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CATTOD-8827; No. of Pages6
ARTICLE IN PRESS
H. Li et al. / Catalysis Today xxx (2014) xxx–xxx
3
of furfural yield as well as xylose conversion efficiency (Table 1,
entry4).
initial xylose weight − remainig xylose weight
Conversion of xylose (%) =
× 100
To understand the influence of different types of polar aprotic
solvents in water phase on xylose dehydration, DMSO, DMF and
DMI were investigated in a modified biphasic system under the
same reaction conditions (Table 1, entries 5–7). Clearly, the yield
of furfural and the conversion efficiency of xylose were related to
the types of polar aprotic solvents. The addition of DMSO, DMF
and DMI to the aqueous phase of the biphasic system can greatly
improves the furfural yield, especially for the DMI solvent. A more
than fifteen-fold increase in furfural yield was achieved with DMI
in comparison with the non-polar-aprotic system (Table 1, entry
4). However, xylose conversion efficiency increased relatively lit-
tle, which indicated that DMI could greatly inhibit the unwanted
side-reactions and thereby improve the furfural selectivity. From
these observations, DMI is the most suitable auxiliary solvent along
with the modified extracting solvents for the furfural production.
This phenomenon demonstrated that the modified biphasic sys-
tem was in favor of the generation of furfural, thus restrained the
formation of byproducts and increased the selectivity of the main
product.
initial xylose weight
(2)
3. Results and discussion
3.1. Influence of different modified biphasic systems on furfural
yield and xylose conversion
Recently solid acid catalysts with good thermal and chemical
version. Zirconia-based and titanium-based solid acid SO42−/TiO2-
ZrO2/La3+ has emerged as an attractive alternative catalyst for a
variety of organic transformations such as cracking, alkylation and
isomerization reactions due to its strong acidity, high thermosta-
found that SO42−/TiO2-ZrO2/La3+ prepared showed high catalytic
layst was used again in the dehydration of xylose in a biphasic
system. Table 1 shows the dehydration of xylose in different reac-
tion media. When the aqueous sytem was used in the dehydration
of xylose (Table 1, entry 1), 46.1 mol of furfural/g of xylose with
40.0% xylose conversion efficiency was obtained under 120 ◦C at
a reaction time of 4 h. This may be attributed to a large amount of
acidic sites on the surface of the prepared catalyst, which was com-
firmed by NH3-TPD and pyridine FT-IR (data not shown) [31,35].
Besides, the existing of La3+ loaded on the solid acid catalyst may
enhance its catlytic performance by changing the chemical state
3.2. Influence of the co-solvent amount in the modified biphasic
The modified biphasic system mentioned above obviously
improved the furfural yield and the xylose conversion efficiency,
thus the influence of the amounts of the best co-solvents (DMI and
2-butanol) on the xylose dehydration is discussed in Fig. 1. The
dehydration reaction was conducted in the xylose/catalyst weight
ratio of 2:1 at 120 ◦C for 4 h, and the volume of water phase and
organic phase was set to 30 mL, respectively. As shown in Fig. 1b,
with a decrease of water/DMI volume ratio from 9:1 to 8:2, fur-
fural yield remarkably increased from 581.4 mol to 936.6 mol
from per gram of xylose. However, further decreasing the ratio,
which meant increasing DMI content, led to the decrease in furfural
yield, which was due to the reducing of extracting power of solvent
conversion efficiency of xylose sharply increased firstly and then
leveled off. Thus the amount of DMI in aqueous phase of biphasic
system had important impact on the dehydration of xylose, and the
desirable water/DMI volume ratio was kept at 8:2.
Fig. 1b shows the furfural yield and xylose conversion efficiency
as a function of MIBK/2-butnal volume ratio. There was no obvi-
ous change in the furfural yield and xylose conversion efficiency as
the volume ratio of MIBK and 2-butanol decreased from 9:1 to 7:3.
However, as the volume ratio decreased to 6:4, xylose conversion
efficiency increased while furfural yield reduced quickly. This phe-
nomenon was attributed to the accessibility of part of 2-butanol
accessible to water phase, resulting in an increment of the solubil-
ity of furfural in water phase, thus leading to secondary reactions
[1].
2−
of exterior atoms, thus strengthening the interaction of SO4
and TiO2-ZrO2/1.0 wt%-La3+ and thereby increasing the number of
effective active center of catalysts [36]. Although water was con-
sidered as a green solvent in many processes, it was apparently
between furfural and intermediates of the xylose-to-furfural in
aqueous solution [7,37].
Compared to the pure water system, water/MIBK as a biphasic
system (Table 1, entry 2) yielded the relatively higher furfural yield
and xylose conversion of 60.6 mol of furfural/g of xylose and
49.2%, respectively, under the same reaction condition. This may be
due to the higher solubility of furfural in MIBK phase than in water.
When DMSO as a co-solvent was added in this aqueous phase, the
biphasic system resulted in 409.7 mol of furfural/g of xylose (entry
3), which was increased by 576.0% compared with the water/MIBK
system. While no obvious difference occurred in xylose conver-
sion efficiency. These results were consistent with the literature
reported that DMSO can effectively depress side-reactions in dehy-
dration reactions and increase the selectivity of furfural product [2].
However, the addition of 2-butanol as a co-solvent into the MIBK
phase in the biphasic system had small impacts on the increasing
Table 1
Influence of the reaction media composition on furfural yield and xylose conversion efficiency.a
Entry
Solvents
Furfural yield (mol of furfural/g of xylose)
Conversion (%)
1
2
3
4
5
6
7
Water
Water:MIBK (1:1)
(8:2 water:DMSO): MIBK
Water: (7:3 MIBK:2-butanol)
(8:2 water:DMSO):(7:3 MIBK:2-butanol)
(8:2 water:DMF):(7:3 MIBK:2-butanol)
(8:2 water:DMI):(7:3 MIBK:2-butanol)
46.1
60.6
409.7
61.4
717.8
541.4
936.6
40.0
49.2
46.0
50.0
60.8
63.4
56.1
Reaction conditions: 120 ◦C, 4 h, 0.2 g xylose, 0.1 g SO42−/TiO2-ZrO2/1.0 wt%-La3+, V(water phase) = V(organic phase) = 30 mL.
a
Please cite this article in press as: H. Li, et al., A modified biphasic system for the dehydration of d-xylose into furfural using SO42−/TiO2-ZrO2/La3+