Homogeneous catalyst for in-situ hydrotreating of heavy oils

Accepted Manuscript Title: Homogeneous catalyst for in-situ hydrotreating of heavy oils Authors: Persi Schacht-Hern´andez, Benjam´ın Portales-Mart´ınez, Georgina C. Laredo, Patricia P´erezRomo, Jos´e M. Dom´ınguez-Esquivel PII: DOI: Reference:

S0926-860X(19)30135-8 https://doi.org/10.1016/j.apcata.2019.03.020 APCATA 17025

To appear in:

Applied Catalysis A: General

Received date: Revised date: Accepted date:

16 January 2019 20 March 2019 25 March 2019

Please cite this article as: Schacht-Hern´andez P, Portales-Mart´ınez B, Laredo GC, P´erezRomo P, Dom´ınguez-Esquivel JM, Homogeneous catalyst for in-situ hydrotreating of heavy oils, Applied Catalysis A, General (2019), https://doi.org/10.1016/j.apcata.2019.03.020 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.

Homogeneous Catalyst for In-situ Hydrotreating of Heavy Oils Persi Schacht-Hernández a, Benjamín Portales-Martínez b, Georgina C. Laredo* a, Patricia

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Pérez-Romoa, and José M. Domínguez-Esquivel a

a

Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas No 152, México D.F. 07730, México.

b

CONACYT-Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas No 152, México D.F.

07730, México.

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Graphical abstract

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100 80 60

20

Diesel

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50 30

Heavy Gas Oil

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70

40

Residue

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90

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Distribution of distillates, wt%

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Distribution of distillated fractions on the hydrotreated crude oil

Gasoline

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0

Crude oil

350 °, 30 min

350 °C, 60 min

350 °C, 90 min

390 °C, 60 min

400 °C, 60 min

Liquid Ni-Mo catalyst, 10.8 MPa, Batch reactor

Highlights 1

The upgrading of heavy oils by hydrotreatment using liquid Ni-Mo catalyst aiming to develop an “inside reservoir” technology was studied in bench scale tests.

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The synthesis of the catalyst was attained by mixing solutions at room temperature under acidic conditions.

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Test were conducted by mixing the catalyst and the oil in in a 500 ml batch reactor at 350, 390 and 400 °C during 0.5, 1 and 1.5 hours

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Liquid catalyst enhanced the quality of the heavy oil by increasing the API gravity and decreasing the kinematic viscosity, the sulfur and the nitrogen contents

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

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Abstract

The upgrading of the physical and chemical properties of heavy oil by hydrotreating using a liquid Ni-

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Mo catalyst was studied through bench-scale tests aiming at developing "inside-reservoir" technology.

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The liquid Ni-Mo catalyst was synthesized by a very simple method consisting in preparing and mixing

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solutions at room temperature under acidic conditions. Mixtures of liquid Ni-Mo catalyst and heavy oil were evaluated in a 500-mL batch reactor at 350, 390 and 400 °C for 30, 60 and 90 min. The results showed that the liquid Ni-Mo catalyst improved the crude oil properties by increasing the API gravity

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from 12.5 to 22 and decreasing the kinematic viscosity from 13,490 to 72 cST at 15.6 °C; the sulfur

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content from 5.5 to 3.1 % and the nitrogen content from 750 to 392 ppm were also reduced. Furthermore, the volume of gasoline and diesel by Simulated Distillation were increased to 8 and 14

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vol. %, due to the change in chemical composition. Aromatic and saturated hydrocarbon compounds increased at the expense of asphaltenes and resins.

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*Corresponding author: [email protected].

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Keywords: Heavy oils, hydrotreating, homogeneus, Ni-Mo, in situ

1. - Introduction Some countries like Canada, Mexico and Venezuela, which could be considered as good crude oil suppliers in America, unfortunately, produce very heavy crude oils, and this condition has increased the difficulties for processing them from the extraction to the transportation to refineries for fuel production. These oils present high molecular weight, density and viscosity with very high contents of 2

undesirable compounds like sulfur and nitrogen aromatic hydrocarbons, metals, etc. Therefore, the processing for commercial applications linked to the complying with environmental regulations is very challenging and sometimes impossible [1- 3]. Recently, extra efforts have been made to find better technologies to overcome this problem. Some of these efforts have been carried out only on the bench scale [4 – 6]. Among the technologies studied outside the lab are “in-situ” combustion [7] and fracking

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[8], however, the products obtained from these approaches, even at a commercial level, have not been capable of complying with environmental regulations. As an example, water, sand and chemicals need to be injected into the rock at high pressure to accomplish good results for the fracking technology. On the one hand, a high amount of water must be transported to the site at significant environmental cost and on the other hand, chemicals may leak during drilling and contaminate groundwater around the fracking site.

It is well known that by applying any colloidal solution to a solid, it is possible to change its chemical

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properties [9], e.g., the hydrocracking of aromatic compounds through fluid catalytic cracking using

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steam injection or chemical agents. By this procedure, it is possible to change physical properties such

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as viscosity and surface tension [11]. However, this type of technologies has not been applied with enough success in petroleum refineries [10, 12]. Another approach is the use of THAI–CAPRI™ (Toe-

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to-Heel Air Injection and its add-on Catalytic upgrading Process In-situ), which combines “in-situ” combustion, catalytic upgrading and horizontal wellbore technologies for down-hole or in-situ recovery

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and upgrading of heavy oil and bitumen to improve fluidity and consequently add commercial value to

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the produced oil. The process commences by burning a small fraction of the oil in the reservoir, thereby releasing high-temperature oxidation energy from the combustion reaction between the injected

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enriched air and hydrocarbon. The continuous air injection propagates the combustion front of the toeposition to the heel of the horizontal producer well. The mobilized oil ahead of the combustion front

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flows a short-distance downstream by gravity into the horizontal producer well. This process uses an active catalyst (Ni-Mo and Co-Mo) layer between the concentric slotted liners of the horizontal production wells [13]. Experiments using Lloydminster heavy crude oil with 11.9° API gravity and a

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Co-Mo catalyst could produce upgraded oil with 23° API gravity and low viscosity of 20-30 mPa [14] as a result of transforming high to low molecular weight compounds [15]. This procedure is considered non-destructive through hydrogenation or hydrotreating reactions, where the crude oil quality is also improved by removing some contaminants, similar to sulfur removal by In-situ Upgrading [16]. A typical catalyst used in the “in-situ hydrotreating reactions” consists of nickel, molybdenum and tungsten [17, 18]. Since the type of used catalyst depends on the desired products, the

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hydrodesulfurization (HDS) process uses the Co-Mo type to perform such reactions. The Ni-Mo type is employed for hydrogenation and hydrodenitrogenation (HDN) reactions and Ni-W is used for the hydrogenation of very low sulfur fractions, for sulfur and heavy metals could poison the catalyst during the industrial process, provoking a decrease in the catalytic activity [19, 20]. Hydrocracking of vacuum distillates and residue is also used to transform heavy oils into lighter fractions; this procedure can be

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divided into mild hydrocracking and conventional hydrocracking [21]. Although the conversion is important for both hydrocracking processes and are similar in terms of reactions, the products may vary due to reaction conditions, which usually range from 9.6 to 17.6 MPa [22]. A significant hydrocracking reaction is the partial hydrogenation of polycyclic aromatics, producing aromatic compounds attached to saturated rings, which are in turn transformed, through hydrocracking, into monocyclic aromatics. In the case of residue conversion, hydrocracking contributes as much as hydrodesulfurization and hydrodenitrogenation for obtaining lower boiling point distillates [23]. These reactions take place in

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the presence of a bi-functional catalyst, allowing the breaking of hydrocarbon chains by hydrogen

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addition. The aromatics and olefins are hydrogenated to produce naphthenes and alkanes. Secondary

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reactions that allow coke formation are inhibited by the presence of hydrogen. Some studies have shown that silica-alumina supported catalysts stimulate cracking reactions, where platinum, tungsten oxide or

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nickel contribute to hydrogenation reactions [24]. One major difference between hydrocracking and hydrotreating is the residence time and the decomposition of non-heteroatom components. The upper

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limits of hydrotreating often overlap with lower limits of hydrocracking [25] as it has been observed in

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some extremely large molecules that consist of highly condensed heterocyclic and aromatic rings with sulfur, nitrogen, oxygen, and metals (mainly vanadium and nickel), which are possible to break by using

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mainly hydrogenating catalysts doped with transition metals [26, 27]. In this work, a study about upgrading heavy crude oils by using a homogeneous liquid Ni-Mo catalyst

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under hydrotreating conditions was proposed. The analysis of the reaction products showed a remarkable variation of the kinematic viscosity and chemical composition. The hydrogenation of heavy compounds increased the API gravity. The main goal of this work was to develop bench-scale

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technology to be used in reservoirs to upgrade crude oil before being submitted to further refining with the concomitant reduction of production costs.

2. - Experimental Section 2.1 Catalyst preparation The liquid Ni-Mo catalyst was prepared as follows: 4

1) In a conventional flask, phosphoric acid (H3PO4, J.T. Baker, 98%) and ammonium heptamolybdate ((NH4) 6Mo7O24•4H2O, Sigma-Aldrich) were mixed at 25 °C until obtaining a clear solution. The pH of the solution was 1-2. 2) Nickelous sulfate hexahydrate (NiSO4•6H2O, Sigma-Aldrich) was dissolved in distilled water under stirring conditions at 25 °C.

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3) Finally, aqueous solutions of the corresponding precursors were mixed under stirring conditions at room temperature for 24 h. The final molar ratio of the liquid Ni-Mo catalyst was 1.0 Ni: 0.084 Mo: 0.295 H+: 14.42 H2O at pH 1-3.

2.2 Catalyst characterization

The metallic composition of the Ni-Mo was obtained by elemental analysis, using a Perkin-Elmer Model 3100 Atomic Absorption Spectrophotometer. The acid sites of the Ni-Mo catalyst were

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determined by FTIR-pyridine desorption using an FTIR spectrometer THERMO-NICOLET model

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MAGNA560 with 4 cm-1 and a 50-scan resolution. For the FTIR analysis, the catalyst was supported

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on -alumina (inner matrix). Physical properties (density and viscosity) were evaluated using the ASTM−D7042 method (Test Method for Dynamic Viscosity and Density of Liquids by Stabinger

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Viscometer (and The Calculation of Kinematic Viscosity)). The thermogravimetric and Differential Thermal Analysis (TGA- DTA) were obtained with a Perkin-Elmer 1700 equipment. XRD patterns of

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the catalyst were recorded on a Bruker D8 Advance diffractometer, using Cu K radiation ( =

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1.5406Å) with a scan rate of 0.02° s-1 in the 4 - 80° range. The pattern was referenced to the JCPDS powder diffraction files. The samples were studied by high-resolution transmission electron microscopy

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(HRTEM) and the micrographs were obtained in a TITAN 80-300 with Schottky type field emission gun operating at 300 KV. HRTEM digital images were obtained using a CCD camera and the Digital

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Micrograph Software from GATAN. A Scanning Electron Microscope SEM SU1510 was also used.

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The samples were dispersed in ethanol and supported on holey-carbon-coated-copper grids.

2.3 Characterization of heavy crude oil Physical and chemical properties of the feedstock and products established by the following methods: Total Acid Number (TAN) by the ASTM D664 method titration technique (Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration). Total Base Number (TBN) by Potentiometric Perchloric Acid Titration, ASTM D2896 (Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration). API gravity was measured by the 5

ASTM-D287 method (Standard Test Method for API Gravity of Crude Petroleum and Petroleum Products (Hydrometer Method)). The kinematic viscosity, ASTM-D445 (Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)) was determined using a rotary viscosimeter. SARA (saturates, aromatics, resins and asphaltenes) was determined by the ASTM-D4124 method (Standard Test Method for Separation of Asphalt into Four

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Fractions). The sulfur contents were measured by the ASTM-D4294 method (Standard Test Method for Sulfur in Petroleum and Petroleum Products by Energy Dispersive X-ray Fluorescence Spectrometry). The ASTM D5373 method (Standard Test Methods for Determination of Carbon, Hydrogen and Nitrogen in Analysis Samples of Coal and Carbon in Analysis Samples of Coal and Coke) was used for the analysis of coke. The distillation curves were obtained by the ASTM-D2887 method (Standard Test Method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography). The quantification of nickel in crude oil fractions was analyzed by the ASTM-D5863

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method (Standard Test Methods for Determination of Nickel, Vanadium, Iron, and Sodium in Crude

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oils and Residual Fuels by Flame Atomic Absorption Spectrometry). The atmospheric distillation of

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petroleum products using laboratory batch distillation equipment was obtained following the ASTMD86 method (Standard Test Method for Distillation of Petroleum Products and Liquid Fuels at

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Atmospheric Pressure).

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2.4 Catalytic activity assessments

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The liquid Ni-Mo catalyst evaluation was carried out in a Parr batch reactor to emulate the reactions taking place in the reservoir as follows: 200 g of heavy crude oil were mixed with 5 g of liquid Ni-Mo

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catalyst. Before each experimental test, the reactor was tested for leaks, purged with N2 and stabilized before heating. The reaction was carried out with hydrogen at 9.8 MPa and heated at 350, 390 and

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400°C, under stirring at 1000 rpm and for 30, 60 and 90 min. Experiments 1, 2 and 3 (denoted as Tests 1, 2, and 3) were carried out at 9.8 MPa and 350 °C at 30, 60 and 90 min. The temperature was varied in Experiments 4 and 5 (390 and 400 °C, respectively, named Tests 4 and 5) for 60 min at 9.8 MPa.

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Once the reaction time was completed, the reactor was cooled down, opened and the products were recovered. The physical and chemical properties of the products and feedstock were characterized according to the methods mentioned above.

3. - Results

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3.1 Elemental analysis and physical properties of the liquid Ni-Mo catalyst The liquid Ni-Mo catalyst composition was verified by using the analytical technique of atomic absorption spectroscopy as described in [28]. The analytical technique confirmed a Ni content of 7 wt. %, and Mo content of 0.8 wt. %. It is worth mentioning that nickel and molybdenum oxides were transformed into sulfide active phases during the catalytic reaction.

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The density and viscosity of the synthesized liquid Ni-Mo catalyst were measured in the interval ranging from 25 to 90 °C with increments of 10 °C at atmospheric pressure (Table 1). The results indicate that both density and viscosity present a linear behavior as the temperature increased.

3.2 Thermogravimetric and Differential Thermal Analysis (DTA -TGA) of the liquid Ni-Mo catalyst

DTA calibration was accomplished using calcined aluminum oxide as standard. TGA and DTA

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experiments were carried out at room temperature up to 800 °C, and the results are presented graphically

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in Figure 1. The liquid Ni-Mo catalyst was thermally treated at a rate of 5 °C∙min-1 under nitrogen flow

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(50 ml∙min-1) to obtain the thermogravimetric curve (TGA) and the differential thermal analysis (DTA). The results of the DTA/TGA analysis confirmed that the precursors of the Ni-Mo-P catalysts exhibited

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five endothermic peaks corresponding to dehydration reactions of the nickel and molybdenum hydrated salts and to the phosphoric acid condensation. The TGA analysis of the Ni-Mo catalyst exhibited a

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different weight loss that depends partly on the sample composition, in agreement with Tomaszewicz

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et al. and Cavus et al. [29, 30]. The evaporation of free water was observed at about 78 °C with an evident mass loss of about 44 wt. %, according to the initial water content of the sample. The “A zone”

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showed peaks at 105 and 122 °C. These peaks represent the water loss from the nickel and molybdenum hydrated form. The “A zone” was characterized by an increment in the mass loss rate corresponding to

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30 wt. % due to the removal of water in the crystalline structure. The “B zone” was characterized by small variations in the mass loss rate; in this case, a mass loss of 6 wt. %, which resulted from the condensation reaction of phosphoric acid. The “C zone”, between 376 to 450°C, can be related to the

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nickel-molybdenum interactions [31]. Finally, up to 650 °C (D zone), the salts were transformed presumably into an oxide form.

3.3 X-ray diffraction of the spent Ni-Mo catalyst. After processing the heavy crude oil with the Ni-Mo catalyst, a thin layer of a solid product was found at the bottom of the Parr batch reactor, which was analyzed by X-ray powder diffraction (XRD). Figure

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2 shows the XRD patterns of the catalyst after the reaction. The sample exhibited some crystalline phases that were matched with the Joint Committee on Powder Diffraction Standards (JCPDS) with card number 03-065-3419 for NiS, 00-014-0364 for Ni7S6, 00-012-0692 for Mo2S3, and 00-005-0507 MoO3 phases, indicating that the sulfhydration reaction of the metals took place during the reaction. The peak intensity can be related to the stacking and highly disordered packing of sulfide phases.

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Nevertheless, the sulfide catalyst was synthesized successfully.

3.3 Characterization of the catalyst acidity.

The pyridine adsorption–desorption spectra were obtained at different temperatures by impregnating the liquid Ni-Mo catalyst on an inner matrix (Figure 3). Bands at around 1450 and 1550 cm-1 were assigned to pyridine adsorbed on Lewis and Brönsted sites, respectively while the band at 1495 cm-1 was due to pyridine molecules adsorbed on both Brönsted and Lewis acid sites. It can be clearly seen

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that the Ni-Mo catalyst exhibited predominantly Lewis acid sites with medium acidity [32].

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As expected, after degassing at up to 300 °C, all these bands disappeared completely as shown in the

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same figure [33].

In Figure 4, the neutralization profile of the acid sites of the liquid Ni-Mo catalyst is presented, showing

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a maximum acid strength (MFA), [first point of titration] with a value of about +1 MV, which according to the classification reported for this technique, corresponds to strong acid sites, although these types

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of site concentrations were very low. Most of the acid sites in this particular Ni-Mo catalyst were

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considered weak because they presented signals below 0 mV. The signals between 0 and -70 mV, compiled for a total concentration of about 2.8 meq of n-butylamine per gram of solid. These results

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are in good agreement with the pyridine programmed desorption temperature results presented before.

3.5 Morphological aspects by SEM and High-Resolution TEM To investigate the morphology of the spent Ni-Mo catalyst, SEM characterizations were employed to

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obtain detailed morphological information. The presence of irregularly shaped porous agglomerates was revealed by the SEM micrograph (Figure 5A) [34]. The HRTEM characterization of the catalyst was carried out to get more information about the active phase nanoclusters. The HRTEM micrograph is shown in Figure 5B. The characteristic black thread-like fringes [35] with high stacking numbers and long slab lengths were detected. Finally, the micrograph shows that after the reaction, the Ni-Mo catalyst is in the sulfide form, which is also confirmed by the XRD patterns.

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4. - Catalytic Activity Measurements 4.1 Total Acid Number (TAN) of feedstock and products. A set of experiments was carried out to determine the acidity degree, i.e., the number of acid compounds that were present in the feedstock and products. Table 2 shows the TAN and TBN obtained for the feedstock and products for the Tests 1, 2 and 3 (9.8 MPa, 350 °C for 30, 60 and 90 min). The oil industry

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rule indicates that if the TAN in the crude oil is lower than 0.5 mg∙g-1, it can be processed without risk for the refinery, although as described by Barth et al., there are some exceptions to this rule [36]. The untreated crude oil had a TAN of 1.6 mg KOH∙g-1, and the hydrotreated oil had an average TAN of 0.75 mg KOH∙g-1. The measurements indicate the amount of KOH required for neutralizing the acids present in the sample.

The TBN presented a similar tendency when compared with the TAN values. TBN confirmed a low

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acidity in the treated sample of crude oil. The TBN also decreased after the catalytic treatment, and

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there was a good correlation between the TAN and TBN. The results suggest that the acid-base

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equilibrium can be important for the observed oil acidity; however, the specific identification of the functional groups that contribute to the acidity is still required to evaluate the performance of the

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conjugated acids and bases related to the measured acidity and basicity of the oil.

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4.2 Effects on the viscosity and API gravity

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Table 3 shows that after the reaction using the liquid Ni-Mo catalyst, the API gravity of the products increased from 12 (for the feedstock) to 15-22 for the products due to the hydrocracking, hydrogenating

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and hydrotreating reactions that took place in the reactor. As a consequence, the kinematic viscosity was reduced from 4883 to 120-164 cSt at 25 °C as a result of lower molecular weight structures. Likewise, it was observed that by increasing either the residence time (30, 60 and 90 min) or the

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temperature (350, 390 and 400 °C), the quality of products was improved with respect to the initial

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heavy crude oil, which is in agreement with Al-Marshed et al. who used similar techniques [37].

4.3 Effect on the composition of the heavy oil By SARA analysis, it was possible to determine the saturate, aromatic, resin and asphaltene contents from the untreated heavy crude oil (Table 3). It was found that the untreated sample presented the following data: saturates (18 wt.%), aromatics (26 wt.%), resins (34 wt.%) and asphaltenes (26 wt. %). Once the reaction took place, an increment in the saturated and aromatic hydrocarbons was observed

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due to the hydrogenation, hydrocracking and hydrotreating reactions undergone by the compounds present in the feedstock, which is in good agreement with previous reports [38]. The obtained SARA values indicate an upgrading effect with an increasing in: a) the reaction time and b) reaction temperature by using the liquid Ni-Mo catalyst. Moreover, by a closer analysis of the results, it can be observed that the reaction temperature exerted a higher effect on the composition, favoring the

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formation of aromatic and saturated compounds at the expense of asphaltenes and resins instead of that of the reaction time, however, the coke production increased with the reaction temperature.

4.4 Effect of the catalyst on the sulfur and nitrogen content of the products.

The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions are exothermic and not

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severely thermodynamically limited and in general, the equilibrium constant of both reactions decreases with the temperature increase. Nitrogen removal requires the hydrogenation of the ring containing the

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nitrogen atom before hydrogenolysis can occur while sulfur removal can proceed by two different

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routes, namely hydrogenation and direct desulfurization. Hydrodesulfurization reactions are essentially

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irreversible and can proceed to completion if hydrogen is present in a stoichiometric amount. [39-40]. The results of this section are shown in Table 3. Regarding sulfur, when using the liquid Ni-Mo catalyst,

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it was observed that when the reaction time was increased from 30 to 90 min, the sulfur removal was

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also increased from 28.9 to 35.6 wt. %, respectively while when the temperature reaction was increased, the removal of sulfur compounds was increased reaching 44.2 wt.%. As expected, the reaction

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temperature effect on the HDS and HDN activity was more important than the one observed with the reaction time. The maximal HDS and HDN removal percentages obtained at 400°C and 60 min of

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reaction were 44.2 and 47.7 wt. %, respectively whereas at 90 min and 350°C, the removal of sulfur compounds reached 35.6 wt. % while the elimination of nitrogen compounds was about 45.2 wt. %. Due to the high nickel percentage in the catalyst, high denitrogenation activity was expected. It was

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found that the Co-Mo sulfide is the preferred combination for the HDS processes and the Ni-Mo sulfide yields excellent HDN and hydrogenation performances, but also, wider applications could be found due to the high tolerance toward H2S and NH3, which are inevitable poisons produced during hydrotreating operations [41, 42]. These last results show that the hydrotreating activity was favored by the temperature increase and these changes are related to the conversion of resins and asphaltenes. 10

The catalyst presented better hydrogenation behavior and relatively low coke formation in all cases. Similar results have been reported in the literature and are included in Table 3 [43]. 4.5 Chromatographic SIMDI To get an insight into the composition of the products, a series of simulated distillation (SIMDI) analysis was carried out to verify the changes in the products obtained after reaction. [44] The results show

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(Table 4) an improvement in the quality of the products depending on the reaction time. The increments related to the feed in the gasoline and diesel products were 8 and 14 wt.%, respectively, with 90 min of reaction time and 350°C. On the other hand, when the reaction temperature was increased, the amount of gasoline related to the feedstock decreased by 1 wt.% and diesel increased in 16 wt. %. The test was carried out to confirm the improvement of the products by the distillation curves (Figure 6).

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4.6 ASTM-D86 Distillation for Hydrotreated Crude oil obtained at 623K for recovering Fuels

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In order to find out if some amount of nickel was present in the products, a distillation experiment [ASTM-D86] using the product obtained at 350 °C was carried out. Samples of gasoline, diesel and

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residue fractions were examined (Table 5). Nickel in these samples was analyzed using atomic

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absorption spectroscopy. The gasoline and diesel obtained by distillation presented very low nickel contents of 0.06 and 0.98 wt-ppm, respectively while the molybdenum amount was nil. Therefore, the

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use of a liquid Ni-Mo catalyst will not generate problems when using the products of this technology

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for combustion purposes. Thus, this technology will not damage any of the mechanical components or the fuel engine and will not be hazardous for the catalytic converter in transportation vehicles (just to mention an application). However, a high amount of nickel was found in the residue fraction, where a

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value of 3,656 wt-ppm was obtained.

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5. - Discussion

A liquid Ni-Mo catalyst was prepared, which was put in contact with oil in a batch reactor and the

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sulfhydration step was carried out during the reaction. From the XRD pattern, the presence of the binary transition-metal catalyst obtained at the end of the sulfiding reaction is evident. These findings were corroborated with the HRTEM technique by the presence of the basal planes attributed to nickel and molybdenum sulfide nanoparticles. In spite of the results obtained by the thermogravimetric analysis that show the feasibility of synthesizing a bimetallic Ni-Mo phase, the final obtained catalyst displayed monometallic sulfide combinations. It is assumed that the acid function required for promoting the

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breaking of the hydrocarbon chain (hydrocracking reactions) can be found in the phosphoric acid used in the preparation step of the catalyst as well as in the TAN exhibited by the crude oil. The results obtained after the reaction show that the breaking of complex hydrocarbons took place because saturated and aromatic compounds were increased in the products at the expense of asphaltenes and resins. In general, due to the fact that the hydrocracking and hydrotreating reactions used the same

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metal active phases for breaking hydrocarbon chains, it can be expected that nitrogen and sulfur heteroatoms were also broken during the reactions.

Accordingly, the reaction was evaluated using similar conditions to those used in the hydrotreating of heavy crude oil in the presence of hydrogen and active metals. Since desulfurization depends on the type of involved carbon-sulfur bonds and alkyl sulfide compounds have weak carbon-sulfur bonds, it was expected that they could react rapidly and completely under hydroprocessing conditions. It is known that the disappearance rates of thiophene type compounds with increasing numbers of aromatic

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rings decrease while nonthiophenic aromatic sulfur compounds react more quickly than

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dibenzothiophenes, and due to the inherent difficulty of the alkyl substituted dibenzothiophenes for

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reacting, it is clear that they persist in the hydrotreated products. As for hydrodesulfuration, it can proceed via two pathways; the first one is hydrogenolysis in which both carbon-sulfur bonds are

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replaced by carbon-hydrogen bonds, which lead to ring opening; in the second one, hydrogenation can occur initially and then, the intermediate product undergoes a hydrogenolysis step [45-47]. The

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predominant HDN pathway proceeds via the breaking of the C (sp3) bond. On the other hand,

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hydrocracking can proceed via the carbenium ion formation, which can be explained by the acid character exhibited by the liquid Ni-Mo catalyst, which promotes the ion formation and the metal sites

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take part in the hydrogenation-dehydrogenation reactions. However, more experiments need to be done

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to propose a reaction mechanism.

6. - Conclusions

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This work presents a new route for upgrading crude oil using a liquid Ni-Mo catalyst. Experiments were carried out using a bench-scale reactor. The results show that from a heavy feedstock, it is possible to obtain hydrotreated crude oil with higher API gravity and lower kinematic viscosity, sulfur, nitrogen, resin and asphaltene contents. From simulated distillation, a residue fraction decrease from 7 to 22 wt. % (>538 °C) was observed by using the liquid Ni-Mo catalyst. The increase in reaction times and temperature exerted an improved effect on the products. It is important to mention that after treatment,

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properties like API gravity and viscosity were enhanced while the acidity and basicity decreased; therefore, the ability to flow without damaging the pipelines was improved. In addition, relatively low

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economic costs and wider applications could be foreseen.

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Acknowledgements The authors are grateful for the financial support by the SENER-Hydrocarbon Fund provided by

A

CONACYT and acknowledge the Mexican Petroleum Institute for the permission granted to publish this work.

16

Table 1. Effect of the temperature on the density and viscosity of the aqueous catalyst.

Dynamic Viscosity

[C]

[mPa∙s]

20

4.35

30

3.72

40

3.22

50

2.50

60

1.96

70

1.61

80

1.34

90

1.22

[g∙cm-3] 1.3310 1.3284 1.3257 1.3200

U

1.3137

N

A M D TE EP CC A

17

Density

SC RI PT

Temperature

1.3070 1.2990 1.2880

Table 2. Total acid number (TAN) and total basic number (TBN).

TBN mg /g

Heavy oil

1.6

3.38

Test 1a

0.75

Test 2b

0.75

Test 3c

0.76

SC RI PT

TAN mg /g

2.64 2.76 2.77

9.8 MPa, 350 °C, 30 min 9.8 MPa, 350 °C, 60 min 9.8 MPa, 350 °C, 90 min

A

CC

EP

TE

D

M

A

N

U

a. b. c.

Sample

18

Table 3. Physical and chemical properties of the feedstock and products obtained after reaction

Properties

Crude oil

Test 1

Test 2

SC RI PT

with the aqueous catalyst

Test 3

Test 4

Test 5

Rohallah

Hashemi [15]

30

60

90

60

60

120

Temperature, C

350

350

350

390

400

340

Pressure, MPa

9.8

9.8

9.8

9.8

9.8

6.9

12.5

15

17

18

19

22

17

15 °C

13,490

190.2

135.8

125.7

103

72

---

25 °C

4,883

120.7

90

69

82

64

---

37.8 °C

1,550

73.1

40

55

49

75

Total Sulfur, wt. %

5.56

3.97

3.71

3.58

3.6

3.1

3.3

Total Nitrogen, ppm

750

438

425

411

401

392

225

0.5

1.0

1.2

2

4

3.0

29.1

28.9

30.7

30.2

33.58

17.2

10.9

13.1

12.7

---

Coke, wt. % 18

Resins

34

N

D

Saturates

12.6

Aromatics

22

40.1

45.7

46.9

44.9

57.6

---

Asphaltenes

26

13.6

12.7

11.5

11.8

11.4

---

TE

SARA, wt. %

55.6

A

Viscosity, cSt

M

API gravity

U

Time, min

A

CC

EP

[15] Energy Fuels 2014, 28, 1338−1350

19

Table 4. Distribution of distillate fractions in the hydrotreated crude oil

Fractions Temp. °C Crude oil

Test 1

Test 2

Test 3

Test 4

Test 5

13

17

18

24

21

25

28

37

34

35

25

23

100

100

100

Gasoline

<221

8

11

13

Diesel

221-343

15

16

16

343-538

29

33

30

Residue

>538

48

40

41

Total

-

100

100

100

Heavy

A

CC

EP

TE

D

M

A

N

U

Gas Oil

SC RI PT

(wt. %)

20

Table 5. Impact of nickel content on the improved crude oil fractions

Boiling Point, C

Nickel (wt-ppm)

Molybdenum (wt-ppm)

Gasoline

<221

0.06

Not detected

Diesel

<343

0.98

Residue

>538

3,656

A

CC

EP

TE

D

M

A

N

U

SC RI PT

Crude oil Fractions

21

0.04 65

Figure captions

Figure 1. DTA/TGA curve of the aqueous Ni-Mo catalyst in nitrogen atmosphere. Figure 2. X-ray diffraction of the Ni-Mo catalyst after reaction.

NiS,

Ni7S6,

Mo2S3,

MoO3

Figure 3. Distribution of acid sites by pyridine thermo programmed desorption.

SC RI PT

Figure 4. Neutralization profile of the Ni-Mo catalyst.

Figure 5. a) SEM and b) HRTEM images of the aqueous Ni-Mo catalyst.

A

CC

EP

TE

D

M

A

N

U

Figure 6. Simulated distillation of heavy oil and the hydrotreating product.

22

D

TE

EP

CC

A

SC RI PT

U

N

A

M

Figure 1.

23

D

TE

EP

CC

A

SC RI PT

U

N

A

M

Figure 2.

24

D

TE

EP

CC

A

SC RI PT

U

N

A

M

Figure 3.

25

D

TE

EP

CC

A Figure 4.

26

SC RI PT

U

N

A

M

D

TE

EP

CC

A

SC RI PT

U

N

A

M

5A

Figure 5.

27

5B

. 800 Crude Oil Test 1 Test 2 Test 3 Test 4 Test 5

600

SC RI PT

Boiling Point Distribution (C)

700

500 400 300 200

U

100

10

20

30

40

50

M A

CC

EP

TE

D

Figure 6

60

70

Mass Recovery (%)

A

0

N

0

28

80

90

100