Liquid-phase dehydration of sorbitol under microwave irradiation in the presence of acidic resin catalysts

Article abstract of DOI:10.1007/s11164-011-0389-5

Liquid-phase dehydration of sorbitol has been investigated in wide reaction conditions especially under microwave irradiation in the presence of acidic resin catalysts. From the selectivity for sorbitan and isosorbide, it can be understood that the dehydration is a consecutive reaction (sorbitol to sorbitan, and finally to isosorbide) and that the sorbitan is an intermediate of the dehydration. By using microwave irradiation, the dehydration can be accelerated by around 20-34 times compared with the rate by conventional electric heating at the same temperature, or the reaction temperature can be decreased by around 40 °C for the comparable conversion in a similar reaction time. However, the microwaves do not have noticeable effects on the selectivity for isosorbide or sorbitan. The accelerated dehydration under microwaves is mainly due to decreased activation energy.

Full text of DOI:10.1007/s11164-011-0389-5

Res Chem Intermed (2011) 37:1231–1238
DOI 10.1007/s11164-011-0389-5
Liquid-phase dehydration of sorbitol under microwave
irradiation in the presence of acidic resin catalysts
•
Nazmul Abedin Khan Dinesh Kumar Mishra
•
•
Jin-Soo Hwang Young-Woo Kwak Sung Hwa Jhung
•
Received: 31 May 2011 / Accepted: 12 July 2011 / Published online: 13 September 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Liquid-phase dehydration of sorbitol has been investigated in wide
reaction conditions especially under microwave irradiation in the presence of acidic
resin catalysts. From the selectivity for sorbitan and isosorbide, it can be understood
that the dehydration is a consecutive reaction (sorbitol to sorbitan, and finally to
isosorbide) and that the sorbitan is an intermediate of the dehydration. By using
microwave irradiation, the dehydration can be accelerated by around 20–34 times
compared with the rate by conventional electric heating at the same temperature, or
the reaction temperature can be decreased by around 40 °C for the comparable
conversion in a similar reaction time. However, the microwaves do not have
noticeable effects on the selectivity for isosorbide or sorbitan. The accelerated
dehydration under microwaves is mainly due to decreased activation energy.
Keywords Sorbitol dehydration Á Isosorbide Á Solid acid Á Microwave irradiation
Introduction
Recently, the utilization of renewable biomass has attracted much attention because
of concerns for the environment and for saving energy [1]. Sorbitol is one of the
useful biomass-derived chemicals that can be converted into polyols, and it can be
obtained from cellulose via glucose. Isosorbide that can be obtained from
N. A. Khan Á Y.-W. Kwak Á S. H. Jhung (&)
Department of Chemistry and Green-Nano Materials Research Center,
Kyungpook National University, Daegu 702-701, Korea
e-mail: sung@knu.ac.kr
D. K. Mishra Á J.-S. Hwang
Bio-Refinerary Research Center, Korea Research Institute of Chemical Technology,
P.O. Box 107, Yusung, Daejeon 305-600, Korea
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N. A. Khan et al.
dehydration of sorbitol is one of the useful chemicals in polymers and medicines
[2–6].
Dehydration of sorbitol has been carried out in the presence of mineral acids like
sulfuric acid and hydrochloric acid. However, the process using mineral acids has
drawbacks with regard to the environment and to safety. Therefore, very recently,
several solid catalysts like sulfated copper oxides [3], supported heteropoly acids
[4], Nb2O5 modified with phosphoric acid [5] and metal phosphates [6], have been
tried for the isosorbide production from sorbitol. Yamaguchi et al. [2] suggested
dehydration with pure water (and in the absence of any catalyst) at high temperature
because the dissociation of water molecules increases with increasing temperature.
Even though the dehydration is not a difficult reaction, the rapid reaction is
beneficial for high throughput, energy saving and continuous operation. Especially,
a rapid reaction may decrease the reaction temperature, which can be helpful for
energy efficiency and for reducing investment costs. Microwaves (MWs) have been
widely used to accelerate not only organic reactions [7] but also inorganic syntheses
[8, 9]. To the best of our knowledge, however, there has been no attempt to use
MWs in the dehydration of sorbitol. Moreover, the reason for accelerated syntheses
or reactions under MWs has not been thoroughly understood.
In this work, the dehydration of sorbitol, in the presence of resin catalysts, has
been studied under MW irradiation in order to accelerate the dehydration or to
decrease the reaction temperature. The acceleration degree has been estimated
quantitatively and the possibility of reducing the reaction temperature is suggested.
The accelerated dehydration is mainly due to a decreased activation energy;
however, there is little change in the selectivity for isosorbide and sorbitan with
MW irradiation.
Experimental
The dehydration of sorbitol has been carried out at 130–170 °C with both
conventional electric (CE) heating and microwave (MW) heating. Fifteen g of
sorbitol (97%, Daejung Chemicals and Metals) was loaded into a 100-mL Teflon
autoclave and allowed to melt at 120 °C in a conventional oven. Resin catalyst
Amberlyst-15 (0.3 g, Aldrich, acid capacity 4.7 mequiv. H?/g) was added to the
liquid sorbitol of the Teflon autoclave which was sealed and placed in a preheated
electric oven or in a MW oven (MARS-5, CEM, maximum power of 1,200 W). The
autoclave in the MW oven was heated to the reaction temperature in 2 min and
maintained for a predetermined time. The MW power was 400 W throughout all the
synthesis steps including the heating-up stage. After the reaction for a fixed time, the
autoclave was cooled to *100 °C and the liquid product was recovered by filtration
using a glass filter. The filtration was carried out inside a CE oven (at about 100 °C)
to avoid the solidification of the product. Part of the dehydrated water was
evaporated during filtration, and the products were further kept in an oven for 4 h to
evaporate the remaining water.
The composition of the dried product was analyzed using HPLC (Younglin
Instrument, Acme 9000) equipped with a refractive index (RI) detector and
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Liquid-phase dehydration
1233
Asahipak column (NH2P-50 4E, No. N712004). Acetonitrile/water (80/20) mixture
was used as an eluent for the analysis with the flow rate of 1.0 mL/min. The
temperature of RI detector was maintained at 35 °C throughout the analysis. The
typical HPLC chromatogram which can separate sorbitol, sorbitan and isosorbide is
shown in Fig. 1. The selectivities or yields of sorbitan or isosorbide were based on
molar composition.
The kinetics of the dehydration was interpreted with the first-order kinetics based
on the concentration of remaining sorbitol. The activation energy (Ea) and pre-
exponential factor (A) of the dehydration were calculated using the kinetic constants
at various temperatures with the Arrhenius equation.
Results and discussion
The dehydration of sorbitol has been conducted in wide reaction conditions and the
typical results are displayed in Fig. 2. With increasing reaction time, the sorbitol
conversion and isosorbide selectivity increase; however, the sorbitan selectivity
Fig. 1 Typical HPLC chromatogram of the obtained dehydrated products
(a)
(b)
100
80
60
40
20
0
100
80
60
40
20
0
Sorbitol conversion
Isosorbide selectivity
Sorbitan selectivity
Sorbitol conversion
Isosorbide selectivity
Sorbitan selectivity
0
3
6
9
12
15
0
1
2
3
Time (h)
Time (h)
Fig. 2 Effect of heating methods (a MW; b CE) and reaction time on the sorbitol conversion and
selectivity for sorbitan and isosorbide
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N. A. Khan et al.
decreases. Remarkably, the rate of sorbitol dehydration is very high under MW
irradiation to show complete conversion of sorbitol in 2 h. Under CE dehydration,
however, the conversion cannot be reached up to 100 % even at 15 h of dehydration.
The steady decrease and increase of sorbitan and isosorbide, respectively, with
reaction time show the consecutive reaction (from sorbitol to isosorbide) of the
sorbitol dehydration, and the sorbitan is an intermediate, in agreement with the
reported results [2–4, 6].
To compare the relative kinetics of dehydration of sorbitol, the reactions were
carried out at various times at 130–150 °C. The rates of reaction have been
interpreted with the first-order kinetics based on the remaining concentration of
sorbitol. As shown in Fig. 3, the kinetic constants with MW heating are very high
compared with those of the dehydration with CE heating. The summarized kinetic
constants are shown in Table 1 and it can be understood that the kinetic constants
with MW heating are around 20–34 times of those with the CE heating at the same
temperature.
So far, little comprehensive study has been done [7–10] to explain why reaction
time is drastically decreased under MWs even though rapid syntheses of several
materials have been observed. Instead, several hypotheses [8–11] have been
proposed to explain the fast synthesis with MW, namely, (1) an increase in the
heating rate of the reaction mixture, (2) more uniform heating of the reaction
mixture, (3) change in association between species within the mixture, (4)
superheating of the mixture, (5) creation of hot spots, and (6) enhancement of the
dissolution of the precursor gel. According to Conner et al., rapid heating and
creation of hot spots are important factors associated with an increase in synthesis
rates under MWs [8, 11].
The accelerated reaction under MWs has been explained with various factors
such as decreased activation energy or increased pre-exponential factor. For
example, the accelerated process with MWs has been explained with low Ea in
alumina sintering [12], polymerization of e-caprolactone [13], a curing of a
phenylethynyl terminated imide compound [14] and in an imidization reaction [15].
However, accelerated MW-syntheses of Cu2O [16], molecular sieves like AlPO-
11 and SAPO-11 [17] and metal–organic frameworks (MOFs) such as iron-
benzenedicarboxylate [18] and copper-benzenetricarboxylate [19] are mainly due to
a very large increase in pre-exponential factors (even with increased Ea). Very
recently, Ahnfeldt et al. [20] have shown the accelerated synthesis of a MOF (CAU-
1-(OH)2) with MWs is due to an increase of pre-exponential factor. However, they
have shown that the Ea does not change noticeably with heating methods.
To explain the accelerated dehydration under MWs, the reaction activation
energy (Ea) and pre-exponential factor (A) of the Arrhenius equation are obtained
from the Arrhenius plots (Fig. 4). The Ea values of MW and CE dehydration are
50.3 and 86.1 kJ/mol, respectively, showing the remarkable decrease of the Ea with
MW heating. However, the A of MW heating (1.2 9 107/h) is also decreased
compared with the A of CE heating (1.4 9 1010/h). Therefore, the high dehydration
rate under MWs is mainly due to decreased Ea of the dehydration rather than the
increased pre-exponential factor.
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Liquid-phase dehydration
1235
(a) 4
Fig. 3 First-order kinetics
based on the remaining sorbitol
concentration at different
temperature (a 130, b 140,
c 150 °C) with MW and CE
heating
3
CE
MW
2
1
0
0
3
6
9
12
15
Time (h)
(b) 4
3
CE
MW
2
1
0
0
3
6
9
12
15
Time (h)
(c) 4
3
2
1
0
CE
MW
0
2
4
6
8
Time (h)
Table 1 First-order kinetic
constants of sorbitol dehydration
with heating method and
temperature
Heating
method
Temperature (°C)
k /h
Ratio of
k (kMW/kCE
)
MW
CE
130
130
140
140
150
150
3.6
1.1 9 10-1
34.0
32.4
20.4
MW
CE
4.8
1.5 9 10-1
7.3
MW
CE
3.6 9 10-1
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1236
N. A. Khan et al.
Fig. 4 Arrhenius plots to
obtain the activation energy and
pre-exponential factor for the
sorbitol dehydration under MW
and CE heating
3
2
1
CE
MW
0
-1
-2
-3
0.00234
0.00240
0.00246
0.00252
1/T(1/K)
(b)
(a)
100
100
80
60
40
20
CE
MW
80
60
40
CE
MW
20
0
0
0
20
40
60
80
100
0
20
40
60
80
100
Conversion (%)
Conversion (%)
Fig. 5 Effect of sorbitol conversion on the selectivity for a sorbitan and b isosorbide with MW and CE
heating
The dependence of isosorbide or sorbitan selectivity on the sorbitol conversion
has been analyzed to check whether there is any effect of MWs on the selectivity for
the isosorbide or sorbitan. As shown in Fig. 5, irrespective of heating method, the
isosorbide selectivity increases (and sorbitan selectivity decreases accordingly) with
increasing sorbitol conversion in agreement with the fact of the consecutive reaction
(sorbitol ? sorbitan ? isosorbide). However, there is negligible effect of MW or
CE heating on the isosorbide or sorbitan selectivity, suggesting little effect of MWs
on the mechanism or selectivity of the dehydration. In other words, accelerations
may be obtained similarly both in the stage of sorbitol dehydration (to sorbitan) and
sorbitan dehydration. Therefore, it may be suggested that MWs decrease the
activation energies of the two consecutive dehydrations. However, further work is
needed to confirm whether the reduction in the activation energy is true or
superficial (by hot spots, transient temperature and pressure).
Even though the detailed reason of accelerated dehydration under MWs is not
clear, it can be said that the MW-dehydration is a very efficient method to dehydrate
sorbitol to isosorbide. Figure 6 compares the dehydration results at two different
conditions (MW at 130 °C; CE at 170 °C) and it can be confirmed that the activity
of sorbitol dehydration with MWs at a much lower temperature (130 °C) is higher
123

Liquid-phase dehydration
1237
(a)
(b)
100
100
80
60
40
20
0
80
60
40
20
0
Sorbitol conversion
Isosorbide selectivity
Sorbitan selectivity
Sorbitol conversion
Isosorbide selectivity
Sorbitan selectivity
0.0
0.5
1.0
1.5
0
2
4
6
Time (h)
Time (h)
Fig. 6 Effect of heating methods, temperature (a MW at 130 °C; b CE at 170 °C) and reaction time on
the sorbitol conversion and selectivity for sorbitan and isosorbide
than high temperature (170 °C) dehydration with CE heating. Therefore, the MW
heating is very helpful to dehydrate facilely even at very low temperature.
Conclusions
From the liquid-phase dehydration of sorbitol in the presence of acidic resin
catalysts, the following conclusions can be derived. The dehydration can be
accelerated by 20–34 times (or the reaction temperature can be decreased by 40 °C
for similar conversion in a similar reaction time) with MW irradiation at the same
reaction temperature. The accelerated dehydration under MW irradiation is mainly
due to decreased activation energy rather than increased pre-exponential factor. The
MWs accelerate both the two stages of dehydration (sorbitol to sorbitan and sorbitan
to isosorbide) and do not have noticeable effects on the selectivity for sorbitan and
isosorbide.
Acknowledgments This study was supported by a grant (B551179-10-03-00) from the cooperative
R&D Program funded by the Korea Research Council Industrial Science and Technology, Republic of
Korea. The authors thank Dr. Jong-Min Lee for helpful discussions.
References
1. A. Corma, S. Iborra, A. Velty, Chem. Rev. 107, 2411–2502 (2007)
2. A. Yamaguchi, N. Hiyoshi, O. Sato, M. Shirai, Green Chem. 13, 873–881 (2011)
3. J. Xia, D. Yu, Y. Hu, B. Zou, P. Sun, H. Li, H. Huang, Catal. Commun. 12, 544–547 (2011)
4. P. Sun, D.H. Yu, Y. Hu, Z.C. Tang, J.J. Xia, H. Li, H. Huang, Korean J. Chem. Eng. 28, 99–105
(2011)
5. Z.-C. Tang, D.-H. Yu, P. Sun, H. Li, H. Huang, Bull. Korean Chem. Soc. 31, 3679–3683 (2010)
6. M. Gu, D. Yu, H. Zhang, P. Sun, H. Zhang, Catal. Lett. 133, 214–220 (2009)
´
´
7. A. de la Hoz, A. Dıaz-Ortiz, A. Moreno, Chem. Soc. Rev. 34, 164–178 (2005)
8. G. Tompsett, W.C. Conner, K.S. Yngvesson, ChemPhysChem 7, 296–319 (2006)
9. S.-E. Park, J.-S. Chang, Y.K. Hwang, D.S. Kim, S.H. Jhung, J.-S. Hwang, Catal. Surv. Asia 8,
91–110 (2004)
123

1238
N. A. Khan et al.
10. J. Klinowski, F.A.A. Paz, P. Silva, J. Rocha, Dalton Trans. 40, 321–330 (2011)
11. W.C. Conner, G. Tompsett, K.-H. Lee, K.S. Yngvesson, J. Phys Chem. B 108, 13913–13920 (2004)
12. K.H. Brosnan, G.L. Messing, D.K. Agrawal, J. Am. Ceramic Soc. 86, 1307–1312 (2003)
13. G. Sivalingam, N. Agarwal, G. Madras, J. Appl. Polym. Sci. 91, 1450–1456 (2004)
14. X. Fang, R. Hutcheon, D.A. Scola, J. Polym. Sci. A 38, 2526–2535 (2000)
15. D.A. Lewis, J.D. Summers, T.C. Ward, J.E. McGrath, J. Polym. Sci. A 30, 1647–1653 (1992)
16. E. Haque, C.M. Kim, S.H. Jhung, CrystEngComm 13, 4060–4068 (2011)
17. M. Gharibeh, G.A. Tompsett, W.C. Conner, K.S. Yngvesson, ChemPhysChem 9, 2580–2591 (2008)
18. E. Haque, N.A. Khan, J.H. Park, S.H. Jhung, Chem. Eur. J. 16, 1046–1052 (2010)
19. N.A. Khan, E. Haque, S.H. Jhung, Phys. Chem. Chem. Phys. 12, 2625–2631 (2010)
20. T. Ahnfeldt, J. Moellmer, V. Guillerm, R. Staudt, C. Serre, N. Stock, Chem. Eur. J. 17, 6462–6468
(2011)
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