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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

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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

I. Ahmed et al. / Chemical Engineering Science 93 (2013) 919592


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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.

I. Ahmed et al. / Chemical Engineering Science 93 (2013) 9195 93


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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


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


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.

I. Ahmed et al. / Chemical Engineering Science 93 (2013) 919594


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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

I. Ahmed et al. / Chemical Engineering Science 93 (2013) 9195 95