Trifluoromethanesulfonic acid-based DESs as extractants and catalysts for removal of DBT from model oil

Article abstract of DOI:10.1039/c6ra28448e

A series of deep eutectic solvents (DESs) of ChCl/XCF₃SO₃H (X from 1.0 to 2.0) were synthesized by stirring a mixture of choline chloride (ChCl) and trifluoromethanesulfonic acid (CF₃SO₃H) at room temperature. The DESs were characterized by Fourier transform infrared (FT-IR) and ¹H nuclear magnetic resonance (¹H NMR). The oxidative desulfurization of model oil was investigated using ChCl/1.5CF₃SO₃H as a catalyst and extraction agent, and H₂O₂ as the oxidant. Some reaction parameters such as type of DES, molar ratio of CF₃SO₃H and ChCl in DESs, H₂O₂ dose, reaction temperature, DES dose and type of sulfur compound were investigated. Under the optimum conditions, the removal rate of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) can reach up to 98.65% and 96.8%, respectively. After five recycling runs, the removal rate of DBT can still reach 97.16%.

Full text of DOI:10.1039/c6ra28448e

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Trifluoromethanesulfonic acid-based DESs as
extractants and catalysts for removal of DBT from
model oil
Cite this: RSC Adv., 2017, 7, 12805
*
Chunfeng Mao, Rongxiang Zhao, Xiuping Li and Xiaohan Gao
A series of deep eutectic solvents (DESs) of ChCl/XCF3SO3H (X from 1.0 to 2.0) were synthesized by
stirring a mixture of choline chloride (ChCl) and trifluoromethanesulfonic acid (CF3SO3H) at room
temperature. The DESs were characterized by Fourier transform infrared (FT-IR) and 1H nuclear
magnetic resonance (1H NMR). The oxidative desulfurization of model oil was investigated using
ChCl/1.5CF3SO3H as a catalyst and extraction agent, and H2O2 as the oxidant. Some reaction
parameters such as type of DES, molar ratio of CF3SO3H and ChCl in DESs, H2O2 dose, reaction
temperature, DES dose and type of sulfur compound were investigated. Under the optimum
conditions, the removal rate of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-
DMDBT) can reach up to 98.65% and 96.8%, respectively. After five recycling runs, the removal rate
of DBT can still reach 97.16%.
Received 20th December 2016
Accepted 10th February 2017
DOI: 10.1039/c6ra28448e
rsc.li/rsc-advances
In recent years, a Brønsted acid based ionic liquid was used
in the oxidative desulfurization process. Fang et al.11 reported
1 Introduction
the synthesis of 1-butyl-3-methyl-imidazolium triuoroacetic
acid ([C4mim]TFA) ionic liquids and their application in
oxidative desulfurization and found that the anion of the ionic
liquid has an important inuence on the desulfurization rate.
Lu et al.12 synthesized 1-methylimidazolium tetrauoroborate
([HMIm]BF4) ionic liquids and the sulfur removal of DBT in
model oil can reach 93% under optimum conditions. Gao
et al.13 synthesized an acidic ionic liquid N-butyl-N-methyl-
imidazolium hydrogen sulfate ([BMIm]HSO4), its oxidative
desulfurization rate can reach 100% for DBT in model oil. The
[BMIm]HSO4 ionic liquid can be recycled 5 times with only
a slight reduction in activity. Zhao et al.14 synthesized the
Brønsted acid ionic liquid N-methyl-pyrrolidonium tetra-
uoroborate ([Hnmp]BF4) and used as the extractant and cata-
lyst for desulfurization (ODS) of model oil. The experimental
results indicated that 99.4% sulfur compounds in diesel fuel
can be removed. Although these ionic liquids have better
desulfurization activity in the oxidative desulfurization system,
the raw materials of ionic liquids are expensive and the prepa-
ration process is complex.
As a new type of solvent, deep eutectic solvents have attracted
great attention because of its excellent physical and chemical
properties, which is friendly for environment. DESs are
composed of two or more components that interact via inter-
molecular hydrogen bonds.15 Compared with the traditional
ionic liquids, DESs have many advantages such as cheap and
easily accessible raw material, a simple preparation process,
and wide range of applications.16 In developmental history of
DESs, ChCl-based DESs are rst reported by Abbott and his co-
SOx emission, which is mainly produced by vehicles, not only
pollutes the environment, such as acid rain,1 but also harms the
health of humans, such as cancer. In order to decrease the
pollution caused by SOx, many countries have laid down a series
of rules for restricting the sulfur content of fuel oil. It is an aim
to achieve little sulfur in oil (sulfur content < 10 mg gꢀ1).2 The
traditional hydrodesulfurization (HDS) process, removing
aliphatic and acyclic sulfur compounds, has been considered as
a mature technology. However, HDS nds it difficult to remove
aromatic sulfur compounds3,4 such as thiophene (TH), benzo-
thiophene (BT) dibenzothiophene (DBT) and their derivatives
because of their large steric hindrance. Therefore, some non-
hydrodesulfurization processes, such as oxidative desulfuriza-
tion (ODS),5 biodesulfurization (BDS),6 extractive desulfuriza-
tion (EDS)7 and adsorption desulfurization (ADS),8 etc., have
attracted wide attention.
Among these non-hydrodesulfurization processes, oxidative
desulfurization (ODS) was considered as one of the most
promising technologies due to its advantages,9 such as the high
desulfurization rate and the mild reaction conditions. Various
oxidants such as H2O2, NO2, O2, O3, K2FeO4, and organic
peroxides have been investigated in the oxidative desulfuriza-
tion system. Among these oxidants, H2O2 is widely employed
due to its high activity and low price.10
College of Chemistry, Chemical Engineering and Environmental Engineering, Liaoning
Shihua University, Fushun 113001, China. E-mail: maochunfeng555@163.com;
zylhzrx@126.com
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workers, its physical properties have been researched.17 There- Chemical Reagent Co. Ltd. Gas chromatography was carried
aer, DESs are used in various elds such as electrochemistry, out on an Agilent 7890A GC with an FID detector using a 30 m
organic synthesis and separation processes.18–21 DESs also are packed HP5 column. Infrared spectra of DBT, oxidation of
used in the desulfurization process of fuels. For example, Zhu DBT, DESs and raw materials were determined on Fourier-
et al.22 reported the synthesis of ChCl$2CH3COOH and it was transform infrared spectrometer (WQF-520; Beijing Beifen
used as the extractant of oxidation desulfurization process. The Ruili Instrument Company, China). 1H NMR of DESs were
study found that the removal rate of DBT in model oil can up to determined by using the Mercury Plus 400 MHz spectrometer
98.6% under UV light irradiation. Gano Z. S. et al.23 reported (Varian Co., Ltd. American).
that the FeCl3-based deep eutectic solvents for the extractive
desulfurization of liquid fuels. Experimental results show the
2.2 Synthesis of ChCl/XCF3SO3H
desulfurization efficiencies of 64% and 44% can be achieved for
ChCl/XCF3SO3H was synthesized by stirring a mixing of ChCl
DBT and thiophene, respectively. Yin et al.24 reported that the
and CF3SO3H at room temperature. The specic process is as
synthesis of ChCl/p-TsOH and the desulfurization efficiencies of
follows: ChCl was added to a 100 mL round-bottomed ask.
ChCl/p-TsOH can reach up to 97.25%, which are much higher
Then, the CF3SO3H was carefully added according to a certain
than those obtained with traditional and functional ionic
molar ratio under stirring conditions. The two raw materials
liquids. Our research group has synthesized phenylpropanoic
were stirred vigorously for 1 h in order to fully release the
acid-based DESs and was applied to the oxidation desulfuriza-
reaction heat. Aer the reaction, the ChCl/XCF3SO3H (X from
1.0 to 2.0) DESs homogeneous liquid was obtained. The reac-
tion process.25 In the synthesis, the acid-based DESs was
synthesized by heating method. As is known to all, simpler
tion was shown in Fig. 1. TBAC/CF3SO3H and TEAC/CF3SO3H
preparation process and higher acidity of DESs are favorable for
were synthesized according to the same method.
the desulfurization.26 Therefore, it is necessary to develop a new
1H NMR spectra of CF3SO3H, ChCl and ChCl/CF3SO3H were
DES using a simple preparation method and apply it to the
obtained on hydrogen spectrum detector. Coupling constants
oxidative desulfurization process.
(J1) in Hz and chemical shis (d) are given in ppm. The
Triuoromethanesulfonic acid (CF3SO3H) is one of the
multiplicities of signals in 1H NMR are given with chemical
strongest organic acids, it is widely used in the synthesis reac-
tion. In this work, the novel CF3SO3H-based DESs were
synthesized by stirring a mixture of ChCl and CF3SO3H at the
room temperature. The removal rate of DBT from model oil was
investigated using CF3SO3H-based DESs as an extraction agent
and catalyst, H2O2 as the oxidant. The inuence of different type
DESs, the molar ratio of ChCl to CF3SO3H, the oxygen to sulfur
(O/S) molar ratio, the reaction temperature and the amount of
shis (s ¼ singlet, d ¼ doublet, t ¼ triplet, q ¼ quartet, m ¼
multiplet), and the data are listed as follows:
1
CF3SO3H for H NMR (500 MHz, D2O) d 4.86 (s, 1H).
1
ChCl for H NMR (500 MHz, D2O) d 4.71 (d, 26H), 4.08 (m,
59H), 3.56–3.46 (m, 39H), 3.25 (s, J ¼ 68.7 Hz, 30H), 3.18 (d,
176H), 3.03 (s, 2H).
1
ChCl/CF3SO3H for H NMR (500 MHz, D2O) d 4.77 (s, 2H),
3.90 (ddd, J ¼ 7.7, 5.3, 2.8 Hz, 1H), 3.35 (dd, J ¼ 5.8, 4.2 Hz, 1H),
DESs on the desulfurization rate was investigated. Under the
optimum conditions, the removal rate of dibenzothiophene
3.04 (s, 5H).
(DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) can
reach up to 98.65% and 96.8%, respectively. Aer ve recycling
2.3 Desulfurization experiment
The 500 mg gꢀ1 model oil was prepared by dissolving 1.437 g
DBT in 500 mL n-octane. The model oil, DESs, and 30 wt% H2O2
were added into a three-necked ask. The mixture was stirred in
a water bath at a certain temperature. A small amount of the
upper oil phase was removed every 20 min and determined by
gas chromatography. The desulfurization rate was calculated
using the following formula:
runs, the removal rate of DBT can still reach 97.16%.
2 Experimental
2.1 Chemical regent and instrument
Dibenzothiophene (DBT, 98%), benzothiophene (BT, 97%),
thiophene (TH, 99.8%) and 4,6-dimethyldibenzothiophene
(4,6-DMDBT, 97%) were purchased from Aladdin Chemistry
Co. Ltd. The choline chloride (ChCl, AR), tetrabutylammo-
nium chloride (TBAC, AR), tetraethylammonium chloride
Stot ꢀ Sres
ODS rate ¼
ꢁ 100%
Stot
(TEAC, AR), n-octane, carbon tetrachloride (CCl4, 99.5%), tri- where Stot (500 mg gꢀ1) is the initial concentration of the sulfur
uoromethanesulfonic acid (CF3SO3H, 98%), and hydrogen compound in the model oil and Sres is the residual concentra-
peroxide (H2O2, 30 wt%) were purchased from Sinopharm tion of the sulfur compound aer the ODS process.
Fig. 1 Synthetic mechanism of DESs.
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peak of ChCl labeled “4” and the peak of hydrogen bond in
CF3SO3H disappeared and there is a new peak of hydrogen bond
appeared in ChCl/1.5CF3SO3H. These results demonstrate that
there are formation of hydrogen bond between ChCl and
CF3SO3H.22
3 Results and discussion
3.1 Characterization
3.1.1 Infrared spectra analysis. The infrared spectra of
ChCl, CF3SO3H and ChCl/1.5CF3SO3H were shown in Fig. 2.
Compared with the peaks of ChCl and CF3SO3H, the stretching
vibration peak of O–H at 3272 cmꢀ1, stretching vibration peak
of C–H at 3018 cmꢀ1 and stretching vibration peak of S]O at
1406 cmꢀ1 in ChCl, and stretching vibration peak of F–C at 947
cmꢀ1 and bending vibration peak of F–C at 621 cmꢀ1 in
CF3SO3H shi to 3466, 3048, 1416, 960 and 644 cmꢀ1 in ChCl/
1.5CF3SO3H were clearly seen (Fig. 2). The peaks happening to
shi are attribute to the formation of hydrogen bond in the
DES.27
3.2 Oxidative desulfurization reaction conditions
3.2.1 Desulfurization rate of different desulfurization
system. In this study, the removal rate of DBT in desulfurization
system of ChCl/CF3SO3H, TBAC/CF3SO3H and TEAC/CF3SO3H
was investigated. The results are shown in Fig. 4(a). It can be
seen from Fig. 4(a), the desulfurization rate of DBT reached
90.58% for ChCl/CF3SO3H, 41.54% for TBAC/CF3SO3H and
85.38% for TEAC/CF3SO3H aer the 180 min, respectively. The
difference of desulfurization rate may be due to the difference
in steric hindrance of DESs. It is well known that the steric
hindrance of DESs follow the order TBAC/CF3SO3H > TEAC/
CF3SO3H > ChCl/CF3SO3H. The order of desulfurization rate
with these DESs is ChCl/CF3SO3H > TEAC/CF3SO3H > TBAC/
CF3SO3H. The research shows that the bigger steric hindrance
of long cation chain is not conducive to the oxidative desul-
furization.28 Four cation chains of TBAC/CF3SO3H are the
longest, therefore its steric hindrance is the biggest result in
lowest desulfurization rate. Four cation chains of ChCl/
CF3SO3H was the shortest, so the its steric hindrance is the
smallest result in the highest desulfurization rate. Therefore,
ChCl/CF3SO3H was chosen as the catalyst and extractant for the
system of oxidation desulfurization.
3.1.2 1H NMR characterization. In order to further conrm
the interactions between ChCl and CF3SO3H, 1H NMR spectra of
CF3SO3H, ChCl and DESs were obtained in Fig. 3. The 1H NMR
spectra of ChCl/1.5CF3SO3H in Fig. 3(c), the peak of hydrogen
bond obviously became stronger and slightly shi to right
1
compare with ChCl in Fig. 3(b). H NMR spectra of CF3SO3H
demonstrate there is a peak of hydrogen bond in Fig. 3(a). The
3.2.2 Inuence of acidity of DESs on desulfurization rate.
ChCl/XCF3SO3H were synthesized using CF3SO3H and ChCl as
raw materials. A series of ChCl/XCF3SO3H (X from 1.0 to 2.0)
with different acidity were investigated by changing the molar
ratio of ChCl to CF3SO3H. As shown in Fig. 4(b), the desulfur-
ization rate obviously increased from 90.58% to 98.85% when
the molar ratio of CF3SO3H to ChCl were increased from 1 to
1.5. However, the desulfurization rate dropped from 98.85% to
87.3% when the molar ratio of CF3SO3H to ChCl was increased
to 2. It is because that acidity of DESs is too strong when the
molar ratio of CF3SO3H to ChCl was increased to 2. It could be
attributed to the higher acidity rapidly decomposed H2O2 into
oxygen, thereby decrease the oxidative ability of the system.29
The highest desulfurization rate of 98.85% can be attached
when the molar ratio of ChCl to CF3SO3H is 1.5. Moreover, the
viscosity of DESs have important inuence on desulfurization,
the high viscosity of DESs decrease extractive ability of DESs.30
The high conductivity show there are a lot of ions in DESs.12
Therefore, high conductivity is benet for desulfurization. As
shown in Table 1, the conductivity and viscosity of DESs
decrease with increasing molar ratio of CF3SO3H to ChCl. The
consideration for inuence of acidity, the conductivity and the
viscosity of DESs on desulfurization, ChCl/1.5CF3SO3H can be
selected as extractant and catalyst in the desulfurization system.
3.2.3 Inuence of O/S molar ratio on desulfurization rate.
Amount of H2O2 has an important inuence on the desulfur-
ization rate. The removal of DBT from the model oil in the ChCl/
Fig. 2 IR-FT (a) ChCl; (b) CF3SO3H; (c) ChCl/1.5CF3SO3H.
Fig. 3 1H NMR spectra of (a) CF3SO3H; (b) ChCl; (c) ChCl/1.5CF3SO3H. 1.5CF3SO3H–H2O2 system with various O/S molar ratio was
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Fig. 4 (a) Influence of different type DESs on desulfurization rate (5 mL model oil, O/S molar ratio of 8, 1 mL DESs, 40 ꢂC); (b) influence of
different acidity DESs on desulfurization rate (5 mL model oil, O/S molar ratio of 8, 1 mL DESs, 40 ꢂC); (c) influence of amount of H2O2 on
desulfurization rate (5 mL model oil, 1 mL DESs, 40 ꢂC); (d) influence of reaction temperature on desulfurization rate (5 mL model oil, O/S molar
ratio of 6, 1 mL DESs); (e) influence of amount of DESs on desulfurization rate (5 mL model oil, O/S molar ratio of 6, 40 ꢂC).
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Table 1 Conductivity and viscosity of DESs at 25 ꢂ
C
inuencing oxidative desulfurization. As shown in Fig. 4(d), the
reaction rate of desulfurization was obviously increased and
removal rate of DBT increase from 98.27% to 98.65% when the
Conductivity
Viscosity (h)/
(mPa s)
DESs
(d)/(ms cmꢀ1
)
ꢂ
ꢂ
reaction temperature increased from 30 C to 40 C. However,
the desulfurization rate no longer increased when the reaction
ChCl/1.0CF3SO3H
ChCl/1.5CF3SO3H
ChCl/2.0CF3SO3H
5200
4200
4000
100
85
70
ꢂ
temperature was beyond 40 C. It could be attributed to high
temperature accelerate the decomposition of H2O2,32 which
decrease oxidative ability in the oxidative desulfurization
process. So, the optimal temperature in the oxidative desulfur-
ꢂ
ization system is 40 C.
3.2.5 Inuence of volume ratio of DESs/oil on desulfur-
ization rate. Fig. 4(e) illustrates the DESs dosage has an
important inuence on removal of DBT. The removal rate for
DBT was increased from 98.46% to 98.65 when the volume ratio
of DESs/oil increased from 0.15 to 0.2. Continue to increase the
DESs/oil ratio, removal rate of DBT no longer increase. So, it can
be concluded that the optimal volume ratio of DESs/oil is 0.2 in
the desulfurization system.
3.2.6 Inuence of different sulfur compounds on desul-
furization rate. In this study, DBT in model oil could be effec-
tively removed using ChCl/1.5CF3SO3H as the catalyst and
extractant, with H2O2 as the oxidant. In order to determine the
desulfurization efficiency of the ChCl/1.5CF3SO3H for other
organic suldes in fuels, such as 4,6-DMDBT, BT and TH were
researched in oxidation desulfurization under identical condi-
tions. The results are shown in Fig. 5. The removal rate of BT,
DBT, 4,6-DMDBT and TH were 39.53%, 98.65%, 96.8% and
24.35% aer 180 min, respectively. The removal rate of four
sulfur compound in the desulfurization system followed the
order DBT > 4,6-DMBT > BT > TH. The desulfurization rate is
related to the electron density of the sulfur atoms in organic
sulde. The electron cloud densities of these compounds are
5.758 for DBT, 5.760 for 4,6-DMDBT, 5.739 for BT, and 5.696 for
TH,33,34 respectively. The electron cloud densities of 4,6-DMDBT
and DBT are very approximation. However, removal rate for DBT
was higher than 4,6-DMDBT due to the steric hindrance of the
methyl substituent in 4,6-DMDBT.35 Therefore, the removal rate
of 4,6-DMDBT is a little lower than DBT.
Fig. 5 Influence of different sulfur compounds on desulfurization rate
(5 mL model oil, O/S molar ratio of 6, 1 mL DESs, 40 ꢂC).
investigated. As shown in Fig. 4(c), removal rate of DBT is only
3.42% in the absence of H2O2. When the hydrogen peroxide was
added into the oxidative desulfurization system, the desulfur-
ization rate obviously increases. The desulfurization rate
increased from 57.69% to 98.65% when O/S was increased from
2 to 6. According to stoichiometry, 2 molar H2O2 can transform
1 molar DBT to DBTO2. However, the removal rate of DBT is only
66.1% with O/S molar ratio of 2. The reasons are the decom-
position of H2O2.31 When the O/S molar ratio is 4, the desul-
furization rate can attach to 96.4% and continue to increase the
O/S ratio, desulfurization rate increase slightly. So, the O/S
molar ratio of 6 was the optimal choice.
According to the experimental results, ChCl/1.5CF3SO3H
show excellent oxidative desulfurization activity. Table 2 shows
a
comparison of the desulfurization activity of ChCl/
1.5CF3SO3H and other acidic ionic liquids. It can be seen that
ChCl/1.5CF3SO3H has a high desulfurization rate under mild
experimental conditions. Furthermore, ChCl/1.5CF3SO3H can
be prepared by a simple method and the raw material are easily
obtained.
3.2.4 Inuence of reaction temperature on desulfurization
rate. The reaction temperature is also an important factor
Table 2 Comparison of the desulfurization activity of ChCl/1.5CF3SO3H and other acidic ionic liquids
Removal
of DBT
Catalysts
S content (mg gꢀ1
)
Reaction conditions
Ref.
[C4mim]TFA
[HMIm]BF4
[BMIM][HSO4]
[Hnmp]BF4
202
IL : oil ¼ 1 : 35, H2O2 ¼ 1 mL, 70 ꢂC, 30 min
IL : oil ¼ 5 : 3.2, O/S ¼ 10, 90 ꢂC, 360 min
IL : oil ¼ 1 : 2, O/S ¼ 5, 25 ꢂC, 90 min
IL : oil ¼ 1 : 1, O/S ¼ 3, 60 ꢂC, 60 min
IL : oil ¼ 1 : 5, O/S ¼ 6, 40 ꢂC, 60 min
100%
93%
99.6%
100%
98.65%
20
21
22
23
1000
1000
1550
500
ChCl/1.5CF3SO3H
This work
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Fig. 8 Mechanism of oxidative desulfurization.
can be found that the white substance is quickly dissolved into
carbon tetrachloride. Aer the carbon tetrachloride were
remove by distillation, the white powder was obtained. The
infrared analysis of the white powder is shown in Fig. 7(b).
Three infrared absorption peaks are observed at 1166, 1047, and
1288 cmꢀ1 corresponding to the three characterization peaks of
DBTO2.36,37 This shows that the DBT was oxidized to DBTO2 in
the oxidative desulfurization system.
3.2.9 Mechanism of catalytic oxidative desulfurization. As
seen in Fig. 8, H2O2 is a strong oxidant in the acidic medium.
DBT was extracted into the DESs phase and was oxidized to
DBTO2 under the action of ChCl/1.5CF3SO3H and H2O2. During
oxidative desulfurization process, DESs acted as not only
extractant but also catalyst, so a continuous decrease of the
content of DBT in n-octane was observed until H2O2 was
completely decomposed.
Fig. 6 Recovery and regeneration of DESs (5 mL model oil, O/S molar
ratio of 6, 1 mL DESs, 40 ꢂC).
3.2.7 Recovery and regeneration of DESs. Aer the oxida-
tive desulfurization reaction, the upper oil phase was removed
by using a separating funnel. The water in the DESs was
removed by rotary evaporation. The DESs were extracted three
times using CCl4 of equal volume. Fresh H2O2, recovered DESs
were added into model oil under the optimal conditions. As
shown in Fig. 6, the removal rate of DBT decreased from 98.65%
to 97.16% aer ve recycles. Two reasons result in the decrease
of desulfurization rate. On the one hand, it could be attributed
to minimal loss in DESs during the recovery process; on the
other hand, it might be attributed to a little of residual oxida-
tion products of sulde in the recovered DESs.
3.2.8 FT-IR characterization of oxidative production. As
shown in Fig. 7(a), the mixture of oil phase and DESs phase is
transparent liquid before the desulfurization reaction.
However, there is white precipitate between oil and DESs aer
the desulfurization reaction in Fig. 7(a). In order to identify the
white precipitate, a reverse extraction experiment was carried
out using carbon tetrachloride (CCl4) as the extraction agent
and the DESs as the extraction phase at room temperature. It
3.3 Catalytic oxidative desulfurization of diesel oil
The S-removal activity of ChCl/1.5CF3SO3H for the real diesel oil
with a total S-content of 375 mg Lꢀ1 was also investigated. Under
the optimal condition, the desulfurization rate of 68.5% was ob-
tained. Sulfur removal efficiency was found to be lower in diesel
oil than that obtained in model oil (98.65%), which may be
attributed to the more complex chemical composition of diesel.38
Fig. 7 (a) Contrast diagram of before and after reaction; (b) FTIR characterization of oxidative production (A) DBT, (B) DBTO2.
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A series of ChCl/XCF3SO3H (X from 1.0 to 2.0) were synthesized
by stirring a mixture of ChCl and CF3SO3H. The DESs were used
as extractant and catalyst in the oxidative desulfurization
process. Compared to other acidic ionic liquids, the synthesis
method of ChCl/XCF3SO3H is simple. The ChCl/1.5CF3SO3H
exhibits a high desulfurization activity for DBT in model oil and
can be recycled 5 times without a signicant decrease in activity.
The results demonstrate the DESs exhibit the high catalytic
activity and stability for the desulfurization system.
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Natural Science Foundation of China (Project no. 21003069);
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