Effect of Catalyst, Temperature, and Hydrogen ... - Wiley Online Library

Research Article

Solmaz Akmaz Pegah Amiri Caglayan Istanbul University, Department of Chemical Engineering, Avcilar, Istanbul, Turkey.

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Effect of Catalyst, Temperature, and Hydrogen Pressure on Slurry Hydrocracking Reactions of Naphthalene Hydrocracking reactions of naphthalene were investigated in a slurry-type reactor with different catalyst compositions consisting of iron-based compounds, metal oxides, and elementary sulfur in order to evaluate the most efficient catalyst composition. The reactions were repeated with the optimal catalyst composition at different H2 initial pressures, temperatures, and holding times to determine the influence of these parameters. At the end of each reaction, liquid samples were analyzed by gas chromatography and mass spectrometry. The most effective catalyst composition for hyrocracking reaction of naphthalene was found to be a mixture of FeSO4H2O, Fe2O3, Al2O3, and sulfur. It can be concluded that hydrogenation, isomerization, cracking, and dealkylation take place during the hydrocracking reaction of naphthalene. Keywords: Catalyst, Gas chromatography, Hydrocracking, Naphthalene, Slurry hydrocracking Received: May 13, 2014; revised: December 28, 2014; accepted: March 11, 2015 DOI: 10.1002/ceat.201400300

1

Introduction

Different refinery methods are currently applied to process heavy petroleum and residue. Diverse upgrading methods for transforming petroleum into useful products with economically high value are reported [1–5] with hydrocracking being one of the most efficient upgrading processes to convert heavy hydrocarbons to lighter ones due to the growing demand of lighter and high-quality products [6, 7]. It is useful for feedstocks which contain high amounts of heavy metal, asphaltene, and aromatic compounds [8]. Especially, slurry-phase hydrocracking applications have gained importance in recent years [9]. Slurry processes are highly effective on heteroatoms, olefinic and aromatic structures in heavy oil [10]. Slurry hydrocracking, a kind of hydrocracking, which occurs under high temperature (400–460 C) and pressure (80–120 bar of hydrogen) by means of a catalyst, has some advantages such as high conversion rate, less coke formation, stable products, and possible adaptation to various feedstocks [11]. The catalysts play also a decisive role in hydrocracking reactions. Slurry hydrocracking catalysts are divided into three categories according to their physical properties in the process: solid powder catalysts, oil-soluble dispersed catalysts, and

– Correspondence: Dr. Solmaz Akmaz ([email protected]), Istanbul University, Department of Chemical Engineering, Avcilar, 34320 Istanbul, Turkey.

Chem. Eng. Technol. 2015, 38, No. 5, 917–930

water-soluble dispersed catalysts [10–12]. Solid powder catalysts, mainly Fe-, Ni-, and V-containing catalysts, are dispersed in raw materials before processing [11]. Fe-containing catalysts of slurry hydrocracking technology were found to be effective. The most preferable catalyst is iron sulfate salt which is able to reduce the amount of heavy fractions of petroleum that cause formation of a coke fraction [13, 14]. Red mud, a disposable iron-based catalyst, is also suitable for hydrocracking reactions of heavy oil. Nguyen-Huy et al. [15] used red mud after modification as catalysts for the slurry-phase catalytic hydrocracking of vacuum residue. They found that the liquid yield increased and the coke amount decreased in the presence of modified red mud-derived materials [15]. The type and cost of the catalyst has to be considered in the selection of a catalyst for the hydrocracking process. Applying more than one substance as the catalyst instead of a single agent may be the best choice. Heavy petroleum includes aromatic compounds, the amounts of which vary in the range of 10 % and 50 % depending on the type of petroleum. A high amount of high-boiling aromatic compounds makes the oil refinery process more difficult and reduces the quality of products. Heavy petroleum generally contains significant quantities of aromatic compounds such as naphthalene, pyrene, and anthracene [1, 7, 16]. Since petroleum includes thousands of complex molecules, it is not possible to explain the reactions during hydrocracking. Therefore, the information obtained from the hydrocracking reactions of model compounds can be used as a means to elucidate hydrocracking of petroleum. Studies were carried out in order to understand the hydrocracking reactions of aromatic model compounds under differ-

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Research Article

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ent conditions in the presence of various catalysts [17–19]. Hydrogenation, isomerization, and cracking take place during hydrocracking of aromatic compounds. NiW/USY zeolite catalyst [6, 20, 21], silica alumina-supported molybdenum oxide, cobalt oxide, nickel oxide, a mixture of metal oxides [18], and zeolite-supported Ni2P [22] were generally preferred as catalysts for hydrocracking reactions of aromatic model compounds. Tang and Curtis [23] studied slurry hydrocracking reactions of model aromatic compounds using organic-based catalysts such as iron stearate, iron naphthenate, and molybdenum naphthenate with the addition of sulfur. The most recent studies on the processing of heavy oils showed that the untreated cheap Fe-containing solid heterogeneous catalysts in the form of powder led to efficient results [14, 24]. Aromatic hydrocarbons were converted into light products using high-efficient and low-cost catalysts. Slurry hydrocracking reactions of naphthalene, which served as an aromatic model compound, were performed in the presence of different disposable catalysts. The highest naphthalene conversion was achieved by a mixture of FeSO4H2O+Fe2O3+Al2O3+S. The effects of reaction temperature, time, and H2 pressure on the hydrocracking reactions of naphthalene were evaluated.

2

Experimental

2.1 Materials Naphthalene (Merck, 99 wt %) served as a model aromatic compound. FeSO47H2O (Merck, 99.5 wt %), Fe2(SO4)3xH2O (Sigma-Aldrich, 99.5 wt %), Fe2O3 (Sigma-Aldrich, 99 wt %), Al2O3 (Sigma-Aldrich, 99 wt %), CaO (Sigma-Aldrich, 98 wt %), and SiO2 (Sigma-Aldrich, 99 wt %) were used for preparing different catalyst compositions. Dichloromethane (Merck, 99.8 wt %) was employed as solvent and biphenyl (Merck, 99 wt %) as external standard to analyze reaction products by gas chromatography (GC).

2.2 Preparation of Catalyst Mixtures Different amounts of FeSO4H2O, Fe2(SO4)3xH2O, Fe2O3, Al2O3, CaO, SiO2, elementary sulfur (S), and their mixtures were used as catalysts to investigate the efficiency of catalyst compositions. FeSO47H2O which was dried at 120 C for 90 min to remove 6 mol of water was converted to FeSO4H2O [14]. This catalyst and other metal oxides were grounded to powder in a ball mill system to obtain a homogenous and suitable mesh size for a better performance during experiments. The powder was sieved to 50–325 mesh by a Retsch AS 450 seperator system. The various mixtures of FeSO4H2O, Fe2(SO4)3 xH2O, metal oxides, and elementary sulfur (S) used as catalyst are listed in Tab. 1.

2.3 Hyrocracking Reactions Reactions were performed in a 10-mL stainless-steel batch bomb-type reactor with stainless-steel Swagelok tube fittings. A

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stainless-steel ball with 9.5 mm diameter was placed into the reactor for stirring the reaction mixture by a specially designed vertical mixer system working at a speed of 200 rpm. The reactor was loaded with 1 g of naphthalene and each catalyst listed in Tab. 1, purged several times with high-pressure H2, and then plunged into an isothermal fluidized sandbath that had been preheated to the desired reaction temperature. Reactions were carried out at 100 bar of H2 initial pressure at 425 C for 90 min [25] and also using the most efficient catalyst composition at 100 bar of H2 initial pressure at 400 C, 425 C, and 450 C for holding times from 10 to 90 min. Reactions were performed at 425 C for 90 min at 50 and 120 bar of H2 initial pressure to investigate the effect of hydrogen pressure on the hydrocracking reactions. After the desired reaction time, the reactor was removed from the sandbath and immediately cooled to stop the reaction. The yield of each product fraction was determined gravimetrically. After disconnecting the reactor from the shut-off valve, the gas yields were released and specified gravimetrically. Remaining reaction products were eluted with dichloromethane. Liquid products were separated with dichloromethane from the solid phase and solids were washed with dichloromethane. The liquid yields were determined by evaporating dichloromethane. Subsequently, insoluble solids were dried and weighed. The recovery of products from the reactor was in the range of 90–95 %. The loss of material was assumed to be due to the entrainment of products in the gas phase and evaporation during separation of products. The process was also performed without catalyst to evaluate the effect of catalyst on conversion of naphthalene and kind of products.

2.4 Product Analysis At the end of each reaction, the products were analyzed by GC and mass spectrometry. The reaction products were determined by an Agilent Technologies 7890A gas chromatograph equipped with an Agilent Technologies 5975C mass detector. A capillary column HP-5MS (30 m ·0.25 mm ·0.25 mm) was operated with a helium flow rate of 116.81 mL min–1. GC analysis was performed at a controlled temperature of 303 K, where it was held for 1 min and then increased to 358 K with a temperature gradient of 10 K min–1. This temperature was held for 2 min and then increased to 423 K with a temperature gradient of 10 K min–1 and held for 10 min. Response factors were determined by measuring the relationship between the weight ratios and the area ratios of the products to an external standard. Biphenyl served as the external standard to identify products quantitatively. The response factors of products were 1.00 ± 0.1. The values which could not be measured were assumed to be equal to 1.0. The different catalyst compositions were also analyzed by X-ray diffraction (XRD) before and after the reactions. Structural analysis of the catalysts was carried out by X-ray powder diffraction on a Rigaku D/Max-2200/PC diffractometer with a monochromatic Cu resource (A4 1L-Cu/60 kV, 2.0 kW), the 2q angle ranging from 0 to 70 with a Cu Ka radiation (l = 1.5404 Å). The average crystallite size of FeS was calculated by the Scherrer method, where the constant K was taken as 0.9.



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Table 1. Catalyst compositions. FeSO4H2O [g]

Al2O3 [g]

Fe2O3 [g]

CaO [g]

SiO2 [g]

Fe2(SO4)3xH2O [g] Sulfur [g]

AI

0.05

–

–

–

–

–

–

AII

0.025

0.025

–

–

–

–

–

AIII

0.025

–

0.025

–

–

–

–

AIV

0.025

–

–

0.025

–

–

–

AV

0.025

–

–

–

0.025

–

–

BI

–

–

–

–

–

0.05

–

BII

–

0.025

–

–

–

0.025

–

CI

–

–

0.05

–

–

–

0.05

CII

–

0.025

0.025

–

–

–

0.15

CIII

–

–

0.025

–

0.025

–

0.15

CIV

–

0.025

0.025

–

0.025

–

0.15

Nomenclature FeSO4H2O (A)

Fe2(SO4)3xH2O (B)

Fe2O3 and S (C)

FeSO4H2O, Al2O3, Fe2O3, and S (D) DI

0.05

0.023

0.05

–

–

–

0.06

DII

0.05

0.05

0.05

–

–

–

0.1

Fe2(SO4)3xH2O, Al2O3, Fe2O3 and S (E) EI

–

0.05

0.05

–

–

0.05

0.05

EII

–

0.05

0.05

–

–

0.05

0.1

A Thermo Finnigan Flash Model EA 1112 elemental analyzer helped to check whether insoluble carbonaceous solids were formed in the solid phase after the hydrocracking reactions.

3

Results and Discussion

3.1 Effect of Catalyst Composition on Slurry Hydrocracking Reactions of Naphthalene Hydrocracking reactions of naphthalene using different catalyst compositions were carried out to determine the activity of each catalyst composition containing different Fe-based materials, S-based materials, and/or elemental S. The amount of Fe and the ratio of Fe to S were calculated for each catalyst composition. Naphthalene conversions for hydrocracking reactions with respect to the amount of Fe and the ratio of Fe to S are listed in Tab. 2. According to Figs. 1 and 2, naphthalene conversion increased generally with higher amount of Fe and with decreasing the ratio of Fe to S, but some catalysts did not follow this trend because of using different Fe-based materials, elemental S, and other materials such as Al2O3 and SiO2. As observed in Fig. 1, although the AIII catalyst contained a high Fe amount


(4.6 ·10–4 mol), lower naphthalene conversion was obtained using this catalyst. The ratio of Fe to S in the AIII catalyst was higher than other A group catalysts as well as B and C group catalysts. The maximum naphthalene conversion was achieved with the DII catalyst with 9.2 ·10–4 mol Fe content. The amount of Fe in the DI catalyst was also 9.2 ·10–4 mol but the ratio of Fe to S in the DII catalyst was lower than that of DI. As indicated in Fig. 2, the CII, CIII, and CIV catalysts had a minimum ratio of Fe to S but naphthalene conversions with these catalysts were lower than those of D and E group catalysts. The excess of S may have adversely affected the naphthalene conversion by covering the catalyst pores. These results showed the effect of the amount of Fe and S on the conversion of naphthalene. An increase in the weight of the solid portion did not occur as a result of any hydrocracking reaction conducted with the different catalyst compositions. Elemental analysis was also carried out to detect the carbon amount of solids. Carbon was not determined in the catalyst compositions after the hydrocracking reactions. Coke, an insoluble solid, was only found after the hydrocracking reaction of naphthalene without catalyst, with a yield of 4 wt %. The gas and liquid product yields, remaining naphthalenes, naphthalene conversions, and selectivities of hyrocracking reactions with regard to the ratio of liquid yields


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Table 2. Product distributions (gas yields, liquid yields, remaining naphthalenes), naphthalene conversions and selectivities (ratio of liquid yields to naphthalene conversion) of the naphthalene hydrocracking reactions with respect to the amount of Fe and the ratio of Fe:S in the catalysts. Composition

Fe ·10–4 [mol]

Fe:S [mol mol–1]

Without catalyst

–

–

AI

FeSO4H2O

2.95

AII

FeSO4H2O+Al2O3

AIII

Catalyst

Liquid yield [wt %]

Rem. naph. [wt %]

Napht. conv. [wt %]

Selectivity [wt %]

2.0

14.9

79.1

20.9

0.72

1.00

7.3

22.9

69.8

30.2

0.76

1.47

1.00

4.7

26.4

68.9

31.1

0.85

FeSO4H2O+ Fe2O3

4.60

3.13

5.4

21.4

73.2

26.8

0.80

AIV

FeSO4H2O+CaO

1.47

1.00

4.2

20.3

75.5

24.5

0.83

AV

FeSO4H2O+SiO2

1.47

1.00

4.5

18.2

77.3

22.7

0.80

BI

Fe2(SO4)3xH2O

2.50

0.67

3.5

29.8

66.7

33.3

0.89

BII

Fe2(SO4)3xH2O+Al2O3

1.25

0.67

5.1

30.5

64.4

35.6

0.86

CI

Fe2O3+S

6.25

0.40

11.0

38.5

50.5

49.5

0.78

CII

Fe2O3+Al2O3+S

3.13

0.07

15.8

48.3

35.9

64.1

0.75

CIII

Fe2O3+SiO2+S

3.13

0.07

17.4

47.8

34.8

65.2

0.73

CIV

Fe2O3+ SiO2+Al2O3+S

3.13

0.07

14.5

41.4

44.1

55.9

0.74

DI

FeSO4H2O+Al2O3+Fe2O3+S

9.20

0.42

9.0

50.1

40.9

59.1

0.85

DII

FeSO4H2O+Al2O3+Fe2O3+S

9.20

0.27

10.3

62.8

26.9

73.1

0.86

EI

Fe2(SO4)3xH2O+Al2O3+Fe2O3+S 8.75

0.45

16.8

49.9

33.3

66.7

0.75

EII

Fe2(SO4)3xH2O+Al2O3+Fe2O3+S 8.75

0.25

11.8

61.1

27.1

72.9

0.84

DII

(at 400 C for 90 min)

9.20

0.27

5.2

54.2

40.6

59.4

0.91

DII

(at 450 C for 90 min)

9.20

0.27

25.5

63.7

10.8

89.2

0.71

DII

(at 50 bar for 90 min)

9.20

0.27

2.6

25.4

72.0

28.0

0.91

DII

(at 120 bar for 90 min)

9.20

0.27

22.8

58.6

18.6

81.4

0.72

to naphthalene conversions are also listed in Tab. 2 with respect to the used catalyst composition. The gas and liquid yields generally increased with higher amount of Fe, the usage of elemental S, and decreasing the ratio of Fe to S. The experimentally determined gas yields were between 3.5 and 17.4 wt % and the liquid yields ranged from 18.2 to 62.8 wt % at 425 C for 90 min at 100 bar of H2. The selectivities were between 0.73 and 0.89 and the selectivities of the reactions with high S content (C group catalysts) were lower than others. Although the amounts of reaction products are varying, the kinds of the reaction products are similar at the end of the hydrocracking reactions of naphthalene for each different catalyst composition. Liquid products are mainly tetralin, 1-methylindane, indane, butylbenzene, ethylbenzene, toluene, and benzene. Liquid product distributions for the hydrocracking reactions of naphthalene using FeSO4H2O (A group) and Fe2(SO4)3 xH2O (B group) and metal oxides are illustrated in Fig. 3. Tetralin and ethylbenzene were major products when applying FeSO4H2O with different metal oxides and without catalyst. However, the formation of benzene and toluene increased using Fe2(SO4)3xH2O and Fe2(SO4)3xH2O+Al2O3. Overall,

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Gas yield [wt %]

the conversion of naphthalene ranged between 22.7 and 31.1 wt % using FeSO4H2O with different metal oxides and between 33.3 and 35.6 wt % for Fe2(SO4)3xH2O (see Tab. 2). The results demonstrate that the conversion of naphthalene increased when Al2O3 with FeSO4H2O and Fe2(SO4)3xH2O were utilized. The decrease in the ratio of Fe to S also affected the conversion. The ratio of Fe to S was lower for the B group (0.67) catalysts than that for the A group catalysts (1.00). The formation of tetralin resulted from primary hydrogenation of naphthalene [6]. The amounts of other products formed by secondary reactions were at a low level. Therefore, hydrogenation was predominant for hydrocracking reactions using FeSO4H2O with different metal oxides. 1-Methylindane formed by isomerization of tetralin undergoes dealkylation and ring opening to produce ethylbenzene [6]. Hydrocracking reactions were also achieved by a mixture of Fe2O3 with metal oxides and elementary sulfur (C group) without FeSO4H2O and Fe2(SO4)3xH2O; the distribution of liquid products is displayed in Fig. 4. The amount of tetralin decreased and that of ethylbenzene, toluene, and benzene increased using a mixture of elementary sulfur and Fe2O3 as cata-



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100

Naphthalene Conversion, wt-%

90 80

Fe 3.13x10-4

60

Fe 8.75x10-4

Fe 3.13x10-4

70

Fe 1.25x10-4

Fe 1.47x10-4

Fe 1.47x10-4

30 without catalyst 20

Fe 9.20x10-4

Fe 6.25x10-4

50 40

Fe 9.20x10-4

Fe 2.95x10-4

Fe 4.6x10-4

10 0 N

BII

AV

AIV AII BI AI Fe Fe 1.47x10-4 2.50x10-4

CIV

CII CIII Fe 3.13x10-4

AIII

CI

EI

EII DI Fe 8.75x10-4

DII

Catalyst

Figure 1. Naphthalene conversion (wt %) after hydrocracking reactions of naphthalene with respect to Fe amount (mol) in catalysts. 100

Naphthalene Conversion, wt-%

90 Fe:S=0.27 Fe:S=0.25

80 Fe:S=0.45 Fe:S=0.42

70 60

Fe:S=0.07

Fe:S=0.4

50

Fe:S=0.07 Fe:S=0.07

Fe:S=0.67

40

Fe:S=0.67 Fe:S=1 Fe:S=3.1 Fe:S=1 Fe:S=1 30 without Fe:S=1 catalyst 20 10 0 N

AIII

AV

AIV

AI

AII

BI

BII

EI

DI

CI

DII

EII

CIV

CII

CIII

Catalyst

Figure 2. Naphthalene conversion (wt %) after hydrocracking reactions of naphthalene with respect to the ratio of Fe to S (mol mol–1) in catalysts.

lyst in comparison to FeSO4H2O and Fe2(SO4)3xH2O with metal oxides. The amounts of ethylbenzene, toluene, and benzene formed by secondary reactions are larger. Therefore, secondary reactions are predominant for hydrocracking reactions using these catalysts. Adding metal oxides and increasing the amount of elementary sulfur led to higher amounts of benzene, toluene, and ethylbenzene. The activity of the iron catalyst improved in the presence of sulfur [23]. The lower ratio of Fe to S in the catalyst CII with 0.15 g sulfur improved the conversion of naphthalene to approximately 65 wt % (see Tab. 2).


In order to evaluate the effect of the different types of sulfur and iron compounds on the activity of the catalyst composition, FeSO4H2O and Fe2(SO4)3xH2O was added to the catalyst mixture with 0.06 g and 0.1 g of sulfur (D and E groups), respectively. The distributions of liquid products are presented in Fig. 5. The catalyst mixture with 0.1 g of sulfur (DII) was more effective for the hydrocracking reaction of naphthalene. Adding FeSO4H2O to the mixture of Fe2O3 and Al2O3, the amount of Fe in the catalyst composition increased from 3.13 ·10–4 mol to 9.2 ·10–4 mol. Lowering the amount of elementary sulfur from 0.15 g to 0.1 g caused higher conversion of


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10

10

8

8

Benzene

6

wt %

wt %

6

Toluene

4

4

2

2

0

0 N

AI

AII AIII AIV AV

BI

BII

N

AI

AII AIII AIV AV

Catalyst

BI

BII

BI

BII

Catalyst

10 Ethylbenzene

4

6

Indane

wt %

wt %

8

2

4 2

0

0 N

AI

AII

AIII AIV AV

BI

N

BII

AI

AII

Catalyst

Catalyst 2

5 4 wt %

Butylbenzene wt %

AIII AIV AV

1

1-methylindane

3 2 1 0

0 N

AI

AII

AIII AIV AV

BI

N

BII

AI

AII

10

100 90

6 4 2 0 AI

AII

AIII AIV AV

BII

Naphthalene

80 wt %

wt %

Tetralin

N

BI

Catalyst

Catalyst

8

AIII AIV AV

BI

BII

70 60 50 40 30 20 10 0 N

Catalyst

AI

AII

AIII AIV AV

BI

BII

Catalyst

Figure 3. Liquid products after hydrocracking reaction of naphthalene using a mixture of FeSO4H2O and Fe2(SO4)3 with metal oxides.

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30

20

25

Toluene

Benzene 15 wt %

wt %

20 15

10

10 5 5 0

0 CI

CII

CIII

CI

CIV

CII

Catalyst

CIII

CIV

Catalyst

20 Indane

wt %

wt %

4

Ethylbenzene

15

10

2

5 0

0 CI

CII

CIII

CI

CIV

CII

Catalyst 2

CIV

5 4 wt %

Butylbenzene wt %

CIII

Catalyst

1

1-methylindane

3 2 1 0

0 CI

CII

CIII

CI

CIV

CIII

10

100 90

8

Tetralin wt %

6 4 2 0 CI

CII

CIII

Catalyst

CIV

Catalyst

Catalyst

wt %

CII

CIV

Naphthalene

80 70 60 50 40 30 20 10 0 CI

CII

CIII

CIV

Catalyst

Figure 4. Liquid products after hydrocracking reaction of naphthalene using a mixture of sulfur and metal oxides.



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40

20 Toluene

35 Benzene

30

15 wt %

wt %

25 20

10

15 10

5

5 0

0 DI

DII

EI

EII

DI

Catalyst

DII

EI

EII

Catalyst

15 Ethylbenzene 4

Indane

wt %

wt %

10 2

5

0

0 DI

DII

EI

DI

EII

DII

EII

Catalyst

Catalyst 2

5 4 wt %

Butylbenzene wt %

EI

1

1-methylindane

3 2 1 0

0 DI

DII

EI

DI

EII

EI

EII

Catalyst

Catalyst 10

100

Naphthalene

90

8

Tetralin

6 wt %

wt %

DII

4 2

80 70 60 50 40 30 20 10

0 DI

DII

EI

EII

0 DI

Catalyst

DII

EI

EII

Catalyst

Figure 5. Liquid products after hydrocracking reaction of naphthalene using a mixture of iron(II) and iron(III) sulfate with sulfur and metal oxides.

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naphthalene to 73.1 wt %. The selectivities of hydrocracking reactions using DI and DII catalysts with regard to the ratio of liquid yields to naphthalene conversions were higher than those of the C group catalysts with higher elemental S amount (see Tab. 2). The catalyst which enables the highest conversion for naphthalene is the mixture of sulfur, FeSO4H2O, Fe2O3, and Al2O3 (DII).

3.2 Effect of Temperature and Time on Slurry Hydrocracking Reactions of Naphthalene The most effective catalyst found was applied for hydrocracking reactions at 400 C, 425 C, and 450 C for holding times ranging from 10 to 90 min at 100 bar of H2 initial pressure. The distributions of liquid products are illustrated in Fig. 6. Naphthalene yielded liquid products such as tetralin, 1-methylindane, butylbenzene, indane, etyhlbenzene, toluene, benzene, and remaining naphthalene after hydrocracking reactions at all temperatures. With longer reaction time the amount of remaining naphthalene was reduced at 400 C. In general, compared with other products, high amounts of tetralin and 1-methylindane formation were observed at 400 C. Benzene formed after 40 min, toluene and ethylbenzene were generated in very small quantities in shorter reaction times and the amounts of benzene, toluene, and ethylbenzene became larger with increasing time. The amounts of tetralin and 1-methylindane were reduced after 60 min. This suggests that tetralin formed by hydrogenation of naphthalene primarily and 1-methylindane, which developed by isomerization of tetralin, underwent ring opening and then dealkylation to produce etylbenzene, toluene, and benzene [6]. At higher temperature, the conversion of naphthalene rose at 425 C with increasing time. Although the yields of tetralin and 1-methylindane showed a sharp increment at 425 C for 10 min, they consistently decreased with increasing time after 10 min. However, the yield of indane rose to 60 min, and its amount decreased after 60 min. The formation rate of the tertiary products such as ethylbenzene, toluene, and benzene increased rapidly with time. However, at 450 C, when naphthalene conversion was higher and faster, large quantities of toluene and benzene were rapidly produced through tetralin, 1-methylindane, indane, and ethylbenzene, respectively. The highest amount of tetralin, 1-methylindane and indane that occurred at 450 C for 10 min decreased with time. Toluene and benzene yields exhibited growing yields with increasing time and temperature. This shows that hydrogenation reactions predominated at 400 C and ring opening and dealkylation reactions were favored at higher temperatures. As the temperature rose, the disappearance rate of naphthalene increased. The ultimate naphthalene conversions for 90 min reached 59.4, 73.1, and 89.2 wt % at 400, 425, and 450 C, respectively (see Tab. 2). The experimentally determined remaining naphthalene yields were between 14.5 and 77.8 % in the liquid products at 400, 425, and 450 C for holding times ranging between 10 and 90 min. Qader and Hill [18] reached at 475 C for 120 min at 1000 psi H2 pressure 74–75 % conversion as a result of naphthalene hydrocracking and found


~ 7 % coke formation. Korre et al. [6] and Yun and Lee [22] achieved 87 % and 90 % conversion of naphthalene for hydrocracking reactions over prepared and pretreated catalysts.

3.3 Effect of Hydrogen Pressure on Slurry Hydrocracking Reactions of Naphthalene Hydrocracking reactions were repeated at 425 C for 90 min at 50 and 120 bar of H2 initial pressures to investigate the effect of hydrogen pressure on the hydrocracking reactions. The distribution of liquid products is presented in Fig. 7. Low conversion of naphthalene was found at 50 bar of H2 initial pressure compared to the reactions carried out at higher pressures. The yield of light products such as ethylbenzene, toluene, and benzene and conversion of naphthalene increased with higher hydrogen pressure. The maximum conversion was 81.4 wt % at 120 bar of H2 (see Tab. 2). The amount of remaining naphthalene for the hydrocracking reaction without catalyst at 100 bar of H2 was ~ 79.1 % and 26.9 % in the presence of catalyst DII for the same reaction condition. The difference of the amounts of the remaining naphthalene shows the efficiency of the catalyst.

3.4 Structural Analysis of the Catalysts Structural changes of catalyst compositions were analyzed by XRD. XRD patterns of unused and used catalyst consisting of FeSO4H2O+Al2O3 are given in Fig. 8. The peaks at 18, 25.8, 28.7, 57.5, and 35.4 of 2q angles represent the existence of FeSO4H2O in the mixture. The peaks of the catalyst mixture at about 29.8, 33.7, 43.6, and 56.2 of 2q angles indicate the formation of Fe1–xS from iron sulfate during the hydrocracking reaction. The iron sulfide formed during the reaction is the active form of the catalyst [14]. XRD patterns in Figs. 8, 9, and 10 show that Fe1–xS also occurred from Fe2(SO4)3+Al2O3, Fe2O3+S, Fe2O3+S+Al2O3, and FeSO4H2O+Fe2O3+S+Al2O3 during the hydrocracking reactions. Bhattacharyya and Mezza [14] studied hydrocracking reactions of heavy oil with FeSO4H2O and Fe2O3+Al2O3 and also explained the formation of FeS from FeSO4H2O and Fe2O3+Al2O3 during the hydrocracking reaction. Iron in the iron oxide, in the presence of sulfur and aluminum oxide without any pretreatment, is converted quickly to iron sulfide during hydrocracking reaction. Iron sulfide has several molecular forms and, therefore, it is generally represented by the formula FexS where x takes values ranging from 0.7 to 1.3. They also determined that all of the iron oxide is converted to iron sulfide at 410 C with the reaction between iron oxide and H2S formed by reaction of the sulfur in the heavy oil and hydrogen. XRD patterns of the catalyst consisting of FeSO4 H2O+Fe2O3+S+Al2O3 used at 400, 425, and 450 C are displayed in Fig. 10. The peaks at 18, 25.8, 28.7, 57.5, and 35.4 of 2q angles indicate the existence of FeSO4H2O. The peaks at about 29.8, 33.7, 43.6, and 56.2 of 2q angles point to the formation of Fe1–xS from catalysts during reactions at 400, 425, and 450 C. The catalyst containing FeSO4H2O+Fe2O3+S is converted to Fe1–xS during the hydrocracking reactions.


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50,0

50,0 400 ° C 425 ° C 450 ° C

45,0 40,0

Benzene

35,0

45,0 35,0 30,0 wt %

wt %

30,0 25,0 20,0

25,0 20,0

15,0

15,0

10,0

10,0

5,0

5,0 0,0

0,0 10

20

40 Time (min.)

60

10

90

50,0

20

40 Time (min.)

60

90

20,0

45,0 40,0

Ethylbenzene

35,0

400 ° C 425 ° C 450 ° C wt %

25,0

400 ° C 425 ° C 450 ° C

Indane

15,0

30,0

wt %

400 ° C 425 ° C 450 ° C

Toluene

40,0

10,0

20,0 15,0

5,0

10,0 5,0 0,0

0,0 10

20

40 Time (min.)

60

90

10

10,0

40 Time (min.)

20,0 400 ° C 425 ° C 450 ° C

1-methylindane 15,0 wt %

Butylbenzene

wt %

20

5,0

60

90

400 ° C 425 ° C 450 ° C

10,0

5,0

0,0

0,0 10

20

40 Time (min.)

60

90

10

40,0

40 Time (min.)

60

90

100,0 400 ° C 425 ° C 450 ° C

35,0 Tetralin

30,0

90,0

Naphthalene

80,0 70,0 wt %

25,0 wt %

20

20,0

400 ° C 425 ° C 450 ° C

60,0 50,0 40,0

15,0

30,0

10,0

20,0

5,0

10,0

0,0

0,0 10

20

40 Time (min.)

60

90

10

20

40 Time (min.)

60

90

Figure 6. Temporal variations of hydrocracking products.

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927

40

25

35

20

Benzene

25

wt %

wt %

30 20

Toluene

15 10

15 10

5

5 0

0 Without Cat.

50 bar

100 bar

Without Cat.

120 bar

Catalyst

50 bar

100 bar

120 bar

Catalyst

25 Ethylbenzene

4

15

Indane

wt %

wt %

20

10

2

5 0

0 Without Cat.

50 bar

100 bar

Without Cat.

120 bar

Catalyst

100 bar

120 bar

Catalyst

5

2

4 wt %

Butylbenzene wt %

50 bar

1

1-methylindane

3 2 1 0

0 Without Cat.

50 bar

100 bar

Without Cat.

120 bar

Catalyst

50 bar

120 bar

Catalyst

100

10

Naphthalene

90

8

80

Tetralin

70

6

wt %

wt %

100 bar

4

60 50 40 30

2

20 10

0 Without Cat.

50 bar

100 bar

Catalyst

120 bar

0 Without Cat.

50 bar

100 bar

120 bar

Catalyst

Figure 7. Liquid products of hydrocracking of naphthalene for different H2 pressures.



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Fe1-xS

Fe1-xS

Fe1-xS

Fe1-xS

Fe1-xS

Al 2O3

Al 2O3

1600

Fe2(SO4)3.xH2O+Al2O3 After reaction

Al2O3

Coke Fe1-xS Al2O3

800

Fe1-xS

Fe2(SO4)3.xH2O+Al2O3

Fe1-xS Fe S Al2O3 1-x

Intensity / cps

Fe1-xS Fe1-xS Al2O3

Fe1-xS Fe1-xS

Intensity / cps

Fe1-xS Fe1-xS Al 2O3

Al 2O3

Fe1-xS

XRD patterns of recovered solids from hydrocracking reactions with all catalyst compositions at 90 min exhibit the same Fe1–xS formation. Additionally, Fe1–xS formation was the same for different reaction conditions such as various temperatures of 400, 425, and 600 Fe2O3+Al2O3+S 450 C. Fe1–xS, also known as pyrrhotite, is a non-stoichiometric iron monosulfide and Nguyen-Huy et al. explained in their study that it is thermodynamically stable at temperatures above 200 C [15, 26]. So, the 300 Fe2O3+S morphology of the Fe–S can be assumed to remain stable for all reaction conditions. XRD patterns of the solid phase formed during hydrocracking of naphCoke thalene without catalyst are illustrated in Figs. 8, 9, and 10. The peak at about 0 30 60 26 of 2q angles represents the formao 2θ / tion of an insoluble solid carbonaceous phase, i.e., coke. Bhattacharyya and Figure 9. XRD analysis of Fe2O3+S and Fe2O3+Al2O3+S after hydrocracking and of coke from Mezza [14] also determined the solid naphthalene of the hydrocracking reaction without catalyst at 425 C for 90 min at 100 bar mesophase peak in the range between of hydrogen pressure. about 20 and 29.5 in the XRD pattern lated by the Scherrer method. The results in Tab. 3 indicate that of the utilized catalyst after hydrocracking reactions of heavy particle crystallite sizes of FeS formed from different catalyst oil. The insoluble carbonaceous phase was only determined compositions are between ~ 16 and 25 nm. The particle crysafter the hydrocracking reaction of naphthalene without catatallite size of Fe1–xS formed from the catalyst containing lyst. FeSO4H2O (AII) and Fe2(SO4)3xH2O (BII) without elemental After the determination of Fe1–xS in catalyst mixtures by sulfur is around 25 nm, that of Fe1–xS achieved from catalysts XRD analysis, the average crystallite sizes of FeS were calcu-

FeSO4.H2O+Al2O3 After reaction FeSO4.H2O

0 0

30

2θ / ο

60

Figure 8. XRD analysis of FeSO4H2O+Al2O3 and Fe2(SO4)3xH2O+Al2O3 after hydrocracking and of coke from naphthalene of the hydrocracking reaction without catalyst at 425 C for 90 min at 100 bar of hydrogen pressure.

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Research Article

Fe1-xS

450 oC

425 oC

1200

400 oC

0

30

Fe2O3 Al2O3

Coke Al2O3 Fe2O3

FeSO4.H2O FeSO4.H2O

600

S S S FeSO4.H2O Fe2O3 Al2O3 FeSO4.H2O

Intensity / cps

Fe1-xS Fe1-xS Al2O3

1800

Fe1-xS Al2O3

929

before reaction 60

2θ /ο

Figure 10. XRD analysis for a mixture of FeSO4H2O+Fe2O3+Al2O3+S after hydrocracking at 400 C, 425 C, and 450 C and for coke from naphthalene of the hydrocracking reaction without catalyst.

Table 3. 2q angle and particle crystallite sizes (d) of Fe1–xS formed from different catalyst compositions.

Table 4. 2q angle and particle crystallite sizes (d) of Fe1–xS formed from the DII catalyst for different reaction temperatures.

Catalyst composition

2q [o]

d [nm]

Temperature

2q

d [nm]

AII: FeSO4H2O+Al2O3

44.13

25.0

400 C

43.48

20.4

BII: Fe2(SO4)3xH2O+Al2O3

43.22

21.9

425 C

43.21

16.1

CI: Fe2O3+S

43.58

22.0

450 C

43.39

16.4

CII: Fe2O3+Al2O3+S

43.19

19.6

DII: FeSO4H2O+Fe2O3+Al2O3+S

43.21

16.1

containing Fe2O3 and elemental sulfur (CI and CII) range between about 19.6 and 22 nm, and of Fe1–xS from the catalyst containing FeSO4H2O, Fe2O3, and elemental sulfur (DII), which enables the highest conversion of naphthalene, is about 16 nm. According to Tab. 4, the particle crystallite sizes of Fe1–xS formed from catalysts which are used for the hydrocracking reactions at 400, 425, and 450 C are between ~ 16 and 20.4 nm. The particle crystallite size of Fe1–xS occurring from the most efficient catalyst composition during the reaction at 400 C is around 20.4 nm and the smallest particle crystallite sizes of Fe1–xS generated from the catalyst composition during the reactions at 425 C and 450 C range between 16.1 and 16.4 nm, respectively. Bahattacharyya and Mezza [14] reported that the particle crystallite size of FeS derived from the mixture of Fe2O3 and Al2O3 during the hydrocracking reaction of heavy oil ranges between about 1 and 25 nm, although the preferred size is between ~ 5 and 15 nm. In this study, the particle size of FeS


DII: FeSO4H2O+Fe2O3+ Al2O3+S

obtained during the reactions is in the range of 16 and 25 nm and the particle size of FeS formed in the most efficient catalyst composition is 16 nm, being the closest value to the preferred range of the partical crystallite size of FeS for hydrocracking reactions.

4

Conclusions

Hydrogenation, isomerization, cracking, and dealkylation take place during hydrocracking of aromatic compounds. First of all, tetralin occurs by hydrogenation of naphthalene while 1-methylindane is formed by isomerization. The amounts of tetralin and 1-methylindane decrease and those of ethylbenzene, toluene, and benzene increase with ring opening and dealkylation reactions by applying catalysts containing elementary sulfur, Fe2O3, and metal oxides. The most efficient catalyst consists of FeSO4H2O, Fe2O3, Al2O3, and sulfur. By increasing the temperature and reaction time, the amount of remaining naphthalene decreases while that of light products such as toluene and benzene grows after the hydrocracking re-


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actions. The highest conversion of naphthalene is achieved at 450 C for 90 min. By raising the pressure of hydrogen, the amount of remaining naphthalene decreases while that of the light products toluene and benzene increases.

[9]

[10] [11]

Acknowledgment This work was supported by the Scientific Research Projects Coordination Unit of Istanbul University, Project No. 21739 and UDP-46462. The authors have declared no conflict of interest.

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