Deep desulfurization of light oil through extraction and oxidation processes using H2O2/tungstophosphoric acid in room-temperature ionic liquids

Article abstract of DOI:10.1002/jccs.201100672

In this research, using room-temperature ionic liquids (RTILs) as the solvents to combine solvent extraction and chemical oxidation processes in one-pot operation for the desulfurization of fuel oil was pursued. In this solvent extraction and chemical oxidation desulfurization (SECOD), RTILs as media are immiscible with oil; sulfur compounds in oil are extracted into RTILs and oxidized thereafter to the corresponding sulfones by H₂O ₂/TPA (tungstophosphoric acid). During SECOD, these high polar sulfones partition mainly in the ionic liquid phase. Hence, it results in their continuous removal from oil, which leads to deep desulfurization. To study the SECOD, we employed dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in hexadecane asmodel oil systems and compared the effects of RTILs on the removal of DBT and 4,6-DMDBT. The desulfurization rates followed the order OMIM⁺PF₆ - > BMIM⁺PF₆ - > BMIM⁺BF₄ -. Both OMIM⁺PF₆ - and BMIM⁺PF₆ - are water-immiscible and form three-phase (oil-water- ionic liquid) reaction systems; these three-phase systems offer higher removal efficiencies of sulfur compounds from oil. Under the optimized conditions, SECOD process reduced the sulfur content of diesel light oil from 897 to 42 ppm (i.e., 95% desulfurization efficiency) in a one-batch operation.

Full text of DOI:10.1002/jccs.201100672

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Deep Desulfurization of Light Oil through Extraction and Oxidation Processes using
H2O2/Tungstophosphoric Acid in Room-temperature Ionic Liquids
Li-Lin Chuang,a Jung-Fu Huang,a Wen-Hen Lob and Guor-Tzo Weia,*
aDepartment of Chemistry and Biochemistry, National Chung Cheng University, Ming-Hsiung, Chia-Yi, 62102 Taiwan
bCPC Refining & Manufacturing Center, Chia-Yi, 60036, Taiwan
(Received: Nov. 20, 2011; Accepted: Jan. 18, 2012; Published Online: Feb. 8, 2012; DOI: 10.1002/jccs.201100672)
In this research, using room-temperature ionic liquids (RTILs) as the solvents to combine solvent extrac-
tion and chemical oxidation processes in one-pot operation for the desulfurization of fuel oil was pursued.
In this solvent extraction and chemical oxidation desulfurization (SECOD), RTILs as media are immisci-
ble with oil; sulfur compounds in oil are extracted into RTILs and oxidized thereafter to the corresponding
sulfones by H2O2/TPA (tungstophosphoric acid). During SECOD, these high polar sulfones partition
mainly in the ionic liquid phase. Hence, it results in their continuous removal from oil, which leads to deep
desulfurization. To study the SECOD, we employed dibenzothiophene (DBT) and 4,6-dimethyldibenzo-
thiophene (4,6-DMDBT) in hexadecane as model oil systems and compared the effects of RTILs on the re-
moval of DBT and 4,6-DMDBT. The desulfurization rates followed the order OMIM+PF6– > BMIM+PF6
–
> BMIM+BF4 . Both OMIM+PF6– and BMIM+PF6– are water-immiscible and form three-phase (oil–wa-
–
ter–ionic liquid) reaction systems; these three-phase systems offer higher removal efficiencies of sulfur
compounds from oil. Under the optimized conditions, SECOD process reduced the sulfur content of diesel
light oil from 897 to 42 ppm (i.e., 95% desulfurization efficiency) in a one-batch operation.
Keywords: Room-temperature ionic liquid; Oxidative desulfurization; Fuel oil.
INTRODUCTION
Petroleum-derived middle feedstocks, such as light
desulfurization,8 oxidative desulfurization (ODS)1,9-19 and
so on. Among them, ODS has attracted wildly interest be-
cause it is carried out under mild conditions: at low temper-
ature and under atmospheric pressure, etc. ODS method
has great potential to be a complementary process of tradi-
tional HDS for producing very low sulfurs of diesel oils.14
The ODS process usually involves oxidizing the sul-
fur compounds in oils thus transforming them into sulfones
in the first step. The sulfones are then removed by a selec-
tive extraction in a second step. Different catalysis and oxi-
dants have been employed in the first step of ODS, such as
H2O2/HCOOH,18 H2O2/CH3COOH,9-11 H2O2/CF3COOH,19
H2O2/methyltrioxorhenium(VII),20 H2O2/TPA,14,21-24 H2O2/
vanadium peroxocomplexes,25-26 H2O2/vanadiumsilicate,27
H2O2/Titanium silicalite28 and other non-H2O2 system (eq.
Ozone, t-BuOOH, etc.).29,30 A polar organic solvent, such
as acetonitrile, dimethyl sulfoxide, or N,N-dimethylform-
amide, is usually utilized as extraction solvent in the sec-
ond step.8 These solvents are generally flammable and vol-
atile organic compound (VOCs). The use of VOCs causes
environmental and safety concerns, such as hazardous gas
emission and fire hazard.
oils, usually contain a high amount of sulfur impurity. The
sulfur compounds in diesel light oils are converted by com-
bustion to SOx, which are the major source of acid rain and
air pollution.1 Regulations limit sulfur content in light oil to
reduce the air pollution.2 The production of light oils con-
taining very low sulfur is, therefore, an important task for
oil refineries. The removal of sulfur compounds in oils is
carried out industrially by a catalytic hydrodesulfurization
(HDS) method. This method is operated at both high tem-
perature and high pressure of hydrogen gas. HDS is gener-
ally carried out under much sever conditions like higher
temperature, higher hydrogen pressure and more active ca-
talysis to produce the light oil that has lower content of sul-
fur compounds to meet the requirements of new regula-
tions. Meanwhile the desulfurization efficiency of HDS is
limited, especially for polyaromatic sulfur containing com-
pounds such as DBT and its derivative 4,6-DMDBT, etc.
To overcome this problem, alternative non-HDS desulfu-
rization methods have been reported. These non-HDS ap-
proaches include adsorption,3-5 solvent extraction,6,7 bio-
Dedicated to the memory of Professor Yung-Son Hon (1955–2011).
* Corresponding author. Tel: +886-5-2428121; Fax: +886-5-2721040; E-mail: chegtw@ccu.edu.tw
324
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Oxidative Desulfurization in Ionic Liquids
Compared with VOCs, RTILs have many unique
properties, such as non-volatile, negligible vapor pressure,
non-explosive, easy to recycle, and high thermal stability
etc. RTILs are regarded as green solvents and have recently
gained recognition as environmentally benign alternative
solvents for synthesis, separation, electrochemistry, cataly-
sis, etc.31-43 RTILs were also employed for removing sul-
furs from fuels by solvent extractions recently.7,44-47 How-
ever, the efficiency of sulfur removal by solvent extraction
is limited and multiple-extraction is required to obtain the
fuels with low content of sulfurs. Although, multiple-ex-
traction with special ionic liquid can effectively remove
sulfurs from oils, it has the problem of cross-solubility of
oil, i.e. portion of oil is extracted by ionic liquid.44 Our pre-
vious work demonstrated that we were able to reduce the
oil sulfur content from 8040 ppm down to 1000 ppm by
SECOD method with BMIM+PF6–.11 Although the sulfur
content is still high, an order of magnitude improvement in
the desulfurization yield was obtained by SECOD method
using RTILs, as compared with that of merely extraction.
The major advantages of using RTILs in SECOD method
over traditional ODS are: (1) it combines oxidation and
separation operation to one operation, (2) the benefits of
RTILs over VOCs for chemical operation can be realized
because of no emission loss with RTILs in an open reactor
at ambient pressure, (3) it simplified the reaction system
due to the solubility properties of RTILs, and (4) water im-
miscible RTILs provide favor reaction conditions for ODS.
For example, phase transfer reagent is not required for cata-
lytic reaction because RTILs are able to dissolve non-polar,
polar and charged compounds.21,25 This process has been
widely investigated recently.48-58
rameters on the desulfurization. The desulfurization behav-
ior of SECOD is discussed and the effectiveness of this
method for the desulfurization of light oils is presented to
demonstrate the capability of SECOD to produce low sul-
furs of fuel oils.
EXPERIMENTAL
RTILs synthesis
The synthesis of BMIM+PF6 , OMIM+PF6 and
–
–
BMIM+BF4 were prepared by a literature procedure.32
–
BMIM+Cl– or OMIM+Cl– was prepared by adding equi-
molar amounts (0.3 mole) of 1-methylimidazole and chlo-
robutane or chlorooctane to a round-bottom flask fitted
with a reflux condenser and heated at 70 °C for 48~72 h.
The resulting viscous and yellowish liquid was cooled to
room temperature and then washed three times with ethyl
acetate. The remaining ethyl acetate was removed by rotary
evaporation. The residue was poured into acetone or water
(150 mL), the equimolar amount (0.3 moles) of the NaBF4
(in acetone) or KPF6 (in water) was needed, and the mixture
was stirred for 24 h at room temperature. The resulting pre-
cipitate of NaCl (from BMIM+BF4 ) was filtered off; KCl
–
(from BMIM+PF6– and OMIM+PF6 ) was washed off with
–
water until no precipitation occurred when the sample
tested with AgNO3 solution. The solvent (acetone or water)
was removed through rotary evaporation under vacuum.
NMR spectroscopy was employed to verify the structures
and purities of the RTILs. The purity and structure of final
product was characterized with 1H-NMR.
Oxidation/extraction desulfurization
Desulfurization of model oil was carried out as fol-
lows: Weight 0.110 g DBT or 4,6-DMDBT dissolve in 100
mL C16H34 as a stock solution. The sulfur stock solution (5
mL) was mixed with an equal volume of RTIL and then a
35% H2O2 solution (0.583 mL) containing TPA (3.5 mmol)
was added. The mixture was stirred and heated to 70 °C.
The upper phase (C16H34) was withdrawn periodically for
analysis of its sulfur content using a UV–Vis spectrometer
(Shimadzu UV-3170PC) with detection at 320 nm.
Further investigations of SECOD for desulfurization
of oil with RTILs are essential to realize its potential appli-
cation for the desulfurization of light oils. Here, the use of
H2O2/TPA as catalytic oxidation reagents and 1-butyl-3-
methylimidazollium tetrafluoroborate (BMIM+BF4 ), 1-
–
butyl-3-methylimidazollium
hexafluorophosphate
(BMIM+PF6 ) or 1-octyl-3-methylimidazollium hexafluo-
–
rophosphate (OMIM+PF6 ) as the solvent for the desulfu-
Oxidations of DBT and 4,6-DMDBT in the RTILs
were performed as follows: DBT or 4,6-DMDBT (0.011 g)
was dissolved in an RTIL stock solution (10 mL). The DBT
or 4,6-DMDBT stock solution (2.5 mL) was mixed with a
35% H2O2 (0.291 mL) solution containing TPA (1.75 mmol)
to form the sulfur-containing RTIL mixture. The mixture
was heated to 70, 80, and 90 °C and stirred vigorously dur-
ing the reaction. The solutions were periodically with-
–
rization of light oils of SECOD method was carried out.
Hydrogen peroxide/Polyoxometalates reaction system
have long been studied for oxidation reactions,12-17 while
the solution of H2O2/TPAwas shown to have the highest re-
activity of H2O2/polyoxometalate reaction system.23 In this
work, DBT and 4,6-DMDBT dissolved in hexadecane were
employed as model oils to study the effect of various pa-
J. Chin. Chem. Soc. 2012, 59, 324-330
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Chuang et al.
drawn and analyzed for their sulfur content using re-
versed-phase high-performance liquid chromatography
(RP-HPLC; Shimadzu LC-6A equipped with a SPD-6A de-
tector) with detection at 241 nm.
the oxidation process, as shown in Fig. 1 and Fig. 2. These
findings are similar to those of our previous report in which
we employed acetic acid/H2O2 as the catalyst/oxidant.11
The sulfur content at time zero reflects the ability of each
ionic liquid to extract sulfur from model oil. Fig. 1 reveals
Desulfurization of light oil was carried out as fol-
lows: 10 mL light oil mixed with 10 mL ionic liquid and
added 6.99 mL containing 12.5 umole TPA. The mixture
was stirred at 70 °C. The amount of sulfur in the light oil
was determined by Antek pyroreactor 771, which was
equipped with an Antek UV fluorescence detector 714. The
total contents of saturated hydrocarbon and one-, two-,
poly-ring aromatic hydrocarbons in the light were analyzed
by reversed-phase HPLC (Shimadzu LC-6A equipped with
a refractive-index detector RID-6A).
that BMIM+BF4 , BMIM+PF6 , and OMIM+PF6 extract
–
–
–
53, 52 and 64%, respectively, of DBT from model oil. Fig.
–
–
2
indicates that BMIM+BF4 , BMIM+PF6 , and
OMIM+PF6 extract 28, 27 and 48%, respectively, of
4,6-DMDBT from model oil. Figs. 1 and 2 both indicate
that OMIM+PF6– has the best extraction efficiency of these
three RTILs. Nevertheless, the yields of these solvent ex-
tractions are limited and multiple extractions would be re-
quired to obtain low-sulfur oils.45 The data also show that
sulfur concentration in oil continuously decreases after
adding chemical oxidation to solvent extraction. This situa-
tion arises because chemical oxidation of the sulfur com-
–
RESULT AND DISCUSSION
Effect of ionic liquids on desulfurization
DBT or 4,6-DMDBT dissolved in C16H34 was em-
ployed as a sulfur containing model oil. Mixing an ionic
liquid with the model oil forms a biphasic liquid-liquid sys-
tem because of immiscibility between ionic liquid and oil.
Sulfur compounds will participate in both oil and ionic liq-
uids. This leads to the extraction of sulfurs compounds
from oil. This approach has been employed in several re-
ports.44-47 However, the efficiency of solvent extraction re-
mains limited. In this SECOD method, DBT and 4,6-
DMDBT in the model oil were extracted into the ionic liq-
uid phase, where they were oxidized by TPA/H2O2 to their
sulfones (hexavalent sulfur species), as indicated in
Scheme I.11 These oxidized sulfones have high polarities
and, therefore, they are highly partitioned in the ionic liq-
uid phase. Consequently, a continuous decrease in the con-
centration of sulfurs in hexadecane was observed during
Fig. 1. Oxidation/Extraction of DBT in the H2O2/TPA
system at 70 °C.
Reaction mechanism of DBT and 4,6-
DMDBT in the H2O2/TPA system
Scheme I
Fig. 2. Oxidation/Extraction of 4,6-DMDBT in the
H2O2/TPA system at 70 °C.
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Oxidative Desulfurization in Ionic Liquids
pounds in the ionic liquid phase to their corresponding sul-
fones results in a shift in the partition equilibrium of the
sulfur compounds between the oil and ionic liquid phases,
which leads to further extraction from the oil. Conse-
quently, a continuous extraction and oxidation cause the
continuous decrease of sulfur concentration in oil. In less
than an hour, this process could remove more than 99% of
4,6-DMDBT in different ionic liquids are in the order of
OMIM+PF6– > BMIM+PF6– > BMIM+BF4 . As the results
–
of Fig. 1-4 indicate that OMIM+PF6– not only has the high-
est extraction efficiency and also has the highest oxidation
reactivity, thus has the best performance for removing re-
fractory sulfurs from oil, as shown in Fig. 1 and Fig. 2. The
reason of the highest oxidation reactivity of OMIM+PF6
–
DBT in model oil with BMIM+PF6 , and OMIM+PF6 . It
can be attributed to its lowest concentration of water. Previ-
ous works indicated that oxidation of DBT by H2O2/
CH3COOH was a reciprocal of H2O concentration.11 In pre-
–
–
took somewhat longer to decrease the yield of 4,6-DMDBT
accordingly. The efficiencies of the sulfur removals using
these three RTILs followed the order OMIM+PF6
vious report, BMIM+PF6 (a water immiscible ionic liquid)
–
–
>
BMIM+PF6 > BMIM+BF4 . This order results, in part,
has better yield of sulfur removal than that of BMIM+BF4
–
–
–
from the fact that OMIM+PF6 has the highest extraction ef-
(a water miscible ionic liquid). Here, similar trend was ob-
served with TPA/H2O2. Therefore, water concentration has
strong influence on the reactivity of refractory sulfurs with
–
ficiency, but it might also reflect the different reaction ac-
tivities of the sulfur compounds in the different RTILs (see
below).
TPA/H2O2 and OMIM+PF6 is the most water immiscible of
–
Oxidation reactivity of DBT and 4,6-DMDBT in ionic
liquids
all three RTILs employed. As a result, OMIM+PF6– has the
highest desulfurization yield and reactivity.
The reactivity of DBT and 4,6-DMDBT in oil are low
with HDS method because of their steric hindrance. These
low reactivity compounds in HDS method are called re-
fractory sulfurs. HDS process has the difficulty to produce
low sulfur oil because it is unable to remove the refractory
sulfurs from oils effectively. Conversely, ODS method has
been described to be a potential alternative or complemen-
tary method of HDS for its high efficiency to remove the re-
fractory sulfurs from oils.14 In order to understand the oxi-
dation reactivity of DBT and 4,6-DMDBT in SECOD pro-
cess, we directly dissolved DBT and 4,6-DMDBT in RTILs
and then added H2O2/TPA for oxidation. The oxidation
rates of DBT and 4,6-DMDBT in RTILs are shown in Fig. 3
and Fig. 4. The data indicate that the reactivity of DBT and
For oxidation, pseudo-first-order is carried out be-
cause excess H2O2 was employed. The oxidation rate con-
stants of the DBT and 4,6-DMDBT in Fig. 3-4 were calcu-
lated from a plot of ln(Ct/C0) versus reaction time, where C0
is the initial sulfur concentration and Ct is the sulfur con-
centration at oxidation t (min). The slopes of the plot are
the rate constants and listed in Table 1. The data indicate
that reactivity of DBT is higher than that of 4,6-DMDBT.
The same reactivity trend was reported by using H2O2 solu-
tions of TPA.22 However, this is in reversed order to that of
catalytic oxidation by HOOH18 and CH3COOH.9-11 Te et al.
has described the detail about the difference of these two
oxidant/catalyst systems for the oxidation of refractory sul-
furs.22 They attributed the difference in reactivities of two
Fig. 4. Oxidation of 4,6-DMDBT in the H2O2/TPA
system at 70 °C.
Fig. 3. Oxidation of DBT in the H2O2/TPA system at
70 °C.
J. Chin. Chem. Soc. 2012, 59, 324-330
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Table 1. DBT and 4,6-DMDBT oxidation rate constant at 70 oC
Rate constants Correlation
indicate that SECOD is strongly temperature-dependent.
Because the RTILs are stable at rather high temperatures
and because the reactivities of the sulfur compounds to-
ward oxidation are strongly temperature-dependent, higher
temperature can be employed in the SECOD method to ac-
celerate these reactions.
Reactants
IL
(mim-1)
factor (R2)
DBT
C4MIMBF4
C4MIMPF6
C8MIMPF6
C4MIMBF4
C4MIMPF6
C8MIMPF6
0.0089
0.2096
0.4344
0.0772
0.1186
0.1229
0.9917
0.9931
0.9681
0.9982
0.9962
0.9892
4,6-DMDBT
Desulfurization of light oil with SECOD
We used a light oil containing 897 ppm sulfur to eval-
uate the performance and capability of SECOD process
with different RTILs. The component of the raw oil and
treated oil are shown in Table 2. The sulfur contents are
oxidation systems is due to the molecular sizes of catalysts
not the intrinsic reactivities of sulfurs. TPA is a large mo-
lecular catalyst while HOOH or CH3COOH is a small mo-
lecular catalyst. Steric effect of the sulfurs plays important
role for the oxidation with large molecular catalyst, such as
TPA. While the reactivity results from small molecular cat-
alyst, such as HCOOH, reflect the intrinsic reaction of sul-
803, 786, and 675 ppm after extracted with BMIM+BF4 ,
–
BMIM+PF6 , and OMIM+PF6 , respectively. The sulfur
–
–
contents were reduced to 365, 113, and 42 ppm after treated
the oil by SECOD process using BMIM+BF4 , BMIM+PF6 ,
–
–
OMIM+PF6 , respectively. The desulfurization yields of
–
SECOD are 59.3, 87.4, and 95.3% with BMIM+BF4 ,
–
BMIM+PF6 , and OMIM+PF6 , respectively. The results in
Table 2 clearly demonstrate the effectiveness of the SECOD
process.
–
–
furs. Table 1 also indicates that the reactivities of both sul-
furs in three RTILs are in the order of OMIM+PF6
–
>
BMIM+PF6– > BMIM+BF4 . The reason of this sequence
–
We were interested to find out what types of sulfur
compounds remained in the oil after performing the SECOD
process. We employed sulfur-specific gas chromatography
to measure the sulfur compounds within the light oil before
and after SECOD with OMIM+PF6– (Fig. 7). The residual
sulfur compound present in the oil after SECOD process-
ing appears to be alkyl benzothiophene (C4-BT). A previ-
ous report indicated that BTs are difficult to be removed
when using the ODS method.30
has been described in last paragraph.
The rate constants of DBT and 4,6-DMDBT in
C4MIM+PF6 at different temperatures were also per-
–
formed, as shown in Fig. 5. Using these rate constants at
different temperature, a plot of -ln k verse 1/T for the oxida-
tive reaction gave a straight line, as shown in Fig. 6. The ac-
tivation energy (Ea) of DBT and 4,6-DMDBT are esti-
mated from the Arrhenius equation to be 51.2 and 56.7
kJ/mole, respectively. These values are slightly lower than
those of reported by Te et al. (53.8 and 58.7 kJ/mol for DBT
and 4,6-DMDBT, respectively). These reactivity studies
In addition, we noted a difference between the aro-
matics in the light oil after desulfurization. The composi-
Fig. 6. Arrhenius activation energies for DBT and
4,6-DMDBT oxidation in the H2O2/TPA sys-
tem.
Fig. 5. Pseudo-first order rate for DBT and 4,6-
DMDBT oxidation rate at 70 °C in different
ILs.
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JOURNAL OF THE CHINESE
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Oxidative Desulfurization in Ionic Liquids
Table 2. Constants of aromatic and sulfur compounds in light gas oil before and after contact with ionic liquid
Saturated One-ring Two-ring Poly-ring Sulfur
Desulfurization
Sample
hydrocarbon aromatics aromatics aromatics content
yield
(%)
(vol %)
(vol %)
(vol %)
(vol %)
(ppm)
Feed
Extractiona
Untreated
81.0
82.2
81.8
82.5
82.6
83.6
83.7
13.0
12.9
12.7
12.8
12.7
12.8
13.5
5.8
4.1
5.4
3.5
4.6
3.5
2.8
0.2
0.2
0.1
0.1
0.1
0.1
0
897
803
365
786
113
675
42
---
With C4MIMBF4
Extraction/Oxidationb With C4MIMBF4
10.5
59.3
12.4
87.4
24.7
95.3
Extractiona
With C4MIMPF6
With C4MIMPF6
With C8MIMPF6
With C8MIMPF6
Extraction/Oxidationb
Extractiona
Extraction/Oxidationb
a No oxidation reagents; b With oxidation reagents added to the extraction system.
tion of aromatic hydrocarbons after desulfurization was
lower than that in the feed light oils. This situation arose
because these aromatic hydrocarbons were extracted into
the ionic liquid phase. After the oxidative reaction, the aro-
matic compounds in the light oils were highly oxidized.7
The effect that extraction has on the composition of the
polyaromatic hydrocarbons in the oxidized oil is more sig-
nificant than those of the mono- and bicyclic aromatic hy-
drocarbons. This situation leads to a larger reduction in the
content of aromatic hydrocarbons in the light oil after per-
forming sulfur removal.
The system was recharged with the oxidizing agent (H2O2)
with OMIM+PF6 , the yield was maintained for four cycles
–
of operation.
ACKNOWLEDGMENTS
We gratefully acknowledge support of this work by
the National Science Council and the College of Science at
the National Chung Cheng University, Taiwan.
REFERENCES
1. Babich, I. V.; Moulijn, J. A. Fuel 2003, 82, 607.
2. EPA-Diesel RIA. United States Environmental Protection
Agency. Air and Radiation. EPA420-R-00-026, December
2000.
Regeneration/recycling of RTILs
We followed the approach that we had described pre-
viously to recycle the ionic liquids.11 At the end of each
run, the reacted ionic liquids were washed out with water
and then the ionic liquid phase was filtered, the volatiles
were evaporated, and the residue extracted with diethyl
ether. 1H NMR spectroscopy confirmed that the purities of
3. McKinley, S. G.; Angelici, R. J. Chem. Commun. 2003,
2620.
4. Yang, R. T.; Hernández-Maldonado, A. J.; Yang, F. H. Sci-
ence 2003, 301, 79.
5. Sévignon, M.; Macaud, M.; Favre-Réguillon, A.; Schulz, J.;
Rocault, M.; Faure, R.; Vrinatd, M.; Lemaire, M. Green
Chem. 2005, 7, 413.
BMIM+BF4 , BMIM+PF6 , and OMIM+PF6– were retained.
–
–
6. Bösmann, A.; Datsevich, L.; Jess, A.; Lauter, A.; Schmitz,
C.; Wasserscheid, P. Chem. Commun. 2001, 2494.
7. Zhang, S.; Zhang, Z. C. Green Chem. 2002, 4, 376.
8. Monticello, D. J. Curr. Opin. Biotechnol. 2000, 11, 540.
9. Heimlich, B. N.; Wallace, T. J. Tetrahedron 1966, 22, 3571.
10. Song, C.; Ma, X. Appl. Catal., B 2003, 41, 207.
11. Lo, W.-H.; Yang, H.-Y.; Wei, G.-T. Green Chem. 2003, 5,
639.
12. Tam, P. S.; Kettrel, J. R.; Eldridge, J. W. Ind. Eng. Chem.
Res. 1990, 29, 321.
13. Zannikos, F.; Lois, E.; Stournas, S. Fuel Process. Technol.
1995, 42, 35.
14. Collins, F. M.; Lucy, A. R.; Sharp, C. J. Mol. Catal. A: Chem.
1997, 117, 397.
15. Houalla, M.; Broderick, D. H.; Sapre, A. V.; Nag, N. K.; De
Beer, V. H.; Gates, J. B. C.; Kwart, H. J. Catal. 1980, 61,
523.
Fig. 7. GC-AED chromatograms of light oil of (A) un-
treated and (B) oxidation/extraction with
OMIM+PF6 .
–
J. Chin. Chem. Soc. 2012, 59, 324-330
© 2012 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.jccs.wiley-vch.de
329

Article
Chuang et al.
16. Hulea, V.; Fajula, F.; Bousquet, J. J. Catal. 2001, 198, 179.
17. Shiraishi, Y.; Tachibana, K.; Hirai, T.; Komasawa, I. Ind.
Eng. Chem. Res. 2002, 41, 4362.
37. Plechkova, N. V.; Seddon, K. R. Chem. Soc. Rev. 2008, 37,
123.
38. Soukup-Hein, R. J.; Remsburg, J. W.; Breitbach, Z. S.;
Sharma, P. S.; Payagala, T.; Wanigasekara, E.; Huang, J.;
Armstrong, D. W. Anal. Chem. 2008, 80, 2612.
39. Wijethunga, P. A. L.; Nanayakkara, Y. S.; Kunchala, P.;
Armstrong, D. W.; Moon, H. Anal. Chem. 2011, 83, 1658.
40. Branco, L. C.; Serbanovic, A.; da Ponte, M. N.; Afonso, C.
A. M. ACS Catal. 2011, 1, 1408.
18. Otsuki, S.; Nonaka, T.; Takashima, N.; Qian, W.; Ishihara,
A.; Imai, T.; Kabe, T. Energy Fuels 2000, 14, 1232.
19. Treiber, A.; Dansette, P. M.; El Amri, H.; Girault, J. P.;
Ginderow, D.; Mornon, J. P.; Mansuy, D. J. Am. Chem. Soc.
1997, 119, 1565.
20. Brown, K. N.; Espenson, J. H. Inorg. Chem. 1996, 35, 7211.
21. Li, C.; Jiang, Z.; Gao, J.; Yang, Y.; Wang, S.; Tian, F.; Sun,
F.; Sun, X.; Ying, P.; Han, C. Chem. Eur. J. 2004, 10, 2277.
22. Te, M.; Fairbridge, C.; Ring, Z. Appl. Catal., A 2001, 219,
267.
41. Dupont, J. Acc. Chem. Res. 2011, 44 , 1223.
42. Fitzgerald, J.; Kunnath, P.; Walker, A. V. Anal. Chem. 2010,
82, 4413.
43. Angell, C. A.; Byrne, N.; Belieres, J. Acc. Chem. Res.
2007, 40, 1228.
23. Yazu, K.; Yammamoto, Y.; Furuya, T.; Miki, K.; Ukegawa,
K. Energy Fuels 2001, 15, 1535.
44. Eßer, J.; Wasserscheid, P.; Jess, A. Green Chem. 2004, 6,
316.
24. Yazu, K.; Furuya, T.; Miki, K.; Ukegawa, K. Chem. Lett.
2003, 32, 920.
45. Zhang, S.; Zhang, Q.; Zhang, Z. C. Ind. Eng. Chem. Res.
2004, 43, 614.
25. Anisimov, A. V.; Fedorova, E. V.; Lesnugin, A. Z.; Senyavin,
V. M.; Aslanov, L. A.; Rybakov, V. B.; Tarakanova, A. V.
Catal. Today 2003, 78, 319.
46. Alonso, L.; Arce, A.; Francisco, M.; Rodríguez, O.; Soto, A.
AIChE J. 2007, 53, 3108.
26. Maurya, M. R.; Arya, A.; Kumar, A.; Kuznetsov, M. L.;
Avecilla, F.; Pessoa, J. C. Inorg. Chem. 2010, 49, 6586.
27. Shiriraishi, Y.; Naito, T.; Hirai, T. Ind. Eng. Chem. Res.
2003, 42, 6034.
47. Jiang, X.; Nie, Y.; Li, C.; Wang, Z. Fuel 2008, 87, 79.
48. Zhu, W.; Li, H.; Jiang, X.; Yan, Y.; Lu, J.; Xia, J. Energy Fu-
els 2007, 21, 2514.
49. Sun, Z.; Li, F.; Liu, R.; Sha, H. Energy Fuels 2008, 22, 3065.
50. He, L.; Li, H.; Zhu, W.; Guo, J.; Jiang, X.; Lu, J.; Yan, Y. Ind.
Eng. Chem. Res. 2008, 47, 6890.
28. Kong, L. Y.; Li, G.; Wang, X. S. Catal. Today 2004, 93–95,
341.
29. Paybarah, A.; Bone, R. L.; Corcoran, W. H. Ind. Eng. Chem.
Prod. Des. Dev. 1982, 21, 426.
51. Zhao, D.; Liu, R.; Wang, J.; Liu, B. Energy Fuels 2008, 22,
1100.
30. Wang, D.; Qian, E. W.; Amano, H.; Okata, K.; Ishihara, A.;
Kabe, T. Appl. Catal. A: Gen. 2003, 253, 91.
31. Wilkes, J. S.; Zaworotko, M. J. J. Chem. Soc., Chem.
Commun. 1992, 965.
52. Lissner, E.; de Souza, W. F.; Ferrera, B.; Dupont, J. Chem.
Sus. Chem. 2009, 2, 962.
53. Li, F.; Liu, R.; Wen, J.; Zhao, D.; Sun, Z.; Liu, Y. Green
Chem. 2009, 11, 883.
32. Anderson, J. L.; Armstrong, D. W. Anal. Chem. 2003,75,
4851.
54. Zhao, D.; Wang, Y.; Duan, E. Molecules 2009, 14, 435.
55. Cui, X.; Zhang, S.; Shi, F.; Zhang, Q.; Ma, X.; Lu, L.; Deng,
Y. ChemSusChem. 2010, 3, 1043.
33. Ding, J.; Welton, T.; Armstrong, D. W. Anal. Chem. 2004,
76, 6819.
56. Wang, L.; Zhao, D.; Li, K. Energy Fuels 2010, 24, 2527.
57. Zhu, W.; Li, H.; Gu, Q.; Wu, P.; Zhu, G.; Yan, Y.; Chen, G. J.
Mol. Catal. A: Chem. 2011, 336, 16.
34. Welton, T. Chem. Rev. 1999, 9, 2071.
35. Revell, J. D.; Ganesan, A. Org. Lett. 2002, 4, 3071.
36. MacFarlane, D. R.; Huang, J.; Forsyth, M. Nature 1999, 402,
792.
58. Zhang, J.; Wang, A.; Li, X.; Ma, X. Oxidative J. Catal. 2011,
279, 269.
330
www.jccs.wiley-vch.de
© 2012 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J. Chin. Chem. Soc. 2012, 59, 324-330