Article pubs.acs.org/EF
A Conceptual Catalytic Cracking Process to Treat Vacuum Residue and Vacuum Gas Oil in Different Reactors Haohua Gao,† Gang Wang,†,* Hao Wang,‡ Jianliang Chen,† Chunming Xu,† and Jinsen Gao† †
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China Petrochina Planning and Engineering Institute, Beijing 100083, China
‡
ABSTRACT: The catalytic cracking performances of vacuum gas oil (VGO), vacuum residue (VR), and their mixtures with different blend ratios of VR (R0) were investigated in a fixed fluidized bed reactor. The results indicate that a competitive adsorption effect developed between VGO and VR and further retarded VGO cracking. In accordance with the results and analysis of their reaction characteristics, a conceptual catalytic cracking process was proposed, and simulation experiments were carried out in a technical pilot scale riser (TPSR) apparatus. The results show that, compared with routine residue fluid catalytic cracking (RFCC), the competitive adsorption effect could be alleviated to some extent, and higher conversion and more desirable products could be obtained. Moreover, the balance of hydrogen for the products indicates that the decrease in coke and heavy cycle oil (HCO) at the optimal reaction conditions of the conceptual catalytic cracking process led to more hydrogen in the feed being distributed into the desired products.
1. INTRODUCTION In recent years, the supply of crude oil has become heavier and inferior, resulting in a higher quantity of residue per barrel of crude oil processed. Moreover, demand for high-value petroleum products, such as middle distillate and gasoline, has been increasing, while need has been decreasing for lowvalue products, such as fuel oil and residue-based products. As a result, it has become necessary to upgrade residual oils to sustain profitability.1−3 Fluid catalytic cracking (FCC) is one of the key operations in upgrading heavy hydrocarbon fractions to various higher-value light products in the oil refinery industry, especially in China,4,5 and will thus play an important role in this trend.6 The conventional residue fluid catalytic cracking (RFCC) process is blending residues such as atmospheric residual (AR) or vacuum residue (VR), deasphalted oil, aromatic extracts, etc., into vacuum gas oil (VGO). The inclusion of residues in VGO is not a new approach but a standard operating strategy; also, the blending ratio has been increasing steadily for about a decade because of the process’s versatility and high efficiency.7,8 It is well-known that the distillation range and physicochemical properties of VR differ from those of VGO.7−9 Compared with VGO, VR usually has a higher molecular weight and boiling point, and contains more sulfur and nitrogen heteroatom species that cause poisoning of acid sites. Most catalyst contaminant metals in crude oil, such as nickel, vanadium, sodium, and iron, are concentrated in VR, which contributes to more contaminant coke and irreversible deactivation of catalysts. Moreover, VR contains more resins and asphaltenes, causing a lower atomic ratio of hydrogen to carbon, a higher Conradson carbon residue (CCR), and polycyclic aromatics with strong coking.4,7 It is precisely these differences that lead to the diverse reaction characteristics of VGO and VR. However, in routine RFCC, they are usually premixed and then cracked in one common reactor at the same reaction conditions, which ultimately causes a competitive © 2012 American Chemical Society
adsorption effect between them, further retarding the reaction.4,10 To reduce the retardation effect on the reaction and improve product distribution by considering the reaction characteristics of different feedstock in FCC, some novel FCC processes have been proposed. Chen et al.11 introduced a maximum gas and diesel process (MGD), which divided a riser into four reaction zones, including gasoline, heavy hydrocarbon feedstock, light hydrocarbon feedstock, and a total reaction depth control zone. Xu et al.12,13 proposed a modified FCC process for maximizing i-paraffins (MIP) that has been put into commercial use; its advantages include providing favorable reaction conditions for heavy feedstock cracking into intermediate products and for upgrading gasoline. Additionally, some other novel RFCC processes were reported by U.S. open patents. Harandi et al.14 proposed a multizone catalytic cracking process, which generally comprises two reaction zones. In the first zone, a relatively light hydrocarbon feedstock makes contact with the first catalyst stream comprising spent catalyst. In the second zone, another relatively heavy hydrocarbon feedstock makes contact with the second catalyst stream comprising freshly regenerated catalyst. Herbst et al.15 also proposed a multiple riser catalytic cracking process comprising (1) converting a first hydro-deficient heavy hydrocarbon feedstock in the first riser; (2) converting a hydrogen-rich hydrocarbon feedstock in a lower region of the second riser, and (3) feeding a second relatively hydro-deficient heavy hydrocarbon feedstock into an upper region of the second riser. However, no further progress of these processes has been reported. Therefore, processing heavy oil more efficiently requires an economic, simple, and feasible process. Received: November 18, 2011 Revised: February 3, 2012 Published: February 3, 2012 1870
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The work presented here investigated the catalytic cracking performance of VGO, VR, and various blend levels of VR in VGO to evaluate their competitive adsorption effect in FCC. In accordance with the above results and analysis of their reaction characteristics, a conceptual catalytic cracking process was proposed. Simulation experiments were then carried out to verify the feasibility and the effect of the process in a technical pilot scale riser (TPSR) FCC apparatus.
Table 2. Properties of Commercial Equilibrium Catalysts items
2. EXPERIMENTS 2.1. Feed and Catalyst. Changqing VGO and VR were the experimental feeds, which were obtained from China National
Table 1. Properties of VGO and VR items
VGO
862.6 density (20 °C) (kg/m3) viscosity (80 °C) (mm2/s) 9.61 Conradson carbon residue (CCR) (wt %) 0.13 molecular weight (g/mol) 363 Elemental Composition (wt %) C 86.88 H 13.01 S 0.12 N 0.18 SARA Analysis (wt %) saturates 80.2 aromatics 15.8 resins 4.0 asphaltenes Ni content (μg/g) polycyclic cycloalkanes > alkenes > monocyclic aromatics with alkyl side chains > cycloalkanes > alkanes. However, the cracking rate of various hydrocarbons on active sites is not consistent with adsorption capacity, and even contradicts it. The order of reactivity is approximately as follows: alkene > monocyclic aromatics with long alkyl chains > i-paraffin or cycloalkanes > monocyclic aromatics with short alkyl side chains > n-alkane > polycyclic aromatics. Therefore, inconsistencies in the two sequences lead to hydrocarbons with strong adsorption and weak reaction ability preferentially adsorbing the limited active sites on the catalyst surface during FCC reactions.19,25 They further retard the remaining hydrocarbons with better reactivity and cause a competitive adsorption effect. We found that the polycyclic aromatics and polycyclic cycloalkanes are key incompatible components from the sequences above. Another primary factor is the nitrogencontaining compound,26 but those refractory and incompatible compounds are almost completely concentrated in aromatics, resins, and asphaltenes, especially the last two, while the crackable components are contained mainly in saturates.27 Comparing the chemical composition of VGO and VR (Table 1) reveals that VGO contains more saturates (80.2 wt %). In contrast, VR has a high content of aromatics (31.0 wt %), resins (19.9 wt %), and asphaltenes (1.6 wt %), leading to large amounts of refractory polycyclic aromatic hydrocarbons and nonhydrocarbon compounds. Therefore, under divisional catalytic cracking, the chemical composition of the feeds (VGO and VR) and the reaction conditions are essentially unchanged, while the contradiction between various types of hydrocarbons and nonhydrocarbon compounds is alleviated to some extent. As a result of the weakened competition adsorption effect, VGO crackability could take adequate effect, resulting in more of the desired products being obtained. 3.2.1. A Conceptual Catalytic Cracking Process Proposed. Analysis of Reaction Characteristics. In the FCC process, the chemical composition of feedstock is a decisive factor in reaction performance. Because of differences
Table 5. Calculated Product Distributiona of the Mixtures of VGO and VR feedstock
yield of light oil (wt %) yield of dry gas + coke (wt %) conversion (wt %) dry gas LPG gasoline LCO HCO coke
70 wt % VGO + 30 wt % VR
50 wt % VGO + 50 wt % VR
30 wt % VGO + 70 wt % VR
LVR− 60R
CDC
LVR− 60R
CDC
LVR− 60R
CDC
69.10
60.16
68.25
58.78
67.39
57.30
7.28
8.26
8.65
9.63
10.03
11.01
70.02 %) 1.80 18.19 42.20 16.53 13.45 7.84
78.05
69.53
2.20 14.67 53.35 14.04 7.90 7.83
1.98 18.05 40.48 16.83 13.64 9.02
77.78 70.51 77.91 Product Distribution (wt 1.93 1.61 2.06 14.94 18.32 14.81 55.56 43.93 54.46 13.54 16.23 13.79 8.68 13.26 8.29 5.35 6.65 6.59
a Ycalculated = YVGO × (1 − R0) + YVR × R0; R0 is defined as the weight ratio of VR to the sum of VGO and VR; reaction temperature = 500 °C, CTO = 6, WHSV = 20 h−1.
investigating the competitive adsorption effect between VGO and VR: Ycalculated,i = YVGO,i × (1 − R 0) + YVR,i × R 0
(3)
Figure 2 shows the yield difference value in light oil, and coke plus dry gas versus R0. The yield difference value is defined as a calculated product yield in a given R0 subtracted from the corresponding product yield generated by the mixture. In this paper, the calculated product distribution represents divisional catalytic cracking, while conventional catalytic cracking is denoted by the product distribution of the mixtures. Compared with the product distribution of conventional catalytic cracking, the light oil yield of divisional catalytic cracking increased by 0.1−2.1 wt %, while the yield of coke plus dry gas decreased by 0.1−1.4 wt %. Similar observations were reported by Arandes 1873
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Figure 3. Schematic of the routine RFCC and the conceptual catalytic cracking process.
higher CTO enforces the cracking of residue and weakens the competitive adsorption of the polycyclic aromatic hydrocarbons with the other hydrocarbons, effectively leading to more active sites for the intrinsic reaction of catalytic cracking. Moreover, the heavy molecules in VR usually require more time for evaporation, cracking, and condensation. The routine reaction time is sufficient for VGO but is not enough for VR, resulting in many heavy components reacting insufficiently, with a relatively high content of hydrogen in the coke.30 Therefore, an appropriate reaction condition of VR would be a higher CTO, a longer reaction time, and an appropriate reaction temperature. 3.2.2. Description of the Conceptual Catalytic Cracking Process. A conceptual catalytic cracking process was proposed according to the experiment results and analysis of reaction characteristics. Figure 3 shows the schematic of the routine RFCC process and the conceptual catalytic cracking process. In contrast to the state-of-the-art practice of the RFCC process, the conceptual catalytic cracking process involves two reactors. VGO is cracked in the conventional riser reaction zone, while VR is converted in the other modified reactor composed of the transport bed and fast bed. Moreover, two catalyst coolers are used to lower the temperature of the regenerated catalyst for enhancing the CTO. The higher CTO provides sufficient energy to feed evaporation and catalytic activity to hydrocarbon cracking. Further, such operating parameters as CTO, reaction temperature, and regenerated temperature are dissociated from the heat balance of the FCC unit. The objective of the improvement is to weaken the competitive adsorption effect between VGO and VR and provide favorable reaction conditions. Ultimately, a desirable product distribution could be achieved.
in composition, the favorable reaction conditions for both should differ. VGO usually has better reaction characteristic owing to a high content of saturates. Its low viscosity and boiling point favor atomization and vaporization. Thus, to reduce an excessive thermal cracking reaction during the initial catalyst− oil contact time, a low-temperature difference between VGO and the regenerated catalysts, matched with high CTO, should be taken.28 Moreover, FCC is a typical parallel-series reaction, and product distribution in the process is closely associated with reaction time when other operating parameters are fixed. Gasoline and LCO as intermediates are the desired products, while gas and coke are the final products. It is well-known that the routine FCC reaction time is about 3.0 s, and the FCC catalyst deactivates rapidly during this time. The relative microactivity index at the exit of the riser is less than 30% that at the entrance.29 As reaction time is prolonged, conversion increases, and the ratio of thermal cracking and the secondary reaction is enhanced, giving rise to more undesirable products. Therefore, reaction time should be shortened to less than 3.0 s to improve the selectivity of intermediates. VR, however, usually contains a large amount of refractory hydrocarbons, resulting in poor reactivity. The primary method for maintaining sufficient conversion is enhancing the severity of the reaction, such as by using a higher temperature and CTO and a longer reaction time. Since the activation energy of the thermal cracking reaction (210−290 kJ/mol) is much larger than that of the catalytic cracking reaction (42−125 kJ/mol),4 thermal cracking is more sensitive to reaction temperature. Therefore, a higher conversion of heavy oil cannot be obtained by increasing the temperature only. Wang et al.28,30 believed that enhancing the CTO increases the heat of the catalyst−oil mixing and the probability of a molecular collision between catalyst and oil and intensifies the mass and heat transfers. The 1874
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Figure 4. Effects of operation parameters on product distribution and conversion of VGO.
increases as well and passes through a maximum at 240 °C. Therefore, the optimal Tpre of VGO is 240 °C. In Figure 4b, the conversion and product distribution versus various Tout is represented at 240 °C Tpre, 690 °C TRC, 6.6 CTO, and a 2.0 s residence time. As the Tout increases, so does the conversion. The yields of light oil and coke decrease, while the dry gas yield increases rapidly after 500 °C. Thus, to obtain a relatively high yield of light oil product, the optimal reaction temperature is about 500 °C. In Figure 4c, the data for product distribution and conversion versus residence time is presented at 240 °C Tpre, 500 °C Tout, 690 °C TRC, and 6.6 CTO, respectively. During residence times from 1.5 to 2.8 s, light oil overcracking is observed, while the coke and dry gas yield increase. The light yield goes through a maximum at 1.7 s. According to the experiments, to obtain a more desirable product, optimal residence time is about 1.7−2.0 s. Figure 4d shows the data for conversion and product distribution as a function of CTO at
3.3.1. Simulation Experiments of the Conceptual Catalytic Cracking Process. Determination of Optimal Reaction Conditions. The performance of the feed depends on a large number of parameters. Besides feed composition and catalyst properties, operation parameters such as residence time, CTO, and temperature all influence the conversion process in their own way. The catalytic cracking experiments of VGO were carried out in the routine riser reactor of the TPSR apparatus. Figure 4 shows the effects of the preheated temperature of the feed (Tpre), the riser outlet temperature (Tout), residence time, CTO, and the temperature of the regenerated catalyst (TRC) on the performance of VGO. Figure 4a shows the data for conversion and product distribution as a function of Tpre at the fixed 500 °C Tout, 690 °C TRC, 6.6 CTO, and a 2.0 s residence time. As the Tpre increases from 200 to 300 °C, the conversion, dry gas, and coke yield also increase; the yield of light oil 1875
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Figure 5. Effects of operation parameters on product distribution and conversion of VR.
the fixed Tpre 240 °C, Tout 500 °C, TRC 690 °C, and a residence time of 1.7 s. As the CTO increases from 6 to 10, it profoundly influences the conversion and product distribution. About 62.37 wt % of the feed is cracked at a CTO of 6, while the data reach 86.48 wt % at a CTO of 10. With the increase in CTO, the yield of liquid product (gasoline, diesel, and LPG) continues to increase until CTO 9 is reached. In the range 7−9, light oil yield almost remains stable. Under such a relatively high CTO 8−9, a better product distribution with the maximum liquid product can be obtained. In Figure 4e, the conversion and product distribution versus various TRC are represented at a fixed Tpre of 240 °C, Tout of 500, CTO of 9, and a residence time of 1.7 s. As TRC increases, so does the yield of light oil, which passes through a maximum at 660 °C, while the conversion also increases to 83.23%. Under the cracking condition of a low temperature of regenerated catalyst, less dry gas and coke can be obtained because of the reduction of
thermal cracking in the initial catalyst−oil contacting regime. Consequently, the optimal TRC is about 660 °C. The effects of Tpre, Tout, WHSV, CTO, and TRC on the performance of VR were also investigated in the modified riser reactor in the TPSR apparatus. WHSV is defined as the weight per hour of feedstock divided by the catalyst inventory in the fast bed, which is regulated by the bed pressure drop. In this study, residence time in the transport bed is a fixed time of 0.3 s. Figure 5 shows the effects of these parameters on the performance of VR. Similar effects are observed. The optimal reaction conditions of VR are Tpre 300 °C, Tout 500 °C, WHSV 11−12 h−1, CTO 8, and TRC 670 °C. 3.3.2. Product Distribution. To simulate the conceptual catalytic cracking process, simulation experiments were carried out in the TPSR. Table 6 shows the operating conditions of the routine RFCC and the conceptual catalytic cracking process, as well as their product distribution. For the routine RFCC, a 1876
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Table 6. Effect of Different Operating Mannersa on Product Distribution routine RFCC process base test 60 wt % VGO + 40 wt % VR weighting coefficient Tpre (°C) Tout (°C) TRC (°C) residence time (s) WHSV (h−1) CTO (kg·kg−1) conversion (wt %) yield of light oil (wt %) yield of liquid product (wt %) selectivity of dry gas (%) selectivity of coke (%) selectivity of light oil (%)
7.0 76.24 58.18 79.74 2.64 8.87 76.31
dry gas LPG gasoline LCO HCO coke
2.01 21.56 45.90 12.27 11.49 6.76
conceptual catalytic cracking process comparative test 1 VGO 0.6 280 500 690 2.0
280 500 690 2.0
VR 0.4 280 500 690 2.0
7.0 7.0 83.34 80.92 66.31 55.88 90.40 76.13 1.82 3.21 3.32 17.03 79.57 69.06 Product Distribution (wt %) 1.52 2.60 24.09 20.25 54.97 44.29 11.34 11.59 5.31 7.49 2.77 13.78
calcdb
comparative test 2 VGO
VR
test 1
test 2
9.0 83.32 69.22 90.96 1.53 2.84 83.08
0.4 300 500 670 0.3c 11.0d 8.0 83.75 57.60 78.86 3.51 15.74 68.77
82.37 62.14 84.69 2.36 8.71 75.43
83.49 64.57 86.12 2.32 8.01 77.36
1.28 21.75 57.92 11.29 5.39 2.37
2.94 21.26 46.36 11.23 5.02 13.18
1.95 22.55 50.70 11.44 6.18 7.17
1.94 21.55 53.30 11.27 5.24 6.69
0.6 240 500 660 1.7
The experiments were carried out under catalyst LVR−60R only. bYcalculated = YVGO × 0.6 + YVR × 0.4. cResidence time of oil gas in the transport bed. dWHSV is defined as the weight per hour of feedstock divided by the catalyst inventory in the fast bed. a
Table 7. Effect of Different Operating Mannersa on Properties of Gasoline and Diesel
mixture of 60 wt % VGO and 40 wt % VR was converted. The proportion of VR was representative in refineries, especially in China. Catalytic cracking of the base experiment was carried out under the reaction conditions of Tpre 280, Tout 500, CTO 7, TRC 690, and a residence time of 2.0 s. For the conceptual catalytic cracking process, two comparative tests were designed for VGO and VR, respectively. The reaction condition for comparative test 1 was the same as used in the base experiment. In comparative test 2, the optimal reaction conditions for VGO and VR were used. VGO was reacted at Tpre 240 °C, Tout 500 °C, residence time 1.7 s, CTO 9, and TRC 660 °C; VR was cracked under at Tpre 300 °C, Tout 500 °C, CTO 8, TRC 670 °C, residence time of 0.3 s in the transported bed, and WHSV of 11 h−1 in the fast bed. Table 6 shows that the conversions of the conceptual catalytic cracking process under the two comparative tests are higher, and the product distributions are superior to those of the routine RFCC under the base reaction test. The conversions increase by 6.1 and 7.3 wt %, and the gasoline yield increases by 4.8 and 7.4 wt %, while LCO decreases by 0.8 and 1.0 wt %. The yield of dry gas also decreases slightly. The coke yields change in different directions, increasing by 0.5 wt % in test 1 and decreasing by 0.1 wt % in test 2, but their selectivity all decreases to some extent. These results are attributed to alleviating the competitive adsorption effect between VGO and VR in the conceptual catalytic cracking process. The process creates favorable reaction conditions for VGO and VR, resulting in higher conversion and greater yields of light oil. 3.3.3. Properties of Gasoline and Diesel. Table 7 lists the properties of gasoline and diesel. The gasoline composition of the conceptual catalytic cracking process in comparative test 2 differs from that of the base test for routine RFCC. The iparaffin and n-paraffin contents of comparative test 2 are both higher than in the base test, while the naphthalene and
routine RFCC process base test 60 wt % VGO + 40 wt % VR weighting coefficient Tpre (°C) Tout (°C) TRC (°C) residence time (s) WHSV (h−1) CTO (kg/kg) density (g/cm3) sulfur content (ppm) RONb n-paraffins i-paraffins olefins naphthenes aromatics density (g/cm3) condensation point (°C) aniline point (°C) cetane no.b
280 500 690 2.0
conceptual catalytic cracking process comparative test 2 VGO 0.6
0.4
240 500 660 1.7
300 500 670 0.3 11.0 8.0
7.0 9.0 Properties of Gasoline 0.7514 0.7318 106 52 91.8 90.8 Composition of PIONA (wt %) 3.86 4.17 17.77 19.27 41.62 48.06 7.00 7.13 29.74 21.36 Properties of Diesel 0.8882 0.8950 −35 −10 27.8 29.5
VR
31.4 34.5
test 2 (meas.)
0.7566 152
0.7417 92
94.2
92.4
3.70 20.23 31.97 4.38 39.73
3.98 19.65 41.62 6.03 28.71
0.9246 −65
0.9068
19.8 21.0
29.0
a
The experiments were carried out under catalyst LVR−60R only. b The uncertainties of RON and cetane number are less than 0.5.
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aromatics clearly decrease. Therefore, it can be deduced that the gasoline composition changes because of the optimum reaction condition of both VGO and VR. More catalytic active centers in the catalysts not only lead to heavy oil cracking into smaller hydrocarbon molecules for better product distribution but also strengthen ideal reactions such as isomerization and hydrogen transfer for improving gasoline quality. Because of the increase in i-paraffin, the research octane number (RON) of the gasoline in the conceptual catalytic cracking process increases despite the small decrease in aromatics. For the conceptual catalytic cracking process, the densities of diesel are higher than in the base test, and the cetane number declines slightly. The diesel fraction is susceptible to serial cracking reactions. The long-chain paraffins and long side chains of aromatics or naphthenes are easier to crack at a high CTO. As a result, more hydrocarbons with aromatic structure remain in the diesel in comparative test 2, leading to the diesel’s higher density and lower cetane number. 3.3.4. Analysis of Hydrogen Balance. To obtain more liquid products, the rational distribution of the hydrogen in the feed into the products is the key factor. In the product distribution of FCC, coke, HCO (or slurry), and LCO are the “H-donors”, which have lower hydrogen content than the feedstock. At the same time, dry gas, LPG, and gasoline are the “H-acceptors”, which have higher hydrogen content than the feedstock; their formation in FCC comes through receiving the hydrogen from the H-donors. If coke and HCO (or slurry) with a high carbon/ hydrogen ratio does not form, it is impossible to obtain LPG and gasoline with a high hydrogen/carbon ratio in FCC. To evaluate hydrogen utilization in the feedstock, the effective utilization rate of hydrogen is defined as follows: EH =
H of LPG + H of gasoline + H of LCO % H of feedstock
Table 8. Hydrogen Balance of Different Operating Mannersa routine RFCC process base test 60 wt % VGO and 40 wt % VR weighting coefficient Tpre (°C) Tout (°C) TRC (°C) residence time (s) WHSV (h−1) CTO (kg/kg) dry gas LPG gasoline LCO HCO coke hydrogen in feedstock dry gas LPG gasoline LCO HCO coke ∑ hydrogen in products relative error (%) EH (%)
(4)
Table 8 shows the hydrogen content of different products and hydrogen balance for different operating manners with the catalyst LVR−60R, which is calculated according to the components in each product and the hydrogen content of each component. Here, the hydrogen content of LCO, HCO, and coke is measured using Flash EA1112, an organic elementary analyzer. The sum of hydrogen in all products is close to that in the feed, and the relative error is below 1.87%. In Table 8, more hydrogen is distributed into the liquid products during the conceptual catalytic cracking process. With coke, HCO, and LCO as the H-donors, the decrease in their hydrogen content effectively favors improvement of hydrogen utilization. EH increases by 7.45 wt % in the modified process over that of routine RFCC.
a
280 500 690 2.0
multizone residue catalytic cracking process comparative test 2 VGO
VR
0.6
0.4
240 500 660 1.7
300 500 670 0.3 11.0 8.0
7.0 9.0 Hydrogen Content of Products (wt %) 22.99 23.75 26.22 13.75 14.19 14.46 13.12 13.59 12.62 11.21 11.06 10.04 11.05 10.36 9.01 7.52 6.50 6.05 Hydrogen Balance (wt %) 12.84 13.40 12.00 hydrogen in products 0.46 0.30 2.96 3.09 6.02 7.87 1.38 1.25 1.27 0.56 0.51 0.15 12.60 13.22 1.87 80.69
1.34 91.12
test 2 (calcd)
24.74 14.30 13.20 10.65 9.82 6.32 12.84
0.76 3.07 5.85 1.12 0.45 0.79 12.12
0.48 3.08 7.06 1.20 0.50 0.41 12.77
−0.33 83.67
0.55 88.14
The experiments were carried out under catalyst LVR−60R only.
A conceptual catalytic cracking process was proposed based on the experimental results and the difference in reaction characteristics between VGO and VR, which involved two reactors and two catalyst coolers. VGO was cracked in the conventional riser; VR was cracked in the other modified reactor composed of the transport bed and the fast bed. The simulation experiments were carried out in a TPSR FCC apparatus. The results show that, compared with routine RFCC, higher conversion and better product distribution could be obtained under the conceptual catalytic cracking process, resulting in the liquid product yield increasing by 5.0−6.4 wt %. Moreover, the quality of gasoline and LCO also improved because of the strengthening of some ideal reactions. Catalytic cracking is a carbon-rejection process in which the carbon−carbon scission of hydrocarbons abides by the mass balance law of hydrogen and carbon. The balance of hydrogen for the products indicates that the decrease in coke and HCO at the optimal reaction conditions of the conceptual catalytic cracking process led to more hydrogen in the feed being distributed into the desired products, as well as obvious improvement in the effective utilization rate of the hydrogen.
4. CONCLUSION VR, as an inferior feedstock, is usually blended into VGO as a part of RFCC unit input. Compared with VGO, VR is characterized by a low hydrogen-to-carbon ratio as well as saturates, high resins, asphaltenes, and content of sulfur, nitrogen, and heavy metal. These differences give rise to the dissimilarities in reaction performance. Compared with the product distribution of a mixture of VGO and VR in a given R0, the calculated product distribution based on the reactants (VGO and VR) catalytic cracking alone obviously improves. As R0 increases, the improvement of the desired product is enlarged gradually. Moreover, the experimental results indicate that a competitive adsorption effect developed between VGO and VR. 1878
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AUTHOR INFORMATION
Corresponding Author
* Tel.: 8610-8973-3085. Fax: 8610-6972-4721. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors acknowledge the financial support provided by the National Science Fund of China (21176252), the National Natural Science Foundation for Young Scholars (20906103), and the National Science Foundation for Distinguished Young Scholars of China (20725620).
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dx.doi.org/10.1021/ef201815z | Energy Fuels 2012, 26, 1870−1879
