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Adjustment of products distribution over bifunctional Ca12Al14O33– supported MnOx catalyst from cracking gasification of petroleum residue Ruiyuan Tang, Shengjia Wang, Yuanjun Che, Yuanyu Tian, Yingyun Qiao, and Guoming Zhao Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 28 Apr 2017 Downloaded from http://pubs.acs.org on April 29, 2017
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Energy & Fuels
Adjustment of products distribution over bifunctional Ca12Al14O33–supported MnOx catalyst from cracking gasification of petroleum residue Ruiyuan Tanga, Shengjia Wangb, Yuanjun Chea, Yuanyu Tiana,b*, Yingyun Qiaoa*, Guoming Zhaob a
State Key Laboratory of Heavy Oil Processing, China University of Petroleum (East
China), Qingdao Shandong 266580, China. b
Key Laboratory of Low-carbon Energy and Chemical Engineering, Shandong
University of Science and Technology, Qingdao Shandong 266590, China.
*
Corresponding author. Tel.: +86-0532-86057766. E-mail addresses:
[email protected] (Y. Tian);
[email protected] (Y. Qiao).
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Abstract: Cracking gasification of petroleum residue towards expected gas and light oil products is catalyzed in a fluidized bed reactor by using calcium aluminate (C12A7) and Mn-modified C12A7 as the bifunctional catalysts. The performances of the reaction temperature and the Mn-modified C12A7 catalysts on the products distribution for the vacuum residue cracking are studied. The results showed that ethylene, propylene and butylene are the primary products of petroleum residue cracking over the C12A7, which reflects in the C2−C4 olefinicity of 63.4% at 650 oC with the catalyst-to-oil of 7.0. For Mn-modified C12A7 catalysts, the C2−C4 olefinicity of 0.4 wt%-Mn/C12A7 catalysts is increased to 66.9%, while that of 1.0 wt%-Mn/C12A7 and 2.0 wt%-Mn/C12A7 catalysts is decreased to 40.1% and 25.1%, respectively. Besides, the C4−C5 hydrocarbon yield is increased from about 3.0 wt% over the C12A7 and 0.4 wt%-Mn/C12A7 catalysts to approximately 11.5 wt% over the 1.0 wt%-Mn/C12A7 and 2.0 wt%-Mn/C12A7 catalysts. This indicated that a technical feasible for adjusting the products distribution by using Mn-modified C12A7 catalysts. Moreover, the Mn-modified catalysts showed proper the residue cracking activity to allow both the expected light liquid yields of about 50 wt% and the heavy oil conversion ratio of up to 92.0 wt%. Steam gasification of coke on the C12A7 and Mn-modified C12A7 catalysts resulted in the syngas products containing H2 and CO2 content to be about 58.0 and 24.0 vol%, respectively. Furthermore, it is also verified the possibility of circulating the modified C12A7 catalysts in vacuum residue cracking gasification process. Key words: Bifunctional, Adjustment, Light products, Ca12Al14O33, Manganese
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1. Introduction Heavy oil occupied a higher proportion and quality degradation in the petroleum crude, which is receiving more attention in the refinery. Processing these above-mentioned oil feedstocks would inevitably generate petroleum residue a large amount. Generally, there are two typical technical routes to convert petroleum residue based on carbon rejection and hydrogen addition 1.2. Of which carbon rejection is associated with the process of thermal or catalytic thermal conversion. Now, petroleum residue converted into the light products via catalytic thermal conversion has been reported in the literature with various cracking catalysts, such as the MnOx dispersed on different supports 3, incorporated alkali-metal oxides 2.4 and supported transition metals 5. The residues cracking over the catalysts might lead to deteriorate its catalytic activity or even coking deactivation because of the poisons by the contaminants (such as N, S, V and Ni). Moreover, higher activity of hydrogen transfer and coking of the catalyst is also might lead to the cracking products contained higher paraffins and coke 6. On the other hand, hydrogen is very important for upgrading low-grade oil and raw materials for several industrial products (i.e., hydrogenation, catalytic hydro-cracking and synthesis ammonia). At present, in the petroleum industry, hydrogen is produced mainly via separation from H2-rich off-gases (the dry gas and LPG) or catalytic reforming of naphtha. The modified catalyst cracking gasification petroleum residue could realize the adjustment of the products distribution, and co-production hydrogen via gasifying the cracking-generated coke.
In this study, a modified catalyst cracking gasification vacuum residue is proposed to realize the adjustment of the products distribution and co-production H2-rich syngas. 3
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This coupling process is conducted with the reaction temperature of above 600 oC in the fluidized bed reactor. It is essentially to realize value-added utilization and hierarchical conversion of petroleum residues 7. To realize the adjustment of products distribution in the vacuum residue cracking gasification, catalysts with different activity component modification and implemented a proper catalytic activity is needed, and steam has to be used to strip the cracking products quickly from the reaction system and not deteriorated the catalysts in an atmosphere of steam. Furthermore, for combining these two types of reactions, the regenerated catalysts could be again circulated into this reactor to provide endothermic heat and catalytic activity required for the cracking reaction.
In the past years, many research efforts have performed to the development of the upgrade catalysts for petroleum feedstocks cracking. The literature research showed that calcium aluminate catalysts have contributed to produce the products of light olefins and reduce the required temperature 8.9 in the petroleum feedstock cracking. Also, in comparison with the zeolite catalysts, Tang et al. 10 and Zhang et al. 11 found that calcium aluminate catalysts have the advantages of the moderate reactivity, anti-coking property, bifunctional characteristics and good hydrothermal stability from cracking gasification of vacuum residue. Also, the properties of high reactivity and production selectivity 10.12 have been found in the reactions of coke gasification10,13 and producing biodiesel 14 over such a catalyst. There are many literature studies on optimizing the petroleum feedstock upgrading catalysts 15–17 that is required to adjust the products distribution. Lu et al. 18.19 found that a trace amount of the transition metal modified ZSM-5 catalyst could produce the higher light olefins yields. But so far, the modified 4
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calcium aluminate catalyst has mainly applied in enhancing the yields of light olefins, reducing the coke formation for a given conversion. Nowak et al. 20 found that carbon deposited on the used catalysts is reduced by using promoted calcium aluminate catalyst containing CaO. Mukhopadhyay et al. 15 found that the light olefins yield is increased whereas carbon deposited on the catalysts is significantly decreased by using potassium modified calcium aluminate catalysts. But there is little literature study on developing transition metal modified calcium aluminate as a bifunctional catalyst for adjusting the products distribution, and also promoting coke gasification to produce H2-rich syngas.
The aim of this research is to investigate the effects of transition metal modified calcium aluminate as a bifunctional catalyst for adjusting the cracking products distribution, and catalyzing the residues hierarchical conversion. Calcium aluminate catalysts preparation method is selected on the basis of previous reports 10.21–23. Vacuum residue cracking effects variation with the catalyst properties and the reaction conditions are studied over both silica sand and calcium aluminate. Silica sand is adopted as a reference to study the thermal cracking effects of vacuum residue. The Mn-modified method is performed for the tested catalysts with the purpose of adjusting its cracking activity and products distribution. Coke steam gasification is conducted to gasify the coke, and the possibility of vacuum residue cracking gasification is also tested. 2. Experiment 2.1 Materials and Reagents. CaCO3 and Al2O3 were purchased from Tianjin Kemiou Chemical Reagent Co., Ltd, China, and calcined in air at 200 oC for 1 h without further
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purification. Nitric acid and Sesbania powder were purchased from Qingdao Jingke Chemical Reagent Co., Ltd, China. Carbon black (nano-meter powder) was purchased from Alfa Aesar, and dried at 120 oC overnight before further use. Vacuum residue was provided by Shenghua refining, China, and its properties are listed in Table 1. Table 1 Properties of vacuum residue Properties
Value
Density 20 oC/g·cm–3 o
2
0.98
–1
Viscosity 80 C/mm ·s
900
H/C ratio
1.67
Carbon residue/wt%
13.5
Elemental analysis/wt%
Group composition/wt%
C
87.0
Saturates
38.6
H
12.0
Aromatics
33.5
S
0.3
Resins
26.8
N
0.4
Asphaltenes
1.1
O (by difference)
0.3
2.2 Catalyst Preparation. Ca12Al14O33 catalyst is synthetized via solid-state synthesis method. Schematic diagram of the formation process of Ca12Al14O33 catalyst is shown in Fig.1. Firstly, CaCO3 and Al2O3 are mixed with a molar ratio of 12:7, followed with the addition of carbon black of 3.0 wt%. Then these mixtures are triturated in a grinding miller for 3 min (3000 r·min–1), and then calcined in Ar at 1350 oC for 2 h with the heating rate of 8 oC·min–1. Subsequently, the catalysts are cooled to room temperature in a drying vessel and denoted as C12A7 catalyst. The impregnation technique is used for the deposition of 0.5 wt%, 1.0 wt% and 2.0 wt% Mn on the Ca12Al14O33 substrate. An ethanol solution of Mn(NO3)2·4H2O is the precursor of MnOx. These mixtures are calcined in air at 600 °C for 4 h to decompose the manganese nitrate, and then at 900 °C for another 3 h. The prepared catalysts are denoted as 0.4 wt%-Mn/C12A7, 1.0 wt%-Mn 6
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/C12A7 and 2.0 wt%-Mn/C12A7 catalysts, respectively. Finally, the prepared catalysts are stirred into 100 mL the aqueous solution with the addition of 6.0 wt% Sesbania powder and 4.0 wt% HNO3, and then compression molding in 50 MPa for 5 min. After being calcined at 600 °C for 2 h and then 900 °C for another 3 h, and crushed to 150−250 µm.
Fig.1. Schematic diagram of the formation process of Ca12Al14O33 catalysts
2.3 Cracking Gasification Test. Petroleum residue cracking to produce the products of light products is performed in a fluidized bed reactor. The schematic diagram of the test device is exhibited in Fig. 2. It is seen that the device consists of the feeding system, the reaction system and separation system. This fluidized bed reactor is composed of the stainless steel with a total length of 800 mm and an inner diameter of 25 mm. It is worth noting that the expanded section has a length of 200 mm and an inner diameter of 90 mm on the top of the reactor. Steam and stainless steel porous distributor are designed to atomize vacuum residue and fluidize the catalyst particles. Furthermore, steam is also part of the reagent gas for the cracking-generated coke gasification. A certain amount of oxygen is fed into this reactor for combusting the remaining coke in the gasification process. Nitrogen is used as the protect gas during the heating stage.
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Fig.2. Schematic diagram of vacuum residue catalytic cracking (red line represented electric tracing band)
For the residue cracking process, the fluidized bed reactor is firstly heated to the preset temperature in Ar. And then vacuum residue and water is preheated to 150 and 200 oC separated. Of this steam is used to fluidize the catalyst particles and mixed with vacuum residue in the preheated section. Then the oil-steam mixtures are atomized into a tiny oil drop by a stainless porous distributor. The gaseous products are separated via the oil-gas separation section. The gas volume and gas composition are measured and analyzed by a wet gas meter and gas chromatography separated. Gas chromatography is able to monitor the components of H2, CO2, CO and C1–C6 hydrocarbons. The liquid products are collected by two successive collectors. The heavier fractions are collected by the first collectors, and the lighter fractions are gathered by the second one with the cooling water at about 1 oC. The produced oil yield is measured by mixed together both collected liquid (get rid of water). And the coke characteristics on the catalysts could be
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measured when the residues cracking gasification process is not carried out. In order to gasify the coke on the catalysts, the fluidization steam to this reactor is switched to Ar to purge the whole system and heated the reactor to the preset temperature. And then the gasification reagent of steam is added into the reactor to gasify the coke until no carbon -containing gas is detected. The produced syngas products are first condensing with a cooling water of 1 oC, then measure and analysis by wet gas meter and GC separated. And the catalyst stability could be evaluated via vacuum residue cracking gasification cycle process. Each test is reproduced for at least twice and the obtained mass balance is above 95.0%.
2.4 Characterization and Analysis. Textural properties are characterized by the N2 adsorption/desorption at –196 oC with a Tristar II 3020 apparatus (Micromeritics Corp., USA). The samples are degassed for 4 h at 300 oC under vacuum. Specific surface area (SBET) of the catalysts is calculated using the Brunauer–Emmett–Teller (BET) equation, and the total pore volume (Vt) is calculated at P/P0=0.98. The X-ray diffraction (XRD) patterns are recorded on an X-ray diffractometer X’Pert PRO MPD (PANalytical B.V. Netherlands) by using an acceleration voltage of 40 kV and 40 mA with a step of 8°·min–1 from 5° to 75°. The crystal size of the sample is estimated using the Debye– Scherrer equation. The base strength and total base number of the tested catalysts are measured by the Hammett indicator method, including bromthymol (H_=7.2), phenolphthalein (H_=9.8), 2,4-dinitroaniline (H_=15.0) and 4-nitroaniline (H_=18.4). The base strength of the tested catalyst (about 0.3 g) is measured by the indicator -ethanol solution. Total base number of the catalyst is measured by the consumption of 9
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benzoic acid. Surface chemical composition of the catalysts is analyzed by the X-ray photoelectron spectroscopy (XPS) performed on a VG ESCALAB 250 spectrometer (Thermo Electron, UK) with a monochromatized Al Kα anode (1486.6 eV, 30 kV), and the C1s peak is taken as the internal standard. The microscopic feature of the tested catalyst is observed by the cold field scanning electron microscopy (SEM) (S-4800, Hitachi, Japan). Prior to the test, the tested catalysts are sprayed with gold by using a gold-sputtering device to increase the electroconductivity.
GC analysis is conducted to provide the detailed contents of the cracking products. The non-condensable gas are divided into two groups, the dry gas (H2, CO, CO2 and C1–C2) and the liquefied petroleum gas (C3–C5), and analyzed using two Agilent GC equipped with alumina plot capillary column with the flame ionization and thermal conductivity detectors. The gas products mass yield is calculated according to the total gas products volume and the ideal gas law. The cracking liquid products are tested with an Agilent 7890A simulated distillation GC. The distillation fractions divided by the boiling points, which included the fractions of gasoline (IBP–180 oC), diesel (180–350 oC) and vacuum gas oil (350–500 oC), and heavy oil (>500 oC). Besides, the heavy oil fraction is defined as unconverted part in the residue cracking. The coke on the catalysts is tested by the coke analyzer (HX–HW8B, Huaxin, China). The coke is burnt in pure oxygen and measured the CO2 content with a GC detector. 3. Results and discussion 3.1 Catalyst Characterization. Fig. 3 presents the XRD pattern of Mn-modified C12A7 and C12A7 catalysts. It is found that all of the catalysts exhibited good crystallinity and 10
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diffraction peak intensity. For all tested catalysts, the crystal structure of Ca12Al14O33 is observed. Additionally, a certain quantity of the CaO crystal structure is also found in the patterns of all prepared C12A7 catalysts. However, the diffraction peak intensity of all of Mn-modified C12A7 catalysts is slightly strengthened in comparison with those of C12A7 catalyst. Also, MnOx diffraction peak is not found in the patterns of Mn-modified C12A7 catalysts. This might be because MnOx has highly dispersed on the surface of the C12A7 catalyst.
★
★--Ca12Al14O33
★
--CaO
●
★ ★★ ★ 2.0 wt%-Mn/C12A7
★ ★ ★★★ ★ ★ ● ★★ ★
Intensity(a.u.)
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1.0 wt%-Mn/C12A7
0.4 wt%-Mn/C12A7
C12A7
10
20
30
40
50
2theta (degree)
60
70
Fig.3. XRD patterns for C12A7 and Mn-modified C12A7 catalysts.
Table 2 represents the structural properties of silica sand, the Mn-modified C12A7 and C12A7 catalysts. The surface area and total pore volume of silica sand are below the detection limits of N2 physical absorption. The SBET and Vt of C12A7 catalyst (21.7 m2·g– 1
and 0.15 cm3·g–1) is detected, and those are higher than the results as reported earlier
10.21–23
. This indicated that adopting carbon black as hard template could effectively
prevent the prepared catalyst particles agglomeration during the calcination process, and thus increasing the SBET of C12A7 catalyst. After the MnOx–loading by the immersion method, SBET and Vt of all the Mn-modified C12A7 catalysts are slight increased, which respectively reached 27.0 m2·g–1 and 0.30 cm3·g–1. The reason should be because the 11
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decomposition of Mn(NO3)2 could slightly increase SBET of the tested C12A7 catalysts. Average pore diameter of C12A7 catalyst is 5.3 nm, while that of the Mn-modified C12A7 catalysts are around 11.5 nm with the typical mesoporous structure. Average crystallite size of all of the tested C12A7 catalysts materials is around 31.0 nm. Bulk density of the C12A7 catalyst is 1.2 g·cm–3 in comparison with about 1.0 g·cm–3 for the Mn-modified C12A7 catalysts. This should be because the surface properties of the catalysts varied a lot, and thus led to the variation in the bulk density of the catalysts. Table 2 Structural properties of the tested catalysts Catalyst
SBET a/m2·g–1
Vt/cm3·g–1
DPD b/nm
Bulk density/g·cm–3
DXRD c/nm
Silica sand
–
–
–
2.56
–
C12A7
21.7
0.15
5.3
1.20
33.8
0.4 wt%-Mn/C12A7
27.3
0.33
11.9
1.01
31.5
1.0 wt%-Mn/C12A7
27.1
0.32
12.0
0.99
30.4
2.0 wt%-Mn/C12A7
26.8
0.30
11.1
0.95
32.7
a
SBET, derived from BET equation. b D=average pore diameter. c DXRD=average crystallite size,
derived from XRD pattern by using Debye–Scherrer equation. Table 3 Base strength and total base number of the used catalysts Base strength a
Total base number a
Catalyst
–1
/H–
/mmol·g
Base density b –2
/µmol·m
Silica sand
H–
