Selective hydrogenation of aromatics in coal-derived liquids over novel NiW and NiMo carbide catalysts

Fuel 244 (2019) 359–365

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Selective hydrogenation of aromatics in coal-derived liquids over novel NiW and NiMo carbide catalysts

T

⁎

Haiyong Zhanga, , Genwei Chena, Lei Baib, Ning Changa, Yonggang Wanga a b

School of Chemical & Environmental Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China Department of Chemical and Biomedical Engineering, West Virginia University, Morgantown 26506, WV, United States

A R T I C LE I N FO

A B S T R A C T

Keywords: Aromatics Hydrogenation Coal derived liquids Carbide catalysts

Novel bimetallic NiW/Al2O3 and NiMo/Al2O3 carbide catalysts were prepared by temperature-programmed reaction with CH4-H2 mixture. The catalysts were characterized by N2 adsorption, XRD, TPR and their performance for selective hydrogenation of aromatics in coal derived liquids were compared with their sulfide counterparts. Direct coal liquefaction oil (DCLO) fraction in 180∼290 °C and aromatic component separated from low temperature coal tar (LTCT) fraction in 210∼290 °C were selected as feedstock and hydrogenated on a fixed bed micro-reactor. The results of elemental analysis, simulated distillation and GC-MS show that the hydrodearomatization (HDA) activity was: NiMo-C > NiW-C > NiW-S > NiMo-S. The HDA, Hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) for DCLO hydrogenation over NiMo-C is 91%, 29.54% and 75.23%, respectively. The hydroaromatics and cycloalkanes in hydrogenated LTCT and DCLO products were 67.1% and 74.8%, respectively. Thus, NiMo carbide is a promising catalyst for selective hydrogenation of CDLs to obtain high performance jet fuel blend which is rich in hydroaromatics and cycloalkanes.

1. Introduction Due to increasing demand for clean engine fuels and growing concerns about petroleum depletion crisis, many efforts are being dedicated to develop various alternatives or substitutes. Coal derived liquid (CDL) has emerged as one of the important options due to the abundant reserve of coal. As a main utilization method of low rank coal, mild pyrolysis would produce large amount of low temperature coal tar (LTCT) every year. In China, about 10 million tons of coal tar is produced in 2015 by pyrolysis, coking and gasification of coal [1]. Besides, a 1 Mt/a direct coal liquefaction (DCL) industrial plant is in commercial operation. Nonetheless, the high content of aromatics, heteroatoms (such as N, O, and S) and asphaltene in CDLs limit their direct application as motor fuels [2].Strict environmental regulations for exhaust emission also specify reduced contents of aromatics and heteroatoms in the fuels. Catalytic hydroprocessing is one of the most effective ways for CDLs upgrading [3–15] and extensive studies have been done to produce gasoline and diesel fuels from CDLs [6–14]. However, some problems still exist such as low product yield [11], unsatisfied octane number index for gasoline [12,13], and relative severe reaction conditions [14]. These issues are partially caused by the significant difference between the molecular structure of CDLs and petroleum fractions. Since the ⁎

aromatics in CDLs are difficult to be cracked and hydrogenated, or isomerized to alkanes, the hydrotreated CDLs is difficult to be lightened and meet the requirement of standard gasoline and diesel [14]. Fortunately, hydroaromatics and cycloalkanes produced by selective hydrogenation of aromatics were found to be ideal blend for high performance jet fuels with high energy density and thermal stability [16–18]. This means that CDLs abounded with aromatics are promising feedstock for jet fuel production. Previous studies [12–14,19–21] about hydroprocessing of CDLs were concerning ring-opening, hydrocracking or removal of heteroatoms, in which the acidity of catalysts was always adjusted to scissoring C-X bonds and meanwhile severe cracking would probably happen. On the other hand, higher temperature used for improving the catalytic activity over 350 °C would also cause severe coking and cracking [2]. Therefore, catalysts with (a) high activity for hydrogenation of aromatics at mild temperature and (b) resistance to heteroatoms seem to be essential for selective hydrogenation of aromatics in CDLs. Besides, to remove the high content of cyclic N-compounds in CDLs by hydrodenitrogenation (HDN), high hydrogenation activity is also required for complete hydrogenation of aromatic rings since C=N bond is difficult to break in an aromatic ring [22]. Sulfide Co(Ni)Mo(W)/Al2O3 catalysts were generally involved and noble metal catalysts like Ru2S [23,24] and Pr-Pd [25] were also tested for aromatics hydrogenation. Mo nitrides were also compared with sulfides for

Corresponding authors. E-mail address: [email protected] (Y. Wang).

https://doi.org/10.1016/j.fuel.2019.02.015 Received 30 October 2018; Received in revised form 10 January 2019; Accepted 6 February 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.

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hydrotreating of coal derived naphtha [26] and model reaction [27]. Transition metal carbides are novel effective catalysts for a wide range of chemical reactions, especially those reactions involving hydrogen transfer such as hydrogenation and hydrogenolysis [28–33]. The hydrogenation activities of WC and Mo2C are even comparable with those noble metal catalysts [33–35] during hydrogenation of toluene or tetralin. Besides, carbide catalysts are also resistant to heteroatoms and can be used for removal of heteroatomic compounds [36–40]. However, most of the work were performed by model reactions, hydrogenation of real coal-derived feedstocks on carbide catalysts, to the best of our knowledge, were seldom evaluated. In this study, novel NiMo/Al2O3 and NiW/Al2O3 carbides with promising hydrogenation potential were prepared and used for hydroprocessing of CDLs. DCLO fraction in 180∼290 °C and the aromatic component separated from LTCT fraction in 210∼290 °C were used as real feedstock to produce high-performance jet fuel blend which is rich in hydroaromatics and cycloalkanes. The product compositions were analyzed and the catalytic performance of carbides for selective hydrogenation of aromatics was compared with NiMo/Al2O3 and NiW/ Al2O3 sulfides. This study aims to elucidate the potential application of transition metal carbides in selective hydrogenation of CDLs.

Fig. 1. Schematic diagram of coal pyrolysis to produce LTCT.

Table 1 Proximate and elemental analysis of coal samples. Proximate Analysis

2. Experimental HLH YL

2.1. Catalyst preparation and characterization

Elemental Analysis

Mad

Ad

Vdaf

FCdaf

C

H

N

S

O*

H/C

7.55 10.57

29.84 4.09

49.14 37.69

50.87 62.31

70.13 81.55

4.38 5.07

1.21 1.24

0.60 0.27

23.43 11.87

0.75 0.74

*by difference; d: dry base; ad: air dried; daf: dry ash free.

NiW/γ-Al2O3 and NiMo/γ-Al2O3 catalysts were prepared by incipient wetness co-impregnation method. 20∼40 mesh γ-Al2O3 (Mingyuan Alumina, Shandong, China) was impregnated with an aqueous mixture of nickel nitrate (Ni(NO3)2·6H2O) and ammonium metatungstate ((NH4)6W7O24·6H2O) or ammonium heptamolybdate ((NH4)6Mo7O24·4H2O). The catalyst compositions were designed according to literatures which showed good performance for hydrorefining. NiW/Al2O3 catalyst was designed according to our previous study [41], with the Ni/(Ni + W) atom ratio equals to 0.32 and the total metal oxides loading to 30%. For NiMo catalysts, the Ni/ (Ni + Mo) atom ratio is 0.28 and the metal oxides was 24% [42]. After impregnation, the catalysts were dried at 120 °C for 3 h and calcined at 500 °C for 4 h. The catalysts were characterized by N2 adsorption, XRD and H2TPR. Nitrogen adsorption-desorption was tested on a Quadrasorb porosimeter (SI-MP) at −196 °C. The BET specific surface area was calculated at relative partial pressure (P/P0) from 0.05 to 0.3. Pore volume and pore size distribution were calculated with the BJH model. Before measurement, the samples were pretreated in vacuum at 110 °C for 3 h. XRD patterns were obtained on a Smartlab-3 kW diffractionmeter using Cu Kα radiation (λ = 1.54056 Å) at a scanning speed of 4°/min. The diffraction spectra were analyzed using standard files. H2-TPR was carried out on a Micromeritics AutoChem II 2920 instrument. 0.1 g sample was pretreated in argon air at 110 °C for 3 h, after cooled to 25 °C the sample was reduced under 5% H2/N2 at a constant flow rate of 50 mL/min, to 1000 °C at the rate of 10 °C/min. The signal of H2 consumption was recorded by TCD.

Fig. 2. Schematic diagram of coal liquefaction to produce DCLO.

Table 2 Compositions of LTCT and DCLO raw materials.

Elemental composition/w% C H N S O* H/C Compounds composition**/w% Aliphatics Hydro-Aromatics Aromatics O-Compounds N-compounds Polyheteroatoms

2.2. Preparation of feedstock The LTCT was obtained from a pilot plant for lignite pyrolysis operated at 650 °C on a 3-stage fixed-bed reactor in Huolinhe, Inner Mongolia, China. The schematic diagram [43] of coal pyrolysis and the properties of raw coal (HLH) are shown in Fig. 1 and Table 1, respectively. The DCLO was obtained by catalytic hydro-liquefaction of longflame coal (from Yulin, Shaanxi, China) on a 0.1 t/d bench scale reactor at 450 °C, 19 MPa. The schematic diagram of coal liquefaction[44] and the properties of raw coal (YL) are shown in Fig. 2 and Table 1, respectively. The compositions of LTCT and DCLO raw material were listed in Table 2. They show typical composition of CDLs, with high

*by difference; **by column chromatography.

360

Raw LTCT

Raw DCLO

81.63 6.37 1.68 1.65 8.68 0.94

86.37 9.83 0.45 0.11 3.24 1.37

13.60 0 22.47 31.39 17.66 10.79

9.06 36.32 17.85 15.39 16.21 0

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programmed sulfidation with H2 and 5% CS2 n-heptane solution at the condition of 4 MPa, LHSV = 2 h−1, H2/oil = 600(v/v). The temperature was elevated at 5/min to 230 °C and 400 °C and hold at each temperature for 2 h [46]. To make carbide catalysts, the oxide precursors were carburized by temperature-programmed carburization in 200 mL/min 20% CH4/H2 (v/v) mixture by two steps. First, the oxides were quickly heated from room temperature to 300 °C. Second, the materials were heated at 1 °C/min to 700 °C and held for 3 h for deep carburization[47]. The hydrogenation processes started in situ when the reactor cooling down to 300 °C after catalyst carburization/sulfidation. The hydrogenating reactions were performed at 300 °C, 5 MPa H2 pressure, LHSV = 1 h−1, and H2/oil = 1200 (v/v). After reaction, the hydrogenated products were collected at the 2nd hour for analysis. The pipeline and collector were swept for 1 h to avoid CS2 pollution during sulfidation process. Thus, the products over carbide catalysts were also collected after 1st hour to keep the same with their sulfide counterparts. The compositions of reactants and hydrogenated products were analyzed by GC–MS, elemental analysis and simulated distillation. The GC–MS analysis was performed on a VARIAN 4000 equipped with a DB5 ms column (60 m × 0.25 mm × 0.25 μm). The compositions of oil samples were semi-quantified by direct area normalization of total ion chromatogram (TIC spectrum). Chemical elemental analysis was performed under standard test methods in petrochemical industry of China. The C and H content was analyzed under SH/T 0656-2004 (ASTM D5291), while S and N were analyzed under GB/T 17040-2018 (ASTM D4294) and SH/T 0704-2010 (ASTM D5762), respectively. The boiling range distribution was determined by simulated distillation on gas chromatography under SH/T 0558-2016 (ASTM D2887)

Fig. 3. Separation steps of low temperature coal tar.

content of O-compounds and aromatics. The aromatic fraction was separated from LTCT for hydrogenation. This was based on a coal tar upgrading process developed by our group, which is firstly separating coal tar into aliphatics, aromatics and phenols, and then the hydrocarbons could be upgraded separately according to their usage. The separation steps of aromatic fraction was shown in Fig. 3. Firstly, the raw tar was filtered through a 1000 mesh filter under pressure to remove the solid particles caused by fracturing of coal/char. Then the fraction from 210 to 290 °C was collected by atmospheric distillation. The aromatic component was enriched by solvent extraction with Nmethyl-2-pyrrolidone (NMP) aqueous solution and CaCl2 solution. Detailed separating conditions could be seen elsewhere [45]. The fraction of DCLO in 180–290 °C was distillated under atmospheric pressure for hydrogenation.

3. Results and discussion 3.1. Characterization of the catalysts

2.3. Hydrogenation reaction and analysis

N2 adsorption-desorption isotherms and pore diameter distribution of the support and catalysts are shown in Fig. 5. All of the isotherms are type-IV hysteresis loop which is the characteristic of mesoporous structure. Pore size distributions of the samples show similar unimodal distribution with the most probable pore diameter around 10 nm. The intensity of the main peak decreases in the order: γ-Al2O3 > NiMo/γAl2O3 > NiW/γ-Al2O3. Table 3 summarizes the textural parameters and the composition of the support and catalysts. After metal loading, both catalysts show decreased specific surface area and pore volume than the support. Both the NiW and NiMo catalysts have a BET surface area of ∼100 m2/g. However, the pore volume of NiW/γ-Al2O3 is lower

The prepared oxide precursors were transformed to sulfides and carbides in a continuous flow fixed-bed micro-reactor (Fig. 4) before use. For each run, 1 g catalyst was diluted with quartz powder to 10 mL and then placed in the middle isothermal zone of the stainless steel reactor (Φ8 mm). The sulfide catalysts were prepared by temperature-

Fig. 5. N2 adsorption-desorption isotherms and pore diameter distributions of the support and catalysts.

Fig. 4. Schematic diagram of continuous flow fixed-bed micro-reactor. 361

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Table 3 Compositions and textures of γ-Al2O3 and catalysts.

2

SBET (m /g) V (cm3/g) −

d (nm) NiO /wt% WO3 /wt% MoO3 /wt%

γ-Al2O3

NiW/Al2O3

NiMo/Al2O3

146.8 0.569 9.755

100.8 0.363 9.772

108.3 0.420 9.762

– – –

4.01 26.00 –

4.00 – 20.00

Fig. 7. TPR profiles of alumina supported NiMo and NiW catalysts.

Fig. 6. XRD patterns of the support and catalysts.

than that of NiMo/γ-Al2O3, which is consistent with the pore size distribution in Fig. 5. Previous studied showed that bulk MO2C or W2C or bimetallic carbides usually had small specific surface area, from several to tens of m2/g [47–50]. Supported carbides would enhance the surface area significantly compared to that of the support [39,40,51]. Besides, the acid sites on the support are also required for the bifunctional hydrorefining catalysts. XRD patterns of the catalysts (Fig. 6) exhibited only the characteristic peaks of γ-Al2O3 support. No obvious peaks belonging to Ni, Mo and W oxide species are observed, which could be regarded as that the active metal species were well dispersed, either amorphous or composed of crystallites under the detect limit. These results are well consistent with those of previous studies [46,52] showing good performance for hydrotreating reactions. NiMo/Al2O3 catalyst shows similar pattern to phosphorus modified NiMo/Al2O3 with high performance for hydroprocessing of crude oil [53]. H2-TPR profiles of the catalysts are shown in Fig. 7 and compared with previous studies [46,54,55]. The TPR profiles are typical of these kinds of catalysts. NiMo/Al2O3 is easier to be reduced than NiW/Al2O3. The profiles can also provide evidence that these 2 catalysts would be transformed to carbides at such aforementioned carburization conditions even though carbide is more difficult to produce [32]. Nagai et al. [56] studied Ketjen carbon supported NiW carbides prepared at conditions similar with this work, and found a mixture of α-W2C and WC by XRD.

Fig. 8. GC–MS TIC spectra of LTCT fraction and its products hydrogenated on different catalysts.

increased the N content. The peaks of naphthalene and phenanthrene are labeled, which shows that the compounds in the aromatic fraction are mainly composed of 2- to 3-ring aromatics. After hydrogenation, the peak of NMP reduced, especially over NiMo-C catalyst that NMP was almost removed. The distribution of aromatic compounds move left in the spectra, which indicates that the compounds became lighter after hydrogenation. Fig. 9 shows the TIC spectrum of hydrogenated product over NiMo-C catalyst. The compounds identified are almost hydroaromatics and cycloalkanes (with some cycloalkenes), such as alkyl cyclohexane (cyclohexene), alkyl decalin and tetralin, alkyl octahydrophenanthrene. The compositions semi-quantified by peak areas from TIC spectra are summarized in Fig. 10. Aromatic hydrocarbons consist up to 66% of the separated LTCT fraction. After hydrogenation, the aromatics are removed significantly. The hydrodearomatization (HDA) activity on carbides is higher than that on sulfides, especially on NiMo-C catalyst, with the HDA efficiency up to 92.4%. However, NiW-S catalyst performed slightly better than NiMo-S, which is consistent with previous studies that NiW sulfide is better for aromatics hydrogenation over NiMo sulfide catalyst [57]. Correspondingly, the content of hydrogenated aromatic hydrocarbons increases sharply after reaction, especially over NiMo-C catalyst. The content of hydroaromatics and cycloalkanes in the hydrogenated product on NiMo-C is up to 67.1%, which is much more than that over the other catalysts. Therefore, NiMo

3.2. Hydrogenation of LTCT fraction The aromatic fraction separated from low temperature coal tar was diluted in toluene and used as feedstock for hydrotreating. The catalytic performance of NiW and NiMo carbides were compared with their sulfide counterparts. The GC–MS TIC spectra of feed and hydrogenated products were shown in Fig. 8. Due to the immature separation method, the extract solvent NMP can still be detected in the feed, which 362

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Fig. 9. GC–MS TIC spectrum of hydrogenated LTCT fraction over NiMoC catalyst.

Fig. 12. Compositions of DCLO fraction and its hydrogenated products on different catalysts.

carbide is shown in Fig. 11. Besides the hydroaromatics and cycloalkanes, there are some full hydrogenated aromatics in hydrogenated DCLO fraction, such as 12H-phenalene, 14H-anthracene (or 14H- phenanthrere), 16H-pyrene, which may be benefited from partial hydrogenation during the coal liquefaction process. The composition of samples calculated from TIC spectra is summarized in Fig. 12. Due to hydrogenation of crude oil during the coal liquefaction process, the hydroaromatics accounts up to 52.6% of the feed, which is much more than that in the LTCT fraction. The aromatic component in the feed is 32.2%, and after hydrogenation it is removed by 72.5% and 91.0% over NiW and NiMo carbides, respectively. The content of hydroaromatics increased to 62.2% and 64.9% on NiW and NiMo catalysts, respectively. Besides, the content of cycloalkanes, which are mainly from the deep hydrogenation of alkylbenzene, increases from nearly 0 to 2.3% and 9.9% over NiW-C and NiMo-C, respectively. Thus, the total amount of hydroaromatics and cycloalkanes in the hydrogenated products are 64.5% and 74.8% over NiW-C and NiMo-C, respectively. The “others” component consists of isomerized hydroaromatics, such as alkyl indane, hydrogenated acenaphthene. This component over NiW carbide is higher than NiMo, which may be ascribed to more acidity in NiW carbide. The boiling point distribution of the oil samples before and after hydrogenation is shown in Fig. 13. It is obvious that the hydrogenated products show similar boiling point distribution and are lighter than the feed. The distillate range is summarized and lists in Table 4 with elemental composition together. After hydrogenation, the initial boiling

Fig. 10. Compositions of LTCT fraction and its products hydrogenated on different catalysts.

carbide catalyst shows the best performance for hydrogenation of LTCT fraction. 3.3. Hydrogenation of DCLO fraction Based on the result above, NiW and NiMo carbides were selected for hydrogenating of DCLO fraction. The feed and hydrogenated products were analyzed by GC–MS and the TIC spectrum of sample over NiMo

Fig. 11. GC–MS TIC spectrum of hydrogenated DCLO fraction over NiMo-C catalyst.

Fig. 13. Simulated distillation of DCLO feedstock and hydrogenated products. 363

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perhydrophenanthrene. NiMo-C catalyst shows higher selectivity for middle distillate while a little more light compounds produced by cracking over NiW-C catalyst. The H/C, HDN and HDS over NiMo-C is also higher than that over NiW-C. NiMo carbide shows good potential for hydrogenation of CDLs to obtain high performance jet fuel composition.

Table 4 Properties of DCLO and its hydrogenated products.

Elemental analysis H/C (Atom) S /wt.% N /wt.% HDS /% HDN /% Distillation range IBP /°C 10% /°C 50% /°C 90% /°C FBP /°C

DCLO

NiW-C

NiMo-C

1.46 0.18 0.17 – –

1.56 0.08 0.15 56.59 11.92

1.68 0.04 0.12 75.23 29.54

158 213 259 310 357

127 196 248 294 336

102 195 250 301 345

Acknowledgements This study was funded by National Natural Science Foundation of China (NSFC) No. 21506251 and U1261213. China Coal Research Institute Co., LTD was appreciated for providing DCLO. References [1] Xu J, Yang Y, Li,. YW. Recent development in converting coal to clean fuels in China. Fuel 2015;152(s):122–30. [2] Cui WG, Li WH, Gao R, Ma HX, Li D, Niu ML, et al. Hydroprocessing of LowTemperature Coal Tar for the Production of Clean Fuel over Fluorinated NiW/ Al2O3-SiO2 Catalyst. Energy Fuels 2017;31(4):3768–83. [3] Lei Z, Gao L, Shui H, Chen W, Wang Z, Ren S. Hydrotreatment of heavy oil from a direct coal liquefaction process on sulfided Ni–W/SBA-15 catalysts. Fuel Process Technol 2011;92(10):2055–60. [4] Tang W, Fang M, Wang H, Yu P, Wang Q, Luo Z. Mild hydrotreatment of low temperature coal tar distillate: product composition. Chem Eng J 2014;236:529–37. [5] Šafářová M, Kusý J, Anděl L. Brown coal tar hydrotreatment. J Anal Appl Pyrolysis 2010;89(2):265–70. [6] Meng JP, Wang ZY, Ma YH, Lu JY. Hydrocracking of low-temperature coal tar over NiMo/Beta-KIT-6 catalyst to produce gasoline oil. Fuel Process Technol 2017;165:62–71. [7] Sun RJ, Shen SG, Zhang DF, Ren YP, Fan JM. Hydrofining of Coal Tar Light Oil to Produce High Octane Gasoline Blending Components over gamma-Al2O3- and etaAl2O3-Supported Catalysts. Energy Fuels 2015;29(11):7005–13. [8] Adesanwo T, Rahman M, Gupta R, de Klerk A. Characterization and Refining Pathways of Straight-Run Heavy Naphtha and Distillate from the Solvent Extraction of Lignite. Energy Fuels 2014;28(7):4486–95. [9] Wang HY, Cao YM, Li D, Muhammad U, Li CS, Li ZX, et al. Catalytic hydrorefining of tar to liquid fuel over multi-metals (W-Mo-Ni) catalysts. J Renew Sustain Ener 2013;5(5).. [10] Li J, Yang JL, Liu ZY. Hydro-treatment of a direct coal liquefaction residue and its components. Catal Today 2008;130(2–4):389–94. [11] Kan T, Wang H, He H, Li C, Zhang S. Experimental study on two-stage catalytic hydroprocessing of middle-temperature coal tar to clean liquid fuels. Fuel 2011;90(11):3404–9. [12] Li D, Cui W, Zhang X, Meng Q, Zhou Q, Ma B, et al. Production of Clean Fuels by Catalytic Hydrotreating a Low Temperature Coal Tar Distillate in a Pilot-Scale Reactor. Energy Fuels 2017;31(10):11495–508. [13] Li D, Li Z, Li W, Liu Q, Feng Z, Fan Z. Hydrotreating of low temperature coal tar to produce clean liquid fuels. J Anal Appl Pyrolysis 2013;100:245–52. [14] Kan T, Sun XY, Wang HY, Li CS, Muhammad U. Production of Gasoline and Diesel from Coal Tar via Its Catalytic Hydrogenation in Serial Fixed Beds. Energy Fuels 2012;26(6):3604–11. [15] Sato Y. Hydrotreating of heavy distillate derived from wandoan coal liquefaction. Catal Today 1997;39(1–2):89–98. [16] Butnark S, Badger MW, Schobert HH, Wilson GR. Coal-based jet fuel– composition, thermal stability and properties. Prepr Pap - Am Chem Soc, Div Fuel Chem 2003;48(1):158–61. [17] Gül Ö, Rudnick LR, Schobert HH. The Effect of Chemical Composition of Coal-Based Jet Fuels on the Deposit Tendency and Morphology. Energy Fuels 2006;20(6):2478–85. [18] Balster LM, Corporan E, DeWitt MJ, Edwards JT, Ervin JS, Graham JL, et al. Development of an advanced, thermally stable, coal-based jet fuel. Fuel Process Technol 2008;89(4):364–78. [19] Majka M, Tomaszewicz G, Mianowski A. Experimental study on the coal tar hydrocracking process over different catalysts. J Energy Inst 2018;91(6):1164–76. [20] Nishijima A, Kameoka T, Sato T, Matsubayashi N, Nishimura Y. Catalyst design and development for upgrading aromatic hydrocarbons. Catal Today 1998;45(1–4):261–9. [21] Demirel B, Wiser WH, Oblad AG, Zmierczak W, Shabtai J. Production of high octane gasoline components by hydroprocessing of coal-derived aromatic hydrocarbons. Fuel 1998;77(4):301–11. [22] Murti SDS, Choi K-H, Sakanishi K, Okuma O, Korai Y, Mochida I. Analysis and removal of heteroatom containing species in coal liquid distillate over NiMo catalysts. Fuel 2005;84(2–3):135–42. [23] Raje AP, Liaw S-J, Srinivasan R, Davis BH. Second row transition metal sulfides for the hydrotreatment of coal-derived naphtha I. Catalyst preparation, characterization and comparison of rate of simultaneous removal of total sulfur, nitrogen and oxygen. Appl Catal, A 1997;150(2):297–318. [24] Sun C, Peltre M-J, Briend M, Blanchard J, Fajerwerg K, Krafft J-M, et al. Catalysts for aromatics hydrogenation in presence of sulfur: reactivities of nanoparticles of ruthenium metal and sulfide dispersed in acidic Y zeolites. Appl Catal, A

point (IBP) decreases from 158 °C for the feed to 127 °C and 102 °C for products over NiMo-C and NiW-C, respectively. The < 200 °C fraction (ca. 10%) over NiW-C is lighter than that over NiMo-C. Most of the compounds in this fraction should be 1-ring aromatics or cycloalkanes, however, the content of cycloalkanes in the product over NiMo-C is much more than that over NiW-C (shown in Fig. 12), which indicates that more severe hydrocracking occurred on NiW-C catalyst than on NiMo-C catalyst to produce light alkylbenzenes. This can also indicate that the cycloalkanes in the product over NiMo-C catalyst are mainly obtained by hydrogenation of its “original” alkylbenzenes, biphenyl, and etc. Since the saturation of 1-ring aromatics is much more difficult, the higher content of cycloalkenes means that NiMo-C is more active for aromatic hydrogenation. From 200 °C to 250 °C the two samples show almost the same distribution, and are about 10 °C lighter than the feed. However, the distillate over 270 °C on NiMo-C is about 5 °C lighter than that on NiW-C catalyst. The boiling point distribution shows that NiMoC catalyst is more efficient for conversion of heavier compounds, with better selectivity for middle distillate. The elemental composition in Table 4 shows that NiMo-C catalyst has better hydrogenation activity than NiW-C, with higher H/C molar ratio of 1.68. The HDS and HDN activities of NiMo-C catalyst are also higher than that of NiW-C catalyst. The removal of heteroatoms on each catalyst were in the order of HDN < HDS, which is consistent with their reaction difficulties. The HDN and HDS activities in this reaction are relatively lower than that in petroleum refining, which is also shown in others research [22,58]. Murti et al. [22] studied removal of different S-, O- and N-compounds in CDL distillate over conventional and modified NiMoS/Al2O3 catalysts, and found that the removal of heteroatomic species was difficult, especially over conventional NiMoS/Al2O3 catalyst. This may be partially ascribed to that the S- and N-compounds exist in DCLO is more refractory, since these more active ones were removed during the coal liquefaction process. Besides, higher temperature would also enhance the activities significantly [22,59]. Compared with the standard of JP-8 and coal-based JP-900 [18], further hydrogenation would still be necessary to increase the hydrogen content and remove heteroatoms, by optimizing reaction conditions and/or enhancing the catalytic performance. 4. Conclusions In this work, NiMo/Al2O3 and NiW/Al2O3 carbide and sulfide catalysts were prepared. Their catalytic performance for selective hydrogenation of aromatics in DCLO fraction and the aromatic component separated from LTCT were compared. Results show that during hydrogenation of aromatic component from LTCT fraction, the HDA activity decreases in the order: NiMo-C > NiW-C > NiW-S > NiMo-S, with 92.4% on NiMo-C catalyst. HDA of DCLO fraction over NiMo-C and NiW-C is 91% and 72.5%, respectively. The hydroaromatics and cycloalkanes in hydrogenated DCLO fraction is up to 74.8%, with certain amount of deep hydrogenated aromatics such as 364

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