Oxidative desulfurization of gasoline by ionic liquids coupled with extraction by organic solvents

Article abstract of DOI:10.5935/0103-5053.20150355

In this work, desulfurization of real fluidized catalytic cracking (FCC) gasoline was investigated in dual steps; first in oxidative desulfurization (ODS) using imidazolium and pyrrolidonium based Br?nsted acidic ionic liquids (ILs) as solvent and catalyst and hydrogen peroxide as oxidant. In second step, extractive desulfurization took place using organic solvents of furfural, furfural alcohol and ethylene glycol. Variety of factors such as temperature, time, mass ratio of oil/ILs and regeneration and recycling of ILs, multiple-step desulfurization of ILs and organic solvents and solvent/oil ratio were also investigated. The S-content was significantly decreased to ca. 18 ppm from initial S-content of 260 ppm with a total S-removal of ca. 95percent in one-step ODS using pyrrolidonium based ILs coupled with five-step extraction desulfurization (EDS) using furfural alcohol as extractant. This work shows that oxidative desulfurization using ionic liquids coupled with extractive desulfurization using organic solvents is a potential method to produce clean gasoline.

Full text of DOI:10.5935/0103-5053.20150355

http://dx.doi.org/10.5935/0103-5053.20150355
J. Braz. Chem. Soc., Vol. 27, No. 6, 998-1006, 2016.
Printed in Brazil - ©2016 Sociedade Brasileira de Química
0
103 - 5053 $6.00+0.00
Article
Oxidative Desulfurization of Gasoline by Ionic Liquids Coupled with Extraction by
Organic Solvents
a
a
,a
,a
b
Rashid Abro, Shurong Gao, Xiaochun Chen,* Guangren Yu,* Ahmed A. Abdeltawab
b
and Salem S. Al-Deyab
a
Beijing Key Laboratory of Membrane Science and Technology & College of Chemical Engineering,
Beijing University of Chemical Technology, 100029 Beijing, P. R. China
b
Department of Chemistry, College of Science, King Saud University, 11451 Riyadh,
Saudi Arabia
In this work, desulfurization of real fluidized catalytic cracking (FCC) gasoline was investigated
in dual steps; first in oxidative desulfurization (ODS) using imidazolium and pyrrolidonium
based Brønsted acidic ionic liquids (ILs) as solvent and catalyst and hydrogen peroxide as
oxidant. In second step, extractive desulfurization took place using organic solvents of furfural,
furfural alcohol and ethylene glycol. Variety of factors such as temperature, time, mass ratio of
oil/ILs and regeneration and recycling of ILs, multiple-step desulfurization of ILs and organic
solvents and solvent/oil ratio were also investigated. The S-content was significantly decreased
to ca. 18 ppm from initial S-content of 260 ppm with a total S-removal of ca. 95% in one-step
ODS using pyrrolidonium based ILs coupled with five-step extraction desulfurization (EDS) using
furfural alcohol as extractant. This work shows that oxidative desulfurization using ionic liquids
coupled with extractive desulfurization using organic solvents is a potential method to produce
clean gasoline.
Keywords: gasoline, oxidative desulfurization, extractive desulfurization, ionic liquids,
ultra-clean fuel oil
Introduction
have imposed taxes on fuel oil refineries that fail to meet
the standard (Figure 1 shows the maximum gasoline
S-limits in different regions). The goal, of course, is to
realize ultra-low, possibly zero, S-content in gasoline in
the not-too-distant future.
4
The emission of sulfur (S) during combustion from
light fuel oils, coupled with increasing automobiles has
heightened concern on environmental pollution. The
sustained emission of these gases leads to air pollution,
acid rain, and global climate change as well as increases
health risk from continuous exposure to this smog.
Economically, it affects the catalytic converter emission
of vehicles resulting in inefficient fuel utilization and
poor performance. In 1998, the European Union instituted
legislations to monitor the S-limits in fuel oils by setting
up mandatory S-content limit to be less than 10 ppm
USA
5
4
3
00
00
00
Japan
EU
China (Beijing)
1
-3
or negligible level. In March 2014, the United States
Environmental ProtectionAgency proposed new standards
to further reduce the S-content from the current 30 to
200
1
00
0
1
0 ppm. In recent years, Japan has also made significant
efforts to reduce the S-content from 500 to 50 ppm. Some
European countries including Denmark and Germany
2
000
2005
2010
2015
Year
3
,5
*
e-mail: gryu@mail.buct.edu.cn, chenxc@mail.buct.edu.cn
Figure 1. Proposed sulfur limitations in gasoline in different countries.

Vol. 27, No. 6, 2016
Abro et al.
999
2
6-28
Hydrodesulfurization (HDS) is the well-established
method employed in industry for this regard, where
and “designer” solvents. Several ILs have been studied as
solvent in EDS for S-removal from fuel oils such as [1-butyl-
2
9,30
29,30
S-compounds are converted into hydrogen sulfide (H S)
3-methylimidazolium (Bmim)]PF6,
[1-methyl-3-octylimidazolium (Omim)]BF ,
[Bmim][CF SO ], [Omim][OcSO ], [Bmim]AlCl4,
[Bmim]BF4,
2
3
1,32
in the presence of catalyst at elevated temperatures and
pressures. HDS has some disadvantages such as the
need for expensive catalysts, high temperature (300 to
4
3
3
33
34
3
3
4
35
[Bmim]Cl/Cu Cl , [1-ethyl-3-methylimidazolium (Emim)]
2
3
3
6
37
3
40 °C) and high pressure (20 to 100 atm of H ). More
dicyanamide (DCA) and [Bmim]DCA. Compared
with EDS alone using ILs, some researchers observed
that ODS is much more efficient and S-removal can be
increased up to 90% from 10-40% in EDS, such as [butyl-
6-methylquinolinium (Bmimquin)]DCA in ODS process
removed 99.9% of S-contents at mild conditions from
2
importantly, aliphatic thiols and sulfides can effectively
be removed in HDS while thiophene and its derivatives
are not easily removed because of the steric hindrance
6
for catalysis. Therefore, some alternative techniques
7
-9
such as adsorption desulfurization (ADS), extraction
1
0-12
38
desulfurization (EDS),
oxidation desulfurization
model diesel fuel. In a typical ODS, S-compounds in
1
3,14
15,16
(
ODS),
and biodesulfurization (BDS)
are sought
gasoline fuel are extracted into the IL phase first, then
oxidized by some oxidant, and the oxidized product is
more polar and easily removable. The oxidant is usually
the cheap and environmentally benign hydrogen peroxide
(H O ) solution, while the catalysts are usually acetic acid,
vanadium pentoxide, decatungstates, peroxotungsten, or
in order to complement the HDS process. ODS is more
competitive and efficient in removing the thiophenic
17-19
S-compounds under mild conditions with low costs. The
use of molecular organic solvents such as dimethylsulfoxide
39
2
2
40
41
(
DMSO), dimethylformamide (DMF) and acetonitrile
42
in ODS has been patented; some problems, however,
exist in employing these organic solvents such as loss,
contamination, regeneration, recycling and safety issues
peroxomolybdenum complexes.
Due to regeneration and contamination problems of
acid catalyst, recently, some acidic ILs have been used in
ODS, where those ILs act as both catalyst and solvent,
and no other acid catalyst is added, as shown in Figure 2.
In the literature, most emphases are placed on model fuel
oils, which are configured by S-compounds (thiophene,
dibenzothiphene, and their derivatives) and a certain amount
of aliphatic (hexane, heptane, n-dodecane, etc.) and aromatic
(usually toluene) compounds while the investigations on real
feedstock are rather scarce, as listed in Table 1. The results
for model oils may not present a conclusive argument.
20-25
stemming from the volatile nature of organic solvents.
Recently, ionic liquids (ILs) have attracted increasing
attention thanks to their desirable physicochemical properties
such as negligible volatility, easy alteration of cation/anion
structure for specific applications, high thermochemical
stability and remarkable ability in dissolving organic/
inorganic compounds. With wide-ranging applications
in separation technology, nanotechnology, catalysis,
electrochemistry, etc., ILs are being acclaimed as “green”
Oil phase
IL phase
S
H O
2
2
S
S
IL
O
O
DBT
H O
2 2
DBT-sulfone
Figure 2. Oxidation of S-component using H O and ILs.
2
2

1
000
Oxidative Desulfurization of Gasoline by Ionic Liquids Coupled with Extraction by Organic Solvents
J. Braz. Chem. Soc.
Table 1. ODS of real fuels by ILs
Reaction conditions
IL/oil mass ratio
S0 / Desulfurization
ppm efficiency / %
ODS using IL system
Oil
Reference
Temperature /
K
ODS
steps molar ratio
O/S
time / h
[
[
Bmim]BF + H O
2
light oil
light oil
diesel
3640
1300
492
460
1000
795
97
54.72
83.83
87.3
63.5
73.0
64.3
85.5
87.7
49.5
45
333
333
333
313
363
333
RT
10
10
4
n/a
6
6
6
6
–
6
–
7
5
–
–
6
6
n/a
n/a
16
40
40
16
5
43
43
44
45
46
47
48
49
49
50
51
52
52
4
2
Bmim]PF + H O
2
n/a
6
2
C H NO·SnCl + H O
2
1
5
9
2
2
[
[
[
[
[
[
[
[
[
[
Bmim]Cl/3ZnCl -H O
diesel
3
1/2
2
2
2
Hmim]BF + H O
2
diesel
6
5:3.2 (v/v)
4
2
Hnmp]H PO + H O
2
diesel
4
1
2
4
2
Bmim]HSO + H O
2
diesel
2
1
1 or 1/2
4
2
Bmim]Cl/2ZnCl + H O
diesel
5380
64
363
363
298
328.15
333
333
1
50
50
6
2
2
2
Bmim]Cl/2ZnCl + H O
diesel
1
1 and 1/2
2
2
2
OmPy]FeCl + H O
gasoline
gasoline
diesel
468
780
225
225
0.5
0.5
3
1/5 or 1/3
4
2
2
BPy]BF + H O
56.3
83.9
97
IL/oil/H O = 1:1:0.4 (v/v/v)
–
4
2
2
2
2
Hnmp]Cl/ZnCl -H O
2
1
1
50
50
2
2
Hnmp]Cl/ZnCl -H O
2
diesel
3
2
2
with one EDS step with furfural at 313 K; 1 h, sol/oil ratio = 1
[
[
Hnmp]HSO + H O
2
gasoline
gasoline
260
260
57
94
333
333
4
4
1
1
6
1
16
16
this work
this work
4
2
Hnmp]HSO + H O +
4
2
2
furfural alcohol
with 5 EDS steps with furfural alcohol at 313 K, 1 h, sol/oil ratio = 1
[
[
Hnmp]H PO + H O
2
gasoline
gasoline
260
260
62
93
333
333
4
4
1
1
6
1
16
16
this work
this work
2
4
2
Hnmp]H PO + H O +
2
4
2
2
furfural alcohol
with 5 EDS steps with furfural alcohol at 313 K, 1 h, sol/oil ratio = 1
[
[
Bmim]H PO + H O
gasoline
gasoline
260
260
20.9
18.2
333
333
4
4
1
1
6
6
16
16
this work
this work
2
4
2
2
Bmim]HSO + H O
2
4
2
ODS: oxidative desulfurization; IL: ionic liquid; S : initial S-content; Bmim: 1-butyl-3-methylimidazolium; n/a: not applicable; Hmim: 1-hexyl-3-
0
methylimidazolium; Hnmp: N-methyl pyrrolidonium; RT: room temperature; OmPy: 1-octyl-3-methylpyridinium; BPy: N-butylpyridinium.
In this work, we synthesized four Brønsted acidic
ILs namely [Hnmp]HSO , [Hnmp]H PO , [Bmim]H PO
work shows that ODS using ILs coupled with EDS using
organic solvents is a potential method to produce clean
gasoline.
4
2
4
2
4
and [Bmim]HSO and investigated the desulfurization of
4
real fluidized catalytic cracking (FCC) gasoline in two
steps: the first in ODS using above ILs as extractant and
catalyst and H O as oxidant; the second in EDS using
Experimental
2
2
different organic solvents of furfural, furfural alcohol and
ethylene glycol (the ILs, also organic solvents, used in
this work are illustrated in Figure 3), involving a variety
of factors such as temperature, time, and regeneration of
ILs, multiple-step desulfurization and solvent/oil mass
ratio. These ILs act as both catalyst and solvent, also can
easily be prepared with cheaper starting materials and
can be regenerated easily, whereas all selected organic
solvents are also reasonable candidates for EDS due
to their physical characteristics, i.e., immiscible with
gasoline (gasoline is miscible with most organic solvents),
low volatility, less operational problems, good thermal
Chemicals and material
The chemicals are: N-methylimidazole (≥ 99.0%)
(Shanghai SenHao Fine Chemical); ethyl acetate (≥ 99.0%),
H O aqueous solution (30 wt.%), H SO (98%), H PO
2
2
2
4
2
4
(85%), N-methylpyrrolidone (NMP), furfural alcohol,
furfural and ethylene glycol (Beijing Chemical Plant).
N-Methylimidazole is further purified by distillation, and
the other chemicals were used as received without further
purification. Real FFC gasoline fuel with a total S-content
of 260 ppm was supplied by SINOPEC Beijing Yanshan
Petrochemical Co., Ltd (properties of gasoline are given
in Table 2).
o
stability and high boiling points (160-200 C). This

Vol. 27, No. 6, 2016
Abro et al.
1001
infrared (FTIR) spectroscopy and nuclear magnetic
resonance (NMR) spectra.
NH
N
HSO4
N
HSO4
CH3
CH3
O
[Hnmp]HSO4
-1
IR (KBr) νmax / cm 3406.2, 2979.5, 2895.7, 2521.7,
825.8, 1698.4, 1495.5, 1460.9, 1409.8, 1313.0, 1230.4,
167.7, 1021.7, 982.6, 881.0, 645.5, 578.4, 465, 434.8;
[
Bmim]HSO4
[Hnmp]HSO4
1
1
1
NH
N
H PO
4
H NMR (400 MHz, D O) d 4.88 (bs, 1H), 3.24-3.20 (t,
2
N
2
CH3
H PO
2
CH3
2H), 2.54 (s, 3H), 2.17-2.13 (d, 1H).1.77-1.73 (m, 2H).
4
O
[Bmim]H PO4
2
[
2
Hnmp]H PO4
[
Hnmp]H PO4
2
-1
IR (KBr) νmax / cm 2940.0, 2891.3, 1627.7, 1509.0,
1
6
408.8, 1307.6, 1260.9, 1117.0, 1003.7, 884.1, 747.8,
O
1
65.1, 665.1, 617.7, 486.2, 403; H NMR (400 MHz, D O)
2
O
O
OH
d 4.82 (bs, 1H), 3.32-3.28 (t, 2H), 2.45 (s, 3H), 2.08-2.04
d, 1H), 1.7-1.67 (m, 2H).
H
(
Furfural alcohol
OH
Furfural
OH
Preparation of [Bmim]HSO and [Bmim]H PO
4 2 4
[
Bmim]HSO and [Bmim]H PO derived from
4 2 4
Ethylene glycol
imidazole chloride salts were obtained by a drop-wise
addition of one equivalent of concentrated H SO
98%) or H PO (85%) to solution of the corresponding
1-butyl-3-methylimidazolium chloride in anhydrous
methylene chloride. The reaction proceeded at room
temperature for 24 h with vigorous stirring under a
stream of dry nitrogen. Then, the mixture was dried in
vacuum by a rotary evaporator to remove the HCl and
Figure 3. Structures of ILs and organic solvents used in this work.
Table 2. Physicochemical properties of gasoline
2
4
(
2 4
Property
Value
S-content
260 ppm
2
-1
Viscosity (20 °C)
Boiling point
Density
0.701 mm s
initially 40 °C
solvent to obtain the viscous clear [Bmim]HSO and
Bmim]H PO .
4
[
-
3
2 4
0.7-0.8 g cm
pale brown
Color
Desulfurization and recycling
Vapor pressure
Flash point
ca. 600 mm Hg
–46 °C
IL and desired amount of 30 wt.% H O were introduced
2
2
into a 150 mL round-bottom flask. The FCC gasoline fuel
was added, then mixture was magnetically stirred for
specified time and temperature for ODS process. Then
the mixture was allowed to settle for 5 min to obtain
phase splitting and the S-content in the upper oil phase
was measured. For EDS using organic solvents, desired
amount of organic solvent and FCC gasoline fuel were
put into 150 mL round-bottom flask. Then mixture was
magnetically stirred at a desired time and temperature. The
upper oil phase was periodically removed and analyzed
for S-content. After each ODS, the bottom IL phase was
treated with a rotary evaporator to remove impurities, and
the IL was recycled.
Synthesis of ILs
[
Hnmp]HSO , [Hnmp]H PO , [Bmim]HSO and
4 2 4 4
[
Bmim]H PO were synthesized according to the
2 4
5
3-55
procedures as mentioned in the literature.
Preparation of [Hnmp]HSO and [Hnmp]H PO
4
4
2
NMP (60 mL) was placed in a three-necked flask, which
was provided with a stirrer at room temperature. Then,
stoichiometric amount of H SO (98%) or H PO (85%) was
added to the three-necked flask slowly over a period of 1 h
while stirring at room temperature. The reaction mixture
2
4
2
4
o
was stirred and heated to 80 C for 2 h. The residual reactant
and water were removed by a rotary evaporator. The IL was
dried in vacuum to give the product as a colorless liquid.
S-content analysis
The nature of cation and anion in [Hnmp]HSO and
Hnmp]H PO was determined with Fourier transform
2 4
The S-content in real FFC gasoline fuel oil was
analyzed by a WK-2D microcoulomb analyzer (Jiangfen
4
[

1
002
Oxidative Desulfurization of Gasoline by Ionic Liquids Coupled with Extraction by Organic Solvents
J. Braz. Chem. Soc.
Electroanalysis Co., Ltd.), in which high purity nitrogen
gas was used as carrier gas while oxygen gas was used as
reaction gas; select vaporization zone temperature: 620 °C;
combustion zone temperature: 820 °C; temperature of
stable segment: 720 °C.
Reaction time
The ODS results using [Hnmp]HSO and [Hnmp]H PO
4
4
2
at 2, 4, and 6 h are shown in Figure 5. Four hours are
enough to reach the equilibrium of desulfurization when the
S-removal efficiencies are 25.4 and 23.7% for [Hnmp]HSO4
and [Hnmp]H PO , respectively, at 60 °C, IL/oil = 1 and
O/S = 16 after single step, while S-removal are only slightly
increased to 25.6 and 24.1%, respectively, after 6 h. Two
hours are too short when the S-removal efficiencies are
16.2 and 17.1% for [Hnmp]HSO and [Hnmp]H PO ,
Results and Discussion
ODS using ILs
2
4
The ODS results of FFC gasoline fuel by four Brønsted
4
2
4
o
ILs for one step at 60 C, time = 4 h, IL/oil mass ratio = 1
respectively. Thus, 4 h may be considered as a moderate
time for better ODS desulfurization result.
and O/S molar ratio = 16 are shown in Figure 4. Efficiency
of S-removal from FFC gasoline follows the order
4
3
2
0
0
0
[
Hnmp]HSO > [Hnmp]H PO > [Bmim]HSO >
[Hnmp]HSO4
4
2
4
4
[
2
Hnmp]H PO4
[
Bmim]H PO with S-removal efficiencies of 25.3 >
2
4
2
3.8 > 20.9 > 18.2%, respectively. Here, the S-removal
efficiency is defined as
(1)
where S is the S-content in the gasoline before ODS
0
and S is the S-content after ODS. The acidities of
10
f
[
Hnmp]HSO and [Hnmp]H PO are expected to be
4 2 4
stronger than that of [Bmim]HSO and [Bmim]H PO ,
4
2
4
+
respectively, because there is acidic proton on [Hnmp] ,
which is favorable when ILs act as acidic catalyst.
0
2
4
time / h
6
[
Hnmp]HSO and[Hnmp]H PO withhighestdesulfurization
4 2 4
Figure 5. Influence of time on ODS S-removal efficiency of
Hnmp]H PO and [Hnmp]HSO (after one-step ODS, 60 °C, 260 ppm
of initial S-content, 16 of molar ratio of O/S, 1:1 of mass ratio of IL/oil).
efficiency are chosen to undergo further investigation for
the different parameters on S-removal efficiency such as
reaction time, temperature, multiple ODS steps, recycling
efficiency.
[
2
4
4
Reaction temperature
The effects of temperature on ODS desulfurization
performance by [Hnmp]HSO and [Hnmp]H PO are
2
2
1
1
5
0
5
0
5
0
4
o
2
4
investigated at 30, 45 and 60 C. The results are shown
in Figure 6. A rise in the reaction temperature from 30
o
to 60 C leads to a remarkable increase in the S-removal
efficiency using [Hnmp]HSO and [Hnmp]H PO from 12
4
2
4
to 25.3% and 11.6 to 23.7%, respectively, with one step
4 h, IL/oil = 1, O/S = 16). These results can be explained
(
by the strong dependence of the oxidation reaction rate on
the reaction temperature. In addition, higher temperature
may decrease the viscosity of ILs, enhance effective mixing
and inter-phase mass transfer, and H O may be used
2
2
50-52
effectively after decomposition.
On the other hand, too
[
Hnmp]HSO4 [Hnmp]H PO
[Bmim]HSO4 [Bmim]H PO4
2
2
4
high temperatures are not good choice and might lead to
auxiliary risk of explosion in the process, although high
Figure 4. ODS S-removal efficiency by four Brønsted acidic ILs:
Hnmp]HSO , [Hnmp]H PO , [Bmim]HSO , and [Bmim]H PO (after
one-step ODS, 60 °C, 4 h, 260 ppm of initial S-content, 16 of molar ratio
of O/S, 1:1 of mass ratio of IL/oil).
[
4
2
4
4
2
4
temperature enhances H O decomposition. Therefore,
2
2
reaction at higher temperature should be carefully avoided.

Vol. 27, No. 6, 2016
Abro et al.
1003
3
2
2
1
1
0
5
0
5
0
5
0
Thus, a moderate temperature of 60 °C presents the best
desulfurization result.
[
Hnmp]HSO4
30
25
20
15
10
5
0
[
[
Hnmp]HSO4
Hnmp]H PO
2
4
1
2
3
4
5
6
Regeneration cycle
30
30
45
60
[Hnmp]H PO4
2
o
Temperature /
C
25
20
15
10
5
0
Figure 6. Influence of temperature for ODS S-removal efficiency of
Hnmp]H PO and [Hnmp]HSO (after one-step ODS, 4 h, 260 ppm of
initial S-content, 16 of molar ratio of O/S, 1:1 of mass ratio of IL/oil).
[
2
4
4
IL regeneration
Regeneration of ILs is a necessary process from
environmental and economical point of view.After each ODS
run, the ILs phase undergoes rotary evaporation to remove
impurities, and then the system is charged again with fresh
H O solution for the next ODS cycle. The desulfurization
2
2
results by [Hnmp]HSO and [Hnmp]H PO after six cycles
4
2
4
1
2
3
4
5
6
are shown in Figure 7. Results indicate that [Hnmp]HSO and
4
Regeneration cycle
[
Hnmp]H PO can be regenerated and then recycled more
2 4
Figure 7. Influence of IL recycling on S-removal efficiency by
Hnmp]HSO and [Hnmp]H PO (after one-step ODS, 60 °C, 4 h, 260 ppm
of initial S-content, 16 of molar ratio of O/S, 1:1 of mass ratio of IL/oil).
than six times with no notable decline in efficiency, e.g., the
S-removal only drops from 25.2 to 23.7% for [Hnmp]HSO4
and 23.8 to 22.4% for [Hnmp]H PO . This small decline
[
4
2
4
2
4
52
might be ascribed to accumulation of oxidation products.
EDS using organic solvent after ODS
Multiple-step ODS
The EDS results by furfural, ethylene glycol and furfural
alcohol for gasolinesA and B are shown in Figure 9, where
gasolineAisthegasolineafterone-stepODSby[Hnmp]HSO4
and gasoline B is that after one-step ODS by [Hnmp]H PO .
ODS by multiple-step is an effective way to reduce the
S-content of heterocyclic compounds in FCC gasoline.
The desulfurization results after multiple-step are shown
in Figure 8. After first ODS step, S-content from real
FCC gasoline decreased from 260 to 194.6 ppm by
2
4
As shown in Figure 9, these solvents present very different
EDS capability. It is observed interestingly that the final
S-contents in gasoline can be reduced to < 20 ppm with
about 95% S-removal after 5-step EDS by furfural and
furfural alcohol; while the EDS capability by ethylene
glycol is far from that by furfural and furfural alcohol, e.g.,
the final S-content in gasoline is larger than 110 ppm with
only about 55% S-removal by ethylene glycol. As shown
in Table 1, where some ODS results of real gasoline and
diesel fuel using ILs are summarized, our results are very
competitive. It has to be mentioned that the ODS results
[
Hnmp]HSO , and to 198 ppm by [Hnmp]H PO with 25.3
4
2
4
and 23.8% desulfurization efficiencies.After six ODS cycles,
desulfurization efficiencies of real FFC gasoline fuel by
[
Hnmp]HSO and [Hnmp]H PO increased to 57 and 62%,
4 2 4
respectively. Overall, this performance is not at desired
level, when we compare these results with ODS using ILs
of model fuels from literature due to complex composition
of real FCC gasoline.

1
004
Oxidative Desulfurization of Gasoline by Ionic Liquids Coupled with Extraction by Organic Solvents
J. Braz. Chem. Soc.
[
Hnmp]HSO4
160
(a)
Furfural
Furfural alcohol
Ethylene glycol
2
50
00
50
00
1
1
1
40
20
00
2
1
1
80
60
40
20
0
5
0
0
0
1
2
3
4
5
6
1
2
3
4
5
Step
Extraction step
2
2
1
1
50
00
50
00
[Hnmp]H PO4
2
Furfural
(
b)
1
1
1
1
60
40
20
00
Furfural alcohol
Ethylene glycol
8
6
4
2
0
0
0
0
0
5
0
0
0
1
2
3
4
5
6
Step
1
2
3
4
5
Figure 8. Influence of multiple steps of ODS desulfurization of
Extraction step
[
Hnmp]HSO and [Hnmp]H PO (60 °C, 4 h, 260 ppm of initial S-content,
4
2
4
1
6 of molar ratio of O/S, 1:1 of mass ratio of IL/oil).
Figure 9. EDS S-removal efficiency of (a) gasoline A and (b) gasoline B
by organic solvents (40 °C, 1 h, 1:1 of mass ratio of solvent/oil).
for gasoline are not as good as diesel fuel, which might
be ascribed to the different S-species in gasoline and
diesel fuel. Further, Figure 9 shows furfural alcohol has
slightly better ODS capacity than furfural, and furfural
alcohol can reduce the S-content in gasolineA to 16.1 ppm
2
1
00
90
Gasoline A
Gasoline B
(
93% S-removal) and in gasoline B to 16.8 ppm (94%
180
S-removal). Furfural alcohol was chosen to undergo further
investigation for the extraction temperature, extraction time,
and solvent/gasoline ratio for gasolines A and B.
1
1
1
70
60
50
Extraction temperature
The results of one-step EDS by furfural alcohol for
140
130
o
gasolines A and B at 30, 40, 50 and 60 C are shown in
o
Figure 10. The best results are obtained at 40 C, where the
3
0
35
40
45
50
55
60
S-contents are reduced to 144 and 142 ppm for gasolinesA
and B, respectively (1 h, mass ratio of solvent/oil 1:1). The
S-removals at 30 C are slightly lower than that at 40 C,
which might be ascribed to the slow mass transfer at lower
o
C
Temperature /
Figure 10. Influence of temperature for EDS S-removal efficiency
for gasolines A and B (after one-step EDS, 1 h, 1:1 of mass ratio of
solvent/oil).
o
o

Vol. 27, No. 6, 2016
Abro et al.
1005
temperature.As a whole, the temperature has limited impact
on desulfurization in the investigated temperature range.
180
165
Gasoline A
Gasoline B
1
50
Extraction time
135
1
1
20
05
The results of one-step EDS by furfural alcohol for
gasolines A and B at 15, 30, 60 and 120 min are shown in
Figure 11.As shown in Figure 11, the extractive equilibrium
can be reached after 30 min, when the S-contents are
decreased to 143 and 145 ppm for gasolines A and B,
respectively.
9
7
6
4
3
1
0
5
0
5
0
5
0
2
1
1
1
1
1
1
1
1
00
90
80
70
60
50
40
30
20
Gasoline A
Gasoline B
3
:1
2:1
1:1
1:2
Solvent/oil ratio
Figure 12. Influence of solvent/oil ratio for EDS S-removal efficiency
for gasolines A and B (after one-step EDS, 40 °C, 1 h).
furfural alcohol and ethylene glycol as extractants. The more
acidic [Hnmp] ILs with proton have better ODS performance
than [Bmim] ILs, following [Hnmp]HSO > [Hnmp]H PO >
Bmim]HSO > [Bmim]HPO . The S-content in the FCC
gasoline with initial S-content of 260 ppm can be decreased
4
2
4
110
[
4
4
1
00
9
8
0
0
to 194 ppm (25.3% S-removal) by [Hnmp]HSO and
98 ppm (23.7% S-removal) by [Hnmp]H PO after one-step
4
1
2 4
0
20
40
60
80
100
120
ODS (60 °C, IL/oil = 1, O/S = 16), and be further decreased
to 111 ppm (57% S-removal) and 99 ppm (62% S-removal),
respectively, after six-step ODS at the same conditions. The
S-content in gasoline after one-step ODS can be significantly
decreased to < 20 ppm by EDS using organic solvents, e.g.,
the five-step EDS using furfural alcohol as extractant (40 °C,
1 h, mass ratio of solvent/oil 1:1) can reduce the S-content
to 16-17 ppm with ca. 94% S-removal. The work shows that
ODS using ILs coupled with EDS using organic solvents is
a potential method to produce clean gasoline.
Extraction time / min
Figure 11. Influence of time for EDS S-removal efficiency for gasolines
A and B (after one-step EDS, 40 °C, 1:1 of mass ratio of solvent/oil).
Solvent/oil ratio
The solvent/oil mass ratio is one of the important factors
for the selectivity of solvent for desulfurization. The results
of one-step EDS by furfural alcohol for gasolines A and
B at the solvent/oil mass ratios of 3:1, 2:1, 1:1 and 1:2
are shown in Figure 12. As expected, more S-removal is
observed with more furfural alcohol, i.e., a larger solvent/
oil mass ratio. We have to carefully select the solvent/oil
mass ratio and compare between the S-removal efficiency
and the solvent cost in industry.
Acknowledgments
This work was financially supported by National
Natural Science Foundation of China (21176021,
2
1276020). We extend our appreciation to the Deanship of
Conclusions
Scientific Research at King Saud University for funding the
work through the research group project No. RG-1436-026.
ODS by ILs, as an alternative method to HDS, has been
intensively studied recently. In this work, we synthesized
four Brønsted acidic ILs of [Hnmp]HSO , [Hnmp]H PO ,
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