Bifunctional polyacrylonitrile fiber-mediated conversion of sucrose to 5-hydroxymethylfurfural in mixed-aqueous systems

Article abstract of DOI:10.1002/asia.201403338

A highly efficient catalytic system composed of a bifunctional polyacrylonitrile fiber (PANF-PA[BnBr]) and a metal chloride was employed to produce 5-hydroxyme-thylfurfural (HMF) from sucrose in mixed-aqueous systems. The promoter of PANF-PA[BnBr] incorporates protonic acid groups that promote the hydrolysis of the glycosidic bond to convert sucrose into glucose and fructose, and then catalyzes fructose dehydration to HMF, while the ammonium moiety may promote synergetically with the metal chloride the isomerization of glucose to fructose and transfer HMF from the aqueous to the organic phase. The detailed characterization by elemental analysis, FTIR spectroscopy, and SEM confirmed the rangeability of the fiber promoter during the modification and utilization processes. Excellent results in terms of high yield (72.8%) of HMF, superior recyclability (6 cycles) of the process, and effective scale-up and simple separation procedures of the catalytic system were obtained. Moreover, the prominent features (high strength, good flexibility, etc.) of the fibers are very attractive for fix-bed reactor.

Full text of DOI:10.1002/asia.201403338

DOI: 10.1002/asia.201403338
Full Paper
Biomass
Bifunctional Polyacrylonitrile Fiber-Mediated Conversion of
Sucrose to 5-Hydroxymethylfurfural in Mixed-Aqueous Systems
Xian-Lei Shi,*[a, c] Min Zhang,[b, c] Huikun Lin,[a, c] Minli Tao,[a, c] Yongdan Li,[b, c] and
Wenqin Zhang*[a, c]
Abstract: A highly efficient catalytic system composed of
a bifunctional polyacrylonitrile fiber (PANF-PA[BnBr]) and
a metal chloride was employed to produce 5-hydroxyme-
thylfurfural (HMF) from sucrose in mixed-aqueous systems.
The promoter of PANF-PA[BnBr] incorporates protonic acid
groups that promote the hydrolysis of the glycosidic bond
to convert sucrose into glucose and fructose, and then cata-
lyzes fructose dehydration to HMF, while the ammonium
moiety may promote synergetically with the metal chloride
the isomerization of glucose to fructose and transfer HMF
from the aqueous to the organic phase. The detailed charac-
terization by elemental analysis, FTIR spectroscopy, and SEM
confirmed the rangeability of the fiber promoter during the
modification and utilization processes. Excellent results in
terms of high yield (72.8%) of HMF, superior recyclability
(6 cycles) of the process, and effective scale-up and simple
separation procedures of the catalytic system were obtained.
Moreover, the prominent features (high strength, good flexi-
bility, etc.) of the fibers are very attractive for fix-bed reactor.
Introduction
obtained by acid-catalyzed dehydration of carbohydrates (e.g.,
fructose, glucose, and sucrose, Scheme 1), is a particularly val-
uable and versatile intermediate in biofuel chemistry and the
pharmaceutical industry.[7,8] Recently, great efforts have been
devoted towards converting carbohydrates into HMF; however,
In recent years, with growing concerns about diminishing
fossil fuel reserves, global warming and environmental pollu-
tion, the development of alternative sources for energy and
chemicals has attracted much attention of research-
ers worldwide.[1,2] In this respect, renewable biomass
is abundant and carbon-neutral, thus constituting
a promising alternative for the sustainable supply of
liquid fuels and valuable intermediates.[3,4] Particular-
ly, carbohydrates comprise the main class of biomass
compounds, and finding feasible ways to convert
them into useful chemicals, such as 5-hydroxymethyl-
furfural (HMF), 2,5-furandicarboxylic acid and others,
has become increasingly important.[5,6] HMF, which is
Scheme 1. The dehydration of sucrose to HMF.
to the best of our knowledge, low yields are normally ob-
tained, strongly hampering its industrial application.[9] Fructose
has been shown to be the preferred feedstock for a higher
yield,[10] while it is clear that generation of ample amounts of
HMF will require more inexpensive and abundantly available
raw materials, such as glucose and sucrose. Especially sucrose,
a disaccharide consisting of glucose and fructose units, is a key
low-molecular-weight carbohydrate resource derived from
cane or beet, and widely present in the plant kingdom. Be-
sides, the dehydration of glucose has been extensively investi-
gated. Accordingly, the development of highly efficient and en-
vironmentally acceptable approaches for the production of
HMF from low-cost sucrose would be of great value and signif-
icance.
[a] Dr. X.-L. Shi, H. Lin, M. Tao, Prof. Dr. W. Zhang
Department of Chemistry, School of Science
Tianjin University
Tianjin 300072 (P. R. China)
E-mail: shixl@tju.edu.cn
zhangwenqin@tju.edu.cn
[b] M. Zhang, Prof. Dr. Y. Li
School of Chemical Engineering
Tianjin University
Tianjin Key Laboratory of Applied Catalysis Science and Technology
and State Key Laboratory of Chemical Engineering
Tianjin 300072 (P. R. China)
[c] Dr. X.-L. Shi, M. Zhang, H. Lin, M. Tao, Prof. Dr. Y. Li, Prof. Dr. W. Zhang
Collaborative Innovation Center of Chemical Science and Engineering (Tian-
jin)
The production of HMF from sucrose has been investigated
in practice, and generally conversion of sucrose to HMF in-
volves two steps, that is, sucrose first rapidly hydrolyzes to the
Tianjin 300072 (P. R. China)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/asia.201403338.
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monosaccharides glucose and fructose, which is followed by
their dehydration to give HMF.[11] Currently, the majority of the
evaluated catalysts were mineral and organic acids,[12–14] solid
acids,[15,16] and metallic compounds[17,18] in multiple reaction
media, including water, organic solvents, ionic liquids, and
mixed-aqueous systems.[19] However, in these reports, the
yields of HMF are relatively low, and the apparent reason is
that only the fructose moiety from sucrose was efficiently
transformed into HMF, which left most of glucose molecules
unconverted.[20] For instance, Chheda and co-workers studied
the conversion of sucrose into HMF using HCl as the catalyst in
a biphasic reactor system (an aqueous phase modified with
DMSO and an organic extracting phase consisting of a 7:3 (w/
w) methyl isobutyl ketone (MIBK)/2-butanol mixture), and only
a 50% yield of HMF was achieved.[12] It is worth mentioning
that the conversion of glucose into HMF further needs an iso-
merization process to fructose; however, many acid catalysts
are unfavorable for this transformation. Recently, catalytic sys-
tems consisting of metallic halides and ionic liquids were used
for the conversion of sucrose into HMF, and good results were
obtained. Hu et al.[21] reported that sucrose could be converted
into HMF in good yield (65%) by using SnCl4 in 1-ethyl-3-
methyl imidazolium tetrafluoroborate ([BMIM]BF4) medium.
Later, Qi et al.[22] studied the production of HMF from sucrose
in 1-butyl-3-methyl imidazolium chloride ([BMIM]Cl) with CrCl3
as the catalyst, and a 76% yield of HMF was obtained by mi-
crowave irradiation. The above two methods for the conver-
sion of sucrose into HMF appear to be promising; however,
they depend on the use of expensive ionic liquids as solvents.
plication of a fixed-bed reactor in biphasic systems might be
a good choice.
In our previous work, a highly efficient and selective process
for the production of HMF from sucrose has been achieved in
the presence of metal chlorides and ammonium halides in N,N-
dimethylacetamide (DMAc) solvent. NH4Br was verified to be
an effective promoter for this transformation, and a possible
mechanism for this catalytic process has been proposed.[23] In
addition, we have firstly exploited polypropylene fiber as
a new support for a class of reusable fiber-supported ionic liq-
uids (FSILs), and the FSILs were used to catalyze the dehydra-
tion of fructose to HMF in DMSO and a mixed-aqueous
system.[24] Moreover, we also adequately demonstrated the
easily synthesized polyacrylonitrile fiber-supported poly(ammo-
nium methanesulfonate)s as active and recyclable heterogene-
ous Brønsted acid catalysts for different types of reactions in-
cluding the conversion of fructose into HMF.[25] Following our
pioneering studies on fiber catalysts and carbohydrate dehy-
dration, especially our excellent results obtained in aqueous
systems, and given their several advantages such as low cost,
high strength, light density, larger coverage area as well as po-
tential performance for a fixed-bed reactor of fiber, we investi-
gated the use of fibers in further work on biomass conversion.
Herein, we report a new efficient catalytic system composed of
a bifunctional polyacrylonitrile fiber (PANF) promoter and
a metal chloride that was employed to form HMF from sucrose
in mixed-aqueous systems under mild conditions.
Improvements have been made in recent years by applying Results and Discussion
different solvent types and extraction methods, and by apply-
The preparation of the fiber promoters
ing bifunctional catalytic systems. In fact, the large-scale, cost-
effective transformation of carbohydrates to HMF will require
the development of new, functional-group-tolerant catalysts
compatible with continuous processing. Among those, the ap-
Based on our previous work,[25] we started this study to synthe-
size the designed fiber promoters. The functional PANFs were
prepared according to a simple two-step strategy as shown in
Scheme 2. Preparation of the fiber promoters.
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Scheme 2. The first step is an amination procedure, and the
extent of immobilization was measured by weight gain
(weight gain=[(W2ÀW1)/W1]ꢁ100%, where W1 and W2 are the
weight of the fiber sample before and after amination, respec-
tively). Under the screened conditions of amination with poly-
ethylene polyamine in water, a weight gain of 35% polyethy-
lene polyamine-functionalized PANF (PANF-PA) was acquired.
The next step is salt formation with haloid acids in water and
benzyl halides in acetonitrile, respectively. Finally, four types of
functional PANFs were obtained. PANF-supported poly(benzy-
lammonium bromide)s (PANF-PA[BnBr]) was selected as
a model in view of its performance, and the final ammonium
moiety loading was 2.56 mmolgÀ1 by weight.
The characterization of fiber promoters
Figure 1. FTIR spectra of (a) PANF, (b) PANF-PA, (c) PANF-PA[BnBr], (d) PANF-
To avoid any errors during the preparation process and investi-
gate the rangeability of the fiber promoters before and after
the conversion of sucrose into HMF, we performed a detailed
characterization of fiber samples at different stages. The origi-
nal PANF, PANF-PA, PANF-PA[BnBr], the promoter recovered
after the first cycle in the dehydration of sucrose (PANF-
PA[BnBr]-1), and the promoter recovered after the 6th cycle
(PANF-PA[BnBr]-6) were all characterized by means of elemen-
tal analysis (EA), Fourier transform infrared spectroscopy (FTIR),
and scanning electron microscopy (SEM).
PA[BnBr]-1, and (e) PANF-PA[BnBr]-6.
Fourier transform infrared spectroscopy (FTIR). Samples of
PANF, PANF-PA, PANF-PA[BnBr], PANF-PA[BnBr]-1, and PANF-
PA[BnBr]-6 were pulverized by cutting and then prepared into
KBr pellets, and their FTIR spectra are shown in Figure 1. Com-
paring the FTIR spectra of PANF-PA (Figure 1b) and PANF (Fig-
ure 1a), the most striking change is in the high wavenumber:
the broad absorption bands around 3250 cmÀ1 can be charac-
terized as the N-H stretching vibration; besides, the strong ab-
sorption band at 1650 cmÀ1 is assigned to the amide I bands.
After salt formation, the PANF-PA[BnBr] (Figure 1c) displays
two new absorption bands at 745 and 702 cmÀ1, which belong
to the vibrational modes of the benzene ring and provide evi-
dence that PANF-PA[BnBr] has been successfully prepared.
Moreover, the specific absorption peaks of PANF-PA[BnBr]-
1 (Figure 1d) and PANF-PA[BnBr]-6 (Figure 1e) are quite similar
to that of PANF-PA[BnBr], which indicates that PANF-PA[BnBr]
is very stable and can be reused several times.
Elemental analyses (EA). EA data of PANF, PANF-PA, PANF-
PA[BnBr], PANF-PA[BnBr]-1, and PANF-PA[BnBr]-6 are listed in
Table 1. Compared to the original PANF, the C and N contents
of PANF-PA were decreased and the H content was increased,
as expected (Table 1, entries 1 and 2). After the formation of
salt, the amounts of C, H, and N of PANF-PA[BnBr] all decrease
Table 1. Elemental analysis of PANF, PANF-PA, PANF-PA[BnBr], PANF-
PA[BnBr]-1, and PANF-PA[BnBr]-6.
Scanning electron microscopy (SEM). Figure 2 presents the
SEM images of PANF, PANF-PA, PANF-PA[BnBr], PANF-PA[BnBr]-
1, and PANF-PA[BnBr]-6. After amination, the diameter of
Entry
Fiber sample
C [%]
H [%]
N [%]
1
2
3
4
5
PANF
PANF-PA
PANF-PA[BnBr]
PANF-PA[BnBr]-1
PANF-PA[BnBr]-6
65.55
55.51
54.00
57.64
57.86
5.669
7.503
6.054
6.327
6.215
23.54
20.52
14.64
13.36
13.03
because benzyl bromide has no N and less H and C than
PANF-PA. After the PANF-PA[BnBr] was used as the promoter in
the dehydration of sucrose for one and six times (Table 1, en-
tries 4 and 5), the C content was increased, especially for the
first cycle (PANF-PA[BnBr]-1), while the H and N contents of
PANF-PA[BnBr]-1 and PANF-PA[BnBr]-6 varied slightly. These re-
sults are perhaps due to the combined effect of the absorption
of insoluble substances (such as humins, see SEM images and
color change in the Supporting Information)[26] and damages
to the fiber sample (the hydrolysis of cyano or amide groups
with acid on the fiber is cannot be completely avoided). Al-
though the absorption amount increases with the number of
cycles, the hydrolysis shows the same changing trend, which
led to the final results of elemental analyses data.
Figure 2. SEM images of (a) PANF, (b) PANF-PA, (c) PANF-PA[BnBr], (d) PANF-
PA[BnBr]-1, and (e) PANF-PA[BnBr]-6.
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PANF-PA body extended obviously, and the surface of the
PANF-PA was thickly dotted with scarring (Figure 2b). With
each sequential modification or utilization, the surface of the
fiber samples became increasingly coarser, especially PANF-
PA[BnBr]-1 (Figure 2d) and PANF-PA[BnBr]-6 (Figure 2e), which
provided further evidence that some of the insoluble humins
were adsorbed to the surface of the fiber promoter. However,
the overall integrity of the fiber was untouched. This means
that PANF possesses good properties for PANF-PA[BnBr] as
a promoter in the conversion of sucrose into HMF.
water to the system may impede the coordination ability of
chromium with glucose, which would then reduce the forma-
tion of HMF from a glucose unit. Sucrose is a disaccharide con-
sisting of glucose and fructose linked by a glycosidic bond,
and the glycosidic bond can be easily hydrolyzed by an acid
catalyst. Besides, porous coordination polymers with acid
groups showed high conversion of glucose into fructose.[32]
Thus, acidic functional fibers were added into the system to
test the effect for the dehydration of sucrose. Polyacrylonitrile
fiber-supported poly(ammonium hydrochloride)s (PANF-
PA[HCl], Table 2, entry 7) and poly(ammonium hydrobromide)s
(PANF-PA[HBr], Table 2, entry 8) were used first. The results
show that both fiber promoters were active for this conversion,
and the yields increased to 46.9% and 54.1%, respectively.
Based on these results, the use of another two functional
fibers, PANF-supported poly(benzylammonium chloride)s
(PANF-PA[BnCl], Table 2, entry 9) and PANF-PA[BnBr] (Table 2,
entry 10) was examined. Gratifyingly, the yields of HMF in-
creased to 48.3% and 55.6%, respectively. Moreover, it is
worth noting that the functional fibers with the bromide ions
were more effective than those with the chloride ions. As dis-
cussed in our previous work,[23] bromide, which offers the opti-
mal balance between coordination ability and nucleophilicity,
is more effective as an ionic additive than chloride for the iso-
merization of glucose to fructose. These results are in agree-
ment with the halide effect reported by Binder.[29] As PANF-
PA[BnBr] afforded the best result it was used for further optimi-
zation. Next, the influence of the catalyst dosage (Table 2 en-
tries 11–14) and promoter loading (Table 2 entries 15–18) were
examined concisely. It was found that 15 mol% of SnCl4 with
20 mol% promoter loading gave the best result, affording
HMF in a yield of 62.1% (Table 2 entry 17).
Application of the fiber promoters for the conversion of su-
crose into HMF
Screening the fiber promoters for the dehydration of su-
crose to HMF. Water is the most clean and abundant solvent
for organic reactions, and sucrose is particularly soluble in
water, so the investigation of water as a co-solvent for the pro-
duction of HMF from sucrose is worthwhile.[27,28] Metal chlor-
[31]
ides such as CrCl3,[22,29] SnCl4,[21] AlCl3,[30] and FeCl3 are com-
monly used for glucose isomerization to fructose and have
been verified to be efficient for the dehydration of sugars.
Based on our previous work[23] and with the object of convert-
ing sucrose into HMF in mixed-aqueous systems, we first
screened a series of metal chlorides for this transformation in
a mixed water/DMAc solvent (DMAc has been verified to be
the most efficient solvent for sucrose dehydration[23,29]). As can
be seen from Table 2 (entries 1–6), at 10 mol% (based on the
substrate), CrCl3·6H2O, SnCl4·5H2O (abbreviated as SnCl4 in the
following), SnCl2·2H2O, and AlCl3·6H2O were all active. In partic-
ular, SnCl4 was the most efficient and was selected as the cata-
lyst for further study. Although CrCl3·6H2O has been verified to
be the most efficient catalyst in a previous work,[23] addition of
HMF can be isolated by extraction with various organic sol-
vents, such as methyl isobutyl ketone (MIBK),[2,33] 2-
butanol,[12] ethyl acetate,[34] diethyl ether,[10,35] and tol-
uene.[36] Here we chose a multiphase system includ-
Table 2. Optimization of the conversion of sucrose into HMF using the functional
fibers as the promoter.[a]
ing an aqueous phase modified with DMAc and or-
ganic solvents to further verify the promoting activity
of PANF-PA[BnBr] (Table 3). Based on our previous
work[24], MIBK was first selected as the extractant for
this attempt (Table 3, entry 1). Using a mixture of
MIBK/water/DMAc (2:3:5, v/v/v), the yield of HMF in-
creased to 68.2%. Encouraged by this good result,
we examined other organic solvents in further tests.
Extractants such as esters or toluene were not very
efficient for this dehydration (Table 3, entries 2–4),
while alcohols also had a positive effect on this trans-
formation (Table 2, entries 5–7). Finally, the mixed-
aqueous system composed of MIBK/water/DMAc was
selected to be further tested (Table 3, entries 8–16).
After further optimization of the composition of sol-
vent and the reaction time, the results show that the
MIBK/water/DMAc mixture at the ratio of 3:2:5 (v/v/
v) at a reaction time of 2.5 h gave the highest yield
of 72.8% (Table 3, entry 15). Moreover, the promoter
PANF-PA[HBr] was also investigated under the opti-
mized conditions; however, no higher yield of HMF
Entry Cat.
Catalyst
loading [mol%]
Promoter
Promoter
loading [mol%]
Yield [%][b]
1
2
CrCl3·6H2O 10
SnCl4·5H2O 10
–
–
–
–
–
–
–
–
–
–
–
–
10
10
19.9
30.2
12.5
traces
traces
14.7
46.9
54.1
48.3
55.6
36.6
44.5
58.7
58.9
46.4
60.7
62.1
61.4
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
SnCl2·2H2O 10
CuCl2·2H2O 10
FeCl3·6H2O 10
AlCl3·6H2O 10
SnCl4·5H2O 10
SnCl4·5H2O 10
SnCl4·5H2O 10
SnCl4·5H2O 10
PANF-PA[HCl]
PANF-PA[HBr]
PANF-PA[BnCl] 10
PANF-PA[BnBr] 10
PANF-PA[BnBr] 10
PANF-PA[BnBr] 10
PANF-PA[BnBr] 10
PANF-PA[BnBr] 10
SnCl4·5H2O
SnCl4·5H2O
0
5
SnCl4·5H2O 15
SnCl4·5H2O 20
SnCl4·5H2O 15
SnCl4·5H2O 15
SnCl4·5H2O 15
SnCl4·5H2O 15
PANF-PA[BnBr]
5
PANF-PA[BnBr] 15
PANF-PA[BnBr] 20
PANF-PA[BnBr] 25
[a] Reaction conditions: Sucrose (0.5 g), 10 mL of solvent (water/DMAc, 3:7, v/v) at
908C for 2 h. [b] Yield determined by HPLC.
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tries 1 and 2). Moreover, glucose was also efficiently dehydrat-
ed to give HMF in 50.1% yield (Table 4, entry 3). Furthermore,
the conversions of inulin, starch and cellulose were studied.
The HMF yields from inulin and starch could reach up to
69.7% and 26.4%, respectively, under the corresponding con-
ditions (Table 4, entries 4 and 6). However, when cellulose was
used as the substrate in the dehydration, only 1.9% yield of
HMF was obtained after 2.5 h (Table 4, entry 7), and when the
reaction time was prolonged to 6 h, the HMF yield was in-
creased to 4.6% (Table 4, entry 8). These results indicated that
the bifunctional fiber-mediated system can promote the con-
version of a range of carbohydrates and furthermore provided
a new direction for further studies.
Table 3. Further optimization for the conversion of sucrose to HMF in
a mixed-aqueous system using functional fibers as the promoter.[a]
Entry Mixed solvent
Composition (v/v) t [h] Yield [%][b]
1
MIBK/water/DMAc
2:3:5
2:3:5
2:3:5
2:3:5
2:3:5
2:3:5
2
2
2
2
2
2
2
2
2
2
2
2
2
68.2
45.6
62.4
62.9
63.2
65.5
67.6
49.4
67.1
69.6
69.5
68.9
67.7
2[c]
3
Ethyl acetate/water/DMAc
Butyl acetate/water/DMAc
Toluene/water/DMAc
1-Butanol/water/DMAc
2-Butanol/water/DMAc
4
5
6
7
8
9
10
11
12
13
14
15
16
17
MIBK/2-butanol/water/DMAc 1:1:3:5
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
MIBK/water/DMAc
2:4:4
2:1:7
3:2:5
3:1:6
4:1:5
4:2:4
3:2:5
3:2:5
3:2:5
3:2:5
The recyclability of the bifunctional fiber-mediated con-
version of sucrose into HMF in mixed-aqueous systems. To
evaluate the reusability of the fiber promoter and the recycla-
bility of the process, PANF-PA[BnBr] was reused in the mixed-
aqueous system. After completion of each cycle, PANF-
PA[BnBr] was simply taken out with common tweezers and
washed with MIBK. The remaining liquid was separated and ex-
tracted three times with the above MIBK, and then the recy-
cled fiber promoter and the aqueous phase (without additional
SnCl4) were used directly for the next cycle without any further
treatment. The results show that the reaction proceeded
smoothly without any extension of reaction time or marked
loss in the yield (72.7–69.0%, Figure 3). Moreover, the weight
1.5 64.9
2.5 72.8
3
70.3
2.5 70.5[d]
[a] Reaction conditions: Sucrose (0.5 g), 15 mol% SnCl4 and 20 mol%
PANF-PA[BnBr] with 10 mL of solvent at 908C at the indicated time.
[b] Yield determined by HPLC. [c] At 808C. [d] Promoted by PANF-PA[HBr].
was obtained (Table 3, entry 17). Taken together, the results
suggest that both PANF-PA[BnBr] and SnCl4 play a role in this
reaction, and they may have a synergistic effect on the forma-
tion of HMF. The promoter PANF-PA[BnBr] incorporates proton-
ic acid groups that are very active for the hydrolysis of glycosi-
dic bond to convert sucrose into glucose and fructose, and
then catalyze fructose dehydration to HMF; in the meantime,
the ammonium moiety may have a synergetic effect with SnCl4
to promote the isomerization of glucose to fructose (the possi-
ble mechanism was discussed in our previous work[23]) and
transfer HMF from the aqueous to the organic phase.
The production of HMF from different sugars promoted
by PANF-PA[BnBr]. In order to further reveal the merits of the
fiber promoter, the conversions of fructose, glucose, inulin,
starch, and cellulose were investigated in the screened mixed-
aqueous system, and the results are summarized in Table 4. It
was found that the system is efficient for the dehydration of
fructose to HMF, affording HMF in 71.6% and 80.9% yield at
a reaction time of 2.5 h and 1.0 h, respectively (Table 4, en-
Figure 3. Recyclability of the fiber promoter for the conversion of sucrose
into HMF in the mixed-aqueous system.
Table 4. The dehydration of different sugars in the mixed-aqueous sys-
of PANF-PA[BnBr] was almost unchanged after 6 cycles (from
0.1145 to 0.1139 g), which is consistent with the EA data
(Table 1, entries 3 and 5), further demonstrating the high stabil-
ity of the fiber promoter under the vigorous operating condi-
tions in the mixed-aqueous system.
tem.[a]
Entry
Sugar
t [h]
Yield [%][b]
1
2
3
4
5
6
7
8
Fructose
Fructose
Glucose
Inulin
Starch
Starch
2.5
1.0
2.5
2.5
2.5
6
71.6
80.9
50.1
69.7
14.5
26.4
1.9
Scale-up procedure for the conversion of sucrose into
HMF. Finally, to illustrate the utility of the fiber promoter-medi-
ated system, a large-scale experiment for the production of
HMF from sucrose was also conducted. The process was scaled
up to gram scale, and HMF was obtained simply by distillation.
It is worth noting that the reaction proceeded smoothly with-
out any extension of reaction time to afford HMF in an isolated
yield of 61%. From the above results and the prominent
Cellulose
Cellulose
2.5
8
4.6
[a] Reaction conditions: Substrate (0.5 g), 15 mol% SnCl4 and 20 mol%
PANF-PA[BnBr] with 10 mL of solvent (BIMK/water/DMAc, 3:2:5, v/v/v) at
908C at the indicated time. [b] Yield determined by HPLC.
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simple separation operation of the mixed-aqueous system, it is
obvious that the fiber promoter-mediated system is very at-
tractive for application in the chemical industry.
chemical industry for the production of HMF. Further studies
on the dehydration of different sugars such as starch and cellu-
lose using the fiber promoter in mixed-aqueous systems are
ongoing.
Comparison of the dehydration of sucrose in different cata-
lytic systems
Experimental Section
According to the results above and compared with different
catalytic systems under the optimized experimental conditions
(Table 5), it is worth mentioning that the performance of
a system depends both on the type of catalyst and solvent.
Commercially available polyacrylonitrile fiber (PANF, the number
average molecular weight of the spinning solution is 53000 to
106000, 93.0% acrylonitrile, 6.5% methyl acrylate and 0.4–0.5%
sodium styrene sulfonate) with a length of 10 cm and a diameter
of 30Æ0.5 mm (from the Fushun
Petrochemical
China) was used. All the sugars,
polyethylene polyamine, HCl
Corporation
of
Table 5. Comparison of the dehydration of sucrose to HMF using different catalytic systems.
(37.5%, aq), HBr (68.8%, aq),
benzyl chloride, benzyl bromide
and the other reagents used were
of analytical grade and employed
without further purification. Water
was deionized. A standard sample
of HMF was obtained from J&K Co.
Ltd.
Entry Catalytic system[a]
Catalyst dosage[b] T [8C]
t
HMF yield [%][c] Ref.
1
2
3
4
5
6
7
8
9
HCl, pH 1 (MIBK/2-BuOH/water/DMSO)
CrCl2 (choline chloride[d]
Hydrotalcite/Amberlyst 15 (DMF)
H-form Zeolite (water/MIBK)
GeCl4 ([BMIm]Cl)
SnCl4 ([EMIm]BF4)
CrCl3 ([BMIm]Cl)
Al-TUD-1/(toluene/water)
SnCl4/PANF-PA[BnBr] (MIBK/water/DMAc) 15 mol%
–
170
100
120
165
120
100
100
170
90
5 min 50
1 h
3 h
1 h
0.5 h
3 h
5 min[e] 76
6 h
2.5 h
[12]
)
10 mol%
200 wt%
29 wt%
10 mol%
10 mol%
20 mol%
200 wt%
62
54
28
55
65
[13]
[15]
[17]
[18]
[21]
[22]
17
[36]
The elemental analyses (EA) were
performed on a Vario micro cube
analyzer (Elementar). Fourier trans-
form infrared (FTIR) spectra were
obtained with an AVATAR 360 FTIR
spectrometer (Thermo Nicolet), KBr
72.8
This work
[a] Solvents are listed in parenthesis. [b] Catalyst/substrate. [c] Yields under optimized experimental conditions.
[d] Melt. [e] Under microwave irradiation.
disc. A scanning electron microscope (Hitachi, model S-4800) was
used to characterize the surface of the fibers. The quantitative
analyses of the product were performed on a Waters 1525 HPLC
system equipped with both UV and refractive index detectors.
However, the fiber promoter-mediated system still has some
advantages with regard to reaction conditions, yield of HMF,
and excellent reusability and recyclability of the catalyst lack-
ing in most previous reports. Moreover, the commercially avail-
ability of the fibers (PANF), easy process for fiber promoter
preparation, the efficient scaled-up procedure, as well as
simple post-processing make the fiber promoter-mediated
system a highly attractive alternative to current methodolo-
gies. Furthermore, the good flexibility and high mechanical
strength of the fiber are very attractive for fixed-bed reactors
in continuous processing.
Preparation of fiber promoters
Step 1. Dried PANF (3.00 g), polyethylene polyamine (30 g) and de-
ionized water (30 mL) were introduced into a three-necked flask
connected with a condenser. The mixture was refluxed (1058C)
with stirring for 24 h. The fiber was filtered off and washed repeat-
edly with water (60–708C) until the pH of the filtrate was 7, and
then the fiber sample was dried overnight at 608C under vacuum
to give PANF-PA (4.05 g, with a weight gain of 35%).
Step 2. A typical procedure for the preparation of fiber promoter is
as follows: Benzyl bromide (10 g) was dissolved in acetonitrile
(80 mL), and then the dried PANF-PA (3.00 g) was introduced into
the solution. The mixture was stirred under reflux for 24 h. Finally,
the sample was filtered off, rinsed with acetonitrile (20 mL), and
then dried overnight at 608C under vacuum to give PANF-PA[BnBr]
(5.34 g, 2.56 mmolgÀ1 ammonium moiety loading by weight).
Conclusions
In summary, a series of functional PANFs have been synthe-
sized and successfully used as promoter for the conversion of
sucrose into HMF in mixed-aqueous systems. The detailed
characterization of functional PANFs by elemental analysis, IR
spectroscopy, and SEM confirmed that ammonium moieties
were immobilized to the surface layer of PANF and were recy-
cled with excellent stability. Such fiber promoters were used
for the first time in the dehydration of sucrose to HMF and dis-
played high activity and reusability. The yield of HMF reached
up to 72.8% in a mixed-aqueous system, and the fiber promot-
er and the aqueous phase (containing the catalyst SnCl4) could
be recycled for at least six times. In addition, the dual role of
the fiber promoter for this transformation with high activity in
a mixed-aqueous system is revealed. The prominent features
of PANF and the remarkable performance of the fiber promot-
ers are very attractive for their use in a fix-bed reactor in the
General procedure for the conversion of sucrose into HMF
All the dehydration experiments were performed in a 50 mL flask
equipped with magnetic stirring and a condenser. A typical proce-
dure for the dehydration of sucrose is as follows: Sucrose (0.5 g,
1.46 mmol), SnCl4 (15% mol, 0.0768 g) PANF-PA[BnBr] (20% mol,
0.1141 g) and 10 mL of mixed-aqueous solvent (MIBK/water/DMAc,
3:2:5, v/v/v) were added into the flask. The mixture was stirred and
preheated to 908C and then maintained at 908C for 2.5 h. After
completion of the reaction, PANF-PA[BnBr] was taken out with
common tweezers and rinsed with MIBK (15 mL), which was com-
bined with the reaction mixture. The mixture was then decanted
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Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (Nos. 20834002 and 21306133),
Tianjin Research Program of Application Foundation and Ad-
vanced Technology (No. 14JCYBJC22600), and Project support-
ed by the Scientific Research Foundation of Yunan Provincial
Education Department (No. 2014Y535).
Keywords: 5-hydroxymethylfurfural · fiber promoter · green
chemistry · mixed-aqueous system · sucrose
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Published online on && &&, 0000
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FULL PAPER
Biomass
High in fiber: A highly efficient bifunc-
tional polyacrylonitrile fiber-mediated
system for the production of 5-hydroxy-
methylfurfural (HMF) from sucrose in
a mixed-aqueous solvent is presented.
Excellent results were obtained in terms
of high yield of HMF, superior recyclabil-
ity of the process, and effective scale-up
and operation procedure of the catalytic
system. Moreover, the prominent fea-
tures of the fiber are very attractive for
fixed-bed reactors.
Xian-Lei Shi,* Min Zhang, Huikun Lin,
Minli Tao, Yongdan Li, Wenqin Zhang*
&& – &&
Bifunctional Polyacrylonitrile Fiber-
Mediated Conversion of Sucrose to 5-
Hydroxymethylfurfural in Mixed-
Aqueous Systems
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