ARTICLE pubs.acs.org/EF
Reaction Performance and Chemical Structure Changes of Oil Sand Bitumen during the Fluid Thermal Process An-gui Zhang, Jinsen Gao, Gang Wang,* Chunming Xu, Xinying Lan, Guoqing Ning, and Yongmei Liang State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China ABSTRACT: This study investigated the reaction behavior of oil sand bitumen from Inner Mongolia using a fluid-bed thermal reactor. The optimal temperature and reaction time were obtained. The results showed that the fluid thermal reaction was a feasible carbon rejection process that could be used to obtain high-quality liquid products from oil sand bitumen. The structures of bitumen and their liquid products derived from fluid thermal conversion were analyzed using an infrared spectrum and proton nuclear magnetic resonance techniques, and the average structural parameters were determined using the modified Brown Ladner method. In comparison to native bitumen, the average structural parameters of liquid products were significantly changed. For different oil sand bitumen, the structural changes revealed a similar tendency for the coking formation of polycyclic aromatics and the cleavage of long paraffin side chains during fluid thermal conversion.
1. INTRODUCTION The depletion of conventional crude oil reserves and an increase in crude oil prices have led to the consumption of unconventional oil resources. In the future, oil sand, an alternative fossil fuel resource,1 will play an important role in fulfilling the needs of consumers around the world.2,3 Oil sand is mainly used as a source of bitumen products, which can be recovered through open-pit and underground mining processes. The openpit mining recovery method includes oil sand mining and subsequent surface processing to recover bitumen from the sand matrix. The hot water extraction method is the most widely used process for separating and recovering bitumen from oil sands.4,5 However, hot-water extraction is limited by the type of oil sand, and high bitumen recovery yields can only be obtained from water-wet oil sands.6 The solvent extraction process can increase the bitumen recovery yields of oil-wet oil sand but requires a large amount of organic solvent, resulting in high treatment costs and potential environmental pollution. Therefore, a more feasible process for oil-wet oil sand should be explored, such as processing oil sands in direct thermal conversion, to obtain bitumenderived liquid products. Some studies on the thermal conversion of oil sand bitumen have been conducted. To optimize the process, a thermogravimetric analyzer has been used to investigate the effects of the heating rate on the thermal conversion behaviors and reaction kinetics of oil sand bitumen.6 10 Most investigations on the thermal conversion of oil sand bitumen have focused on obtaining the liquid products in fixed beds,10,11 rotary kilns,12 17 and fluidized-bed reactors.17 22 Among these methods, thermal conversion using a fluidized-bed reactor has shown a significant advantage over the others, although studies are still in the pilot scale. The fluid thermal process, together with continuous feeding and operation flexibilities, may improve the bitumen recovery yields of oil-wet oil sands. Oil sands are found in China and other parts of the world,7 9 indicating that they could be exploited to be an important substitute energy resource soon. In view of this, Lu et al. patented a process of oil sand processing to r 2011 American Chemical Society
obtain liquid products for subsequent processes.23 In a previous study, we found that the reaction temperature and time were the key factors for product distributions. However, for different types of oil sands, the bitumen reaction behaviors of fluid thermal conversion show different cracking performances because oil sands are deposited in differing geological environments and have noticeably discrepant properties. Therefore, the thermal reaction behaviors of oil sand bitumen in a fluid thermal reactor are also worthy of investigation to widen the feedstock resources for fluid thermal processing. Oil sand bitumen is a complex compound containing a large number of different functional groups, molecular structures, and fairly broad molecular-weight distributions. Therefore, the composition of bitumen has a great significance because of its vital role in determining its fluid thermal processing and performance-related properties. The structural parameter was first proposed by Brown and Ladner and was used to obtain the average structure of coal liquid in the late 1950s.24 Subsequently, the Brown Ladner (B L) method was modified for relatively aromatic feedstock.25 Several researchers adopted this method to characterize the chemical changes of bitumen and/or shale oil during thermal recovery,26,27 catalytic hydrotreatment,28,29 coking, and hydrocracking.30 Zhao and his co-workers also used this method to describe the average molecular structure for asphaltenes, heavy gas oils, and other types of heavy oil.31,32 This well-known method has been commonly used for the structural analysis of petroleum and its fractions. With this method, the overall structural differences between the feedstock and its product can be evaluated. At present, the comprehensive study of oil sand use is only just beginning in China, and there is a dearth of information available regarding the fluid thermal reaction behaviors of Inner Mongolia oil sand bitumen. Studies on the chemical structural change of oil sand bitumen are indispensable to better understand the reaction Received: April 27, 2011 Revised: June 28, 2011 Published: July 01, 2011 3615
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Table 1. Content of Bitumen (Dean Stark) and Yield of Oil (Fischer Assay) Dean Stark
Fischer assay
sample
bitumen (wt %)
moisture (wt %)
sand (wt %)
oil (wt %)
gas (wt %)
water (wt %)
semicoke (wt %)
A
10.09
14.04
75.87
8.40
1.74
11.59
78.28
B
11.59
11.96
76.45
8.72
2.34
9.42
79.52
C
18.23
2.09
79.68
14.41
2.58
2.93
80.08
Table 2. Proximate Analysis of Inner Mongolia Oil Sand sample volatile (wt %) ash (wt %) moisture (wt %) fixed carbon (wt %) A
11.83
80.19
7.32
Table 4. Physical Properties of the Heat Carrier for Fluid Thermal Conversion of Oil Sand Bitumen items
0.66
A
B
C
2
B
11.48
84.01
3.29
1.22
BET surface area (m /g)
5.312
4.725
4.567
C
17.67
78.96
2.21
1.16
pore volume (cm3/g)
0.014
0.013
0.015
average pore diameter (nm) bulk density (g/cm3)
11.07 1.199
10.96 1.398
11.07 1.471
particle density (g/cm3)
2.03
2.493
2.503
450 μm
12.82 0
12.70 0.31
14.12 11.93
Table 3. Composition Analysis of the Heat Carrier (wt %) sample SiO2 Al2O3 Fe2O3 TiO2 CaO MgO K2O Na2O MnO2 P2O5 SO3 A
80.03 10.97 1.16 0.53 0.57 0.24 3.31 2.62
0.03 0.02 0.09
B
80.39 10.73 1.06 0.73 0.48 0.28 3.22 2.67
0.02 0.02 0.08
C
79.80 11.25 1.26 0
0.05 0.02 0.11
0.44 0.20 3.42 2.68
behaviors of oil sand bitumen during fluid thermal conversion and improve their performance. In this study, thermal reaction performances of Inner Mongolia oil sand bitumen were investigated in a confined fluid-bed reactor. To select the subsequent processes for upgrading and/or refining, the liquid products of fluid thermal conversion were analyzed and compared to native bitumen. In combination with the proton nuclear magnetic resonance (1H NMR) determination, elemental analysis, and average molecular weight, the average molecular formula of the oil sands bitumen and their liquid products from thermal conversion were determined and the chemical structural changes of oil sand bitumen during the fluid thermal reaction were discussed.
2. EXPERIMENTAL SECTION 2.1. Feedstocks and Heat Carrier. Three oil sand samples used in this study were obtained from different parts of the Songliao Basin of Inner Mongolia in northeastern China. The bitumen and water contents of the oil sands were determined using the Dean Stark extraction method.6,33 The basic properties of the oil sands are presented in Tables 1 and 2. Heat carriers are sands obtained after coke removal from coked sands in a muffle furnace; their physicochemical properties are shown in Tables 3 and 4. The fluidization behavior of the heat carrier is crucial because it determines the efficiency of the system. The heat carrier falls under the Geldart B classification,34 and its fluidization behavior is as well-understood as that of common sand. 2.2. Experimental Apparatus. Fluid thermal reaction experiments were performed in a confined fluid-bed reactor system (Figure 1). It was comprised of five sections, including the oil sand feeder, a steam input system, a fluidized-bed reactor, a temperature control system, and a product separation and collection system. The oil sand feeder was located at the upper part of the fluidized-bed reactor. To avoid the agglomeration of oil sand during heating while feeding, an external cooling water jacket that cools the feeding tube was installed.
particle size distribution (wt %)
In each experiment, 100 g of heat carrier was loaded into the reactor. A certain amount of distilled water was pumped into a furnace to generate steam to keep the heat carrier fluidized. The fluidized heat carrier was heated to approximately 50 °C higher than the reaction temperature, and then 50 g of oil sand was loaded into the reactor. The heat carrier should possess high mass- and good heat-transfer efficiency, so that the reactor can reach the target temperature within a few seconds after contact between the oil sand and the fluidized heat carrier. Then, the conversion of bitumen can be initiated immediately. In the reaction phase, the mixed oil and gas product ejected by the reactor through a filter was cooled and separated into a liquid product sampler and a gas collection vessel. When the reaction time was complete, the reactor furnace was removed and the reactor was immediately quenched to 350 °C by a self-made water-cooling device to terminate the reaction within 15 s. Finally, the oil sand and heat carrier were stripped for 40 min to completely recover the product. The experiments were conducted in a batch mode, and only a fixed amount of oil sands was processed during each run. During all tests, the mass balances, which were based on the bitumen fed to the reactor, were all within 97 100 wt %. 2.3. Product Analysis. In the fluid thermal reaction experiments, the product gases were analyzed using an Agilent 6890 gas chromatograph with Chem Station software to determine the volume percentage of the components. The state equation for ideal gases was used to convert the volume data into mass percentages. The liquid products were weighed and then analyzed using simulated distillation gas chromatography to obtain the weight percentages of gasoline (C5 200 °C), diesel oil (200 350 °C), and heavy oil (>350 °C). The coke content on the heat carrier and coked sand was measured using a coke analyzer. The infrared (IR) spectrum of bitumen and the liquid products was recorded on a Nicolet Magna-IR 560 enhanced syncronization protocol (ESP) spectrophotometer as a KBr pellet. Spectra ranging from 4000 to 400 cm 1 wave numbers were acquired at a resolution of 0.35 cm 1. The 1H NMR spectra for bitumen and liquid products were recorded on a Varian UNITY INOVA II 500 MHz with deuterated chloroform (CDCl3) as a solvent. The chemical shift refers to the tetramethylsilane 3616
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Figure 1. Schematic diagram of the fluid thermal conversion reactor unit: (1) water tank, (2) water pump, (3) temperature control instruments, (4) steam furnace, (5) feeder tank, (6) cool water jacket, (7) reactor, (8) reactor furnace, (9) filter, (10) condenser, (11) liquid product sampler, (12) gas collection vessel, (13) water collection vessel, and (14) electronic scales.
Table 5. Operating Conditions for Fluid Thermal Conversion of Oil Sand Bitumen items
value
temperature of the reactor (°C)
450 520
reactor time (min)
2 10
temperature of the steam furnace (°C) water inflow (mL/min)
350 1.0 5.0
loaded heat carrier (g)
50 150
mass ratio of heat carrier/oil sand
2 6
stripping time (min)
40
(TMS) standard. Some other conditions for NMR measurements are a sweep width of 7000 Hz or 14 ppm, an acquisition time of 5.6 ms, a number of scans of 3000, and a relaxation delay time of 2 s. For 1H NMR, the spectrum was divided into four regions [6 9 ppm, aromatic hydrogen (HA); 2 4 ppm, R hydrogen aromatic ring (HR); 1 2 ppm, β hydrogen aromatic ring (Hβ); and 0.2 1.0 ppm, γ hydrogen aromatic ring (Hγ)].
3. RESULTS AND DISCUSSION 3.1. Fluid Thermal Reaction. The reaction temperature and time are the main operating conditions that control the thermal conversion of oil sand bitumen. Therefore, we investigated the effects of the reaction temperature and time on the product distributions. The operating conditions for the main thermal conversion tests are listed in Table 5. The weight hourly space velocity (WHSV) is defined as the ratio of the water flow rate to the total weight of the heat carrier and the oil sand loaded in the reactor. The liquid product is defined as the sum of gasoline, diesel oil, and heavy oil. The feedstock conversion refers to the sum of the yields of dry gas (H2, C1 C2), liquid petroleum gas (LPG, C3 C4), gasoline, diesel oil, and coke.
3.1.1. Effect of the Reaction Temperature. To determine the optimal temperature for the fluid thermal reaction of oil sand bitumen, experiments under temperatures ranging from 450 to 530 °C were conducted at a fixed reaction time of 5 min, a WHSV of 0.6 h 1, and a heat carrier/oil sand mass ratio of 2:1. The experimental results are shown in Figure 2. As the reaction temperature increased, both the feedstock conversion and the yield of dry gas, LPG, gasoline, and light oil increased, whereas the yield of heavy oil decreased significantly. A high reaction temperature leads to very strong thermal conversion. Because dry gas is the end product of a thermal reaction, the yield increases when the reaction temperature increases. LPG, gasoline, diesel, and heavy oil were intermediate products whose yields decreased after reaching their maximum yield because of secondary reactions. Maximum yields of gasoline and LPG were not observed because the reaction temperature range was relatively narrow. Diesel oil yields were at their maximum at approximately 510, 485, and 500 °C for oil sand bitumen A, B, and C, respectively; however, the changes in diesel oil yield were relatively small. The decrease in the heavy oil yield and the increase in the yields of dry gas, LPG, and gasoline with an increasing temperature were due to the increased severity of the thermal cracking. The coke yield from the heat carrier showed a minimal value at 500 °C for oil sand bitumen A and showed slight maxima for oil sand bitumen B, whereas the yield of coke for oil sand bitumen C was almost constant. The maximum yields of liquid products (79.87, 78.93, and 85.64 wt %) were obtained at reaction temperatures of 490, 485, and 495 °C, respectively. Part of heavy oil was converted to dry gas and LPG, resulting in the reduction of total liquid product yields above the optimal reaction temperature. The fluid thermal conversion of oil sands directly converts bitumen with high-boiling components into low boiling liquid products at high temperatures on the oil sand surface. It also involves free-radical mechanisms mainly on the heat carrier 3617
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Figure 2. Effect of the reaction temperature on product distributions and feedstock conversion.
surface and in the interspaces between the heat carrier particles. The heavy hydrocarbon molecules of bitumen cracked into smaller hydrocarbon elements, such as dry gas, LPG, gasoline, diesel, and heavy oil, which were then volatized and passed from the reactor. Intermediate products (e.g., gasoline, diesel, and heavy oil) may undergo secondary reactions, such as cracking and polymerization. Coke serves as a fuel to provide heat to the process and was produced and deposited on the heat carrier. The mixture of oil and gas was charged into the fractionation equipment and recovered to serve as a feedstock for the subsequent processes, such as catalytic cracking and hydrotreating. Fluid thermal processing was conducted to maximize the liquid product derived from the oil sand. Accordingly, maximum liquid products of 79.87, 78.93, and 85.64 wt % for
oil sand bitumen A, B, and C were obtained at optimal reaction temperatures of 490, 485, and 495 °C, respectively. Therefore, the optimal reaction temperature for bitumen thermal conversion is 485 495 °C. 3.1.2. Effect of the Reaction Time. The reaction temperature, WHSV, and mass ratio of heat carrier/oil sand were fixed at 500 °C, 0.6 h 1, and 2:1, respectively. The reaction time was varied within a range of 2 10 min to determine its effect on the product distributions and yields. The results are presented in Figure 3. The yields of dry gas, LPG, gasoline, diesel oil, and heavy oil increased as the reaction time increased from 2 to 5 min. No further increase was observed after 5 min, suggesting that the optimal reaction time is 5 min. 3618
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Figure 3. Effect of the reaction time on product distributions and yields.
3.2. Characterization of the Liquid Product and Native Bitumen. It is important to determine the extent of the
improvement of the liquid products compared to the native bitumen products because the qualities of the liquid products have an impact on the selection of the subsequent processes for the upgrading and/or refining of the liquid products. In light of this, we performed a comparative study of the properties of the liquid products obtained by the fluid thermal process and the native bitumen obtained by the organic solvent extraction. The native bitumen samples were obtained by the solvent extraction of the oil sand with toluene in a Soxhlet extraction apparatus. The solvent was stripped from the solvent bitumen solution under a vacuum to recover the native bitumen for subsequent characterization. The liquid products for comparison were obtained at a reaction temperature of 500 °C, a reaction time of 5 min, a
WHSV of 0.6 h 1, and a heat carrier/oil sand mass ratio of 2:1. The detailed properties of the native bitumen and liquid products are presented in Table 6. The results of the comparative study showed that the density and Conradson carbon residue of the liquid products were markedly decreased in comparison to those of the native bitumen. The viscosity of the liquid products decreased by several orders of magnitude compared to that of the native bitumen at the same temperature. The mass percentages of C and H were higher than those of the native bitumen, whereas the mass percentages of S, N, and O were much lower. The amounts of heteroatoms (S, N, and O) and trace metals (Ni and V) were substantially reduced in the liquid products, indicating that most of the heteroatoms and trace metals were deposited on the heat carrier. The amount of preferred components (saturated and 3619
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Table 6. Physical and Chemical Properties of Native Bitumen and Their Liquid Products from Fluid Thermal Conversion A items
B
C
bitumen
liquid product
bitumen
liquid product
bitumen
liquid product
density at 20 °C (g/cm )
1.0837
0.9628
1.0611
0.9611
0.9735
0.9125
viscosity at 20 °C (mPa s)
>50,000
38.34
>50,000
26.84
557.2
15.89
Conradson carbon residue (wt %)
16.55
2.16
12.31
2.21
9.90
1.69
C
83.84
86.6
84.81
86.12
85.48
86.68
H
11.38
12.25
11.37
11.84
11.47
12.11
S
0.35
0.126
0.36
0.127
0.30
0.254
N O
0.86 3.57
0.136 0.888
1.00 2.94
0.14 1.773
1.03 1.72
0.171 0.785
H/C atomic ratio
1.63
1.70
1.61
1.65
1.61
1.68
molecular weight (g/mol)
1341
316
1299
316
826
352
Ni (ng/g)
4639
57.8
4666
57.8
3481
15
V (ng/g)
6904
94.7
3806
94.7
6283
261
saturated (wt %)
14.1
66.99
21.84
66.99
20.32
34.70
aromatic (wt %) resin (wt %)
8.87 18.33
22.19 10.09
26.66 25.57
22.19 10.09
22.88 30.85
50.78 14.05
asphaltene (wt %)
58.7
0.73
25.93
0.73
25.95
0.47
IBP
320
100.2
297.6
81.6
248.2
85.2
5%
427
174.4
416
137.9
341.6
135.8
10%
481.6
222
470
195.6
404.4
184.8
20%
551.4
296.6
545
275.3
477.4
271.7
30% 40%
594.4 641.2
348 392.8
589 637
322.7 361.2
541.8 591
322.4 371.2
50%
688.8
429.6
680
415.0
642.6
414.2
60%
735.6
461.6
720
451.9
694.4
448.2
743.2
483.8
3
elemental analysis (wt %)
SARA analysis
boiling point distribution (°C)
70%
495.2
494.3
80%
530.4
517.5
521.6
90%
567.8
561.6
562.6
FBP
611.6
610.6
611.4
aromatics) in the liquid products increased at the expense of resin and asphaltenes. This indicates that the fluid thermal reaction is a feasible carbon rejection process capable of obtaining highquality liquid products from oil sand bitumen. In addition, the liquid products exhibited a significant shift in their boiling range compared to the native bitumen. Consequently, the quality of the liquid products from the thermal conversion of oil sand bitumen showed significant improvement compared to that of the native bitumen. Therefore, it could act as an excellent feedstock for further processing and use in a refinery. Thermal conversion processing presents an obvious advantage over the organic solvent extraction separation process of bitumen sand because it can obtain higher quality liquid products. 3.3. Chemical Structural Changes during the Fluid Thermal Reaction for Oil Sand Bitumen. Because oil sand bitumen is a complex mixture, its structural information is usually determined by IR spectroscopy and NMR. These methods provide more structural information than a component analysis. 3.3.1. IR Analysis. IR spectroscopy was employed to determine the presence of functional groups in both native bitumen and its liquid products. IR analysis can reveal information about the functionality and constituents of bitumen and its liquid
products. The IR spectra of bitumen and its liquid products with an expansion of the 4000 400 cm 1 region are shown in Figure 4. The most prominent aliphatic C H stretching vibrations found in the higher frequency region in bitumen are the inphase stretching of CH2 at 2922 cm 1 and the out-of-phase stretching of CH2 at 2852 cm 1. In the present study, the lower region of frequency plays a more important role in comparing the chemical changes occurring in the C H environment. The most significant C H vibrations found in bitumen were symmetric deformation or bending vibration in CH3 at 1377 cm 1 and asymmetric deformation in both CH2 and CH3 groups at 1463 cm 1. For organic compounds, a band of 1463 cm 1 is frequently stronger than at 1377 cm 1. The band 1602 cm 1 can be ascribed to aromatic CdC stretching vibration. The IR spectra displayed a distinct and very important CdO stretch absorption at 1705 cm 1 because of carbonyl and/or carboxyl groups. The band 1301 cm 1 represents CH2 out-of-plane deformation wagging vibration. The region of 700 900 cm 1 contained various bands related to the aromatic, out-of-plane C H bending, which indicates that the aromatic hydrogen was located in aromatic rings with a high degree of substitution. The rocking band at 722 cm 1 was due to the (CH2)n group, 3620
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Figure 4. IR spectrum of oil sand bitumen and its liquid products from fluid thermal conversion.
Table 7. Average Formula of Native Bitumen and Its Liquid Products from Fluid Thermal Conversion sample A B C
Table 9. Structural Parameter Identification structural
average formula
parameters
bitumen
C93.17H151.39S0.15N0.82O2.99
fA
fraction of aromatic carbons (aromaticity)
liquid product
C22.79H38.40S0.01N0.03O0.18
fN
fraction of naphthenic carbons
bitumen liquid product
C91.73H146.52S0.15N0.93O2.39 C23.38H38.29S0.01N0.03O0.36
fP
fraction of paraffinic carbons
CA
number of aromatic carbons
bitumen
C58.79H93.99S0.08N0.61O0.89
CN
number of naphthenic carbons
liquid product
C25.40H42.29S0.03N0.04O0.17
CP
number of paraffinic carbons
HAU/CA
aromatic carbon index
σ RT
ratio of substituted carbons/peripheral aromatic carbons number of total rings (aromatic rings and naphthenic rings)
RA
number of aromatic rings
RN
number of naphthenic rings
RA/RN
ratio of aromatic rings/naphthenic rings
Table 8. H Distribution of Native Bitumen and Its Liquid Products from Fluid Thermal Conversion A H distribution (%) HA
identification
B
liquid
C
liquid
liquid
bitumen product bitumen product bitumen product 2.90
5.36
5.22 6.45
6.11
3.39
5.49
HR
5.04
9.65
12.00
8.21
10.88
Hβ
71.48
60.74
67.7
58.94
68.19
60.09
Hγ
20.59
24.25
20.63
22.95
20.21
23.55
with n g 6. The IR spectrum of the liquid product was slightly different from that of the bitumen. C H deformation vibrations of alkenes were observed at 965, 908, and 812 cm 1. This means that the paraffin and/or alkyl side chain in the aromatic ring and naphthenic ring were cracked and then olefin was formed in the liquid product. 3.3.2. Molecular Structural Parameters. On the basis of the molecular weight and elemental analysis results in Table 6, the average formula for oil sand bitumen (A, B, and C) and their liquid products is listed in Table 7. The chemical structural changes during the fluid thermal conversion were studied by 1H NMR, and the average structural parameters of oil sand bitumen and its liquid products were calculated using 1H NMR data (Table 8), elemental analysis, and molecular weight with the modified B L method. A detailed description of the modified B L method can be found in the previously mentioned references.35 A description of the structural parameters and their calculated values are listed in Tables 9 and 10. The aromacity fA indicates that there is approximately onefourth to one-third carbon atom compound in aromatic rings.
The values of the total ring numbers (RT) for oil sand bitumen indicate that a large quantity of compounds with complex ring structures exist in the bitumen. After fluid thermal conversion, the average structural parameters of liquid products from the fluid thermal conversion changed significantly compared to native bitumen. The increase in aromaticity and the decrease in fA could be a consequence of the removal of alkyl chains and their breakage into shorter chains. Gas and gasoline are produced in these ruptures, and the global effect for oil sand bitumen is similar to hydrogen removal. Therefore, a higher CA can yield more gas and gasoline. According to HAU/CA, the shape of the skeleton of the aromatic ring shows a change from a catacondensed type for oil sand bitumen to a pericondensed type for the liquid products. The decreasing σ of the liquid products means that it is easy to cause deakylation reactions for large bitumen molecules during fluid thermal conversion. There were also remarkable differences in the ring structure for oil sand bitumen and its liquid products, for the total ring number (RT), aromatic ring number (RA), and cycle ring number (RN), which decreased from 6.10 8.64 to 2, from 3.13 6.10 to 1, and from 2.22 3.42 to 1, respectively. The condensation reactions of oil sand bitumen are the preliminary steps in coke formation. Several primary fragments from bitumen cracking form the liquid product fraction because of their molecular masses and structural characteristics. The changes in the average structural parameters showed an essentially identical tendency for the coking formation of polycyclic aromatics and 3621
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Table 10. Average Structural Parameters of Native Bitumen and Their Liquid Products from Fluid Thermal Conversion A sample
B
C
bitumen
liquid product
bitumen
liquid product
bitumen
liquid product
fA
0.21
0.22
0.24
0.26
0.23
0.23
fN
0.11
0.21
0.07
0.21
0.15
0.2
fP
0.68
0.57
0.68
0.53
0.62
0.56
CA
19.66
5.06
22.29
5.97
13.39
5.97
CN
10.27
4.86
6.67
5
8.91
5.13
CP
63.24
12.87
62.76
12.41
36.49
14.31
HAU/CA
0.42
0.69
0.56
0.68
0.53
0.68
σ RA
0.46 5.22
0.41 0.84
0.38 6.1
0.42 1
0.55 3.13
0.43 0.99
RT
8.64
2.06
8.32
2.25
6.1
2.28
RN
3.42
1.21
2.22
1.25
2.97
1.28
RA/RN
1.53
2.73
1.05
0.69
0.8
0.78
the cleavage of a long paraffin side chain during fluid thermal conversion.
4. CONCLUSION The obtained results indicate that fluid thermal conversion of oil sands is a feasible process for the production of an upgraded bitumen-derived liquid from Inner Mongolian oil sand. The reaction temperature and reaction time of the fluid thermal conversion were the key operating conditions affecting the product distribution and yields in the fluidized-bed reactor. An optimal reaction temperature of 485 495 °C and an optimal reaction time of 5 min were obtained. Under the optimal operation conditions, maximum liquid yields of 79.87, 78.93, and 85.64 wt % were obtained for oil sand bitumen A, B, and C, respectively. The quality of the liquid products from the thermal conversion of oil sand was significantly better than that of the native bitumen, indicating that it would be an excellent feedstock for further processing and use in a refinery. After the fluid thermal conversion, the average structural parameters of the liquid products from the fluid thermal conversion changed significantly compared to native bitumen. The increase in fA and the decrease in fN could be a consequence of the removal of alkyl chains as well as their breakage to shorter chains. The deakylation and condensation reactions of oil sand bitumen were the preliminary steps in coke formation during the fluid thermal conversion. The changes in the average structural parameters showed an essentially identical tendency for the coking formation of polycyclic aromatics and the cleavage of long paraffin side chains during the fluid thermal conversion. ’ AUTHOR INFORMATION Corresponding Author
*Telephone: 8610-8973-3775. Fax: 8610-6972-4721. E-mail:
[email protected].
’ ACKNOWLEDGMENT The authors acknowledge the financial support provided by the National Science Foundation for Distinguished Young Scholars of China (20725620) and the National Natural Science Foundation for Young Scholars of China (20906103).
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