6890
Ind. Eng. Chem. Res. 2008, 47, 6890–6895
Deep Oxidative Desulfurization of Fuels Using Peroxophosphomolybdate Catalysts in Ionic Liquids Lining He,†,‡ Huaming Li,*,†,§ Wenshuai Zhu,† Junxiang Guo,† Xue Jiang,† Jidong Lu,§ and Yongsheng Yan† College of Chemistry and Chemical Engineering, Jiangsu UniVersity, Zhenjiang 212013, People’s Republic of China, College of the EnVironment, Jiangsu UniVersity, Zhenjiang 212013, People’s Republic of China, and State Key Laboratory of Coal Combustion, Huazhong UniVersity of Science and Technology, Wuhan 430074, People’s Republic of China
A combination of catalytic oxidation and extraction in ionic liquid (IL) was used for the removal of benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) from the model oil. Three peroxophosphomolybdates Q3{PO4[MoO(O2)2]4} (Q ) [(C4H9)4N]+, [C14H29N(CH3)3]+ and [C16H33NC5H5]+) were synthesized and characterized. In the catalytic oxidation desulfurization (CODS) system containing the peroxophosphomolybdate with short alkyl chain ([(C4H9)4N]3{PO4[MoO(O2)2]4}) and H2O2, the process exhibited low sulfur removal (16.8%). However, with addition of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), the extraction and catalytic oxidative desulfurization (ECODS) system remarkably increased the removal of sulfur to 97.3% (with stoichiometric amounts of H2O2). The process was superior to the simple extraction with IL (16.3%). The results demonstrated that the ECODS system could deeply remove DBT from the model oil, and this desulfurization system could be recycled 4 times with slight decrease in activity. We also found that the catalysts with short alkyl chains exhibited higher catalytic activity than that with long alkyl chain in the ECODS system. Moreover, the reactivity of sulfur compounds decreased in the order of DBT > 4,6-DMDBT > BT. 1. Introduction Sulfur compounds in fuels have been a major source of air pollution. For environmental protection purposes, more stringent regulations and fuel specifications have been regulated and desulfurization of fuels has attracted wide attention.1,2 The future trend will be to produce sulfur-free gasoline and diesel in the next several years. In the petroleum refining industry, hydrodesulfurization (HDS) is a conventional method for the removal of sulfur compounds. However, some refractory sulfur compounds, such as benzothiophene (BT), dibenzothiophene (DBT), and their derivatives are difficult to remove due to their steric hindrance. To gain the desired low levels of sulfur in fuels, it requires both high temperatures and high hydrogen pressures to decrease the sulfur content, which lead to high capital expenditure. In the past several years, alternative deep desulfurization techniques have been extensively investigated, for example, oxidation,3–21 extraction,22–28 adsorption,29–31 and bioprocesses.32 Among these processes, oxidative desulfurization (ODS) has attracted much attention in the last few decades. ODS combined with extraction is considered as one of the most promising processes. Various studies on the ODS process have employed different oxidizing agents such as molecular oxygen,3 hydrogen peroxide,4–14 nitric acid/NO2,15 and tert-butyl hydroperoxide (tBuOOH).21 Among those oxidants, hydrogen peroxide has been widely used, because it is cheap, nonpolluting, not strongly corrosive and commercially available. It has been used in the presence of catalysts like polyoxometalates, amphiphilic cata* To whom correspondence should be addressed. Tel: 86 51188791800. Fax: 86 511 88791708. E-mail:
[email protected]. † College of Chemistry and Chemical Engineering, Jiangsu University. ‡ College of the Environment, Jiangsu University. § State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology.
lysts of polyoxometalates associated with long-chain-containing quaternary ammonium ions in emulsions.4–6 The ODS process can oxidize sulfur compounds into their corresponding sulfones, which are then removed by selective extraction with organic solvents. By the two processes, low-sulfur fuels can be achieved. However, a large number of flammable and volatile organic compounds (VOCs) are used as extractants, which raise further environmental and safety concerns. The room temperature ionic liquids (RTILs) are considered as “green solvents”33 and environmentally benign alternative solvents for catalysis and separations. In recent papers, the desulfurization of fuels by extraction with RTILs has been reported.22–28 However, the effect of sulfur removal is rather low due to the similarity between the sulfur-containing molecules and the remaining fuels. For instance, Bosmann23 has described that [Bmim]PF6, [Bmim]BF4, and [Bmim]OcSO4 are utilized as extractants, the sulfur removal only reached 12%, 16%, and 30%, respectively. A combination of chemical oxidation and extraction with RTILs can remarkably increase the sulfur removal. Lo34 has reported that [Bmim]PF6 and H2O2-acetic acid are employed together to remove DBT from model oil. The desulfurization system of the acidic ionic liquid ([HMim]BF4 and [Hnmp]BF4) and H2O2 has been studied by Lu35 and Zhao,36 the sulfur removal can reach above 90%. The results of these experiments show that the oxidation/extraction is superior to the mere extraction with IL. In previous work,37 our group has found that peroxotungsten complex is used for removing sulfur compounds from model oil. But a large amount of hydrogen peroxide (O/S ) 10) is employed. The useful efficiency of hydrogen peroxide is low. More efficient desulfurization methods should be developed from the industrial perspective. Polymolybdates are efficient catalysts and are usually adopted in organic reaction. For example, alumina-supported polymolybdates have been used for denitrogenation.21 Peroxomolybdates have been employed in catalytic oxidation of tertiary amines,
10.1021/ie800857a CCC: $40.75 2008 American Chemical Society Published on Web 08/06/2008
Ind. Eng. Chem. Res., Vol. 47, No. 18, 2008 6891 Scheme 1. Representative Extraction and Catalytic Oxidation Reaction of DBT In an Oil-Ionic Liquid System
alkenes, and alcohols.38 Few reports have presented that the peroxophosphomolybdate with short alkyl chain is employed for deep desulfurization of fuel. In this paper, the use of a novel combination of the peroxophosphomolybdate with short alkyl chain, hydrogen peroxide, and IL for extraction and catalytic oxidation desulfurization (ECODS) of fuel oil is described. The ILs 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-n-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF4), 1butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6), 1-noctyl-3-methylimidazolium hexafluorophosphate ([Omim]PF6),and 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA) are immiscible with n-octane phase and formed biphasic system, in which the n-octane phase is the upper layer and IL phase is the lower layer. DBT is extracted from model oil and is oxidized in IL, the corresponding sulfone products can be readily separated from the fuel (Scheme 1). When the catalyst with short alkyl chain ([(C4H9)4N]3{PO4[MoO(O2)2]4}) and H2O2 are employed together in the absence of IL, the sulfur removal only reaches 16.8%. However, with addition of [Bmim]BF4, the ECODS system remarkably increases the sulfur removal to 97.3%. [(C4H9)4N]3{PO4[MoO(O2)2]4} dissolved into [Bmim]BF4 exhibits high catalytic activity in the oxidation of DBT. With stoichiometric amounts of H2O2, the sulfur compounds can be almost completely removed from the model oil. 2. Experimental Section 2.1. Preparation of Peroxophosphomolybdates.39,40 [(C4H9)4N]3{PO4[MoO(O2)2]4} (I). A solution of tetrabutylammonium bromide [(C4H9)4N]Br (1.0 g, 3.1 mmol) in 30% H2O2 (40 mL) was added to phosphomolybdic acid hydrate H3PMo12O40 · 13H2O, (2.1 g, 1.0 mmol) in 30% H2O2 (10 mL). The mixture was stirred vigorously at 40 °C for 4 h. The suspended mixture was cooled to room temperature until a white precipitate was produced, which was filtered off and washed with deionized water and ethanol and dried. The preparation of the compounds [C16H33NC5H5]3{PO4[MoO(O2)2]4} and [C14H29N(CH3)3]3{PO4[MoO(O2)2]4} was
similar to the compound I. But short chain quaternary ammonium cation was replaced by long chain lipophilic cation. 2.2. Preparation of Different Model Oil. Dibenzothiophene (1.466 g, 7.793 mmol, 98%) was dissolved in a solvent of n-octane (250 mL). The sulfur content of model oil containing DBT was 1000 ppm. With the same method, the sulfur content of model oil containing BT and 4,6-DMDBT was 1000 ppm and 500 ppm, respectively. 2.3. DBT Oxidation. The ionic liquids were prepared by the published procedures.41–43 The oxidative and extractive desulfurization experiments of the model oil were carried out in a homemade 40 mL two-necked flask. 0.00156 mmol of catalyst [n(DBT)/n(catalyst) ) 100], 0.032 mL of 30 wt % H2O2 [n(H2O2)/n(DBT) ) 2] and the extracting solvent with IL (1 mL) was dissolved in the flask and then 5 mL of model oil (sulfur concentration was 1000 ppm) was added. The resulting mixture was stirred vigorously and heated to 70 °C in oil bath. The upper phase (n-octane) was withdrawn and analyzed for sulfur content by GC-flame ionization detector (GC-FID), SE54 capillary column (15 m × 0.32 mm inner diameter × 1.0 µm film thickness). 2.4. Instrumentation. The FT-IR spectrum was performed on a Nicolet FT-IR spectrophotometer (Nexus 470, Thermo Electron Corporation) using KBr disks at room temperature. Elementary (C, H, and N) analyses were performed using CHN-O-Rapid (Heraeus Corporation). The UV-vis spectrum was recorded on UV-2450 spectrophotometer (Shimadzu Corporation, Japan) in acetonitrile. TG/DTA was done on STA449C Jupiter (NETZSCH Corporation, Germany). The content of peroxo species was measured by the iodine titration. 3. Results and Discussion 3.1. Characterization of Catalysts. Compared with the calculated values, the elementary analyses and the content of peroxo species of catalysts showed similar results. (Found: H, 7.47;C,39.57;N,2.64;O22-,8.45.Calcdfor[(C4H9)4N]3{PO4[MoO-
6892 Ind. Eng. Chem. Res., Vol. 47, No. 18, 2008 Table 1. Data of IR and UV-Vis entry
FT-IR(cm-1)
catalyst Q3{PO4[MoO(O2)2]4} ν(PO4)
1 2 3
[(C4H9)4N]+ [C16H33NC5H5]+ [C14H29N(CH3)3]+
1070 1070 1070
UV-vis(nm)
ν(MdO)
ν(O-O)
νasym [M(O)2]
νsym [M(O)2]
963 970 984
874 868 869
587 588 592
543 541 543
1042 1041 1049
λmax 269 261 270
Figure 1. TG/DTA curves of [(C4H9)4N]3{PO4[MoO(O2)2]4}.
Figure 2. TG/DTA curves of [C14H29N(CH3)3]3{PO4[MoO(O2)2]4} and [C16H33NC5H5]3{PO4[MoO(O2)2]4}.
(O2)2]4}: H, 7.13; C, 37.78; N, 2.75; O22-, 8.38. Found: H, 7.22; C, 38.24; N, 2.72, O22-, 8.12. Calcd for [C14H29N(CH3)3]3{PO4[MoO(O2)2]4}: H, 7.33; C, 39.06; N, 2.68; O22-, 8.16. Found: H, 6.93; C, 45.57; N, 2.42; O22-, 7.51. Calcd for [C16H33NC5H5]3{PO4[MoO(O2)2]4}: H, 6.71; C, 44.19; N, 2.45; O22-, 7.48). The FT-IR and UV-vis spectroscopy of the catalysts are collected in Table 1. A similar IR spectrum of [N(C6H13)4]3{PO4[MoO(O2)2]4} was obtained by Dengel.39 Thermogravimetry (TG) and differential thermal analysis (DTA) of [(C4H9)4N]3{PO4[MoO(O2)2]4} under nitrogen showed that compound I excluded crystalline water because there was no mass loss under 100 °C, as shown in Figure 1. This result demonstrated that the catalyst did not contain crystalline water and coordinated water.38 Compound I decomposed with mass loss in the first step from 125.8 °C to 152.4 °C and the corresponding exothermic peak of DTA curve emerged at 152.4 °C, which indicated that peroxo species decomposed. Then, from 180.2 °C to 475.4 °C, compound I went on decomposing; the mass loss of the second step contributed to the organic cation [(C4H9)4N]+ leaving. The corresponding endothermic peak of DTA curve emerged. The final remainders were phosphor oxide and molybdenum oxide. The other compounds of TG/DTA curves were shown a similar decomposition process (Figure 2). 3.2. Influence of Different Desulfurization System For Model Oil. The sulfur removal of different reaction systems are listed in Table 2. The catalyst and H2O2 could dissolve in [Bmim]BF4; then the biphasic system was formed, in which the oil phase was the upper layer and the IL phase, along with catalyst and oxidizing agent, was the lower layer. In the catalytic oxidation desulfurization (CODS) system, the catalyst with a short alkyl chain exhibited stronger hydrophilicity rather than hydrophobicity, and it cannot form the metastable emulsion droplet system, nor can it catalyze the oxidation of sulfides in the model oil due to the poor emulsifying ability of the catalyst, as a result of which the removal of sulfur was low (16.8%). Interestingly, with addition of [Bmim]BF4, the removal of DBT could reach 97.3% with stoichiometric amounts of H2O2, which demonstrated that IL played a vital role in the
ECODS process. DBT was extracted into IL and was oxidized in IL. The process was also superior to the simple extraction with IL (16.3%) or the oxidation/extraction without catalyst (31.5%). This experiment clearly indicated that a combination of extraction and catalytic oxidation can deeply remove DBT from a model oil. From the result, we concluded that [Bmim]BF4 was a benign extractant and reaction media. The results also demonstrated the obvious advantage of this process over the desulfurization system of H2O2/CH3COOH/ [Bmim]BF4.34 In this experiment, two catalysts with long alkyl chains ([C14H29N(CH3)3]3{PO4[MoO(O2)2]4} and [C16H33NC5H5]3{PO4[MoO(O2)2]4}) exhibited high catalytic activity in the absence of IL. The results obtained in this work corresponded to that described for the emulsion droplet system.5 In the CODS system, Li6 described that long alkyl chain quaternary ammonium ions associated with polyoxometalates exhibited high catalytic activity in the oxidation of DBT and its derivatives because metastable emulsion droplets (water in oil) were formed when the catalyst and H2O2 were mixed in the fuel. However, after addition of [Bmim]BF4 in the CODS system, the activity of long alkyl chain catalyst decreased. This phenomenon lay in that long alkyl chain catalyst dissolved in IL and the metastable emulsion droplets were destroyed, leading to low sulfur removal. Moreover, as the length of the alkyl chain of catalyst increased, the sulfur removal decreased. The reactivity order of the catalyst was [(C4H9)4N]+ > [C14H29N(CH3)3]+ > [C16H33NC5H5]+. The activity of the catalyst with long alkyl chain in the ECODS system showed the reverse trend compared to the emulsion droplet system. When considered in this manner, this trend can be explained as follows: Steric hindrance of the long alkyl chain of the catalytic active species became an obstacle for the approach of the sulfur atom to the catalytic active species in IL. Therefore, in the ECODS system, the catalyst with the short alkyl chain exhibited higher catalytic activity than that with the long alkyl chain. 3.3. Influence of the H2O2/Sulfer Molar Ratio (O/S) on the Reaction. In the experiments described above, the desulfurization system containing [(C4H9)4N]3{PO4[MoO(O2)2]4}, H2O2, and [Bmim]BF4 exhibited high catalytic activity. To study the effect of the amount of oxidizing agent on the
Ind. Eng. Chem. Res., Vol. 47, No. 18, 2008 6893 a,b
Table 2. Sulfur Removal of Different Desulfurization System in Model Oil entry
catalyst
S-removal of different desulfurization system/%
Q3{PO4[MoO(O2)2]4}
catalyst + H2O2
IL + catalyst + H2O2
16.8 90.9 96.2
97.3 88.1 81.3
[(C4H9)4N]+ [C14H29N(CH3)3]+ [C16H33NC5H5]+
1 2 3 4
IL + H2O2
IL
31.5
16.3
Conditions: T ) 70 °C, t ) 3 h, model oil ) 5 mL, IL ) 1 mL, [n(H2O2)/n(DBT)/n(catalyst) ) 200:100:1]. Model oil: 1000 ppm sulfur as DBT in n-octane; IL: [Bmim]BF4; the different amphiphilic quaternary ammonium peroxophosphomolybdates as the catalysts (Q3{PO4[MoO(O2)2]4}; Q ) quaternary ammonium cations). a
b
Figure 3. Removal of DBT in model oil versus the ratio of H2O2 and sulfur. Conditions: T ) 70 °C, t ) 3 h, model oil ) 5 mL, [Bmim]BF4 ) 1 mL, and [n(DBT)/n(catalyst) ) 100:1].
Figure 4. Influence of the reaction temperature on sulfur removal. Conditions: model oil ) 5 mL, [Bmim]BF4 ) 1 mL, [n(H2O2)/n(DBT)/ n(catalyst) ) 200:100:1].
Table 3. Influence of the Different Sulfur/Catalyst Molar Ratio on the Removal of DBTa
Table 4. Different ILs on DBT desulfurizationa
entry
1
2
3
4
n(sulfur)/n(catalyst) sulfur removal (%)
200:1 86.7
150:1 90.6
100:1 97.3
50:1 98.3
a Reaction conditions: T ) 70 °C, t ) 3 h, model oil ) 5 mL, [Bmim]BF4 ) 1 mL, [n(H2O2)/n(DBT) ) 2:1].
oxidative properties, the desulfurization reactions under various H2O2/sulfur (O/S) molar ratios were carried out at 70 °C for 3 h. According to the stoichiometric reaction, 2 mol of hydrogen peroxide are consumed for every 1 mol of sulfur-containing compound. The sulfur removal of different molar ratios of H2O2 and DBT are shown in Figure 3. From the figure, we can know that the molar ratio of H2O2 and DBT had a strong influence on the reaction. As the molar ratio of H2O2 and DBT increased from 2:1 to 6:1, the removal of DBT from the model oil increased from 97.3% to 99.2%. Compared with other reported work,34,35,37 hydrogen peroxide showed higher useful efficiency in the ECODS system, which may be because IL stabilized the hydrogen peroxide in the reaction. 3.4. Influence of DBT/Catalyst Molar Ratio. Table 3 shows the removal of DBT in the model oil after the extraction and catalytic oxidation. When the molar ratio of DBT and catalyst decreased from 200:1 to 50:1, the sulfur removal of model oil increased from 86.7% to 98.3%. In the ECODS system, the sulfur removal increased with increasing catalyst dosage. This experiment clearly demonstrated that the catalyst dosage was a main factor of influencing reaction activity. 3.5. Influence of Reaction Temperature. To investigate the effect of the desulfurization system containing [(C4H9)4N]3{PO4[MoO(O2)2]4, H2O2, and [Bmim]BF4 in various reaction times and temperatures, we carried out these experiments. Figure 4 shows the removal of DBT vs reaction time at different temperatures. The data at time zero reflected the ability of
entry
desulfurization system
sulfur removal (%)
IL + [(C4H9)4N]3{PO4[MoO(O2)2]4} + H2O2 1 2 3 4 5
[Bmim]BF4 [Omim]BF4 [Bmim]PF6 [Omim]PF6 [Omim]TA
97.3 83.2 90.7 94.5 67.6
a Reaction Conditions: T ) 70 °C, t ) 3 h, model oil ) 5 mL, [n(H2O2)/n(DBT)/n(catalyst) ) 200:100:1], IL ) 1 mL.
[Bmim]BF4 to extract DBT from n-octane at room temperature. The sulfur content of the model oil decreased from 1000 to 837 ppm. The higher the reaction temperature became, the faster the oxidation rate of DBT. DBT could be almost completely oxidized into DBT-sulfone at 70 °C in 4 h. The sulfur removal reached 96.5% and 92.6% at 60 and 50 °C, respectively. 3.6. Influence of Different ILs on DBT Desulfurization. From the data of Table 2, we found that the desulfurization system of [Bmim]BF4, [(C4H9)4N]3{PO4[MoO(O2)2]4 and H2O2 could deeply remove DBT from the model oil. To investigate the influence of different ILs on desulfurization, five ILs [Bmim]BF4, [Omim]BF4, [Omim]TA, [Omim]PF6 and [Bmim]PF6 were used as extractants, respectively. The sulfur removal with different ILs in the ECODS system is given in Table 4. The catalyst could dissolve in five ILs, but H2O2 was immiscible with [Omim]BF4, [Omim]PF6, and [Bmim]PF6, and triphasic systems were formed, in which the oil phase was the upper layer, H2O2 was middle layer, and the IL phase, along with catalyst, was the lower layer. For [Bmim]BF4 and [Omim]TA, biphasic systems were formed, in which the oil phase was the upper layer, and the IL phase, along with catalyst and oxidizing agent, was the lower layer. Sulfur removal reached 67.6% in [Omim]TA, 83.2%, 90.7%, and 94.5% in [Omim]BF4, [Bmim]PF6 and [Omim]PF6, respectively.
6894 Ind. Eng. Chem. Res., Vol. 47, No. 18, 2008
Figure 5. Influence of the nature of the substrate in the desulfurization with compound I as catalyst. Conditions: T ) 70 °C, model oil ) 5 mL, [Bmim]BF4 ) 1 mL, [n(H2O2)/n(DBT)/n(catalyst) ) 400:100:1].
It may be pointed out that the nature of IL played an important role in sulfur removal. The sulfur removal of the model oil was higher in a biphasic system than that in a triphasic system, due to partitioning effects. However, in the system containing [(C4H9)4N]3{PO4[MoO(O2)2]4, H2O2, and [Omim]TA, the oxidation of sulfur probably was restrained by the anion ([TA]-) of [Omim]TA. The data also indicated that a combination of extraction with IL and catalytic oxidation showed a high catalytic activity on removing DBT. 3.7. Influence of the Nature of the Substrate. To study the catalytic activity of compound I on different substrates, BT, DBT, and 4,6-DMDBT were chosen as substrates. From the data of Figure 5, the removal of sulfur compounds increased with increasing time. The removal of BT was only 45.8% in 4 h. However, with DBT and 4,6-DMDBT as substrates, the sulfur removal reached 98.8% and 90.2% in 4 h, respectively. BT exhibited the lowest reactivity, which was attributed to the significantly lower electron density on the sulfur atom on BT. For DBT and 4,6-DMDBT, the difference in the electron density on the sulfur was very small (5.758 for DBT, 5.760 for 4,6DMDBT).4 Further, steric hindrance of the methyl of the substrate became an obstacle for the approach of the sulfur atom to the catalytic active species in IL. Because of the two factors, the reactivity of sulfur compounds in the ECODS system decreased in the order of DBT > 4,6-DMDBT > BT. 3.8. Influence of the Recycle of Ionic Liquid. The performance of the desulfurization system for [Bmim]BF4 containing [(C4H9)4N]3{PO4[MoO(O2)2]4} and H2O2 was investigated on the removal of DBT in model oil. After the reaction, the ionic liquid phase (underlayer) was distilled in oil bath at 110 °C until H2O2 was removed entirely, and then, fresh H2O2 and model oil were dissolved in the ionic liquid phase for the next reaction. The data shown in Figure 6 indicated that the desulfurization system could be recycled 4 times with a slight decrease in activity. The sulfur removal dropped from 97.3% to 95.9% under the same experimental conditions. 4. Conclusions In this paper, we presented that a combination of extraction using [Bmim]BF4 and catalytic oxidation with a short alkyl chain catalyst was used for the deep desulfurization of a model oil under moderate conditions. The sulfur content in the model oil could decrease from 1000 to 8 ppm, which was superior to mere solvent extraction with ionic liquids. The reactivity of sulfur
Figure 6. Influence of the recycle times on the sulfur removal with compound I as catalyst. Conditions: T ) 70 °C, t ) 3 h, model oil ) 5 mL, [Bmim]BF4 ) 1 mL, [n(H2O2)/n(DBT)/n(catalyst) ) 200:100:1].
compounds in the ECODS system decreased in the order of DBT > 4,6-DMDBT > BT. The catalyst with the short alkyl chain exhibited higher catalytic activity than that with the long alkyl chain. The deep desulfurization system containing [(C4H9)4N]3{PO4[MoO(O2)2]4}, H2O2, and [Bmim]BF4 can be recycled 4 times with an inconspicuous decrease in activity, which will be developed into a promising, “green” process of deep desulfurization. Acknowledgment This work was financially supported by the National Nature Science Foundation of China (Nos. 20676057, 20777029) and Jiangsu University Scientific Research Funding (No. 04JDG044). Note Added after ASAP Publication: The version of this paper that was published on the Web August 7, 2008 had an error in the data for entry 1 in Table 2. The corrected version of this paper was reposted to the Web August 12, 2008. Literature Cited (1) Yazu, K.; Yamamoto, Y.; Furuya, T.; Miki, K.; Ukegawa, K. Oxidation of Dibenzothiophenes in an Organic Biphasic System and Its Application to Oxidative Desulfurization of Light Oil. Energy Fuels 2001, 15, 1535. (2) Esser, J.; Wasserscheid, P.; Jess, A. Deep Desulfurization of Oil Refinery Streams by Extraction with Ionic Liquids. Green Chem. 2004, 6, 316. (3) Lu¨, H. Y.; Gao, J. B.; Jiang, Z. X.; Yang, Y. X.; Song, B.; Li, C. Oxidative Desulfurization of Dibenzothiophene with Molecular Oxygen Using Emulsion Catalysis. Chem. Commun. 2007, 150. (4) Lu¨, H. Y.; Gao, J. B.; Jiang, Z. X.; Jing, F.; Yang, Y. X.; Wang, G.; Li, C. Ultra-Deep Desulfurization of Diesel by Selective Oxidation with [C18H37N(CH3)3]4[H2NaPW10O36] Catalyst Assembled in Emulsion Droplets. J. Catal. 2006, 239, 369. (5) Gao, J. B.; Wang, S. G.; Jiang, Z. X.; Lu, H. Y.; Yang, Y. X.; Jing, F.; Li, C. Deep Desulfurization from Fuel Oil via Selective Oxidation Using an Amphiphilic Peroxotungsten Catalyst Assembled in Emulsion Droplets. J. Mol. Catal. A: Chem. 2006, 258, 261. (6) Li, C.; Jiang, Z. X.; Gao, J. B.; Yang, Y. X.; Wang, S. J.; Tian, F. P.; Sun, F. X.; Sun, X. P.; Ying, P. L.; Han, C. R. Ultra-Deep Desulfurization of Diesel: Oxidation with a Recoverable Catalyst Assembled in Emulsion. Chem. Eur. J. 2004, 10, 2277. (7) Otsuki, S.; Nonaka, T.; Takashima, N.; Qian, W. H.; Ishihara, A.; Imai, T.; Kabe, T. Oxidative Desulfurization of Light Gas Oil and Vacuum Gas Oil by Oxidation and Solvent Extraction. Energy Fuels 2000, 14, 1232. (8) Campos-Martin, J. M.; Capel-Sanchez, M. C.; Fierro, J. L. G. Highly Efficient Deep Desulfurization of Fuels by Chemical Oxidation. Green Chem. 2004, 6, 557.
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ReceiVed for reView March 28, 2008 Accepted June 5, 2008 IE800857A
