Article pubs.acs.org/EF
Desulfurization of Kerosene by the Electrochemical Oxidation and Extraction Process Xiao-dong Tang,†,‡ Tao Hu,‡ Jing-jing Li,*,‡ Fang Wang,‡ and Da-yong Qing‡ †
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, and ‡College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, People’s Republic of China ABSTRACT: To meet the environmental requirements, kerosene, as the major component of jet fuel, is necessary for deep desulfurization. An electrochemical oxidation−extraction method was proposed to reduce the sulfur content in kerosene in this work. First, the electrochemical oxidation of kerosene was carried out in NaCl solution. Then, N-methyl-2-pyrrolidone (NMP) was used as an extractant to remove the oxidized organic sulfides. Gas chromatography−flame photometric detector (GC−FPD), gas chromatography−mass spectrometry (GC−MS), Fourier transform infrared (FTIR) spectroscopy, and ion chromatography were used to determine 1-heptyl mercaptan, one of the main organic sulfides in kerosene, and its products after electrochemical oxidation. The results showed that 1-heptyl mercaptan was effectively oxidized to diheptyl disulfide, 1-heptanesulfonyl chloride, and sulfate in electrochemical oxidation and removed after extraction. After electrochemical oxidation−extraction, the sulfur content of kerosene decreased from 180.0 to 13.2 μg/g and the desulfurization efficiency reached 92.67%. By gas chromatography−flame ionization detector (GC−FID) analysis of kerosene, the electrochemical oxidation process has no impact on the properties of kerosene. On the basis of these experimental results, a mechanism of electrochemical oxidative desulfurization was proposed.
1. INTRODUCTION Organic sulfides in transportation fuels remain a major source of air pollution because the burning of high-sulfur-containing fuels will result in acid rain and hazy weather.1 To reduce the air pollution, increasingly stringent regulations have been imposed to control the sulfur content of fuels to a very low level. In the U.S.A., the sulfur content of gasoline and diesel has been limited to 30 and 15 μg/g, respectively. In Europe, the maximum sulfur content has been defined as less than 10 μg/g in transportation fuels from the year 2010. The Chinese government requires that the sulfur content in transportation fuels should be no higher than 50 μg/g from 2014.2,3 To meet the new standards, innovative approaches are needed to produce cleaner fuels. Conventional methods for reducing the sulfur content of transportation fuels are hydrodesulfurization (HDS) technology. However, a high temperature, high pressure, and large amount of hydrogen and active catalysts are necessary for HDS.4,5 In addition, the investment and operation costs of this method are very high. To make up for shortages of HDS and obtain cleaner fuels, many non-HDS technologies have been developed in recent decades, such as oxidation, adsorption, extraction, alkylation, biodesulfurization, and their combinations.6−11 Among these methods, numerous studies on oxidative desulfurization technology have been issued. In comparison to traditional hydrogenation technology, oxidative desulfurization technology possesses the advantages of low investment and operation costs, mild reactive conditions, and a more simple technological process. The common oxidants of oxidative desulfurization are H2O2, O2, and peroxy acid.12,13 It can be observed in recent studies that the combination of oxidation with adsorption or extraction could obtain a better desulfurization effect.14 However, a tremendous © 2015 American Chemical Society
amount of oxidant consumption and a large amount of wastewater restrict the industrial application of this technology. As a new type of oxidative desulfurization method, electrochemical oxidative desulfurization of fuels has been investigated in recent years. In comparison to ordinary oxidation, no consumption of oxidants and a small amount of wastewater make this technology with high research values. Schucker et al.15 invented a new electrochemical process for removing sulfides from a hydrocarbon stream, and the organic sulfides linked up to form the sulfur oligomers in the reactor and were finally swept out by distillation. Wang et al.16,17 developed an electrochemical desulfurization method to remove organic sulfides in gasoline in an electrochemical fluidized-bed reactor using particle group anode (i.e., β-PbO2/ C or CeO2/C). The experimental results showed that the particle group anode could considerably improve the electrochemical catalysis performance and promote the electrochemical oxidation reaction rate for the desulfurization reaction. The total desulfurization ratio reached 87% by extraction after electrochemical catalytic oxidation. Liu et al.18 reported that dibenzothiophene (DBT) could be oxidized to DBTO and DBTO2 in an acetonitrile−alcohol−water−acetic acid system at normal temperatures and pressures. Under the optimal conditions, the conversion rate of DBT in the model oil reached 98.4%. Furthermore, the sulfur content in real diesel oil decreased from 884 to 57 μg/g. Zhao et al.19,20 claimed a process to eliminate organic sulfides from coal using NaCl solution as an electrolyte. Received: October 30, 2014 Revised: February 26, 2015 Published: March 12, 2015 2097
DOI: 10.1021/ef502437m Energy Fuels 2015, 29, 2097−2103
Article
Energy & Fuels
oxidation, 20 mL of model oil (n-heptane + 1-heptyl mercaptan) and a certain amount of NaCl solution were put into the electrolytic cell. After electrochemical oxidation, the model oil and the electrolytes were recovered and prepared for further analysis. 2.3. Analysis Methods. The total sulfur content of kerosene before and after the electrochemical oxidation−extraction process was determined by a WKL-3000 sulfur−chlorine analyzer (Taizhou Guochang Analytical Instruments Co., Ltd.). The group compositions of kerosene before and after desulfurization were analyzed by gas chromatography−flame ionization detector (GC−FID, GC-9790II, Zhejiang Fuli Analytical Instrument Co., Ltd.) with a KB-1 capillary column (60 m × 0.25 mm × 0.25 μm). The conversions of organic sulfides in kerosene before and after desulfurization were analyzed by gas chromatography−flame photometric detector (GC−FPD, GC9790II, Zhejiang Fuli Analytical Instrument Co., Ltd.) with a DMPLOT S capillary column (30 m × 0.53 mm × 20.00 μm). The water content of kerosene before and after desulfurization was determined through a Dean−Stark method. 1-Heptyl mercaptan in model oil before and after desulfurization was analyzed by gas chromatography− mass spectrometry [GC−MS, 7890A GC system with a HP-5MS capillary column (30 m × 0.25 mm × 0.25 μm) and 5975C MSD, Agilent Technologies, Inc.] and Fourier transform infrared (FTIR) spectroscopy (Beijing Beifen-Ruili Analytical Instruments Co., Ltd.). Simultaneously, the electrolyte were also analyzed by ion chromatography (883 Basic IC plus, Metrohm China, Ltd.), equipped with a Metrosep A Supp 5-250/4.0 ion chromatographic column (250 × 4.0 mm inner diameter, 6.1006.530). In addition, the total desulfurization efficiency (XS) of kerosene was calculated as follows:
It is well-known that mercaptans (R−SH) are the main organic sulfide components in kerosene.21 HDS and Merox UOP technology are commonly used as desulfurization methods of kerosene.22 However, few studies are focused on electrochemical oxidative desulfurization of kerosene. Related experimental studies and mechanism studies were scarce. In this paper, a new process for deep desulfurization of kerosene through electrochemical oxidation using NaCl as an electrolyte was systematically researched. Mechanisms of electrochemical oxidative desulfurization were also studied and discussed.
2. EXPERIMENTAL SECTION 2.1. Chemical Materials. The sample of kerosene was supplied by PetroChina Qingyang Petrochemical Company, and the main properties of kerosene are listed in Table 1. NaCl (AR, 99.5%), N-
Table 1. Main Properties of Kerosene distillation range (°C) 3
density (kg/m )
S content (μg/g)
IBP
10%
50%
90%
FBP
800.2
180.0
150
168
196
222
234
methyl-2-pyrrolidone (NMP, AR, 99%), and n-heptane (AR, 99%) were obtained from Chengdu Kelong Chemical Co., Ltd. 1-Heptyl mercaptan (GC, 98%) was purchased from Shanghai Aladdin Reagent Co., Ltd. All reagents were used without further purification. All solutions were prepared in ultrapure water, which was obtained from a water purification system, and the electrical resistant was 18.25 MΩ cm. 2.2. Experimental Methods. As shown in Figure 1, electrochemical oxidation experiments of kerosene were carried out in an
XS =
S0 − S T × 100% S0
where XS was the desulfurization efficiency (%) of kerosene and S0 and ST were the sulfur contents (μg/g) of raw oil and product, respectively.
3. RESULTS AND DISCUSSION 3.1. Electrochemical Oxidative Desulfurization of Kerosene. 3.1.1. Electrolyte Concentration. It is well-known that Cl− can be oxidized at an anode to produce Cl2 and ClO−, which can oxidize organic sulfides to sulfoxide and sulfone.23 The effect of the electrolyte concentration on the desulfurization efficiency is shown in Figure 2. As seen from this diagram, the desulfurization efficiency increased initially and then decreased with the increase of the weight percent of NaCl.
Figure 1. Sketch of the electrochemical desulfurization experimental setup: (1) potentiostat, (2) anode, (3) electrolysis cell, (4) raw oil, (5) electrolyte, (6) thermostat water bath, (7) cathode, and (8) stirrer. electrolytic cell with different concentrations of NaCl solution as the supporting electrolyte. Two graphite electrodes with a dimension of 20 × 20 mm were worked as the anode and cathode with a distance of 2.5 cm. A total of 20 mL of kerosene was filled into the electrolytic cell and mixed with an amount of prescribed NaCl solution by stirring at a certain speed under atmospheric pressure. After tens of minutes for electrochemical oxidation and standing, oil and electrolyte were layered. The lower electrolyte was separated by a separating funnel, and the organic sulfides (oxidation products) in the upper kerosene phase were removed by solvent extraction with NMP (1:1 volume ratio). The desulfured kerosene was collected and prepared for further analysis. Meanwhile, the optimal conditions of electrochemical oxidative desulfurization were examined. 1-Heptyl mercaptan was used as the model sulfur compound to study and discuss the mechanisms of the electrochemical oxidative desulfurization process. Under optimal conditions of electrochemical
Figure 2. Effect of the electrolyte weight percent on electrochemical desulfurization (experimental conditions: cell voltage, 4 V; electrolysis temperature, 20 °C; electrolysis time, 60 min; volume ratio of electrolyte/oil, 1.0; and stirring rate, 500 revolutions/min). 2098
DOI: 10.1021/ef502437m Energy Fuels 2015, 29, 2097−2103
Article
Energy & Fuels When the weight percent of NaCl was maintained at 20%, the desulfurization efficiency reached the maximum value. The reason was that the increase of the electrolyte concentration provided more Cl−, which could produce more Cl2 and ClO− to promote the oxidative reaction of organic sulfides. However, when the electrolyte concentration was raised to a certain value, Cl2 produced at the anode could not be released immediately; this may affect the oxidative reaction on the anode surface. Thus, the optimum weight percent of NaCl was 20%. 3.1.2. Cell Voltage. Wang et al.16 reported that cell voltage has a great influence on the electrode reactions. Figure 3
Figure 4. Effect of the electrolysis temperature on electrochemical desulfurization (experimental conditions: electrolyte weight percent, 20%; cell voltage, 4 V; electrolysis time, 60 min; volume ratio of electrolyte/oil, 1.0; and stirring rate, 500 revolutions/min).
Figure 3. Effect of the cell voltage on electrochemical desulfurization [●, desulfurization efficiency (XS); ▲, current] (experimental conditions: electrolyte weight percent, 20%; electrolysis temperature, 20 °C; electrolysis time, 60 min; volume ratio of electrolyte/oil, 1.0; and stirring rate, 500 revolutions/min).
showed that both desulfurization efficiency and current were raised with the increase of the cell voltage, because the higher cell voltage could provide more energy to promote the electrochemical oxidative reaction. However, an excessive cell voltage would lead to power loss and current efficiency drops because of anodic oxygen evolution. Moreover, in this experiment, a high cell voltage (>5 V) would cause the oxidation of effective components in kerosene, resulting in the color change of kerosene. Therefore, an appropriate cell voltage was necessary. According to the experimental results, 4 V was the optimal cell voltage. 3.1.3. Electrolysis Temperature. The effect of the temperature on desulfurization is shown in Figure 4. The desulfurization efficiency first increased with the increase of the electrolysis temperature, reaching the maximum value at 50 °C, and then decreased. Referring to other reports by researchers,19,24 the temperature effect was complex. On one side, the temperature rise is good for desulfurization. It not only accelerates the reaction rate but also promotes the masstransfer rate. On the other hand, the temperature rise has disadvantages. A high temperature was not conducive to the desulfurization reaction because of the electrochemical oxidation reaction releasing heat. Furthermore, a high temperature was beneficial to the oxygen evolution from water, which would result in a loss of energy. Consequently, there is an optimal temperature for electrolysis, and 50 °C was the suitable reaction temperature by our experimental tests. 3.1.4. Electrolysis Time. As shown in Figure 5, the desulfurization efficiency rose with the increase of the
Figure 5. Effect of the electrolysis time on electrochemical desulfurization (experimental conditions: electrolyte weight percent, 20%; cell voltage, 4 V; electrolysis temperature, 50 °C; volume ratio of electrolyte/oil, 1.0; and stirring rate, 500 revolutions/min).
electrolysis time. When the electrolysis time was less than 60 min, extending the reaction time could effectively improve the desulfurization rate. When the electrolysis time exceeded 60 min, the increase rate of desulfurization efficiency became slow. The reasons were described as follows: with the increase of the reaction time, Cl2 and ClO− produced at the anode could continue to oxidize the organic sulfides. However, when the sulfur content reduced to a very low level, extending the reaction time cannot improve the rate of desulfurization effectively. Considering the economy and efficiency, 60 min was the optimal reaction time. 3.1.5. Volume Ratio of Electrolyte/Oil. The volume ratio of electrolyte/oil affects mass-transfer and reaction rates.25 In Figure 6, the desulfurization efficiency grew very quickly with the increase of the volume ratio of electrolyte/oil. The reason was that the increase of the electrolyte volume provided more Cl−, which would produce more Cl2 and ClO− to oxidize the organic sulfides. The desulfurization efficiency reached 92.67% when the volume ratio of electrolyte/oil was 3.0. When the 2099
DOI: 10.1021/ef502437m Energy Fuels 2015, 29, 2097−2103
Article
Energy & Fuels
with the increase of the stirring rate and trended to stationary after 500 revolutions/min. When the stirring rate was 0 revolutions/min (without stirring), the desulfurization efficiency was very low, only 64.58%. When the stirring rate exceeded 500 revolutions/min and the interphase diffusion is not limiting, the desulfurization efficiency reached 92.67%. Therefore, 500 revolutions/min was the optimum stirring rate. The optimum operating conditions of electrochemical oxidation were summarized as follows: weight percent of NaCl, 20%; cell voltage, 4 V; electrolysis temperature, 50 °C; reaction time, 60 min; volume ratio of electrolyte/oil, 3.0; and stirring rate, 500 revolutions/min. After extraction with NMP, the desulfurization efficiency reached 92.67% and the sulfur content of kerosene decreased from 180.0 to 13.2 μg/g. 3.1.7. Properties of Kerosene before and after Desulfurization. The properties of kerosene before and after desulfurization are shown in Table 2. Electrochemical oxidation− extraction has the highest desulfurization efficiency. Although direct extraction with NMP can decrease the sulfur content to 109.5 μg/g, it is much higher than electrochemical oxidation− extraction. Besides, it is useless for direct wash by electrolyte (blank group). These results suggested that the electrolyte (NaCl solution) itself has no desulfurization ability. Only passed an electric current, the oxidants that produced at the anode have a desulfurization effect. However, exactly what kinds of oxidants possess a desulfurization function still need further study. The water content of kerosene before and after desulfurization was very low, which means that the properties of kerosene would not be affected by water. Both the volume yields of kerosene after direct extraction and oxidation− extraction were close to 90%. These results suggested that the yield loss of kerosene was mainly caused by the extraction process. The electrochemical oxidation process did not result in a kerosene yield loss. The group compositions of kerosene before and after desulfurization are shown in Figure 8. The compositions of kerosene before and after electrochemical oxidation did not change. Only small amounts of NMP (7.5 min) dissolved in kerosene after extraction. The conversions of organic sulfides in kerosene before and after electrochemical oxidation−extraction are shown in Figure 9. It can confirm from this diagram that the main organic sulfides in raw kerosene were mercaptans (such as 1-heptyl mercaptan), benzothiophene (BT) and alkyl benzothiophene (alkyl BT). Most organic sulfides, such as BT and alkyl BT, could be removed after extraction with NMP, except mercaptans. That was the reason that the total desulfurization efficiency of kerosene was only 39.17% after direct extraction. However, after electrochemical oxidation−extraction, almost all organic sulfides had been removed and the total desulfurization efficiency of kerosene reached 92.67%. These results suggested that, after electrochemical oxidation, mercaptans were converted into other types of sulfides, which were easily dissolved in NMP. For this reason, the study of the reaction process and
Figure 6. Effect of the volume ratio of electrolyte/oil on electrochemical desulfurization (experimental conditions: electrolyte weight percent, 20%; cell voltage, 4 V; electrolysis temperature, 50 °C; electrolysis time, 60 min; and stirring rate, 500 revolutions/min).
volume ratio exceeded 3.0, the desulfurization rate almost remained the same. Therefore, 3.0 was a suitable volume ratio of electrolyte/oil in these experiments. 3.1.6. Stirring Rate. Mass transfer is a very important factor for multiphase reaction. To keep a low mass-transfer resistance of electrochemical desulfurization, the relationship between desulfurization efficiency and stirring rate was discussed in Figure 7. It was showed that the desulfurization efficiency rose
Figure 7. Effect of the stirring rate on electrochemical desulfurization (experimental conditions: electrolyte weight percent, 20%; cell voltage, 4 V; electrolysis temperature, 50 °C; electrolysis time, 60 min; and volume ratio of electrolyte/oil, 3.0).
Table 2. Properties of Kerosene before and after Desulfurization oil sample
sulfur content (μg/g)
raw kerosene direct wash by electrolyte direct extraction electrochemical oxidation−extraction
180.0 180.0 109.5 13.2
XS (%)
39.17 92.67 2100
volume yield (%)
water content
90 90
trace trace trace trace DOI: 10.1021/ef502437m Energy Fuels 2015, 29, 2097−2103
Article
Energy & Fuels
oxidation products of mercaptans in electrochemical oxidation was necessary. 3.2. Mechanisms of Electrochemical Oxidative Desulfurization. In this part, the mixture of 1-heptyl mercaptan and n-heptane was selected as model oil to study and discuss the mechanisms of the electrochemical oxidative desulfurization process under the optimal conditions without extraction. Wang et al.17 indicated that the electrolysis desulfurization of gasoline was an indirect oxidation process and the final oxidation products of organic sulfides were sulfoxide and sulfone. Chen et al.26 and Zhong et al.27 used electrochemical methods to remove organic sulfides from coal. Their reports indicated that the mercapto group (−SH) of mercaptans first oxidized to the disulfide bond (−S−S−) and sulfo group (−SO3H). After that, the disulfide bond would be oxidized to sulfoxide (−SO), sulfone (−SO2), and then partially hydrolyze to SO42−. Meanwhile, the sulfo group would also be hydrolyzed to SO42−. 3.2.1. GC−MS and FTIR Analysis of Model Oil. Figure 10 showed the GC−MS chromatograms of model oil before and
Figure 8. GC−FID chromatograms of kerosene before and after desulfurization: (A) raw kerosene, (B) direct oxidation, (C) direct extraction, and (D) oxidation−extraction.
Figure 10. GC−MS chromatograms of model oil before and after desulfurization.
after electrochemical oxidation. A solvent delay had been set to mask the solvent peaks. It can be seen that the content of 1heptyl mercaptan (2.7 min) dropped significantly after reaction. Besides, two kinds of oxidation products (1-heptanesulfonyl chloride at 5.1 min and diheptyl disulfide at 8.2 min) were observed. This result indicated that 1-heptyl mercaptan (C7H15−SH) in model oil may first be oxidized to 1heptanesulfonic acid (C7H15−SO3H) and diheptyl disulfide (C7H15−S−S−C7H15). After that, the hydroxyl of the sulfo group (−SO 3 H) continued to react with Cl 2 to 1heptanesulfonyl chloride (C7H15−SO2Cl). However, deep oxidation products, such as sulfoxide and sulfone, cannot be detected because of the high boiling point and strong polarity. The FTIR spectra of model oil before and after electrochemical oxidation are shown in Figure 11. This diagram illustrated the conversion of 1-heptyl mercaptan in the electrochemical oxidation process. The peaks of 1377 and 1137 cm−1 (−SO2), 1068 cm−1 (−SO), 725 cm−1 (−C−Cl), and 425 cm−1 (−S−S−) were observed after oxidation. However, the stretching vibration of the mercapto group was
Figure 9. GC−FPD chromatograms of kerosene before and after desulfurization: (A) raw kerosene, (B) direct extraction, (C) oxidation−extraction, and (D) model sulfides. 2101
DOI: 10.1021/ef502437m Energy Fuels 2015, 29, 2097−2103
Article
Energy & Fuels
small amount of sulfate (23.38 min) was observed after oxidation. Because model oil was pure n-heptane + 1-heptyl mercaptan and the electrolyte was NaCl solution, SO42− could only come from the hydrolysis of 1-heptanesulfonic acid, sulfoxide, and sulfone. The existence of ClO−, which cannot be determined by ion chromatography, was demonstrated by an indicator. After oxidation, a few drops of phenolphthalein were added to the electrolyte. The color of the electrolyte immediately turned to pink and soon faded. These results indicated that large amounts of OH− and ClO− had been generated after electrochemical oxidation. 3.2.3. Mechanism of Electrochemical Oxidative Desulfurization. On the basis of the above analyses and previous reports16,17,25−27 about oxidative desulfurization, a possible desulfurization mechanism of kerosene by electrochemical oxidation was proposed, as shown in Figure 13. Because of weak reducibility and low space steric hindrance of 1-heptyl mercaptan, the oxidization of 1-heptyl mercaptan could occur more easily than thioethers and thiophenes. NaCl solution was used as the electrolyte. Cl2 and ClO− which were generated by Cl− at the anode, play a critical role of oxidative medium during the desulfurizing process. Besides, a small number of highly active oxidants (especially the hydroxyl radicals) generated by H2O at the anode may promote the oxidative reaction. We defined all of the chemical oxidants discussed above as [O] in Figure 13. As shown in Figure 13, 1-heptyl mercaptan (C7H15−SH) first oxidized to intermediates, such as 1-heptanesulfonic acid (C7H15−SO3H) and diheptyl disulfide (C7H15−S−S−C7H15). 1-Heptanesulfonic acid could continue to react with Cl2 to 1heptanesulfonyl chloride (C7H15−SO2Cl) and finally hydrolyzed to 1-heptanol (C7H15−OH) and sulfate. Meanwhile, diheptyl disulfide would be oxidized to sulfoxide by oxidants first, then to sulfone, and partially hydrolyzed to 1-heptanol and SO42− at last. Besides, oxidation products with strong polarity could be removed using polarity extraction agents, such as NMP.
Figure 11. FTIR spectra of model oil before and after desulfurization.
so weak that it cannot be detected under the detecting conditions. According to previous studies,12,15,27 the peaks at 1377, 1137, and 1068 cm−1 came from sulfoxide and sulfone. These results indicated that a part of disulfides has been oxidized to sulfoxide and sulfone in oxidation experiments. 3.2.2. Ion Chromatographic Analysis of the Electrolyte. The anion ion chromatographic results of electrolyte before and after electrochemical oxidation are shown in Figure 12. A
4. CONCLUSION The removal of organic sulfides from kerosene by electrochemical oxidation in NaCl solution and extraction with NMP has been studied. The optimum desulfurization conditions of kerosene were achieved. Under the optimal conditions, such as weight percent of NaCl, 20%; cell voltage, 4 V; electrolysis temperature, 50 °C; reaction time, 60 min; volume ratio of electrolyte/oil, 3.0; stirring rate, 500 revolutions/min, and volume ratio of NMP/kerosene, 1.0, the sulfur content of kerosene decreased from 180.0 to 13.2 μg/g and the desulfurization efficiency reached 92.67%. The volume yield
Figure 12. Ion chromatography of the electrolyte before and after desulfurization.
Figure 13. Mechanism of electrochemical oxidative desulfurization. 2102
DOI: 10.1021/ef502437m Energy Fuels 2015, 29, 2097−2103
Article
Energy & Fuels
(19) Zhao, W.; Zhu, H.; Zong, Z. M.; Xia, J. H.; Wei, X. Y. Fuel 2005, 84 (2−3), 235−238. (20) Zhao, W.; Xu, W. J.; Zhong, S. T.; Zong, Z. M. J. China Univ. Min. Technol. 2008, 18 (4), 571−574. (21) Ferreira, A. R.; Freire, M. G.; Ribeiro, J. C.; Lopes, F. M.; Crespo, J. G.; Coutinho, J. A. P. Fuel 2014, 128, 314−329. (22) Farshi, A.; Rabiei, Z. Pet. Coal 2005, 47 (1), 49−56. (23) Wang, Y. G.; Wei, X. Y.; Yan, H. L.; Liu, F. J.; Li, P.; Zong, Z. M. Fuel Process. Technol. 2014, 125, 182−189. (24) Jin, X.; Botte, G. G. J. Power Sources 2010, 195 (15), 4935− 4942. (25) Shu, C.; Sun, T.; Jia, J.; Lou, Z. Fuel 2013, 113, 187−195. (26) Chen, Z. D.; Gong, X. Z.; Wang, Z.; Wang, Y. G.; Zhang, S.; Xu, D. P. J. Fuel Chem. Technol. 2013, 41 (8), 928−936 (in Chinese). (27) Zhong, S. T.; Zhao, W.; Sheng, C.; Xu, W. J.; Zong, Z. M.; Wei, X. Y. Energy Fuels 2011, 25 (8), 3687−3692.
of kerosene after electrochemical oxidation−extraction was close to 90%. The experimental results showed that mercaptans, as one of the main organic sulfides in kerosene, were difficult to be swept out by direct extraction but can be removed by electrochemical oxidation−extraction. The results of the mechanism research proved that, in the electrochemical oxidation process, 1-heptyl mercaptan, as the representative of mercaptans, can be easily translated to diheptyl disulfide and 1-heptanesulfonyl chloride. Deep oxidation products, such as sulfoxide and sulfone, with high boiling point and strong polarity could be removed by solvent extraction. A part of oxidation products may be hydrolyzed to SO42−.
■
AUTHOR INFORMATION
Corresponding Author
*Telephone/Fax: +86-28-83033009. E-mail: lijingjing771216@ gmail.com. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work is financially supported by the Young Scholars Development Fund of Southwest Petroleum University (SWPU, 201131010032). The authors thank the editors and anonymous reviewers for the suggestions on improving this manuscript.
■
REFERENCES
(1) Yang, R. T.; Hernandez-Maldonado, A. J.; Yang, F. H. Science 2003, 301 (5629), 79−81. (2) Li, F. T.; Liu, Y.; Sun, Z. M.; Chen, L. J.; Zhao, D. S.; Liu, R. H.; Kou, C. G. Energy Fuels 2010, 24 (8), 4285−4289. (3) Chen, X.; Song, D.; Asumana, C.; Yu, G. J. Mol. Catal. A: Chem. 2012, 359, 8−13. (4) Di, L.; Chenguang, L. China Pet. Process. Petrochem. Technol. 2013, 15 (4), 38−43. (5) Tao, H.; Nakazato, T.; Sato, S. Fuel 2009, 88 (10), 1961−1969. (6) Yu, G.; Zhao, J.; Song, D.; Asumana, C.; Zhang, X.; Chen, X. Ind. Eng. Chem. Res. 2011, 50 (20), 11690−11697. (7) Velu, S.; Ma, X.; Song, C. Ind. Eng. Chem. Res. 2003, 42 (21), 5293−5304. (8) Gao, H.; Guo, C.; Xing, J.; Liu, H. Sep. Sci. Technol. 2012, 47 (2), 325−330. (9) Dupuy, B.; Laforge, S.; Morais, C.; Bachmann, C.; Magnoux, P.; Richard, F. Appl. Catal., A 2012, 413−414, 192−204. (10) Ma, T.; Li, G.; Li, J.; Li, S.; Li, H.; Liang, F.; Liu, R. Chin. J. Chem. Eng. 2006, 57 (11), 2705. (11) Guchhait, S.; Biswas, D.; Bhattacharya, P.; Chowdhury, R. Chem. Eng. J. 2005, 112 (1), 145−151. (12) Zhang, H.; Gao, J.; Meng, H.; Li, C.-X. Ind. Eng. Chem. Res. 2012, 51 (19), 6658−6665. (13) Tang, X.; Cui, Y.; Yu, Z.; An, R. Acta Pet. Sin. 2006, 22 (1), 91− 94 (in Chinese). (14) Otsuki, S.; Nonaka, T.; Takashima, N.; Qian, W.; Ishihara, A.; Imai, T.; Kabe, T. Energy Fuels 2000, 14 (6), 1232−1239. (15) Schucker, R. C.; Baird, W. C., Jr. Electrochemical oxidation of sulfur compounds in naphtha using ionic liquids. U.S. Patent 6,274,026, 2001. (16) Wang, W.; Wang, S.; Liu, H.; Wang, Z. Fuel 2007, 86 (17−18), 2747−2753. (17) Wang, W.; Wang, S.; Wang, Y.; Liu, H.; Wang, Z. Fuel Process. Technol. 2007, 88 (10), 1002−1008. (18) Liu, C.; Li, D.; Yang, S. Petrochem. Technol. 2014, 43 (1), 24−29 (in Chinese). 2103
DOI: 10.1021/ef502437m Energy Fuels 2015, 29, 2097−2103
