Characterization of condensed aromatics and heteroatomic species in Yanshan petroleum coke through ruthenium ion-catalyzed oxidation using three mass spectrometers

Abstract

Ruthenium ion-catalyzed oxidation (RICO) of Yanshan petroleum coke (YPC) was performed to characterize condensed aromatics and heteroatomic species in YPC. The analysis with gas chromatograph/mass spectrometer mainly offers information on the distributions of side chain groups and bridged linkages, while the analyses with atmospheric pressure solid analysis probe/time-of-flight mass spectrometer and direct analysis in real time ion source coupled to time-of-flight mass spectrometer complement information on heteroatomic species and highly condensed aromatic moieties in YPC. The results indicate that YPC is rich in highly condensed aromatic moieties with tiny portions of alkyl/alkenyl side chains and alkyl/cycloalkyl bridged linkages. The organic oxygen, nitrogen, and sulfur exist in different aromatic rings (including isobenzofuran-1,3-dione, dioxoisoindoline, phenylquinoline, pyridine, and thiophene rings) and different functional groups (including methoxy, epoxy, nitro, and cyano groups). The formation of fluorine- and chlorine-containing species reveals the existence of fluorine- and chlorine-containing moieties in YPC. In addition, a series of heavier arenecarboxylic acids were produced from RICO of YPC. Their possible aromatic rings could be naphthalene, biphenyl, anthracene, phenanthrene, dihydroanthracene, dihydrophenanthrene, phenylnaphthalene, and methyl(phenyl)tetrahydroanthracene, further confirming the existence of highly condensed aromatic rings in YPC. This investigation provides an effective approach both for value-added utilization and for understanding the structural features of YPC.

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1. Introduction

Recently, petroleum cokes, the solid by-products of petroleum distillation, have achieved a high production rate with the development of deep conversion refining technology.^1,2 At the end of 2013, it was estimated that 84 million tonnes of petroleum cokes had been stockpiled.³ To solve the stockpile problem, petroleum cokes are usually combusted as traditional fuels similar to coals due to their high carbon contents, high heating values, and low ash contents.^4–7 However, the coking process enriches environmentally harmful elements, such as sulfur, nitrogen, and vanadium, which would be released as SO_x, NO_x and V₂O₅ during combustion, causing serious environmental impact.^8,9 Therefore, non-fuel utilization of petroleum cokes is more promising.

Unlike petroleum, petroleum cokes are rich in highly condensed aromatics, which are value-added chemicals. They are used to produce dyes, nanoelectronic devices, solar cells, and polyester materials.^10–13 In addition, they can also be used as ligands for fluorescence probes and DNA.^14,15 Moreover, the price of aromatics increases sharply with the increase of aromatic ring number and heteroatom-containing aromatics are much more expensive than condensed arenes with the same aromatic ring number. Therefore, it is necessary to make full use of the highly condensed aromatics, including heteroatom-containing aromatics in petroleum cokes. For this purpose, understanding the composition and structure of organic matters in petroleum cokes is a primary requirement.

Due to the highly condensed core structure of petroleum cokes, separating the complex mixtures into individual compounds is difficult and non-destructive analytical techniques cannot characterize the structural features of petroleum cokes in detail.¹⁶ Ruthenium ion-catalyzed oxidation (RICO), as a useful sample preparation technique for investigating the molecular structures of aromatic units,¹⁷ has been widely used to characterize structural features in fossil resources such as coals and their derivatives,^18,19 kerogens, coal macerals,^20,21 oil sand bitumen, and heavy oil asphaltenes.^22,23 On the other hand, RICO can also leave the heteroatom-containing units intact, thus it can also be an effective approach for understanding the information on heteroatomic species.

Atmospheric-pressure solid analysis probe/time-of-flight mass spectrometry (ASAP/TOF-MS) and direct analysis in real time ion source coupled to time-of-flight mass spectrometry (DARTIS/TOF-MS) have been powerful and rapidly developing techniques for identifying steroids,^24,25 contaminants,²⁶ drugs,²⁷ and crude oils.²⁸ Without complicated sample pretreatments, ASAP/TOF-MS and DARTIS/TOF-MS can analyze volatile and semi-volatile solid as well as liquid samples at ambient pressure and at ground potentials in seconds.^24,29 Moreover, they can broaden the detection range and polarity of gas chromatograph/mass spectrometer (GC/MS) and thus offer information on condensed aromatics and heteroatomic species. Many scholars studied petroleum cokes using various analytical techniques similar to those employed for the traditional fuel utilization due to their high carbon contents.^{1,3,4,30–32} Gazulla et al. described a methodology to analyze the organic oxygen in petroleum cokes, which can determine the suitability of fuels for coking, liquefaction, or gasification, using a pyrolysis furnace followed by IR detection.³⁰ Mochizuki et al. investigated the pore structure and surface chemistry of the activated carbons prepared from petroleum cokes.³¹ Oliveira et al. proposed a method for the simultaneous determination of nickel, vanadium, and sulfur in petroleum cokes by inductively coupled plasma optical emission spectrometry.³² However, to the best of our knowledge, no report has been issued on the detailed structural features of petroleum cokes by analyses with ASAP/TOF-MS and DARTIS/TOF-MS for determining the value-added chemicals.

In this study, Yanshan petroleum coke (YPC) was subjected to RICO along with subsequent product analysis with GC/MS, ASAP/TOF-MS, and DARTIS/TOF-MS to characterize condensed aromatics and heteroatomic species in YPC.

2. Experimental

2.1. Materials

YPC was produced by coking Yanshan petroleum and pulverized to pass through a 200-mesh sieve followed by desiccation in a vacuum at 80 °C for 24 h prior to use. Table 1 lists the proximate and ultimate analyses of YPC. RuCl₃, NaIO₄, CH₂N₂, (CH₃CH₂)₂O, CH₃CN, CCl₄, and anhydrous MgSO₄ used in the experiments are commercially purchased analytical reagents. All the organic solvents in the reagents were distilled before use.

Table 1 Proximate and ultimate analyses (wt%) of YPC^a

Sample	Proximate analysis			Ultimate analysis (daf)				St,d
	Mad	Ad	Vdaf	C	H	N	Odiff.
a Odiff. is calculated by the subtraction method.
YPC	5.41	12.60	9.48	90.77	4.01	1.99	>1.84	1.39

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2.2. RICO of YPC

RICO of YPC and subsequent treatments were conducted as reported elsewhere.³³ Esterification of (CH₃CH₂)₂O-inextractable portion (IEP) and extractable portion (EP) was carried out to obtain methyl esterified inextractable portion (MEIEP) and methyl esterified extractable portion (MEEP), which were suitable for the subsequent analyses. Repeated experiments were carried out to ensure the data accuracy.

2.3. Sample analyses

Both MEIEP and MEEP were analyzed with a Hewlett-Packard 6890/5973 GC/MS, an IonSense/Agilent 6210 ASAP/TOF-MS, and an IonSense/Agilent 6210 DARTIS/TOF-MS. The GC/MS is equipped with a capillary column coated with HP-5MS (cross-link 5% PH ME siloxane, 60 m length, 0.25 mm inner diameter, 0.25 μm film thickness), a quadrupole analyzer and was operated in electron impact (70 eV) mode. Compounds were identified by comparing mass spectra with NIST11 library data. The ASAP/TOF-MS is equipped with an atmospheric pressure chemical ionization (APCI) source with only a simple modification. The hot nitrogen gas stream flowing from the APCI probe vaporizes the MEIEP and MEEP, and the corona ionizes the vapors by corona discharge under standard APCI conditions. The corona discharge current and capillary voltage were set to 4.0 μA and 4 kV, and the hot nitrogen stream and drying gas temperatures were set to 250 °C and 350 °C, respectively. The DART is interfaced to the TOF-MS using helium as the discharge gas and nitrogen as an alternative gas at a flow rate of 2 L min⁻¹ and operated at 450 °C. Both ASAP/TOF-MS and DARTIS/TOF-MS were run in positive mode and mass spectral data were processed using MassHunter software. The analysis reproducibility for MEIEP and MEEP was assessed by the duplicated injection of samples and all corresponding quantitative data are expressed as the average values.

3. Results and discussion

3.1. Analysis with GC/MS

According to analysis with GC/MS, 76 products were detected from RICO of YPC (Fig. S1 and S2 in the ESI† along with Tables 2–4). They include an alkanoic acid (AA), 2 alkenoic acids (AA's), 10 alkanedioic acids (ADAs), an alkanetricarboxylic acid (ATCA), 3 cyclic carboxylic acids (CCAs), 7 heterocyclic carboxylic acids (HCCAs), 34 benzenecarboxylic acids (BCAs), 3 anthracenecarboxylic acids (ACAs), and 15 other species (OSs). All the yields are expressed as the average values obtained from the repeated experiments. As illustrated in Fig. 1, BCAs are dominant in both IEP and EP with relative abundances more than 90%, indicating that low condensation degree aromatics rarely exist in YPC. In addition, all the OSs contain heteroatoms and no arenes with 1 or 2 ring(s) were identified with GC/MS. In addition to BCAs, ACAs were also detected in EP. The results further confirm the high condensation degree of YPC.

Table 2 Yields (wt%, daf) of AA, AA's, ADAs, ATCA, CCAs, HCCAs, and ACAs from RICO of YPC with GC/MS^a

Peak	Parent compound	Structure	Yield in
			IEP	EP
a R denotes alkyl substituents.
AA
55	Palmitic acid		Trace	0.01
Normal AA′
21	2-Heptenoic acid		0.01
Oxygen-containing group-substituted AA′
9	4,4-Dimethoxy-2-butenoic acid		Trace
Normal ADAs
2	Oxalic acid		0.07
4	Succinic acid		0.07	0.07
11	Glutaric acid		0.02	0.06
12	Adipic acid			Trace
Branched ADAs
5	Methylsuccinic acid		Trace	0.02
14	3-Methylglutaric acid			0.01
15	2-Methylglutaric acid			0.02
Oxygen-containing group-substituted ADAs
7	2-Methoxymalonic acid		0.01
13	2-Methyloxirane-2,3-dicarboxylic acid			0.04
19	2,3-Dimethoxysuccinic acid		0.03
ATCA
28	Propane-1,2,3-tricarboxylic acid		0.01	0.01
CCAs
22	1,2-Cyclopentanedicarboxylic acid			Trace
24	1,3-Cyclopentanedicarboxylic acid			Trace
26	Cyclohex-1-enecarboxylic acid			Trace
HCCAs
61	Thiophenetetracarboxylic acid		0.03
63	2-Methyl-1,3-dioxoisoindoline-5,6-dicarboxylic acid		0.15	0.38
64	2-Methyl-1,3-dioxoisoindoline-4,5-dicarboxylic acid			0.49
66	2-Methyl-1,3-dioxoisoindoline-4,6-dicarboxylic acid			0.08
69	2-Methyl-1,3-dioxoisoindoline-4,5,6-tricarboxylic acid		0.18	0.08
71	7-Methyl-1,3-dioxoisoindoline-4,5,6-tricarboxylic acid		0.13
75	2-Methyl-1,3-dioxoisoindoline-4,5,6,7-tetracarboxylic acid		0.47
ACAs
72	4,8,9,10-Tetramethylanthracene-1,2,3-tricarboxylic acid			0.30
73	3,8,9,10-Tetramethylanthracene-1,2,4-tricarboxylic acid			0.17
74	1,3,4,8-Tetramethylanthracene-2,9,10-tricarboxylic acid			0.46

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Table 3 Yields (wt%, daf) of BCAs from RICO of YPC with GC/MS^a

Peak	Parent compound	Structure	Yield in
			IEP	EP
a R denotes alkyl substituents.
Non-substituted BCAs
8	Benzoic acid			0.01
35	PA		0.53	5.82
37	Terephthalic acid			0.10
38	Isophthalic acid		Trace	0.23
52	Hemimellitic acid		1.41	2.22
53	Trimellitic acid		0.52	5.86
56	Trimesic acid		0.04	0.93
62	Prehnitic acid		4.95	1.73
65	Pyromellitic acid		3.52	4.32
67	Benzene-1,2,3,5-tetracarboxylic acid		1.59	1.04
70	Benzenepentacarboxylic acid		6.92	0.39
76	Mellitic acid		5.32
Alkyl-substituted BCAs
16	3-Methylbenzoic acid			0.01
18	4-Methylbenzoic acid			Trace
25	2,4-Dimethylbenzoic acid			Trace
40	3-Methylphthalic acid		0.18	0.14
41	4-Methylphthalic acid		0.07	1.39
44	5-Methylisophthalic acid			0.07
46	4,5-Dimethylphthalic acid			0.07
48	3,4-Dimethylphthalic acid			0.07
49	4-tert-Butylbenzoic acid		0.01
54	4-Methylhemimellitic acid		0.06	0.18
57	3-Methyltrimellitic acid		0.07	0.29
58	2-Methyltrimesic acid		0.10
68	5-Methylprehnitic acid		0.22	0.12
Halogen-containing group-substituted BCAs
27	4-Chloro-3-methylbenzoic acid			Trace
30	4-Chloro-2,3-dimethylbenzoic acid			Trace
Halogen-containing group-substituted BCAs
43	4-Chlorophthalic acid			0.04
45	2-((3,5-Difluorophenoxy)carbonyl)benzoic acid		0.03
59	3,4,5,6-Tetrafluorophthalic acid		0.04	0.09
Oxygen- & nitrogen-containing group-substituted BCAs
32	2-Nitrobenzoic acid			0.01
39	2-(Ethoxycarbonyl)benzoic acid			0.05
50	4-Nitrophthalic acid			0.03
51	2-Cyanoterephthalic acid		0.02	0.22

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Table 4 Yields (wt%, daf) of OSs from RICO of YPC with GC/MS

Peak	Parent compound	Structure	Yield in
			IEP	EP
1	Acetamide		0.58
3	4-Methoxybiphenyl		0.12
6	Prop-1-ene-thiol			Trace
10	Pyrrolidine-2-thione		Trace
17	1,3-Dimethylimidazolidine-2,4,5-trione			0.01
20	Iodoform		0.02
23	Phthalic anhydride		0.07	0.01
29	3-Methylphthalic anhydride		Trace
31	2-Methylisoindoline-1,3-dione		Trace	0.26
33	Benzofuran		Trace
34	4-Methylphthalic anhydride			Trace
36	2-Ethylisoindoline-1,3-dione			0.01
42	Diethyl phthalate		0.04
47	Indene-1,2,3-trione		0.04
60	2,3,4-Trimethylbenzo[h]quinoline		0.16

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Fig. 1 Relative abundance (a) and total yield and relative abundance (b) of the products from RICO of YPC in MEIEP and MEEP.

Palmitic acid is the only AA detected from RICO of YPC. It was also identified in coal derivatives.^34,35 It might be related to the biotic input of fossil resources. AA's include a normal AA′ and an oxygen-containing group-substituted AA′, indicating the existence of hexenyl and dimethoxybutenyl side chains.

ADAs include 4 normal ADAs, 3 branched ADAs, and 3 oxygen-containing group-substituted species. The range of carbon number in ADAs is 2 to 6 (except 3) and succinic acid is the most abundant (Table 2). The oxygen-containing groups in oxygen-containing group-substituted ADAs are methoxy and epoxy. The detection of propane-1,2,3-tricarboxylic acid, 1,2-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, and cyclohex-1-enecarboxylic acid suggests the existence of , cyclopentane, and cyclohexene moieties as bridged linkages connecting aromatic rings in YPC. However, the yields of AA, AA's, ATCA, and CCAs are quite low, even less than 0.1%, proving that very few alkyl/alkenyl side chains and alkyl/cycloalkyl bridged linkages exist in YPC.

As listed in Table 2, 8 HCCAs, including thiophenetetracarboxylic acid and 6 dioxoisoindolinepolycarboxylic acids, were detected in the products from RICO of YPC. The formation of HCCAs indicates that the existing forms of organic oxygen, nitrogen, and sulfur are dioxoisoindoline and thiophene rings. Many oxygen-containing,³⁶ nitrogen-containing, and sulfur-containing species^37–39 have been detected in coal extracts and derivatives and they usually exist in the rings of furan, pyridine and pyrrole, and thiophene and dithiole, respectively. However, to the best of our knowledge, few reports have been issued on the detection of dioxoisoindolines as the existing form of organic oxygen and nitrogen. Dioxoisoindolinepolycarboxylic acids detected include 3 dioxoisoindolinedicarboxylic acids, 2 dioxoisoindolinetricarboxylic acids, and 2-methyl-1,3-dioxoisoindoline-4,5,6,7-tetracarboxylic acid, implying different condensation degrees of dioxoisoindoline structural units. Dioxoisoindolinedicarboxylic acids are mainly present in EP, while others mainly appear in IEP. This result could be related to the hydrophilicity of carboxylic groups.

As Table 3 shows, the BCAs produced from RICO of YPC include 12 non-substituted BCAs, 13 alkyl-substituted BCAs, 5 halogen-containing group-substituted BCAs, and 4 oxygen- and nitrogen-containing group-substituted BCAs. Benzenepentacarboxylic acid, pyromellitic acid, and prehnitic acid are the most abundant products. The detection of halogen-containing group-substituted BCAs implies that organochlorines and organofluorines could exist in YPC, and the formation of oxygen- and nitrogen-containing group-substituted BCAs indicates that in addition to heterocyclic nitrogen atoms, nitro and cyano groups could also be the existing forms of organic nitrogen. In addition, the numbers of carboxylic groups on benzene rings of these compounds are 1 or 2, suggesting that chloric and fluoric as well as nitro and cyano groups do not exist in highly condensed aromatic moieties. BCAs are important chemicals with wide applications. For example, phthalic acid is mainly used to synthesize phthalates, which are plasticizers for plastic products and additives for the fabrication of multilayer ceramic capacitors, paper coatings, cosmetics, inks, and paints;⁴⁰ terephthalic acid and pyromellitic acid are intensively used in the polymer industry, and trimesic and mellitic acids are employed in the pharmaceuticals industry;⁴¹ benzenepentacarboxylic acid, mellitic acid, and their derivatives are important ligands for the formation of metal complexes and polymers;^42–44 the variety of ligand conformations of the functional complexes built with BCAs can be used for preparing fluorescent probes, light-emitting materials, nonlinear optical materials, and porous materials.^45–47 Recently, adsorption and desorption using hydrophilic hyper-cross-linked polymer resins and column chromatography combined with sequential extraction have been successfully applied in isolation and to obtain BCAs.^48–50

All the OSs contain heteroatoms and acetamide is the most abundant OS. Interestingly, acetamide is not inconsiderable even compared with other carboxylic acids. It might be produced from the scission of fatty acid amides because some fatty acid amides have been detected in fossil resources such as coal and oil shale derivatives.^51,52 The detection of 2-methylisoindoline-1,3-dione and 2-ethylisoindoline-1,3-dione is consistent with the analysis of HCCAs stated above. In addition, prop-1-ene-1-thiol and pyrrolidine-2-thione were also detected as sulfur-containing species.

3.2. Analysis with ASAP/TOF-MS

The molecular mass distributions of products detected with ASAP/TOF-MS in MEIEP and MEEP range from 150 to 860 u and from 100 to 770 u, respectively (Fig. 2), enlarging the detection range of GC/MS. According to previous studies, arenepolycarboxylic acids can be deduced according to the quasi-molecular ion [M-31]⁺ values.⁵³ As Table S1† shows, the detection of BCAs with 1 to 6 carboxylic group(s) and 0, 1, or 2 alkyl side chain(s) is consistent with the result mentioned above. Remarkably, 5 types of heavier arenepolycarboxylic acids were also detected. They have 2–11 carboxylic groups and 0–8 alkyl side chain(s), and their possible aromatic rings could be naphthalene, biphenyl, anthracene and/or phenanthrene, phenylnaphthalene, and methyl(phenyl)tetrahydroanthracene rings. Dichloronaphthalenepolycarboxylic acid is one of the heavier arenepolycarboxylic acids, further confirming the existence of organochlorines. In addition, 3 types of HCCAs, i.e., isobenzofuran-1,3-dionepolycarboxylic acids, phenylquinolinepolycarboxylic acids, and 2-methylisoindoline-1,3-dionepolycarboxylic acids, were identified (Table S1†), suggesting that isobenzofuran-1,3-dione, phenylquinoline, and 2-methylisoindoline-1,3-dione structural units exist in the highly condensed aromatic moieties of YPC. As demonstrated in Fig. 3, there is no doubt that BCAs are predominant products; however, HCCAs, especially isobenzofuran-1,3-dionepoly-carboxylic acids, account for a certain proportion of both IEP and EP. More HCCAs were isolated into IEP, indicating the better hydrophilicities of HCCAs.

Fig. 2 Mass spectra of MEIEP and MEEP from RICO of YPC by analysis with ASAP/TOF-MS.

Fig. 3 Distribution of the products from RICO of YPC from analysis by ASAP/TOF-MS.

3.3. Analysis with DARTIS/TOF-MS

Helium primarily produces the (2³S) electronic excited state, which rapidly reacts with atmospheric water to produce [(H₂O)_nH]⁺. Transfer of a proton then occurs to form a protonated quasi-molecular ion [M + H]⁺. In addition, samples can also be ionized by charge transfer to create radical molecular cations M⁺˙.²⁹ As displayed in Fig. 4 and 5 and Tables S2 and S3,† the products detected from RICO of YPC can be classified into pyridinepolycarboxylic acids, biphenylpolycarboxylic acids, anthracene- and/or phenanthrenecarboxylic acids, dihydroanthracene- and/or phenanthrenecarboxylic acids, methyl(phenyl)tetrahydroanthracenecarboxylic acids, and OSs. Unlike analysis with ASAP/TOF-MS, besides arenepolycarboxylic acids with 2–8 carboxylic groups and 0–9 alkyl side chain(s), more than 20% OSs were also identified with DARTIS/TOF-MS, all of which are heteroatom-containing species. These OSs include quinolines and 2-methylthiopene. They are more polar species than esters. The analysis with DARTIS/TOF-MS shows that the existing forms of organic nitrogen and sulfur are pyridine, quinoline, and thiophene rings, which differs from the analysis with GC/MS mentioned above due to the difference in detection range between DARTIS/TOF-MS and GC/MS. The detection of 6 chlorine-containing dihydroanthracene- and/or dihydrophenanthrenecarboxylic acids with 5–6 carboxyl groups shows the existence of organochlorines in highly condensed aromatic moieties in YPC. Fig. 6 illustrates that anthracene and/or phenanthrenecarboxylic acids are the most abundant. Moreover, nitrogen-containing compounds, including pyridinepolycarboxylic acids and quinolines, account for ca. 30% both in IEP and EP. Interestingly, different from the analysis with ASAP/TOF-MS, no BCAs were detected with DARTIS/TOF-MS, perhaps due to the differences in discharge gas and ionization process between the two mass spectrometric methods. The high contents of heteroatom-containing carboxylic acids and OSs indicate that DARTIS/TOF-MS has a better response not only to nitrogen-containing species, but also to species with a higher polarity than ASAP/TOF-MS.

Fig. 4 Mass spectra of MEIEP from RICO of YPC from analysis by DARTIS/TOF-MS.

Fig. 5 Mass spectra of MEEP from RICO of YPC from analysis by DARTIS/TOF-MS.

Fig. 6 Distribution of products from RICO of YPC from DARTIS/TOF-MS analysis.

4. Conclusion

Three mass spectrometries were applied to investigate structural features of macromolecular aromatic species and heteroatomic compounds in YPC. BCAs account for over 90% and 75% of products identified with GC/MS and ASAP/TOF-MS, respectively, while no BCAs were detected with DARTIS/TOF-MS resulting from the different discharge gas and ionization process. DARTIS/TOF-MS has a good response to species with a higher polarity compared to ASAP/TOF-MS. According to the detailed analysis of the oxidation products, YPC is made up of highly condensed aromatic moieties with tiny potions of alkyl/alkenyl side chains, alkyl/cycloalkyl bridged linkages, and heteroatom-containing substituents. The heteroatoms include oxygen, nitrogen, sulfur, and halogen atoms, revealing the existing forms of organic oxygen, nitrogen, sulfur, and halogen species in YPC; such a structural feature is improper for thermal conversion. On account of the highly condensed structure of YPC, selective oxidation of YPC to BCAs and subsequent fine separation could be promising approaches for effective utilization of YPC.

Acknowledgements

This study was supported by the Key Project of Joint Fund from National Natural Science Foundation of China and the Government of Xinjiang Uygur Autonomous Region (Grant U1503293), National Natural Science Foundation of China (Grant 20276268), Strategic Chinese – Japanese Joint Research Program (Grant 2013DFG60060), the Fundamental Research Fund for the Doctoral Program of Higher Education (Grant 20120095110006), the Foundation of State Key Laboratory of Multi Phase Complex System (Grant MPCS-2014-D-02), the Research and Innovation Project for College Graduates of Jiangsu Province (Grant KYLX15_1410), and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.

References

1. Y. M. Zhang, M. Q. Yao, S. Q. Gao, G. G. Sun and G. W. Xu, Appl. Energy, 2015, 160, 820–828.
2. C. C. Small, Z. Hashisho and A. C. Ulrich, Fuel, 2012, 92, 69–76.
3. J. E. Zuliani, T. Miyata, T. Mizoguchi, J. Feng, D. W. Kirk and C. Q. Jia, Fuel, 2016, 178, 124–128.
4. D. J. Marchand, A. Abrams, B. R. Heiser, Y. Kim, J. Kim and S. H. Kim, Fuel Process. Technol., 2016, 144, 290–298.
5. X. L. Zhan, Z. J. Zhou, W. Z. Kang and F. C. Wang, Fuel Process. Technol., 2010, 91, 1256–1260.
6. R. K. Wang, J. Z. Liu, F. Y. Gao, J. H. Zhou and K. F. Cen, Fuel Process. Technol., 2012, 104, 57–66.
7. X. Y. Ma, Y. F. Duan and M. Liu, Exp. Therm. Fluid Sci., 2013, 48, 238–244.
8. E. Furimsky, Fuel Process. Technol., 1998, 56, 263–290.
9. L. Zychlinski, J. Z. Byczkowski and A. P. Kulkarni, Arch. Environ. Contam. Toxicol., 1991, 20, 295–298.
10. Y. J. Dappe and J. I. Martinez, Carbon, 2013, 54, 113–123.
11. C. C. Yu, K. J. Jiang, J. H. Huang, F. Zhang, X. Bao, F. W. Wang, L. M. Yang and Y. L. Song, Org. Electron., 2013, 14, 445–450.
12. N. Tyutyulkov, S. Karabunarliev, K. Müllen and M. Baumgarten, Synth. Met., 1992, 52, 71–85.
13. E. Lucenti, C. Botta, E. Cariati, S. Righetto, M. Scarpellini, E. Tordin and R. Ugo, Dyes Pigm., 2013, 96, 748–755.
14. K. W. Street, W. E. Acree, J. C. Fetzer, P. H. Shetty and C. F. Poole, Appl. Spectrosc., 1989, 43, 1149–1153.
15. V. Casagrande, A. Alvino, A. Bianco, G. Ortaggi and M. Franceschin, J. Mass Spectrom., 2009, 44, 530–540.
16. C. S. Hsu, Energy Fuels, 2012, 26, 1169–1177.
17. Z. G. Zhang, S. Guo, S. Zhao, G. Yan, L. Song and L. Chen, Energy Fuels, 2008, 23, 374–385.
18. Z. S. Yao, X. Y. Wei, J. Lv, F. G. Liu, Y. G. Huang, J. J. Xu, F. J. Chen, Y. Huang, Y. Li, Y. Lu and Z. M. Zong, Energy Fuels, 2010, 24, 1801–1808.
19. Y. G. Huang, Z. M. Zong, Z. S. Yao, Y. X. Zheng, J. Mou, G. F. Liu, J. P. Cao, M. J. Ding, K. Y. Cai, F. Wang, W. Zhao, Z. L. Xia, L. Wu and X. Y. Wei, Energy Fuels, 2008, 22, 1799–1806.
20. R. J. Boucher, G. Standen and G. Eglinton, Fuel, 1991, 70, 695–702.
21. P. Blanc, J. Valisolalao, P. Albrecht, J. P. Kohut, J. F. Muller and J. M. Duchene, Energy Fuels, 1991, 5, 875–884.
22. T. W. Mojelsky, T. M. Ignasiak, Z. Frakman, D. D. McIntyre, E. M. Lown, D. S. Montgomery and O. P. Strausz, Energy Fuels, 1992, 6, 83–96.
23. A. L. Ma, S. C. Zhang, D. J. Zhang, Z. J. Jin, X. J. Ma and Q. T. Chen, Chin. J. Geochem., 2005, 24, 28–36.
24. C. N. Mcewen, R. G. Mckay and B. S. Larsen, Anal. Chem., 2005, 77, 7826–7831.
25. C. N. Mcewen and B. S. Larsen, J. Am. Soc. Mass Spectrom., 2009, 20, 1518–1521.
26. E. A. Bruns, V. Perraud, J. Greaves and B. J. Finlayson-pitts, Anal. Chem., 2010, 82, 5922–5927.
27. Y. L. Bennani, Drug Discovery Today, 2011, 16, 779–792.
28. A. Ahmed, Y. J. Cho, M. H. No, J. Koh, N. Tomczyk, K. Giles, J. S. Yoo and S. Kim, Anal. Chem., 2010, 83, 77–83.
29. R. B. Cody, J. A. Laramée and H. Dupont Durst, Anal. Chem., 2005, 77, 2297–2302.
30. M. F. Gazulla, M. Rodrigo, M. Orduna and M. J. Ventura, Microchem. J., 2016, 126, 538–544.
31. T. Mochizuki, M. Kubota, H. Matsuda and L. F. D. Camacho, Fuel Process. Technol., 2016, 144, 164–169.
32. J. S. S. Oliveira, R. S. Picoloto, C. A. Bizzi, P. A. Mello, J. S. Barin and E. M. M. Flores, Talanta, 2015, 144, 1052–1058.
33. J. H. Lv, X. Y. Wei, Y. Qing, Y. H. Wang, Z. Wen, Y. Zhu, Y. G. Wang and Z. M. Zong, Fuel, 2014, 128, 231–239.
34. J. H. Lv, X. Y. Wei, Y. H. Wang, T. M. Wang, J. Liu, D. D. Zhang and Z. M. Zong, RSC Adv., 2016, 6, 11952–11958.
35. F. J. Liu, X. Y. Wei, J. Gui, Y. G. Wang, P. Li and Z. M. Zong, Energy Fuels, 2013, 27, 7369–7378.
36. J. A. MacPhee, J. P. Charland and L. Giroux, Fuel Process. Technol., 2006, 87, 335–341.
37. P. Rutkiwski, G. Gryglewicz, S. Mullens and J. Yperman, Energy Fuels, 2003, 17, 1416–1422.
38. G. Gryglewicz, P. Rutkowski and J. Yperman, Energy Fuels, 2004, 18, 1595–1602.
39. S. R. Kelemen, M. Afeworki, M. L. Gorbaty, P. J. Kwiatek, M. Sansone and C. C. Walters, Energy Fuels, 2006, 20, 635–652.
40. J. W. Wang, Z. H. Luo, W. Xu, J. F. Ding and T. L. Zheng, Int. Biodeterior. Biodegrad., 2016, 109, 223–228.
41. W. H. Wang, Y. C. Hou, M. G. Niu, T. Wu and W. Z. Wu, Fuel Process. Technol., 2013, 110, 184–189.
42. L. P. Wu, M. Munakata, S. T. Kuroda, M. Maekawa and Y. Suenaga, Inorg. Chim. Acta, 1996, 249, 183–189.
43. A. Kyono, M. Kimata and T. Hatta, Inorg. Chim. Acta, 2004, 357, 2519–2524.
44. D. R. Turner, H. J. Strachn and S. R. Batten, Z. Anorg. Allg. Chem., 2009, 635, 439–444.
45. J. Mroainski, A. Bienko, P. Kopel and V. Lamger, Inorg. Chim. Acta, 2008, 361, 3723–3729.
46. X. L. Wang, J. Li, H. Y. Lin, H. L. Hu, B. K. Chen and B. Mu, Solid State Sci., 2009, 11, 2118–2124.
47. Y. Y. Karabach, A. M. Kirillov, M. Haukka, M. N. Kopylovich and A. J. L. Pombeiro, J. Inorg. Biochem., 2008, 102, 1190–1194.
48. W. M. Zhang, Z. W. Xu, B. C. Pan, L. Lv, Q. J. Zhang, Q. R. Zhang, W. Du, B. J. Pan and Q. X. Zhang, J. Colloid Interface Sci., 2007, 311, 382–390.
49. G. Z. Gong, X. Y. Wei and Z. M. Zong, J. Fuel Chem. Technol., 2012, 40, 1–7.
50. Z. W. Liu, Z. M. Zong, J. N. Li, C. F. Chen, H. Jiang, Y. L. Peng, J. Q. Xue, X. L. Yang, Y. X. Zheng, X. Zhou, R. L. Xie and X. Y. Wei, Energy Fuels, 2009, 23, 588–590.
51. J. P. Cao, Z. M. Zong, X. Y. Zhao, M. Zhou, X. X. Ma, G. J. Zhou, P. Wu, W. Zhao, B. M. Li and X. Y. Wei, Energy Fuels, 2007, 21, 1193–1194.
52. X. Y. Zhao, Z. M. Zong, J. P. Cao, Y. M. Ma, L. Han, G. F. Liu, W. Zhao, W. Y. Li, K. C. Xie, X. F. Bai and X. Y. Wei, Fuel, 2008, 87, 565–575.
53. Y. G. Wang, X. Y. Wei, H. L. Yan, D. L. Shi, F. J. Liu, P. Li, X. Fan, Y. P. Zhao and Z. M. Zong, Energy Fuels, 2013, 27, 4632–4638.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra09194f

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