JOURNAL OF FUEL CHEMISTRY AND TECHNOLOGY

Volume 35, Issue 4, August 2007 Online English edition of the Chinese language journal

Received: 2007-01-15; Revised: 2007-04-11 * Corresponding author. Tel: +86-546-8399373; Fax: +86-546-8396054; E-mail: lichuan_upc@163.com Foundation item: Supported by the Innovation Fund of China University of Petroleum (East China) (b2006-10). Copyright©2007, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved.

Cite this article as: J Fuel Chem Technol, 2007, 35(4), 407−411 R

Application of Co-Mo/CNT catalyst in hydro-cracof Gudao vacuum residue LI Chuan1,*, SHI Bin1, CUI Min2, SHANG Hong-yan3, QUE Guo-he1

1 State Key Laboratory of Heavy Oil Processing, College of Chemistry and Chemical Engineering, China UnChina), Dongying 257061, China 2 College of Chemistry & Chemical Engineering, China University of Petroleum (East China), Dongying 257061, C3 Key Laboratory of Catalysis, CNPC, Dongying 257061, China

Abstract: Carbon nanotube-supported Co-Mo catalysts with different Co/Mo atomic ratio were prepimpregnation. These catalysts were used in the hydro-cracking reaction of Gudao vacuum residue, and the cacompared with γ-Al2O3-supported Co-Mo catalysts under the same reaction conditions. It was found that theCo-Mo/carbon nanotube (CNT) catalysts are inferior to Co-Mo/γ-Al2O3. However, the Co/Mo atomic ratio hcatalytic activity of Co-Mo/CNT; the Co-Mo/CNT catalyst with Co/Mo atomic ratio of 0.5 has the best catalyfor Co-Mo/γ-Al2O3 catalyst the best Co/Mo atomic ratio is 0.35. Key Words: carbon nanotube-supported Co-Mo catalysts; γ-Al2O3-supported Co-Mo catalysts; hydro-crackiCo/Mo atomic ratio; catalytic properties

It is well-known that Co-Mo catalysts, typical for hydrodesulfurization (HDS), are widely used in petroleum processing. γ-Al2O3 is a kind of common support, which has good characteristics such as high mechanical strength and rich pore structures. There are currently many studies on γ-Al2O3 support[1−3]. However, metal catalyst supported on γ-Al2O3 has limitations in HDS and anti-coking performance. In order to improve this state, new catalyst supports were being developed. In recent years, oxides of metal used as HDS catalysts such as Mo, W, Co or Ni supported on activated carbon have received much attention because high HDS activities have been reported. In addition, carbons have better features than γ-Al2O3 such as reduced coking activity[4]. Carbon nanotube (CNT, namely buckytube) is a material with especial nano-meter structure and pore diameter. With the discovery of CNT, much attention was focused on it[5].

Planeix[6] prepared Ru/carbon nanotube catalyst first, and studied the composition of products for cinnamyl alcohol in the hydrogenation of cinnamaldehyde. It appears that Ru/carbon nanotube catalyst is better than Ru/Al2O3 or Ru/carbon catalyst in activity, selectivity and stability. Zhang[7] investigated propene hydroformylation catalyzed by Rh-phosphine complex catalysts supported by carbon

nanotubes, and compared with thasilica gel), TDX-601 (a carbon moactive carbon), and GDX-102 (a polyshowed that the carbon nanotubes-scomplex catalysts displayed not onlyconversion, but also excellent reproduct. In 1994, the catalysts of supporting on carbon nanotubes weret al.[8] and heated in hydrocarbcatalytic activity of these catalystshydrocarbons, was considerably hisupported on either active carbon othe same conditions. Moreover, thheat stability. The HDS activity of was investigated using dibenzothiocompound by Shang[9]. The resuCo-Mo/CNT catalysts were exCo-Mo/γ-Al2O3 in HDS of DBT.

Up to now, CNT has been appliedchemistry, material science, and catfew studies have focused on the apploil processing. In this study, some CNT used in heavy oil hydro-crack

RESEARCH PAPE

king

iversity of Petroleum (East

hina

ared by pore volume talytic properties were catalytic properties of as great effect on the

tic properties, whereas

ng of vacuum residue;

t supported by SiO2 (a lecular sieve), AC (an mer carrier). The results upported Rh-phosphine high activity of propene gion selectivity to the Fe-Cu and Fe particles e prepared by Rodriguez on environments. The , for the conversion of gher than those which r γ-Al2O3 treated under

ese catalysts had better several Co-Mo catalysts phene (DBT) as model lts indicated that the tremely active than

in the field of physics, alysis. However, only a ication of CNT in heavy application prospect of ing was explored. The

LI Chuan et al. / Journal of Fuel Chemistry and Technology, 2007, 35(4): 407−411

reaction activities of Co-Mo/CNT catalysts were evaluated in an autoclave and compared with that of the conventional Co-Mo/γ-Al2O3 under the same reaction condition. 1 Experimental 1.1 Materials

Characterizations of Gudao vacuum residue (GDVR) are

included in Table 1. Carbon nanotube was obtained from Tsinghua University.

Table 1 Properties of Gudao vacuum residue

Property GDVR

Density (20°C) ρ / g⋅cm−3 0.990

Viscosity (100°C) µ / mm²⋅s−1 2057

Carbon residue w / % 15.67

Sulfur w / % 2.30

Nitrogen w / % 1.15

H/C atomic ratio 1.57

Condensation point t / °C 8.0

wNi / µg⋅g−1 46.4

wV / µg⋅g−1 8.8

wFe / µg⋅g−1 14.9

wCa / µg⋅g−1 82.6

Saturates w / % 17.8

Aromatics w / % 31.4

Resins w / % 48.9

C7-asphaltene w / % 1.9

1.2 Catalysts preparation and characterization

A series of mono- and bimetallic Co-Mo catalysts

supporting on carbon nanotube or γ-Al2O3 (140 screen meshes) were prepared by wetness impregnation. The bimetallic samples, prepared by co-impregnation of aqueous ammonium heptamolybdate and Co-nitrate solutions, had Co/Mo atomic ratios of 0.2, 0.35, 0.5, 0.7, and 1.0. In this series, the amount of MoO3 was kept constant for all catalysts at 10 wt%, while the amount of Co was changed accordingly. The monometallic catalysts were prepared with loadings of 10 wt% Co and 10 wt%, 11 wt%, 12.6 wt%, and 13.6 wt% Mo, respectively. After impregnation, the solids were dried 24 h at 120°C and then cooled to room temperature. Once cooled, the samples were calcined for 8 h at 500°C in N2 flow.

Properties of the catalysts are included in Table 2. The results of BET surface area, average pore diameter and pore volume for the prepared catalysts are given in Table 3.

Table 2 List of catalysts and their properties

Catalysts Properties

Co-Mo/γ-Al2O3* Co/Mo atomic ratio = 0.20, 0.35, 0.50, 0.70

Co-Mo/CNT* Co/Mo atomic ratio = 0.20, 0.35, 0.50, 0.70, 1.0

Mo/CNT* content of MoO3 = 10.00%, 11.10%, 12.60%, 13.60%

Co/CNT content of CoO = 10.00%

* content of MoO3 in Co-Mo/γ-Al2O3 or Co-Mo/CNT was 10 wt%

Table 3 Physical properties of various catalysts

Sample

Co/Mo

atomic

ratio

Content of

MoO3

w / %

BET surface

area

A / m2⋅g−1

Average

pore

diameter

d / nm

Pore

volume

v / cm3⋅g−1

CNT – – 193.6 16.7 0.83

0.20 10.00 181.2 15.1 0.70

0.35 10.00 179.9 14.7 0.67

0.50 10.00 178.8 14.2 0.65

0.70 10.00 176.3 13.5 0.58

Co-Mo/CNT

1.0 10.00 173.2 12.6 0.50

10.00 183.1 15.7 0.72

11.10 181.4 15.5 0.71

12.60 179.0 14.5 0.65 Mo/CNT –

13.60 177.2 13.8 0.61

Co/CNT* – – 185.4 15.8 0.75

γ-Al2O3 – – 281.5 8.8 0.79

0.20 10.00 209.4 7.1 0.51

0.35 10.00 205.7 6.5 0.45

0.50 10.00 200.2 5.8 0.40 Co-Mo/γ-Al2O3

0.70 10.00 197.5 5.1 0.36

* content of CoO in Co/CNT was 10.00 wt% 1.3 Reaction and analysis

GDVR (240 g), catalyst with granularity of 140 meshes

and mass concentration of catalyst from 0.075% to 0.5% and sulfur (0.2 g) were put in 0.5 L autoclave, respectively. Air was then expelled from the autoclave using 2 MPa H2 to wash autoclave thrice and the autoclave was weighed (w1). The initial H2 pressure in autoclave was 8 MPa and was heated at 7°C⋅min−1 up to 300°C to carry out the sulfuration reaction for 2 h. After that, the temperature was increased to 430°C and kept for 1.5 h to finish the hydro-cracking reaction. When the reaction was complete, the autoclave was cooled quickly in cold water to room temperature. The gas was then put out and the autoclave was weighed again (w2).

The weight of gas is the margin of w1 and w2. The weight of gasoline, diesel oil, VGO and VR of liquid product without coke are obtained by atmospheric and vacuum distillation. The weight of coke is obtained by centrifugal method and vacuum drying. The weight of sulfur of the liquid product without coke is determined by WK-3 type

LI Chuan et al. / Journal of Fuel Chemistry and Technology, 2007, 35(4): 407−411

micro-coulometer. 2 Results and discussion 2.1 Catalytic effect of Co-Mo/CNT with different Co/Mo atomic ratio on GDVR hydro-cracking reaction

Figure 1 shows the properties of GDVR hydro-cracking

products over Co-Mo/CNT catalysts with different Co/Mo atomic ratios (the mass percentage of catalyst is 0.1%).

0.2 0.4 0.6 0.8 1.00

10

20

30

40

50

60

(1)

(3)

(2)

(5)

Anal

ysis

of p

rodu

cts

w /

%

Co/Mo atomic ratio

(4)

Fig. 1 Effect of different Co/Mo atomic ratios on products

distribution (1): coke yield; (2): desulfurization ratio; (3): gas yield; (4): yield of gasoline

and diesel oil; (5): yield of VGO and VR

When the Co/Mo atomic ratio increases, the yield of coke,

gas and light oil (gasoline and diesel oil) decreases first, and then increases, whereas heavy oil yield (VGO and VR) and the ratio of desulfurization increase first, and then decrease. This illustrates that the catalytic effect of Co-Mo/CNT catalysts was enhanced first, and then weakened with the increasing Co/Mo atomic ratio. And when the Co/Mo atomic ratio is 0.5, the Co-Mo/CNT catalyst has the best catalytic effect in hydro-cracking reaction of GDVR.

2.2 Effect of catalyst concentration on hydro-cracking of GDVR

Figure 2 shows the properties of GDVR hydro-cracking

products with Co-Mo/CNT catalyst with different concentration (Co/Mo atomic ratio is 0.35). When the concentration of the catalyst increases, yields of coke, gas and light oil (gasoline and diesel oil) decrease, and heavy oil yield (VGO and VR) increases. This shows that increasing concentration of the catalyst improves its catalytic effect on GDVR hydro-cracking reaction. And the result is applicable for other Co-Mo/CNT catalysts.

0.0 0.1 0.2 0.3 0.4 0.5

5

10

15

20

25

30

35

40

45

50

55(4)

(3)

(2)

(1)

Ana

lysi

s of

pro

duct

s w

/ %

Content of catalyst w / %

Fig. 2 Effect of different contents catalyst on the products

distribution (1): coke yield; (2): gas yield; (3): yield of gasoline and diesel oil; (4): yield

of VGO and VR

2.3 Effect of compound metal Co on the catalytic effect of CNT-supported metal catalysts

In order to confirm the function of compound metal Co, a

series of experiments for CNT-supported single metal catalysts were processed. The results are listed in Table 4.

Table 4 Catalytic properties of CNT-supported metal catalysts during hydro-cracking of GDVR Catalyst Mo/CNT Co-Mo/CNT Co/CNT

Total metal content w / % 10.00 11.10 12.60 13.60 11.10 12.60 13.60 10.00

Co/Mo atomic ratio – – – – 0.20 0.50 0.70 –

Catalyst content w / % 0.10

Gas yield w / % 8.68 8.24 7.10 4.19 9.10 5.01 6.22 11.76

Yield of gasoline and diesel oil w / % 44.08 38.63 37.74 37.64 56.57 43.17 46.70 39.70

Yield of VGO and VR w / % 47.24 53.13 55.16 58.17 34.33 51.82 47.08 48.54

Coke yield w / % 7.11 6.60 5.62 4.89 5.53 4.40 4.76 5.96

Desulfurization ratio w / % 37.25 39.95 41.67 40.69 45.83 54.08 43.63 36.27

LI Chuan et al. / Journal of Fuel Chemistry and Technology, 2007, 35(4): 407−411

In GDVR hydro-cracking reaction with Co/CNT or Mo/CNT, the coke yield is high and the desulfurization ratio is low, which shows that the catalytic effect of CNT-supported single metal catalyst is not good. When Co-Mo/CNT and Mo/CNT have the same concentration of total metal, compared with the Mo/CNT, Co-Mo/CNT can make the yield of coke yield, gas and the light oil (gasoline and diesel oil) decrease, and the heavy oil yield (VGO and VR) and the desulfurization ratio increase in GDVR hydro-cracking reaction. This indicates that the compound

metal Co can improve the catalytic effect of CNT supported metal catalyst in GDVR hydro-cracking reaction. 2.4 Comparison of catalytic effect of Co-Mo/CNT and Co-Mo/γ-Al2O3 in GDVR hydro-cracking reaction

Table 5 compares the products of GDVR hydro-cracking

reaction with Co-Mo/CNT catalysts and Co-Mo/γ-Al2O3

catalysts.

Table 5 Comparison of catalytic properties of Co-Mo/γ-Al2O3 catalysts and Co-Mo/CNT catalysts

during hydro-cracking of GDVR with the same catalyst content Catalyst I II I II I II I II

Co/Mo atomic ratio 0.20 0.35 0.50 0.70

Catalyst content w / % 0.10

Gas yield w / % 7.99 9.10 4.24 7.23 9.82 5.01 10.99 6.22

Yield of gasoline and diesel w / % 40.01 56.57 42.37 45.81 40.44 43.17 41.23 46.70

Yield of VGO and VR w / % 52.00 34.33 53.40 46.96 49.70 51.82 47.80 47.08

Coke yield w / % 3.64 5.53 3.20 5.17 4.17 4.40 3.47 4.76

Desulfurization ratio w / % 48.53 45.83 56.28 48.20 49.51 54.08 45.51 43.63

I is Co-Mo/γ-Al2O3 catalysts; II is Co-Mo/CNT catalysts

When the Co/Mo atomic ratio is the same (except 0.5), the

light oil (gasoline and diesel oil) yield and coke yield in the product of GDVR hydro-cracking reaction with Co-Mo/γ-Al2O3 catalysts are lower than that with Co-Mo/CNT catalysts, whereas the heavy oil (VGO and VR) yield is more. It shows the better activity of the former catalyst.

When the Co/Mo atomic ratio is 0.5, Co-Mo/CNT catalyst has the best catalytic effect, which is better than the Co-Mo/γ-Al2O3 catalyst with the same Co/Mo atomic ratio. Co-Mo/γ-Al2O3 catalyst has the best catalytic effect with Co/Mo atomic ratio of 0.35, which is the best among all the catalysts in this experiment. 3 Conclusions

Carbon nanotube is a new kind of material as catalyst support, but its catalytic effect in residue hydro-cracking reaction is not well known. On the basis of the experiment in this study, the following conclusions are drawn: (1) On the same condition of GDVR hydro-cracking reaction, the effect of HDS and coking inhibition is better at higher concentration of Co-Mo/CNT catalyst. Compound metal Co can improve the catalytic effect of CNT-supported metal catalyst in GDVR hydro-cracking reaction. (2) When the Co/Mo atomic ratio is the same (except for 0.5), the catalytic effect of Co-Mo/γ-Al2O3 catalysts is better than Co-Mo/CNT catalysts in GDVR hydro-cracking reaction. (3) On the same condition of GDVR hydro-cracking reaction,

the catalytic effects of Co-Mo/γ-Al2O3 catalysts and Co-Mo/CNT catalysts both improve first, and then weaken with increasing Co/Mo atomic ratio. When Co/Mo atomic ratio is 0.5, Co-Mo/CNT catalyst has the best catalytic effect, whereas Co-Mo/γ-Al2O3 catalyst has the best catalytic effect with Co/Mo atomic ratio of 0.35.

References

[1] Wei Z B, Xin Q, Sheng S S, Chen H R, Liu J L, Jiang J M.

Studies on CoMo/TiO2 and CoMo/γ-Al2O3 hydrodesulfurization catalysts. Chinese Journal of Catalysis, 1994, 15(4): 243−248.

[2] Li J W, Li Y X, Chen B H, Li C Y, Zhang X G. Macrokinetics for catalytic hydrogenation of thiophenic sulfides in pyrolysis gasoline over Co-Mo/Al2O3 catalyst. Journal of Fuel Chemistry and Technology, 2005, 33(5): 576−581.

[3] Li J W, Li Y X, Chen B H, Li C Y, Zhang X G. Macrokinetics of olefin hydrogenation in pyrolysis gasoline over Co-Mo/Al2O3 catalyst. Journal of Fuel Chemistry and Technology, 2006, 34(2): 170−174.

[4] Farag H, Whitehurst D D, Sakanishi K, Mochida I. Carbon versus alumina as a support for Co-Mo catalysts reactivity towards HDS of dibenzothiophenes and diesel fuel. Catal Today, 1999, 50(1): 9−17.

[5] Lijima S. Helical microtubules of graphitic carbon. Nature, 1991, 354(6348): 56−58.

[6] Planeix J M, Coustel N, Coq B, Kumbhar P S, Dutartre R, Geneste P, Bernier P, Ajayan P M. Application of carbon

LI Chuan et al. / Journal of Fuel Chemistry and Technology, 2007, 35(4): 407−411

nanotubes as supports in heterogeneous catalysis. J Am Chem Soc, 1994, 116(17): 7935−7936.

[7] Zhang Y, Zhang H-B, Lin G-D, Chen P, Yuan Y-Z, Tsai K R. Preparation, characterization and catalytic hydroformylatrion properties of carbon nanotubes-supported Rh-phosphine catalyst. Appl Catal A, 1999, 187(2): 213−224.

[8] Rodriguez N M, Kim M S, Baker T K. Carbon nanofibers: A

unique catalyst support medium. J Phys Chem, 1994, 98(50): 13108−13111.

[9] Shang H-Y, Liu C-G, Chai Y-M, Xing J-X. Study of adsorption behavior of dibenzothiophene on the surface of CoMo/CNT catalyst. Acta Chimica Sinica, 2004, 62(9): 888−894.