Applications of Pulsed Electron Paramagnetic Resonance

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Applications of pulsed EPR spectroscopy in the identification of vanadyl complexes in asphaltene fractions. Part II: Hydrotreatment monitoring. Karima Ben Tayeb, Olivier Delpoux, Jeremie Barbier, Pascal Chatron-Michaud, Mathieu Digne, and Hervé Vezin Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01526 • Publication Date (Web): 08 Feb 2017 Downloaded from http://pubs.acs.org on February 10, 2017

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Applications of pulsed EPR spectroscopy in the identification of vanadyl complexes in asphaltene fractions. Part II: Hydrotreatment monitoring. Karima Ben Tayeb*a, Olivier Delpouxb, Jérémie Barbierb, Pascal Chatron-Michaudb, Mathieu Digneb and Hervé Vezina

a

LASIR UMR CNRS 8516, Université Lille 1 Sciences et Technologies, 59655 Villeneuve

d'Ascq, France b

IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, 69360 Solaize, France

(* corresponding author: [email protected])

Abstract: The potential of the electron paramagnetic resonance (EPR) spectroscopy to provide structural information of vanadyl species in asphaltene fractions was evaluated. The evolution of the chemical environment of the vanadium during fixed bed hydrotreating process was studied. This study shows that asphaltenes are composed of two types of environment: porphyrinic and non-porphyrinic structures. The hydroconversion process reduced by 40% the participation of non-porphyrinic species while the porphyrinic complexes only diminished by 15% which demonstrates that porphyrinic species are the most refractory to hydroconversion.

Keywords: Asphaltene, Vanadyl structures, Porphyrinic species, EPR spectroscopy.

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1. Introduction Many techniques are used to characterize asphaltenes [1]. Spectroscopic techniques, such as infrared (IR) [2], nuclear magnetic resonance (NMR) [3], mass spectroscopy (MS) [4,5], sizeexclusion chromatography (SEC) [6,7], and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) [8] provide informations about the chemical nature of asphaltenes, but this is not sufficient to establish its molecular composition. Several authors showed that according to the crude oil origin, asphaltenes display varied differences in composition and structure [6,9,10]. Nowadays, the chemical structures of metallic compounds are not well known and not yet well understood due to the complexity of the matrix [11]. Several authors highlighted the presence of metals (nickel and vanadium) in porphyrinic structures in petroleum samples. Many authors pointed out the presence of second structure as non-porphyrinic which is debate within the scientific community [12,13]. High-resolution mass spectrometry is currently very used to determine the metallic complexes structure in asphaltenes [14-16]. Electron Paramagnetic Resonance (EPR) has long been recognized as a powerful tool for the characterization, as the high sensitivity of the technique permits the detection of low concentrations of species [17]. It was demonstrated that all vanadium in petroleum samples was present in +IV oxidation state [18]. The combination of EPR and UVvisible techniques proved the presence of non-porphyrin structure [19]. The use of EPR spectroscopy at higher frequency (34 GHz) did not allow to predict the different coordination of vanadyl complexes in various asphaltenes [20]. Since several years, the pulsed EPR became an indispensable technique to characterize paramagnetic species. Indeed, HYSCORE sequence (HYperfine Sublevel CORrElation [22]) was used to study vanadyl ions of porphyrin complexes encapsulated in silica [21]. The goal of this work is to evaluate the performance of EPR spectroscopy to provide information on the structure of the vanadyl species. The first part of this work focused on the impact of vanadyl structures on the

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geographic origin of feedstocks [23]. The second and present paper will focus on the application of this technique to follow the evolution of the chemical environment of the vanadium during hydrotreating.

2. Experimental The materials, hydrotreating experiments and sampling are identical to those presented in reference [7]. They are only summarized in the next sections and the reader could read Ref. [7] for further details. 2.1. Materials Feedstock and catalysts loading: The feed used is a blend of Arabian Heavy Atmospheric Residue and Arabian Light Vacuum Residue (AH AR/AL VR) in 70/30 wt/wt proportions. The AH AR/AL VR properties in terms of density, metals content and heteroatoms content are described in Table 1. During the hydrotreatment, three different catalysts were used, and their properties (porosity, surface area, mesopore diameter, Mo and Ni+Co contents) are gathered in Table 2. Each catalyst has a precise role: the catalyst 1 is used to hydrodemetalation (HDM) reactions, the catalyst 2 exhibits a balance between HDM and hydrodesulfidation (HDS) functions while the catalyst 3 is used to HDS reactions. 2.2. Hydroconversion experiments Experimental Setup and Operating Conditions: After the two fixed-bed reactors, a highpressure separator allows to send the effluent into a hydrogen rich gas stream and a liquid phase stream. A suitable separation between the liquid stream and the sour gas is performed by a low-pressure separator. Gas streams are analyzed and quantified by in situ-gas chromatography (GC). The liquid effluent is exposed to nitrogen atmosphere to obtain a liquid effluent without H2S, NH3, and light gases. The catalysts introduced in the reactors need to be reduced through a sulfidation to be active. This sulfidation is carried out at 140 bar

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of pressure with 2 wt.% of dimethyldisulfide (DMDS) as sulfurizing agent. After sulfiding, the feed is treated for about 3000 h to study the stability. Each reactor works at 370°C but to maintain the same impurities levels in the hydrotreated effluents, the reactor temperatures are increased. Two tests - with similar time on stream of 2000 h - are performed to determine the reactivity and the selectivity of the different catalysts. In the first test, catalysts 1 and 2 were used in each reactor (metal content of 35 wt ppm and a sulfur content of 1.2 wt %). In the second test, the catalyst 3 was used in the second reactor while catalysts 1 and 2 were used in the first reactor (sulfur content in the effluents respectively 1.2 and 0.25 wt%). Samples: After the two hydrotreating tests, samples were collected as describe in Figure 1. The feed is noted (F) while effluents are noted (E). E1, E2, and E3 are respectively the samples recovered after catalyst 1, 2, and 3. E1 and E2 were formed after test 1 and E3 was formed after test 2. The separation of the asphaltene fraction (noted A) from the maltene fraction (noted M) is performed by precipitation of the sample into heptane. Asphaltenes yields are provided in Figure 1.

2.3. Elemental analysis: The carbon and hydrogen were analyzed by thermal conductivity measurements. The sulfur, nickel and vanadium contents were determined through wavelength dispersive X-ray fluorescence (XRF). The content in wt.% and ppm are gathered in Table 3. 2.4. EPR spectroscopy: The existence of paramagnetic species and their quantification were done thanks to the Continuous Wave–Electron Paramagnetic Resonance (CW-EPR). These experiments were performed with a Bruker ELEXSYS 500-FT spectrometer operating in X-band. All spectra were recorded at a 100 KHz modulation field frequency and a microwave frequency of 9.8 GHz, with an amplitude modulation of 1G and a microwave power of 6 mW corresponding to

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non-saturation conditions. To perform the vanadium quantification, a commercial (SigmaAldrich) reference (5,10,15,20-Tetraphenyl-21H,23H-porphine vanadium IV oxide) noted VOTPP was used and contained a known concentration of vanadium in ppm. It was analysed under the same operating conditions as the asphaltene samples. The spin concentration is given by the double integration of the first derivative of the EPR signal. The pulsed EPR experiments were performed on a Bruker ELEXSYS 580-FT spectrometer. The spectrometer is equipped with a helium flow cryostat to do measurements at low temperature (4K). For pulsed experiments, 2-pulses echo field sweep detection was performed using standard Hahn echo sequence π/2-τ-π echo with respectively π/2 and π pulses set to 16 and 32 ns while τ was to 200 ns. The 2D-HYSCORE (hyperfine sublevel correlation) measurements were carried out with the four pulse sequence π/2-τ-π/2-t1-π-t2-π/2-τ echo, and a four-step phase cycle where the echo is measured as a function of t1 and t2. The pulse lengths of π/2 and π pulses in these experiments were 16 and 32 ns, respectively. The 2D-HYSCORE experiments were recorded with a delay τ value of 200 ns that corresponds to the optimum preventing from blind spots effects. Prior to Fourier transformation of the HYSCORE data, the background decay was removed by a polynomial fit and apodized with a Hamming function.

3. Results and Discussion 3.1. Elemental analysis: The elemental analysis and the atomic ratios of asphaltenes are summarized in Table 3. As expected, the hydroprocessing has a strong impact on nickel, vanadium and sulfur content with a loss of respectively 8, 27 and 29%. The S/C atomic ratios proved that the sulfur amount is higher in the feed than the effluents. Moreover, the aromatic character of the asphaltenes is determined by H/C ratio. Indeed, a high value of H/C ratio corresponds to low aromaticity [6]. The aromaticity increases during the catalytic process. Long aliphatic chains are present on feed asphaltene as described by the higher value of H/C ratio. 5


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3.2. Continuous-Wave EPR characterization In this study, CW-EPR is used to determine the nature of paramagnetic species and to follow the quantification of vanadium during the hydrotreatment process. Asphaltene samples present an identical spectral fingerprint with two species: the first one is organic radical and the second one is vanadium

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V4+ (Figure 2) as already seen in the literature [23-25]. The

most intense line with Lorentzian lineshape centered at a g factor of ~2.0024 close to ge (ge is g of free electron equivalent to 2.0023) (Table 4) is characteristic of carbon centered radical. This unique line with a linewidth of 6.3 G presents unresolved hyperfine couplings with 1H protons [26]. The EPR spectrum of V4+ specie is more complex and is characteristic by an axial symmetry with g⊥ = 1.994 > g|| = 1.963 and A⊥ = 59.10-4 cm-1 < A||= 171.10-4 cm-1 which is in good agreement with literature [20,27]. All samples display the same g and A values indicating a similar V4+ environment (Table 4). It is known that vanadium is a poison for catalysts used during hydroprocessing [28]. Consequently, it is essential to quantify precisely the vanadium content along the different phases of hydrotreatment. In CW-EPR, the quantification of vanadium is possible because the integrated intensity of signal is proportional to the spin concentration. In the literature, several authors quantified V4+ by using different method such as colorimetric determination or calibration line [29,30]. In this work, we decided to use a reference with similar feature, vanadyl-tetraphenyl porphyrin (VOTPP) appeared to be the right candidate. In crude oils, all vanadium exists in its paramagnetic VO2+ form [18]. By using CW-EPR spectroscopy, only vanadium present in its V4+ form is quantified. The absorption spectra are integrated, normalized and compared to the VOTPP reference which allows to determine V4+ quantification (Table 3). CW-EPR analysis leads to under-estimate the V content in comparison to the SEC/ICP-MS analysis. As expected, the amount of total available vanadium on the samples evaluated by XRF decreases

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during the hydrotreatment of approximately 27% (Table 3). Finally, we will consider the concentrations provided by XRF as references for the next calculations. 3.3. Pulsed EPR characterization: identification of vanadium environment One of the major defects in the CW-EPR was its lack of resolution when interactions were smaller than the linewidth. EPR pulses will help to correct this defect on condition that the EPR line is inhomogeneous that is to say composed of a set of spin packets that can be refocused to give a spin echo. The pulsed EPR technique is used to measure weak hyperfine interactions between a paramagnetic center and distant nuclei. In this section, the HYSCORE technique is most useful than ESEEM sequence (Electron Spin Echo Envelope Modulation) to analyze systems where several nuclei are coupled. Indeed, interactions with MHz), and

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14

N (ν=1.054

C (ν=3.67 MHz) nuclei can be measured using HYSCORE sequence which is

more adapted to nuclei with small magnetic moments and small hyperfine interactions. Moreover, this two-dimensional sequence permits to separate the nuclei that interact strongly or weakly with the unpaired electron of vanadium. Nuclear modulations in the (+,+) quadrant correspond to the “weak coupling case” characterized by |A| < 2|νI|, while the (+,-) quadrant corresponds to the “strong coupling case”, with |A| > 2|νI|. Indeed, all nuclei present in quadrant (+,-) are chelating the vanadium (or are very close) while all nuclei present in quadrant (+,+) are characteristic of the structure of ligand. The study of quadrant (+,-) allows to obtain informations concerning the first coordination sphere of vanadium which corresponds to the chelating nuclei. 2D-HYSCORE spectra of VOTPP reference and C7 asphaltene samples, in same conditions, are compared in Figure 3. Some disparities are observed: VOTPP spectrum is largely dominated by two sharp peaks corresponding to single and double quantum transitions of nitrogen as observed by Gourier et al [21]. Two experimental parameters are obtained from a direct measurement: the quadrupolar interaction 3Pzz is equal to 4.1 MHz for double quantum correlations against 2.1

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MHz for single quantum correlations with a hyperfine value A = 4.7 MHz. From VOTPP spectrum, we can deduce that these two ridges are attributed to the porphyrinic nitrogen will be noted N1. 2D-HYSCORE spectra of C7 asphaltenes are composed of same peaks but less intense than observed in VOTPP spectrum corresponding to the {sq,sq} and {dq,dq} transitions for porphyrinic species N1. Two others peaks are observed and are attributed to nitrogens chelating the vanadium or are very close but they are not characteristic of prophyrinic structure. In the literature [31,32], these species are attributed to vanadyl complex other than porphyrins in the petroleum crude. It is indicated as non-porphyrinic structure and it will be noted N2. A fifth signal is characteristic of carbon

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C (the contour intensity is

multiply by a constant varying between 2 and 3 to observe the ridge). The experimental data (3Pzz, A) of nitrogens N1 are similar to those of VOTPP reference. The quadrupolar interaction 3Pzz for nitrogens N2 is equal to 2 MHz and 5.2 MHz for respectively the ridge at low and at high frequency (Fig. 3). A strong coupling of electron with carbon

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C is also

observed in all samples with a hyperfine coupling lower than VOTPP reference: 9.3 MHz against 11.8 MHz. These spectra show that C7 asphaltenes during the catalytic process are composed of the same types of environment among the porphyrinic and non-porphyrinic structures. We can note that the different steps of hydroprocessing permit to reduce the presence of N1 and N2 species around the vanadium. Indeed, the ridges intensity decreases progressively between F-A and E3-A samples. This observation proves the useful of pulsed EPR because we can directly analyze the local chemical environment of vanadium. The relative amounts of each species vary during hydroconversion: the amount of non porphyrinic species 14N2 reduced by 40% (from 270 ppm to 163 ppm at the end of the catalytic process) whereas the porphyrinic complexes 14N1 only decreased by 15% (from 282 ppm to 240 ppm) as described in Figure 4. Thus, porphyrinic species are the most refractory to hydroconversion as already observed in previous work [23]. Barbier et al. showed that the

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metal compounds of high molecular weight are the most refractory to conversion by using the SEC-ICP/MS analyses of samples collected after catalytic hydrotreatment [33]. The study of quadrant (+,+) allows to obtain informations concerning the second coordination sphere for the study of ligand structure around vanadium. 2D-HYSCORE spectra are presented in Figure 5. As observed in VOTPP spectrum, three nuclei (1H, 13C and 14

N) composed the ligand structure. 1H and

14

N nuclei exhibit a very weak signal along the

diagonal as observed in VOTPP. The ridges of 14N nucleus at frequencies of 6.0 and 9.6 MHz correspond to porphyrinic species. The ridges at 9.6 MHz were detected only by increasing the intensity of ridge contour (multiply by 2 or 5 according to the sample). The central peak along the diagonal at 14.6 MHz corresponds to distant hydrogen which no structural information can be drawn. Concerning the carbon, there is some disparities. Indeed, the shape of carbon ridge is different: VOTPP exhibits an isotropic signal with a maximum coupling of 5.7 MHz while asphaltenes display two types of carbon with a maximum coupling of 4.6 MHz. On the feed and effluent E1-A samples, a ridge at 3.1 MHz is observed with a hyperfine coupling of 4 MHz. This ridge corresponds to the double quanta of

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N. Despite the low

abundance of this isotope (0.37%), the ridge is detectable because all nitrogen is concentrated around the vanadium on F-A and E1-A samples. A total disappearance of

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N rigde is

accompanied by a simplification of the 13C and 14N1 ridges shape for E2-A and E3-A samples. It is probable that

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N nucleus is connected to unknown specie which is no refractory to

hydroprocessing because on E3-A sample, no signal is observed. In conclusion, it seems that the second coordination sphere was also impacted by the hydrotreatment. The pulsed EPR spectroscopy proves its beneficial contribution to track changes on the asphaltene structure.

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4. Conclusion On the basis of the results, it appears that EPR spectroscopy is a useful tool to characterize Vcontaining asphaltene molecules which permits to follow qualitatively (2D HYSCORE) and quantitatively (CW) the evolution of asphaltene molecules during the different steps of hydrotreatment. Two types of molecules were identified by pulsed EPR: one of porphyrinic structure which appears the most refractory to conversion and a second of unknown structure which is easier to eliminate by hydrotreatment. The contribution of non porphyrinic species is reduced by 40% whereas the porphyrinic complexes only decreased by 15% which confirms the previous results obtained in the first part of these works on one feed.

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References [1] Amorim, F.A.; Welz, B.; Costa, A.S.; Lepri, F.G.; Vale, M.G.; Ferreira, S.L. Talanta 2007, 72, 349-359. Pearson, C.D.; Green, J.B. Energ. Fuel 1993, 7, 338-346. Merdrignac, I.; Espinat, D.; Oil Gas Sci. Technol, 2007 62, 7-37. Mullins, O. C.; Sabbah, H.; Eyssautier, J.; Pomerantz, A. E.; Barré, L.; Andrews, A. B.; Ruiz-Morales, Y.; Mostowfi, F.; McFarlane, R.; Goual, L.; Lepkowicz, R.; Cooper, T.; Orbulescu, J.; Leblanc, R. M.; Edwards, J.; Zare, R. N.; Energ. Fuel 2012, 26, 3986-4003. [2] Adebiyi, F.M.,Thoss, V. ; Fuel, 2014, 118, 426-431. [3] Ledoux, M.J.; Hantzer,S. ; Catal. Today, 1990, 7, 479-496. [4] Loos, M., Ascone, I., Friant, P., Ruiz-Lopez, M.F., Goulon, J. ; Barbe, J.M., Sengle, N., Guilard, R., Faure, D., Des Courières, T.; Catal. Today, 1990, 7, 497-513. [5] Mitchell, P.C.H., Scott, C.E.; Catal. Today, 1990, 7, 467-477. [6] Leyva, C. Ancheyta, J., Berrueco, C. Millán, M.; Fuel Process. Technol., 2013, 106, 734738. [7] Barbier, J., Lienemann, C.P., Le Masle, A., Chatron-Michaud, P., Guichard, B., Digne, M., Energ. Fuel, 2013, 27, 6567-6574. [8] Liu, H., Mu, J., Wang, Z., Ji, S., Shi, Q., Guo, A., Chen, K., Lu, J., Energ. Fuel 2015, 29, 4803-4813. McKenna, A.M., Purcell, J.M., Rodgers, R.P., Marshall, A.G., Energ. Fuel 2009, 23, 2122-2128. Klein, G.C., Kim, S., Rodgers, R.P., Marshall, A.G., Energ. Fuel 2006, 20, 1973-1979. [9] Ferreira, C., Tayakout-Fayolle, M., Guibard, I., Lemos, F., Toulhoat, H., Ribeiro, F.R.; Fuel, 2012 , 98, 218-228 [10] Ovalles, C., Rogel, E., Lopez, J., Pradhan, A., Moir, M. Energ. Fuel, 2013 27,6552-6559 [11] Gauthier, T., Heraud, J. P., Kressmann, S., Verstraete, J., Chem. Eng. Sci. 2007, 62, 5409-5417.

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[12] Fish, RH., Komlenic, J.J., Anal. Chem., 1984, 56, 510-517 [13] Fish, RH, Komlenic, J.J., Wines, BK, Anal. Chem., 1984, 56, 2452-2460 [14] Zhao, X., Liu, Y., Chunming, X., Yan, Y., Zhang, Y., Zhnag, Q., Zhao, S., Chung, K., Gray, M.R., Shi, Q. Energ. Fuel, 2013, 27, 2874-2882 [15] Qian, K.N., Edwards, K.E., Mennito, A.S., walters, C.C., Kushnerick, J.D. Anal. Chem., 2010, 82, 413-419 [16] Mc Kenna, A.M., Purcell, J.M., Rodgers, R.P., Marshall, A.G. Energ. Fuel, 23, 2009, 2122-2128 [17] Abragam A., Bleaney B. Electron Paramagnetic Resonance of transition ions. Oxford, England: Oxford University Press, 1970. [18] Saraceno, A. J.; Coggeshall, N. D.; Fanale, D. T. Anal. Chem. 1961, 33, 500-505 [19] Yen, T. F.; Boucher, L. J.; Dickie, J. P.; Tynan, E. C.; Vaughan G. B. J. Inst. Petrol., 1969, 55, 87–99. [20] Malhotra, V. M.; Buckmaster, H. A. Fuel, 1985, 64, 335–341. [21] Gourier D., Delpoux O., Bonduelle A., Binet L., Ciofini I., Vezin H., J Phys Chem B, 2010, 114, 3714-3725. [22] Höfer P., Grupp A., Nebenfürh H., Mehring M., Chem. Phys. Lett, 1986 132, 279–282. [23] Ben Tayeb, K., Delpoux, O, Barbier, J., Marques, J., Verstraete, J. Vezin, H. Energy Fuels, 2015, 29, 4608-4615 [24] Wong, G.K., Yen, T.F., J. Petrol. Sci. Eng., 2000, 28 55-64. [25] Benamsili, L., Korb, J.P., Hamon, G., Louis-Joseph, A., Bouyssiere, B., Zhou, H., Bryant, R. G. Energ. Fuel, 2014, 28, 1629-1640.

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[26] Scotti, R., Montanari, L., Molecular structure and intermolecular interaction of asphaltenes by FT-IR, NMR, EPR. Structures and Dynamics of Asphaltenes. Plenum, New York, 1998, pp. 79-113. [27] Premovic, P.I., Tonsa, I.R., Pajovic, M.T. , Lopez, L. , Monaco, S.L. , Dordevic, D.M. , Pavlovi, M.S.; Fuel ,2001, 80, 635-639. [28] Gawrys, K.L., Blankenship, G.A., Kilpatrick, P.K.; Energ. Fuel, 2006, 20, 705-714. [29] Yen, T.F., Erdman, J.G., Saraceno, A.J., Anal. Chem. 1962, 34, 694-700. [30] Schultz, K. F., Selucky, M. L., Fuel, 1981, 60, 951-956. [31] Dickson, F. E. Kunesh, C. J. McGinnis, E. L., Petrakis, L., Anal. Chem., 1972, 44, 978981. [32] F. E. Dickson, L. Petrakis, Anal. Chem. 1974, 46, 1129-1130. [33] Barbier, J., Marques, J., Caumette, G., Merdrignac, I., Bouyssiere, B., Lobinski, R., Lienemann, C.P., Fuel Process. Technol., 2014,119, 185-189.

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Table captions Table 1

Bulk properties of the AH AR/AL VR feed.

Table 2

Commercial Catalysts Properties.

Table 3

Elemental analysis and atomic molar ratios for C7 asphaltenes of feed and after hydrotreatment.

Table 4

Magnetic parameters obtained from CW-EPR

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Properties Density 15°C Sulfur content Nickel Vanadium Total nitrogen content Conradson carbon residue (CCR) Asphaltenes (C7)

Unit g/mL wt % wt ppm wt ppm wt ppm wt % wt %

0.9861 3.97 21.6 67.9 2955 13.08 4.3

Table 1. Bulk properties of the AH AR/AL VR feed

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Catalyst Type Porosity Bulk density Surface area Mesopore diameter Mo Ni+Co Metal capacity

g/mL m²/g nm wt% wt%

1 HDM Mesoporousmacroporous 0.40-0.55 100-180 12-20 3-5 0.2-0.6 High

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2 HDM/HDS Mesoporous

3 HDS mesoporous

0.55-0.65 120-200 12-20 5-7 0.5-1.5 Median

0.65-0.80 160-240 9-14 9-11 1.5-3.5 low

Table 2. Commercial Catalysts Properties

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Asphaltenes Carbon Hydrogen Sulfur H/C S/C Nickel Total Vanadium V4+

Feed F-A Elemental analysis, wt% 82.5 7.4 7.4 Atomic molar ratios 1.076 0.033 XRF, ppm 148 552 CW-EPR, ppm 275

Effluent E1-A

Effluent E2-A

Effluent E3-A

83.2 7.4 6.8

84.6 7.3 6.1

85.2 7.3 5.2

1.068 0.030

1.035 0.027

1.028 0.023

178 463

173 426

163 403

316

330

304

Table 3. Elemental analysis and atomic molar ratios for C7 asphaltenes of feed and after hydrotreatment

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Energy & Fuels

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Asphaltenes g|| g⊥ A|| A⊥ gradical

Feed F-A 1.963 1.994 171.3 59.4 2.0026

Effluent E1-A 1.963 1.993 171.6 59.7 2.0024

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Effluent E2-A 1.962 1.993 172.4 59.2 2.0024

Effluent E3-A 1.962 1.993 172.3 59.6 2.0024

Table 4: Magnetic parameters obtained from CW-EPR

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Energy & Fuels

Figure captions

Figure 1

Schematic representation of sample preparation

Figure 2

(a) CW-EPR spectra recorded at RT and (b) 2-pulses echo field sweep recorded at 4K of C7 asphaltenes after hydrotreatment

Figure 3

Comparison of HYSCORE spectra of the first coordination sphere of the vanadium complexes of the feed and these hydrotreated effluents asphaltenes with the vanadyl tetraphenyl porphyrin reference

Figure 4

Relative contributions of porphyrinic (N1) and non porphyrinic (N2) complexes in the feed and effluents after hydroprocessing. The total amount of V is determined from ICP-MS analysis.

Figure 5

Comparison of HYSCORE spectra of the second coordination sphere of the vanadium complexes of the feed and these hydrotreated effluents asphaltene with the vanadyl tetraphenyl porphyrin reference.

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Energy & Fuels

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Page 20 of 24

F 6.5 wt%

F-M

F-A HDM catalyst

E1

E2 3.8 wt %

E1-M

HDS catalyst

HDM/HDS catalyst

E1-A

2.4 wt %

E2-M E2-A

E3 2.0 wt %

E3-M E3-A

Figure 1: Schematic representation of sample preparation (the yield of asphaltenes precipitation is indicated for each sample).

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Energy & Fuels

(a) Radical

2800 3000 3200 3400 3600 3800 4000 4200

Magnetic field (G)

Az Ax = Ay

2800

3000

3200

3400

3600

3800

4000

4200

Magnetic field (G) (b)

-1/2//, -1/2⊥

3/2 ⊥ -7/2 // F-A E1-A E2-A E3-A 2800

3000

3200

3400

3600

3800

4000

4200

Magnetic field (G) Figure 2: (a) CW-EPR spectra recorded at RT and (b) 2-pulses echo field sweep recorded at 4K of C7 asphaltenes after hydrotreatment – black line F-A, red line E1-A, blue line E2-A and green line E3-A. Arrows shows the different transition positions with -1/2//, -1/2⊥ is used for 2D-HYSCORE experiments

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Energy & Fuels

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Figure 3: Comparison of HYSCORE spectra of the first coordination sphere of the vanadium complexes of the feed and these hydrotreated effluents asphaltenes with the vanadyl tetraphenyl porphyrin reference.

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Energy & Fuels

552

463

426

403

270

230

191

163

Total vanadium (ppm)

N2 N1

282

F-A

230

E1-A

235

E2-A

240

E3-A

Figure 4: Relative contributions of porphyrinic (N1) and non porphyrinic (N2) complexes in the feed and effluents after hydroprocessing. The total amount of V is determined from ICP-MS analysis.

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Energy & Fuels

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Figure 5: Comparison of HYSCORE spectra of the second coordination sphere of the vanadium complexes of the feed and these hydrotreated effluents asphaltene with the vanadyl tetraphenyl porphyrin reference.

24


Applications of Pulsed Electron Paramagnetic Resonance

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