Exploratory Investigation on the Slurry-phase Hydrocracking Reaction

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Exploratory Investigation on the Slurry-phase Hydrocracking Reaction Behavior of Coal Tar and Petroleum-based Heavy Oil Mixed Raw Material Chuan Li, Juntao Du, Tengfei Yang, and Wenan Deng Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b02031 • Publication Date (Web): 13 Aug 2019 Downloaded from pubs.acs.org on August 20, 2019

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Exploratory Investigation on the Slurry-phase Hydrocracking Reaction Behavior of Coal Tar and Petroleum-based Heavy Oil Mixed Raw Material Chuan Lia,*, Juntao Dub, Tengfei Yanga, Wenan Denga a State Key Laboratory of Heavy Oil, China University of Petroleum (East China), Qingdao, Shandong

266580, PR China b

Zhengzhou Institute of Emerging Industrial Technology （ Zhengzhou Branch, Institute of Process

Engineering, Chinese Academy of Sciences）, Zhengzhou 450000, PR China Chuan Li, E-mail: [email protected]; [email protected] Abstract: A petroleum-based atmospheric residue from Merey (MRAR) and a medium/low temperature coal tar atmospheric residue (CTAR) were selected as raw materials and mixed in different proportions to form mixed raw materials. The stability of the mixed raw material, product distribution and properties of coke and asphaltene during the mixed raw material slurry-phase hydrocracking (MSH) reaction were studied to explore the feasibility of the corefining coal tar and petroleum-based heavy oil. The results show that the addition of CTAR can damage the colloidal stability of the mixed system and promote cracking and condensation reactions. However, the destruction degree of system stability was relatively low when the CTAR content was within 40 wt%; the 30 wt% CTAR addition can maximize the raw material conversion rate with moderate increase in coke yield, and both H2 consumption and light oil yield obtained from the MSH reaction are higher than the theoretical weight value. Thus, it is feasible to perform a co-refining reaction with a certain proportion of CTAR and MRAR. The change trend of the structural parameters such as the micelle size, 1

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aromaticity, mean relative molecular mass and ring numbers of asphaltene after the MSH reaction are closely related to the changes in stability of the mixed raw material, product distribution of MSH reaction and properties of coke. Thus, the reaction behavior of MSH can be attributed to a type of synergy between CTAR asphaltene and MRAR asphaltene when CTAR and MRAR are mixed and co-react. Key words: Coal tar; Petroleum-based heavy oil; Slurry-phase hydrocracking; Reaction behavior; Asphaltene 1. Introduction The heavy oil slurry-phase hydrocracking process is a technology capable of handling inferior raw materials 1-3. Although the slurry-phase hydrocracking technology developed by Ente Nazionale Idrocarburi (ENI) company

4

has been industrialized, researchers continue to study the reaction

process, catalyst, mechanism and process flow of the process to reduce the coke yield and increase the raw material conversion rate, which improves the technical economy of this process

5-9.

Mixing

different raw materials and co-refining are also a common method for improving the efficiency of the reaction. Meng 10 studied the reaction process of inferior residual oil and coal tar mixed feedstock for ebullated bed hydrocracking and found that at a certain mass ratio of residue to coal tar, although the compatibility of the mixed raw materials deteriorated, the raw material conversion rate increased, the coke yield decreased, and the reaction efficiency improved. Stratiev

11

found that the addition of a

highly aromatic fluid catalytic cracking (FCC) slurry to the residue could reduce the formation of deposits during the thermal conversion of the residue and attributed this phenomenon to the FCC slurry increasing the solubility of asphaltene in the feedstock and improving the hydrogen supply capacity of the system. Šimáček

12

found that when rapeseed oil was mixed with the vacuum residue and

subsequently subjected to the hydrocracking reaction, the produced gasoline fraction had better fuel performance and low temperature performance, and the kerosene fraction had higher quality with low 2


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sulfur and low aromaticity. Šimáček

13

also studied the hydrocracking reactions of the mixture of

Fischer-Tropsch synthesis product and the vacuum residue and found that compared with the vacuum residue, although the yields of naphtha, diesel oil and residual oil produced by the mixed raw materials were not substantially different, these products had high qualities with lower density and sulfur content. Therefore, mixing a suitable raw material to the inferior heavy oil may effectively improve the conversion efficiency, reduce the coke formation, and improve the product properties during the slurry-phase hydrocracking. Coal tar is an important byproduct of the coal coking industry

14-16.

It is mainly composed of

aromatic hydrocarbon compounds containing between 2 and 15 rings, high contents of asphaltene, aromatic component, metal, oxygenated compound and basic nitrogen 17. Compared with petroleum asphaltene, coal tar asphaltene has higher aromaticity, smaller average relative molecular weight, more and shorter alkyl side chains, and higher contents of heteroatoms and heterocyclic structures 18, 19. In addition, coal tar contains toluene insoluble (TI), which is composed of aromatic hydrocarbons with low H/C atomic ratio or fused aromatic hydrocarbons, inorganic minerals and mechanical impurities, which are dispersed in the coal tar as fine particles or flocculent substances, whose presence makes it very difficult to treat coal tar using the existing mature techniques 20. Therefore, the application of coal tar resources remains in three aspects of combustion, extraction of chemical products from coal tar light components and producing vehicle fuel by the hydrogenation of coal tar light components 21-25, which makes a large amount of heavy components of coal tar unable to be effectively utilized and causes serious environmental problems. The sulfide metal catalyst used in the heavy oil slurry-phase hydrocracking technology is suspended in the raw material in the form of nanoscale or micron solids during the reaction, so the reaction system can accommodate a small amount of solids. Thus, Deng 26 and Wu 27 studied the coal tar slurry-phase hydrocracking reaction process of coal tar atmospheric residue and found that 3


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although the asphaltene content in coal tar was much higher than that of petroleum-based raw materials, the coal tar slurry-phase hydrocracking reaction had a lower coke yield. They believed that the sulfide catalyst particles, micron-sized carbonaceous particles and inorganic minerals in the coal tar atmospheric residue could provide independent condensation nuclear or growth nuclear for macromolecular radicals, which promotes the dispersion of the spherical coke precursor, inhibits the coalescence of the coke precursor, and reduces the formation of coke. Du 28, 29 found that TI in coal tar contained organic aromatic compounds and inorganic minerals, and Fe in inorganic minerals and catalyst metals had a certain synergistic effect, which promotes the ability of hydrogenation and inhibiting coking of the catalyst. Du 30 also found that the asphaltene of coal tar was mainly composed of aromatic rings with oxygen functional groups, and the asphaltene after the slurry-phase hydrocracking reaction possessed a higher aromaticity and shorter aliphatic chains by the eﬀective cracking of carbonyl groups, pyrrolic nitrogen, and alkyl sulfides in the coal tar asphaltene. Considering these reaction characteristics, coal tar can mix with inferior heavy oil for the slurry-phase hydrocracking reaction, but the lack of systematic investigation in previous studies blocks further application of this mixing strategy. Hence, in this paper, the stability of a mixed feedstock of coal tar and petroleum-based heavy oil, the product distribution of the mixed raw material slurry-phase hydrocracking (MSH) reaction, and the structural characteristics of asphaltene and coke in the corefining system were studied to demonstrate the feasibility of the coal tar/heavy oil mixed feedstock for the slurry-phase hydrocracking reaction and investigate whether the mixing of coal tar and heavy oil could improve the efficiency of the slurry-phase hydrocracking reaction, i.e., to obtain a larger raw material conversion rate based on the appropriate coke yield. 2. Experimental Section 2.1. Raw Materials 2.1.1 Feedstock oil and catalyst 4


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A petroleum-based atmospheric residue from Merey (MRAR) and a medium/low temperature coal tar atmospheric residue (CTAR) obtained from Shaanxi Province were used as the materials in this study, and their properties were shown in Table 1. The catalyst was a mixture of laboratory -made oil-soluble molybdenum (Mo) naphthenate and nickel (Ni) naphthenate with a mass ratio of Mo to Ni of 3:2. The molybdenum naphthenate and nickel naphthenate were prepared by some raw materials, such as molybdenum oxide, nickel sulfate, sodium hydroxide, naphthenic acid and oxalic acid, through the acid-base neutralization reaction and metathesis reaction 31. Table 1. Properties of MRAR and CTAR Properties

MRAR

CTAR

Density, 20 °C, g·cm-3

0.9976

1.0210

Carbon residue*, wt%

15.33

17.96

Ash, wt%

0.10

0.14

C, wt%

84.82

84.67

H, wt%

10.87

7.84

S, wt%

2.89

0.22

N, wt%

0.63

0.87

H/C atomic ratio

1.54

1.11

Ni, μg·g-1

65.2

27.7

V, μg·g-1

443.0

28.2

Fe, μg·g-1

21.2

393.1

Ca, μg·g-1

15.2

226.4

Saturated, wt%

31.49

14.57

Aromatics, wt%

39.44

35.62

5


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Resin, wt%

12.06

20.35

C7-asphaltene, wt%

9.29

29.46

TI, wt%

Nil

2.84

* Conradson carbon residue test, ASTM D189-76 As seen from Table 1, MRAR has the characteristics of high density, high carbon residue content, high asphaltene content and high metal content, showing it is a heavy oil with poor qualities that is difficult to process. However, compared with MRAR, CTAR contains TI, and has higher density, lower H/C atomic ratio, and higher contents of asphaltene, carbon residue, Fe and Ca. The asphaltene content and TI content of CTAR are as high as 29.46 wt% and 2.84 wt% respectively, which are much larger than that of MRAR, indicating CTAR is also a kind of inferior feedstock oil. 2.1.2 Preparation of mixed raw material Appropriate amounts of MRAR and CTAR were weighed respectively and mixed in a stirred tank, stirring at 120 °C and 350 rpm for 1 h. The mass ratios of CTAR and MRAR are 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20 and 90:10 respectively. And different mixed raw materials are labeled according to the mass fraction of CTAR, for example, the mixed raw material containing 10 wt% CTAR is labeled as CTAR-10. 2.2 Reaction and analysis 2.2.1 MSH reaction About 150 g mixed raw material was put into a 0.5 L autoclave with 150 μg·g-1 catalyst expressed as metal atom, and 300 μg·g-1 sulfur. After pressure testing to ensure that the reactor is sealed and the air in the reactor is exhausted, an initial pressure of reactor was raised to a certain value with H2, and then the temperature rise was started after recording the temperature and initial pressure. After the system temperature reached 100 °C, the stirring was started at 800 rpm and continued until the end of the reaction. The reaction of MSH was carried out for 1 h at a certain temperature and a certain pressure. 6


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The reaction temperatures were 410 °C, 420 °C, 430 °C, 440 °C and 450 °C, and the initial pressure were 6MPa, 8MPa, 9MPa, 10MPa and 12MPa, which were the reaction parameters to be investigated in this study. When the reaction was completed, the reactor was immediately quenched by cold water to terminate the reaction. When the autoclave was cooled for 4 h and the temperature and pressure inside reactor remained unchanged, a small amount of gas was taken out for gas chromatography analysis to obtain a mole fraction of unreacted H2 after recording the temperature and pressure of the gas in the reactor, and then all of the gas was discharged out of the reactor. It is approximated that the gas volume before and after reaction remains unchanged (350 ml), which is the difference between the volume of the reactor (about 500 ml) and the volume of the raw material (about 150 ml). Based on the recorded temperature and pressure of gas, the gas volume in the autoclave before and after reaction was approximately converted into a standard state gas volume by ideal gas state equation. And then the mass of raw material H2 before the reaction could be calculated, and the mass of unreacted H2 in gaseous product after the reaction can also be calculated in combination with the results of gas chromatography analysis. Then the mass of H2 consumed during the reaction can be obtained by subtracting the mass of unreacted H2 from the mass of raw material H2. The liquid product and solid product were collected and weighted, and then were distilled to get light oil (350 °C fractions) which contained atmospheric residue (AR) and solid product. The atmospheric residue fraction was extracted by toluene to obtain toluene-insoluble solid which was dried and weighted to get the solid product containing formed coke and TI of CTAR, and the AR product was obtained by removing the solvent toluene from the toluene-soluble, which was then used to detect the contents of saturated, aromatics, resin and asphaltene (SARA) 32. The mass of formed coke was calculated by subtracting the mass of TI of CTAR from the mass of solid product. The mass of gaseous products is calculated by the 7


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subtraction method, i.e. the mass of raw material and consumed H2 minus the mass of light oil, AR and coke. The mass ratios of consumed H2 and products are calculated by formula (1), and the raw material conversion rate is calculated by 100 minus the yield of AR product, %. 𝑚p

𝑟p = 𝑚𝑟 × 100%

(1)

In formula (1), rp is the mass ratio of consumed H2 and each product, wt%; mp is the mass of consumed H2 and each product, g; mr is the mass of raw material, g. 2.2.2 Analysis and characterization The gas was analyzed using a gas chromatograph (GC HP5890 SERIES). An Olympus BH-2 optical microscope was used to observe the micelle aggregation in MARA, CTAR and the mixed raw material at room temperature. Elemental analyses were performed using a Vario EL-III elemental analyzer, and the mean relative molecular mass was determined by a vapor pressure osmometry (VPO) Knauer tester. The average molecular structural parameters of asphaltene were calculated through the 1H-NMR

spectra obtained using a Bruker AVANCE 2500 spectrometer with a spectral width of 500

MHz, CDCl3 as the solvent, and tetramethy silane (TMS) as the internal standard. The thermal behavior of the coke products was investigated using the thermal gravimetric analysis from mass changes from ambient temperature to 800°C with a heating rate of 10°C·min-1 in nitrogen. Scanning electron microscopy (SEM) was performed using a JSM-7500F field emission scanning electron microscope, and the samples for the SEM analysis were prepared by grinding and gold spraying. The value of colloidal instability index (CII) 33-36 of system is calculated by formula (2). 𝑚asp. + 𝑚sat.

CII = 𝑚res. + 𝑚aro.

(2)

In formula (2), masp., msat., mres. and maro. are mass ratio of asphaltene, saturated, resin and aromatics respectively, wt%. As a colloidal system, the equilibrium relationship between the components of residue determines the stability of the system. The smaller the CII value, the more 8


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balanced the ratio of resin and asphaltene fractions to saturated and aromatic fractions in the system, and the more stable the colloidal system. During the data analysis process, the difference between experimental value (VE) and theoretical weighted value (VT) is calculated by formula (3). Difference between VE and VT =

VE ― VT VT

× 100%

(3)

The micelle size of asphaltene was detected by small angle X-ray scattering (SAXS) on a SAXSess mc2 small angle X-ray scatterometer with an X-ray tube as light source using a Cu target with 0.1546 nm wavelength, 40 kV operating voltage and 50 mA operating current. During the process of testing sample, the toluene insoluble matter and n-heptane insoluble matter were respectively removed from the sample to obtain the coke-free system and the asphaltene-free system, and the SAXS spectra of the two systems were determined respectively. The SAXS spectrum of the asphaltene-free system was subtracted from the SAXS spectrum of the coke-free system as background to obtain asphaltene micelle data. The SAXSquant software was used to normalize and defuzzify the data. The average radius of asphaltene aggregates was estimated by Guinier program, and then the micelle size of asphaltene was calculated by GIFT software. 3. Results and discussion 3.1 Stability of the mixed raw material Figure 1 shows the optical microscope photos of different mixed raw materials. The oil phase of MRAR is uniform and has no visible impurities because MRAR is a stable colloidal system, where asphaltene, which acts as a dispersed phase, is stably present in the dispersion medium 37, 38. The oil phase of CTAR is distributed with particles with clear edges and different sizes, which are derived from the coal dry distillation process and mainly composed of coke and inorganic minerals

15.

Furthermore, when CTAR is mixed into the MRAR, flocs appear in the system. When the content of CTAR does not exceed 40 wt% (Figure 1: CTAR-10, CTAR-30 and CTAR-40), the amount of flocs 9


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produced in the mixed raw material is large, and the particle size is small. When the content of CTAR increases to 70 wt% (Figure 1: CTAR-50 and CTAR-70), the amount of flocs in the mixed raw material gradually decreases, but the particle size gradually increases. When the CTAR content continues to increase (Figure 1: CTAR-80 and CTAR-90), a large amount of cross-linking occurs in the flocs of mixed raw material. Studies showed that the floc formed in the mixed system was a direct external manifestation of the aggregation of the asphaltene micelles 39, so the results in Figure 1 indicate that when the mass fraction of coal tar in the mixed raw material increases, the phase separation behavior of the mixed system gradually increases. The reason may be that during the mixing of CTAR and MRAR, a new colloidal system is formed, and the polar components in the two feedstocks also interact to form new asphaltene micelles, whose solubility in the system gradually deteriorates and results in the micelle aggregation as shown in Figure 1. In addition, solid particles in CTAR can provide an aggregation center for asphaltene micelles 27, 28.

10


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Figure 1. Optical microscope photo of the mixed raw material (100 times) The colloidal stability of heavy oil depends on the equilibrium state of the peptization capacity between the dispersed phase (asphaltene) and dispersion medium (colloid, aromatic and saturated) in heavy oil

40, 41.

As shown in Figure 2, to further prove the colloidal stability characteristics of the

mixed raw material, the SARA contents of the mixed raw material were determined, and the theoretical weighted contents of SARA components were also calculated for comparison. Furthermore, the CII values of different mixed raw materials calculated according to formula (1) are shown in Figure 2. CII value

1.0

0

20

40

60

80

100

0.9 0.8 0.7 0.6 30

C7-asphaltene (1)

24

Content of SARA component, wt%

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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18

(2)

12 30

Resin

(2)

27 24

(1)

21 40

Aromatics

(2)

35

(1)

30 25 30

Saturated

(1)

25

(2)

20 15 0

20

40

60

80

100

Mass fraction of CTAR, wt%

Figure 2. SARA content and CII value of the mixed raw material: (1) VE; (2) VT In Figure 2, affected by the saturated and aromatics contents of CTAR, the saturated content of mixed raw material increases, and the aromatics content decreases when the CTAR content increases. Moreover, VEs of the saturated content and aromatics content is basically consistent with their VTs, which indicates that the mixing of CTAR and MRAR does not significantly affect the saturated and aromatic hydrocarbons in the mixed system. However, when the content of CTAR 11


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increase, VE of the resin content was smaller than VT, and VE of the asphaltene content was bigger than VT. Furthermore, the difference between VE and VT of resin content and asphaltene content in Figure 3 can visually show that the change trend of the resin reduction is basically consistent with the change trend of the asphaltene increase. Thus, there should be some interaction between the resin and asphaltene of MRAR and CTAR, which would transform the resin component into an asphaltene-like substance 42 and lead to an increase in the asphaltene content of the system and a decrease in the resin content, thus destroying the colloidal stability of the system to produce some flocs, as shown in Figure 1.

Difference between VE and VT , %

14

-14

C7-asphaltene content Resin content

12

-12

10

-10

8

-8

6

-6

4

-4

2

-2

0

0 0

20

40

60

80

Difference between VE and VT , %

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 12 of 34

100


Figure 3. Differences between VE and VT of the resin content and asphaltene content The CII values of different mixed raw materials in Figure 2 also prove this phenomenon. The MRAR has a smaller CII value than the CTAR, i.e., the colloidal stability of MRAR is better than CTAR, probably because CTAR contains some solid impurities. Adding only 10 wt% CTAR into MRAR can increase the CII value rapidly, which indicates that the colloidal stability of the mixed system is degraded. When the CTAR content does not exceed 40 wt%, the increase in CTAR content causes a slow increase in CII value with a small amplitude, which shows that the stability of the mixed system is destroyed, but it is not very serious at this stage. When the CTAR content exceeds 40 wt% and continues to increase, the CII value starts to significantly increase, which indicates that the degree of damage to the stability of the mixed system is increased, and the CII value reaches the maximum 12


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when the CTAR content is 70 wt%, i.e., the colloid stability is the worst at this time. As the CTAR content continues to increase, the CII value decreases, which indicates that the colloidal stability of the mixed system at this stage has improved. The reason for this phenomenon may be that at the stage of a small amount of CTAR in the mixed raw material (not more than 40 wt%), the resin and asphaltene components of CTAR with poor stability hardly affect the resin and asphaltene component of MRAR, and the system of mixed raw material can accommodate the small amount of asphaltene-like substances produced in this process. Thus, the colloidal stability of the system slightly changes at this stage, less flocs precipitate from the system (Figure 1: CTAR-10~CTAR-40), and the decrease in resin content and increase in asphaltene content are not large. When the CTAR content in the mixed raw material continues to increase, the amount of produced asphaltene-like substances greatly increases and exceeds the system capacity. Thus, a large amount of flocs is precipitated from the system, which rapidly decreases the stability of the system, and the decrease in resin content and increase in asphaltene content also significantly increase. When the CTAR content in a mixed raw material exceeds 70 wt%, the main body of the system is CTAR, so reducing the MRAR content in the mixed raw material (i.e., increasing the CTAR content) can reduce the damage of MRAR to the colloidal stability of CTAR and improve the dispersion state of impurities in mixed raw materials (Figure 1: CTAR-80 and CTAR-90), which improves the colloidal stability of mixed system at this stage. In summary, when CTAR and MRAR are directly mixed, the colloidal stability of the mixed raw material will be damaged to varying degrees. When the CTAR content of the mixed raw material does not exceed 40 wt%, the system is relatively stable. After the CTAR exceeds 40 wt%, the colloidal stability of the mixed system deteriorates, and a large amount of flocs is precipitated. The reasons for the change in colloidal stability of the MRAR and CTAR mixed systems; the methods to improve the stability of a mixed raw material require more in-depth research in the later stage. 13


Energy & Fuels

3.2 Reaction behavior of MSH 3.2.1 Product distribution and system colloidal stability of MSH The effects of the CTAR content on the product distribution of MSH are shown in Figure 4. 0

20

40

60

80

100

H2 consumption (1)

0.8 0.7

(2)

0.6

Coke

3

H2 consumption and yield of product, wt%

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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(1)

2 1

(2)

56

AR (2)

48 40 64

(1)

Gas+Light oil

56

(1)

(2)

48 56

Light oil (1)

48

(2)

40 10

Gas

8

(2) (1)

6 0

20

40

60

80

100


Figure 4. Effects of the CTAR content on the product distribution of MSH (initial H2 pressure is 9 MPa and reaction temperature is 430 °C): (1) VE; (2) VT In Figure 4, when a small amount of CTAR was added to the MRAR (CTAR-10), the gas yield and AR yield decreased, the H2 consumption, light oil yield and coke yield increased, and the total yield of gas and light oil increased. When the CTAR content in the mixed raw materials continued to increase, the H2 consumption and gas yield continuously increased, the yield of AR product first decreased and subsequently increased, and the light oil yield, coke yield, and total yield of gas and light oil first increased and subsequently decreased. All extreme values appeared when the CTAR content was 30 wt% (CTAR-30). At that time, the gas yield was 8.08 wt%, the light oil yield was 51.56 wt%, the AR yield was 38.40 wt%, and the coke yield was 2.67 wt%. 14


Page 15 of 34

In addition, compared with VT of the product distribution, the MSH reaction system could obtain higher light oil yield under moderate coke formation and higher H2 consumption, which indicates that the addition of CTAR can increase the degree of hydroconversion and improve the product distribution of the MSH reaction. Moreover, under identical reaction conditions, CTAR-30 can produce more light oil and had higher conversion rate of raw material than other mixed raw materials. The reason may be that CTAR-30 can maintain better colloidal stability during the reaction process, which makes the asphaltene micelles in the system more susceptible to the transformation reaction, obtains higher light oil yield and improves product distribution. To prove this point, the conversion rate of asphaltene and the CII value after MSH reactions were measured, and the results are shown in Figure 5.

Conversion rate of C7-asphaltene, %

80

0

2

4

6

8

10

Before reaction After reaction

70

1.0

60 0.8

50 40

0.6 30 20

CII value

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

Energy & Fuels

0.4

10 0

0

20

40

60

80

100

0.2


Figure 5. Conversion rate of asphaltene and CII value after the MSH reaction (initial H2 pressure is 9 MPa and reaction temperature is 430 °C) As shown in Figure 5, with the increase in CTAR content, the asphaltene conversion rate in the MSH reaction system first increased and subsequently decreased. In the range of CTAR content of 2050 wt%, the asphaltene conversion rate was relatively high and did not significantly change. When the mass fraction of CTAR exceeded 50 wt%, as the CTAR content continued to increase, the asphaltene conversion rate significantly decreased. Figure 5 also shows that when the CTAR content increased, the CII value after the MSH reaction first decreased and subsequently increased, and the peak appeared 15


Energy & Fuels

when the CTAR content was 30 wt%, which suggests that with the increase in CTAR content in the mixed raw material, the colloidal stability of the reaction system was first enhanced and subsequently weakened. When the mixed raw material was CTAR-30, the interaction between MRAR and CTAR was in a relatively balanced state, which was more conducive to the MSH reaction. In addition, the CII value after the MSH reaction was significantly smaller than the CII value of the mixed raw material, which indicates that the slurry-phase hydrocracking reaction can significantly improve the stability of the mixed raw material reaction system. When the CTAR content of the mixed raw material is approximately 30 wt%, the highest conversion rate of asphaltene and best colloidal stability of the reaction system can explain the characteristics of product distribution in Figure 4, which is consistent with the previous inference. 3.2.2 Effects of the reaction temperature and initial H2 pressure on the product distribution The effect of the reaction temperature on the product distribution of MSH reaction was studied with CTAR-30 as the representative mixed raw material. The slurry-phase hydrocracking reactions of MRAR and CTAR under identical reaction conditions were performed for comparison. The results are shown in Figure 6. ℃ 0

2

(a) 1.0

4

6

8

10 10

MRAR CTAR-30 CTAR

70

0

2

(b) 60

8

0.8 6 0.6 4 0.4

Yield of product, wt%

1.2

H2 consumption, wt%

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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4

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MRAR CTAR-30 CTAR

8

50 6

40 30

4

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0.2

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Reaction temperature, 。C

450

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420

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440

。 Reaction temperature, C

450

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Page 17 of 34

Energy & Fuels 2

4

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70

8

(c)

MRAR CTAR-30 CTAR

60


10 10

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8 6

6 40 4

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(d)

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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

4

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MRAR CTAR-30 CTAR

8

6 4 4 2 2

2

10 410

420

430

440


0

0

450

410

420

430

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450

0

Figure 6. Effect of the reaction temperature on the product distribution of the MSH reaction (Mass ratio of MRAR to CTAR is 70:30 and the initial H2 pressure is 9 MPa): (a) H2 consumption; (b) yield of gas and light oil; (c) yield of AR product; (d) yield of coke Figure 6 shows that in the three reaction systems of MRAR, CTAR-30 and CTAR, when the reaction temperature increased, the H2 consumption, total yield of gas and light oil, and coke yield increased, while the yield of AR product decreased, which indicates that the increase in reaction temperature can promote the cracking and hydrogenation of heavy oil molecules and improve the conversion rate of raw material and H2 consumption. Meanwhile, the elevated temperature can further destroy the colloidal stability of heavy oil, promote the polycondensation of asphaltene to form macromolecular fused aromatic hydrocarbons, and result in an increase in coke amount 43. Figure 6 also shows that the H2 consumption and total yield of gas and light oil obtained from the CTAR reaction were higher than that from the MRAR reaction, while the coke yield was smaller, which is basically consistent with the results in the literature 26. The reason is that the weaker colloidal stability of CTAR makes it more susceptible to the reaction than MRAR, and compared with the relatively stable MRAR asphaltene micelles

44,

coal tar has asphaltene with a higher degree of

aromaticity, more heteroatoms and heterocycles, more and shorter branches, lower average relative molecular weight and weaker association

18, 30,

and some TI, which can promote the hydrogenation

reaction and inhibit the coke formation 26-28. Thus, compared with petroleum-based heavy oil, coal tar 17


Energy & Fuels

asphaltene is not easy to polycondense at high temperature to produce a carbonaceous mesophase 45 and subsequently form coke. Theoretically, the yield of various products obtained by the MSH reaction should be between the yield of the reaction products of MRAR and CTAR. As shown in Figure 6, the product yield of CTAR30 at a reaction temperature below 430°C was indeed between the product yield of MRAR and CTAR; however, when the reaction temperature reaches 430 °C, although the H2 consumption remained between that of MRAR and CTAR, the raw material conversion rate and total yield of gas and light oil of CTAR-30 were higher than that of MRAR and CTAR, which indicates a compounding reaction effect between MRAR and CTAR at a higher temperature in the mixed raw material. The reason may be that the addition of coal tar changes the colloidal chemical characteristics of the mixing system, which is beneficial to the hydrogen reaction and can improve the transformation depth. In addition, the TI in coal tar can act as the coking center to inhibit the coke formation, and the inorganic minerals in TI have a catalytic effect, which can promote the hydrogenation abilities of the catalyst and restrain the coke formation 27-29. 0

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(a) 1.0

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10 10

65

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H2 consumption, wt%

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 18 of 34

0.6

0.4

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MRAR CTAR-30 CTAR

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Initial H2 pressure, MPa

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Page 19 of 34 60

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55


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

Energy & Fuels

50

10 10

MRAR CTAR-30 CTAR

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6 45

4 40

35

30

6

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10

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6

2

2

1

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Figure 7. Effect of the reaction pressure on the product distribution of the MSH reaction (Mass ratio of MRAR to CTAR is 70:30 and the reaction temperature is 430 °C): (a) H2 consumption; (b) yield of gas and light oil; (c) yield of AR product; (d) yield of coke As shown in Figure 7, in the three reaction systems of MRAR, CTAR and CTAR-30, increasing H2 pressure reduced the total yield of gas and light oil, raw material conversion rate and coke yield but increased the H2 consumption, which indicates that the higher H2 pressure can effectively restrain the coke formation but also inhibit the cracking reaction. Within the pressure level range of this study, relative to a high pressure, the effect of increasing the reaction pressure at low pressure on the reaction effect was more obvious. The reason is that in the heavy oil slurry-phase hydrocracking reaction, increasing H2 pressure can promote the formation of more activated hydrogen in the active center of the catalyst metal, which is beneficial to the quenching of molecular free radicals such as asphaltene, inhibits the condensation of molecules and suppresses the coke formation. However, increasing H2 pressure can also inhibit the cracking reaction of molecules, which decreases the light oil yield and conversion rate of the raw material. Therefore, the increase in H2 pressure inhibits the coke formation of the heavy oil slurry-phase hydrocracking reaction and inhibits the depth of hydrogen conversion. In addition, under all pressure conditions studied, the total yield of gas and light oil, raw material conversion rate and coke yield of CTAR-30 were greater than the corresponding values of MRAR and CTAR, but the H2 consumption of CTAR-30 is between that of MRAR and CTAR, which is consistent 19


Energy & Fuels

with the result at the reaction temperature of 430°C in Figure 6. 3.3 Properties of coke and asphaltene during the MSH reaction The process of coke formation from asphaltene macromolecules is an important reaction characteristic of heavy oil slurry-phase hydrocracking. The coke yield and asphaltene content of the mixed raw material before and after the reaction are shown in Figure 8.

Coke yield, wt%

3.0

0

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10 30


2.5

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Content of C7-asphaltene, wt%

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Page 20 of 34

0


Figure 8. Coke yield and asphaltene content during the MSH reaction (The initial H2 pressure is 9 MPa and reaction temperature is 430 °C) As shown in Figure 4, VE of coke yield during the MSH reaction was larger than VT, which indicates a synergy between MRAR and CTAR. Theoretically, because the CTAR asphaltene content was much higher than MRAR asphaltene, the asphaltene content of the mixed raw material should gradually increase with the increase in CTAR content. However, in Figure 8, with the increase in CTAR content, the coke yield of the mixed system first increased and subsequently decreased, while the asphaltene content first decreased and subsequently increased. When MRAR dominated the mixed feedstock (the CTAR content was less than 50 wt%), with the increase in CTAR content (from CTAR10 to CTAR-50), the asphaltene content of the mixed system after the reaction did not significantly change, but the coke yield significantly increased. Thus, the addition of CTAR asphaltene can promote the association of asphaltene in the mixed system, and the asphaltene in the mixed system easily 20


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Energy & Fuels

polycondensed into larger molecules and converted to coke, which increases the coke yield but decreases the changes in asphaltene content. When CTAR dominated the mixed raw material (the MRAR content is less than 50 wt%), with the increase in CTAR content (CTAR-50~CTAR-90), the smaller average molecular weight and weaker association ability of CTAR asphaltene made the quality of asphaltene converted to coke much smaller than the increase in asphaltene quality caused by the addition of CTAR. Thus, the asphaltene content of the mixed system increased, but the coke yield decreased. 3.3.1 Structure and association of asphaltene Asphaltene is the most complex polar component in heavy oil

46,

whose peptization state

determines the coking tendency of the reaction system. A good peptization state makes asphaltene free radicals easier to quench by colliding with the surrounding small molecule free radicals, reduces the chance of further condensation between asphaltene free radicals, and inhibits coking 47. In addition, the association of asphaltene determines its aggregation tendency; the strong association makes the asphaltene easy to aggregate and form a second liquid phase, which evolves into coke 48. When the heavy raw material is subject to the slurry-phase hydrocracking reaction, the cracking and condensation reactions are simultaneously performed. A portion of the product has low mean relative molecular mass and low aromaticity, and another portion of the product has high molecular weight and high aromaticity, which destroys the colloidal stability of the system and causes the association and polycondensation of asphaltene free radicals to produce coke 49. In other words, the asphaltene in the MSH reaction system acts as the coke precursor, and the degree of difficulty of the asphaltene polycondensation to form coke determines the conversion depth that the reaction system can achieve 50.

Therefore, the structural properties of asphaltene directly affect the efficiency of the co-refining

reaction 51. The structure parameters of asphaltene

52, 53

before and after the MSH reaction are shown in

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

Page 22 of 34

Figure 9. Before the reaction, with the increase in CTAR content, the aromaticity of asphaltene in the mixed raw material showed an upward trend, while the mean relative molecular mass and ring number of asphaltene showed a downward trend because of the properties of CTAR asphaltene. CTAR asphaltene has higher aromaticity but smaller mean relative molecular mass and fewer rings than MRAR asphaltene. Compared with asphaltene in the raw material, after the reaction, the aromaticity, aromatic ring number and mean relative molecular mass of asphaltene increased, and the number of asphaltene naphthenic rings decreased in the range of CTAR content of 20-60 wt%. Hence, asphaltene experiences a significant condensation reaction during the slurry-phase hydrocracking reaction, which causes the increase in number of aromatic rings, aromaticity and mean relative molecular mass of asphaltene. Simultaneously, the moderate ring-opening and dehydroaromatization reactions of naphthenic rings occurred at high temperature, which slightly decreased the number of asphaltene naphthenic rings. After the reaction, when the CTAR content did not exceed 50 wt%, the aromaticity of asphaltene slightly increased as the CTAR content increased, and the number of asphaltene aromatic rings and mean relative molecular mass of asphaltene significantly decreased. After the reaction, when the CTAR content was 50-70 wt%, the increase in aromaticity of asphaltene and decrease in aromatic ring number of asphaltene tended to increase, and the downward trend of the mean relative molecular mass of asphaltene decreased. When the CTAR content exceeded 70 wt%, after the reaction, the rising tendency of the asphaltene aromaticity and decreasing tendency of the asphaltene aromatic ring number tended to be flat. The three stages of the change in asphaltene properties after the reaction are similar to the three stages of the changes in CII value in Figure 2 and coke yield in Figure 8.

22


Page 23 of 34

Energy & Fuels 0.85

2

4

6

8

10 10

2500

0

2

4

6

0.75 6

0.70 0.65

4

0.60

(a)


0.55

2

Mean relative molecular mass

8

8

10 10


(b)

0.80

Aromaticity (fA)

2000

8

6 1500 4 1000 2

500

0.50

0

20

40

60

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100

0

20

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60

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Mass fraction of CTAR, wt% 2

4

40

(c)

6

8

10 10

Before reaction Total rings per average molecule (RT)

35

Aromatic rings per average molecule (RA)

8

Naphthenic rings per average molecule (RN)

30

After reaction

Ring number

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

0

25

RT

RA

6

RN

20 4 15 10

2

5 0

0

20

40

60

80

100

0


Figure 9. Structure parameters of asphaltene before and after the MSH reaction (The initial H2 pressure is 9 MPa and reaction temperature is 430 °C): (a) Aromaticity (fA); (b) Mean relative molecular mass; (c) Ring number The micelle sizes of asphaltene before and after the MSH reaction are shown in Figure 10. The MRAR asphaltene has a micelle size of approximately 9 nm, and the CTAR asphaltene has a micelle size of approximately 5 nm. With the increase in CTAR content in the mixed raw material, the micelle size of asphaltene in the mixed raw material gradually decreased, but the CTAR content of 0-70 wt% had a smaller decreasing trend than the CTAR content of 70-100 wt%. Before the reaction, the change in asphaltene micelle sizes in the mixed raw material is similar to the change trend of asphaltene content in the mixed raw material in Figure 8. VEs of both are higher than VTs, and both of them change when the raw material is CTAR-70. In addition, the micelle size of asphaltene after the reaction is larger than that in the raw material. 23


Energy & Fuels

When the CTAR content increased from 0 wt% to 30 wt%, the micelle size of asphaltene gradually increased after the reaction, reaching the highest value of approximately 16 nm when the mixed raw material was CTAT-30. When the CTAR content continued to increase, the asphaltene micelle size began to slowly decrease until the CTAR content was 70 wt%; when the CTAR content exceeded 70 wt%, the decreasing tendency of the asphaltene micelle size rapidly increased. The change trend of the micelle size of asphaltene after the reaction is consistent with the change trend of the coke yield in Figure 8, which indicates the association of asphaltene with coke formation. It is speculated from the above analysis that CTAR asphaltene will destroy the stable peptization relationship between MRAR asphaltene and resin, which worsens the colloidal stability of the mixed system but simultaneously makes the heavy components of the mixed system more likely to react; thus, the mixed system has higher coke yield and feedstock conversion than the theoretical values. 18


16

Micelle size of asphaltene, nm

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 24 of 34

14 12 10

(1)

8 6 4

(2) 0

20

40

60

80

100


Figure 10. Micelle size of asphaltene before and after the MSH reaction (The initial H2 pressure is 9 MPa and reaction temperature is 430 °C): (1) VE; (2) VT 3.3.2 Composition and morphology of coke To further understand the composition characteristics of coke during the co-refining reaction, thermogravimetric analysis was performed on coke produced by 5 raw materials: MRAR, CTAR-30, CTAR-50, CTAR-70 and CTAR, as shown in Figure 11. The 5 coke products have obvious weight 24


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Energy & Fuels

loss in the range of 200~500°C. Above 500°C, the weight loss curve tends to be gentle, but the degree of weight loss is notably different, which indicates that the 5 coke products contain similar types of volatile or pyrolyzable organic components but with different contents. The pyrolyzable organic matter in the coke produced by MRAR is obviously smaller than the coke produced by CTAR, which indicates that the condensation degree of MRAR asphaltene in the reaction process is higher than that of CTAR asphaltene, resulting in a greater degree of carbonization and stronger thermal stability of the formed coke. Considering the physical blending, the content of pyrolyzable organic matter in the coke produced by the mixed raw material should be between the content of organic matter in the coke produced by MRAR and CTAR, i.e., higher than MRAR and lower than CTAR. However, as shown in Figure 11, the content of organic matter in coke produced by CTAR30 was lower than that of the coke produced by MRAR, which indicates that the addition of a small amount of CTAR asphaltene can deepen the association of MRAR asphaltene and promote the coke formation. When the content of CTAR in the mixed raw material increases, the content of pyrolyzable organic matter in the coke product also increases, which indicates that the thermal stability of the formed coke deteriorates. Because the mean relative molecular mass of CTAR asphaltene is small, the degree of intermolecular association is weak, and the degree of coke condensation is low 54, when the content of CTAR asphaltene in the mixed raw material gradually increases, and the asphaltene properties of the mixed system gradually approaches the CTAR asphaltene. Hence, the associating ability of asphaltenes is weakened, the amount of coke decreases, and the carbonization degree of coke decreases.

25


Energy & Fuels

100

90

Mass weight, wt%

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 26 of 34

80

CTAR-30

70

CTAR-50 MRAR CTAR-70 CTAR

60

50

100

200

300

400

500

600

700

800

900

1000

Thermogravimetric temperature, ℃

Figure 11. TG curves of coke produced by different raw materials (The initial H2 pressure is 9 MPa and reaction temperature is 430 °C) The apparent morphology of 5 coke products is shown in Figure 12. When the CTAR mass fraction in the mixed feedstock increases, the size of the coke particles gradually decreases. Bagheri 55

found that the chemical structure of heavy oil asphaltenes was a key factor in determining the

formation and size of coke particles, but the catalyst particles would agglomerate and adsorb on the surface of the mesophase carbon microspheres to inhibit their coalescence and growth. Therefore, in the mixed system, when the content of CTAR asphaltene with a relatively small mean relative molecular mass and a weak association degree gradually increases, the coke particles are also relatively small. Simultaneously, with the increase in CTAR mass fraction, the inorganic minerals in CTAR gradually increase, which inhibits the aggregation and growth of coke particles 28 and gradually decreases the size of coke particles.

26


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Energy & Fuels

Figure 12. SEM images of coke produced by different raw materials magnified 5k times and 20k times (The initial H2 pressure is 9 MPa and reaction temperature is 430 °C) 4. Conclusions The reaction behavior of the MRAR and CTAR mixed raw material slurry-phase hydrocracking 27


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

Page 28 of 34

was described and illustrated in this study. The results show that the addition of CTAR to MRAR can destroy the system colloidal stability, but the degree of damage is relatively low when the CTAR content is within 40 wt%, and the MSH reaction can improve the stability of system. The addition of CTAR can promote the cracking reaction and condensation reaction to obtain a high raw material conversion rate and high H2 consumption with moderate increase in coke yield. The reaction results are the best when the CTAR content is 30 wt%. Increasing the reaction temperature and decreasing reaction pressure can increase the raw material conversion rate and coke yield of the MSH reaction. Compared with asphaltene in the raw material, after the MSH reaction, the mean relative molecular mass, micelle size, fA, RA and RT of asphaltene in the mixed system increase, and RN slightly decreases. With the increase in CTAR content, the change trends of the asphaltene content and structural parameters are closely correlated to the changes in stability of the mixed raw material, product distribution of the MSH reaction and properties of coke, which indicates that the reaction behavior of MSH can be attributed to the synergy between CTAR asphaltene and MRAR asphaltene when CTAR is mixed into MRAR. References: (1) Zhang, S.; Liu, D.; Deng, W.; Que, G. A review of slurry-phase hydrocracking heavy oil technology. Energy Fuels 2007, 21(6), 3057-3062. (2) Sahu, R.; Song, B. J.; Im, J. S.; Jeon, Y.-P.; Lee, C. W. A review of recent advances in catalytic hydrocracking of heavy residues. J. Ind. Eng. Chem. 2015, 27, 12-24. (3) Calderón, C. J.; Ancheyta, J. Modeling of slurry-phase reactors for hydrocracking of heavy oils. Energy Fuels 2016, 30(4), 2525-2543. (4) Montanari, R.; Marchionna, M.; Rosi, S.; Panariti, N.; Delbianco, A. Process for the conversion of heavy charges such as heavy crude oils and distillation residues. US7691256B2, Apr. 6, 2010. (5) Rezaei, H.; Ardakani, S. J.; Smith, K. J. Comparison of MoS2 catalysts prepared from Mo-micelle 28


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and Mo-octoate precursors for hydroconversion of Cold Lake vacuum residue: catalyst activity, coke properties and catalyst recycle. Energy Fuels 2012, 26(5), 2768-2778. (6) Quitian, A.; Leyva, C.; Ramírez, S.; Ancheyta, J. Exploratory study for the upgrading of transport properties of heavy oil by slurry-phase hydrocracking. Energy Fuels 2015, 29(1), 9-15. (7) Deng, W.; Lu, J.; Li, C. Hydrogenation behavior of bicyclic aromatic hydrocarbons in the presence of a dispersed catalyst. Energy Fuels 2015, 29(9), 5600-5608. (8) Quitian, A.; Ancheyta, J. Experimental methods for developing kinetic models for hydroracking reactions with slurry-phase catalyst using batch reactors. Energy Fuels 2016, 30(6), 4419-4437. (9) Quitian, A.; Ancheyta, J. Characterization of upgraded oil fractions obtained by slurry-phase hydrocracking at low-severity conditions using analytical and ore catalyst. Energy Fuels 2017, 31(9), 9162-9178. (10) Meng, Z.; Yang, S.; Yang, T.; Guo, R. Study on stability of vacuum residue blending coal tar and hydrocracking of mixture. Pet. Process. Petroche. 2014, 45(5), 25-28. (11) Stratiev, D. S.; Russell, C. A.; Sharpe, R.; Shishkova, I. K.; Dinkov, R. K.; Marinov, I. M.; Petkova, N. B.; Mitkova, M.; Botev, T.; Obryvalina, A. N.; Telyashev, R. G.; Stanulov, K. Investigation on sediment formation in residue thermal conversion based processes. Fuel Process. Technol. 2014, 128, 509-518. (12) Šimáček, P.; Kubička, D. Hydrocracking of petroleum vacuum distillate containing rapeseed oil: Evaluation of diesel fuel. Fuel 2010, 89(7), 1508-1513. (13) Šimáček, P.; Kubička, D.; Pospíšil, M.; Rubáš, V.; Hora, L.; Šebor, G. Fischer-Tropsch product as a co-feed for refinery hydrocracking unit. Fuel 2013, 105, 432-439. (14) Pan, N.; Cui, D.; Li, R.; Shi, Q.; Chung, K. H.; Long, H.; Li, Y.; Zhang, Y.; Zhao, S.; Xu, C. Characterization of middle-temperature gasification coal tar. Part 1: bulk properties and molecular compositions of distillates and basic fractions. Energy Fuels 2012, 26 (9), 5719-5728. 29


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(15) Han, J.; Wang, X.; Yue, J.; Gao, S.; Xu, G. Catalytic upgrading of coal pyrolysis tar over charbased catalysts. Fuel Process. Technol. 2014, 122, 98-106. (16) Dai, F.; Gao, M.; Li, C.; Xiang, S.; Zhang, S. Detailed description of coal tar hydrogenation process using the kinetic lumping approach. Energy Fuels 2011, 25 (11), 4878-4885. (17) Li, Y.; Ma, X.; Yang, R.; Zhao, W.; Liu, Y. Progress in the study of thermodynamic properties of the coal tar. Coal Chem. Ind. 2012, (6), 18-21. (18) Sun, M.; Ma, X.; Yao, Q.; Wang, R.; Ma, Y.; Feng, G.; Shang, J.; Xu, L.; Yang, Y. GC-MS and TG-FTIR study of petroleum ether extract and residue from low temperature coal tar. Energy Fuels 2011, 25 (3), 1140-1145. (19) Majumdar, D. R.; Bake, K. D.; Ratna, Y.; Pomerantz, A. E.; Mullins, O. C.; Gerken, M.; Hazendonk, P. Single-core PAHs in petroleum- and coal-derived asphaltenes: Size and distribution from solid-state NMR spectroscopy and optical absorption measurements. Energy Fuels 2016, 30(9), 6892-6906. (20) Li, D.; Liu, X.; Sun, Z.; Li, W.; Ma, W. Property and composition analysis of toluene insoluble material in coal tar. Acta Pet. Sin., Pet. Process. Sect. 2014, 30(1), 76-82. (21) Hasan, T.; Gerhard, J. I.; Hadden, R.; Rein, G. Self-sustaining smouldering combustion of coal tar for the remediation of contaminated sand: two-dimensional experiments and computational simulations. Fuel 2015, 150, 288-297. (22) Jiao, T.; Gong, M.; Zhuang, X.; Li, C.; Zhang, S. A new separation method for phenolic compounds from low-temperature coal tar with urea by complex formation. J. Ind. Eng. Chem. 2015, 29, 344-348. (23) Li, X.; Zong, Z. M.; Ma, W. W.; Cao, J. P.; Mayyas, M.; Wei, Z. H.; Li, Y.; Yan, H. L.; Wang, D.; Yang, R.; Wei, X. Y. Multifunctional and highly active Ni/microfiber attapulgite for catalytic hydroconversion of model compounds and coal tars. Fuel Process. Technol. 2015, 134, 39-45. 30


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formation and coalescence in catalytic hydroconversion of vacuum residue using a stirred hot-stage reactor. Energy Fuels 2012, 26(6), 3167-3178. Acknowledgement This work was supported by Shandong Provincial Natural Science Foundation, China (ZR2017MB026) and National Natural Science Foundation Young Investigator Grant Program of China (21106186).

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Exploratory Investigation on the Slurry-phase Hydrocracking Reaction

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