose and produce some volatiles at 525 K. The
exothermic effect might result from cross-linking reactions dur-
ing the thermal degradation of chitosan. The second decomposition
step, which appeared at higher temperature, might result from the
thermal degradation of the new cross-linked materials that have
formed in the first degradation process (Pawlak & Mucha, 2003).
because adequate kinetic description of chemical and physical
processes can be profitably applied for process design and opti-
mization.
3.1.3. FT-IR characterization of gas products
The gas products evolved from thermal degradation of chitosan
were online analyzed by FT-IR. Fig. 3 recorded the correspond-
ing infrared spectra of gas products at the 26.8 min (568 K) and
35.4 min (654 K), respectively. The most characteristic bands were
the strong and sharp peaks around 1750–1780 cm−1, which were
corresponding to the aldehyde carbonyl group. The sharp peaks
around 1591and 1512 cm−1 are very characteristic of aromatic het-
erocyclics.
3.1.2. Determination of apparent activation energy
The Ea for the thermal degradation of chitosan was determined
from the TG curves using iso-conversional method proposed by
Ozawa–Flynn–Wall (Britto & Campana-Filho, 2007; Tang, Wang, &
Chen, 2005). This iso-conversional method is based on the assump-
tion that the reaction model is independent of the heating program.
According to this method, a set of experiments are carried out at
different heating programs, the activation energy is determined at
a specific extent of conversion value by linear fitting the following
equation:
3.2. Isothermal pyrolysis of chitosan and GC/MS analysis of the
volatile products
The volatile products evolved from pyrolysis of chitosan at 553 K
should be examined by GC–MS. Fig. 4 showed the gas chromatog-
raphy of volatiles generated from pyrolysis of chitosan, and the
volatiles were listed in Table 1. A total of 13 compounds were identi-
fied, including furans, pyridines, pyrroles and pyrazines. The major
compounds were methylpyrazine, 2-(2-furyl)-(6)-methylpyrazine,
2-acetyl pyridine, 2,5-di(2-furyl)pyrazine, 2-(2-furyl)pyrazine,
2-acetyl-6-(2-furyl)pyrazine, 2-acetylfuran and 2-acetylpyrrole in
decreasing order.
ꢀ
ꢁ
A Ea
g(˛)R
Ea
RT
log ˇ = log
− 1.0573
where ˛ is the extent of conversion, R is the gas constant, A is
the pre-exponential factor, T is reaction temperature, and g(˛) is
a temperature-independent function that represents the reaction
model. Therefore, a set of experiments were run at different heat-
ing rates ˇ (Fig. 2), then the value of Ea was obtained from the plot
of log ˇ against 1/T for a fixed degree of conversion. The Ea was
137 kJ/mol (˛ = 0.30).
3.3. Discussion
Polysaccharides represent the largest fraction of biomass and
previous work in understanding the polysaccharides pyrolysis
mechanisms and kinetics have been well reported in the litera-
tures (Aléna, Kuoppalab, & Oeschb, 1996; Antal & Varhegyi, 1995;
The knowledge of the thermal pyrolysis kinetics of chitosan may
help better understanding and planning of the industrial process
Table 1
Volatile compounds identified in the pyrolysis of chitosan at 553 K.
Retention time (min)
m/z
41.03
RI (area)
Compounds
Reference
6.73
7.79
7.89
8.30
8.39
9.02
9.49
9.94
10.46
10.53
10.66
11.18
11.33
13.43
515
1070
1226
3067
3000
784
1620
1494
4250
6250
Acetonitrile
2-Methylpyridine
Trimethylpyrazine
2,5-Di(2-furyl)pyrazine
2-(2-Furyl)pyrazine
2-Ethylpyrazine
2-Acetylpyrrole
2-Acetamidofuran
2-Acetylpyridine
2-(2-Furyl)-5(6)-methylpyrazine
Methylpyrazine
2-Acetyl-6-(2-furyl)pyrazine
4-Cyanic-2-methylpyridine
2-Acetyl-3-methylpyridine
Lib
Lib
Lib
Lib
Lib
Lib
Lib
Lib
93.06
122.17
212.06
146.05
108.14
109.05
125.05
121.05
160.06
94.11
Lib
Chen and Ho (1998)
Lib
Chen and Ho (1998)
Lib
Lib
10,138
188.06
118.05
135.07
2983
1692
1268

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L. Zeng et al. / Carbohydrate Polymers 83 (2011) 1553–1557
Fig. 5. The proposed mechanisms for pyrolysis of chitosan and formation of volatile compounds.
Bridgwater, 1999; Patwardhan, Satrio, Brown, & Shanks, 2009;
Ponder & Richards, 1994).
tures and under dry conditions. The extensive reviews on pyrazines
in food were published (Maga, 1992).
Volatile compounds such as pyrazines, pyridines, pyrroles and
furans are generated from the pyrolysis of glucosamine. Pyrazine
compounds are the most important products among the volatiles
identified. The furan ring was suggested as a result of the dehydra-
tion reaction from the intermediate polyhydroxypyrazines, which
were dimerization products of glucosamine (Chen & Ho, 1998).
When chitin was pyrolyzed at over 300 ◦C, acetamide and a series
of methyl-substituted pyrazines were generated (Knorr, Wampler,
& Teutonico, 1985). Pyrazine compounds are widely distributed in
food systems, especially when foods are processed at high tempera-
Pyrazines were the most important products in the pyrolysis of
chitosan, which was similar to the decomposition of glucosamine.
Pyrozines are widely distributed in food systems, especially when
foods are processed at high temperatures and under dry conditions.
There are several precursors and pathways for the generation of
pyrazine compound. The ␣-amino carbonyls, which can be formed
from the degradation of chitosan, were generally considered to be
the precursors of pyrazine compounds. The proposed pathway for
formation of pyrazines was illustrated in Fig. 5. Glucosamine has
␣-amino carbonyl structure, which can react with each other to

L. Zeng et al. / Carbohydrate Polymers 83 (2011) 1553–1557
1557
form pyrazine compounds (Chen & Ho, 1998; Wang & Odell, 1998).
Pyridine derivatives also generated when chitosan was pyrolyzed.
López, F. A., Mercê, A. L. R., Alguacil, F. J., & López-Delgado, A. (2008). A kinetic study
on the thermal behaviour of chitosan. Journal of Thermal Analysis and Calorimetry,
91, 633–639.
Knorr, D., Wampler, T. P., & Teutonico, R. A. (1985). Formation of pyrazines by chitin
pyrolysis. Journal of Food Science, 50, 1762–1763.
4. Conclusions
Kumar, M. N. V. R., Muzzarelli, R. A. A., Muzzarelli, C., Sashiwa, H., & Domb, A. J.
(2004). Chitosan chemistry and pharmaceutical perspectives. Chemical Reviews,
104, 6017–6084.
Maga, J. A. (1992). Pyrazine update. Food Reviews International, 8, 479–558.
Nieto, J. M., Peniche-Covas, C., & Padrón, G. (1991). Characterization of chitosan
by pyrolysis-mass spectrometry, thermal analysis and differential scanning
calorimetry. Thermochimica Acta, 176, 63–68.
Patwardhan, P. R., Satrio, J. A., Brown, R. C., & Shanks, B. H. (2009). Product distri-
bution from fast pyrolysis of glucose-based carbohydrates. Journal of Analytical
and Applied Pyrolysis, 86, 323–330.
Peniche-Covas, C., Argüelles-Monal, W., & Román, J. S. (1993). A kinetic study of the
thermal degradation of chitosan and a mercaptan derivative of chitosan. Polymer
Degradation and Stability, 39, 21–28.
In this study, chitosan was found to decompose and char when
the temperature reached to 525 K. The volatile products included
pyrazines, pyridines, pyrroles and furans, and pyrazines were the
major volatile aromatic products. Chitosan is the potential biomass
source to produce nitrogen-containing aromatic heterocyclics. The
process conditions should be further investigated for utilizing chi-
tosan to produce the chemicals.
Acknowledgements
Ponder, G. R., & Richards, G. N. (1994). A review of some recent studies on mecha-
nisms of pyrolysis of polysaccharides. Biomass and Bioenergy, 7, 1–24.
Pawlak, A., & Mucha, M. (2003). Thermogravimetric and FTIR studies of chitosan
blends. Thermochimica Acta, 396, 153–166.
Qin, C. Q., Du, Y. M., Zong, L. T., Zeng, F. G., & Liu, Y. (2003). Effect of hemicellulase
on the molecular weight and structure of chitosan. Polymer Degradation and
Stability, 80, 435–441.
Sato, H., Mizutani, S., Ohtani, H., Tsuge, S., Aoi, K., Seki, T., & Okada, M. (2002). Deter-
mination of degree of substitution in N-carboxyethylated chitin derivatives by
pyrolysis-gas chromatography in the presence of oxalic acid. Journal of Analytical
and Applied Pyrolysis, 64, 177–185.
Tang, W. J., Wang, C. X., & Chen, D. H. (2005). Kinetic studies on the pyrolysis of chitin
and chitosan. Polymer Degradation and Stability, 87, 389–394.
Wang, P. S., & Odell, G. V. (1998). Formation of pyrazines from thermal treatment of
some amino-hydroxy compounds. Journal of Agriculture and Food Chemistry, 21,
868–870.
We gratefully acknowledge the financial support of National
Natural Science Foundation of China (20942011), and Hubei Provin-
cial Educational Department (Z200626001).
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