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Extraction combined catalytic oxidation desulfurization of petcoke in ionic liquid under mild conditions
Fuel 260 (2020) 116200
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Full Length Article
Extraction combined catalytic oxidation desulfurization of petcoke in ionic liquid under mild conditions
T
Hui Liua,1, Huanhuan Xua,1, Mingqing Huaa, LinLin Chena, Yanchen Weib, Chao Wangc, ⁎ Peiwen Wua, Fengxia Zhud, Xiaozhong Chud, Huaming Lia, Wenshuai Zhua, a
School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, PR China School of Materials Science and Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, PR China c School of Environment and Safety Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, PR China d School of Chemistry and Chemical Engineering, Huaiyin Normal University, PR China b
ARTICLE INFO
ABSTRACT
Keywords: High-sulfur petcoke Oxidative desulfurization Polyoxometalate ionic liquids Sulfate Mild conditions
The desulfurization of high-sulfur petcoke under mild condition is a great challenge due to the structurally stable aromatic ring skeleton with a large steric hindrance of sulfur compounds. Herein, by using polyoxometalate ionic liquid [Bmim]3PW12O40 and H2O2 as catalyst and oxidant, respectively, the sulfur content in the petcoke was reduced from 4.46 wt% to 2.85 wt% in green solvent [Bmim]BF4. Moreover, the reaction performed at a mild temperature (80 °C), significantly lower than that in the industrial methods (≥1700 °C). It realized the conversion of high-sulfur petcoke from waste to resources. The experimental results indicated that sulfides in petcoke were oxidized to sulfate, sulfone and sulfoxide, while SO2 was not produced in the process of desulfurization. The possible oxidative desulfurization mechanism was proposed based on the series of characterizations.
1. Introduction Petcoke is a by-product of the refining industry, which possesses low ash (< 1.2 wt%) and high carbon (> 85 wt%) contents by comparison to other carbon materials [1,2]. It is able to be the major feedstock for producing carbon products, such as carbon anodes [3,4]. With the deterioration of crude oil’s quality [5–9], more than 10 million tons of high-sulfur petcoke are produced annually. However, high-sulfur petcoke (sulfur content > 3 wt%) is unable to produce carbon products, and it can only be classified as waste which causes environmental issues and need to be handled with considerable cost [10–14]. Therefore, reducing the sulfur content in high-sulfur petcoke is badly-needed and significant for environment and economy. The sulfur in petcoke is mainly ascribed to thiophene and its derivatives [15–18]. The difficulty in desulfurization of petcoke is that the sulfur presents on the structurally stable aromatic ring skeleton with a large steric hindrance. Generally, several common desulfurization methods for petcoke are shown in Table 1 [16,19–26]. High temperature desulfurization is used in industry currently [19–22] which calcines petcoke at 1700 °C to reduce sulfur content. However, this desulfurization method requires high temperature and causes the
emission of SO2, resulting in environmental issues and considerable treatment cost. As the improving methods in laboratory, co-heat reduction method [24] and hot alkali treatment method [26] are still carried out at 550 °C, at least. Therefore, in order to respond to the new requirements of national energy conservation and environmental protection, finding a new method of petcoke desulfurization under mild conditions has become one of the focuses. Oxidative desulfurization (ODS) has excellent removal performance for aromatic sulfides, and operates under the moderate reaction conditions [27–37]. Therefore, ODS could be adopted to desulfurize highsulfur petcoke at low temperature. As is known to all, many types of polyoxometalate ionic liquids (POM-ILs) [38–40] possess excellent selective oxidation performances for sulfides. Because of their simple composition, strong acidity and oxidation, unique “pseudo-liquid” properties, high activity at low temperature and good thermal stability, POM-ILs have attracted much attention. In our previous work [41,42], a series of POM-ILs as catalysts have been applied to the oxidative desulfurization of thiophene-type sulfide in fuel oil, the sulfur removal was 100%. In this work, the POM-IL [Bmim]3PW12O40 was prepared by the one-pot method and was used as a catalyst for ODS of petcoke, in
Corresponding author. E-mail address: [email protected] (W. Zhu). 1 These authors contributed equally to this work. ⁎
https://doi.org/10.1016/j.fuel.2019.116200 Received 12 July 2019; Received in revised form 6 September 2019; Accepted 10 September 2019 Available online 15 October 2019 0016-2361/ © 2019 Published by Elsevier Ltd.
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Table 1 Desulfurization methods of petcoke.
Sulfur removal (%) = (W0
Desulfurization method
Temperature
Ref.
Ultrahigh-temperature desulfurization High temperature oxidation desulfurization Vacuum high temperature desulfurization Co-heat reduction desulfurization Hydrodesulfurization Hot alkali treatment desulfurization Oxidative desulfurization
2500 °C 1700 °C 1500 °C 800 °C 700 °C 550 °C 80 °C
[25] [19–22] [23] [24] [16] [26] This work
Wt )/W0 × 100%
where W0 and Wt (wt%) were the initial sulfur content and the sulfur content at time t, respectively. 2.6. Characterization method
company with green solvent [Bmim]BF4 and oxidant H2O2. The desulfurization system was valid and environmental-friendly for ODS of petcoke, and the sulfur content of high-sulfur petcoke was reduced to less than 3 wt% at 80 °C under 1 atm. The reaction condition is more moderate in comparison with that required for the current industrial methods (Table 1). Additionally, the catalyst, petcoke and the oxidative products were characterized by a variety of spectroscopy and analytical techniques. Finally, the possible mechanism of ODS was inferred.
A Nicolet Nexus 470 Fourier Transform Infrared Spectoscopy (FTIR) recorded the spectra of [Bmim]3PW12O40 and petcoke, and the FTIR spectra were collected in KBr pellets from 4000 cm−1 with 400 cm−1. Raman scattering spectroscopy was obtained at room temperature using DXR Raman microscope with 532 nm laser source. The morphology of petcoke was characterized by scanning electron microscope (SEM, JSM-6010 PLUS/LA). The samples used for SEM were prepared by dispersing some samples in ethanol, then a drop of the solution was placed on a silicon pellet and the ethanol was evaporated under UV light. The crystalline phases of materials were analyzed by Xray diffraction (XRD) with high-intensity Cu Kα (λ = 1.54 Å). X-ray photoelectron spectrometer (XPS) spectra were performed on a VG MultiLab 2000 spectrometer using Mg KR (1253.6 eV) radiation.
2. Experimental
3. Results and discussion
2.1. Materials
3.1. FT-IR and XRD characterization of catalyst
The petcoke (specification: 4#A) used in this experiment was from Zhenjiang Carbon Products Plant. 1-Butyl-3-methylimidazolium Chloride ([Bmim]Cl), and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) were purchased from Chengjie Reagent Co., Ltd. Tetrabutylammonium chloride, phosphotungstic acid, 30% H2O2 were purchased from Sinopharm Reagent Co., Ltd. All the reagents were used directly without any further treatment.
FT-IR spectra of [Bmim]Cl, [Bmim]3PW12O40 and H3PW12O40 are displayed in Fig. 1. For [Bmim]Cl, the stretching vibration peaks of CeH in the imidazole and CeH on the substituent group appeared at 3146 and 2960 cm−1, respectively. The C]N vibration of [Bmim]Cl could be observed at 1569 cm−1, and the peak at 1170 cm−1 was ascribed to the vibration of imidazole ring [45]. [Bmim]3PW12O40 catalyst showed the characteristic absorption band of [Bmim]Cl at 3146, 2959, 1568 and 1167 cm−1, which proves that [Bmim]+ ion does not be destroyed in the synthesized catalyst. From the spectrum of H3PW12O40, four typical characteristic peaks located at 1076, 983, 890 and 805 cm−1, respectively, were observed. These peaks are belonged to the stretching vibration absorption of central tetrahedral PeO, W] O, WeOaeW and WeObeW [46,47]. Similar characteristic peaks at 1079, 977, 895 and 804 cm−1 were found in the spectra of [Bmim]3PW12O40, which indicates that [Bmim]3PW12O40 catalyst is successfully prepared. The prepared catalyst is also characterized by XRD. As shown in Fig. 1d, some diffraction peaks of [Bmim]PW12O40 at 10.9, 17.1, 24.2, 25.7, 26.8, 33.8 and 63.1° are significantly different from the H3PW12O40. The difference may be due to the substitution of secondary structure protons of H3PW12O40 by [Bmim]+ [39], which leads to the appearance of the coordination water H3O+ and H5O2+ interacting with the anion of Keggin structure. It is further proved that the catalyst is successfully prepared [48,49].
2.2. Synthesis of catalyst [Bmim]3PW12O40 Phosphotungstic acid (0.01 mol) was dissolved in H2O (100 mL) to form solution. Then [Bmim]Cl (0.06 mol) was put in the solution, and the compound was stirred for 12 h at 25 °C. A white precipitate was obtained. After filtration and washing with water until there is no chloride ions in the filtrate. Finally, the product was dried at 80 °C overnight to obtain white powder [Bmim]3PW12O40 [43,44]. 2.3. Pre-treatment of high-sulfur petcoke The pre-treatment experiment was carried out in two-necked flask by mixing tetrabutylammonium chloride (6 g) with high-sulfur petcoke (1 g) at 150 °C for 4 h. After filtration and washing with water, the pretreated petcoke was dried for subsequent use. 2.4. Oxidative desulfurization of the high-sulfur petcoke
3.2. Effects of pre-treated and catalyst
In the desulfurization experiment, a mixture with 5 mL [Bmim]BF4, 0.5 g [Bmim]3PW12O40, 0.5 g pre-treated petcoke, and 5 mL 30% H2O2 (add 1 mL·h−1) in a 100 mL flask was stirred at 80 °C for 5 h. Then, the solution was filtered and the residue was washed with acetonitrile to remove catalyst. After washing with acetonitrile several times, the residual acetonitrile was removed by washing with H2O. The obtained petcoke was dried at 100 °C for 24 h.
The sulfur content has been only reduced to 3.85 wt% (Sulfur removal 13.67%) by oxidative desulfurization of the high-sulfur petcoke (Sulfur content 4.46 wt%) in [Bmim]BF4, with using [Bmim]3PW12O40 and H2O2 as catalyst and oxidant, respectively (Table 2, entry 1). This may be attributed to the small amount of exposed sulfur in the outer layer of petcoke with the low specific surface area (2.0 m2/g). Fortunately, the sulfur content has been decreased to 2.85 wt% (< 3 wt%, and sulfur removal 36.10%) under the same conditions with using the pre-treated high-sulfur petcoke by tetrabutylammonium chloride, which has more than double specific surface area (4.3 m2/g) (Table 2, entry 2). The desulfurization performance of different catalysts in oxidative desulfurization of pre-treated high-sulfur petcoke were tested and the results are depicted in Table 3. The sulfur content of petcoke decreases
2.5. Determination of sulfur content in petcoke The sulfur content of petcoke was determinated by CLS-3000 microcomputer Cullen sulfur analyzer, and the temperature control range of the instrument is between 0 and 2000 °C. The initial sulfur content of petcoke was determined to be 4.46 wt%. The calculation formula for the desulfurization rate is as follows: 2
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Fig. 1. FT-IR spectra of samples: (a) [Bmim]Cl, (b) H3PW12O40, (c) [Bmim]3PW12O40; XRD pattern (d) of [Bmim]3PW12O40 and H3PW12O40.
and H3PW12O40. The sulfur content of petcoke can be reduced to 2.85 wt%. Probably because [PW12O40]3− in [Bmim]3PW12O40 can convert to [PO4{W(O) (O2)2}4]3− reactive oxygen species in the presence of excessive H2O2, which has stronger oxidation ability. As a comparison, the low catalytic performance of H3PW12O40 may be due to the poor solubility of H3PW12O40 in the reaction solvent [Bmim]BF4, resulting in unsatisfied contraction of catalyst with high-sulfur petcoke.
Table 2 Effect of pre-treated of petcoke. Entry
Sample
SBET (m2/ g)
Sulfur content (wt %)
Sulfur removal (%)
1 2
petcoke pre-treated petcoke
2.0 4.3
3.85 2.85
13.67 36.10
Experimental conditions: m (petcoke) = 0.5 g, m ([Bmim]3PW12O40) = 0.5 g, V (H2O2) = 5 mL, V ([Bmim]BF4) = 5 mL, T = 80 °C, t = 5 h.
3.3. Optimization of ODS reaction conditions The influence of reaction parameters, such as temperature, time and the amount of H2O2 on oxidation of sulfur were studied using [Bmim]3PW12O40 as the catalyst. (Fig. 2). The result of the influence of temperature on sulfur conversion is shown in Fig. 2a. The maximum desulfurization activity at 80 °C could be achieved and the sulfur content of petcoke reduced to 2.85 wt%. Two parallel reactions including the catalytic oxidation of petcoke and thermal decomposition of H2O2 carry out in the reaction process. Desulfurization activity is correlated closely with the thermal decomposition of H2O2. As the temperature increases, the rate of thermal decomposition of H2O2 is accelerated, resulting in the worse utilization of H2O2 at high temperature. Fig. 2b shows the residual sulfur content of petcoke vs reaction time at the same temperature (80 °C). It was found that the sulfur content declined obviously with reacting for 1 h, indicating that [Bmim]3PW12O40 has excellent catalytic performance for the desulfurization of petcoke. With the prolonging of reaction time, the sulfur content of petcoke continuously decreased. But the decreasing tendency became smooth. The sulfur content of petcoke could be reduced to
Table 3 Desulfurization performance of different catalyst. Entry
Catalyst
Sulfur content (wt%)
Sulfur removal (%)
1 2 3 4
[Bmim]Cl H3PW12O40 [Bmim]3PW12O40 No catalyst
3.80 3.76 2.85 4.05
14.80 15.69 36.10 9.19
Experimental conditions: m (pre-treated petcoke) = 0.5 g, m (catalyst) = 0.5 g, V (H2O2) = 5 mL, V ([Bmim] BF4) = 5 mL. T = 80 °C, t = 5 h.
slightly without catalyst, showing that the solvent almost has no effect on the desulfurization of petcoke. When [Bmim]Cl or commercial H3PW12O40 was used as the catalyst, the sulfur content in petcoke is reduced to 3.80 wt% and 3.76 wt%, respectively. The desulfurization rate has no obvious increase compared to that without catalyst. [Bmim]3PW12O40 exhibits better catalytic performance than [Bmim]Cl 3
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Fig. 2. The influence of different reaction parameters on sulfur conversion. (a: temperature, b: reaction time, c: the amount of H2O2). Experimental conditions: m (pre-treated petcoke) = 0.5 g, V ([Bmim]BF4) = 5 mL, m ([Bmim]3PW12O40) = 0.5 g.
Fig. 3. SEM images of raw petcoke (a, c) and desulfurized petcoke (b, d).
2.85 wt% for 5 h. Further increasing the reaction time, the reduction in sulfur content was not obvious. This is mainly because the oxidant reacts more sufficiently with the sulfur-containing compound in the petcoke with the increasing reaction time. When the time exceeded 5 h,
the reaction had sufficiently proceeded, and at this time, the sulfur content did not substantially decrease. Therefore, the optimal reaction time for this experiment was 5 h. To investigate the effect of the amount of H2O2 on the oxidative 4
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Fig. 4. XRD pattern (A): (a) raw petcoke, (b) desulfurized petcoke and Raman spectrum (B): (a) raw petcoke, (b) desulfurized petcoke.
Fig. 5. The image of magenta solution (A): (a) initial magenta solution, (b) magenta solution after importing the tail gas of ODS and FT-IR spectra of petcoke (B): (a) raw petcoke, (b) desulfurized petcoke.
Fig. 6. XPS spectra of (a) raw petcoke, (b) desulfurized petcoke.
properties, a series of experiments were carried out at 80 °C for 5 h. As presented in Fig. 2c, the amount of H2O2 had a powerful effect on the reaction. Not to be ignored, there is a competitive relationship between H2O2 decomposition and sulfur oxidation reaction. Residual sulfur content of petcoke only reached 3.12 wt% with 3 mL H2O2, which may
be due to the H2O2 decomposition. Due to the growth of the concentration of H2O2, the sulfur content of petcoke could be reduced to below 3 wt% with increasing the amount of H2O2. When the amount of H2O2 was 5 mL, the sulfur content in petcoke of 2.85 wt% could be attained in the desulfurization system. Considering the need to save 5
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3.5. Analysis of oxidation products To verify whether SO2 was produced in the process of desulfurization, magenta solution was used to detect the existence of SO2. As demonstrated in Fig. 5, it can be seen that the color of magenta solution did not change significantly before and after importing the tail gas of ODS. The color comparison proves that no SO2 was produced during oxidative desulfurization of high-sulfur petcoke. In order to further discuss the oxidation products of sulfur in petcoke, a series of characterizations are given as follows. Qualitative analysis of the oxidation products was carried out as follows. After the oxidation desulfurization process was completed, the oxidized petcoke was separated by filtration from the solution, and washed with water, then dried for FT-IR and XPS analysis. The results are displayed in Fig. 5B and Fig. 6. From the FT-IR spectra, compared with the raw petcoke, the desulfurized petcoke showed a new peak at 1304 cm−1, which is attributed to the stretching vibration peak of O] S]O. This infrared result can initially confirm that the sulfide fraction in petcoke was oxidized. To further demonstrate the product after oxidative desulfurization, XPS analysis was used for detecting the oxidative product of thiophene sulfide in the raw petcoke. Aromatic sulfide (thiophene sulfur) was the main sulfide in the raw petcoke and the form of sulfur was relatively simple (Fig. 6a). After oxidation (Fig. 6b), three types of sulfide including sulfone, sulfoxide and thiophene sulfur were found. Desulfurized petcoke still contains thiophene sulfur, indicating that the organic sulfur in the petcoke was not completely oxidized. The sulfur atom in petcoke is often in the form of the negative divalent state with two lone electron pairs, so the electronegativity is very strong. Under the action of the oxidant, the less polar thiophene sulfur is partially oxidized to soluble form. The XPS analysis results is consistent with that of FT-IR spectra. After the reaction was completed, the BaCl2 solution was put in the filtered ionic liquid. For a moment, a white precipitation appeared. The precipitation was washed with water and dried for XRD analysis. As shown in the Fig. 7, it is vivid that the XRD spectra of obtained precipitation is consistent with the standard card of BaSO4. This result explains that partial sulfur in petcoke was oxidized into sulfate. In conclusion, part of thiophene in the petcoke is oxidized to sulfone, sulfoxide and sulfate in the [Bmim]3PW12O40 /H2O2 system and no SO2 is produced during the oxidation process.
Fig. 7. XRD pattern of unknown solid (The solid was attained from the reaction solution after adding Ba2+) and the standard card of BaSO4.
commercial costs, the H2O2 amount of 5 mL was chosen in present study. 3.4. Characterizations of petcoke The morphology of raw petcoke and desulfurized petcoke was observed by SEM. The SEM image of raw petcoke (Fig. 3a and c) displayed typical bulk morphology, similar with the morphology of the desulfurized petcoke (Fig. 3b and d). The result indicates that the method of oxidative desulfurization does not affect the morphology of petcoke. The appearance of petcoke maintains under the premise of reducing certain sulfur content. The XRD pattern of raw petcoke and desulfurized petcoke is displayed in Fig. 4A. The characteristic peaks in the pattern of two samples were all attributed to the graphite crystal structure, indicating that the graphite crystal structure was not changed after desulfurization. However, the full width at half maximum (FWHM) of (0 0 2) peak was enlarged significantly. It exhibits that in the catalytic oxidation process, not only the sulfur of the petcoke is removed, but also part of the carbon skeleton of petcoke is destroyed, resulting in a decrease in its order. In addition, the characteristic peaks of 1350 cm−1 (D-band) and 1580 cm−1 (G-band) in the Raman spectrums are related to the defects and the In-plane vibration of sp2-carbon atoms, respectively [14,50–52]. It can be seen from the Raman spectroscopy (Fig. 4B) that ID/IG intensity ratio of desulfurized petcoke was higher than that of petcoke. This further indicates that the order of petcoke reduces.
3.6. Supposed mechanism The supposed oxidative desulfurization mechanism of petcoke in the [Bmim]3PW12O40 / H2O2 system is shown in Scheme 1. First, [PW12O40]3− is decomposed to form peroxide [PO4{WO(O2)2}4]3−
Scheme 1. The mechanism for the oxidation of petcoke in the [Bmim]3PW12O40/H2O2 system.
6
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[53,54], then aromatic sulfides in petcoke are oxidized to sulfate, sulfone and sulfoxide. Among them, sulfate can be removed from petcoke and enter into the solvent. Thus, reducing the sulfur content in highsulfur petcoke from 4.46 wt% to 2.85 wt% can be achieved under mild conditions.
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4. Conclusion In this contribution, the application of POM-IL ([Bmim]3PW12O40) as catalyst in oxidative desulfurization of high-sulfur petcoke was described. From the results of FT-IR and XRD, [Bmim]3PW12O40 was easily prepared through the mixing of [Bmim]Cl and H3PW12O40, and remained the structure of two raw materials. The desulfurization results showed that [Bmim]3PW12O40 exhibited superior catalytic performance for the oxidative desulfurization of high-sulfur petcoke with H2O2 as the oxidant. The sulfur content was reduced to 2.85 wt% for 5 h at a mild temperature (80 °C) and the sulfur removal reached 36.10%. It was different from the industrial methods that the reaction temperature was fairly moderate and no SO2 was released during the oxidation process. It was proved by FT-IR, XRD and XPS that thiophene sulfides in petcoke were oxidized to sulfone, sulfoxide and sulfate. The present study provides a fresh approach with mild conditions for the badly-needed desulfurization of high-sulfur petcoke. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Nos. 21606113, 21722604, 21576122), the Postdoctoral Foundation of China (No. 2017M611726). References [1] Olmeda J, Sánchez de Rojas MI, Frías M, Donatello S, Cheeseman CR. Effect of petroleum (pet) coke addition on the density and thermal conductivity of cement pastes and mortars. Fuel 2013;107:138–46. [2] Wang J, Anthony EJ, Abanades JC. Clean and efficient use of petroleum coke for combustion and power generation. Fuel 2004;83(10):1341–8. [3] Kubota M, Ito T, Watanabe F, Matsuda H. Pore structure and water adsorptivity of petroleum coke-derived activated carbon for adsorption heat pump–influence of hydrogen content of coke. Appl Therm Eng 2011;31(8–9):1495–8. [4] Wu J, Montes V, Virla LD, Hill JM. Impacts of amount of chemical agent and addition of steam for activation of petroleum coke with KOH or NaOH. Fuel Process Technol 2018;181:53–60. [5] Geng JC, Xue DM, Liu XQ, Shi YQ, Sun LB. N-doped porous carbons for CO2 capture: rational choice of N-containing polymer with high phenyl density as precursor. AIChE J 2017;63(5):1648–58. [6] Xiao J, Wang XX, Fujii M, Yang QJ, Song CS. A novel approach for ultra-deep adsorptive desulfurization of diesel fuel over TiO2-CeO2/MCM-48 under ambient conditions. AIChE J 2013;59(5):1441–5. [7] Chen FF, Huang K, Fan JP, Tao DJ. Chemical solvent in chemical solvent: a class of hybrid materials for effective capture of CO2. AIChE J 2018;64(2):632–9. [8] Peng HL, Zhang JB, Zhang JY, Zhong FY, Wu PK, Huang K, et al. Chitosan-derived mesoporous carbon with ultrahigh pore volume for amine impregnation and highly efficient CO2 capture. Chem Eng J 2019;359:1159–65. [9] Xiao J, Sitamraju S, Chen YS, Watanabe S, Fujii M, Janik M, et al. Air-promoted adsorptive desulfurization of diesel fuel over Ti-Ce mixed metal oxides. AIChE J 2015;61(2):631–9. [10] Chen JH, Lu XF. Progress of petroleum coke combusting in circulating fluidized bed boilers—a review and future perspectives. Resour Conserv Recycl 2007;49(3):203–16. [11] Zhu WS, Zhu GP, Li HM, Chao YH, Zhang M, Du DL, et al. Catalytic kinetics of oxidative desulfurization with surfactant-type polyoxometalate-based ionic liquids. Fuel Process Technol 2013;106:70–6. [12] Choi J, Barnard ZG, Zhang S, Hill JM. Ni catalysts supported on activated carbon from petcoke and their activity for toluene hydrogenation. Can J Chem Eng 2012;90(3):631–6. [13] Mochizuki T, Kubota M, Matsuda H, D'Elia Camacho LF. Adsorption behaviors of ammonia and hydrogen sulfide on activated carbon prepared from petroleum coke by KOH chemical activation. Fuel Process Technol 2016;144:164–9. [14] Wu MB, Liu Y, Zhu YL, Lin J, Liu JY, Hu H, et al. Supramolecular polymerizationassisted synthesis of nitrogen and sulfur dual-doped porous graphene networks from petroleum coke as efficient metal-free electrocatalysts for the oxygen reduction reaction. J Mater Chem A 2017;5(22):11331–9. [15] Li TS, Li J, Zhang HL, Sun KN, Xiao J. DFT research on benzothiophene pyrolysis reaction mechanism. J Phys Chem A 2019;123(4):796–810. [16] Al-Haj-Ibrahim H, Morsi BI. Desulfurization of petroleum coke: a review. Ind Eng
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benzothiophene using the Keggin-type lacunary polytungstophosphate as catalysts in emulsion. J Mol Catal A: Chem 2010;332(1–2):59–64. Izumi Y, Urabel K. Catalysts of heteropolyacids entrapped in activated carbon. Chem Lett 1981;10:663–6. Misono M. Unique acid catalysis of heteropoly compounds (heteropolyoxometalates) in the solid state. Chem Commun 2001;13:1141–52. Wu ZS, Ren WC, Xu L, Li F, Cheng HM. Doped graphene sheets as anode materials with superhigh rate and large capacity for lithium ion batteries. ACS Nano 2011;5(7):5463–71. Li P, Liu JY, Wang YW, Liu Y, Wang XN, Nam KW, et al. Synthesis of ultrathin
hollow carbon shell from petroleum asphalt for high-performance anode material in lithium-ion batteries. Chem Eng J 2016;286:632–9. [52] Xu CG, Ning GQ, Zhu X, Wang G, Liu XF, Gao JS, et al. Synthesis of graphene from asphaltene molecules adsorbed on vermiculite layers. Carbon 2013;62:213–21. [53] Zhang HX, Gao JJ, Meng H, Li CX. Removal of thiophenic sulfurs using an extractive oxidative desulfurization process with three new phosphotungstate catalysts. Ind Eng Chem Res 2012;51(19):6658–65. [54] Zhang C, Pan XY, Wang F, Liu XQ. Extraction–oxidation desulfurization by pyridinium-based task-specific ionic liquids. Fuel 2012;102:580–4.
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Full Length Article
Extraction combined catalytic oxidation desulfurization of petcoke in ionic liquid under mild conditions
T
Hui Liua,1, Huanhuan Xua,1, Mingqing Huaa, LinLin Chena, Yanchen Weib, Chao Wangc, ⁎ Peiwen Wua, Fengxia Zhud, Xiaozhong Chud, Huaming Lia, Wenshuai Zhua, a
School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, PR China School of Materials Science and Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, PR China c School of Environment and Safety Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, PR China d School of Chemistry and Chemical Engineering, Huaiyin Normal University, PR China b
ARTICLE INFO
ABSTRACT
Keywords: High-sulfur petcoke Oxidative desulfurization Polyoxometalate ionic liquids Sulfate Mild conditions
The desulfurization of high-sulfur petcoke under mild condition is a great challenge due to the structurally stable aromatic ring skeleton with a large steric hindrance of sulfur compounds. Herein, by using polyoxometalate ionic liquid [Bmim]3PW12O40 and H2O2 as catalyst and oxidant, respectively, the sulfur content in the petcoke was reduced from 4.46 wt% to 2.85 wt% in green solvent [Bmim]BF4. Moreover, the reaction performed at a mild temperature (80 °C), significantly lower than that in the industrial methods (≥1700 °C). It realized the conversion of high-sulfur petcoke from waste to resources. The experimental results indicated that sulfides in petcoke were oxidized to sulfate, sulfone and sulfoxide, while SO2 was not produced in the process of desulfurization. The possible oxidative desulfurization mechanism was proposed based on the series of characterizations.
1. Introduction Petcoke is a by-product of the refining industry, which possesses low ash (< 1.2 wt%) and high carbon (> 85 wt%) contents by comparison to other carbon materials [1,2]. It is able to be the major feedstock for producing carbon products, such as carbon anodes [3,4]. With the deterioration of crude oil’s quality [5–9], more than 10 million tons of high-sulfur petcoke are produced annually. However, high-sulfur petcoke (sulfur content > 3 wt%) is unable to produce carbon products, and it can only be classified as waste which causes environmental issues and need to be handled with considerable cost [10–14]. Therefore, reducing the sulfur content in high-sulfur petcoke is badly-needed and significant for environment and economy. The sulfur in petcoke is mainly ascribed to thiophene and its derivatives [15–18]. The difficulty in desulfurization of petcoke is that the sulfur presents on the structurally stable aromatic ring skeleton with a large steric hindrance. Generally, several common desulfurization methods for petcoke are shown in Table 1 [16,19–26]. High temperature desulfurization is used in industry currently [19–22] which calcines petcoke at 1700 °C to reduce sulfur content. However, this desulfurization method requires high temperature and causes the
emission of SO2, resulting in environmental issues and considerable treatment cost. As the improving methods in laboratory, co-heat reduction method [24] and hot alkali treatment method [26] are still carried out at 550 °C, at least. Therefore, in order to respond to the new requirements of national energy conservation and environmental protection, finding a new method of petcoke desulfurization under mild conditions has become one of the focuses. Oxidative desulfurization (ODS) has excellent removal performance for aromatic sulfides, and operates under the moderate reaction conditions [27–37]. Therefore, ODS could be adopted to desulfurize highsulfur petcoke at low temperature. As is known to all, many types of polyoxometalate ionic liquids (POM-ILs) [38–40] possess excellent selective oxidation performances for sulfides. Because of their simple composition, strong acidity and oxidation, unique “pseudo-liquid” properties, high activity at low temperature and good thermal stability, POM-ILs have attracted much attention. In our previous work [41,42], a series of POM-ILs as catalysts have been applied to the oxidative desulfurization of thiophene-type sulfide in fuel oil, the sulfur removal was 100%. In this work, the POM-IL [Bmim]3PW12O40 was prepared by the one-pot method and was used as a catalyst for ODS of petcoke, in
Corresponding author. E-mail address: [email protected] (W. Zhu). 1 These authors contributed equally to this work. ⁎
https://doi.org/10.1016/j.fuel.2019.116200 Received 12 July 2019; Received in revised form 6 September 2019; Accepted 10 September 2019 Available online 15 October 2019 0016-2361/ © 2019 Published by Elsevier Ltd.
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Table 1 Desulfurization methods of petcoke.
Sulfur removal (%) = (W0
Desulfurization method
Temperature
Ref.
Ultrahigh-temperature desulfurization High temperature oxidation desulfurization Vacuum high temperature desulfurization Co-heat reduction desulfurization Hydrodesulfurization Hot alkali treatment desulfurization Oxidative desulfurization
2500 °C 1700 °C 1500 °C 800 °C 700 °C 550 °C 80 °C
[25] [19–22] [23] [24] [16] [26] This work
Wt )/W0 × 100%
where W0 and Wt (wt%) were the initial sulfur content and the sulfur content at time t, respectively. 2.6. Characterization method
company with green solvent [Bmim]BF4 and oxidant H2O2. The desulfurization system was valid and environmental-friendly for ODS of petcoke, and the sulfur content of high-sulfur petcoke was reduced to less than 3 wt% at 80 °C under 1 atm. The reaction condition is more moderate in comparison with that required for the current industrial methods (Table 1). Additionally, the catalyst, petcoke and the oxidative products were characterized by a variety of spectroscopy and analytical techniques. Finally, the possible mechanism of ODS was inferred.
A Nicolet Nexus 470 Fourier Transform Infrared Spectoscopy (FTIR) recorded the spectra of [Bmim]3PW12O40 and petcoke, and the FTIR spectra were collected in KBr pellets from 4000 cm−1 with 400 cm−1. Raman scattering spectroscopy was obtained at room temperature using DXR Raman microscope with 532 nm laser source. The morphology of petcoke was characterized by scanning electron microscope (SEM, JSM-6010 PLUS/LA). The samples used for SEM were prepared by dispersing some samples in ethanol, then a drop of the solution was placed on a silicon pellet and the ethanol was evaporated under UV light. The crystalline phases of materials were analyzed by Xray diffraction (XRD) with high-intensity Cu Kα (λ = 1.54 Å). X-ray photoelectron spectrometer (XPS) spectra were performed on a VG MultiLab 2000 spectrometer using Mg KR (1253.6 eV) radiation.
2. Experimental
3. Results and discussion
2.1. Materials
3.1. FT-IR and XRD characterization of catalyst
The petcoke (specification: 4#A) used in this experiment was from Zhenjiang Carbon Products Plant. 1-Butyl-3-methylimidazolium Chloride ([Bmim]Cl), and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) were purchased from Chengjie Reagent Co., Ltd. Tetrabutylammonium chloride, phosphotungstic acid, 30% H2O2 were purchased from Sinopharm Reagent Co., Ltd. All the reagents were used directly without any further treatment.
FT-IR spectra of [Bmim]Cl, [Bmim]3PW12O40 and H3PW12O40 are displayed in Fig. 1. For [Bmim]Cl, the stretching vibration peaks of CeH in the imidazole and CeH on the substituent group appeared at 3146 and 2960 cm−1, respectively. The C]N vibration of [Bmim]Cl could be observed at 1569 cm−1, and the peak at 1170 cm−1 was ascribed to the vibration of imidazole ring [45]. [Bmim]3PW12O40 catalyst showed the characteristic absorption band of [Bmim]Cl at 3146, 2959, 1568 and 1167 cm−1, which proves that [Bmim]+ ion does not be destroyed in the synthesized catalyst. From the spectrum of H3PW12O40, four typical characteristic peaks located at 1076, 983, 890 and 805 cm−1, respectively, were observed. These peaks are belonged to the stretching vibration absorption of central tetrahedral PeO, W] O, WeOaeW and WeObeW [46,47]. Similar characteristic peaks at 1079, 977, 895 and 804 cm−1 were found in the spectra of [Bmim]3PW12O40, which indicates that [Bmim]3PW12O40 catalyst is successfully prepared. The prepared catalyst is also characterized by XRD. As shown in Fig. 1d, some diffraction peaks of [Bmim]PW12O40 at 10.9, 17.1, 24.2, 25.7, 26.8, 33.8 and 63.1° are significantly different from the H3PW12O40. The difference may be due to the substitution of secondary structure protons of H3PW12O40 by [Bmim]+ [39], which leads to the appearance of the coordination water H3O+ and H5O2+ interacting with the anion of Keggin structure. It is further proved that the catalyst is successfully prepared [48,49].
2.2. Synthesis of catalyst [Bmim]3PW12O40 Phosphotungstic acid (0.01 mol) was dissolved in H2O (100 mL) to form solution. Then [Bmim]Cl (0.06 mol) was put in the solution, and the compound was stirred for 12 h at 25 °C. A white precipitate was obtained. After filtration and washing with water until there is no chloride ions in the filtrate. Finally, the product was dried at 80 °C overnight to obtain white powder [Bmim]3PW12O40 [43,44]. 2.3. Pre-treatment of high-sulfur petcoke The pre-treatment experiment was carried out in two-necked flask by mixing tetrabutylammonium chloride (6 g) with high-sulfur petcoke (1 g) at 150 °C for 4 h. After filtration and washing with water, the pretreated petcoke was dried for subsequent use. 2.4. Oxidative desulfurization of the high-sulfur petcoke
3.2. Effects of pre-treated and catalyst
In the desulfurization experiment, a mixture with 5 mL [Bmim]BF4, 0.5 g [Bmim]3PW12O40, 0.5 g pre-treated petcoke, and 5 mL 30% H2O2 (add 1 mL·h−1) in a 100 mL flask was stirred at 80 °C for 5 h. Then, the solution was filtered and the residue was washed with acetonitrile to remove catalyst. After washing with acetonitrile several times, the residual acetonitrile was removed by washing with H2O. The obtained petcoke was dried at 100 °C for 24 h.
The sulfur content has been only reduced to 3.85 wt% (Sulfur removal 13.67%) by oxidative desulfurization of the high-sulfur petcoke (Sulfur content 4.46 wt%) in [Bmim]BF4, with using [Bmim]3PW12O40 and H2O2 as catalyst and oxidant, respectively (Table 2, entry 1). This may be attributed to the small amount of exposed sulfur in the outer layer of petcoke with the low specific surface area (2.0 m2/g). Fortunately, the sulfur content has been decreased to 2.85 wt% (< 3 wt%, and sulfur removal 36.10%) under the same conditions with using the pre-treated high-sulfur petcoke by tetrabutylammonium chloride, which has more than double specific surface area (4.3 m2/g) (Table 2, entry 2). The desulfurization performance of different catalysts in oxidative desulfurization of pre-treated high-sulfur petcoke were tested and the results are depicted in Table 3. The sulfur content of petcoke decreases
2.5. Determination of sulfur content in petcoke The sulfur content of petcoke was determinated by CLS-3000 microcomputer Cullen sulfur analyzer, and the temperature control range of the instrument is between 0 and 2000 °C. The initial sulfur content of petcoke was determined to be 4.46 wt%. The calculation formula for the desulfurization rate is as follows: 2
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Fig. 1. FT-IR spectra of samples: (a) [Bmim]Cl, (b) H3PW12O40, (c) [Bmim]3PW12O40; XRD pattern (d) of [Bmim]3PW12O40 and H3PW12O40.
and H3PW12O40. The sulfur content of petcoke can be reduced to 2.85 wt%. Probably because [PW12O40]3− in [Bmim]3PW12O40 can convert to [PO4{W(O) (O2)2}4]3− reactive oxygen species in the presence of excessive H2O2, which has stronger oxidation ability. As a comparison, the low catalytic performance of H3PW12O40 may be due to the poor solubility of H3PW12O40 in the reaction solvent [Bmim]BF4, resulting in unsatisfied contraction of catalyst with high-sulfur petcoke.
Table 2 Effect of pre-treated of petcoke. Entry
Sample
SBET (m2/ g)
Sulfur content (wt %)
Sulfur removal (%)
1 2
petcoke pre-treated petcoke
2.0 4.3
3.85 2.85
13.67 36.10
Experimental conditions: m (petcoke) = 0.5 g, m ([Bmim]3PW12O40) = 0.5 g, V (H2O2) = 5 mL, V ([Bmim]BF4) = 5 mL, T = 80 °C, t = 5 h.
3.3. Optimization of ODS reaction conditions The influence of reaction parameters, such as temperature, time and the amount of H2O2 on oxidation of sulfur were studied using [Bmim]3PW12O40 as the catalyst. (Fig. 2). The result of the influence of temperature on sulfur conversion is shown in Fig. 2a. The maximum desulfurization activity at 80 °C could be achieved and the sulfur content of petcoke reduced to 2.85 wt%. Two parallel reactions including the catalytic oxidation of petcoke and thermal decomposition of H2O2 carry out in the reaction process. Desulfurization activity is correlated closely with the thermal decomposition of H2O2. As the temperature increases, the rate of thermal decomposition of H2O2 is accelerated, resulting in the worse utilization of H2O2 at high temperature. Fig. 2b shows the residual sulfur content of petcoke vs reaction time at the same temperature (80 °C). It was found that the sulfur content declined obviously with reacting for 1 h, indicating that [Bmim]3PW12O40 has excellent catalytic performance for the desulfurization of petcoke. With the prolonging of reaction time, the sulfur content of petcoke continuously decreased. But the decreasing tendency became smooth. The sulfur content of petcoke could be reduced to
Table 3 Desulfurization performance of different catalyst. Entry
Catalyst
Sulfur content (wt%)
Sulfur removal (%)
1 2 3 4
[Bmim]Cl H3PW12O40 [Bmim]3PW12O40 No catalyst
3.80 3.76 2.85 4.05
14.80 15.69 36.10 9.19
Experimental conditions: m (pre-treated petcoke) = 0.5 g, m (catalyst) = 0.5 g, V (H2O2) = 5 mL, V ([Bmim] BF4) = 5 mL. T = 80 °C, t = 5 h.
slightly without catalyst, showing that the solvent almost has no effect on the desulfurization of petcoke. When [Bmim]Cl or commercial H3PW12O40 was used as the catalyst, the sulfur content in petcoke is reduced to 3.80 wt% and 3.76 wt%, respectively. The desulfurization rate has no obvious increase compared to that without catalyst. [Bmim]3PW12O40 exhibits better catalytic performance than [Bmim]Cl 3
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Fig. 2. The influence of different reaction parameters on sulfur conversion. (a: temperature, b: reaction time, c: the amount of H2O2). Experimental conditions: m (pre-treated petcoke) = 0.5 g, V ([Bmim]BF4) = 5 mL, m ([Bmim]3PW12O40) = 0.5 g.
Fig. 3. SEM images of raw petcoke (a, c) and desulfurized petcoke (b, d).
2.85 wt% for 5 h. Further increasing the reaction time, the reduction in sulfur content was not obvious. This is mainly because the oxidant reacts more sufficiently with the sulfur-containing compound in the petcoke with the increasing reaction time. When the time exceeded 5 h,
the reaction had sufficiently proceeded, and at this time, the sulfur content did not substantially decrease. Therefore, the optimal reaction time for this experiment was 5 h. To investigate the effect of the amount of H2O2 on the oxidative 4
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Fig. 4. XRD pattern (A): (a) raw petcoke, (b) desulfurized petcoke and Raman spectrum (B): (a) raw petcoke, (b) desulfurized petcoke.
Fig. 5. The image of magenta solution (A): (a) initial magenta solution, (b) magenta solution after importing the tail gas of ODS and FT-IR spectra of petcoke (B): (a) raw petcoke, (b) desulfurized petcoke.
Fig. 6. XPS spectra of (a) raw petcoke, (b) desulfurized petcoke.
properties, a series of experiments were carried out at 80 °C for 5 h. As presented in Fig. 2c, the amount of H2O2 had a powerful effect on the reaction. Not to be ignored, there is a competitive relationship between H2O2 decomposition and sulfur oxidation reaction. Residual sulfur content of petcoke only reached 3.12 wt% with 3 mL H2O2, which may
be due to the H2O2 decomposition. Due to the growth of the concentration of H2O2, the sulfur content of petcoke could be reduced to below 3 wt% with increasing the amount of H2O2. When the amount of H2O2 was 5 mL, the sulfur content in petcoke of 2.85 wt% could be attained in the desulfurization system. Considering the need to save 5
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3.5. Analysis of oxidation products To verify whether SO2 was produced in the process of desulfurization, magenta solution was used to detect the existence of SO2. As demonstrated in Fig. 5, it can be seen that the color of magenta solution did not change significantly before and after importing the tail gas of ODS. The color comparison proves that no SO2 was produced during oxidative desulfurization of high-sulfur petcoke. In order to further discuss the oxidation products of sulfur in petcoke, a series of characterizations are given as follows. Qualitative analysis of the oxidation products was carried out as follows. After the oxidation desulfurization process was completed, the oxidized petcoke was separated by filtration from the solution, and washed with water, then dried for FT-IR and XPS analysis. The results are displayed in Fig. 5B and Fig. 6. From the FT-IR spectra, compared with the raw petcoke, the desulfurized petcoke showed a new peak at 1304 cm−1, which is attributed to the stretching vibration peak of O] S]O. This infrared result can initially confirm that the sulfide fraction in petcoke was oxidized. To further demonstrate the product after oxidative desulfurization, XPS analysis was used for detecting the oxidative product of thiophene sulfide in the raw petcoke. Aromatic sulfide (thiophene sulfur) was the main sulfide in the raw petcoke and the form of sulfur was relatively simple (Fig. 6a). After oxidation (Fig. 6b), three types of sulfide including sulfone, sulfoxide and thiophene sulfur were found. Desulfurized petcoke still contains thiophene sulfur, indicating that the organic sulfur in the petcoke was not completely oxidized. The sulfur atom in petcoke is often in the form of the negative divalent state with two lone electron pairs, so the electronegativity is very strong. Under the action of the oxidant, the less polar thiophene sulfur is partially oxidized to soluble form. The XPS analysis results is consistent with that of FT-IR spectra. After the reaction was completed, the BaCl2 solution was put in the filtered ionic liquid. For a moment, a white precipitation appeared. The precipitation was washed with water and dried for XRD analysis. As shown in the Fig. 7, it is vivid that the XRD spectra of obtained precipitation is consistent with the standard card of BaSO4. This result explains that partial sulfur in petcoke was oxidized into sulfate. In conclusion, part of thiophene in the petcoke is oxidized to sulfone, sulfoxide and sulfate in the [Bmim]3PW12O40 /H2O2 system and no SO2 is produced during the oxidation process.
Fig. 7. XRD pattern of unknown solid (The solid was attained from the reaction solution after adding Ba2+) and the standard card of BaSO4.
commercial costs, the H2O2 amount of 5 mL was chosen in present study. 3.4. Characterizations of petcoke The morphology of raw petcoke and desulfurized petcoke was observed by SEM. The SEM image of raw petcoke (Fig. 3a and c) displayed typical bulk morphology, similar with the morphology of the desulfurized petcoke (Fig. 3b and d). The result indicates that the method of oxidative desulfurization does not affect the morphology of petcoke. The appearance of petcoke maintains under the premise of reducing certain sulfur content. The XRD pattern of raw petcoke and desulfurized petcoke is displayed in Fig. 4A. The characteristic peaks in the pattern of two samples were all attributed to the graphite crystal structure, indicating that the graphite crystal structure was not changed after desulfurization. However, the full width at half maximum (FWHM) of (0 0 2) peak was enlarged significantly. It exhibits that in the catalytic oxidation process, not only the sulfur of the petcoke is removed, but also part of the carbon skeleton of petcoke is destroyed, resulting in a decrease in its order. In addition, the characteristic peaks of 1350 cm−1 (D-band) and 1580 cm−1 (G-band) in the Raman spectrums are related to the defects and the In-plane vibration of sp2-carbon atoms, respectively [14,50–52]. It can be seen from the Raman spectroscopy (Fig. 4B) that ID/IG intensity ratio of desulfurized petcoke was higher than that of petcoke. This further indicates that the order of petcoke reduces.
3.6. Supposed mechanism The supposed oxidative desulfurization mechanism of petcoke in the [Bmim]3PW12O40 / H2O2 system is shown in Scheme 1. First, [PW12O40]3− is decomposed to form peroxide [PO4{WO(O2)2}4]3−
Scheme 1. The mechanism for the oxidation of petcoke in the [Bmim]3PW12O40/H2O2 system.
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[53,54], then aromatic sulfides in petcoke are oxidized to sulfate, sulfone and sulfoxide. Among them, sulfate can be removed from petcoke and enter into the solvent. Thus, reducing the sulfur content in highsulfur petcoke from 4.46 wt% to 2.85 wt% can be achieved under mild conditions.
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4. Conclusion In this contribution, the application of POM-IL ([Bmim]3PW12O40) as catalyst in oxidative desulfurization of high-sulfur petcoke was described. From the results of FT-IR and XRD, [Bmim]3PW12O40 was easily prepared through the mixing of [Bmim]Cl and H3PW12O40, and remained the structure of two raw materials. The desulfurization results showed that [Bmim]3PW12O40 exhibited superior catalytic performance for the oxidative desulfurization of high-sulfur petcoke with H2O2 as the oxidant. The sulfur content was reduced to 2.85 wt% for 5 h at a mild temperature (80 °C) and the sulfur removal reached 36.10%. It was different from the industrial methods that the reaction temperature was fairly moderate and no SO2 was released during the oxidation process. It was proved by FT-IR, XRD and XPS that thiophene sulfides in petcoke were oxidized to sulfone, sulfoxide and sulfate. The present study provides a fresh approach with mild conditions for the badly-needed desulfurization of high-sulfur petcoke. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Nos. 21606113, 21722604, 21576122), the Postdoctoral Foundation of China (No. 2017M611726). References [1] Olmeda J, Sánchez de Rojas MI, Frías M, Donatello S, Cheeseman CR. Effect of petroleum (pet) coke addition on the density and thermal conductivity of cement pastes and mortars. Fuel 2013;107:138–46. [2] Wang J, Anthony EJ, Abanades JC. Clean and efficient use of petroleum coke for combustion and power generation. Fuel 2004;83(10):1341–8. [3] Kubota M, Ito T, Watanabe F, Matsuda H. Pore structure and water adsorptivity of petroleum coke-derived activated carbon for adsorption heat pump–influence of hydrogen content of coke. Appl Therm Eng 2011;31(8–9):1495–8. [4] Wu J, Montes V, Virla LD, Hill JM. Impacts of amount of chemical agent and addition of steam for activation of petroleum coke with KOH or NaOH. Fuel Process Technol 2018;181:53–60. [5] Geng JC, Xue DM, Liu XQ, Shi YQ, Sun LB. N-doped porous carbons for CO2 capture: rational choice of N-containing polymer with high phenyl density as precursor. AIChE J 2017;63(5):1648–58. [6] Xiao J, Wang XX, Fujii M, Yang QJ, Song CS. A novel approach for ultra-deep adsorptive desulfurization of diesel fuel over TiO2-CeO2/MCM-48 under ambient conditions. AIChE J 2013;59(5):1441–5. [7] Chen FF, Huang K, Fan JP, Tao DJ. Chemical solvent in chemical solvent: a class of hybrid materials for effective capture of CO2. AIChE J 2018;64(2):632–9. [8] Peng HL, Zhang JB, Zhang JY, Zhong FY, Wu PK, Huang K, et al. Chitosan-derived mesoporous carbon with ultrahigh pore volume for amine impregnation and highly efficient CO2 capture. Chem Eng J 2019;359:1159–65. [9] Xiao J, Sitamraju S, Chen YS, Watanabe S, Fujii M, Janik M, et al. Air-promoted adsorptive desulfurization of diesel fuel over Ti-Ce mixed metal oxides. AIChE J 2015;61(2):631–9. [10] Chen JH, Lu XF. Progress of petroleum coke combusting in circulating fluidized bed boilers—a review and future perspectives. Resour Conserv Recycl 2007;49(3):203–16. [11] Zhu WS, Zhu GP, Li HM, Chao YH, Zhang M, Du DL, et al. Catalytic kinetics of oxidative desulfurization with surfactant-type polyoxometalate-based ionic liquids. Fuel Process Technol 2013;106:70–6. [12] Choi J, Barnard ZG, Zhang S, Hill JM. Ni catalysts supported on activated carbon from petcoke and their activity for toluene hydrogenation. Can J Chem Eng 2012;90(3):631–6. [13] Mochizuki T, Kubota M, Matsuda H, D'Elia Camacho LF. Adsorption behaviors of ammonia and hydrogen sulfide on activated carbon prepared from petroleum coke by KOH chemical activation. Fuel Process Technol 2016;144:164–9. [14] Wu MB, Liu Y, Zhu YL, Lin J, Liu JY, Hu H, et al. Supramolecular polymerizationassisted synthesis of nitrogen and sulfur dual-doped porous graphene networks from petroleum coke as efficient metal-free electrocatalysts for the oxygen reduction reaction. J Mater Chem A 2017;5(22):11331–9. [15] Li TS, Li J, Zhang HL, Sun KN, Xiao J. DFT research on benzothiophene pyrolysis reaction mechanism. J Phys Chem A 2019;123(4):796–810. [16] Al-Haj-Ibrahim H, Morsi BI. Desulfurization of petroleum coke: a review. Ind Eng
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