Coke removal from a deactivated industrial diesel hydrogenation

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Catalysis and Kinetics

Coke removal from a deactivated industrial diesel hydrogenation catalyst by tetralin at 300-400 °C Xinge Shi, Qingya Liu, Zhenyu Liu, Lei Shi, Wei Han, Mingfeng Li, Zhang Le, and Hong Nie Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03983 • Publication Date (Web): 30 Jan 2019 Downloaded from http://pubs.acs.org on January 31, 2019

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Coke removal from a deactivated industrial diesel hydrogenation catalyst by tetralin at

2

300-400 C

3 4

Xinge Shi a,b, Qingya Liu b, Zhenyu Liu a,*, Lei Shi b,*, Wei Han c, Mingfeng Li c, Le Zhang c, Hong

5

Nie c,*

6 7

a

Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China

8 9

b

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China

10 11

c

Sinopec Research Institute of Petroleum Processing, Beijing 100083, China

12 13

Abstract: Coke deposition on hydrotreating catalysts is one of the main reasons of deactivation.

14

The in-situ coke removal is advantageous to the off-site coke removal. This paper studies a tetralin

15

(THN) treatment of a deactivated industrial diesel hydrogenation Mo-Co-Ni/W-Al catalyst at

16

conditions similar to the operation, 300-400 C without H2. The results show that the coke on the

17

Mo sulfide sites, corresponding to 19-23% total coke, can be removed in 3 min to fully restore the

18

catalyst’s activity. The coke on the support cannot be removed. Based on the temperature

19

programmed oxidation (TPO), scanning electron microscopy (SEM), energy dispersive x-ray

20

spectroscopy (EDS) and electron spin resonance (ESR) the coke removal mechanism is discussed,

21

which includes activation of H radicals in THN by the Mo sulfide sites and hydrogenation of coke

22

by the H radicals. The minimal requirement for the coke removal is 340 C for 3 min. The side

23

reactions of THN are significant at higher temperatures and longer treatment time. The radical

24

concentration of coke on the Mo sulfide sites is similar to these of lignites and is approximately 10

25

times the coke on the catalyst support.

26 27

Key words: deactivated catalyst, coke removal, hydrogenation, tetralin, radical mechanism

28 29 30

1. Introduction The activity of hydrogenation catalysts used in petroleum refining decreases gradually in 1 / 26

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operation. One of the main reasons for the decreasing activity is the coverage of active sites of the

2

catalysts by coke1,2. Removal of the coke from deactivated hydrogenation catalysts therefor is an

3

important step to recover the catalyst activity.

4

The coke formed on a diesel hydrogenation catalyst originates mainly from the

5

macromolecular organics in the feedstock, such as the long chain aliphatic hydrocarbons, heavy

6

aromatic hydrocarbons and heteroatomic organic compounds, which adsorb on the catalyst

7

surface2,3. During the hydrogenation process, most of the macromolecular organics undergo

8

hydrogenation, isomerization and ring opening reactions that lead to the formation of lighter and

9

smaller molecules which desorb from the catalyst surface. However, some of the macromolecular

10

organic compounds undergo dehydrogenation that leads to the formation of heavier products which

11

cover the catalyst surface, including the active sites.

12

The coke formed on hydrogenation catalysts is very complex in structure and has been studied

13

by many using modern characterization methods. Hanadi et al.4 characterized the coke on a

14

deactivated industrial hydrotreating catalyst using carbon-13 nuclear magnetic resonance (13C-NMR)

15

and elemental analyzer, and showed that 89-94% carbon in the coke was aromatic carbon and the

16

average H/C molar ratio of the coke was 1-1.1. Zbuzek et al.5 analyzed the coke on a

17

hydrodesulfurization catalyst with Raman spectroscopy and showed an E22g peak of graphite at

18

1580-1600 cm-1 with intensity equal to that of the peak at 1350 cm-1, indicating the presence of

19

graphite-like structure in the coke although the graphitic character is weak. Some researchers

20

studied the coke on hydrogenation catalysts by temperature programmed oxidation (TPO)6-9 and

21

showed that most of the coke could only be oxidized at temperatures higher than 500 C, except in a

22

few cases where about 20% coke formed on an industrial diesel hydrogenation catalyst can be

23

oxidized at temperatures below 500 C10. Since the H/C molar ratio of more than 1 contradicts the

24

graphite-like structure, it seems possible that the coke formed on hydrogenation catalysts distributes

25

in different forms, i.e. some of them are more condensed with less hydrogen while some others are

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relatively less condensed with more hydrogen, which is reasonable considering the catalyst surface

27

is heterogeneous consists of at least active sites and support.

28

The current industrial methods for removing coke from deactivated catalysts are mainly

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oxidation or combustion to convert the coke to CO2 and CO. To avoid sintering of the active sites

30

(metals) at high temperatures, the oxidation conditions have to be mild. The oxidation methods 2 / 26


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employed include temperature programmed oxidation11-13, lean oxygen oxidation14, and nitrogen

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oxide oxidation15. These methods, however, have to be carried out off-site and involve shutting

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down the hydrotreating unit, unloading/loading the catalyst and regenerating the deactivated

4

catalyst in different reactors, which consequently are of high cost. Clearly, the in-situ coke removal

5

of deactivated catalysts under hydrotreating conditions is better than the off-site methods.

6

The in-situ methods for coke removal from the deactivated catalysts include thermal

7

dissolution, supercritical extraction and hydrogenation of coke13. Hanadi et al.4 treated a deactivated

8

industrial catalyst at 200 C in a N2 atmosphere with toluene, tetrahydrofuran (THF),

9

dichloromethane, pyridine and methanol, and showed about 45% (including about 30% toluene

10

soluble) coke removal in 5 min. Sagdeev et al.16 and Zhang et al.17 extracted deactivated industrial

11

catalysts with supercritical CO2 at 80 C and 15 MPa and showed 70% recovery of the catalyst’s

12

activity along with 73% recovery of the catalyst’s surface area, 86% recovery of the pore volume

13

and an increase in pore size from 1.82 to 1.87 nm. The high pressure used, however, hampers its

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application in the hydrotreating units. Marecot et al.18 treated a deactivated industrial Pt/Al2O3

15

catalyst by H2 and found that the coke can be partial converted to CH4 in 20 h at temperatures of

16

430 C and higher. The catalyst activity was fully restored with 35% coke removal. Zhao et al.19

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treated a deactivated industrial catalyst at 400 C in the presence of tetralin (THN) or hydrotreated

18

gas oil under a H2 pressure of 10 MPa and showed 73% activity recovery with 28% coke removal.

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Clearly, these studies indicate that the in-situ recovery of deactivated catalysts is effective although

20

the coke removed was not high and the operating temperature and/or pressure were somewhat

21

higher than those suitable for the hydrotreating units.

22

Chen et al. recently reported that the thermal decomposition of organics can be induced to

23

occur at a lower temperature by radicals20 and a hydrotreating catalyst can activate hydrogen in a

24

hydrogen donor solvent to promote hydrogenation of coal21, a matter similar to coke in H/C ratio

25

and rich in aromatic structure. Shi et al. showed that in co-pyrolysis of two solid organic matters,

26

the radicals generated from the early-pyrolyzing matter induced the pyrolysis of the

27

latter-pyrolyzing matter22,23. Furthermore, it has been shown recently that the coke formation in

28

thermal reactions of organic matters involves the formation of stable radicals measurable by

29

electron spin resonance (ESR) and the radical concentration is proportional to the mass of coke

30

formed24-27. These findings suggest that the coke formed on a hydrotreating catalyst may be 3 / 26


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removed by catalytic hydrogenation with hydrogen from a hydrogen donor solvent and/or by

2

induced pyrolysis with hydrogen radicals from the hydrogen donor solvent. With this consideration

3

this paper studies the reaction of coke on a deactivated diesel hydrogenation catalyst with THN at

4

340-400 C under a N2 atmosphere to explore the coke removal efficiency and mechanism.

5 6

2. Experimental section

7

2.1. Catalyst

8

The deactivated industrial catalyst (termed D-cat) was from a fixed bed diesel hydrogenation

9

unit that had been operated 30 months at 8 MPa. The gradual deactivation of the catalyst was

10

compensated by raising of the reaction temperature from 345 to 390 C, about 1.5 C/month. The

11

catalyst was treated in-situ by a light oil at 180 C under N2 purge before being unloaded from the

12

unit. The properties of the catalyst were provided by the Sinopec Research Institute of Petroleum

13

Processing of China and are listed in Table 1. Before the experiment, the D-cat was ground to less

14

than 80 mesh under N2.

15

2.2. Coke removal from D-cat

16

The hydrogen donor solvent used was THN of 98.5% pure. In each experiment, 10±0.5 mg

17

D-cat and 10±0.5 mg THN were fuse-sealed in a glass tube of 2 mm in diameter and 30 mm in

18

length after been purged with N2 for 60 s. The sample-loaded glass tubes were then inserted into a

19

furnace with 20 sample slots at 300, 320, 340, 360, 380 or 400 C. The sample reached the set

20

temperatures in less than 2 min without overshooting24. After being heated for 0.5, 1, 1.5, 2, 3, 4, 5,

21

6, 8 or 10 min, the glass tubes were removed from the furnace and cooled down to room

22

temperature. Three parallel experiments were conducted, one for the measurement of H2 formation,

23

one for the analysis of soluble matter, and one for the evaluation of catalyst activity. THN itself was

24

found reacting little under these conditions. The catalyst subjected to the above experiment is

25

extracted by CS2 and then washed by CS2 for 3 times to yield the recovered catalyst, termed as

26

R-cat.

27

2.3. Determination of hydrogen gas formed in the reaction

28

After the above mentioned reaction, the glass tube was placed in a latex tube of known volume

29

and purged with Ar at the ambient pressure. The latex tube was then isolated from the atmosphere at

30

both end by clamps and the glass tube was broken by hand to allow the gas in the glass tube to 4 / 26


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release to the latex tube. The gas composition including H2 in the latex tube was determined by a

2

GC (Agilent Technology, 7890B) and quantified using Ar as the internal standard. The GC column

3

was packed P-Q and N2 was the carrier gas. The sample size was 0.2 mL and the operating

4

conditions of GC were the injection temperature of 70 C, the column temperature of 70 C, the

5

column flow rate of 8 mL/min, and the TCD temperature of 250 C.

6

2.4. Analysis of liquid product

7

Since carbon disulfide (CS2) is a strong organic solvent and shows no signal in the FID

8

detector it was used to dissolve the reaction liquid. The detailed operation include cutting open the

9

glass tube at the top, placing it into a large glass tube (3 mm in diameter and 270 mm in length) and

10

immersing it in 0.4 ml CS2 (analytical grad, 99% pure) for 24 h for full mixing. The CS2 solution

11

was analyzed by a GC (Agilent Technology, 7890B) with a HP-5 capillary column (0.32  30 m).

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The sample size was 2 L and N2 was the carrier gas at 6 mL/min. The operating conditions were

13

auto-sampling, split ratio of 10, injection temperature of 220 C, initial column temperature of 100

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C for 1 min, column temperature ramping rate of 5 C/min, final column temperature of 220 C for

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10 min, FID temperature of 250 C. The solution usually contained THN, naphthalene (NA) and

16

decalin (DE), indicating the occurrence of Reactions 1, 2 and 3. The recovery of THN and its

17

products (molar amounts) were greater than 98%.

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+ Coke

+

Coke-H

19 20

Reaction 1. Hydrogen donation from THN to coke

21 Catalyst

+ 22 23

2 H2

Reaction 2. The catalytic dehydrogenation of THN

24 5

Catalyst

3

+

2

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Reaction 3. The catalytic disproportionation of THN to NA and DE

27 28

Apparently, all these reactions generate NA. The total amount of THN to NA in these reactions 5 / 26


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is termed as XTHN-to-NA and determined by Eq. (1). The conversion of THN to H2 in Reaction 2 is

2

termed as XTHN-to-H2 and determined by Eq. (2). The conversion of THN to DE in Reaction 3 is

3

termed as XTHN-to-DE and determined by Eq. (3), where the formation of each mole of DE forms also

4

1.5 moles of NA. Based on Eqs. (1) to (3) the conversion of THN for supplying H radicals to the

5

coke on the spent catalyst in Reaction 1, termed as XTHN-to-Coke, is determined by Eq. (4).

6

X THN-to-NA = nNA / nTHN ,Total 100%

（1）

7

X THN-to-H2 = 0.5nH 2 / nTHN ,Total 100%

（2）

8

X THN-to-DE = 2.5nDE / nTHN ,Total  100%

（3）

9

X THN-to-Coke = X THN-to-NA  X THN-to-H2  0.6 X THN-to-DE

（4）

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2.5. Determination of coke on catalyst and coke removal rate

11

The coke contents of D-Cat and R-cat were determined by quantities of CO2 formed in

12

oxidation. The operation involved placing a catalyst in a quartz tube, purging it with N2 for 2 h at 50

13

C to remove residual CS2 (the boiling point of CS2 is 46 C), replacing N2 in the quartz tube with

14

O2, sealing the quartz tube at both ends, and heating the quartz tube to 500 C for 50 min to burn the

15

coke, and quantifying the CO2 by a GC. Since the quantity of O2 in the quartz tube was far more in

16

excess of coke, all the carbon in coke was converted to CO2. The GC used was 7890B (Agilent

17

Technology) with a packed P-Q column and the carrier gas was He at a flow of 8 mL/min. The

18

sample size was 0.2 mL and the operating conditions of the GC are the injection temperature of 70

19

C, the column temperature of 70 C, and the TCD temperature of 250 C. The difference between

20

the coke contents of D-cat and R-cat is the quantity of coke removed. The percent of coke removed

21

from D-cat is termed as coke removal rate. The experimental errors from duplicate runs were found

22

to be less than 5%.

23

2.6. Catalyst activity evaluation

24

The activity of a hydrogenation catalyst can be measured in many ways, such as hydrogenation

25

of a particular feed in a H2 atmosphere as well as dehydrogenation of a hydrogen donor solvent in

26

the absence of H221, because the core role of a catalyst is abstracting (activating) H atoms (i.e. the H

27

radicals) from H2 (by breaking the H-H bond) or from a hydrogen donor solvent (by breaking the

28

H-C bond), and donating the H atoms to feed radicals to form new H-H or H-C bonds. In other

29

words a catalyst promotes only the formation of reaction intermediates regardless of the forward 6 / 26


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and reverse reactions. The activity of catalyst used in this study therefore was characterized by

2

dehydrogenation of THN in the absence of H2 as reported by Chen et al.21. The evaluation was

3

performed with the same amount of catalyst (in mass) at 360 C for 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8 or 10

4

min following the procedure described in subsections 2.2 and 2.3.

5

2.7. TPO-MS analysis of D-cat and R-cat

6

The TPO-MS experiments were carried out in a thermogravimetric analyzer (TGA, SETSYS

7

Evolution 1750, SETARAM) coupled online with a mass spectrometer (MS, OmniStar 200, Blazers)

8

at the ambient pressure under a flow of 14%-O2-in-Ar at a flow rate of 70 mL/min. The catalyst was

9

heated at a rate of 10 °C/min from the ambient temperature to 900 °C, with a 30 min stay at 110 °C

10

to remove the adsorbed water and a 2 min stay at 900 °C, and the weight loss and CO2 release

11

curves were recorded.

12

2.8. Determination of radical concentration of the catalyst

13

The radical concentrations of D-cat and R-cat were determined with an ESR instrument

14

(E-scan, Bruker) operated at 9.76 GHz, 1.578 mW and the ambient temperature. The central

15

magnetic ﬁeld was 3485 G, the modulation amplitude was 1.0 G, the sweep width was 100 G, the

16

sweep time was 0.35 min, and the time constant was 0.04 s. The signals were calibrated by

17

2,2-diphenyl-1-picrylhydrazyl (DPPH).

18

There are two kinds of radicals in the reaction, the stable radicals measurable by ESR and the

19

active radicals not measurable by ESR, such as the H radicals from THN. The stable radical

20

concentration of coke (CRS, μmol/g-coke) on the catalysts is determined by Eq. (5), where nRS is the

21

quantity of radicals determined by ESR, mcat is the mass of catalyst used in the ESR measurement,

22

and fCoke is the mass fraction of coke on the catalyst, 0.04 for D-cat, for example.

23 24

CRS = nRS /(mcat  fCoke )

（5）

2.9. Distribution of coke on the catalysts

25

The distribution of coke on D-cat and R-cat was observed by scanning electron microscope

26

(SEM, JEOL JSM-7800F) equipped with an Energy Dispersive X-ray detector (EDS) for various

27

elements in the catalysts.

28 29

3. Results and discussion

30

3.1. Coke removal from D-cat and recovery of the catalyst activity 7 / 26


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Fig. 1 shows that the coke on D-cat can be partially removed by reacting with THN in the

2

temperature range of 300-400 C. The coke removal rate increased with the increasing temperature

3

in the initial 3 min, varied slightly thereafter and reached 19% at 300 C and 26% at 400 C in 10

4

min. These results are similar to the 28% coke removal rate reported by Zhao et al.19 who also used

5

THN at 400 C but under 10 MPa H2 for 60 min. The coke removal behaviors in Fig. 1 show that a

6

part of coke on D-cat is removable while the rest is difficult to be removed. This information seems

7

to suggest that the removable coke is on the active sites of D-cat due to their hydrogenation activity

8

while the remaining coke is on the catalyst support because it has little hydrogenation activity. This

9

agrees with the general understanding that the active sites cover only a small part of the catalyst

10

surface. Clearly, if this is the case, the trends in Fig. 1 indicates that a higher temperature increases

11

the activity of active sites for abstracting hydrogen from THN and donating the hydrogen to coke.

12

Furthermore the activity of THN to donate hydrogen also increases with increasing temperature.

13

As stated earlier, the activity of catalyst is characterized by dehydrogenation of THN.

14

Therefore, the R-cats obtained from the THN treatment of D-cat at various temperatures in 10 min,

15

as shown in Fig. 1, were reacted with THN at 360 C and the results are compared with those of

16

D-cat and the fresh catalyst (F-cat) in Fig. 2. It is seen that the F-cat showed the highest THN

17

dehydrogenation rate (the slope in 3 min) and the highest THN dehydrogenation conversion in 10

18

min, about 8.8%, while the D-cat showed the lowest THN dehydrogenation rate and the lowest

19

THN dehydrogenation conversion in 10 min, around 6.5%, indicating 26% deactivation of the

20

catalyst. The THN dehydrogenation conversions of R-cats are all higher than that of D-cat and

21

increased with the increasing THN treatment temperature up to 340 C, beyond which the THN

22

dehydrogenation conversions of R-cats are similar to that of F-cat in 10 min. These trends in THN

23

dehydrogenation conversion of R-cats are somewhat different from the corresponding trends of

24

coke removal rate in Fig. 1, where a higher temperature results in a higher coke removal rate even

25

in the temperature range of 340-400 C. This difference between the coke removal rate and the

26

recovery of catalyst’s activity suggests that not all the coke on the catalyst deactivated the activity

27

in the same way or only a small fraction of coke, around 21%, deactivated the catalyst, while the

28

coke removed beyond 21% may be attributed to that on the support. In other words, it is not

29

necessary to remove all the coke on the catalyst to recover the catalyst’s activity.

30

3.2. The mechanism of coke removal from D-cat 8 / 26


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It is interesting to note again that the R-cat that showed a similar THN conversion to F-cat had

2

a coke removal rate of only 21%, indicating that the THN treatment is able to selectively remove

3

the coke from the active sites of catalyst. To explore this inference the R-cat obtained from the THN

4

treatment at 400 C for 10 min was subjected to SEM-EDS analysis and the results are compared

5

with those of D-cat in Fig. 3. The figures in (a) are for D-cat while those in (b) are for the R-cat.

6

The element mapped by EDS is shown in each of the figures, for instance D-cat-EDS-Mo is the

7

molybdenum mapping of D-cat while R-cat-EDS-S is the sulfur mapping of the R-cat.

8

It is seen in Fig. 3 that the large bumps in D-cat-SEM and R-cat-SEM are the Mo sites while

9

the general background are Al and W, i.e. the Mo sites are located on the support containing Al and

10

W. The Co is present on both Mo and Al while the Ni is present on the surface without Mo. The S

11

is present mainly on the Mo but also on the Co and Ni, indicating these metals are in sulfide form.

12

These metals’ distribution generally agrees with that reported in the literature, in which the

13

Co-Mo-S sites were observed28,29, but different from the literature, in which the Ni-Mo-S were also

14

observed30,31. These findings perhaps suggest that the catalyst studied here was prepared by separate

15

impregnation of Ni and Mo. The more important behavior is C, which is present on the Mo sites as

16

well as on other metals, including Al, in D-cat. However, in the R-cat, C is absent on the Mo site

17

but still present on other metals, indicating the coke removal been mainly, if not only, from the Mo

18

sites by the THN treatment. These SEM-EDS results suggest that the coke on Mo sites is less

19

condensed and is easier to be hydrogenated than that on the other surface, or the Mo sulfide

20

promoted hydrogenation of coke and consequently the coke removal.

21

To differentiate the coke removed from that remaining on the catalyst during the THN

22

treatment, the D-cat and various R-cats were subjected to TPO-MS analysis, and the results are

23

shown in Fig. 4. It is apparent that all the catalysts show the same CO2 peak at around 490 C, but

24

the R-cats released less CO2 in the temperature range of 200-490 C. This indicates that the coke

25

removed by the THN treatment is easy to be oxidized compared with the coke remaining on the

26

R-cats. If the active catalyst sites do not promote coke oxidation, these TPO-MS results suggest that

27

the coke removed in the THN treatment contains less condensed aromatic structure and more

28

hydrogen and aliphatic carbon than the coke remaining on the R-cats. This further suggests that the

29

coke on the Mo sulfide sites contains little condensed aromatics due to their hydrogenation activity,

30

while the coke on the WO2/Al2O3 support contains more condensed aromatic structure. Clearly, 9 / 26


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these suggestions are consistent with the literature founding that the coke formed on hydrotreating

2

catalysts contains graphite-like structure but is of high H/C ratio (1-1.1)4,5.

3

As discussed earlier, the D-cat has been used in a fixed bed diesel hydrogenation unit at 8 MPa

4

of H2 and temperatures from 345 to 390 C in a 30-month period, and the coke still contains

5

aliphatic structure, especially that on the Mo sulfide sites. These facts suggest that the coke may

6

undergo cracking and condensation at similar temperatures in the absence of H2 or a hydrogen

7

donor solvent, which can be easily evidenced by an increase in radical concentration as reported in

8

the literature32,33. Similarly, the coke removal process by THN may also be evidenced by decreasing

9

radical concentration due to hydrogenation. Clearly these suggestions are confirmed in Fig. 5,

10

where the coke’s radical concentration increases with increasing temperature and time in the

11

absence of THN (Fig. 5(a), D-cat), but decreases with increasing temperature and time in the

12

presence of THN (Fig. 5(b), R-cat). In Fig. 5(a), the decreases of radical concentration in 0.5 min

13

suggest that the coke soften upon heating that allows some of the radicals moving around and

14

coupling with each other, indicating that some of the coke is not graphite-like but is pitch-like as

15

reported.25 The higher increasing rate of radical concentration beyond 0.5 min at a higher

16

temperature suggests that the coke cracks at the temperature range used, as low as 300 C, similar to

17

the pyrolysis behaviors of coals and pitch in the same temperature range.34 All the behaviors in Fig.

18

5(a) indicate that the coke, at least some of the coke, contains hydrogen-rich structures.

19

The decreasing radical concentration in Fig. 5(b) for the R-cat at 340-400 C suggests that the

20

coke or a part of the coke underwent hydrogenation at these temperatures, which contributed to the

21

coke removal. The similar radical concentration in Fig. 5(b) beyond 3 min for the R-cat indicates

22

completion of the coke removal process in about 3 min, which is consistent with the data in Figs. 1

23

and 4. The slight increases in radical concentration beyond 0.5 min in Fig. 5(b) for the R-cat treated

24

with THN at 300 and 320 C suggest that the amount of coke that underwent hydrogenation is

25

relatively less than the amount of coke that underwent cracking and condensation due to the low

26

hydrogen donation rate of THN and/or low catalyst activity at these temperatures, which again

27

suggests that there are at least two types of coke on the catalysts surface, one is easy to be

28

hydrogenated and locates mainly on the Mo sites while the other one is difficult to be hydrogenated

29

and locates on the catalyst support. The different radical behaviors of the R-cats treated with THN

30

at temperatures of 300-320 C and 340-400 C in Fig. 5(b) indicate that temperatures lower than 10 / 26


Page 11 of 26 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

1

Energy & Fuels

340 C is not effective to remove the coke on Mo sites.

2

It is further noted that the F-cat contains no radical while the D-cat contains radicals, indicating

3

the presence of radicals only in the coke. The radical concentration of coke on D-cat is about 13.2

4

μmol/g-coke, which is similar to that of a lignite (with 72.4 wt.% carbon) reported by Liu et al.32

5

and is higher than that of the petroleum asphaltenes reported by Yen et al.35. The analysis of D-cat

6

by TG-MS in an Ar atmosphere showed a mass loss of 6.8% in the temperature range of 110-400

7

C but little carbon-containing gas was detected, indicating again that some of the coke is pitch-like

8

materials.

9

It is possible that the similar radical concentrations of the R-cat obtained from the THN

10

treatment at temperatures of 340-400 C for more than 3 min in Fig. 5(b) can be attributed to the

11

coke on the support while the decreased radical concentration in 3 min can be attributed to the coke

12

on the Mo sites. With this assumption and the data in Figs. 1 and 5(b), it is estimated that the radical

13

concentration of coke on Mo sites is approximately 42.6 ((13.2-3.4)/0.23) mol/g-coke-removed

14

while that on the catalyst support is 4.4 (3.4/0.77) mol/g-coke-support. Because in average about

15

23% coke removed contributed 9.8 (13.2-3.4) mol radicals while 77% coke on the support

16

contributed 3.4 mol radicals, the radical concentration of coke on Mo sites is approximately 10

17

times the coke on the support. This information suggests that the coke removed from the Mo sulfide

18

sites is much less condensed than the coke remaining on the catalyst support, and possibly the latter

19

contains graphite-like structure that has fewer radicals.

20

It is clear so far that THN played an important role in supplying hydrogen radicals to coke on

21

the Mo sulfide sites of the catalyst by converting itself to NA. The THN however also underwent

22

other reactions to form H2 and DE as indicated in Reactions 2 and 3, and these reactions also form

23

NA. Fig. 6(a) shows the total THN converted to NA (Eq. (1)) under the conditions used in above

24

experiments. Since no THN conversion was observed under the conditions in the absence of the

25

catalyst, the NA formation can be attributed solely to the catalytic effect. It can be seen that the NA

26

formation started immediately upon heating and increased with increasing temperature and time, as

27

observed in many simple reaction kinetics studies, reaching to 11, 14, 19, 23, 29 and 33% THN in

28

10 min at 300, 320, 340, 360, 380 and 400 C, respectively. It is noted that the quantities of H

29

radicals generated in the THN-to-NA process is 4 times the NA formation.

30

Fig. 6(b) shows the portion of THN that yielded H2, XTHN-to-H2 by Eq. (2), in the THN treatment, 11 / 26


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 12 of 26

1

which did not contribute to the coke removal. Interestingly, this fraction of THN was not observed

2

initially in the THN treatment, its amounts were significant only in 4 min at 340 C, 3 min at 360

3

C, 2 min at 380 C and 1 min at 400 C, indicating that the reaction was dependent on factors that

4

became effective gradually during the THN treatment. Based on the observations in Figs. 1 and 5(b)

5

it is possible that the main factor that affects the THN-to-H2 reaction is the quantity of active Mo

6

sulfide sites recovered by coke removal. It seems that the trends of this THN fraction reached

7

asymptotes in 8 min, approximately 4, 6, 8 and 13% at 340, 360, 380 and 400 C, respectively,

8

suggesting that the reaction is reversible as reported in the literature24,36.

9

Fig. 6(c) shows the changes of THN converted for the generation of DE and NA in the THN

10

treatment determined by Eq. (3). Apparently this reaction did not start immediately upon the

11

heating and is barely observable in 10 min at 300-360 C. This behavior indicates that the reaction

12

is dependent on the active Mo sulfide sites recovered by the coke removal as well as on

13

temperature37.

14

It is apparent that the quantities of THN converted to H2 and DE in Figs. 6(b) and 6(c) are less

15

than those converted to NA, in other words the quantities of H radicals from Fig. 6(a) are more than

16

those consumed in Figs. 6(b) and 6(c). In principle, the differences in H radical balance may be

17

attributed to the H radicals consumed in the coke removal as quantified by Eq. (4) and shown in Fig.

18

7. Fig. 7 shows that the fractions of THN that contributed hydrogen radicals to coke, XTHN-to-Coke,

19

increase with THN treatment temperature, reaching to asymptotes in approximately 3 min at

20

340-400 C. The asymptotes are from 13% at 340 C and 18% at 400 C. Clearly, the

21

hydrogenation of coke was fast at these temperatures, in agreement with Figs. 1 and 5(b). The

22

average quantity of H radicals donated to coke in the temperature range of 340-400 C, determined

23

from the THN data, are in the level of 493 mmol/g-coke-removed (4  189 mmol-THN/g-coke,

24

times 15% (THN consumed) and divide by 23% (fraction of coke removed)), which is about 11600

25

times the stable radicals decreased (42.6 mol/g-coke-removed).

26

It should be noted that, in an industrial hydrogenation unit, most of the feed molecules adsorb

27

on the catalyst and then desorb after being hydrogenated, but some of the feed molecules are

28

dehydrogenated to form heavier products that stay on the catalyst surface and becomes coke

29

eventually. However, the THN treatment of coke studied here involves only catalytic hydrogenation

30

of coke by THN and desorption of the hydrogenation products without the formation of more coke. 12 / 26


Page 13 of 26 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

1 2

4. Conclusions

3

About 19-23% coke deposited on a deactivated diesel hydrogenation Mo-Co-Ni/W-Al catalyst

4

can be removed by a THN treatment at 300-400 C in 3 min. This procedure removes all the coke

5

on the Mo sulfide sites at temperatures of 340 C and higher, and restores the catalyst activity. The

6

coke on the catalyst support cannot be removed. The coke on the Mo sulfide sites is pitch-like and

7

reactive with a stable radical concentration around 42.6 mol/g. The coke on the catalyst support is

8

more condensed in structure than that on the Mo sulfide sites, stable in the THN treatment, and has

9

a stable radical concentration of around 4.4 mol/g. A coke removal mechanism is proposed which

10

includes activation (or subtraction) of H in THN and hydrogenation of coke by Mo sulfide, and

11

dissolution of the hydrogenation products. Some of the H radicals activated by Mo sulfide couple to

12

form H2 or transfer to THN to form DE, these reactions however are not significant in the initial 3

13

min at all the temperatures studied or in 10 min below 340 C. The minimal requirement for the

14

coke removal is 340 C for 3 min. The side reactions are significant at higher temperatures and

15

longer treatment time.

16 17

Corresponding Author

18

* Telephone: +86 10 64421073. E-mail: [email protected]

19


20


21 22

Notes

23

The authors declare no competing financial interest.

24 25

Acknowledgments

26

The work was financially supported by the National Key Research and Development Program

27

of China through 2017YFB0306603-02, Natural Science Foundation of China (21506009) and

28

China Petrochemical Corporation (Sinopec Group, 117006).

29 30

References 13 / 26


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

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Page 14 of 26

(1) Marafi, M.; Furimsky, E. Hydroprocessing Catalysts Containing Noble Metals: Deactivation, Regeneration, Metals Reclamation, and Environment and Safety. Energy Fuels 2017, 31, 5711-5750.

3

(2) Furimsky, E.; Massoth, F.E. Deactivation of hydroprocessing catalysts. Catal. Today 1999, 52 , 381-495.

4

(3) Tailleur, R.G. Deactivation of WNiPd/TiO2Al2O3 catalyst during the upgrading of LCO. Fuel 2008, 87,

5 6 7

2551-2562. (4) Abdullah, H. A.; Hauser, A.; Ali, F. A.; Adwani, A. A. Optimal conditions for coke extraction of spent catalyst by accelerated solvent extraction compared to soxhlet. Energy Fuels 2006, 20, 320-323.

8

(5) Zbuzek, M.; Vráblík, A.; Tukač, V.; Veselý, M.; Prokešová, A.; Černý, R. The physico-chemical structure and

9

activity of hydrodesulphurization catalysts aged by accelerated method. Catal. Today 2015, 256, 261-268.

10

(6) González, C.; Marín, P.; Díez, F. V.; Ordóñez, S. Hydrodeoxygenation of acetophenone over supported

11

precious metal catalysts at mild conditions: process optimization and reaction kinetics. Energy Fuels 2015,

12

29, 8208-8215.

13 14 15 16 17 18

(7) Kuznetsova, L. N.; Kazbanova, A. V.; Kuznetsov, P. N.; Tarasova, L. S. Activity of the Pt/WO42−/ZrO2 catalyst in hydroisomerization reaction of n-heptane-benzene mixture. Pet. Chem. 2015, 55, 57-62. (8) Wang, Z.; Adhikari, S.; Valdez, P.; Shakya, R.; Laird, C. Upgrading of hydrothermal liquefaction biocrude from algae grown in municipal wastewater. Fuel Process. Technol. 2016, 142, 147-156. (9) Wang, H.; Wang,Y. Characterization of deactivated bio-oil hydrotreating catalysts. Top. Catal. 2016, 59, 65-72.

19

(10) Zhang, L.; Li, M. F.; Ding, S.; Li, H. F. Effect of feedstock’s properties on NiMoW/Al2O3 catalyst stability in

20

ultra-low sulfur diesel production (in Chinese). Acta Petrolei Sinica (Petrol. Process. Sect.) 2017, 33,

21

834-841.

22 23 24 25 26 27 28 29 30

(11) Trimm, D. L. The regeneration or disposal of deactivated heterogeneous catalysts. Appl. Catal., A 2001, 212, 153-160. (12) Guisnet, M. Regeneration of coked zeolite catalysts. Deactivation and Regeneration of Zeolite Catalysts 2011, 12, 217-231. (13) Maraﬁ, M.; Stanislaus, A.; Furimsky, E. Handbook of Spent Hydroprocessing Catalysts; Elsevier: Amsterdam, The Netherlands, 2010. (14) Kern, C.; Jess, A. Verkokung und Koksabbrand in heterogenen Katalysatoren. Chem. Ing. Tech. 2006, 78, 1033-1048. (15) Hutchings, G. J.; Comninos, H.; Copperthwaite, R. G.; van Rensburg, L. J.; Hunter, R.; Themistocleous, T. 14 / 26


Page 15 of 26 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

1

Reactivation of zeolite and oxide catalysts using nitrous oxide. J. Chem. Soc., Faraday Trans. I. 1989, 85,

2

633-644.

3

(16) Sagdeev, K. A.; Khazipov, M. R.; Galimova, A. T.; Sagdeev, A. A.; Gumerov, F. M.; Yarullin, R. S.

4

Regeneration of an alumopalladium hydrogenation catalyst in the process of supercritical CO2 fluid

5

extraction. Catal. Ind. 2016, 8,1−8.

6 7 8 9 10 11 12 13

(17) Zhang, X.; Zong, B.; Qiao, M. Reactivation of spent Pd/AC catalyst by supercritical CO2 fluid extraction, AIChE J. 2009, 55, 2382-2388. (18) Marecot, P.; Peyrovi, S.; Bahloul, D.; Barbier, J. Regeneration by hydrogen treatment of bifunctional catalysts deactivated by coke deposition. Appl. Catal. 1990, 66, 181−190. (19) Zhao, Y.; Yu, Y.; Wei, F. Reactivation of residue hydroconversion catalyst by solvent treatment (in Chinese), Petrol. Process. Petrochem. 2008, 39, 5-9. (20) Chen, Z.; Zhang, X.; Liu, Z.; Liu, Q.; Xu, T. Quantification of reactive intermediate radicals and their induction effect during pyrolysis of two n -alkylbenzenes, Fuel Process. Technol. 2018, 178, 126-132.

14

(21) Chen, Z.; Xie, J.; Liu, Q.; Wang, H.; Gao, S.; Shi, L.; Liu, Z. Characterization of direct coal liquefaction

15

catalysts by their sulfidation behavior and tetralin dehydrogenation activity. J. Energy Inst. 2018,

16

doi.org/10.1016/j.joei.2018.05.009

17

(22) Shi, L.; Cheng, X.; Liu, Q.; Liu, Z. Reaction of volatiles from a coal and various organic compounds during

18

co-pyrolysis in a TG-MS system. Part 1. Reaction of volatiles in the void space between particles. Fuel 2018,

19

213, 37-47.

20

(23) Shi, L.; Cheng, X.; Liu, Q.; Liu, Z. Reaction of volatiles from a coal and various organic compounds during

21

co-pyrolysis in a TG-MS system. Part 2. Reaction of volatiles in the free gas phase in crucibles. Fuel 2018,

22

213, 22-36.

23 24

(24) Chen, Z.; Yan, Y.; Zhang, X.; Shi, X.; Shi, L.; Liu, Q.; Liu, Z.; Xu, T. Behaviors of coking and stable radicals of a heavy oil during thermal reaction in sealed capillaries. Fuel 2017, 208, 10-19.

25

(25) Yan, Y.; Shi, L.; Liu, Q.; Shi, X.; Wang, T.; Zhou, Q.; Liu, Z.; Han, W.; Li, M. Coke and radicals formation

26

on a sulfided NiMo/γ-Al2O3 catalyst during hydroprocessing of an atmospheric residue in hydrogen donor

27

media, Fuel Process. Technol. 2017, 159, 404-411.

28 29 30

(26) Wu, J.; Liu, Q.; Wang, R.; He, W.; Shi, L.; Guo, X.; Chen, Z.; Ji, L.; Liu, Z. Coke formation during thermal reaction of tar from pyrolysis of a subbituminous coal, Fuel Process. Technol. 2017, 155, 68-73. (27) He, W.; Liu, Z.; Liu, Q.; Ci, D.; Lievens, C.; Guo, X. Behaviors of radical fragments in tar generated from 15 / 26


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

1

Page 16 of 26

pyrolysis of 4 coals. Fuel 2014, 134, 375-380.

2

(28) Sun, R.; Shen, S.; Zhang, D.; Ren, Y.; Fan, J., Hydrofining of coal tar light oil to produce high octane

3

gasoline blending components over γ-Al2O3-and η-Al2O3-supported catalysts. Energy Fuels 2015, 29,

4

7005-7013.

5 6

(29) Zhang, Y.; Han, W.; Long, X.; Nie, H., Redispersion effects of citric acid on CoMo/γ-Al2O3 hydrodesulfurization catalysts. Catal. Commun. 2016, 82, 20-23.

7

(30) de Jong, K. P.; van den Oetelaar, L. C.; Vogt, E. T.; Eijsbouts, S.; Koster, A. J.; Friedrich, H.; de Jongh, P. E.,

8

High-resolution electron tomography study of an industrial Ni-Mo/γ-Al2O3 hydrotreating catalyst. J. Phys.

9

Chem. B 2006, 110, 10209-10212.

10 11 12 13

(31) Gao, Y.; Han, W.; Long, X.; Nie, H.; Li, D., Preparation of hydrodesulfurization catalysts using MoS3 nanoparticles as a precursor. Appl. Catal. B- Environ. 2018, 224, 330-340. (32) Liu, M.; Yang, J.; Yang, Y.; Liu, Z.; Shi, L.; He, W.; Liu, Q. The radical and bond cleavage behaviors of 14 coals during pyrolysis with 9,10-dihydrophenanthrene. Fuel 2016, 182, 480-486.

14

(33) Singer, L. S.; Lewis, I. C. ESR study of the kinetics of carbonization. Carbon 1978, 16, 417-423.

15

(34) Zhang, X.; Liu, Z.; Chen, Z.; Xu, T.; Liu, Q. Bond cleavage and reactive radical intermediates in heavy tar

16 17 18 19 20

thermal cracking. Fuel 2018, 233, 420-426. (35) Yen, T. F.; Erdman, J. G.; Saraceno, A. J. Investigation of the nature of free radicals in petroleum asphaltenes and related substances by electron spin resonance. Anal. Chem. 1962, 34, 694-700. (36) Hillebrand, W.; Hodek, W.; Kölling, G. Steam cracking of coal-derived oils and model compounds 1. Cracking of tetralin and t-decalin. Fuel 1984, 63, 756-761.

21

(37) Ferraz, S. G. A.; Zotin, F. M. Z.; Araujo, L. R. R., Zotin, J. L. Influence of support acidity of NiMoS

22

catalysts in the activity for hydrogenation and hydrocracking of tetralin. Appl. Catal., A 2010, 384, 51-57.

16 / 26


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Energy & Fuels

1

Table Captions

2

Table 1. Properties of deactivated catalyst used for diesel hydrogenation

3 4

Figure Captions

5

Graphical Abstract

6

Figure 1. Coke removal from D-cat under various conditions

7

Figure 2. THN dehydrogenation rate at 360 C over F-cat, D-cat and R-cats

8

Figure 3. The SEM photos and corresponding EDS mapping of Mo, S, C, Ni, Al, Co and W in

9

D-cat (a) and R-cat obtained from THN treatment at 400 C for 10 min (b)

10 11

Figure 4. CO2 signal in TPO-MS of D-cat and R-cats subjected to THN treatment for 3 min (a) and 10 min (b)

12

Figure 5. Radical concentration of coke on catalyst treated without THN (a) and with THN (b)

13

Figure 6. The THN converted to various products during the THN treatment: (a) XTHN-to-NA; (b)

14 15

XTHN-to-H2; (c) XTHN-to-DE. Figure 7. The THN that supplied hydrogen to coke during the THN treatment

17 / 26


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

1 2

3

Page 18 of 26

Table 1. Properties of deactivated catalyst used for diesel hydrogenation Characteristics

Surface area

Pore volume

Content

145 m2/g

0.27 mL/g

Component (wt.%)* MoO3

NiO

WO3

SiO2

C

S

3.4

3.9

15.1

8.8

4.0

8.3

* The total components is 43.5 wt.% with balance Al2O3.

18 / 26


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1 2

Energy & Fuels

Graphical Abstract

19 / 26


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

1 2 3

Figure 1. Coke removal from D-cat under various conditions

20 / 26


Page 20 of 26

Page 21 of 26 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

1 2 3

Energy & Fuels

Figure 2. THN dehydrogenation rate at 360 C over F-cat, D-cat and R-cats

21 / 26


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 26

1 2 3

(a) (b) Figure 3. The SEM photos and corresponding EDS mapping of Mo, S, C, Ni, Al, Co and W in D-cat (a) and R-cat

4 5

obtained from THN treatment at 400 C for 10 min (b)

22 / 26


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1 2 3

Energy & Fuels

Figure 4. CO2 signal in TPO-MS of D-cat and R-cats subjected to THN treatment for 3 min (a) and 10 min (b)

23 / 26


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

1 2 3 4

Figure 5. Radical concentration of coke on catalyst treated without THN (a) and with THN (b)

24 / 26


Page 24 of 26

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Energy & Fuels

1 2 3

Figure 6. The THN converted to various products during the THN treatment: (a) XTHN-to-NA; (b) XTHN-to-H2; (c) XTHN-to-DE.

25 / 26


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

1 2 3

Figure 7. The THN that supplied hydrogen to coke during the THN treatment

26 / 26


Page 26 of 26

Coke removal from a deactivated industrial diesel hydrogenation

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