Combined Hydrotreating and Fluid Catalytic Cracking Processing for

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Combined hydrotreating and FCC processing for the conversion of inferior coker gas oil: Effect on nitrogen compounds and condensed aromatics Qiang Sheng, Gang Wang, Yongjiang Liu, Maen M. Husein, Chengdi Gao, Quan Shi, and Jinsen Gao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00436 • Publication Date (Web): 28 Mar 2018 Downloaded from http://pubs.acs.org on March 28, 2018

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Energy & Fuels

Combined hydrotreating and FCC processing for the conversion of inferior coker gas oil: Effect on nitrogen compounds and condensed aromatics Qiang Sheng1, Gang Wang*1, Yongjiang Liu1, Maen M. Husein2, Chengdi Gao3, Quan Shi1 and Jinsen Gao1 1

State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum, Beijing 102249, China 2 Department of Chemical & Petroleum Engineering, University of Calgary, Calgary, AB, T2N 1N4, Canada 3 College of Science, China University of Petroleum, Beijing 102249, China

*Corresponding Author: Gang Wang, E-mail: [email protected] ABSTRACT Inferior coker gas oil (ICGO) derived from Venezuelan vacuum residue delayed coking is difficult to process using fluid catalytic cracking (FCC) or hydrocracking (HDC). The high content of nitrogen and condensed aromatics leads to major coking, and readily deactivates the acid catalyst. In this work, a sequence of hydrotreating (HDT) and FCC processing is used to effectively convert ICGO to high-value light oil product. The results show a higher overall conversion and a significant increase in the yield of gasoline compared with FCC processing. Molecular level characterization of the nitrogen compounds and condensed aromatics before and after HDT confirms that the nitrogen content and the 2+ ring aromatic content decreased, whereas the single ring aromatics increased. The nitrogen compounds were mainly N1, N1O1, N1O2, and N1S1 class species in basic nitrogen and N1, N1O1, N1O2, N2, and N2O1 class species in non-basic nitrogen. Moreover, the double bond equivalent of these species shifted to lower values. 1

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The decrease in the nitrogen compounds with high heteroatom content reduces coking on the FCC catalyst. Subsequently, FCC unit performance and conversion to light oil increased. Moreover, the decrease in the size of N1 class compounds and the ease of their cracking following HDT improved the performance of the FCC unit. Partial saturation of condensed aromatics following HDT also made it easier to crack these compounds. Keywords: inferior coker gas oil; hydrotreating; FCC; nitrogen compounds; condensed aromatic; molecular characterization List of Abbreviations A-CHGO

coker heavy gas oil derived from Athabasca bitumen

CGO

coker gas oil

CHGO

coker heavy gas oil

CL-CGO

Changling coker gas oil

DQ-CGO

Daqing coker gas oil

DG-CGO

Dagang coker gas oil

DBE

double bond equivalent

ESI FT-ICR MS

electrospray ionization Fourier resonance mass spectrometry

FCC

fluid catalytic cracking

GC-MS

gas chromatography-mass spectrometry

HICGO

hydrotreated inferior coker gas oil

HDC

hydrocracking

2


transform

ion

cyclotron

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HDT

hydrotreatment

HDN

hydrodenitrogenation

HDS

hydrodesulfurization

ICGO

inferior coker gas oil

LHSV

liquid hourly space velocity

LH-CGO

Liaohe coker gas oil

LCO

light cycle oil

NT

total nitrogen

NB

basic nitrogen

SARA

saturates, aromatics, resins, and asphaltenes

SL-CGO

Shengli coker gas oil

TSRFCC

two stage riser FCC

TIC

total ion chromatogram

VGO

vacuum gas oil

WHSV

weight hourly space velocity

1. INTRODUCTION Inferior heavy oil is becoming an important component of the energy platform and its use as a source for liquid fuel is growing.1 Coking is the most common process for converting inferior heavy oil.2-3 Coker gas oil (CGO), which accounts for 20-30 wt% of the coker feed,4 is hard to process by fluid catalytic cracking (FCC) and hydrocracking (HDC) due to its high content of nitrogen compounds and condensed aromatics.5-6 Total nitrogen 3


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compounds refer to the basic (can be titrated by perchloric acid in glacial acetic acid) and non-basic nitrogen compounds. The acidic sites of the FCC and HDC catalysts are readily neutralized by the basic nitrogen compounds.7-10 Non-basic nitrogen compounds and condensed aromatics, on the other hand, easily adsorb onto the catalyst active sites7, where they undergo dehydrogenation and condensation reactions to form coke. CGO derived from inferior heavy oil (called inferior CGO (ICGO)), such as Venezuelan vacuum residue and oil sand bitumen, has higher nitrogen and condensed aromatics content. Subsequently, processing ICGO is even much harder for refineries compared with regular CGO. Different approaches had been proposed in the literature for processing CGO.8, 11-15 Appreciable conversion of CGO was obtained by blending it with regular FCC feedstock, such as VGO.8 Controlling the blend ratio and the operation conditions was a key factor for achieving high conversion. A separate FCC reaction zone to handle nitrogen compounds and condensed aromatics was also explored.11 Applying appropriate conditions for each of the two FCC zones increased the yield of light oil. Yuan et al.12 studied the conversion of CGO by two stage riser FCC (TSRFCC). The results showed that for the same overall conversion, higher yields of light oil and total liquid products were attained compared with conventional FCC. Different processes for treating CGO by FCC were also reported by other researchers.13-15 However, none of these processes considered ICGO, due to the high potential of rapid catalyst deactivated, serious coking and lower yield of light oil. Accordingly, pre-treating ICGO before FCC processing is 4


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inevitable. Solid adsorbents,16 neutralization,17 solvent extraction,18-20 and hydrotreatment (HDT)4, 21 are the most used pre-treatment methods for processing ICGO. The first three led to low liquid yield, high energy consumption, and serious environmental problems, whereas HDT was deemed feasible. Meng et al.4 showed that HDT followed by FCC processing of Liaohe CGO (LH-CGO) improved FCC product quality. The yield of gasoline improved by approximately 14 wt%, whereas the yield of heavy oil and coke decreased by 11.35 and 4.74 wt%, respectively. Yui21 investigated HDT of coker heavy gas oil derived from Athabasca bitumen. The author noted that the hydrotreated coker heavy gas oil constituted a premium feedstock for the FCC process. Nevertheless, the quality of the Athabasca-derived feedstock is still superior to that of the ICGO derived from Venezuelan vacuum residue. Very few studies in fact considered ICGO HDT followed by FCC processing.4, 21 This study considers a sequence of HDT followed by FCC processing of ICGO derived from Venezuelan vacuum residue. In order to provide a complete understanding of the mechanism, the molecular structure of nitrogen compounds and condensed aromatics before and after HDT were determined using electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR MS) and gas chromatography-mass spectrometry (GC-MS). Characterization of these fractions from CGO feedstock by ESI FT-ICR MS and GC-MS was previously reported 7, 11, 22. However, the impact of HDT on the structure of the different compounds present in ICGO was seldom monitored.22 Only the structure of basic nitrogen species of two types of regular CGO before and after HDT 5


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was studied.9 The non-basic nitrogen species23 and condensed aromatics24 were also seldom considered especially for the ICGO. Therefore, there is a knowledge gap on the impact of HDT on the basic and non-basic nitrogen compounds as well as condensed aromatics present in ICGO. The current work is an attempt to fill in this gap. 2. EXPERIMENTAL SECTION 2.1 Feedstock and Catalyst The properties of ICGO derived from Venezuelan Mery-16 crude oil vacuum residue delayed coking unit are listed in Table 1. The properties of coker heavy gas oil (CHGO) derived from Athabasca bitumen (A-CHGO)21 and five kinds of CGOs from China; namely Daqing CGO (DQ-CGO)

8, 25

, Changling CGO (CL-CGO)26, Dagang CGO

(DG-CGO)11, Shengli CGO (SL-CGO)26, and LH-CGO26 are also included in Table 1. Table 1 shows that DQ-CGO and CL-CGO portray lower total nitrogen and aromatic content, which entails no major processing challenges. However, DG-CGO, SL-CGO, and LH-CGO contain a slightly higher total nitrogen, whereas their aromatic content is much lower than that of ICGO. A-CHGO also contains lower total nitrogen compared with ICGO. Therefore, in principle, it is anticipated that ICGO derived from Venezuelan vacuum residue delayed coking unit is harder to process.

Table 1. Properties of different CGOs. item

ICGO

A-CHG O21

density(20 °C), kg·m-3

963.4

1001.7

DQ-CG O8, 25 862.8

CLCGO26

6


DG-CG O11 910.2

SL-CGO2 6

LH-CG O26 963.4

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carbon residue, wt%

0.45

0.095

0.46

0.12

0.23

0.15

molecular weight(VPO)

341

283

341

308

368

355

elemental composition carbon, wt%

85.59

84.21

85.15

86.65

85.93

86.87

hydrogen, wt%

11.20

10.17

12.83

12.75

11.69

11.96

sulfur, wt%

2.71

4.33

2000

0.27

0.78

0.61

total nitrogen, µg·g-1

5063

3783

3400

3400

5400

5500

basic nitrogen, µg·g-1

1494

1200

1100

H/C atom ratio

1.57

1.45

1.81

1.75

1.63

1.64

1.52

1600

6900 2639

SARA analysis, wt% saturate

33.40

78.80

61.5

60.84

51.10

59.34

aromatic

58.80

12.60

28.8

30.47

37.40

27.28

resin

7.80

8.60

9.7

8.69

11.50

12.54

0

0

0

0

0

0.84

asphaltene

A NiMo/Al2O3 catalyst was used for HDT, which was designed and developed by China Petroleum Daqing Petrochemical Research Institute. The catalyst was specially designed to adapt to high nitrogen and condensed aromatic feedstock. The surface area, pore volume, and bulk density of the HDT catalyst were 148 m2·g-1, 0.26 cm3·g-1, and 1.25 g·cm-3, respectively, and the MoO3 and NiO compositions were 15—30 wt% and 4 —10 wt%, respectively. The FCC catalyst used in this study was a typical commercial LVR-60 FCC catalyst supplied by Changqing Petroleum Refinery with properties listed in Table 2. Table 2. Properties of commercial equilibrium FCC catalyst LVR-60. microactivity index

metal content, µg·g-1

bulk density a, g·ml-1

Ni 7


V

Fe

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63.0

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0.88

7776

3868

5640

particle size distribution, wt%

a

0~18.9 µm

18.9~39.5 µm

39.5~82.7 µm

82.7 ~111 µm

＞111 µm

0

7.2

49.5

24.0

19.3

bulk density obtained by filling a certain mass of the catalyst into a container with a known volume.

2.2 Experimental Methods The HDT of ICGO was performed in a fixed bed reactor unit as shown Fig. S1 of the supporting information. The reactor platform consisted of gas control system, oil inlet system, preheater, reaction unit, and hydrogenated oil-gas separation unit. The gas to oil ratio is controlled by a mass flow meter and an oil pump, respectively. The combined stream is mixed and then preheated by a furnace, before allowed into the fixed bed hydrotreating unit from the bottom. The reactor outlet leads into oil and gas separation tank. The FCC reaction was run on a fluidized bed reactor unit (without recirculation) using the liquid product from HDT following a procedure detailed elsewhere.27 HDT reaction was run at 385 °C，8 MPa, liquid hourly space velocity of 1.2 h-1 and hydrogen-to-oil volume ratio of 800:1. Catalyst pre-sulfidation was run at 300 °C, 4.0 MPa, liquid hourly space velocity (LHSV) of 4 h-1 for 5 h using a solution of 2 wt% CS2 in cyclohexane. FCC unit was operated at 510 °C for 3 s using catalyst-to-oil weight ratio of 8, weight hourly space velocity (WHSV) of 15 h-1, feedstock preheating temperature of 350 °C, steam oven temperature of 280 °C, catalyst loading mass of 90 g, water pump rate of 2.5 ml·min-1 and steam stripping time of 20 min.

8


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2.3 Analytical Methods The ICGO and hydrotreated ICGO (HICGO) were used to identify the molecular structure of nitrogen compounds without an extraction step. Positive-ion and negative-ion ESI coupled with a Bruker Apex-Ultra FT-ICR MS equipped with a 9.4 T superconducting magnet were used to characterize the nitrogen compounds. Details on sample preparation and analysis can be found elsewhere.9, 11 The condensed aromatics, on the other hand, were extracted from ICGO and HICGO by formic acid, titanium tetrachloride, and furfural prior to their characterization. The detailed description of the condensed aromatics extraction step is presented in the supporting information. The condensed aromatics characterization was performed on a Thermo-Finnigan Trace DSQ GC-MS coupled with a HP-5MS column (30 m×0.25 mm×0.25 µm). Sample preparation and the equipment parameters can be found elsewhere.11 The analysis of the hydrocarbon types was carried out on MS (Agilent 5973 MS) according to ASTM D2786-91 and D3239-91 methods.28 ICGO and HICGO samples were introduced without any extraction. A non-aqueous titration method was used for basic nitrogen analysis according to UOP269 standard.7 Group composition, i.e. saturates, aromatics, resins, and asphaltenes (SARA), was performed according to a method described by Liang et al.29-30 The gas product, liquid product and the coke content following FCC processing were analyzed according to Wang.31 The FCC liquid product was divided into gasoline (initial boiling point (IBP)-200 °C), light cycle oil (LCO) (200-350 °C), and slurry (above 350 °C) per 9


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simulated distillation results. The simulated distillation was carried out using Agilent 6890 gas chromatograph according to ASTM-2887-D method. The microactivity of the catalyst was tested according to the ASTM 3907 standard. The test was carried out on a fixed-bed reactor.32 The microactivity test was carried out using 235-337 °C Dagang light straight run diesel as the feed at 460 °C, 70 s of reaction time, catalyst-to-oil weight ratio of 3.2, WHSV of 16 h-1. 3. RESULTS AND DISCUSSION 3.1 Effect of HDT on nitrogen compounds and aromatics In order to explore the role of HDT process, nitrogen content, including basic nitrogen and non-basic nitrogen, and aromatics composition were characterized before and after HDT. The data listed in Table 3 show that the total nitrogen (NT) and the basic nitrogen (NB) were significantly reduced, suggesting that part of nitrogen compounds was hydrodenitrogenated (HDN). Even though the total aromatics content decreased only a little (from 58.8 wt% to 52.6 wt%), the composition of the aromatic compounds had undergone a significant change. The 1-ring aromatics increased by approximately 9 wt%, whereas, the aromatics with 2- to 5-rings decreased to different degrees. This observation can be explained by the mechanism of condensed aromatics hydrogenation, HDN, and hydrodesulfurization (HDS). According to the condensed aromatics hydrogenation mechanism, the equilibrium constant of the first ring hydrogenation saturation is the highest, followed by the second ring hydrogenation, all the way until the highest ring 10


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hydrogenation.33-36 Additionally, the hydrogenation activity of single aromatics is much lower than that of condensed aromatics.33-36 Accordingly, the condensed aromatics hydrogenation products should include many 1-ring aromatics. Following the HDN mechanism, the five-membered ring nitrogen compound of indole hydrogenation path is different from other nitrogen compounds. Nitrogen in the five-membered ring nitrogen compounds can be removed without hydrogenation of the adjacent benzene ring resulting in the formation of many 1-ring aromatics.37 Lastly, on the basis of the HDS mechanism, removing the S atom from the benzothiophenes molecules can be accomplished by both hydrogenation and hydrogenolysis paths, and like indole HDN, the benzene ring needs not to be saturated first, which also leads to 1-ring aromatics.38 Table 3. Nitrogen compound and aromatics content of ICGO and HICGO*. nitrogen compound

aromatics, wt%

NT, µg·g-1

NB, µg·g-1

1-ring

2-ring

3-ring

4-ring

5-ring

total

ICGO

5078

1494

21.2

13.3

5.6

4.8

1.4

58.8

HICGO

1320

301

30.0

12.3

3.9

1.1

0.6

52.6

*

The complete hydrocarbon composition analysis of ICGO and HICGO as characterized by MS is listed in Table S1 of the supporting information.

3.2 FCC of ICGO and HICGO FCC processing of ICGO and HICGO feedstocks is compared in Table 4. FCC of HICGO gave higher yield of LPG and gasoline, i.e. light high-value products, at the expense of slurry, coke and LCO. In addition, the overall conversion and the liquid yield were higher than ICGO. These advantages are attributed to the heteroatom removal, 11


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especially N, and the partial saturation of the condensed aromatics in the HICGO feedstock. Accordingly, the FCC catalyst suffered less deactivation, as confirmed by the microactivity test results in Table 5, specially at a lower content of basic nitrogen. The catalytic cracking of the hydrogenated non-basic nitrogen compounds and the partially saturated condensed aromatics is easier and the coking tendency of these compounds is less compared with compounds in ICGO. The increase in the content of 1-ring aromatics following HDT promotes conversion to gasoline, since these compounds are gasoline precursors. The hydrogenation product of benzene rings is naphthenic rings, which contain many secondary and tertiary carbon atoms. It is easy to form the carbonium ion from the secondary or the tertiary carbon of the naphthenic rings, following C—C bond breaking at β position to produce small molecules such as gasoline.39 Furthermore, the products of condensed aromatics hydrogenation were mainly cycloalkylbenzenes. The C—C bond between a cycloalkane ring and an aromatic ring is easily cracked to produce lighter oil.36,

40

Contrary to these reaction routes, the none hydrotreated

condensed aromatics in the ICGO feedstock were dominated by hydrogen transfer and condensation reactions under FCC conditions, which in turn led to more coke formation.39, 41 Table 4. FCC product distribution of ICGO and HICGO (wt%). item

ICGO

HICGO

dry gas

2.51

2.24

LPG

11.02

15.26

12


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gasoline

32.60

46.72

LCO

24.62

21.26

slurry

20.89

7.77

coke

7.99

6.62

loss

0.37

0.13

dry gas plus coke

10.50

8.86

total liquid yield a

89.13

91.01

conversion b, wt%

54.12

70.84

a

total liquid yield = (LPG + gasoline + LCO + slurry) wt% conversion = (dry gas + LPG + gasoline + coke) wt%

b

Table 5. The microactivity of LCR-60 and spent LVR-60 catalysts. item

LVR-60

ICGO spent LVR-60

HICGO spent LCR-60

microactivity index

63.0

15.4

22.3

3.3 Characterization of nitrogen compounds and condensed aromatics In order to provide support for the above proposed reaction routes, the molecular structure of the basic and the non-basic nitrogen compounds as well as the condensed aromatics were characterized for ICGO and HICGO feedstock. The results are discussed below. 3.3.1 Basic nitrogen compounds The positive-ion ESI FT-ICR MS broadband (100-700 Da) mass spectrum of ICGO and HICGO and a close-up view of expanded spectrum obtained under 318 and 319 Da are 13


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presented in Fig. 1. It can be seen that following HDT the relative abundance of some species decreased and the mass center increased from 320 to 340 Da. The increase in mass center is mainly due to the disappearance of the short chain nitrogen compounds, since they are more readily hydrogenated. Subsequently, mostly heavy nitrogen compounds are left behind in the HICGO. The same observation was reported by other researchers.7,

9, 42-43

The mass spectrum shifted to higher m/z value. The relative

abundance of basic nitrogen compound class species of ICGO and HICGO are shown in Fig. 2. The main class species in ICGO and HICGO were N1, N1O1, N1O2, and N1S1. Distinctly, the N1 class basic nitrogen compounds are the dominant species in ICGO and HICGO. Nevertheless, the relative abundance of N1 increased following HDT, which is consistent with published work.9, 44-47 The activity of HDS was higher than that of HDN and hydrodeoxygenation, which led to many N1 class species. In HICGO, the relative abundance of N1S1 and N1O1 class species is clearly less.

14


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Fig. 1. Positive-ion ESI FT-ICR MS spectra of ICGO and HICGO. The inserts are expanded segments used to show the comparison of molecular composition.

DBE

ICGO

N1

N1O1

N1O2

HICGO

N1S1

N1

N1O1 N1O2 N1S1

1 3 5 7 9 11 13 15 17 19 21 23

2 4 6 8 10 12 14 16 18 20 22 24

Fig. 2. Relative abundance of basic nitrogen compound class species of ICGO and HICGO.

The iso-abundance dot-size coded plots are constructed by correlating the DBE and the carbon number distribution of species contained in ICGO and HICGO. The plots of DBE versus carbon number for the different class species are presented in Fig. 3. The main 15


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basic nitrogen compound of N1 class species in ICGO has DBE values of 4-17 and a carbon number of 12-32, whereas DBE of N1 class species in HICGO clearly shifted to lower value and the carbon number slightly changed. The N1 class species with DBE lower than 4 in HICGO are most likely amino compounds, which were produced from pyridine and/or pyrrole type compounds during HDT.48 The N1 class species in ICGO with 9-12 DBE values displayed higher relative abundance, which could possibly be core structure of quinoline connected with a 1-2 benzene ring or a naphthene ring. However, in HICGO the dominant N1 class species displayed 6-10 DBE values, with possible core structure of pyridine connected with a 1-2 benzene ring or a naphthene ring. Following HDT the relative abundance of N1O1 class species with 5-7 and 10-13 DBE values was clearly reduced, and the DBE of N1O2 shifted to a lower value. Additionally, the relative abundance of N1S1 class species decreased due to the high reactivity of sulfide toward hydrogenation.

24

ICGO-N1O1 CGO-N1O1 20 16 DBE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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12 8 4 0 0

5 10 15 20 25 30 35 40 45 50 55 60 Carbon Number

16


Page 17 of 30

24

24

CGO-N1O2 ICGO-N1O2

CGO-N1S1 ICGO-N1S1

20

16

16

12

12

DBE

DBE

20

8

8

4

4

0

0 0

5 10 15 20 25 30 35 40 45 50 55 60

0

5 10 15 20 25 30 35 40 45 50 55 60

Carbon Number

Carbon Number 24

Hy-CGO-N1O1 HICGO-N1O1 20

DBE

16 12 8 4 0 0

5 10 15 20 25 30 35 40 45 50 55 60 Carbon Number

24

Hy-CGO-N1O2 HICGO-N1O2

20 16 DBE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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12 8 4 0 0

5 10 15 20 25 30 35 40 45 50 55 60 Carbon Number

Fig. 3. Plots of DBE versus carbon number for different basic nitrogen class species in ICGO and HICGO.

The reduction in some species relative abundance after HDT is in line with the decrease of basic nitrogen content reported in Table 3. Subsequently, FCC catalyst poisoning by means of acid site neutralization is reduced. Moreover, the decrease in the relative abundance of N1S1 and N1O1 class species in HICGO reduces the coking 17


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tendency of the feedstock upon FCC processing compared with ICGO feedstock. Despite the increase in relative abundance of basic N1 compounds following HDT, the overall molecular size decreased. More importantly, the partial saturation of benzene rings led to more easily creaked basic nitrogen compounds. Consequently, FCC processing of HICGO produced higher yield of light oil. The structure change of N1 compounds is shown in Fig. 3. 3.3.2 Non-basic nitrogen compound The negative-ion ESI FT-ICR MS broadband (150-400 Da) mass spectrum of ICGO and HICGO together with a close-up view of expanded spectrum obtained under 281 and 282 Da are presented in Fig. 4. Fig. 4 shows that following HDT the mass center increased from 270 to 280 Da and the mass spectrum shifted to higher m/z value.

Fig. 4. Negative-ion ESI FT-ICR MS spectra of ICGO and HICGO. The inserts are 18


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expanded segments used to show the comparison of molecular composition.

The relative abundance of non-basic nitrogen compound class species of ICGO and HICGO are showed in Fig. 5. The class species in ICGO can be identified as N1, N1O1, N1O2, N2, and N2O1. On the other hand, the N2 and N2O1 class species were not detected in HICGO. The N1 class non-basic nitrogen compounds were the dominant species in ICGO and HICGO. Except for N1 class species, the relative abundance of all non-basic nitrogen compounds was reduced upon HDT. This can be explained by the high hydrogenation activity of polyatomic nitrogen, especially since the hydrogenation products of polyatomic nitrogen compounds are N1 compounds.8 The iso-abundance dot-size coded plots are constructed by correlating DBE and carbon number distribution of the non-basis nitrogen species in ICGO and HICGO. DBE versus carbon number for the different class species in ICGO and HICGO are presented in Fig. 6. Following HDT, the DBE of N1 and N1O1 class species shifted to lower values, and their relative abundance was reduced. Possible core structures for N1 class species are benzocarbazole in ICGO and carbazole in HICGO. Compounds containing more heteroatoms easily adsorb onto the catalyst leading to more coking. For HICGO feedstock, the N2 and N2O1 compounds disappeared, whereas the relative abundance of N1O1 and N1O2 compounds decreased. In addition, DBE shifted to a low value. All these changes reduce the coking tendency of the feedstock and, in return, FCC conversion of HICGO yielded more light oil. 19


Energy & Fuels

DBE

ICGO

N1

HICGO

N1O1 N1O2

N2

N2O1

N1 N1O1 N1O2 N2 N2O1

0 2 4 6 8 10 12 14 16 18 20 22 24

1 3 5 7 9 11 13 15 17 19 21 23 25

Fig. 5. Relative abundance of non-basic nitrogen compound class species of ICGO and HICGO.

20

N H

ICGO-N1O1 CGO-N1O1

C2 N H

C2

15

DBE

DBE

15

20

ICGO-N1 CGO-N1

10

5 10

10

15

20

25

30

5 10

35

Carbon Number

15 20 25 Carbon Number

30

35

20

20

Hy-CGO-N1 HICGO-N1

Hy-CGO-N1O1 HICGO-N1O1 15 DBE

15 DBE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 30

10

10

5 10

15

20

25

30

5 10

35

15

20

25

30

35

Carbon Number

Carbon Number

Fig. 6. Plots of DBE versus carbon number for different non-basic nitrogen class species in ICGO and HICGO. 3.3.3 Aromatics The condensed aromatic extracts from ICGO and HICGO were characterized by GC-MS. 20


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Energy & Fuels

The total ion chromatogram (TIC) of ICGO and HICGO extracts are included in Fig. S3 of the supporting information. The mass chromatogram of the different types of condensed aromatics (Fig. 7A-E) and the structure of the condensed aromatics in ICGO and HICGO (Fig. 7F) are presented. Only the chromatograms from ICGO TIC were included in Fig. 7. The chromatograms of these condensed aromatics in HICGO TIC looked similar, except for their intensity and, hence, were omitted. The main condensed aromatics in ICGO and HICGO were phenanthrenes, benzonaphthazothiophenes, dibenzothiophenes, pyrenes, chrysenes, and benzofluoranthenes. It should be pointed out that the 1-2 ring aromatics were not detected in the extracts due to their low solubility in furfural and the quantification of aromatics based on GC-MS is not easy to achieve.

Previous results suggest that the proposed combined HDT-FCC processing of ICGO is promising. The economic feasibility of the process lies in offsetting the cost associated with catalyst deactivation and regeneration, SOx and NOx abatement of flue gas from FCC unit in addition to the higher yield of the high value products and the lower yield of the low value products. CONCLUSIONS ICGO derived from Venezuelan vacuum residue delayed coking process has higher nitrogen and condensed aromatics compared with regular CGO. HDT processing of such stream reduced its nitrogen content and partially hydrogenated its condensed aromatics. 21


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Consequently, FCC processing of the hydrotreated ICGO (HICGO) increased the overall conversion and the yield of the light fractions, especially gasoline. The higher conversion and selectively suggest lower FCC catalyst deactivation relative to non-hydrotreated ICGO feedstock. In order to better understand these results, the molecular structure of nitrogen compounds and condensed aromatics for ICGO and HIGCO were analyzed using ESI FT-ICR MS and GC-MS, respectively. Results showed that HDT reduced the content of basic and non-basic nitrogen and partially hydrogenated the condensed aromatics. The content of 1 ring aromatics in HICGO increased, while the 2+ ring aromatics decreased. The condensed aromatics in ICGO and HICGO, on the other hand, were mainly 3-5 rings in ICGO and HICGO. Following HDT, the content of nitrogen compounds with high heteroatom content decreased or completely removed. Subsequently, FCC catalyst suffered less coking and higher light oil yield was obtained. In addition, the size of the N1 class compounds became smaller and their cracking tendency improved following HDT. This also contributed to better performing FCC and more light oil yield.

22


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Page 23 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Energy & Fuels

m/z=192 m/z=206 m/z=220 m/z=234

A

Methylphenanthrene C2-Phenanthrene(Phs)

C4-BNTs

m/z=290

m/z=242 m/z=256

D

Chrysene(Ch)

TIC

26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 28 t / min

30

32

m/z=252 m/z=266

C1- (Chs)

m/z=280

C2- (Chs) C3- (Chs)

m/z=270

C6- (Prs)

m/z=286

TIC

TIC 26 28 30 32 34 36 38 40 42 44 46 48 50 52 t / min

C5- (Prs)

m/z=272

C7- (Dths)

m/z=282

C4- (Prs)

m/z=258

C6- (Dths)

m/z=268

C3-BNTs

m/z=276

C3- (Prs)

m/z=244

C5- (Dths)

m/z=254

C2-BNTs

C2- (Prs)

m/z=230

C4- (Dths)

m/z=240 C1-BNTs

C1- (Prs)

m/z=216

C3- (Dths)

m/z=226

C

Pyrene(Pr)

m/z=202

C2- (Dths)

Benzonaphthathiophenes(BNTs)

m/z=262

B

Methyldibenzothiophene(Dths)

m/z=212

C3-Phs

m/z=248

m/z=228

m/z=198

m/z=294

TIC

34 36

38

40 42 t / min

44

46

48

50 52

Benzo(b)fluoranthene(Bf)

54

E

C1- (Bfs) C2- (Bfs) C3- (Bfs)

TIC

36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 t / min

F

30 32 34 36 38 40 42 44 46 48 50 52 54 56 t / min

Fig. 7. Mass chromatograms of condensed aromatics (A-E) and the summary of the condensed aromatics in ICGO and HICGO (F).

23


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

AUTHOR INFORMATION Corresponding Author *Gang Wang, Tel.: 8610-8973-3085. E-mail: [email protected] NOTES The authors declare no competing financial interest. ACKNOWLEDGEMENTS The authors acknowledge the financial support provided by the National Natural Science Foundation of China Petrochemical Joint Fund (Class A) Project (U1662105), National Natural Science Foundation of China (21476259), the State Key Program of National Natural Science Foundation of China (21336011), and China Scholarship Council. REFERENCES (1) Omajali, J. B.; Hart, A.; Walker, M.; Wood, J.; Macaskie, L. E. In-situ catalytic upgrading of heavy oil using dispersed bionanoparticles supported on gram-positive and gram-negative bacteria. Applied Catalysis B: Environmental 2017, 203, 807-819. (2) Rodriguez-Reinoso, F.; Santana, P.; Palazon, E. R.; Diez, M.-A.; Marsh, H. Delayed coking: industrial and laboratory aspects. Carbon 1998, 36 (1-2), 105-116. (3) Siskin, M.; Kelemen, S.; Gorbaty, M.; Ferrughelli, D.; Brown, L.; Eppig, C.; Kennedy, R. Chemical approach to control morphology of coke produced in delayed coking. Energy & Fuels 2006, 20 (5), 2117-2124. (4) Meng, X.; Xu, C.; Gao, J. Hydrofining and catalytic cracking of coker gas oil. Petroleum Science and Technology 2009, 27 (3), 279-290. 24


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Combined Hydrotreating and Fluid Catalytic Cracking Processing for

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