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Liquid-phase dehydration of sorbitol to isosorbide using sulfated
titania as a solid acid catalyst
Imteaz Ahmed a, Nazmul Abedin Khan a, Dinesh Kumar Mishra b, Ji Sun Lee b,Jin-Soo Hwang b, Sung Hwa Jhung a,n
a Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, Daegu 702-701, Republic of Koreab Bio-refinerary Research Center, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusung, Daejeon 305-600, Republic of Korea
H I G H L I G H T S
cIsosorbide is produced in liquid-
phase dehydration of sorbitol.
cThe liquid-phase dehydration is
carried out firstly with sulfated tita-
nia catalysts.
cSulfated titania is suggested as a
reusable catalyst for the isosorbide
production.
G R A P H I C A L A B S T R A C T
HO
HO OH
HO OH
HO
sorbitol
HO
O
H
H
O
OH
isosorbide
Sulfated-TiO2
-2H2O
a r t i c l e i n f o
Article history:
Received 23 November 2012
Received in revised form15 January 2013
Accepted 26 January 2013Available online 9 February 2013
Keywords:
Sorbitol dehydration
Isosorbide
Solid acid
Titania
Sulfation
Sulfated titania
a b s t r a c t
Liquid-phase dehydration of sorbitol to isosorbide has been carried out for the first time with sulfated
titania (S-TiO2) catalyst and its performance was compared with the catalytic activity of titania (TiO2)
to investigate the effect of sulfation. The catalyst was produced in situfrom titanium isopropoxide andsulfuric acid as the source for TiO2and the sulfate group, respectively. The optimum reaction conditions
e.g. temperature, catalyst dosage and reaction time were investigated for the dehydration reaction
using the sulfated catalyst. As a result, S-TiO2, which contains sulfate acidic sites, is a promising catalyst
for liquid-phase dehydration of sorbitol to isosorbide.
& 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Recently, the utilization of renewable biomasses has attracted
much attention because of the environment and energy (Corma
et al., 2007). Sorbitol is one of the useful biomass-derived
chemicals that can be converted into polyols, and sorbitol can
be obtained from cellulose via glucose. Isosorbide, which can be
obtained from dehydration of sorbitol, is one of the useful
chemicals for polymers and medicines (Yamaguchi et al., 2011;
Xia et al., 2011;Sun et al., 2011;Li et al., 2010;Gu et al., 2009).
Mineral acids like sulfuric acid and hydrochloric acid have
efficient catalytic properties for dehydration of sorbitol. However,the process using mineral acids has drawbacks from an environ-
mental and safety perspective. Moreover, it is cumbersome to
separate the homogenous catalysts from the reaction mixture
which may add extra costs to the commercial synthesis. There-
fore, several solid catalysts such as sulfated copper oxide (Xia
et al., 2011), supported heteropoly acid (Sun et al., 2011), NiO/
activated carbon (Li et al., 2010), metal phosphate (Gu et al.,
2009), sulfated zirconia (Khan et al., 2013) and a resin (Amber-
lyst-15) (Khan et al., 2011) have recently been tried for isosorbide
production from sorbitol. However, liquid-phase dehydration has
not been investigated thoroughly even though the process has the
advantage of high throughput and low energy consumption (Khan
Contents lists available at SciVerse ScienceDirect
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Chemical Engineering Science
0009-2509/$- see front matter & 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.ces.2013.01.068
n Corresponding author. Tel.: 82 53 950 5341.
E-mail address: [email protected] (S.H. Jhung).
Chemical Engineering Science 93 (2013) 9195
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et al., 2011). The acidity of solid catalysts is the most important
factor for acid catalytic reactions. Sulfation is one of the widely
used techniques to improve the acidity of solid catalysts for better
performance in acid catalyzed reactions (Oliveira et al., 2008,
2006; Molochnikov et al., 2006; Corma, 1995; Sun et al., 2005;
Hasan et al., 2012;Lima et al., 2011).
Sulfated titania (S-TiO2) catalysts are very promising in the field of
organic reactions. The catalysts have attracted much attention due to
their strong acidity, non toxicity and high catalytic activity inreactions like nitration of phenol (Sunajadevi and Sugunan, 2005,
2006), synthesis of chalcones, decomposition of isopropanol (Ortiz-
Islas et al., 2005), photocatalytic removal of toluene (Barraud et al.,
2005) and so on. Several methods such as impregnation (Ropero-Vega
et al., 2010), solgel in situ synthesis from precursors (Dalai et al.,
1998;Choo et al., 2000;Krishnakumar and Swaminathan, 2011), etc.
have been used to produce S-TiO2. Precursors for S-TiO2 include
titanium hydroxide (Dalai et al., 1998), titanic acid (Choo et al., 2000),
tetraethyl orthrotitanate (Krishnakumar and Swaminathan, 2011) etc.
In this study, S-TiO2 was synthesized from titanium isoprop-
oxide and used for the first time as a catalyst in the liquid-phase
dehydration of sorbitol to isosorbide. The catalytic activity was
thoroughly investigated for various reaction temperatures, cata-
lyst amounts, and reaction times and its catalytic performance
was compared with that of pure TiO2. As a result, S-TiO2exhibited
promising isosorbide selectivity from among all the reports
available on solid acid catalysis.
2. Experimental
2.1. Material
Titanium (IV) isopropoxide (Ti(OCH(CH3)2)4, 97%) and sodium
chloride (NaCl, 99.5%) were purchased from Sigma Aldrich and Jin
Chemical/Pharma Co., respectively. D-Sorbitol (C6H14O6, 97%),
sodium hydroxide (NaOH, 98%) and acetonitrile (99.5%) were
procured from Daejung Chemicals and Metals Co. Sulfuric acid
(H2SO4, 95%) and hydrochloric acid (HCl, 35%) were purchasedfrom OCI Co. Phenolphthalein was supplied by Duksan Pharma-
ceutical Co. All the chemicals in this study were used without any
further purification.
2.2. Catalyst preparation
S-TiO2 was prepared as previously described (Krishnakumar
and Swaminathan, 2011). Titanium isopropoxide was used as the
source of TiO2. Briefly, titanium isopropoxide (12.5 mL) was
dissolved in 100 mL of 1-propanol. After dissolution under
magnetic stirring, 3.2 mL of 1 M H2SO4 were added dropwise
and stirred for another 4 h to yield a white gel of S-TiO2. The
obtained gel was then filtered, washed and dried in a drying oven
at 100 1C for 12 h. After that, a calcined catalyst was obtained byheating the sample in a muffle furnace at 400 1C for 1 h. To
synthesize TiO2, the same procedure was followed as that of the
S-TiO2; however, H2SO4 was not used in the synthesis of TiO2.
2.3. Catalyst characterization
The crystal phase of the catalysts was verified using an X-ray
diffractometer D2 Phaser (Bruker, with CuKa radiation). FT-IR
spectra were recorded with a Jasco FT/IR-4100 with a resolution
of 1.0 cm1. The nitrogen adsorptions of the catalysts were
obtained at 196 1C with a surface area and porosity analyzer
(Micromeritics, Tristar II 3020) after evacuation at 150 1C for 12 h.
Elemental analyses of the adsorbates were done using an ele-
mental analyzer (Thermo Fisher, Flash-2000) with a TCD detector.
The total acid content (COOH, OH, SO3H, SO42 etc.) was
determined by a previously reported titrimetric method (Wang
et al., 2011). For this, 0.02 g of S-TiO2 were added to 10 ml of
0.01 M NaOH solution and stirred for 3 h. Then it was titrated
with 0.01 M HCl with phenolphthalein indicator and the
consumed amount of NaOH was measured. From the consumed
amount of NaOH, the total acidic sites of the catalyst were
calculated.
2.4. General procedure for the dehydration of sorbitol
The dehydration of sorbitol was carried out in liquid-phase
using a round bottomed 50 mL three-neck flask equipped with a
rectification column and a water-cooled condenser attached to a
vacuum pump. The reaction pressure was always kept at 0.3 bar.
The composition of the dehydrated product was analyzed using a
HPLC (Younglin Instrument, Acme 9000) equipped with a refrac-
tive index detector and Asahipak column (NH2P-50 4E, No.
N712004). An acetonitrile/water (80/20) mixture was used as an
eluent for the analysis. Detailed catalytic and analysis procedures
are shown elsewhere (Khan et al., 2011).
2.5. Procedure for the regeneration of the catalyst
After the reaction, a thick mixture containing catalysts was
thoroughly washed at first with water and then with ethanol.
Next, it was filtered and dried in a drying oven and calcined at
400 1C for 3 h to yield the regenerated white catalyst. This catalyst
was then used again for the dehydration of sorbitol as previously
described. The weight of each reactant including catalyst was
reduced proportionally because of the loss of the catalyst in the
regeneration procedure.
3. Result and discussion
3.1. Characteristics of the catalysts
3.1.1. Structure and porosity of the catalysts
The XRD patterns of both TiO2 and S-TiO2 were similar to each
other (Fig. 1(a)), and have the characteristic peaks (at 2y values of
25.5, 37.4, 48 and 54) of the anatase phase (Sunajadevi and Sugunan,
2005, 2006; Hadjiivanov and Klissurski, 1996). No characteristic
peaks were found for titanium sulfate or other sulfur containing
compounds.
Nitrogen adsorption isotherms of pure and sulfated TiO2samples are shown in Fig. 1(b). The surface areas of TiO2 and
S-TiO2are 137 m2/g and 41 m2/g, respectively. The pore volumes
of these two catalysts are 0.148 cm3/g and 0.033 cm3/g, respec-
tively. The BET surface area of the S-TiO2 was lower than that of
the pure TiO2 which agrees with the reported values (Barraud
et al., 2005) even though various surface areas have been reportedfor S-TiO2 in the literature (Dalai et al., 1998). The reduced
porosity of S-TiO2compared to the TiO2sample can be explained
by the effect of the in situ synthesis of the sulfated catalyst. Since
the XRD patterns of the two materials are similar, the sulfate
groups probably occupy the pore space of the structure, resulting
in the surface area being reduced. Moreover, there is a particle
size effect on the surface area of the S-TiO2(Barraud et al., 2005).
3.1.2. FT-IR spectra of the catalyst:
Fig. 1(c) shows the FT-IR spectra of the TiO2 and S-TiO2samples. Generally, the strong surface acidity in the S-TiO2comes
from the presence of the sulfate groups, which are covalently
bonded to the TiO2 surface in an inorganic chelating bidentate
manner (Tyagi et al., 2010). These bidentate sulfate ions show
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various FT-IR bands between 1230 cm1 and 980 cm1 (Ropero-
Vega et al., 2010). The bands at 1074 cm1 and 1034 cm1 are
assigned to the asymmetric SO stretching vibrations (Noda et al.,
2005;Mishra et al., 2003). On the other hand, the band appearing
at 993 cm1 is assigned to the symmetric SO stretching vibra-
tion (Noda et al., 2005). Another two bands appearing at
1225 cm1 and 1138 cm1 are due to the asymmetric and
symmetric stretching of the SO vibrations, respectively (Noda
et al., 2005;Mishra et al., 2003). Therefore,Fig. 1(c) clearly shows
the bands that were assigned to the SO and SO vibrations for
the synthesized S-TiO2 catalyst in this study. These results prove
that in the S-TiO2, SO42 appears as the sulfate bound to the TiO2
surface. Due to the presence of the sulfate groups, a strong acidity
can be observed in the sulfated catalyst.
3.2. Catalytic dehydration of sorbitol to isosorbide
3.2.1. Effect of the Sulfation
In the S-TiO2, a number of O2 ions from the surface of the
TiO2 are replaced by the O2 of the SO4
2 groups (Waqif et al.,
1992). The S-TiO2 having the concentration of total acidity of
4.3870.24 mmol/g (determined by chemical analysis) showed
much higher isosorbide selectivity compared to the TiO2 even
though the porosity of the TiO2 was higher than that of the
sulfated catalyst. Maximum isosorbide selectivity for TiO2 was
found to be about 12% while S-TiO2 showed around 75%
isosorbide selectivity at the same condition (210 1C, 4 h). There-
fore, it can be easily concluded that the acid sites have a strong
influence on the conversion of sorbitol to isosorbide in the
dehydration reaction.
3.2.2. Effect of reaction conditions
The effect of the catalyst dosage on the conversion of sorbitol
to isosorbide was investigated for reactions at 210 1C for 2 h and
the results are shown in Fig. 2. For a blank experiment without
any catalyst, the sorbitol conversion was only 20% without any
formation of isosorbide. However, the sorbitol conversion and
isosorbide selectivity were 100% and 62%, respectively, with only
0.1 g of S-TiO2. Moreover, the isosorbide selectivity increased
sharply with an increasing amount of catalyst up to 0.2 g and then
no increase in selectivity was observed with further increase in
20 30 40 50 60
0
1500
3000
4500
Intensity(a.u.)
2 theta (deg)
TiO2S-TiO2
80
100
120
1401138
1034
993
1225
Transmita
nce(%)
Wave number (cm-1)
TiO2S-TiO2
1200 1100 1000 900 800
0.00 0.25 0.50 0.75 1.00
0
30
60
90
120
Quantity
adsorbed(cm
3/g)
Relative pressure (P/Po)
TiO2
S-TiO2
Fig. 1. (a) XRD patterns, (b) N2 adsorption isotherms and (c) FT-IR spectra of TiO2 and S-TiO2 used in this study.
0.0 0.1 0.2 0.3 0.4
0
20
40
60
80
100
Conversion&Selectivity(%)
Catalyst amount (g)
Sorbitol conversion
Isosorbide selectivity
Sorbitan selectivity
Unknown
Fig. 2. Effect of catalyst dosage in the conversion of sorbitol at 210 1C for 2 h and
10 g of sorbitol.
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catalyst dosage. Therefore, the optimum dose of the catalyst was
0.2 g and used for further studies.
To investigate the effect of the reaction temperature for the
conversion of sorbitol, the reactions were carried out at tempera-
tures ranging from 190 to 230 1C as shown in Fig. 3. Almost
complete conversion of sorbitol was found in every case and
isosorbide selectivity also did not widely vary after a 4 h reaction.
At 190 1C, the isosorbide selectivity was 70.7% which increased to
75.3% after increasing the temperature to 210 1C. Further increasein the temperature only slightly reduced the selectivity to 71.2%.
The major influence of the temperature is the rate of the
conversion in the sorbitol to isosorbide since equilibrium is
reached rapidly at high temperatures. The effect of the reaction
time was investigated for each temperature from 0.5 to 4.0 h
(Fig. 3). At 190 1C, the rate of isosorbide production was very slow
compared with other temperatures and the selectivity gradually
increased with the reaction time up to 4 h. At 210 1C, the
production of isosorbide was very fast and reached nearly
equilibrium after 2 h, and at 230 1C, the isosorbide selectivity
was almost 90% of its maximum selectivity (at 230 1C) within half
an hour.
From the experimental results (Figs. 2 and 3), the optimumreaction temperature and amount of the catalyst are 210 1C and
0.2 g, respectively. Further increases in the reaction temperature
and in the amount of catalyst hardly showed any beneficial effect
on the conversion and selectivity. The fastest isosorbide production
0
25
50
75
100
Conversion
&selectivity(%)
Time (h)
Sorbitol conversion
Isosorbide selectivity
Sorbitan selectivityUnknown
0
25
50
75
100
Conversion
&selectivity(%)
Time (h)
0 1 2 3 4 0 1 2 3 4
0 1 2 3 4
0
25
50
75
100
Conversion
&selectivity(%)
Time (h)
Fig. 3. Effect of reaction time on the sorbitol conversion with time at (a) 190, (b) 210 and (c) 230 1C. The catalyst dosage is 0.2 g for 10 g of sorbitol.
0
20
40
60
80
100
Conversionandselectivity(%
)
Number of run
Sorbitol conversion
Isosorbide selectivity
Sorbitan selectivity
Unknown
1 2 3 4 1200 1000 800
120
160
200
240 1
225
10
34
993
11
38
Transmitance(%)
Wave number (cm-1)
run 1
run 2
run 3run 4
Fig. 4. Effect of number of regeneration of the catalyst S-TiO2on (a) the performance of sorbitol dehydration (210 1C, 2 h, 10 g sorbitol and 0.2 g catalyst) and (b) FT-IR
spectra.
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was at 230 1C; however, the selectivity was a bit low compared
with that at 210 1C.
3.2.3. Effect of regeneration of the catalyst
The regeneration of the S-TiO2 catalyst was very effective as
shown inFig. 4(a), which presents the effect of the regeneration
on the catalytic performance. Table 1 shows the physiochemical
properties of the fresh and used catalysts after calcinations upto
the beginning of third run. From the reaction results it was
observed that, even after a fourth run the performance of thecatalyst was nearly consistent and the isosorbide selectivity was
quite promising. From the titration experiments, the total acid
contents after first, second and third runs were found as
4.2570.19, 4.3170.22 and 4.2770.17 mmol/g, respectively.
The thermal stability of the catalyst was also high and the sulfate
groups were intact after calcining at 400 1C, as demonstrated by
the FT-IR data in Fig. 4(b). From the figure, the characteristic
sulfate ion peaks remain unchanged up to the fourth run. Thus, it
can be concluded that the S-TiO2 catalyst is easily regenerated
and reused without any noticeable loss of performance.
Compared to previous results in the liquid-phase reactions, the
dehydration of sorbitol into isosorbide using S-TiO2 is promising
because of its high thermal stability and excellent performance
for conversion, isosorbide selectivity and reusability. Moreover,
the highest isosorbide selectivity (75%) that was found in this
study in the liquid-phase reaction was higher than that of the
previously reported solid catalysts, suggesting the applicability of
the S-TiO2catalyst. The previously reported isosorbide selectivity
in liquid-phase reactions was 66% and 60% by using a sulfated
zirconia (Khan et al., 2013) and a resin (Amberlyst-15) (Khan
et al., 2011), respectively.
4. Conclusions
Liquid-phase dehydration of sorbitol to isosorbide was
successfully carried out using a S-TiO2 catalyst in this study.
The conversion and isosorbide selectivity were 100% and 75%,
respectively, for a reaction condition of 210 1C and 2 h. Thecatalyst was easy to synthesize and after the reaction it was
easily regenerated without any remarkable loss in performance.
Compared with other solid acid catalysts, the S-TiO2 catalyst in
this study is one of the best catalysts for isorbide production from
sorbitol.
Acknowledgment
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.
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Table 1
Physiochemical properties of fresh and used S-TiO2.
Catalyst BET surface area
(m2/g)
Micropore volume
(cm3/g)
Total pore
volume (cm3/g)
Fresh S-TiO2 42 4.53104 3.09102
Washed S-TiO2after 1st run
24 2.11104 1.74102
Calcined S-TiO2
after 1st run
36 3.82104 2.88102
Calcined S-TiO2after 2nd run
38 3.87104 2.85102
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