Article pubs.acs.org/EF
Effects of Blending and Heat-Treating on Composition and Distribution of SARA Fractions of Atmospheric Residues Qingyan Cui,† Koji Nakabayashi,† Xiaoliang Ma,‡ Jin Miyawaki,† Adel Al-Mutairi,‡ Abdulazim Mj Marafi,‡ Joo-Il Park,‡ Seong-Ho Yoon,† and Isao Mochida*,§ †
Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka 813-0004, Japan Petroleum Research Center, Kuwait Institute for Scientific Research, Safat 13109, Kuwait § Kyushu Environmental Evaluation Association, Fukuoka 813-0004, Japan Downloaded via IOWA STATE UNIV on January 12, 2019 at 11:15:13 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
‡
ABSTRACT: The effects of blending and heat-treating of two atmospheric residues (ARs) from Lower Fars crude and Kuwait export crude on the distribution and composition of their saturate, aromatic, resin, and asphaltene (SARA) fractions were studied using X-ray diffraction (XRD), high-temperature gas chromatography equipped with an atomic emission detector (HT-GCAED), gel permeation chromatography with detection by ultraviolet absorbance (GPC-UV), and inductively coupled plasma mass spectrometry (GPC-ICP-MS). Although no obvious change in the mass distribution of the SARA fractions is observed, the result from the GPC-ICP-MS analysis shows that blending of the two ARs at room temperature causes the shift of the metal complexes from the asphaltenes to the resins. Heat-treating of the ARs at 330 °C for 3 h under an H2 pressure of 9 MPa changes the mass distribution of the SARA fractions and promotes the shifts of V and Ni complexes in the asphaltenes from the heavy molecular weight to the light molecular weight and further from the asphaltenes to the resins. The results suggest some potential approaches for improving the hydrodemetallization reactivity of AR by releasing the metals complexes from the asphaltenes.
1. INTRODUCTION SARA fractionation, which separates petroleum fractions into saturates, aromatics, resins, and asphaltenes, has been used to characterize and explain the reaction process and mechanism in the hydrotreating and fluid catalytic cracking (FCC) processes.1−5 The SARA fractionation depends on the solubility of petroleum fraction components in a series of solvents and their interaction with the adsorbent in the column. The solubility of a component is mutually influenced by coexisting components in the phase; thus, it is speculated that the composition and distribution of the SARA fractions in petroleum fractions may be modified or changed by mixing with another petroleum fraction and/or heat-treating. Of particular interest are species, such as sulfur (S), nitrogen (N), and metals, present mainly in asphaltenes6,7 and their shifts between resins and asphaltenes by changing the dissolution activity of the components in the fractions. The molecular structures of various metal species in petroleum have a significant impact on the reactivity of the metal species in hydrodemetallization (HDM) processes. Metal species in petroleum have been characterized by Fourier transform ion cyclotron resonance mass spectrometry analysis (FT-ICR-MS), and their molecular structures have been proposed based on the assigned elemental formulas.8−10 Concurrently, the environment (matrix) of the metal species also influences their reactivity. Consequently, blending feedstocks may be a way to change the environment of the metal species in petroleum. Hydrodesulfurization (HDS) of a blend from different middle distillates is an example.11−13 The reactivity of various species (S, N, and metals) in the SARA fractions may be influenced by their surrounding matrixes. For example, a lower conversion rate for asphaltenes in HDS processes is likely due to higher concentrations of the refractory © 2017 American Chemical Society
S species combined with inhibitorier matrix effects from other asphaltenes components. Hence, a targeted reaction of AR may be improved by the blending and/or preheat-treating, which may modify the interaction of sulfur, nitrogen, and metal species with their matrixes. In the present study, effects of the blending and heat-treating of two Kuwait ARs (LF-AR and KEC-AR) from Lower Fars crude (LF) and Kuwait export crude (KEC) on distribution and composition of their SARA fractions were examined. The shifts of the S, N, and metal species among the fractions were monitored by the SARA fractionation and element analysis of each fraction. The changes in molecular weight distributions of the vanadium (V) and nickel (Ni) complexes in ARs and their fractions were examined using gel permeation chromatography with inductively coupled plasma mass spectrometry (GPC-ICPMS) and high-temperature gas chromatography with an atomic emission detector (HT-GC-AED). The objective is to clarify whether there are some shifts of the S, N, and metal species among the fractions and/or the changes of their interaction with the matrix in the blending and heat-treating processes. Understanding these phenomena may provide a hint in improving the reactivity of AR in HDM and HDS processes.
2. EXPERIMENTAL SECTION 2.1. AR Samples. LF and KEC, which were provided by Kuwait National Petroleum Co. (KNPC), have been distillated in a pilot unit to obtain the LF-AR and KEC-AR with a cutting point at 345 °C. A blend (LF/KEC-AR) of LF-AR and KEC-AR with a LF-AR/KEC-AR weight ratio of 1/1 w/w was prepared at room temperature under Received: December 9, 2016 Revised: May 23, 2017 Published: May 26, 2017 6637
DOI: 10.1021/acs.energyfuels.6b03275 Energy Fuels 2017, 31, 6637−6648
Article
Energy & Fuels Table 1. SARA Contents of Single and Mixed ARsa
atmospheric pressure. The densities of LF-AR, KEC-AR, and LF/ KEC-AR are 1.0018, 0.9745, and 0.9873 g/mL, respectively. Three heat-treated AR samples (HT-LF-AR, HT-KEC-AR, and HTLF/KEC-AR) were prepared by heat-treating 20 g of LF-AR, KEC-AR, and LF/KEC-AR at 330 °C under an H2 pressure of 9 MPa with stirring for 3 h in an autoclave. 2.2. SARA Fractionation. About 5 g of the AR sample was dissolved in n-heptane at a ratio of 1/50 (w/w) under stirring at 60 °C for 5 h and then set overnight at room temperature. The mixture of AR and n-heptane was filtered, and the solid cake was washed with nheptane until the filtrate was colorless. The insoluble portion was extracted with toluene in a Soxhlet apparatus, and then the solvent in the solution was removed by rotary evaporating. The received sample was dried at 110 °C for 2 h and weighted to determine the asphaltenes content. The maltene was obtained by rotary evaporating the n-heptane solution and then further fractionated into saturates, aromatics, and resins through a glass column packed with activated neutral alumina. Maltene mixed with a small amount of n-hexane was added on the top of the packed column. The column was sequentially eluted with nheptane, toluene, and toluene/methanol (9/1, v/v) at a solvent-tomaltene ratio of 250 mL to 1 g. The respective solutions were rotary evaporated to obtain saturates, aromatics, and resins. 2.3. Characterization of ARs and Their Fractions. X-ray diffraction (XRD) analysis of the sample was carried out using an AXS D8 ADVANCE diffractometer (Bruker, Billerica MA, USA). Cu Kα radiation (λ = 0.15406 nm at 40 kV, 30 mA) was used, and scan data was recorded at 20 °C for 2θ in the range from 5° to 80° in steps of 0.02° s−1. The molecular weight distributions of the ARs and their fractions were determined by gel permeation chromatography (1200 Infinity Series, Agilent Technologies, Santa Clara, CA, USA) with an ultraviolet diode array detector (DAD at 261 nm) (GPC-UV). The approximate molecular size distributions of the metal complexes in them were measured by GPC coupled with inductively coupled plasma mass spectrometry (7700 series, Agilent) (GPC-ICP-MS) under the plasma condition of 1600 W rf power and calibrated against 51V and 60 Ni isotopes. Some V and Ni species from the Japan Petroleum Society were used as standard samples to develop standard calibration curves (R2 > 0.99) for calculation of the concentrations of V and Ni in the samples. The mobile phase was tetrahydrofuran, and the flow rate was 0.15 mL min−1. The ARs, their resins, and asphaltenes were diluted by 100, 300, and 500 times of tetrahydrofuran in weight, respectively, and then injected into the GPC-UV and GPC-ICP-MS systems for analysis. High-temperature gas chromatography with atomic emission detector (HT-GC-AED) analysis was carried out using gas chromatography (7890; Agilent) coupled with a JAS 2390AA atomic emission detector (Joint Analytical Systems GmbH, Moers, Germany). The gas chromatograph was equipped with a 5 m × 0.53 mm × 0.1 μm column and a programmable high-temperature vaporization (PTV) inlet. The oven temperature was programed from 30 to 430 °C at a rate of 30 °C min−1, while the AED transfer line temperature was 430 °C, and the cavity temperature was 450 °C. The 292 nm V and 301 nm Ni emission lines were used to detect the AED responses. VO- and NiO-octoethyl-etioporphyrins (Sigma-Aldrich, St. Louis, MO, USA) and 5,10,15,20-tetraphenyl porphyrins (Wako Chemicals, Tokyo Japan) were used as metal standard samples. The sample injected into the PTV inlet was dissolved in dichloromethane with a concentration of 5 wt %.
(a) without heat-treating fractions contents saturates, wt % aromatics, wt % resins, wt % asphaltenes, wt % total recovery, wt % fractions contents saturates, wt % aromatics, wt % resins, wt % asphaltenes, wt % total recovery, wt % a
LF-AR
LF/KEC-AR
16.7 ± 0.3 20.7 ± 0.4 51.9 ± 0.7 50.2 ± 0.6 19.5 ± 0.4 19.2 ± 0.2 11.9 ± 0.2 9.9 ± 0.3 96.7 ± 1.1 97.8 ± 1.5 (b) with heat-treating HT-LF-AR 16.7 45.3 25.7 12.3 98.2
± ± ± ± ±
0.2 0.5 0.3 0.1 1.3
(21.2) (50.4) (18.9) (9.6)
HT-LF/KEC-AR 21.7 47.0 21.4 9.8 96.3
± ± ± ± ±
0.4 0.4 0.2 0.2 1.0
(20.4) (44.7) (24.2) (10.7)
KEC-AR 25.7 48.8 18.4 7.2 97.4
± ± ± ± ±
0.4 0.4 0.3 0.2 1.0
HT-KEC-AR 24.2 44.1 22.7 9.1 97.7
± ± ± ± ±
0.3 0.5 0.4 0.2 1.1
Data in parentheses: theoretical value.
from the LF/KEC-AR did not deviate from theoretical expectations based on their respective fractions, indicating that no synergistic effect appeared to take place in the blending at room temperature. Table 2 summarizes the C, H, N, and S elemental analyses of ARs and their SARA fractions. As expected, LF-AR showed higher S and N contents and a lower H/C ratio compared with KEC-AR. Table 3 summarizes the metals (V and Ni) contents in ARs and their resins and asphaltenes. LF-AR contained significantly more V and Ni than KEC-AR. The concentrations of both metals in the asphaltenes were higher than those in the resins for all three ARs. However, the mass distributions of V and Ni in the resins and asphaltenes were similar, except for V in LFAR, in which the amount of V in the asphaltenes was about 1.5 times of that in the resins. It is interesting to find that when the LF-AR and KEC-AR were mixed, both the V and Ni complexes in the asphaltenes markedly shifted from asphaltenes to the resins by about 12% for V and 11% for Ni on the basis of the comparison of the metal amounts (μg/g, based on AR) in the resins and asphaltenes. It indicates clearly that such blending favors the shift of the metals complexes from the asphaltenes to the resins. 3.1.2. XRD of ARs and Their Asphaltenes. The XRD profiles of the ARs and their asphaltenes are shown in Figures 1a and 2a, respectively. There were the broad diffraction peaks at about 10−30°, which reflects the contributions of paraffinic and aromatic aggregation. Both LF-AR and KEC-AR had very similar profiles. Two asphaltenes (LF-As and KEC-As) had slightly broader peaks, with stronger diffraction at a lower angle of about 20°. A sharper shoulder peak at 26° for LF-As was clearer than that for KEC-As, which indicates more aromatic stacking in LF-As. The shoulders in LF/KEC-As and KEC-As were similar, suggesting that the blending loosened the aromatic stacking in LF-As somewhat. 3.1.3. GPC-UV and GPC-ICP-MS of ARs, Their Resins, and Asphaltenes. Figure 3a shows the GPC-UV chromatograms of ARs, their resins, and asphaltenes. The chromatograms of both LF-AR and KEC-AR were very similar. The AR chromatogram consisted of a major peak at 21.0 min and a shoulder at 24.0 min, with a tail at 12.5−17.0 min. The resins and asphaltenes showed peaks at about 20.0 and 18.5 min, respectively, indicating that the average molecular size of the asphaltenes was larger than that of the resins. No obvious difference in the
3. RESULTS 3.1. Effect of Blending on Distribution and Composition of SARA Fractions. 3.1.1. Content and Composition of SARA Fractions. Table 1a compares the contents of the SARA fractions in single and blended ARs. KEC-AR was significantly lighter than LF-AR in terms of the mass distribution of the SARA fractions, which coincides with their densities. The experimental mass recoveries of SARA fractions 6638
DOI: 10.1021/acs.energyfuels.6b03275 Energy Fuels 2017, 31, 6637−6648
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Energy & Fuels Table 2. Chemical Analyses of ARs and Their SARA Fractions by Element Analyses and XRFa samples ARs
saturates
aromatics
resins
asphaltenes
a
LF-AR LF/KEC-AR KEC-AR LF-AR LF/KEC-AR KEC-AR LF-AR LF/KEC-AR KEC-AR LF-AR LF/KEC-AR KEC-AR LF-AR LF/KEC-AR KEC-AR
C wt %
H wt %
82.6 83.4 83.8 86.3 86.0 86.2 82.6 82.8 84.0 80.1 81.0 81.2 80.5 81.1 81.9
10.1 10.5 11.0 13.6 13.8 13.8 10.0 10.3 11.0 8.7 9.1 9.3 7.3 7.5 7.5
N wt % 0.33 0.32 0.29 0.0 0.03 0.0 0.05 0.12 0.07 0.83 0.89 0.73 1.01 0.90 0.89
(0.0)
(0.06)
(0.78)
(0.95)
S wt % 3.44 3.34 3.19 0.15 0.21 0.23 2.37 3.26 3.56 4.40 4.68 4.53 6.78 6.12 6.59
(0.19)
(2.97)
(4.47)
(6.69)
H/C atomic ratio
ash mg/g
1.46 1.51 1.56 1.89 1.93 1.93 1.46 1.49 1.53 1.30 1.35 1.38 1.09 1.11 1.10
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.5 0.5 1.3
Data in parentheses: theoretical value. Standard error: ± 0.5%
Table 3. V and Ni Contents of ARs, Their Resins, and Asphaltenes by GPC-ICP-MSa samples LF
LF/KEC
KEC
a
AR percent in AR, wt % V, ppm μg/1 g base of AR Ni, ppm μg/1 g base of AR percent in AR, wt % V, ppm μg/1 g base of AR μg/1 g moved Ni, ppm μg/1 gg base of AR μg/1 g moved percent in AR, wt % V, ppm μg/1 g base of AR Ni, ppm μg/1 g base of AR
152 ± 1.5 152 24 ± 0.9 24 108 ± 1.2 (111) 108 20 ± 0.6 (19) 20
71 ± 1.1 71 14 ± 0.7 14
resins
asphaltenes
19.5 303 ± 1.3 59 62 ± 0.8 12 19.2 273 ± 1.4 (245) 52 (46) 6 52 ± 0.7 (46) 10 (9) 1 18.4 187 ± 0.9 34 31 ± 0.8 6
11.9 765 ± 1.9 91 113 ± 1.1 13 9.9 587 ± 1.5 (649) 58 (65) 7 91 ± 0.9 (108) 9 (10) 1 7.2 533 ± 1.2 38 103 ± 0.9 7
Data in parentheses: theoretical value.
Figure 1. XRD patterns of (a) ARs and (b) heat-treated ARs.
molecular size distribution for the three resins and for the three asphaltenes was observed. Figure 4 shows the GPC-ICP-MS chromatograms of V and Ni complexes in ARs, their resins, and asphaltenes. The molecular size distributions of the V and Ni complexes were similar in ARs, resins, and asphaltenes from the three crudes, although their intensities were quite different due to their
different metal concentrations. The metal molecular weight distribution can be divided into three groups, i.e., heavy, medium, and light, which correspond to retention times of less than 17.0 min (from 12.0 min), from 17.0 to 20.0 min, and more than 20.0 min (to 24.0 min), respectively, as indicated in Figure 4. The first two groups were dominantly present in asphaltenes, while the latter group was present in both 6639
DOI: 10.1021/acs.energyfuels.6b03275 Energy Fuels 2017, 31, 6637−6648
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Figure 2. XRD patterns of the asphaltene fraction of (a) ARs and (b) heat-treated ARs.
selected as it may be the highest temperature that can be used without coke formation. When heat-treating was carried out below 330 °C, no significant change in the SARA fractions contents of the heat-treated ARs was observed. Heat-treating at 330 °C substantially increased the content of the resins and decreased the content of the aromatics for all three ARs. It indicates that heat-treating of ARs, even under an H2 pressure of 9 MPa, enhanced the coupling of aromatics components and shifted them mainly into the resins. Interestingly, it is found that the blending of ARs moderated such coupling of aromatics components and enhanced the disassociation of the resins and asphaltenes in the heat treatment. This resulted in a decrease of percentages of the resins and asphaltenes but an increase of percentage of the aromatics on the basis of the comparison of experimental data with those (shown in parentheses in Table 1b) expected by linear mixing two single ARs after the heat treatment. 3.2.2. XRD of Heat-Treated ARs and Their Asphaltenes. No significant difference was observed in the XRD profiles of ARs after heat-treating at 330 °C (Figure 1b). In contrast, the peak at 26° for the asphaltenes from the three ARs appeared to slightly intensify after heat treatment, as indicated by comparison of Figure 2a and 2b. It implies that the somewhat enhancement in the aromatic stacking and/or phase separation from the three ARs was observed after heat treatment. 3.2.3. GPC-UV and GPC-ICP-MS of Heat-Treated ARs, Their Resins, and Asphaltenes. Figure 3b illustrates the GPC-UV chromatograms of the heat-treated ARs and their resins and asphaltenes. Heat-treating removed the tails at 12.5−17.0 min for the three ARs and significantly shifted the peak at around 18.5 min to around 20.0 min for the asphaltenes. The peak of HT-LF/KEC-As appeared to be shifted more to longer elution times in comparison with those of the HT-LF-As and HTKEC-As, indicating a reduction of the molecular weight after blending and heat-treating. The GPC-ICP-MS chromatograms of the V and Ni complexes in ARs and their resins and asphaltenes after heattreating at 330 °C are shown in Figure 6. In comparison of Figures 4 and 6, a marked change induced by the heat-treating was observed. The two top peaks in the AR and asphaltenes at 21.0 and 16.5 min were shifted to 22.7 and 23.0 min, respectively. The relative intensities of the peaks also changed, such that the intensities of the peaks at longer elution time for all three asphaltenes were greatly enhanced. The mixed and single ARs had similar peak profiles, and the peak intensity of the resins (HT-LF/KEC-R) from the heat-treated LF/KEC-AR was almost the same as that of the resins (HT-LF-R) from the heat-treated LF-AR, and the peak intensity of the asphaltenes
asphaltenes and resins. The blending of two ARs changed the distribution of the V complexes in asphaltenes, modifying the intensity of the medium and light groups to close to those of KEC-AR. There were a definite increase in the intensity of the V complexes in the resins and a definite decrease in the intensity of the V complexes in the asphaltenes, especially for the medium and light groups of LF/KEC-As, indicating that the blending appeared to shift the metal complexes from the asphaltenes to the resins. It is in agreement with the results shown in Table 3. The distribution of the Ni complexes in the three groups was basically the same as that of the V complexes, although the intensity of Ni complexes was significantly weaker than that of V complexes. The effect of blending on the distribution of Ni complexes was also similar to that of the V complexes. 3.1.4. HT-GC-AED of ARs, Their Resins, and Asphaltenes. The HT-GC-AED chromatograms of ARs, their resins, and asphaltenes are illustrated in Figure 5a for V and Figure 5b for Ni. The V species in AR were broadly distributed in terms of their retention times, i.e., from 9.0 to longer than 13.0 min. The obtained peaks can be classified into two major groups, from 9.0 to 9.7 min and from 9.7 to 10.5 min, respectively. The octoethyl-etioporphyrin VO (Octoethyl-etio-VO) should be included in the first group at about 9.5 min, while the tetraphenyl porphyrin V (TPP-V) appears at about 10.8 min on the basis of their retention times measured by using the standard samples. It indicates that the major V species in the second group were slightly lighter than TPP-V. The relative intensity of the first group to the second group for both LF/ KEC-AR and LF/KEC-R was slightly higher than that of LF-AR and LF-R and similar to that of KEC-AR and KEC-R, indicating a somewhat decrease in the molecular weight of the V species in the blending. This is consistent with the observation by the GPC-ICP-MS analysis. The Ni species detected by HT-GC-AED were located in the same retention time region as that of the V species, but much sharper peaks were observed for Ni species in the first group having retention times from 9.0 to 10.5 min and the second group from 10.5 to 11.5 min. The distributions of each group in the resins and the asphaltenes were different, and the second group was dominantly present in the asphaltenes. The effect of blending on the Ni species distribution was indefinite in this case. 3.2. Effect of Heat-Treating on the Distribution and Composition of SARA Fractions. 3.2.1. SARA Fractions Contents of Heat-Treated ARs. Table 1b summarizes the SARA fraction contents of ARs after heat-treating at 330 °C under an H2 pressure of 9 MPa for 3 h. This condition was 6640
DOI: 10.1021/acs.energyfuels.6b03275 Energy Fuels 2017, 31, 6637−6648
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Energy & Fuels
Figure 3. GPC chromatograms of ARs, their resins, and asphaltenes. (a) ARs, their resins, and asphaltenes. (b) Heat-treated ARs, their resins, and asphaltenes.
to dissociation of the V complexes from their organic compound matrixes. Table 4 summarizes the metal contents of the heat-treated ARs, their resins, and asphaltenes. The content of the V complexes (68 μg/g) in HT-LF-R was higher than that in LF-R (59 μg/g), indicating that heat-treating caused a shift of the V complexes from the asphaltenes to the resins by increasing about 15.2% of the V complexes in the resin for LF-AR. However, such increase in the shift of the V complexes for
(HT-LF/KEC-As) from the heat-treated LF/KEC-AR was similar to those of the asphaltenes (HT-KEC-As) from the heat-treated KEC-AR. This indicates that the heat-treating caused a shift of the metal complexes from the asphaltenes to the resins in the blending. Additionally, the medium and heavy groups of V complexes in HT-LF/KEC-AR and HT-LF/KECAs were eluted similarly to those of HT-KEC-AR and HTKEC-As, which suggests that heat-treating and blending reduced the amount of the heavy V complexes, possibly due 6641
DOI: 10.1021/acs.energyfuels.6b03275 Energy Fuels 2017, 31, 6637−6648
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Energy & Fuels
Figure 4. GPC-ICP-MS chromatograms of ARs, their resins, and asphaltenes: (a) V species; (b) Ni species.
KEC-AR was limited (
