Highly efficient extraction and oxidative desulfurization system using Na7H2LaW10O36·32-H 2O in [bmim]BF4 at room temperature

Article abstract of DOI:10.1002/chem.201102754

Highly efficient, deep desulfurization of model oil containing dibenzothiophene (DBT), benzothiophene (BT), or 4,6-dimethyldibenzothiophene (4,6-DMDBT) has been achieved under mild conditions by using an extraction and catalytic oxidative desulfurization system (ECODS) in which a lanthanide-containing polyoxometalate Na₇H₂LnW ₁₀O₃₆·32-H₂O (LnW₁₀; Ln=Eu, La) acts as catalyst, [bmim]BF₄ (bmim=1-butyl-3-methylimidazolium) as extractant, and H₂O₂ as oxidant. Sulfur removal follows the order DBT>4,6-DMDBT>BT at 30-°C. DBT can be completely oxidized to the corresponding sulfone in 25 min under mild conditions, and the LaW ₁₀/[bmim]BF₄ system could be recycled for ten times with only slight decrease in activity. Thus, LaW₁₀ in [bmim]BF₄ is one of the most efficient systems for desulfurization using ionic liquids as extractant reported so far.

Full text of DOI:10.1002/chem.201102754

FULL PAPER
DOI: 10.1002/chem.201102754
Highly Efficient Extraction and Oxidative Desulfurization System Using
Na H LaW O ·32H O in [bmim]BF at Room Temperature**
7
2
10 36
2
4
[
a]
Junhua Xu, Shen Zhao, Wei Chen, Miao Wang, and Yu-Fei Song*
Abstract: Highly efficient, deep desul-
furization of model oil containing di-
benzothiophene (DBT), benzothio-
phene (BT), or 4,6-dimethyldibenzo-
thiophene (4,6-DMDBT) has been ach-
ieved under mild conditions by using
an extraction and catalytic oxidative
desulfurization system (ECODS) in
which a lanthanide-containing polyoxo-
(LnW ; Ln=Eu, La) acts as catalyst,
[bmim]BF4 (bmim=1-butyl-3-methyli-
308C. DBT can be completely oxidized
to the corresponding sulfone in 25 min
under mild conditions, and the
LaW / ACHTNUGTNERNU[G bmim]BF system could be re-
10 4
cycled for ten times with only slight de-
crease in activity. Thus, LaW10 in
1
0
midazolium) as extractant, and H O as
2
2
oxidant. Sulfur removal follows the
order DBT>4,6-DMDBT>BT at
[bmim]BF is one of the most efficient
4
Keywords: desulfurization
· ionic
systems for desulfurization using ionic
liquids as extractant reported so far.
liquids · lanthanides · oxidation ·
polyoxometalates
metalate
Na H LnW O ·32H O
7 2 10 36 2
[7]
[8]
[9]
Introduction
metalates, O /Ti-containing zeolites, H O /ionic liquids,
2 2 2
[
10]
and non-hydrogen peroxide systems, have been explored.
Among these, a combination of oxidative desulfurization
(ODS) and extractive desulfurization is considered to be
one of the most promising processes, whereby organic sulfur
compounds are oxidized selectively to their corresponding
sulfoxides and sulfones, which are removed in a subsequent
extraction process.
Sulfur-containing compounds can be converted to SOx
during combustion processes, which not only results in the
formation of acid rain, but also poisons noble metal catalysts
for reducing CO and NO emissions. As a result, deep desul-
x
furization has become an urgent task for the petroleum re-
fining industry. Thiophene sulfides account for more than
8
0% of the total sulfur content in diesel fuel, and benzo-
Ionic liquids (ILs), as “green” solvents, are in general
nonvolatile, nonexplosive, recyclable, and easy to handle.
The potential and applications of ILs in the above-men-
tioned extraction process have been studied in recent
thiophene (BT) and dibenzothiophene (DBT) account for
70% of thiophene sulfides. Thus, removal of thiophene sul-
[1,2]
fides is a top priority in industry.
industrial method is catalytic hydrodesulfurization (HDS).
The currently adopted
[3]
[11]
years. ILs can extract mono- and polyaromatic sulfur and
Although HDS is efficient in removing thiols, sulfides, and
disulfides from fuels, it is less effective for refractory sulfur-
containing compounds such as DBT and its derivatives.
nitrogen compounds from gasoline and diesel fuel, and they
have shown better performance than conventional solvents.
However, the sulfur-removal efficiency of ionic liquids is
[4]
[12]
The harsh operating conditions and high capital cost of
HDS greatly restrict its application. Under such circumstan-
ces, an efficient method of deep desulfurization without
using hydrogen or high pressure or high temperature is ur-
gently needed. To date, a number of alternative desulfuriza-
tion processes that operate under mild conditions without
using hydrogen have been extensively investigated. Mean-
while, many oxidative desulfurization systems, including
generally in the range of 12–30%. In 2001, a number of
H O /POM systems were used for the oxidation of DBT and
2
2
its derivatives with good selectivity and efficiency in tolu-
[13]
ene.
Although this work shows that oxidation of DBT
could be achieved under relatively mild reaction conditions,
it suffers from the problem of catalyst recovery. In 2003, Lo
[14]
et al. reported one-pot desulfurization by chemical oxida-
tion and solvent extraction with room-temperature ILs. The
advantage of combining chemical oxidation and ionic-liquid
extraction is that the desulfurization yield can be increased
by about an order of oxidative magnitude compared with
[5]
[6]
H O /organic acid, heteropolyacid/SiO2, H O /polyoxo-
2
2
2
2
[
a] J. Xu, S. Zhao, W. Chen, M. Wang, Prof. Y.-F. Song
[15,16]
State Key Laboratory of Chemical Resource Engineering
Beijing University of Chemical Technology
merely extracting with ILs. Recently, Li et al.
investigat-
ed extraction and catalytic desulfurization (ECODS) sys-
tems, and achieved deep desulfurization by using phospho-
tungstic acid, a peroxotungsten complex, and polymolyb-
1
00029 Beijing (P. R. China)
Fax : (+86)10-64431832
E-mail: songyufei@hotmail.com
songyf@mail.buct.edu.cn
dates as catalysts in ILs in the presence of H O .
2
2
Polyoxometalates (POMs) are a class of metal oxide clus-
ters of early transition metals (V, Mo, W, Nb, etc.), and they
show strong Brønsted acidity, fast reversible multi-electron
[
**] bmim=1-butyl-3-methylimidazolium.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102754.
Chem. Eur. J. 2012, 18, 4775 – 4781
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4775

redox transformations under mild conditions, and adjustable
acid–base and redox properties over a wide range.
DBT to DBTO can be achieved in 8 min for EuW and in
12 min for LaW10 at 708C.
2
10
[17–20]
Therefore, the use of POMs as acidic and redox-bifunctional
catalysts in homogeneous and heterogeneous systems is
their most popular and important application area. Among
the many POMs, lanthanide-containing POMs with unique
It has been demonstrated that [bmim]BF functions solely
4
as extractant for sulfur removal from model oil containing
DBT, and only 16.5% sulfur could be extracted to the ionic
[24]
liquid phase. After addition of H O as oxidizing agent to
2
2
4
f-shell electrons show great potential as luminescent mate-
[bmim]BF , sulfur removal reaches 30% after 3 h at
4
[24]
rials, catalysts, magnets, up/downconversion materials, and
so on.
708C.
When both H O
and POM catalyst
2
2
[21,22]
Moreover, effective and efficient use of rare
([WO(O ) ·Phen·H O],
[MoO(O ) ·Phen],
2
2
2
2 2
earths as important strategic resources is an urgent and
highly important research topic. To date, only a few rare
earth and rare earth/transition metal oxides proved to be
able to carry out desulfurization of gasifier effluents at high
temperature. There is plenty of room for the development
of more efficient and wide-ranging catalysts in different ILs
under mild conditions as new desulfurization systems. Here
we report catalytic oxidative desulfurization of DBT, BT,
MoO(O ) ·C H NO , H PMo O ·xH O; Phen=1,10-phe-
2 2 2 5 2 3 12 40 2
nanthroline) are applied for desulfurization in the presence
of [bmim]BF , sulfur removal can exceed 92% after 3 h at
4
[24,25]
708C,
and the [bmim]BF /Na MoO system yields 99%
4
2
[15]
4
[23]
sulfur removal after 3 h at 708C. These results show the
advantage of ECODS with IL over desulfurization by cata-
lytic oxidation without IL. Furthermore, our experimental
results show that lanthanide-containing POMs EuW10 and
LaW10 exhibit great potential for sulfur removal in the
ECODS process.
and
4,6-DMDBT
in
model
oil
by
applying
Na EuW O ·32H O and Na LaW O ·32H O as catalysts
9
10 36
2
9
10 36
2
in the presence of H O as oxidant, and 1-butyl-3-methylimi-
2
2
dazolium tetrafluoroborate ([bmim]BF4) as extractant.
These systems have shown high efficiency for deep desulfur-
ization under mild conditions, and the catalyst can be recy-
cled at least ten times without obvious loss of activity.
Effect of temperature on sulfur removal of DBT: To investi-
gate the effect of temperature on sulfur removal, oxidation
of DBT was studied at different temperatures (Figure 1).
The H O / ACHTUNGRTNEUNG[ bmim]BF /EuW system shows 100% desulfuri-
2 4 10
2
zation of DBT at 30, 40, 50, 60, and 708C after 30, 25, 15,
0, and 8 min, respectively. The H O /[bmim]BF /LaW
1
ACHTUNGTRENNUNG
2
2
4
10
Results and Discussion
system reaches 100% sulfur removal after 40, 30, 25, 20, and
2 min at 30, 40, 50, 60, and 708C, respectively. Thus, DBT
can be completely removed at room temperature in a rela-
tively short reaction time. Although the H O /[bmim]BF /
1
Investigation of different desulfurization catalysts: The ionic
liquid [bmim]BF was selected for sulfur removal here, as it
ACHTUNGTRENNUNG
2
4
2
4
shows remarkable selectivity for absorption of aromatic S-
containing molecules from model oil. The catalytic activi-
EuW10 system shows a better catalytic oxidative desulfuriza-
tion effect than H O /[bmim]BF /LaW , the latter was se-
[1]
ACHTUNGTRENNUNG
2
2
4
10
ties of different [bmim]BF /POM catalysts for desulfuriza-
lected for the following study for economic reasons.
4
tion of DBT with hydrogen peroxide as oxidant are listed in
Table 1. The selected POMs are H PMo O ·xH O,
3
12 40
2
H PMo V O , Na H EuW O ·32H O (EuW10) and
3
10
2
40
7
2
10 36
2
Na H LaW O ·32H O (LaW ). The conversion of DBT in-
7
2
10 36
2
10
creases from 78 to 93% for [bmim]BF /H PMo O
12 40
4
3
(
Table 1, entry 1) and from 67 to 99% for [bmim]BF4/
H PMo V O (Table 1, entry 2) at 708C after 30 and
3
10
2
40
180 min, respectively. Compared to the classical POM cata-
lysts with Keggin structure, lanthanide-containing POMs
EuW10 (Table 1, entry 3) and LaW10 (Table 1, entry 4) in
[
bmim]BF show remarkable sulfur removal in the presence
4
of H O . Deep desulfurization with 100% conversion of
2
2
Figure 1. Times for 100% sulfur removal at different temperatures with
[
a]
EuW10/IL and LaW10/IL systems in the presence of H
ditions: H 0.048 mL, model oil 5 mL (S content 1000 ppm), IL
[bmim]BF ) 1 mL, H /DBT/catalyst 60:20:1.
2 2
O . Reaction con-
Table 1. Sulfur removal by different catalysts.
2
O
2
Entry
1
Catalyst
t [min]
S removal [%]
(
4
2 2
O
H
3
PMo12
O
40
30
78
93
67
99
100
100
1
1
80
30
80
8
2
H
3
PMo10
V
2
O
40
Effect of H O /DBT molar ratio on the desulfurization of
2
2
model oil: H O is a unique oxidizing agent in the oxidative
2
2
3
4
Na
Na
7
7
H
H
2
EuW10
O
36
desulfurization system. To elucidate the influence of the
amount of H O on the desulfurization, different H O /DBT
2
LaW10
O
36
12
2
2
2
2
[
a] Experimental conditions: T=708C, H
oil 5 mL (S content 1000 ppm), [bmim]BF
0:20:1.
2
O
2
0.048 mL as oxidant, model
molar ratios were applied under the experimental conditions
of T=308C, 5 mL model oil (S content 1000 ppm), 1 mL
4
2 2
1 mL, H O /DBT/catalyst
6
4776
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4775 – 4781

Extraction and Oxidative Desulfurization System
FULL PAPER
[
bmim]BF , molar DBT/LaW ratio 20:1. The catalytic reac-
4
1
0
tion time for more than 99% sulfur removal of DBT de-
creases gradually from 55 to 15 min when the H O /DBT
2
2
molar ratio is increased from 2:1 to 10:1 (Table 2, entries 1–
). Thus,H O /DBT molar ratio has great influence on the
5
2
2
reaction time. The observed competition between hydrogen
peroxide decomposition and DBT oxidation is in line with
[16]
the results of Li and co-workers.
2 2
Table 2. Effect of H O /DBT molar ratio on 99% sulfur removal by the
[a]
4
LaW10/ ACHTUNGTRENNUNG[ bmim]BF system at 308C.
1
Figure 2. H NMR (CDCl
DBTO (standard). Experimental conditions: T=308C, H
model oil 5 mL (S content 1000 ppm), IL 1 mL, H /DBT 5:1.
3
) spectra of DBT, DBTO
2
(recovered), and
Entry
H
2
O
2
/DBT
t [min]
2
2 2
O
0.048 mL,
1
2
3
4
5
2
3
5
8
10
55
40
25
20
15
2 2
O
spectrum of the thus-recovered DBTO is similar to that of
2
standard DBTO (Figure 2). The FTIR spectrum of the ten-
2
[
[
a] Reaction conditions: T=308C, model oil 5 mL (S content 1000 ppm),
bmim]BF 1 mL, DBT/LaW10 20:1.
fold-recycled [bmim]BF4 is the same as that of fresh
4
[
bmim]BF (Figure S3b, Supporting Information), that is, the
4
structure of [bmim]BF is retained during the reaction.
4
Effect of DBT/LaW10 molar ratio on the desulfurization of
model oil: Experiments with different DBT/LaW10 molar
ratios showed that the time for almost 100% sulfur removal
is shortened from 50 to 30 min when the DBT/LaW10 molar
ratio is increased from 100:2 to 100:10 in the presence of
Kinetic study on catalytic oxidation of sulfur compounds: To
obtain the kinetic parameters for oxidation of DBT, experi-
ments were performed with the LaW / ACHTUNGTRENN[NUG bmim]BF /H O
10 4 2 2
system (H O /DBT/LaW 500:100:5) at 308C. Percentage
2
2
10
sulfur removal and ln ACHTUNGTRNEGNU( C /C ) are plotted against reaction
t 0
0
.048 mL of H O2 (Table 3, entries 1–3). Furthermore, by
time in Figure 3, in which C and C are initial DBT concen-
2
0
t
slightly increasing the amount of H O to 0.080 mL, 100%
2
2
sulfur removal can be achieved in only 25 min at room tem-
perature with the optimized H O /DBT/LaW molar ratio
2
2
10
of 500:100:5 at room temperature (Table 3, entry 5).
Table 3. Effect of DBT/LaW10 molar ratio on sulfur removal by the
[a]
LaW10
/
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[bmim]BF
4
system at 308C.
Entry
H
2
O
2
/DBT/LaW10
H
2
O
2
[mL]
t [min]
S removal [%]
1
2
3
4
5
6
7
300:100:10
300:100:5
300:100:2
500:100:10
500:100:5
500:100:2
500:100:1
0.048
0.048
0.048
0.080
0.080
0.080
0.080
30
40
50
15
25
30
40
99
99
99
99
100
99
t 0
Figure 3. Sulfur removal of DBT and ln ACHTNUGTRENNGU(N C /C ) as functions of reaction
time at 308C. H O /DBT/LaW10 500:100:5.
2 2
99
[
[
a] Reaction conditions: T=308C, model oil 5 mL (S content 1000 ppm),
bmim]BF 1 mL.
4
tration and DBT concentration at time t, respectively. The
linear fit of the data reveals that the catalytic reaction ex-
hibits pseudo-first-order kinetics for the desulfurization of
Influence of recycling IL/LaW10 and recovery of DBTO2:
Use of recycled LaW /[bmim]BF for further oxidation of
DBT was investigated. After the first run, the upper layer
was separated by decantation. To speed up volatilization of
residual model oil, the IL phase was distilled in an oil bath
at 708C for 10 h, and then fresh model oil and H O were in-
troduced for the next recycle. The system could be recycled
at least ten times without significant decrease in catalytic
sulfur removal (from 100 to 94.3%; see Table S1 of the Sup-
porting Information). After the tenth cycle, the IL phase
2
A
H
U
G
R
N
N
sulfides (R =0.9923). The rate constant k of the oxidation
1
0
4
ꢀ
1
reaction was determined to be 0.2288 min on the basis of
Equations (1) and (2). Oxidation of DBT to DBTO could
2
be complete in about 25 min. Thus, the catalyst exhibits high
catalytic efficiency for oxidation of sulfide to sulfone, and
the catalytic reaction strictly obeys pseudo-first-order kinet-
ics with 100% selectivity for DBTO2.
2
2
ꢀdC
lnðC =C Þ ¼ kt
=dt ¼ kC
ð1Þ
ð2Þ
t
t
was extracted with CHCl at room temperature, and the sol-
vent of the extract evaporated under vacuum. The H NMR
3
1
0
t
Chem. Eur. J. 2012, 18, 4775 – 4781
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4777

Y.-F. Song et al.
Table 4. Catalytic oxidative desulfurization of DBT by POM/IL systems.
[
a]
Entry
Catalyst
Extractant
DBT/cat
H
2
O
2
/DBT
T [8C]
t [min]
S
A
H
U
G
R
N
N
[ppm]
S removal [%]
Ref.
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[(C
4
H
9
)
4
N]
N]
(C
4
W
10
O
32
A
H
U
G
E
U
G
6
6
6
6
6
100
100
100
100
ꢁ50
20
3
3
3
3
3
3
3
3
5
3
4
4
4
4
6
4
5
5
5
5
60
60
60
60
60
60
60
60
60
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
60
10
20
25
20
60
60
60
60
60
120
180
20
40
30
25
1000
1000
1000
1000
500
1000
1000
1000
1000
1000
500
500
500
500
1000
–
98
97
66
95
98
99
99
99
99
98
81
96
77
99
99
99
99
99
99
100
[9]
[9]
[9]
[9]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[(CH
3
)
4
4
W
10
O
32
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[(C
Na
[(C
2
H
W
H
5
)
3
N
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
7
H
7
)]
4
W
10
O
32
4
10
O
32
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
8
17
)
3
NCH
3
]
2
W
6
O
19
[26]
EuW10
LaW10
LaW10
LaW10
4
this work
this work
this work
this work
[27]
[16]
[16]
[16]
[16]
[28]
[25]
this work
this work
this work
this work
4
4
4
4
4
20
100
100
100
120
120
120
120
20
10
20
100
50
20
1
1
1
1
1
1
1
1
1
1
2
H
3
PW12
O
40
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PSPy]
[PSPy]
[PSPy]
[PSPy]
3
3
3
3
PW12
PW12
PW12
PW12
O
O
O
O
40
40
40
40
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
4
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
V
2
O
5
4
MoO(O
EuW10
LaW10
LaW10
LaW10
2
)
2
C
2
H
5
NO
2
6
4
4
4
4
1000
1000
1000
1000
[
6
a] PSPy=1-(3-sulfopropyl)pyridinium; [omim]PF =1-octyl-3-methylimidazolium hexafluorophosphate.
It is instructive to compare the catalytic oxidative desul-
furization of DBT by IL/POM systems reported so far
Table 4). A few decatungstates with short-chain tetraalkyl
Sulfur removal of BT and 4,6-DMDBT: The performance of
the LaW /[bmim]BF system with different substrates in-
AHCTUNGTNERNUG
10
4
(
cluding BT, DBT, and 4,6-DMDBT was evaluated with
H O as oxidant under mild conditions. It is known that, due
ammonium cations were used as catalysts for extractive cat-
alytic oxidative desulfurization in [bmim]PF with H O as
2
2
to steric hindrance, it is very difficult to remove 4,6-
DMDBT in the HDS process. Under our experimental con-
ditions using ECODS, the LaW / ACHTGNUTRNEUNG[ bmim]BF system exhibits
10 4
high desulfurization efficiency for different substrates in-
cluding DBT, BT, and 4,6-DMDBT. The sulfur content
could be reduced from 1000 to 117 ppm in 90 min at 308C
for BT (Table 5, entry 2), and from 1000 to 48 ppm for 4,6-
6
2
2
oxidant (Table 4, entries 1–4). The best desulfurization
result reported so far was obtained under the experimental
conditions of H O /DBT/decatungstate=300:100:1 at 608C,
2
2
and 98% sulfur removal could be obtained in 30 min. By
utilizing lanthanide-containing POMs as catalysts, we ach-
ieved 99% sulfur removal in only 10 min with H O /DBT/
2
2
EuW10 (60:20:1) at 608C (Table 4, entry 6) and in 20 min
with H O /DBT/LaW (500:100:1) at 608C (Table 4,
entry 9). Recently, three interesting hexatungstate/
2
2
10
Table 5. Sulfur removal of BT and 4,6-DMDBT with LaW10/ ACHTUNGTRENNUNG[ bmim]BF
4
system at 308C.
[a]
[26]
H O / ACHTUNGTRENNUNG[ omim]PF emulsion systems (Table 4, entry 5) were
2 6
2
Entry Catalyst Extractant Substrate
DBT/cat S removal [%]
reported by Li and co-workers, and these multiphase sys-
tems show relatively good sulfur removal efficiency at 608C.
When the catalytic reaction is performed at room tempera-
ture, the sulfur level of actual FCC (fluid catalytic cracking)
gasoline could be reduced from 360 to 70 ppm in the
1
2
3
4
LaW10
LaW10
LaW10
LaW10
A
T
N
R
N
U
G
4
4
4
4
BT
BT
50
20
63
80
73
92
AHCTUNGTRENNUNG
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
4,6-DMDBT 20
[a] Reaction conditions: T=308C, model oil 5 mL (S content 1000 ppm),
[bmim]BF 1 mL, H /substrate 5:1, t=90 min.
ECODS by using H O /
A
H
U
G
R
N
N
[PSPy] PW O in ionic liquids
4
2 2
O
2
2
3
12 40
(
Table 4,
MoO(O ) ·C H NO and H O /AHCTUNGTERNNUNG
2
entries 11–14).
When
H O / ACHTUTGNERNN[UG bmim]PF /
2 2 6
[bmim]BF /V O are used,
2
2
2
5
2
2
4
2
5
although the reaction can be performed at room tempera-
ture, relatively long reaction times are necessary to reach
high degrees of oxidative desulfurization (Table 4, entries 15
and 16). Interestingly, deep desulfurization of fuels catalyzed
DMDBT (Table 5, entry 4) under mild conditions with sub-
strate/LaW =20:1. When the substrate/LaW ratio was in-
1
0
10
creased from 20:1 to 50:1, sulfur removal decreased from 80
to 63% for BT, and from 92 to 73% for 4,6-DMDBT. This
may be because the active centers are not sufficient to cata-
lyze the reaction when the substrate/LaW10 ratio increases
from 20 to 50. The reactivity of sulfur removal follows the
order DBT>4,6-DMDBT>BT under mild conditions with
by H O / ACHTUNGTRENNUNG[ bmim]BF /H PW O shows very good results in
2 4 3 12 40
2
60 min at 308C (Table 4, entry 10). In contrast, deep oxida-
tive desulfurization of DBT by H O /LaW in [bmim]BF4
2
2
10
could be accomplished in 30 min at room temperature with
H O /DBT/LaW =500:100:2 (Table 4, entry 19), which is,
the LaW10/ ACHTUNEGRTNNUNG[ bmim]BF system, which may be correlated with
4
2
2
10
to the best of our knowledge, one of the most efficient sys-
tems using ionic liquids reported so far.
the electronic density of S atoms and the steric hindrance of
the substituents on the substrates. Among the three sub-
strates, BT has the lowest electron density at the S atom,
[29]
4778
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4775 – 4781

Extraction and Oxidative Desulfurization System
FULL PAPER
as well as the lowest reactivity. The difference in electron
density of 4,6-DMDBT and DBT is very slight. Hence, the
steric hindrance of the substrates plays a vital role in sulfur
removal of 4,6-DMDBT and DBT.
sic systems in which DBT is in the oil phase, while LaW10
and H O are in the IL phase. Comparative experiments
2
2
using H O /EuW and H O /LaW as desulfurization sys-
2
2
10
2
2
10
tems showed almost no sulfur removal in the absence of IL
(
Table 7, entries 2 and 3), which suggests that oxidation does
Influence of different extractants on sulfur removal: When
solely extractants including
[bmim]BF4,
[omim]BF4,
[a]
Table 7. Sulfur removal by different desulfurization systems.
[
omim]PF , and [bmim]PF were used for desulfurization of
6
6
Entry
Extractant
Oxidant
Catalyst
t [min]
S removal [%]
DBT-containing model oil, sulfur removal could reach only
less than 15% in 1 h at 308C. When catalysts, H O , and
ionic liquid were employed together, sulfur removal in-
creased dramatically. For example, catalytic oxidative desul-
furization of DBT with [omim]PF or [bmim]PF as extrac-
1
2
3
4
5
6
7
A
T
N
T
E
U
G
4
H
H
H
2
2
2
O
O
O
2
2
2
2
2
2
2
–
60
60
60
60
60
60
60
15
–
2
2
–
–
–
–
EuW10
LaW10
Eu O
La
Eu
–
–
–
H O
2
2
3
H
H
H
2
2
2
O
O
O
2
O
3
6
6
A
H
U
G
R
N
N
4
4
2
O
3
23
16
tant gave sulfur removal in the range of 86–94% in 1 h
Table 6). In contrast, when [omim]BF is used as extractant,
A
H
U
G
R
N
N
La
2
O
3
(
4
[
a] Reaction conditions: T=308C, H
2
O
2
0.048 mL, model oil 5 mL (S
/DBT/catalyst 60:20:1.
greater than 99% sulfur removal could be reached for
EuW10 in 18 min and LaW10 in 22 min, that is, [omim]BF4
could be a very efficient extractant.
content 1000 ppm), [bmim]BF
4
1 mL, H
2
O
2
not take place without IL. On addition of [bmim]BF , sulfur
4
Table 6. Effect of different ionic liquids on sulfur removal of DBT at
[
a]
removal increases significantly, and this suggests that the or-
ganic sulfur has been oxidized in the presence of ionic
liquid. This experiment shows that the substrates could be
extracted by [bmim]BF4 from the oil phase into the IL
phase, where they are further oxidized by active POM-con-
taining peroxo species. The H O /Eu O and H O /La O
3
3
08C.
Entry
Catalyst
IL
[omim]BF
[omim]PF
[bmim]PF
[omim]BF
t [min]
S removal [%]
1
2
3
4
5
6
EuW10
EuW10
EuW10
LaW10
LaW10
LaW10
A
H
N
T
E
N
N
4
18
60
60
22
60
60
99
94
90
99
88
86
A
H
U
T
N
U
G
6
A
H
U
T
E
U
G
6
A
H
U
G
R
N
N
4
2
2
2
3
2
2
2
A
H
U
T
E
N
N
6
6
systems show no conversion (Table 7, entries 4 and 5). The
AHCTUNGTRENNUNG
presence of [bmim]BF in the above systems can slightly in-
4
[
0
a] Reaction conditions:
H
2
O
2
/DBT/LaW10 500:100:5,
.080 mL, T=308C, model oil 5 mL (S content 1000 ppm), [omim]BF
or [bmim]PF 1 mL.
V
A
H
U
G
R
N
U
G
2
O
2
)=
crease the degree of desulfurization to 23.5% for
4
or
H O / ACHTUNGTRENNNGU[ bmim]BF /Eu O and 16.3% for H O / AHCNGERTUTNNUG[ bmim]BF /
2 4 2 3 2 2 4
2
[
omim]PF
6
6
La O (Table 7, entries 6 and 7), but sulfur removal efficien-
2
3
Proposed mechanism of the desulfurization process: The ex-
traction and catalytic oxidation mechanism when using
LaW / ACHTUNGTRENNUNG[ bmim]BF biphasic system in the presence of H O
10 4 2 2
cy is still quite low.
3
+
To better understand the role of Ln ions, a number of
lanthanide-containing sandwich clusters, including YW10,
CeW , NdW , SmW , GdW , TbW , ErW , and YbW ,
as oxidant is similar to those of other ECODS processes re-
1
0
10
10
10
10
[30]
10
10
[9]
ported so far. As shown in Scheme 1, immiscibility of
bmim]BF with model oil results in the formation of bipha-
were prepared and characterized.
ments on the catalytic oxidative desulfurization of DBT in-
dicate that all of these H O /DBT/LnW systems can oxi-
Preliminary experi-
[
4
2
2
10
dize DBT under mild conditions with relatively good sulfur
removal efficiency (Table 8). We note that LaW10 and
EuW10 are more effective desulfurization catalysts than
other LnW , provided that the same catalytic reaction con-
1
0
Table 8. Sulfur removal with different lanthanide-containing POMs as
[
a]
catalyst.
Entry
Catalyst
t [min]
S removal [%]
1
2
3
4
5
6
7
8
9
YW10
40
25
30
40
35
20
30
35
30
40
99
99
99
100
99
99
99
99
99
100
LaW10
CeW10
NdW10
SmW10
EuW10
GdW10
TbW10
ErW10
YbW10
1
0
[
a] Reaction conditions: T=308C, model oil 5 mL (S content=
Scheme 1. Schematic description of the desulfurization process using
[bmim]BF in the presence of H
1000 ppm), [bmim]BF
0.080 mL.
4 2 2 2 2
1 mL, H O /DBT/catalyst 500:100:5, V ACHTUNGTRENNUNG( H O )=
LaW10
/
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
4
2 2
O .
Chem. Eur. J. 2012, 18, 4775 – 4781
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4779

Y.-F. Song et al.
ditions are applied. Comparative experiments (Supporting
Information, Table S3) using other sandwich-type POMs
GC system by using a 30 m 5% phenymethyl silicone capillary column
with an ID of 0.32 mm and 0.25 mm coating (HP-5).
[31]
Preparation of catalysts: Lanthanide-containing POMs with molecular
such as K10
(H O)2 A( ZnW O ) ]·42H O
effective sulfur removal compared to LaW . Based on these
ACHTUNGTRENNUNG[ Co4 ACHTUNGTRENNUNG( H O) AHTCUGNTREUNN(NG PW O ) ]·20H O and Na AHTUNCGTERUNNGN[ WZn -
2 2 9 34 2 2 12 3
formula Na
7 2 2
H LnW10O36·32H O (LnW10; Ln=Y, La, Ce, Nd, Sm, Eu,
[32]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
C
H
T
U
N
G
T
R
E
N
N
U
N
G
for desulfurization show less
2
9
34
2
2
Gd, Tb, Er, Yb) were synthesized and characterized according to the pro-
[30]
1
0
cedure reported in the literature.
LaW10: Na WO ·2H O (41.5 g, 0.126 mol) was dissolved in 100 mL of
water and the pH of the solution was adjusted to 7.0–7.5 with acetic acid.
An aqueous solution containing 4.58 g of EuCl ·6H O or 4.64 g of
LaCl ·7H O was added dropwise to the above solution and the resulting
Typical preparation of EuW10 or
experimental results, we propose that, due to the unique 4f
2
4
2
3
+
orbitals of Ln ions, the lanthanide-containing POMs with
Ln(W ) sandwich structure have a profound influence on
3
2
5
2
3
2
electron migration on the POMs, the “secondary structure”
of the POMs, and hence the catalytic activity.
solution was reduced to 50 mL by heating. Then, the solution was cooled
to 58C and allowed to stand overnight. The resulting crystals were recrys-
tallized three times from warm water. LnW10 were characterized in the
solid state by IR spectroscopy (KBr pellet): EuW10 (Figure S1a of the
The catalytic oxidation process involves the formation of
POM peroxo species as active centers in the presence of
ꢀ
1
Supporting Information): 932, 845, 704, 578, 547, 489 cm ; LaW10 (Fig-
VI
H O . The catalytic cycle starts from the attack of W =O
2
2
ure S1b of the Supporting Information): 948, 844, 790, 705, 570, 541,
species to generate tungsten peroxo radicals. This radical
species can oxidize DBT, extracted by ionic liquid from oil
ꢀ1
5
83 cm
.
The ionic liquids [bmim]BF4, [bmim]PF
6 4 6
, [omim]BF , and [omim]PF
phase to the IL phase, to DBTO . When DBT in the IL
were purchased from Aldrich and used directly without further purifica-
2
[31]
tion. The POMs Na12
(H O) (PW ]·20H
ing to the literature.
A
H
U
G
R
N
N
[WZn
2
O
3
A
T
N
T
E
N
N
2
O)
2
A
T
N
T
N
U
G
9
O
34
)
2
]·42H
2
O
4
and K10 ACHTUNGTRENNUNG[ Co -
phase is oxidized, DBT in the model oil phase is further ex-
tracted into the IL phase to keep the extraction process in
[
32]
A
H
N
T
E
N
N
2
2
A
H
U
T
E
N
N
9
O
34
)
2
were synthesized and characterized accord-
V
equilibrium. At the same time, the reduced W species is
Desulfurization procedure and analysis of sulfur content: A solution of
DBT, BT, and 4,6-DMDBT in n-octane was used as model oil with an S
content of 1000 ppm. In a typical experiment, an oil bath was heated to
a certain temperature (70, 60, 50, 40, or 308C). The catalytic oxidative
desulfurization experiments were performed in a stirred 50 mL two-
VI
oxidized back to W =O, and formation of tungsten peroxo
radicals in the presence of H O is accompanied by the start
2
2
of a new cycle (Scheme 1).
necked flask, to which 0.048 mL of 30 wt% H
mL of [bmim]BF , and 26.5 mg of LaW10 were added. The resulting
molar ratio is H /DBT/LaW10 =60:20:1. During the reaction, samples
2 2
O , 5 mL of model oil,
1
4
Conclusion
2
O
2
of the upper oil phase were periodically withdrawn and analyzed by gas
chromatography coupled with a flame ionization detector (GC-FID). The
contents of DBT, BT, and 4,6-DMDBT were determined by using refer-
ence standards. The conditions were as follows: injection port tempera-
ture 3408C; detector temperature 2508C; oven temperature 708C; carrier
gas: ultrapure nitrogen; sample injection volume 1 mL.
Deep oxidative desulfurization of DBT, BT, and 4,6-
DMDBT has been achieved by the combined extractive and
oxidative desulfurization system LaW / ACHTUNGTRNENUG[ bmim]BF in the
10 4
presence of H O as oxidant. The reaction conditions, in-
2
2
cluding the effect of the amounts of catalyst and H O , reac-
2
2
tion temperature, and recyclability of catalyst, have been in-
vestigated in detail. It is noteworthy that the reaction time
for almost 100% sulfur removal is only 25 min with the opti-
mized H O /DBT/LaW molar ratio of 500:100:5 at 308C.
Acknowledgements
2
2
10
On extending the substrates to 4,6-DMDBT and BT, sulfur
removal efficiency follows the order of DBT>4,6-
DMDBT>BT under mild conditions. Owing to easy prepa-
ration, simple workup procedures, high conversion, short re-
This research was supported by the National Science Foundation of
China (21076020, 20801003), the 973 (2011CBA00504) and 863
(2010AA03A403) projects, the program for New Century Excellent Tal-
ents of the Ministry of Education of China (NCET-09-0201), the Beijing
Nova Program (2009B12), and the Scotland–China Higher Education Re-
search Partnership.
action time, and recyclability, the LaW / ACHTUNGTRNEGNU[ bmim]BF system
10 4
for deep desulfurization of DBT, BT, and 4,6-DMDBT
under mild conditions has great potential for further indus-
trial application.
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www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4775 – 4781

Extraction and Oxidative Desulfurization System
FULL PAPER
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Received: September 4, 2011
Published online: February 28, 2012
2
Chem. Eur. J. 2012, 18, 4775 – 4781
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4781