Hydroprocessing of vacuum residues: Asphaltene characterization and solvent extraction of spent slurry catalysts and the relationships with catalyst deactivation

Accepted Manuscript Title: Hydroprocessing of Vacuum Residues: Asphaltene Characterization and Solvent Extraction of Spent Slurry Catalysts and the Relationships with Catalyst Deactivation. Author: Cesar Ovalles Estrella Rogel Michael E. Moir Axel Brait PII: DOI: Reference:

S0926-860X(16)30621-4 http://dx.doi.org/doi:10.1016/j.apcata.2016.12.017 APCATA 16102

To appear in:

Applied Catalysis A: General

Received date: Revised date: Accepted date:

23-10-2016 7-12-2016 19-12-2016

Please cite this article as: Cesar Ovalles, Estrella Rogel, Michael E.Moir, Axel Brait, Hydroprocessing of Vacuum Residues: Asphaltene Characterization and Solvent Extraction of Spent Slurry Catalysts and the Relationships with Catalyst Deactivation., Applied Catalysis A, General http://dx.doi.org/10.1016/j.apcata.2016.12.017 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Dec. 7th, 2016 To be submitted to Applied Catalysis A: General

Hydroprocessing of Vacuum Residues. Asphaltene Characterization and Solvent Extraction of Spent Slurry Catalysts and the Relationships with Catalyst Deactivation.

By Cesar Ovalles, Estrella Rogel, Michael E. Moir, and Axel Brait Chevron Energy Technology Center, Richmond, CA 94801, USA

Corresponding address: [email protected]

Graphical abstract 8000

100%CH2Cl2 Asphaltenes

Maltenes

HPLC Signal (Arb. Number)

7000

0 h (Feed) 4 h Residence Time

6000

30%CH2Cl2 in C7 Asphaltenes

5000

10%Methanol in CH2Cl2 Asphaltenes

4000 3000

15%CH2Cl2 in C7 Asphaltenes

2000 1000 0 0

10

20

30 Time (min)

40

50

60

2

Highlights 

The results of the slurry phase hydroprocesseing experiments showed that both catalysts (2.5 Mo and 5% Mo) showed signs of deactivation after four- to five-hours of reaction time.



The results of the solvent extraction of spent slurry catalysts showed that more asphaltenes deposited on the 2.5 wt% deactivated catalysts than on the 5 wt% analog.



These results suggested that the fractions removed by solvent extractions are related to coke formation and might be responsible for catalyst deactivation observed after extended reaction times.



Pyridine organic extract was more aromatic (aromaticity and lower H/C molar ratio) and had a higher concentration of the highest solubility parameter asphaltenes.

Abstract Two slurry phase catalysts with two different Mo/feed ratios (2.5 and 5 wt%) were evaluated for the hydroprocessing of a vacuum residue under batch conditions at different reaction times (0-5 hours). Higher API, % HDS, %HDN, % Conv. 1000°F+, H/C molar ratio, and lower MCR and asphaltene content were found for the products of the 5 wt% Mo case than the 2.5 wt% analog. Both catalysts showed signs of deactivation after four- to five-hours of reaction time. Asphaltene characterization of the feed and the hydroprocessed products using the solubility fraction method showed a reduced amount of all asphaltenes fractions. For the 5 wt % Mo catalyst, after 4 h of reaction time only the most polar asphaltene fraction was observed in the product. Solvent extractions of organic material from spent slurry catalyst samples were carried out to obtain a better understanding of the catalyst deactivation during hydroprocessing of

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vacuum residues. A blend of 10% methanol in dichloromethane and pyridine were used as solvents. The results of the solvent extraction showed that the asphaltenes deposited on the 2.5 wt% Mo catalyst had a higher concentration of the less soluble asphaltenes than those observed for the 5 wt% analog. These results suggest that the fractions removed by solvent extractions could be precursors for coke formation and responsible for catalyst deactivation. A higher percentage of organic extracts was found using pyridine (37 wt%) than that obtained by using 10%MeOH/90%CH2Cl2 (33 wt%) and pyridine organic extracts were more aromatic (aromaticity and lower H/C molar ratio) and had a higher concentration of the highest solubility parameter asphaltenes. All these results contribute to a better understanding of the catalyst deactivation process on slurry phase hydroprocessing catalysts.

Keywords: Hydroprocessing; Asphaltene Characterization; Spent Slurry Catalysts; Catalyst Deactivation

Introduction Coke and metal depositions are two of the main pathways for catalyst deactivation during hydroprocessing of heavy feeds.1-10 It has been established that coke deposits rapidly during early reaction stages and then reaches an equilibrium. Alkenes, mono- and polynuclear aromatics, and heterocycles can be converted into higher molecular weight species if sufficient active hydrogen is not available to prevent it.1-4 As known, asphaltenes contain the highest concentration of polynuclear aromatics, heteroatoms, and metals, so it is not surprising that

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asphaltene precipitation is one important source of coke during the hydrotreatment of heavy feeds.11-13 At high-severity hydroprocessing conditions, maltenes (alkane solubles) and asphaltenes (alkane insolubles) undergo drastic chemical changes.5-10 The former fraction is cracked and hydrogenated; therefore, its aromaticity and solvent power decreased. At the same time, asphaltene molecules undergo cracking of the side chains and naphthenic rings, leaving the growing aromatic cores mostly unaffected and incompatible with the maltenes. These changes make the resins/oils more paraffinic, and the unconverted asphaltene cores more aromatic and condensed than those in the feed. In consequence, the asphaltene−resin interactions are disturbed, leading to asphaltene precipitation on the catalyst surface.5-10 Most of the studies on catalyst deactivation due to asphaltene precipitation have been carried out using metal supported catalysts.1,3-4,14-17 During hydroprocessing, asphaltenes can undergo thermal and catalytic retrograde reactions to generate coke along with other lighter products. As mentioned, as asphaltenes become more aromatic and the surrounding media more paraffinic there is an increase of the colloidal instability that leads to asphaltene precipitation onto the catalyst surface. This situation generates coke and metal deposits with the concomitant deactivation of the heterogeneous catalysts. 1,3-4,14-18 In particular, Gray and coworkers evaluated the effect of asphaltene concentration on supercritical n-pentane extracted (SCFE) Athabasca bitumen vacuum residue using a commercial NiMo/-Al2O3 at 440°C.14 The SCFE fractions that contained only saturates, aromatics and resins gave a low yield of carbon on the catalyst.14 On the other hand, the asphaltene-rich fractions gave higher coke yields, both on the catalyst and in the reactor, and a lower H/C ratio

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than the lighter fractions. In the worst case, they found over half of the surface area, and pore volume of the catalyst was lost due to coke deposition.14 Similarly, Maity et al. studied the effect of asphaltene content on metal and coke deposition during hydrotreatment of Maya crude oil using a standard NiMo supported catalyst.16 They found that the catalyst activity toward metal and asphaltene removal decreases with the asphaltene content in the feeds. Also, the presence of the asphaltenes is the main factor responsible for the decrease of the surface area and total pore volume that led to catalyst deactivation.16 In a recent paper, Maity and coworkers reported that catalyst deactivation by metal in resins is less pronounced than that in asphaltenes.17 The authors also found that catalyst deactivation does not always depend on the concentration of the latter fraction but also on the chemical composition of this solubility class.16 Overall feed reactivity toward nitrogen removal and microcarbon residue reduction was found to depend on the nature and amount of asphaltenes.19 In conventional hydroprocessing, metal supported catalysts display short service life, low operational stability, and frequent downtime.

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To address these issues, slurry-phase catalysts

have been developed. In these catalytic systems, most of the cracking reactions occur in the gas phase, and the purpose of the catalyst and hydrogen is to remove heteroatoms and inhibit coke formation.20 Slurry phase catalysts have the advantage of relatively high and stable catalytic activity, and many such processes adopted a one-through catalytic operation mode. However, the costs of fresh catalyst, catalyst separation, and rejuvenation have major impacts on the economics of such processes.21-22 Therefore, the commercialization of slurry phase hydroprocesses will require catalyst separation and recycle to improve the economic prospects of the technology.21 Because of catalyst deactivation, i.e. the loss over time of catalytic activity

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and/or selectivity, is a continuing concern in industrial catalytic processes. An understanding of the fundamental deactivation mechanisms is of paramount importance for the development of the slurry phase hydroprocessing. Surprisingly, the deactivation mechanisms in slurry-phase catalysts have been considerably less studied than their supported counterparts.1-4 Due to the absence of the alumina support and smaller particle sizes, deactivation pathways of unsupported catalysts are not necessarily the same as the ones reported for the supported analogs.23 Rezaei and Smith reported that a MoS2slurry phase catalyst deactivated when it is recycled in a semi-batch hydroprocess reactor at high residue conversion (445°C and 13.8 MPa of H2).23 The authors found that coke yields, and hence, catalyst deactivation depended on MoS2 concentration. As catalyst recycling increased, i.e. higher residence time, the coke generated became more graphitic as shown by a lower H/C and higher aromatic/aliphatic carbon ratios.23 In this work, two slurry phase catalysts with two different Mo/feed ratios (2.5 and 5 wt% Mo/feed ratios) were evaluated for the hydroprocessing of a vacuum residue under batch conditions at different reaction times (0-5 hours). Solvent extractions of organic material filtered from the spent slurry catalysts were carried out to obtain a better understanding of catalyst deactivation process. The hydroprocessed products and organic extracts were characterized by elemental analysis, and by using the asphaltene solubility fraction24 and solubility profile25 methods. Also, the effect of the type of extracting solvent was studied using 10% methanol in dichloromethane and pyridine.

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Experimental Part Materials and Methods. All solvents were analytical grade and used as received. All gases, hydrogen, nitrogen and air, were of high purity (99.9%). Elemental analyses were carried out using a Carlo Erba instrument model NT2500. Proton and Carbon nuclear magnetic resonance spectra (1H-NMR and

13

C-NMR, respectively) were recorded on a Bruker AVANCE 500

spectrometer for determination of aromatic hydrogen/carbon. The inverse-gated protondecoupled 13C NMR spectra were recorded at 125.766 MHz using 30-40% solution of the sample in CDCl3 containing 0.10 M chromium acetylacetone as the relaxation agent and tetramethylsilane (TMS) as the internal standard. 1H NMR analysis was carried out at 500.116 MHz. Hydroprocessing Experiments. The feed used in the hydroprocessing runs is a mixture of 75 wt .% Mexican vacuum residue and 25 wt% VGO with the following characteristics: 4.5°API gravity, 3.58 wt% of sulfur, 0.46 wt% of nitrogen, 14.63% of microcarbon residue (MCRT) according to ASTM D-453026 and 36.5 % of residue 1000°F+ (538°C+). The catalytic hydroprocessing reactions were carried out in a stainless steel 1000 mL batch reactor equipped with a magnetic stirrer, a heating mantle, and a temperature controller. In a typical experiment, the reactor was loaded with 150 g of feed and slurry catalyst, containing 2.5 and 5 wt% of molybdenum based on feed amount, and 0.25 and 0.5 wt% of nickel, respectively. The initial hydrogen pressure was 12.4 MPa (1800 psi). The Mo/Ni catalysts were prepared according to the method reported in the literature and transferred to the reactor immediately after preparation.27 The reactor was heated at 5 °C/ min to 385°C and at 0.7°C/min to 418°C, generating a final pressure of approximately 12.4 MPa (1800 psi). At this moment, the run time was started, and the temperature was kept constant throughout

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the experiments. Hydrogen was continuously added throughout the runs to keep the total pressure constant and replace converted hydrogen. At the end of the reaction time (from 1 to 5 h), the reactor was cooled to room temperature, and the hydroprocessed products were mixed with the condensed overhead materials, filtered with a 1-micron mylar filter, and submitted for analysis. The percentages of hydrodesulfurization (%HDS), hydrodenitrogenation (%HDN), and conversion of 538C+ product (% Conv. 1000°F+) are defined in eq 1-3: %HDS = [(%wt. S in Feed – %wt. S in Product) / %wt. S in Feed] x 100

(1)

%HDN = [(%wt. N in Feed – %wt. N in Product) / %wt. N in Feed] x 100

(2)

% Conv. 1000°F+ = [(%wt. Distillates 1000°F+ in Product – %wt. Distillates 1000°F+ in Feed) / %wt. Distillates 1000°F+ in Feed] x 100

(3)

Asphaltene Characterization. Two on-column filtration methods were used for asphaltene characterization: solubility fraction and solubility profile. 24-25 For the first, the whole sample was dissolved in dichloromethane (0.1 g in 10 mL) and injected (40 µL) into a 10 mm i.d x 250 mm stainless steel column packed with poly(tetrafluoroethylene) (PTFE) using a heptane mobile phase (C7). Maltenes (heptane solubles) eluted as the first peak. The mobile phase was then switched in successive steps to a blend of solvents of increasing solubility parameter: 15% dichloromethane in n-heptane (solubility parameter δ = 16.0 MPa0.5), 30% dichloromethane in nheptane (δ = 16.8 MPa0.5), 100% dichloromethane (δ = 20.2 MPa0.5) and 10% methanol in dichloromethane (δ = 21.1 MPa0.5), to separate the asphaltenes into four different solubility fractions. 24 Percentages of areas were calculated, and the weight percentages of each asphaltene fraction were calculated using the methodology described elsewhere.25, 29

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For calibration purposes, an asphaltene sample was separated preparatively from the Mexican VR using n-heptane following ASTM D-6560.28 In a typical separation a weighed sample of the feed (1 g) was dissolved in 20 mL of hot n-heptane. The solution was stirred and digested at 80°C for one hour. The solution was filtered, and the asphaltenes were washed with hot heptane, dried, and weighed.28 The solubility profile method uses the same set of solvents as the solubility fraction methodology, but the asphaltenes are re-dissolved in a gradient of the mobile phase that changes from pure n-heptane to 90/10 methylene chloride/methanol and then to 100 % methanol.25 For both methods, the eluted fractions are quantified using an Evaporative Light Scattering Detector (ELSD) as described elsewhere.24-25 Solvent Extraction of Spent Slurry Catalysts. The spent slurry catalysts separated by filtration from the hydroprocessed products at different reaction times were solvent extracted in a Soxhlet apparatus using 10% methanol in dichloromethane under a nitrogen blanket for up to 48 h. In a general preparation, 5.0 g or 10.0 g of the spent slurry catalyst was placed in a Soxhlet thimble and solvent extracted until the condensed liquid was colorless. Then, the solvent was removed under a nitrogen stream overnight, and the residue was sent out for analysis. Mass balances are shown in the supplementary material Table A-1 and A-2 for 2.5 and 5 wt% Mo/feed, respectively. The same methodology was followed using pyridine as the extracting solvent. In this case, the spent catalyst was taken from a continuous-flow pilot plant operating at LHSV = 0.1, 17.2 MPa (2500 psi) of H2, and 800°F (426°C). Due to the higher boiling point, pyridine was removed from the extracted solid and organic phase under nitrogen for several days until constant weight was achieved. For comparison purposes, solvent extraction with 10% methanol in

10

dichloromethane was also carried out for the same sample. Mass balances can be seen in Table A-3 of the supplementary material. Result and Discussion Hydroprocessing Experiments. The API gravity and the percentages of microcarbon residue (%MCR) of the products versus the reaction time after hydroprocessing of a Mexican VR/VGO blend can be seen in Fig. 1. As shown, the products showed increases in API gravities from ~4.5°API (feed) to ~18°API and ~21°API, whereas microcarbon residues (MCR) decreased from ~15 wt% (feed) to 4 wt% and 1.4 wt% for the 2.5 wt% and 5 wt% Mo/feed systems, respectively. As expected, the 5 wt% Mo/feed case shows higher API and lower MCR than the 2.5 wt% analog. As shown in Fig. 1A and 1B, the catalytic activities of both materials have the tendency to level off after four- to five-hours due to decrease in reactant concentrations and deactivation of the catalyst.30-31 As shown in Fig. 2, the percentages of hydrodesulfurization (% HDS as determined by eq. 1) and hydrodenitrogenation (% HDN as determined by eq. 2) in the hydroprocessed products increased with reaction time. For the 2.5 wt% Mo/feed case, the percentages of HDS and HDN were 90% and 56%, respectively after 5 h (Fig. 2, black and red solid lines). For the 5 wt% Mo/feed, the percentages of HDS and HDN were 97% and 83 %, respectively at 5 h (Fig. 2, black and red dashed lines). Similar behavior was observed (Fig. 2) for the percentages of conversion of 1000°F+ (% Conv. 1000F+ as determined by eq. 3). The 5 wt% Mo/feed case showed higher percentages of residue conversion (green dashed line) than those obtained with the 2.5 wt% analog (solid green line). As before, both catalysts showed a tendency to level off activity due to decrease in reactants and evidence of deactivation after 4- and 5-h of reaction time.

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Similarly, the asphaltene contents decreased, and the H/C molar ratio increased with reaction time (Fig. 3). After 5 h reaction time and for the 5 wt% Mo/feed case (black dashed line), the percentage of asphaltenes was 0.27 wt% whereas for the 2.5 wt% analog (black solid line), the value was 0.38 wt%. The determination of asphaltenes by the no-column filtration method,24-25 has smaller experimental errors (±0.01 wt%) than those found for the gravimetrical asphaltene determinations (±0.5 wt%). Thus, the differences between the asphaltene contents measured in the products for the two Mo/feed ratios (black solid and dashed lines) are small but above the error of the technique. As before, the 5 wt% Mo/feed case (red dashed line) showed higher H/C molar (~0.55) ratios than those found in the products obtained using the 2.5 wt% Mo/feed system (red lines ~0.45). Next, the analysis of the feed and products using the asphaltene solubility fraction method24 is presented to obtain a better understanding of catalyst deactivation processes during the hydroprocessing of VR by carrying out analysis by solvent extractions of the deactivated catalysts (2.5 wt% Mo/feed) and its comparison with the 5 wt% Mo/feed analog. Asphaltene Characterization of Hydroprocessed Products. The feed and the filtered hydroprocessed products (no slurry catalyst present) from both catalysts were analyzed by using the asphaltene solubility fraction method.24 The LC traces of the feed (darker trace) and a hydroprocessed product (lighter trace) using 2.5 wt% Mo/feed with 4 h of reaction time are presented in Fig. 4. Consistent with the data presented in the previous section, significant reductions of the signal of all asphaltene peaks can be observed by comparing the feed versus the hydroprocessed product. Based on the areas of the asphaltene peaks, the weight percentages of each asphaltene fraction were calculated using the methodology described elsewhere.29 In Fig. 5 and 6, the

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weight percentages of different asphaltene solubility fractions24 of the feed and the hydroprocessed products versus the reaction time are presented for 2.5 wt% and 5 wt% Mo/feed, respectively. For the former catalyst, reductions of the concentration of all asphaltenes fractions are observed in the first hours of reaction. After three hours the asphaltene concentrations stay relatively constant. This loss of activity toward asphaltene processing can be attributed to decrease in reactant concentrations and to catalyst deactivation, as noted previously (Fig. 1-3). Different behavior is observed for the 5 wt% Mo/feed (Fig. 6). The low solubility parameter asphaltene fractions, extracted with 15% dichloromethane in C7 (δ = 16.0 MPa0.5, 30% dichloromethane in C7 (δ = 16.8 MPa0.5), and 100% dichloromethane (δ = 20.2 MPa0.5) are totally consumed during the first 3 h of reaction time. After 4 h, only the most polar asphaltene fraction is observed, 10% methanol in dichloromethane in red triangles (δ = 21.1 MPa0.5). For a Mexican VR asphaltenes and a visbroken product, previous results of preparative separations have indicated that the H/C ratio of the extracted asphaltene fractions decreased and the aromaticity increased as the solubility parameter of the solvent increased.24 In general, the low solubility parameter asphaltenes can be regarded as “easy-to-react” asphaltenes, whereas the higher solubility parameter analogs are “hard-to-process” asphaltenes.24 These two fractions have been linked to feed reactivity19 and sediment formation32 during residue hydroprocessing. Solvent Extraction of Spent Slurry Catalysts. To obtain a better understanding of catalyst deactivation processes during the hydroprocessing of VR, the solids from the filtration of the hydroprocessed products (spent filtered filtrated catalysts) at different reaction times were solvent extracted using 10% methanol in dichloromethane. The solvent extracted organics, and the solids were characterized by elemental analysis and by the asphaltene solubility fraction method.24 In general and for all experiments, overall and element specific (C, H, Mo, Ni, N, and

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S) mass balances were in the 85-110% range which indicates the validity of the data. Percentages of extraction were in the 40-55 wt% range. Mass balances and full characterization results can be found in Tables A1 and A2 of the Supplementary Material for the 2.5 wt% and 5 wt% Mocontaining catalysts, respectively. Carbon to molybdenum molar ratios for the spent filtered catalysts and the solvent extracted solids versus the reaction time are presented in Fig. 7. As seen, all values were approximatively constant for both catalysts in the 1 to 5 h range. In general, the C/Mo molar ratios were lower for the 5 wt% Mo/feed case (dashed lines) than the 2.5 wt% analog (solid lines) due to its higher Mo content. These results suggest that the total amounts of adsorbed organic species are not the main reason the Mo- containing catalysts showed reduction of activity in function of time. The weight percentages of asphaltenes25,

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and H/C molar ratio of the solvent extracted

organic fractions versus the reaction time using 2.5%, and 5% Mo/feed are presented in Fig. 8. As with the hydroprocessed products (Fig. 3), the percentage of asphaltenes decreased with time for both catalytic systems. Also, the amounts for asphaltenes deposited on the 2.5 wt% Mo/feed (solid black line) were higher than those observed for the 5 wt% analog (black dashed line). Furthermore, the H/C molar ratio of the solvent extracted organics decreased slightly with reaction time. The presence of species with low H/C molar ratios adsorbed on the catalyst is consistent with Rezaei and Smith.23 These authors reported that, as catalyst recycling increased (i.e., higher residence time), the coke generated became more graphitic as shown by a lower H/C and higher aromatic/aliphatic carbon ratios.23 These results indicate that the fractions removed by solvent extractions and their asphaltenes could be the precursors for the catalyst deactivation.1, 14, 16-17 A mechanism for deactivation of alumina supported catalysts have been proposed in the literature in which polyaromatics and

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asphaltenes in solution are adsorbed on the catalyst.33,

34

In turn, the adsorbed species are

transformed via polymerization-condensation reactions into deposited coke (eq. 4).31, 32 Asphaltenes in Solution -> Asphaltene Adsorbed -> Deposited Coke

(4)

As seen, there are more asphaltenes in the solvent extracted organics from the deactivated catalyst (2.5 wt% Mo/feed case) and their solubility distributions are different than those found for the 5 wt% counterpart. In Fig. 9 and 10, the weight percentages of the asphaltene solubility fractions24 are presented for the 2.5 wt% and 5 wt% Mo/feed, respectively. As shown, reductions of the concentration of all asphaltenes fractions are observed throughout all reaction times studied. At longer reaction times (Fig. 9), all asphaltene solubility fractions are observed. For the 2.5 wt% Mo/feed case, the two highest solubility parameter asphaltene fractions are the most abundant (100% dichloromethane in green triangles and 10% methanol in dichloromethane in red triangles). For the 5 wt% Mo/feed case, only the last asphaltene fraction was observed in any significant amount (Fig. 10). At the same reaction time of 5 hours, the comparison of the asphaltene solubility distributions between the hydroprocessed products (Fig. 5 and 6) and the solvent extracted organics (Fig. 9 and 10) is shown in Fig. 11. For the 2.5 wt% Mo/feed, the solvent extracted fraction is enriched in the higher solubility parameter asphaltenes (Fig. 11A). For the 5 wt% Mo/feed, the only asphaltene fraction observed was the 10% methanol in dichloromethane soluble (Fig. 11B). The finding that the solvent extracted organic fractions from the lower Mo-containing catalyst (2.5 wt% Mo/feed) had a higher concentration of the higher solubility asphaltenes is very intriguing. This result suggests that the most polar asphaltene fractions could be responsible for the coke formation and catalyst deactivation as depicted in eq. 4. A probable precedent was

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reported by Rahimi et al. in which the amphoteric fraction was the most prone to coke generation than the basic and acidic counterparts for the thermal treatment of Hamaca VR.35 However, the asphaltenes with the highest solubility parameter (10% methanol in dichloromethane) are also found in the 5 wt% Mo/feed case, although they are present in a smaller quantity as the comparison of Figs. 9 and 10 reveals. The low concentration of these species in the catalyst can be a plausible explanation for the difference found in performance. However, additional research is needed to reach definitive conclusions about the effect of asphaltene characteristics and relative content on coke generation. Use of Pyridine Extraction of Spent Slurry Catalysts. To study the effect of a higher solubility parameter solvent on the extraction of spent slurry catalysts, pyridine (δ = 21.8 MPa0.5)35 was used instead of 10% methanol in dichloromethane (δ = 21.1 MPa0.5). 36 The results of the percentages of extraction and characterization of the organic phases are presented in Table 1. For the same sample, a 4 wt% increase of the organic fraction was obtained by using pyridine (37 wt%) in comparison with 10% methanol in dichloromethane (33 wt%). These results are consistent with those reported by Jones and Argasinski.37 These authors obtained ~95 wt% dissolution of coal pre-asphaltenes using pyridine whereas only ~30 wt% and 22 wt% with dichloromethane and methanol, respectively.35 Furthermore, slightly lower H/C molar ratio, and higher nitrogen and sulfur contents, aromaticity

and

aromatic

hydrogens

were

obtained

by

using

pyridine

vs.

MeOH/dichloromethane. These results indicate that a more refractory material was extracted from the spent slurry catalyst using a solvent with higher solubility parameter. The characterization of the solvent extracted organics by the asphaltene solubility profile method25 is shown in Fig. 12. In this method, the maltenes were separated as in the solubility

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fractions methodology,24 but the asphaltenes were re-dissolved in a mobile phase that changes gradually from pure n-heptane to 10% methanol in methylene chloride and then to 100 % methanol.25 Consistent with the results presented in Table 1, there is a higher concentration of higher solubility material at higher retention time. This material seems to be preferentially adsorbed on the catalyst and could be responsible for the catalyst deactivation under hydroprocessing conditions.

Conclusions The results of the slurry phase hydroprocessing experiments showed that the system with 5 wt% Mo/feed yielded higher API, % HDS, %HDN, % Conv. 1000°F+, H/C molar ratio, and lower MCR and asphaltene content than the 2.5 wt% analog. Both catalysts showed signs of deactivation after four- to five-hours of reaction time. For the 2.5 wt% Mo/feed case and by using the solubility fraction method, the asphaltene characterization of the feed and the hydroprocessed products showed reductions of the concentration of all asphaltenes fractions in the first 3 h of run time. After that, the asphaltene concentrations were relatively constant. For the 5% wt% Mo/feed catalyst, only the most polar asphaltene fraction was observed (soluble in 10% methanol in dichloromethane) after 4 h of reaction time. In general, the low solubility parameter asphaltenes are generally called “easy-to react” asphaltenes, whereas the higher solubility parameter analogs are the “hard-to-process” asphaltenes.24 The results of the solvent extraction of spent slurry catalysts showed that more asphaltenes deposited on the 2.5 wt% Mo/feed deactivated catalysts than on the 5 wt% analog. Additionally,

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the asphaltenes deposited on the 2.5 wt% Mo/feed contained more species with a high solubility parameter than those observed for the 5 wt% analog. These results suggested that the fractions removed by solvent extractions are related to coke formation and might be responsible for catalyst deactivation observed after extended reaction times. However, more research is needed to reach definitive conclusions. A higher percentage of organic extracts was found using pyridine (37 wt%) than that obtained by using 10%MeOH/90%CH2Cl2 (33 wt%). Pyridine organic extract was more aromatic (aromaticity and lower H/C molar ratio) and had a higher concentration of the highest solubility parameter asphaltenes.

Acknowledgements The authors wish to thank Chevron Energy Technology Company for the permission to publish this paper. Our gratitude to the Measurement and Chemistry Focus Area for providing funding. The authors also want to thank Lori Thomas for her technical assistance for the solvent extractions and Ajit Pradhan for obtaining the H- and 13C-NMR spectra.

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References 1. Furimsky, E., Catalysts for Upgrading Heavy Petroleum Feeds” in Studies in Surface Science and Catalysis, B. Delmon and J. T. Yates ed., Elsevier 2007, Vol. 169, p148 and references therein 2. Gray, M. R. Upgrading Oilsands Bitumen and Heavy Oil, 1st ed.; The University of Alberta Press: Edmonton, Alberta, Canada, 2015; p 367 and references therein 3. Ancheyta, J., Trejo, F., Rana, M. S. Asphaltenes. Chemical Transformation during Hydroprocessing of Heavy Oils, 1st ed.; CRC, 2009, p192 and references therein 4. Ancheyta, J., Speight, J. G. Hydroprocessing of Heavy Oils and residua, 1st ed.; CRC, 2007, p160 and references therein 5. C. Ovalles, E. Rogel, H. Morazan, M. E. Moir, G. Dickakian, Energy & Fuels 2015, 29, 4956–4965. 6. Wandas, R. Pet. Sci. Technol., 2007, 25, 153 7. Absi-Halabi, M.; Stanislaus, A.; Trimm, D. L. Appl. Catal. 1991, 72, 193. 8. Speight, J. G. Catal. Today 2004, 98, 55. 9. Matsushita, K.; Marafi, A.; Hauser, A.; Stanislaus, A. Fuel 2004, 83, 1669. 10. Stanislaus, A.; Hauser, A.; Marafi, A. Catal. Today 2005, 109, 167. 11. Algelt, K. H., Boduszynski, M. M. Composition and analysis of Heavy Petroleum Fractions 1st ed.; Marcel Dekker 1994, New York, p75 12. Huc, A.-Y. Heavy Crude Oils. From Geology to Upgrading. An Overview, Technip, 2011 Chapter 23 and references therein. 13. Speight, J. G. The Chemistry and Technology of Petroleum, 3rd ed.; Marcel Dekker, 1999 New York, p416. 14. Gray, M. R., Zhao, Y., McKhight, C. M., Komar, D. A., Carruthers, J. D., Energy & Fuels, 2011, 13, 1037. 15. Ali, F. A., Hauser, A., Abdullah, H. A., Al-ADwani, A., Energy & Fuels 2006, 20, 45 16. Maity, S. K., Perez, V. H., Ancheyta, J., Rana, S. Centeno, G., Pet. Sci. Tech. 2007, 25, 241 17. Kohli, K., Prajapati, R., Maity, S. K., Sau, M., Garg, M. O., Fuel 2016, 175, 264. 18. Matsushitaa, K., Marafib, A., Hauserc, A., Stanislaus, A., Fuel 2004, 83, 1669 19. Ovalles, C., Rogel, E., Lopez, J., Pradhan, A., Moir, M. E., Energy & Fuel, 2013, 27, 6552. 20. Zhang, S., Liu, D., Deng, W., Que, G., Energy & Fuel, 2007, 21, 3057. 21. Kramer, D. C. US Patent No. 5,298,152 (1994) 22. Motaghi, M., Subramanian, A.,Ulrich, B., Hydroc. Process., 2011, February, 1. 23. Rezaei, H., Smith, K. J., Energy & Fuel, 2013, 27, 6087. 24. Ovalles, C., Rogel, E., Moir, M. E., Thomas, L., Pradhan, A., Energy & Fuel, 2012, 26, 549. 25. E. Rogel, C. Ovalles, M. E. Moir, Energy & Fuel, 2010, 24, 4369-4374. 26. American Society for Testing and Materials (ASTM). ASTM, D-4530, “Standard Test Method for Determination of Carbon Residue (Micro Method); ASTM International: West Conshohocken, PA, 2006 27. Lopez, J., Pasek, A. U.S. Patent No 5,094,991 (1992).

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28. American Society for Testing and Materials (ASTM). ASTM, D-6560, “Standard Test Method for Determination of Asphaltenes (Heptane Insolubles) in Crude Petroleum and Petroleum Products; ASTM International: West Conshohocken, PA, 2005. 29. Ovalles, C., Rogel, E., Morazan H., Moir, M. E., SPE 173733, presented at the SPE International Symposium on Oilfield Chemistry held in The Woodlands, Texas, USA, 13–15 April 2015. 30. Forzatti, P., Lietti, L., Catal. Today, 1999, 52, 165-181 31. Bartholomew, C. H., Appl. Catal. A: General, 2001, 212, 17-60 32. Rogel, E., Ovalles, C., Pradhan, A., Leung, P., Chen, N., Energy & Fuel, 2013, 27, 6587. 33. Massoth, F. E., Stud. Surf. Sci. Catal., 1997, 111, 275-82. 34. Marchal C., Abdessalem E., Tayakout-Fayolle M., Uzio D., Energy and Fuels, 2010, 24, 4290-4300. 35. Rahimi, P., Gentzis, T., Cotte, E., Energy & Fuels, 1999, 13, 694-701 36. "Handbook of Solubility Parameters and Other Cohesion Parameters", A. F. M. Barton, CRC Press, 2nd Ed., Boca Raton, FL, USA, p96-103. 37. Jones M.B., Argasinski, J.K., Fuel, 1985, 64, 1547-1551.

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Figures Captions Fig. 1. (A) API gravity and (B) percentage of microcarbon residue (%MCR) of the products vs. the reaction time after the hydroprocessing reactions using 2.5 wt% and 5 wt% Mo/feed Fig. 2. Percentages of hydrodesulfurization (%HDS as determined by eq. 1), hydrodenitrogenation (%HDN as determined by eq. 2), and conversion of 1000°F+ (as determined by eq. 3) versus reaction time using 2.5% and 5% Mo/feed (lines were drawn to show tendency) Fig. 3. Weight percentages of asphaltenes24, 29 and molar and H/C molar ratio versus the reaction time using 2.5 wt and 5 wt% Mo/feed (lines were drawn to show tendency) Fig. 4. LC traces of the asphaltene solubility fraction analysis24 of the feed and a hydroprocessed product using 2.5 wt% Mo/feed with 4 h of reaction time. Fig. 5. Weight percentages of different asphaltene solubility fractions24 of the feed and the hydroprocessed products using 2.5 wt% Mo/feed versus the reaction time (lines were drawn to show tendency) Fig. 6. Weight percentages of different asphaltene solubility fractions24 of the feed and the hydroprocessed products using 5 wt% Mo/feed versus the reaction time (lines were drawn to show tendency) Fig. 7. Carbon to Molybdenum molar ratio for the spent filtrated catalysts and the solvent extracted solids versus the reaction time (lines were drawn to show tendency) Fig. 8. Weight percentages of asphaltenes24, 29 and H/C molar ratio of the solvent extracted organic fractions extracted from the filtered solids versus the reaction time using 2.5 wt% and 5 wt% Mo/feed (lines were drawn to show tendency) Fig. 9. Weight percentages of different asphaltene solubility fractions24 of the solvent extracted organic products extracted from the filtered solids using 2.5 wt% Mo/feed (lines were drawn to show tendency) Fig. 10. Weight percentages of different asphaltene solubility fractions24 of the solvent extracted organic products extracted from the filtered solids using 5 wt% Mo/feed (lines were drawn to show tendency) Fig. 11. Weight percentages of different asphaltene solubility fractions24 of the hydroprocessed products and the solvent extracted organics after 5 h of reaction time using: A) 2.5 wt% Mo/feed and B) 5 wt% Mo/feed catalysts Fig. 12. Characterization of the solvent extracted organics by the asphaltene solubility profile method25

21

25

A API Gravity

20

15 2.5 wt% Mo/Feed

5 wt% Mo/Feed 10

5

0

0

1

2

3 4 Reaction Time (h)

5

6

16 2.5 wt% Mo/Feed

14

5 wt% Mo/Feed

B

12

% MCR

10 8

6 4 2 0 0

1

2

3 4 Reaction Time (h)

5

6

Fig. 1. (A) API gravity and (B) percentage of microcarbon residue (%MCR) of the products vs. the reaction time after the hydroprocessing reactions using 2.5 wt% and 5 wt% Mo/feed 100% 90% 80%

Percentage

70% 60%

50%

% HDS (2.5 wt% Mo/Feed)

40%

% HDS (5 wt% Mo/Feed)

30%

% HDN (2.5 wt%Mo/Feed)

20%

% HDN (5 wt% Mo/Feed) % Conv. 1000F+ (2.5 wt% Mo/Feed)

10%

% Conv. 1000F+ (5 wt% Mo/Feed)

0% 0

1

2

3 Reaction Time (h)

4

5

6

22

Fig. 2. Percentages of hydrodesulfurization (%HDS as determined by eq. 1), hydrodenitrogenation (%HDN as determined by eq. 2), and conversion of 1000°F+ (as determined by eq. 3) versus reaction time using 2.5 wt% and 5 wt% Mo/feed (lines were drawn to show tendency)

3.5

1.60

3.0

1.55 1.50

Wt. % Asphaltenes

2.5

1.45 2.0 % Asph. (2.5 wt% Mo/Feed)

1.5

1.40

% Asph. (5 wt% Mo/Feed)

Molar H/C (2.5 wt% Mo/Feed)

1.0

Molar H/C (5 wt% Mo/Feed)

0.5

H/C Molar Ratio

23

1.35 1.30 1.25

0.0

1.20 0

1

2

3

4

5

Reaction Time (h)

Fig. 3. Weight percentages of asphaltenes24, 29 and molar and H/C molar ratio versus the reaction time using 2.5 wt% and 5 wt% Mo/feed (lines were drawn to show tendency)

24

8000

100%CH2Cl2 Asphaltenes

Maltenes

HPLC Signal (Arb. Number)

7000

0 h (Feed) 4 h Residence Time

6000

30%CH2Cl2 in C7 Asphaltenes

5000

10%Methanol in CH2Cl2 Asphaltenes

4000 3000

15%CH2Cl2 in C7 Asphaltenes

2000 1000 0 0

10

20

30 Time (min)

40

50

60

Fig. 4. LC traces of the asphaltene solubility fraction analysis24 of the feed and a hydroprocessed product using 2.5wt% Mo/feed with 4 h of reaction time.

wt. % Asphaltenes by Solubility Fraction Method

25

1.6 1.4 1.2

15/85 CH2Cl2/C7 30/70 CH2Cl2/C7

1.0

100% CH2Cl2

10/90 MeOH/CH2Cl2

0.8 0.6 0.4 0.2 0.0 0

1

2

3

4

5

Reaction Time (h)

Fig. 5. Weight percentages of different asphaltene solubility fractions24 of the feed and the hydroprocessed products using 2.5 wt% Mo/feed versus the reaction time (lines were drawn to show tendency)

wt. % Asphaltenes by Solubility Fraction Method

26

1.6 1.4 15%CH2Cl2/ 85%C7

1.2

30%CH2Cl2/ 70%C7

1.0

100%CH2Cl2 10%MeOH/ 90%CH2Cl2

0.8 0.6

0.4 0.2 0.0 0

1

2

3

4

5

Reaction Time (h)

Fig. 6. Weight percentages of different asphaltene solubility fractions24 of the feed and the hydroprocessed products using 5 wt% Mo/feed versus the reaction time (lines were drawn to show tendency)

27

25

C/Mo Molar Ratio

20

Spent Filtrated Catalys (2.5 wt% Mo/Feed)

15

Spent Filtrated Catalyst (5 wt% Mo/Feed) Solvent Extracted Solid (2.5 wt%Mo/Feed Solvent Extracted Solid (5 wt% Mo/Feed)

10

5

0 0

1

2

3

4

5

6

Reaction Time (h)

Fig. 7. Carbon to Molybdenum molar ratio for the spent filtrated catalysts and the solvent extracted solids versus the reaction time (lines were drawn to show tendency)

28

6%

% Asph. (2.5 wt% Mo/Feed)

1.60

% Asph. (5 wt% Mo/Feed)

Molar H/C (2.5 wt% Mo/Feed)

5%

1.55

4%

1.50

3%

1.45

2%

1.40

1%

1.35

0%

H/C Molar Ratio

Wt. % Asphaltenes

Molar H/C (5 wt% Mo/Feed)

1.30 0

1

2

3

4

5

Reaction Time (h)

Fig. 8. Weight percentages of asphaltenes24, 29 and H/C molar ratio of the solvent extracted organic fractions extracted from the filtered solids versus the reaction time using 2.5 wt% and 5 wt% Mo/feed (lines were drawn to show tendency)

29

wt. % Asphaltenes by Solubility Fraction

3.0 15/85 CH2Cl2/C7 30/70 CH2Cl2/C7

2.5

100% CH2Cl2 10/90 MeOH/CH2Cl2

2.0

1.5 1.0 0.5 0.0 0

1

2

3

4

5

Reaction Time (h)

Fig. 9. Weight percentages of different asphaltene solubility fractions24 of the solvent extracted organic products extracted from the filtered solids using 2.5 wt% Mo/feed (lines were drawn to show tendency)

Wt. % Asphaltenes by Solubility Fraction Method

30

0.7 0.6

15%CH2Cl2/ 85%C7

30%CH2Cl2/ 70%C7

0.5

100%CH2Cl2

0.4

10%MeOH/ 90%CH2Cl2

0.3 0.2 0.1

0.0 0

1

2

3

4

5

Reaction Time (h)

Fig. 10. Weight percentages of different asphaltene solubility fractions24 of the solvent extracted organic products extracted from the filtered solids using 5 wt% Mo/feed (lines were drawn to show tendency)

31 100% 90%

A) 2.5 wt% Mo/Feed

Percentage (wt.)

80% 70% 60%

10/90 MeOH/CH2Cl2

50%

100% CH2Cl2

40%

30/70 CH2Cl2/C7

30%

15/85 CH2Cl2/C7

20%

10% 0%

Hydroprocessed Product

Solvent Extracted Organic

100%

B) 5 wt% Mo/Feed

90%

Percentage (wt.)

80% 70% 60%

10/90 MeOH/CH2Cl2

50%

100% CH2Cl2

40%

30/70 CH2Cl2/C7

30%

15/85 CH2Cl2/C7

20% 10% 0%

Hydroprocessed Product

Solvent Extracted Organic

Fig. 11. Weight percentages of different asphaltene solubility fractions24 of the hydroprocessed products and the solvent extracted organics after 5 h of reaction time using: A) 2.5 wt% Mo and B) 5 wt% Mo/feed catalysts

32

0.009 0.008 MeOH/CH2Cl2 Extract

Normalized Response

0.007

Pyridine Extract 0.006 0.005 0.004

More material in the high solubility parameter area

0.003 0.002 0.001 0 12

14

16

18

20

22

24

Time

Fig. 12. Characterization of the solvent extracted organics by the asphaltene solubility profile method25

33

Table 1. Percentage of extraction and characterization of the organic phase after solvent extraction with 10% Methanol in CH2Cl2 and Pyridinea

b

Wt% of Extraction Wt% Cc Wt% Hd H/C Molar Ratio Wt% Ne Wt% Sf Aromaticityg Aromatic Hydrogenh a

Solvent Used in the Extraction 10% Methanol in CH2Cl2 33 85.62 8.39 1.18 1.00 0.76 0.615 22.0

Pyridine 37 75.45 7.15 1.14 2.10 2.40 0.704 21.3

Spent slurry catalysts were solvent extracted in a Soxhlet apparatus under a nitrogen blanket. bPercentage of extraction calculated as mass extracted organic/ mass of spent catalyst x 100. cCarbon elemental analysis in weight percent. dHydrogen elemental analysis in weight percent. eNitrogen elemental analysis in weight percent. fSulfur elemental analysis in weight percent. gAromaticity determined by 13C-NMR. Percentage of aromatic hydrogen determined by H-NMR