Effects of the Temperature and Initial Hydrogen Pressure on the

Article pubs.acs.org/EF

Effects of the Temperature and Initial Hydrogen Pressure on the Isomerization Reaction in Heavy Oil Slurry-Phase Hydrocracking Hui Du, Dong Liu,* Ming Li, Pingping Wu, and Yuanxi Yang State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, Shandong 266555, People’s Republic of China ABSTRACT: Thermal hydrocracking and slurry-phase hydrocracking of Karamay vacuum residue (KLVR) were studied, and the hydrocracked products were analyzed by gas chromatography (GC) and a paraffins, olefins, naphthalenes, and aromatics (PONA) composition analysis system. The effects of the temperature and initial hydrogen pressure on the isomerization reaction in heavy oil slurry-phase hydrocracking were investigated. Experimental data revealed that the conversion of KLVR increased as the temperature and initial hydrogen pressure increased in both thermal hydrocracking and slurry-phase hydrocracking. Hydrogen consumption of slurry-phase hydrocracking increased with the increase of the temperature and initial hydrogen pressure, while hydrogen consumption in thermal hydrocracking was negligible. Two impact indexes R′G and R′N were proposed to study the isomerization reaction in heavy oil slurry-phase hydrocracking. The results indicated that a high temperature and high initial hydrogen pressure enhanced the isoparaffin restraining effect of a dispersed Mo catalyst. Under a certain reaction temperature, the linear relation between impact indexes and hydrogen consumption was observed, indicating that the isomerization reaction was inhibited by hydrogen participating in a free-radical reaction.

1. INTRODUCTION The slurry-phase hydrocracking process is a newly developed technique for heavy oil processing, especially for inferior heavy crude oil and residue.1−4 In recent decades, many slurry-phase hydrocracking processes have been evaluated, including VCC,5 HDH,6 CANMET,7 EST,8 etc. Generally, the unsupported hydrogenation catalysts are used in heavy oil slurry-phase hydrocracking, which included heterogeneous solid powder catalysts and homogeneous dispersed catalysts.9−12 Recently, two kinds of homogeneous dispersed catalysts, including watersoluble catalyst and oil-soluble catalyst, become the major study direction because of high dispersibility and high hydrogenation activity.13−18 Actually, the so-called “homogeneous dispersed catalysts” are transition metal compounds used as homogeneous catalyst precursors in slurry-phase hydrocracking.19−24 During the slurry-phase hydrocracking process, a homogeneous dispersed catalyst converted to active transition metal sulfides through presulfurization or in situ sulfuration reaction. The near molecular size of transition metal sulfides can realize the highest level of catalyst utilization. Many molybdenum compounds, such as ammonium molybdate, molybdenum dialkyl dithiocarbamate, molybdenum naphthenate, etc., were used as dispersed catalysts in slurry-phase hydrocracking because of the high hydrogenation activity of MoS2.25−28 Dispersed catalyst plays a significant role in slurry-phase hydrocracking of heavy oil. The main functions of dispersed catalyst are converting gaseous hydrogen into active hydrogen, promoting hydroconversion, and preventing coke formation.29−33 Besides being catalytically active, dispersed catalysts serve as the coke getters. Most research on heavy oil slurryphase hydrocracking was to develop new and high-efficiency catalysts; however, little attention has been drawn on the reaction mechanism. The types of catalyst used in slurry-phase hydrocracking and fixed-bed hydrocracking of heavy oil are different. The supported catalyst is used in fixed-bed hydro© XXXX American Chemical Society

cracking of heavy oil, in which the active sites are acid sites and metal centers.34−36 Thus, both the free-radical mechanism and carbonium ion mechanism exist in heavy oil fixed-bed hydrocracking. However, the slurry-phase hydrocracking of heavy oil only follows the free-radical mechanism because the support with acid sites is not used in a homogeneous catalyst.37,38 Hydrocarbon molecules crack and generate hydrocarbon free radicals at high temperatures. Then, the hydrocarbon free radicals may further crack and condense to yield the light and heavy products. However, the active hydrogen generated on the surface of the sulfided catalyst is easy to quench with hydrocarbon free radical, which would suppress the above reactions of hydrocarbon free radicals.13,17,19 In the research of refining processes, the ratio of particular compounds was often used to determine the action mechanism of catalysts. Yang et al. proved the difference of the reaction mechanism between thermal cracking and hydrocracking (using supported NiMo catalysts) by the ratios of toluene/benzene and isobutane/n-butane.39 Meng et al. obtained the relative percentage of the free radical mechanism and carbonium ion mechanism of heavy oil catalytic pyrolysis by the ratio of isobutane/n-butane.40 To our knowledge, there are no reports on the effect of a dispersed catalyst on the isomerization in heavy oil slurry-phase hydrocracking. The main aim of the present work is to quantitatively express the effect of a dispersed Mo catalyst, and the influence of the temperature and initial hydrogen pressure is studied. Thermal hydrocracking and slurry-phase hydrocracking of Karamay vacuum residue (KLVR) were carried out, and two impact indexes R′G and R′N Received: October 28, 2014 Revised: December 9, 2014

A

DOI: 10.1021/ef5024143 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels Table 1. Composition and Properties of KLVR elemental composition (wt %) ρ20 (g cm−1) 0.9665

ν (mm2·s−1)

carbon residue (wt %)

C

H

12.4

86.61

11.96

901.6 (80 °C) SARA (wt %)

S 0.52 metal (μg g−1)

N 0.49

saturate

aromatic

resin

n-C7 asphaltene

Ni

V

Fe

34.68

26.72

25.08

13.52

24.3

10.4

0.70

(the effect of the dispersed Mo catalyst on the composition of gas and naphtha products) were proposed to investigate the isomerization reaction in slurry-phase hydrocracking. Besides, the relationship between hydrogen consumption and the impact indexes was also studied at a certain reaction temperature.

yield of gas (wt %) weight of feedstock − weight of autoclave contents = × 100 weight of feedstock The paraffin, olefin, naphthenic hydrocarbon, and aromatic hydrocarbon (PONA) of naphtha products were analyzed by an Agilent gasoline PONA composition analysis system. Some of experiments were performed 3 times to check the reproducibility, and the value reported are the average values.

2. EXPERIMENTAL SECTION KLVR was applied as a feedstock for thermal hydrocracking and slurryphase hydrocracking. KLVR is the vacuum residue of Karamay crude oil, which is a naphthenic base crude oil. The typical characteristics of KLVR are shown in Table 1. The dispersed Mo catalyst, an oil-soluble catalyst with the molybdenum content of 6.95 wt %, was synthesized according to the literature.41 Sublimate sulfur was used as the sulfurizing reagent. A total of 200 g of KLVR was loaded to a 500 mL batch-type autoclave. The hydrocracking reactions were carried out at different reaction temperatures (400−430 °C) and initial hydrogen pressures (4.0−10.0 MPa) for 1.0 h. The concentration of a dispersed Mo catalyst for slurry-phase hydrocracking in KLVR was 300 μg g−1 (calculated by the molybdenum content), and the concentration of sublimate sulfur in KLVR was 500 μg g−1. The dispersed Mo catalyst was soluble in KLVR, which then converted to finely dispersed MoS2 particles by in situ sulfuration under reaction conditions. Because of the low dosage, there was no need to recover the catalyst at the end of hydrocracking. After the hydrocracking reaction, the autoclave was rapidly cooled and vented. Part of the gas product was gathered by a gas sampling bag to analyze its composition by CP3800 gas chromatography (Varian, Inc.), and the rest of the gas product was vented through an absorption bottle (Figure 1). The autoclave

3. RESULTS AND DISCUSSION 3.1. Effect of the Reaction Temperature on Isomerization. 3.1.1. Product Distribution. As seen in Figure 2, the

Figure 2. Product distribution of KLVR thermal hydrocracking and slurry-phase hydrocracking at 8.0 MPa with different temperatures.

yields of gas, light oil (naphtha and diesel), and coke increased with the increase of the reaction temperature, while the yield of liquid C5+ decreased. However, the yields of gas, naphtha, and coke in slurry-phase hydrocracking are lower than that in thermal hydrocracking; similar conclusions were reached by Huy et al.10 based on slurry-phase hydrocracking of vacuum residue with a disposable red mud catalyst and also by Jeon et al.20 based on the product distribution of oil sands bitumen hydrocracking. Both of the hydrocracking reactions followed a free-radical mechanism. The small hydrocarbon molecule was produced through the thermal cracking of hydrocarbon, which would be promoted by the increase of the temperature, resulting in the increase of gas and light oil yields. Meanwhile, the high reaction temperature facilitated the condensation of hydrocarbon free radical, which increased the yield of coke. Hydrogen was easily split into hydrogen free radicals on the active site of a dispersed Mo catalyst; thus, the high concentration of a hydrogen free radical could inhibit the serious cracking and condensation of a hydrocarbon free radical. Therefore, the yields of gas, naphtha, and coke in slurryphase hydrocracking are lower than that in thermal hydrocracking at the same temperature, which also led to the high yield of liquid C5+ in slurry-phase hydrocracking. The yield of

Figure 1. Schematic of the experimental facility used for heavy oil hydrocracking: (1) hydrogen cylinder, (2) gas inlet, (3) gas outlet, (4) pressure gauge, (5) agitator, (6) 500 mL batch-type autoclave, (7) absorption bottle, and (8) gas sampling bag.

contents were distilled to obtain the naphtha (500 °C) fractions. The distilled bottom was washed by toluene. The toluene soluble was vacuum residue (VR), while the toluene insoluble was coke. Coke was gathered by centrifugation and dried in a vacuum oven at 110 °C for 4 h. The product yields of KLVR are calculated by the following equations: yield of product (wt %) =

weight of product × 100 weight of feedstock B


Article

Energy & Fuels VR decreased with the increase of the temperature in both hydrocracking reactions, indicating that a high temperature facilitated the conversion of KLVR. Moreover, the yield of VR in slurry-phase hydrocracking was lower than that in thermal hydrocracking. The reason is that the cracking degree of a large molecule in the two hydrocracking reactions would be the same under the same hydrogen pressure, reaction temperature, and time. With the presence of a dispersed Mo catalyst, a high hydrogen free-radical concentration promotes the combination of a hydrogen free radical with a hydrocarbon free radical. Thus, the condensation of a hydrocarbon free radical is suppressed, which reduces the yields of heavy products (VR and coke). Therefore, KLVR has a higher conversion during slurry-phase hydrocracking. 3.1.2. Hydrogen Consumption. Most hydrocarbon free radicals were generated in the liquid phase, which were the primary products of heavy oil cracking. The hydrocarbon free radical is unstable unless it could be combined with dissolved H2 in residue or active hydrogen on the catalyst surface, and the latter is the main route. Thus, hydrogen consumption arises. However, the hydrogen consumption in residue thermal hydrocracking was negligible, even though hydrogen participated in reactions.42 The molar volume (Vm) of hydrogen was calculated by the van der Waals equation.

Figure 3. Hydrogen consumption of KLVR slurry-phase hydrocracking at 8.0 MPa with different temperatures.

as the temperature increased;44 thus, more hydrogen could convert to active hydrogen by absorbing on the surface of a dispersed Mo catalyst under high temperatures. 3.1.3. Composition of the Gas Product. Thermal cracking of hydrocarbon follows a free-radical mechanism.37 The secondary hydrocarbon free radical quenches with a small hydrocarbon free radical and generates isoparaffin in thermal hydrocracking, whereas it quenches with a hydrogen free radical and generates n-paraffin in slurry-phase hydrocracking.39 Because of the difference in composition of the gas product during the two hydrocracking reactions, a parameter RG was used to demonstrate the isomerization ratio of the gas product, which was calculated by the following equation:

⎛ a ⎞ ⎟(Vm − b) = RT ⎜p + Vm 2 ⎠ ⎝

In the van der Waals equation, two correction factors a and b are proposed to correct the volume and pressure terms of the real gas system. The van der Waals parameter a of H2 is 0.024 32 Pa m6 mol−2, and b of H2 is 0.266 × 10−4 m3 mol−1. The partial pressure of hydrogen after the slurry-phase hydrocracking reaction was calculated from the total pressure and GC result, and then Vm of H2 was calculated under the assumption that the influence of hydrocarbon gas on hydrogen was disregarded. According to the gas volume and Vm of H2, the mass of hydrogen after the slurry-phase hydrocracking reaction was obtained. The hydrogen consumption of KLVR slurryphase hydrocracking was calculated by the following equation: hydrogen consumption =

RG =

yield of iso‐C4 H10 yield of n‐C4 H10

Moreover, an impact index R′G was proposed to define the effect of a dispersed Mo catalyst on the gas composition in slurryphase hydrocracking R G′ =

R GTH − R GSH R GTH

× 100%

where RGTH was the RG of the gas product in thermal hydrocracking and RSH G was the RG of the gas product in slurry-phase hydrocracking. RG values of gas products in thermal hydrocracking and slurry-phase hydrocracking were calculated according to the GC results, and then R′G values at different temperatures were obtained, as listed in Table 2. SH As shown in Table 2, both RTH G and RG decreased with the increase of the temperature; meanwhile, RSH G was lower than RTH at the same temperature. Macromolecular hydrocarbon G was easily cracked to produce hydrocarbon free radical at a high temperature. Then, the hydrocarbon free radical initiated the

m H′ 2 − m H″ 2 mKLVR

where mH′ 2 was the mass of hydrogen before the slurry-phase hydrocracking reaction (g), m″H2 was the mass of hydrogen after the slurry-phase hydrocracking reaction (g), and mKLVR was the mass of KLVR (kg). Figure 3 shows the hydrogen consumption of KLVR slurry-phase hydrocracking at different temperatures. As shown in Figure 3, the hydrogen consumption increased with the increase of the temperature. Hydrogen consumption increased because of two reasons. On one hand, hydrogen converted to hydrogen free radical through the chain transfer reaction with hydrocarbon free radical during the hydrocracking reaction. Retcofsky et al.43 have studied the effect of the temperature on the concentration of free radical by electron spin resonance (ESR), and the results showed that the concentration of hydrocarbon free radical increased with the increase of the temperature. Therefore, the probability of dissolved hydrogen participation in the chain transfer reaction increased with the increase of the reaction temperature. On the other hand, the solubility of hydrogen in the residue increased

Table 2. RG of the Gas Product in Thermal Hydrocracking and Slurry-Phase Hydrocracking and R′G at 8.0 MPa with Different Temperatures 400 410 420 430 a

C

°C °C °C °C

RTH G

RSH G

R′G (%)

0.962 0.921 0.844 0.821a

0.951 0.879 0.760 0.625a

1.14 4.56 9.95 23.87

Standard deviation in the results is between 0.6 and 1.5%. DOI: 10.1021/ef5024143 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

hydrocracking is much higher than that in thermal hydrocracking at the same temperature. However, the yield of isoparaffin in slurry-phase hydrocracking is slightly higher than that in thermal hydrocracking at the temperature range from 400 to 420 °C, and then it became lower than that in thermal hydrocracking when the temperature increased to 430 °C. Parameters were used to study the effect of a dispersed Mo catalyst on the naphtha composition. RN was introduced to study the isomerization ratio of the naphtha product.

chain transfer reaction, and hydrogen free radical was generated. On one hand, hydrocarbon free radical was consumed by the chain transfer reaction; in that case, isoparaffin generation by the combination of hydrocarbon free radicals was suppressed. On the other hand, the highreactivity hydrogen free radical was easily combined with hydrocarbon free radical. Hence, the RG of the gas product in both hydrocracking reactions decreased as the temperature increase. During the slurry-phase hydrocracking of KLVR, more hydrogen free radical existed in the slurry-phase reaction system, and then the level of isoparaffin suppression increased, which led to a lower RG of the gas product. Although both RTH G and RSH G decreased with the increase of the temperature, the TH decrease extent of RSH G was higher than that of RG , which means that RG′ increased. A significant increase of RG′ was achieved by increasing the temperature from 400 to 430 °C. Previous studies indicated that the high temperature improved hydrogenation activities of the catalyst during the hydroprocessing of heavy oil.45,46 The hydrogen free radical could induce the free-radical reaction and, to a certain extent, could suppress the formation of isoparaffin. Hence, the effect of the dispersed Mo catalyst on composition of the gas product increased as the reaction temperature increased. 3.1.4. Composition of the Naphtha Product. The composition of the naphtha product was analyzed using an Agilent gasoline PONA composition analysis system, and the analysis results of KLVR thermal hydrocracking and slurryphase hydrocracking are listed in Tables 3 and 4, respectively.

RN =

Then, an impact index R′N was proposed to define the effect of a dispersed Mo catalyst on the naphtha composition in slurryphase hydrocracking RN′ =

a

400 °C

410 °C

420 °C

430 °C

n-paraffin isoparaffin olefin naphthenic hydrocarbon aromatic hydrocarbon

20.89 32.31 11.23 22.36 13.21

21.32 32.54 10.85 21.83 13.46

21.64 32.46 10.65 22.07 13.18

21.87a 32.27a 10.02a 22.56a 13.28a

400 410 420 430

a

400 °C

410 °C

420 °C

430 °C

23.48 32.97 11.35 19.88 12.32

23.89 32.85 11.01 20.09 12.16

24.85 32.51 10.51 20.63 11.50

26.13a 31.72a 9.68a 21.35a 11.12a

× 100%

°C °C °C °C

RTH N

RSH N

RN′ (%)

1.547 1.526 1.500 1.476

1.404 1.375 1.308 1.214

9.24 9.90 12.80 17.75

SH As shown in Table 5, both RTH N and RN decreased with the temperature increased; meanwhile, RSH was lower than RTH N N at the same reaction temperature. The results indicated that a high temperature suppressed the formation of isoparaffin by a high concentration of hydrogen free radical; besides, a dispersed Mo catalyst further suppressed the formation of isoparaffin. Moreover, the impact index R′N followed a similar trend of RG′ , which increased with the increase of the temperature. It can be concluded that a high reaction temperature improved the effect of the dispersed Mo catalyst on naphtha composition in KLVR slurry-phase hydrocracking. 3.2. Effect of the Initial Hydrogen Pressure on Isomerization. 3.2.1. Product Distribution. As shown in Figure 4, the yields of light products (gas, naphtha, and diesel), VR, and coke decreased with the increase of the initial hydrogen pressure, while the yield of liquid C5+ increased. Besides, the yield of light products, VR, and coke in slurryphase hydrocracking was lower than that in thermal hydrocracking at the same initial hydrogen pressure. During thermal hydrocracking of KLVR, hydrogen participated in the reaction through a chain transfer reaction with hydrocarbon free radical. The generated hydrogen free radical could accelerate hydroconversion. Meanwhile, it could also suppress the serious cracking and condensation of hydrocarbon free radicals. Therefore, from a macroscopic view, a high initial hydrogen

Table 4. Composition of the Naphtha Product from KLVR Slurry-Phase Hydrocracking at 8.0 MPa with Different Temperatures n-paraffin isoparaffin olefin naphthenic hydrocarbon aromatic hydrocarbon

RNTH

Table 5. RN of the Naphtha Product in Thermal Hydrocracking and Slurry-Phase Hydrocracking and RN′ at 8.0 MPa with Different Temperatures

Standard deviation in the results is between 0.2 and 0.9%.

yield of component (wt %)

RNTH − RNSH

where RTH N was the RN of the naphtha product in thermal hydrocracking and RSH N was the RN of the naphtha product in slurry-phase hydrocracking. RN values of naphtha products in thermal hydrocracking and slurry-phase hydrocracking were calculated by the above equation, and then R′N values at different temperatures were obtained, as listed in Table 5.

Table 3. Composition of the Naphtha Product from KLVR Thermal Hydrocracking at 8.0 MPa with Different Temperatures yield of component (wt %)

yield of isoparaffin yield of n‐paraffin


For both hydrocracking reactions, as the temperature increased, the yields of olefin and aromatic hydrocarbon components in the naphtha product decreased, while the yields of n-paraffin and naphthenic hydrocarbon increased. However, the variation trends of the isoparaffin yield in thermal hydrocracking and slurry-phase hydrocracking were different. It appeared that, with the increase of the temperature from 400 to 430 °C, the yield of isoparaffin in thermal hydrocracking remained nearly unchanged, which decreased continuously in slurry-phase hydrocracking. Besides, the yield of n-paraffin in slurry-phase D


Article

Energy & Fuels

a maximum value. Thus, the quantity of hydrogen participating in the hydroconversion reaction did not increase, although the solubility of hydrogen in heavy oil increased when the hydrogen pressure was higher than 8.0 MPa. SH 3.2.3. Composition of the Gas Product. RTH G , RG , and R′G at different initial hydrogen pressures were calculated, as listed in SH Table 6. The results showed that RTH G and RG decreased with Table 6. RG of the Gas Product in Thermal Hydrocracking and Slurry-Phase Hydrocracking and R′G at 430 °C with Different Initial Hydrogen Pressures 4.0 MPa 6.0 MPa 8.0 MPa 10.0 MPa

Figure 4. Product distribution of KLVR thermal hydrocracking and slurry-phase hydrocracking at 430 °C with different initial hydrogen pressures. a

pressure led to the high conversion of KLVR and the high liquid C5+ yield, which also led to the low yields of light products and coke. With the presence of a dispersed Mo catalyst, more hydrogen participated in slurry-phase hydrocracking. Hence, the initial hydrogen pressure played a greater role in product distribution of KLVR slurry-phase hydrocracking. According to the above analysis, the conversion of KLVR was promoted by a high initial hydrogen pressure in both hydrocracking reactions. Besides, the conversion of KLVR in slurry-phase hydrocracking was higher than that in thermal hydrocracking at the same initial hydrogen pressure. 3.2.2. Hydrogen Consumption. The hydrogen consumptions of KLVR slurry-phase hydrocracking at different initial hydrogen pressures were calculated, as shown in Figure 5. The

RTH G

RSH G

R′G (%)

0.929 0.871 0.821a 0.778

0.852 0.716 0.625a 0.600

8.29 17.79 23.87 24.88


the increase of the initial hydrogen pressure; however, the increasing magnitude dropped when the initial hydrogen pressure was higher than 8.0 MPa. More hydrogen molecules took part in the hydrocracking reaction at a high initial hydrogen pressure, which would suppress the formation of isoparaffin. Nevertheless, when the initial hydrogen pressure increased to a certain extent, the quality of hydrogen participating in the reaction could not be enhanced anymore as well as the hydrogen free-radical concentration in the SH reaction system. Thus, RTH G and RG slightly decreased when the initial hydrogen pressure increased from 8.0 to 10.0 MPa. During the slurry-phase hydrocracking of KLVR, a high initial hydrogen pressure promoted the reaction between a dispersed Mo catalyst and hydrogen molecule, and then the generated active hydrogen species participated in the free-radical reaction. Hence, the effect of a dispersed Mo catalyst on the gas composition in slurry-phase hydrocracking (R′G) increased with the initial hydrogen pressure increasing, as shown in Table 6. 3.2.4. Composition of the Naphtha Product. The PONA compositions of naphtha products from KLVR thermal hydrocracking and slurry-phase hydrocracking are listed in Tables 7 and 8, respectively. The yields of n-paraffin and Table 7. Composition of the Naphtha Product from KLVR Thermal Hydrocracking at 430 °C with Different Initial Hydrogen Pressures

Figure 5. Hydrogen consumption of KLVR slurry-phase hydrocracking at 430 °C with different initial hydrogen pressures.

hydrogen consumption increased as the initial hydrogen pressure increased. More hydrogen molecules dissolved in KLVR because the solubility of hydrogen in heavy oil increased under a high hydrogen pressure;44 as a result, the opportunities of hydrogen participating in hydrocracking reactions increased. In addition, the activation of hydrogen to active hydrogen species on the surface of a dispersed Mo catalyst was the major route of hydrogen to participate in reaction during slurry-phase hydrocracking of KLVR. Therefore, the hydrogen consumption was enhanced by a high initial hydrogen pressure. However, the trend of hydrogen consumption became steady when the initial hydrogen pressure was higher than 8.0 MPa. The reason would be that the hydrocarbon free-radical concentration in the reaction system and active site on a dispersed Mo catalyst have

yield of component (wt %)

4.0 MPa

6.0 MPa

8.0 MPa

10.0 MPa

n-paraffin isoparaffin olefin naphthenic hydrocarbon aromatic hydrocarbon

21.02 32.89 10.74 21.47 13.88

21.51 32.56 10.38 21.98 13.57

21.87a 32.27a 10.02a 22.56a 13.28a

22.13 32.09 10.02 22.64 13.12

a


naphthenic hydrocarbon increased with the increase of the initial hydrogen pressure, but the yields of isoparaffin, olefin, and aromatic hydrocarbon decreased. In comparison of the yields of naphtha components in the two hydrocracking reactions at the same initial hydrogen pressure, it was found that the yield of n-paraffin in slurry-phase hydrocracking was higher than that in thermal hydrocracking; meanwhile, the yield of isoparaffin in slurry-phase hydrocracking was slightly lower. These results indicated that the formation of active hydrogen E


Article

Energy & Fuels Table 8. Composition of the Naphtha Product from KLVR Slurry-Phase Hydrocracking at 430 °C with Different Initial Hydrogen Pressures yield of component (wt %) n-paraffin isoparaffin olefin naphthenic hydrocarbon aromatic hydrocarbon a

4.0 MPa 24.66 32.92 10.38 19.75 12.29

6.0 MPa 25.34 32.29 10.05 20.64 11.68

8.0 MPa

10.0 MPa

a

26.29 31.52 9.45 21.9 10.84

26.13 31.72a 9.68a 21.35a 11.12a


was enhanced by a high initial hydrogen pressure, which improved aromatic saturation and ring opening. The isomerization ratios of naphtha products in thermal SH hydrocracking (RTH N ) and slurry-phase hydrocracking (RN ) and R′N at different initial hydrogen pressures are shown in Table 9.

Figure 6. Effect of the hydrogen consumption on R′G and R′N at 430 °C.

Table 9. RN of the Naphtha Product in Thermal Hydrocracking and Slurry-Phase Hydrocracking and RN′ at 430 °C with Different Initial Hydrogen Pressures 4.0 MPa 6.0 MPa 8.0 MPa 10.0 MPa

RTH N

RSH N

RN′ (%)

1.565 1.514 1.476 1.450

1.335 1.274 1.214 1.199

14.68 15.85 17.75 17.32

different free radicals. The secondary hydrocarbon free radical is formed through continuous decomposition and free-radical addition. Because hydrogen scarcely participates in thermal hydrocracking of hydrocarbon, active hydrogen is almost nonexistent in the reaction system. Thus, the secondary hydrocarbon free radical quenches with a small hydrocarbon free radical and generates isoparaffin (eq 1 in Scheme 1). During slurry-phase hydrocracking, hydrogen would be activated on the surface of a dispersed Mo catalyst and exist in the forms of −SH, −MoH, and H•. Then, the secondary hydrocarbon free radical quenches with active hydrogen and generates n-paraffin during slurry-phase hydrocracking (eq 2 in Scheme 1). Hence, although KLVR cracking degrees of thermal hydrocracking and slurry-phase hydrocracking are the same at the same temperature, less isoparaffin is generated in slurry-phase hydrocracking because of hydrogen participating in the free-radical reaction.

SH As the initial hydrogen pressure increased, both RTH N and RN decreased, while RN′ increased. The experimental data showed good agreement with the results of gas products at different initial hydrogen pressures, which indicated that the high initial hydrogen pressure facilitated the participation of hydrogen in both thermal hydrocracking and slurry-phase hydrocracking; besides, the participation of hydrogen in hydrocracking was further promoted by a dispersed Mo catalyst. Nevertheless, the value of R′N decreased from 17.55 to 17.32% when the initial hydrogen pressure increased from 8.0 to 10.0 MPa. The slight drop of RN′ could be considered as a stable value. Although the solubility of hydrogen increased with the increase of the initial hydrogen pressure, the quantity of hydrogen participating in the slurry-phase hydrocracking was not enhanced because that the number of active sites on a dispersed Mo catalyst was invariant. 3.3. Effect of the Hydrogen Consumption on R′G and RN′ . Because the cracking degree of KLVR changes with the reaction temperature, it is meaningless to discuss the relationship between hydrogen consumption and impact indexes (R′G and R′N) at different temperatures. The effect of the hydrogen consumption on impact indexes at 430 °C was studied, as shown in Figure 6. Both RG′ and RN′ increased linearly as the hydrogen consumption increased, indicating that hydrogen participating in hydrocracking suppressed the isomerization reaction. Slurryphase hydrocracking of heavy oil mainly followed the freeradical mechanism. Hydrogen converted to active hydrogen and influenced the product composition mainly in two aspects: the first aspect was promoting the hydroconversion through a free-radical chain reaction, and the second aspect was inhibiting the generation of isoparaffin through a free-radical quenching reaction. When the cracking of hexadecane is taken as an example,47 as illustrated in Scheme 1, the differences in product composition are reasonably explained by the quenching with

4. CONCLUSION The isomerization ratio of the hydrocracked product would have a great effect on the characteristics of light fuel (such as the octane number of gasoline). Besides, the structural properties of the hydrocracked residue product would have a great effect on its further processing by catalytic cracking. Thus, we proposed quantitative metrics to study the isomerization reaction in heavy oil slurry-phase hydrocracking. From the product distribution and composition of KLVR hydrocracking reactions at different reaction temperatures and initial hydrogen pressures, the following conclusions can be drawn: (1) Increasing the reaction temperature and initial hydrogen pressure facilitates the KLVR conversion in both thermal hydrocracking and slurry-phase hydrocracking. The activation of hydrogen to active hydrogen species on the catalyst surface inhibits the serious cracking and condensation of hydrocarbon free radical. (2) The hydrogen consumption of slurry-phase hydrocracking increases with the increase of the temperature and initial hydrogen pressure, while hydrogen consumption of thermal hydrocracking is negligible. (3) Impact indexes (RG′ and R′N) increase with the temperature and initial hydrogen pressure increasing, which means that a high temperature and high initial hydrogen pressure enhance the isoparaffin restraining effect of a dispersed Mo catalyst. Under a certain temperature, the linear relationship between impact indexes and hydrogen consumption indicates a dispersed Mo catalyst suppressing the isomerization reaction by hydrogen participating in a freeradical reaction. F


Article

Energy & Fuels Scheme 1. Schematic Diagram of the Hydrocracking of C16H34: (1) Thermal Hydrocracking and (2) Slurry-Phase Hydrocracking

■

(14) Yves, J.; Davidson, M.; Le Page, J. F. Process for hydrotreating heavy hydrocarbons in liquid phase in the presence of a dispersed catalyst. U.S. Patent 4,285,804, 1981. (15) Marchionna, M.; Delbianco, A.; Panariti, N. Process for the conversion of heavy charges such as heavy crude oils and distillation residues. U.S. Patent 7,691,256, 2003. (16) Jeon, S. G.; Na, J. G.; Ko, C. H.; Lee, K. B.; Rho, N. S.; Park, S. B. A new approach for preparation of oil-soluble bimetallic dispersed catalyst from layered ammonium nickel molybdate. Mater. Sci. Eng., B 2011, 176 (7), 606−610. (17) Zhang, S.; Deng, W.; Luo, H.; Liu, D.; Que, G. Slurry-phase residue hydrocracking with dispersed nickel catalyst. Energy Fuels 2008, 22 (6), 3583−3586. (18) Liu, D.; Kong, X.; Li, M.; Que, G. Study on a water-soluble catalyst for slurry-phase hydrocracking of an atmospheric residue. Energy Fuels 2009, 23 (2), 958−961. (19) Liu, D.; Cui, W.; Zhang, S.; Que, G. Role of dispersed Ni catalyst sulfurization in hydrocracking of residue from Karamay. Energy Fuels 2008, 22 (6), 4165−4169. (20) Jeon, S. G.; Na, J. G.; Ko, C. H.; Yi, K. B.; Rho, N. S.; Park, S. B. Preparation and application of an oil-soluble CoMo bimetallic catalyst for the hydrocracking of oil sands bitumen. Energy Fuels 2011, 25 (10), 4256−4260. (21) Panariti, N.; Bianco, A.; Piero, G.; Marchionna, M. Petroleum residue upgrading with dispersed catalysts: Part 1. Catalysts activity and selectivity. Appl. Catal., A 2000, 204 (2), 203−213. (22) Bacaud, R. Dispersed phase catalysis: Past and future. Celebrating one century of industrial development. Fuel 2014, 117, 624−632. (23) Galarraga, C. E.; Pereira-Almao, P. Hydrocracking of Athabasca bitumen using submicronic multimetallic catalysts at near in-reservoir conditions. Energy Fuels 2010, 24 (4), 2383−2389. (24) Ortiz-Moreno, H.; Ramírez, J.; Cuevas, R.; Marroquín, G.; Ancheyta, J. Heavy oil upgrading at moderate pressure using dispersed catalysts: Effects of temperature, pressure and catalytic precursor. Fuel 2012, 100, 186−192. (25) Domokos, L.; Jongkind, H.; Rigutto, M. S.; Van De Voort, E. H. C.; Stork, W. H. J. Hydrocracking catalyst composition. U.S. Patent 0,207,917, 2006. (26) Zhu, Y.; Zhou, D. Study on unsupported nano-MoS2 catalyst for clean fuel. Adv. Mater. Res. 2011, 287−290, 1860−1865. (27) Ancheyta, J.; Rana, M. S.; Furimsky, E. Hydroprocessing of heavy petroleum feeds: Tutorial. Catal. Today 2005, 109 (1), 3−15. (28) Liu, C.; Que, G.; Liang, W. The role of dispersed-phase Mo catalyst in the hydrocracking of Gudao residue. I. XRD, SEM and TEM analyses of the active catalytic species. Acta Pet. Sin., Pet. Process. Sect. 1994, 10 (1), 14−21. (29) Matsumura, A.; Kondo, T.; Sato, S.; Saito, I.; de Souza, W. F. Hydrocracking Brazilian Marlim vacuum residue with natural limonite. Part 1: Catalytic activity of natural limonite. Fuel 2005, 84 (4), 411− 416.

AUTHOR INFORMATION

Corresponding Author

*Telephone/Fax: +86-0532-86984629. E-mail: ldongupc@vip. sina.com. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (21176259).

■

REFERENCES

(1) Speight, J. G. New approaches to hydroprocessing. Catal. Today 2004, 98 (1), 55−60. (2) Rana, M. S.; Sámano, V.; Ancheyta, J.; Diaz, J. A. I. A review of recent advances on process technologies for upgrading of heavy oils and residua. Fuel 2007, 86 (9), 1216−1231. (3) Zhang, S.; Liu, D.; Deng, W.; Que, G. A review of slurry-phase hydrocracking heavy oil technology. Energy Fuels 2007, 21 (6), 3057− 3062. (4) Schuetze, B.; Hofmann, H. How to upgrade heavy feeds. Hydrocarbon Process. 1984, 62 (2), 75−78. (5) Dohler, W.; Kretschmar, K.; Merz, L. VEBA-Combi-CrackingA technology for upgrading of heavy oils and bitumen. Prepr.Am. Chem. Soc., Div. Pet. Chem. 1987, 32 (2), 484−489. (6) Drago, G.; Gultian, J.; Krasuk, J. The development of HDH process, a refiners tool for redidual upgrading. Prepr.Am. Chem. Soc., Div. Pet. Chem. 1990, 35 (4), 584−592. (7) Khulbe, C. P.; Ranganathan, R.; Pruden, B. B. Hydrocracking of heavy oils/fly ash slurries. U.S. Patent 4,299,685, 1981. (8) Marchionna, M.; Delbianco, A.; Panariti, N. Process for the conversion of heavy crude oils and distillation residues to distillates. U.S. Patent 5,932,090, 1999. (9) Rupp, M.; Spencer, R.; Cook, B. Proceedings of the 2010 NPRA Annual Meeting; Phoenix, AZ, March 21−23, 2010. (10) Huy, C. N.; Kweon, H.; Kim, H.; Kim, D. K.; Kim, D. W.; Oh, S. H.; Shin, E. W. Slurry-phase hydrocracking of vacuum residue with a disposable red mud catalyst. Appl. Catal., A 2012, 447−448 (7), 186− 192. (11) Khulbe, C. P.; Belinko, K.; Waugh, R. J.; Perreault, M. Process for preparing an iron-coal slurry catalyst for hydrocracking heavy oils. U.S. Patent 4,923,838, 1990. (12) Angeles, M. J.; Leyva, C.; Ancheyta, J.; Ramírez, S. A review of experimental procedures for heavy oil hydrocracking with dispersed catalyst. Catal. Today 2014, 220−222, 274−294. (13) Liu, D.; Li, M.; Deng, W.; Que, G. Reactivity and composition of dispersed Ni catalyst for slurry-phase residue hydrocracking. Energy Fuels 2010, 24 (3), 1958−1962. G


Article

Energy & Fuels (30) Matsumura, A.; Sato, S.; Kondo, T.; Saito, I.; de Souza, W. F. Hydrocracking Marlim vacuum residue with natural limonite. Part 2: Experimental cracking in a slurry-type continuous reactor. Fuel 2005, 84 (4), 417−421. (31) Solari, R. B. HDH hydrocracking as an alternative for high conversion of the bottom of the barrel. Proceedings of the 1990 NPRA Annal Meeting; San Antonio, TX, March 25−27, 1990. (32) Topsϕe, H.; Clausen, B. S.; Massoth, F. E. Catal.: Sci. Technol. 1996, 1, 11−269. (33) Gray, M. R.; McCaffrey, W. C. Role of chain reactions and olefin formation in cracking, hydroconversion, and coking of petroleum and bitumen fractions. Energy Fuels 2002, 16 (3), 756−766. (34) Leyva, C.; Ancheyta, J.; Marie, L.; Travert, A.; Maugé, F. Characterization study of NiMo/SiO2−Al2O3 spent hydroprocessing catalysts for heavy oils. Catal. Today 2014, 220−222, 89−96. (35) Hernández-Beltrán, F.; Moreno-Mayorga, J. C.; QuintanaSolórzano, R.; Sánchez-Valente, J.; Pedraza-Archila, F.; Pérez-Luna, M. Sulfur reduction in cracked naphtha by a commercial additive: Effect of feed and catalyst properties. Appl. Catal., B 2001, 34 (2), 137−148. (36) Byambajav, E.; Ohtsuka, Y. Cracking behavior of asphaltene in the presence of iron catalysts supported on mesoporous molecular sieve with different pore diameters. Fuel 2003, 82 (13), 1571−1577. (37) Zhang, S.; Deng, W.; Luo, H.; Liu, D.; Que, G. Mechanism of slurry phase hydrocracking residue reaction. Acta Petrol. Sin., Pet. Process. Sect. 2009, 25 (2), 145−149. (38) Chianelli, R. R.; Siadati, M. H.; Rosa, M. P.; Berhault, G.; Wilcoxon, J. P.; Bearden, R., Jr.; Abrams, B. L. Catalytic properties of single layers of transition metal sulfide catalytic materials. Catal. Rev. 2006, 48, 1−41. (39) Yang, M.; Nakamura, I.; Fujimoto, K. Hydro-thermal cracking of heavy oils and its model compound. Catal. Today 1998, 43, 273−280. (40) Meng, X.; Xu, C.; Gao, J.; Li, L. Studies on catalytic pyrolysis of heavy oils: Reaction behaviors and mechanistic pathways. Appl. Catal., A 2005, 294, 168−176. (41) Cavitt, S. B. Process for hydrocarbon soluble metal salts. U.S. Patent 3,595,891. 1969. (42) Sanford, E. C. Conradson carbon residue conversion during hydrocracking of Athabasca bitumen: Catalyst mechanism and deactivation. Energy Fuels 1995, 9 (3), 549−559. (43) Retcofsky, H. L.; Sprecher, R. F.; Hough, M. R. ESR spectra of rapidly pyrolyzed coals. Proceedings of the Pittsburgh Conference; Atlantic City, NJ, March 9−13, 1981. (44) Ji, S.; Wang, Z.; Guo, A.; Zhou, Y.; Chen, K. Determination of hydrogen solubility in heavy fractions of crude oils by a modified direct method. J. Chem. Eng. Data 2013, 58 (12), 3453−3457. (45) Ancheyta-Juarez, J.; Maity, S. K.; Betancourt-Rivera, G.; Centeno-Nolasco, G.; Rayo-Mayoral, P.; Gómez-Pérez, M. T. Comparison of different Ni−Mo/alumina catalysts on hydrodemetallization of Maya crude oil. Appl. Catal., A 2001, 216 (1), 195−208. (46) Marroquin, G.; Ancheyta, J.; Esteban, C. A batch reactor study to determine effectiveness factors of commercial HDS catalyst. Catal. Today 2005, 104 (1), 70−75. (47) Liang, W.; Que, G. Petroleum Chemistry; Petroleum University Press: Dongying, China, 2008; pp 283−295.

H


Effects of the Temperature and Initial Hydrogen Pressure on the

Recommend Documents