Transition metal nanocatalysts by modified inverse ...

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Transition metal nanocatalysts by modified inverse microemulsion for the heavy crude oil upgrading at reservoir ⁎

M. Lam-Maldonadoa, J.A. Melo-Bandaa, , D. Macias-Ferrera, B. Portales-Martínezb, J.M. Dominguezc, R. Silva-Rodrigoa, U. Páramo-Garcíaa, J.M. Mata-Padillad a

Centro de Investigación en Petroquímica, Instituto Tecnológico de Cd. Madero, Cd. Madero, Tamaulipas, 89440, Mexico CONACYT-Instituto Mexicano del Petróleo, San Bartolo Atepehuacan, Ciudad de México, 07730, Mexico c Instituto Mexicano del Petróleo, San Bartolo Atepehuacan, Ciudad de México, 07730, Mexico d CONACYT-Centro de Investigación en Química Aplicada, Saltillo, Coahuila, 25294, Mexico b

A R T I C LE I N FO

A B S T R A C T

Keywords: Modified inverse microemulsion method Nickel Molybdenum Iron Nanoparticles

In this work, nanocatalysts as Ni, Mo, Fe nanoparticles (NPs) were synthesized by the modified inverse microemulsion method at room temperature conditions in order to apply them to heavy crude oil (HCO) in situ hydroprocessing and to improve their physicochemical properties. All samples of NPs were characterized by Xray photoelectron emission spectroscopy (XPS), X-ray energy dispersion spectroscopy (EDX), small-angle X-ray scattering (SAXS), and scanning transmission electron microscopy (STEM). Catalytic evaluation of nanocatalysts was performed in a batch reactor at 372 °C, 9.8 MPa of initial H2 pressure and 1 h of reaction time. The reaction products were studied by analysis of saturates, aromatics, resins, and asphaltenes (SARA) fractions, simulated distillation (SIMDIS), API gravity, and both nitrogen and sulfur contents to determine their physicochemical properties. Applied techniques revealed that nanoparticles of Ni, Mo, and Fe with spherical morphology with average sizes in the range (2.5–20) nm and agglomerates smaller than 50 nm were obtained. The nanocatalysts synthesized improved from 13 to 18°API, also of an asphaltenes conversion in the range 20–43%, and moderate sulfur and nitrogen removal were obtained. SARA analysis indicated that saturated and aromatics fractions increased while resins and asphaltenes were reduced, increasing the possibility of a high mobility of crude oil into the reservoir.

1. Introduction Nanocatalysts are one of the most important examples of nanotechnology applications, nanoscale size, shape and an exceptionally high surface area. Due to their structural, electronic, and other specific properties of nanomaterials depend on its size and structure at the atomic level [1]. Different methods have been developed for the preparation of nanoparticles such as the polyol process [2], chemical reactions in an aqueous solution [3,4], sonochemical [5], and microemulsion method [6]. The microemulsion process, also known as the micellar reverse method, is a versatile way that allows the control of the nanoparticles size achieving narrow size distribution [7]. Microemulsions (MEs) are isotropic multicomponent fluids consisting of water, oil and amphiphilic surfactants. Classification of the types of MEs such as oil-in-water (O/W), water-in-oil (W/O), and intermediate bicontinuous are according to the amount of surfactant, cosurfactant, continuous phase and water [8]. The characteristic properties of MEs are a thermodynamic stability, spontaneous formation, ⁎

optically transparent appearance, high interfacial area, high solubility capability and low viscosity [9]. Some advantages of the inverse micellar microemulsion technique are that the metal particles are directly reduced the in situ microemulsion process and it can be used as a suspension catalyst without promoting the thermal treatment [10]. Ag, Cu, Cd, Co, Ni, and Au monometallic NPs and Pt-Ru bimetallic NPs with a size about 5–50 nm were synthesized using an inorganic phase in W/O microemulsión. The factors such as the nature of the stabilizer emulsifier, additives, and the colloidal stability of microemulsion droplets played an important role in the dispersion and size of the nanoparticles [11–13]. Cerium nanoparticles have been synthesized by the inverse microemulsion method, changing the water-surfactant molar ratio (Rw). The diameters of cerium nitrate in the inverse microemulsión, and the particles obtained as a result of this process before and after the addition of ammonia were evaluated by dynamic light scattering (DLS), and SAXS showed similar nanoparticle sizes [14]. Fe2O3 nanoparticles with a size about 50 nm by W/O microemulsion method was the result of

Corresponding author. E-mail address: [email protected] (J.A. Melo-Banda).

https://doi.org/10.1016/j.cattod.2018.05.052 Received 12 December 2017; Received in revised form 20 April 2018; Accepted 23 May 2018 0920-5861/ © 2018 Elsevier B.V. All rights reserved.

Please cite this article as: Lam-Maldonado, M., Catalysis Today (2018), https://doi.org/10.1016/j.cattod.2018.05.052


M. Lam-Maldonado et al.

“micelles with metals-green color” (top), and aqueous phase (bottom). The oil phase was separated which contains the metal nanoparticles in the micelles. Finally, the toluene of oil phase containing the nanoparticles was recovered, obtaining a “gel” that contains the nanoparticles. Similar procedures were applied for Fe and Mo microemulsions.

using AOT as a surfactant and n-heptane as a continuous phase [15]. MnFe2O4 nanoparticles (4–15 nm) were synthesized by the inverse micelle method using sodium dodecylbenzenesulfonate as a surfactant [16]. WS2 nanocatalysts were studied for hydrocracking reaction revealing that the average particle size is an essential factor in the efficiency of this reaction [17]. Unsupported Me/MoS2 catalysts (Me = Co, Ni, Fe) were applied in hydrotreating reactions of dibenzothiophene (DBT) and furfurylamine (FA). In this case, the activation of catalysts was realized under a mixture H2S/H2 (20% v/v) at 400 °C where Ni/ MoS2 catalyst showed a better catalytic performance [18]. Fe3(CO)12 was applied in extra-heavy crude oil to reduce the viscosity and the sulfur content. In this process, methane was used as a source of hydrogen producing in situ active phases such as mixed sulfide species (FeS and Fe-V) in the coke [19]. Gases such as CH4/H2, NH4, and H2S/ H2 were applied to active Ni-Mo carbide, nitride and sulfide catalysts supported on γ-Al2O3. The sulfide catalyst showed a great activity for HDN and HDS of heavy gas oil and light gas oil followed by carbide and nitride catalysts [20]. The principal goal of this work is the design of Ni, Mo and Fe nanoparticles with an average particle size less than 100 nm. These were synthesized by the inverse micellar methodology using water in oil (W/ O) microemulsions, sodium dodecylbenzenesulfonate as a surfactant, toluene as a continuous phase, sodium borohydride as a reducing agent and citric acid as a dispersing agent. The nanocatalysts were applied to heavy crude oil (HCO) in situ hydroprocessing and to upgrade their physicochemical properties in the reservoir.

2.3. Materials characterization To obtain the information regarding the chemical nature of the species, a small ME sample with the content of metal nanoparticles was mixed with methanol and centrifuged at 6000 rpm. Toluene and methanol were recovered and the resulting precipitate of metals and other species was added methanol over and over again and it was centrifuged. Then, the recovered precipitate was dried at 80 °C, and it was analyzed by X-ray photoelectron spectroscopy (XPS) using a SPECS apparatus with an aluminum anode (hv = 1 486.71 eV) as an X-ray source. The sample was treated for 3 h with a vacuum pressure of 1 × 10−9 Torr. The shape and size of the nanoparticles were obtained by SAXS with the SAXSess mc2 equipment from Anton Parr, using Cu-Kα radiation (λ = 0.1542 nm). And finally, the samples were added to a sealed 2mm quartz capillary tube at 25 °C. In the present work, results regarding SAXS profiles, gyration radius (RG), homogeneous spheres radii (Rh), pair distance distribution functions (PDDFs), and sphere size distribution (r) are shown. Scanning transmission electron microscopy (STEM) images in bright-field and X-ray energy dispersion spectroscopy (EDS) spectra were obtained with a field emission scanning electron microscope JSM-7600 F from JEOL and EDS detector from Oxford Instruments operated at 30 keV in TED mode. For the preparation of the microscopy samples, a small ME sample was centrifuged at 6000 rpm and the precipitate was washed with toluene, removing the solvent. Then, a second washing was performed with chloroform and methanol (1:1), and finally, the sample was deposited on a copper grid, followed by a drying process at room temperature. The particle size distribution (PSD) was carried out by a count of about 100 particles.

2. Experimental 2.1. Chemicals Nickel (II) nitrate hexahydrate (Ni(NO3)2·6H2O, 99.999%), iron (III) nitrate nonahydrate (Fe(NO3)3·9H2O, 99.99%), ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O, 99.98%), sodium borohydride (NaBH4, 99%), 1-hexanol (C6H14O, > 99%), sodium dodecyl-benzenesulfonate (C18H29NaO3S, technical grade) were purchased from SigmaAldrich. Citric acid (C6H8O7, 99.5%) and toluene (C6H5CH3, 99.5%) were supplied by Fermont. Ultrapure water (15 MΩ cm−1) was produced by Purelab Option Station.

2.4. Evaluation of catalytic activity Heavy crude oil (HCO), which has 13.1° API and 32.5 C5-asphaltene % wt loading, was used in reaction tests where the properties of HCO are presented in Table 1. The activity tests were carried out using a 100 mL batch-type autoclave reactor from Anton Parr Instrument in order to emulate reactions on the reservoir where 65 g of heavy crude oil were mixed with a gel containing 0.3 g of metal. Before each experimental test, the reactor was purged with H2 two times to remove air. The hydrogen pressure was increased to 9.8 MPa, and the reactor was heated until the reaction temperature of 372 °C at a ramp rate of 24 °C/h. When temperature and pressure were reached, the reaction started with stirring at 1000 rpm and the reaction time was 1 h. Physical and chemical properties of the feed and products were characterized according to the ASTM methods. API gravity was measured using the ASTM D 1298 method, and SARA (saturates, aromatics, resins, and asphaltenes) analysis were determined by ASTM method D4124. Sulfur and nitrogen contents were studied on Perkin-Elmer 2400 elemental analyzer. The fractional analysis of samples were performed by the simulated distillation (SIMDIS) using a gas chromatography analysis (7890A, Agilent Technologies), following the ASTM method D7169. The liquid products were classified as unconverted residue (538 °C+), vacuum gas oil (VGO; 343–538 °C), distillates (204–343 °C), naphtha (IBP-204 °C) according to the boiling point range in SIMDIS analysis in the literature reported [21].

2.2. Synthesis of nanoparticles by the modified inverse microemulsion method (MIMM) The synthesis procedure consisted of mixing two solutions (a) and (b) as shown in Fig. 1. Previous tests were done with different amounts of water, surfactant, co-surfactant and continuous phase. Concluding that 15 ml of water were the optimum amount to achieve the microemulsion stability, and along with the citric acid amount was controlled the particle size and dispersion. For the MEs, solution (a) had a total molar ratio (TM) of Metal Total:NaBH4:C6H8O7 was 1:1:0.5 respectively. For the preparation of solution (b), sodium dodecylbenzenesulfonate (SDBS, C18H29NaO3S) and 1-hexanol (C6H14O) were dissolved in toluene (C6H5CH3), where the weight total ratio of surfactant SDBS:1-hexanol:toluene was 1:0.5:7 respectively. The synthesis of Ni ME started with the preparation of solution (a) stirring nickel (II) nitrate and 10 g of water for 10 min. Then, citric acid (C6H8O7) was added to obtain a better metal dispersion, stirring the mixture for 45 min. After this time, sodium borohydride (NaBH4) was dissolved in 5 g of H2O and finally, it was added dropwise (slowly) to the mixture with a stir for 30 min. The inverse micelles were formed by the addition of the solution (a) with an aqueous-metallic content to the solution (b) with the oil phase, surfactant, and co-surfactant content. The mixture was vigorously stirred for 120 min, but after the first 30 min, the temperature increased to 50 °C, which was kept until the reaction finished. The mixture was aging 48 h, after this, it was observed two phases: oil phase 2



Fig. 1. Synthesis for the preparation of Fe, Ni, and Mo nanoparticles.

by Fourier inversion of the scattering curve is shown in the following equation:

Table 1 Heavy crude oil physical-chemical properties before reaction test. Property

Value

Viscosity @ 25 °C/[cP] API gravity/[°] Saturated/[wt. %] Aromatics/[wt. %] Resins/[wt. %] Asphaltenes/[wt. %] S/[wt. %] N/[ppm]

9691 13.1 15.5 21.5 30.5 32.5 6.0 4687

P(r) =

3.1. SAXS analysis In order to obtain information about the size and morphology of the particles presented in ME, SAXS technique was used, which is suitable to characterize systems with high surfactant contents [14]. The present analysis shows the SAXS profiles, gyration radius (RG), homogeneous spheres radii (Rh), pair distance distribution functions (PDDFs) and sphere size distribution (r). When the nanoparticles assumed a spherical shape, the SAXS results achieve a good fitting according to Guinier approximation model, which involves the gyration radius (RG) related to scattering intensity I(q) given by:

I(q) =

∫0

∞

I(q)(qr)sin(qr)dq

(1)

Where q is the scattering vector, V scattering volume and RG gyration radius [22]. When assuming spherical particles, the average radius of the particles can be calculated from the radius of gyration by the formula:

Rh =

5 RG 3

(3)

In the present work, the P(r) curves were obtained using the software GIFT®. It has been reported that the PDDF for homogeneous spheres shows a symmetrically shaped peak whereas the PDDF is asymmetrical for cylindrical and laminar particles. In the case of nonhomogeneous particles (Core-Shell), the PDDF varies according to the contrast difference of the electronic densities, where the contrast of some regions gives as a result negative the contributions for p(r) [23]. In addition, if the shell is thin the PDDF shows a behavior like as a homogeneous sphere [24]. Fig. 2 shows the SAXS profiles of Ni, Mo and Fe systems, which were obtained through the scattering profile difference of the MEs with the solvent. It can be observed that the slope tendency is adjusted to a spherical structure [23]. It is notable that the Ni system began with a higher intensity in its dispersion profile in

3. Results and discussion

2 2 ⎛ q RG ⎞ ⎜− 3 ⎟ 2 2 q V exp⎝ ⎠

1 2π2

(2)

The information about the shape of the particles through the curves P(r) known as pair distance distribution functions (PDDF) are obtained

Fig. 2. SAXS profiles of Ni, Mo, and Fe nanoparticles. 3



long surfactant chains tend to be flexible being interlacing and bend among them, and the thickness of the external shell (ts) of the aggregate is very thin (Fig. S1(d)), where the electronic density differences between the surfactant and continuous phase are negligible. Due to that, a high quantity of the continuous phase is soaked in the shell (formed by surfactant chains) [24], causing that there is not manifestation the shell in the PDDFs, hence, the obtained information was of a cluster’s core dc (formed by small nanoparticles). Ni system also presents a bimodal sphere size distribution (Fig. S4(a)) showing a great number of nanoparticles with an average diameter about 12 nm, a value closes to that obtained by the Guinier's model.

Table 2 Measurements by SAXS technique for the Ni, Mo, and Fe. Sample

RG (nm)

Rh (nm)

Diameter (nm)

Guinier

PDDF

Peak 1

Peak 2

3.32 (7.62)a 20.20 3.35 (6.15)a 3.20 (5.90)a

–

–

11.90 1.20

18.90 3.24

1

3.04

MS

1.45 ± 0.11

1.87 ± 0.11

3.74 ± 0.11

Ni Mo

5.70 ± 0.01 1.67 ± 0.14

7.36 ± 0.01 2.15 ± 0.37

14.72 ± 0.01 4.30 ± 0.37

Fe

1.48 ± 0.16

1.91 ± 0.13

3.82 ± 0.13

a

Sphere size distribution (nm)

3.2. XPS spectroscopy X-ray photoelectron spectroscopy (XPS) is a versatile surface analysis technique that can be used to evaluate the chemical composition and to determine chemical states. The XPS spectra of some chemical states of the transition metals in Fe, Mo and Ni nanocatalysts are shown in Fig. 3. The Ni nanocatalysts showed a peak at 858.1 eV corresponds to Ni(°) and photoelectron satellite line 2p3/2 sat, which associated with chemical compound Ni [25]. Furthermore, species Ni(II) (2p3/2 sat), Ni(0) (2p1/2 sat), and Ni(II) (2p1/2 sat) were found at 861.7, 874.9 and 881.8 eV associated to chemical compounds Ni(OH)2 [26], Ni [27] and NiO [28] respectively. Fe nanocatalysts presented species Fe(II) (2p3/2) and Fe(III) (2p1/2) at 713.6 and 726.1 eV associated with chemical compounds FeS [29] and Fe2O3 [30] respectively. While Mo nanocatalyst showed species Mo(VI) (3d5/2) at 233.6 eV associated to chemical compounds MoO3 [31]. The presence of oxygen for the three nanocatalysts are detected in the binding energies 532.9 and 537.4 eV attributed to photoelectron line 1s of O. The first peak (532.4 ± 0.5 eV) is related with double bond present in a chemical environment of carboxylic groups (O = C–O) [32], the second peak (537.6 ± 0.5 eV) with lower intensity is assigned to the oxygen in a chemical environment presents in metallic oxides (M2On) [33]. Carbon species present in Ni and Mo show two peaks, the first one at 285.9 ± 0.3 eV, which is attributed to the single carbon-carbon (sp3) bonds [34,35] that are possibly present in the SDBS surfactant chain. And the second one at 289.3 ± 3 eV corresponds to the carbon atoms present in the carboxylic groups [36]. In Fe nanocatalyst, the peak centered at 284.6 eV was identified for C 1s. Identified sulfur, oxygen and carbon species were attributed to the surfactant sodium dodecylbenzenesulfonate.

Shell diameter when the particle is a core-shell system.

opposition to Mo and Fe systems, which showed oscillations with less amplitude. This fact may be due to an important difference in the average sizes of nanoparticles between the Ni system and the Mo and Fe systems. Table 2 shows the gyration radius, average radius, diameters according to Guinier model and PDDF and the values of sphere size distributions of the nanoparticles of Ni, Mo, and Fe. In the present work, the SAXS measurement was performed directly in the microemulsion with and without metals. The micellar solution (MS) presented a PDDF characteristic of a core-shell particle (nonhomogeneous), where a nucleus with 3.32 nm in diameter is shown, which corresponds to the water drop and a shell of 7.62 nm formed by surfactant chains. Core-shell representation of MS is observed in Fig. S1(a) and the PDDF in Fig. S2. According to Guinier’s model, the MEs based on Mo and Fe shown spherical nanoparticles with 4.30 ± 0.37 and 3.82 ± 0.13 nm in average diameter respectively, however a thorough analysis reveals that according with the PDDF’s profiles of Mo ME (Fig. S3(b)) and Fe ME (Fig. S3(c)) shown the existence of core-shell systems whose configuration in Fig. S1(b) is illustrated, where the core is represented by the metals (M) and the shell by the surfactant chains. According to pair-distance distribution functions, the metallic average diameter evaluated for Mo ME and Fe ME were 3.35 and 3.20 nm respectively. Furthermore, a bimodal sphere size distribution for these systems reveals that the largest of the peaks for Mo system (Fig. 4S(b)) corresponding to 3.24 nm, while to the Fe system, 3.04 nm (Fig. S4(c)) in accordance with PDDF diameters evaluated. Moreover, according to Guinier’s model, the Ni ME has spherical nanoparticles with 14.72 ± 0.01 nm in average diameter and with respect to PDDF, 20.2 nm. However, after applying a deconvolution process the peak of its PDDF profile (Fig. S2(a)) reveals the presence of particle aggregates [23] as shown in Fig. S1(c). It could deduce that the aggregates are formed by several smaller particles, where the shell of the small nanoparticles are very thin and they are found among themselves. The

3.3. EDS and STEM analysis EDS technique was applied in order to determine the average chemical composition of nanocatalysts using XMAX detector from Oxford Instruments. The EDS spectra of Ni, Fe, and Mo in Fig. 4 are illustrated and the analysis results in wt% are shown in Table 3.

Fig. 3. XPS spectra of a) Ni, b) Mo, and c) Fe nanocatalysts. 4



Fig. 4. EDS spectra of Ni, Fe, and Mo nanocatalysts.

A statistical analysis of histograms obtained using the Shapiro-Wilk normality test at 0.05 level reveals that all particle size distributions were not significantly drawn from a normally distributed population, which explain the tendency toward bimodal distribution according to sphere size distribution obtained in SAXS analysis.

Table 3 Average chemical composition of Ni, Fe and Mo nanocatalysts. Sample

Ni Fe Mo

EDS (wt%) Ni

Fe

Mo

C

O

Na

S

33.48 0.0 0.0

0.0 37.17 0.0

0.0 0.0 38.66

33.26 34.42 33.45

22.32 11.99 19.93

3.69 5.62 7.96

7.25 10.80 0.0

3.4. Catalytic activity for hydroprocessing of heavy crude oil (HCO) The type of reaction inside the reactor can be followed monitoring the change of pressure. For the hydrocracking reactions in autoclave reactor, the increased overall pressure during the reaction time implies gas formation, which progresses the decomposition by via terminalchain of heavy crude oil. Furthermore, an overall pressure decrease implies that the gasification is comparatively suppressed, and the hydrogen uptake is promoted to produce hydrocracking liquid components [37,38]. The variation of reactor pressure versus reaction time of Ni, Fe and Mo nanocatalysts is shown in Fig. 6. In Fig. 6, it can observe that when the temperature increases the hydroprocessing reaction starts between 240 and 372 °C. Fe nanocatalyst showed that the pressure slightly increased about 240 °C keeping until 372 °C, afterward, reactor pressure slightly decreased when the time reaction finished. This material presents the greater catalytic activity, improving the properties of the HCO. Ni nanocatalysts showed

In Ni, Fe and Mo nanocatalysts, the presence of their corresponding transition metals and oxygen-related with the formation of metallic oxides of the forms [NimOn], [FemOn] and [MomOn] are evident. Furthermore, the chemical elements such as carbon, sulfur, and sodium are traces probably by the surfactant chains according to XPS analysis. For the case of Fe sample, the observed sulfur is also due to the FeS phase. Fig. 5 shows STEM images at 30 keV for the Ni, Fe and Mo nanocatalysts, and their correspondent particle size distribution (PSD’s). For each case, a set of nanoparticles with spherical shapes (Fig. S1(b)) and aggregates of nanoparticles (Fig. S1(c)) can be observed. The particle size distribution was carried out by a visual count of about 100 particles for each case. For the Ni, Fe and Mo nanocatalysts, the average particle size is centered about at 11.19, 2.86 and 2.98 nm respectively.

Fig. 5. STEM images and PSD’s of nanocatalysts: a) Ni; b) Fe, and c) Mo. 5



Table 4 Results of reactions of HCO through nanocatalysts based on Ni, Fe and Mo. Products

HCO

MS

Ni

Mo

Fe

Gas/[wt %] Naphtha/[wt %] Distillates/[wt %] VGO/[wt %] Residue/[wt %] Saturates/[wt %] Aromatics/[wt %] Resins/[wt %] Asphaltenes/[wt %] (conversion [%]) Sulfur/[wt %] Nitrogen/[ppm] API/[°]

0.0 7.3 12.8 26.1 53.8 15.5 21.5 30.5 32.5

1.9 8.3 12.0 25.8 52.0 18.5 23.5 30.0 28 (13.8)

7.8 5.4 13.1 27.7 46.0 19.6 26.6 28.3 25.5 (21.5)

5.9 6.0 13.7 26.9 47.5 20.0 26.5 28.5 25 (23.0)

4.3 9.5 14.7 28.3 43.2 23.5 35.0 23.0 18.5 (43.0)

6.0 4687.0 13.1

5.0 4280.0 14.0

4.2 3301.0 15.0

4.8 4080.0 16.3

4.3 3266.0 18.5

The quantitative results of hydrocracking reaction using Ni, Mo, and Fe nanocatalysts are presented in Table 4, including quality data of liquid products such as saturates, aromatics, resins, asphaltenes, sulfur content, nitrogen, viscosity, and API gravity. The original content of asphaltenes in the HCO was 32.5 wt %, but after the reaction carried out using the prepared nanomaterials its content was reduced. The efficiency in asphaltene conversion has the following order MS < Ni < Mo < Fe. Fe nanocatalyst was more active in hydrocracking of heavy fractions in the HCO obtained an asphaltene conversion of 43%. On the other hand, this nanocatalyst reached a decreasing in resins about 23% with respect to the weight percent evaluated for HCO (30.5 wt %) achieving also an important increasing in API gravity (18.5° API). The initial sulfur content in HCO was 6.0 wt %, after using MS was obtained 5.0 wt %. The sulfur removal activity of Ni, Fe and Mo nanocatalysts were 30.0, 28.3 and 20% of conversion respectively. Ni y Fe were most active materials in the sulfur removal process. In the case of Ni was produced active phases due to the high amount of sulfur in the HCO (6%), H2S production, the presence of H2 and the high temperature during the operation conditions in the catalytic test. Similar behavior was presented by the Mo catalyst. Moreover, Fe nanocatalysts

Fig. 6. The pressure profiles of Ni, Fe, and Mo nanocatalysts during the reaction.

that the pressure slightly increased along with the reaction time, this catalyst was less active in suppressing the gasification which occurs through reaction producing less liquid fuel. MS and Mo presented similar behavior in the pressure, however, they did not improve the physical-chemical properties of the oil heavy crude. The yields of gas, naphtha, distillates, VGO, and residue generated in the hydrocracking reaction using the prepared nanocatalysts in SIMDIS are shown in Fig. 7. In the absence of the transition metals (using micellar solution MS) the naphtha, distillates, VGO, and residues (liquid components) were 8.3, 12.0, 25.8 and 52.0 wt% respectively. The use of Ni, Mo, Fe nanocatalysts reduced notably the residue in comparison with MS and HCO. The decreased residue has the following order HCO < MS < Mo < Ni < Fe. It is notable that the highest gas yield (7.8 wt%) was obtained using Ni nanocatalyst while the smallest yield (4.3 wt %) was produced by Fe material, due to this material has a particle size smaller and FeS phases.

Fig. 7. The yields of gas, naphtha, distillates, VGO and residue generated in the reaction using Ni, Mo, and Fe nanocatalysts. 6



References

presented representative phases FeS for the hydrodesulfurization [18–20]. The original content of nitrogen in the HCO was 4687 ppm, and after the reaction was 4280 ppm using MS. The nitrogen removal activity using the nanomaterials follows the order Fe > Ni > Mo. Fe nanocatalyst is notably active in the hydrodenitrogenation (HDN) along with hydrodesulfurization (HDS) in the reaction tests. The initial values for API gravity and viscosity for HCO were 13.1°API, and after using MS, 14°API was obtained. The values of API gravity of the liquid products produced using nanomaterials are in the range 15–18.5 °API, which could even fall in a category of heavy crude oil [39]. The performance of the prepared nanocatalysts based on nanoparticles of Ni, Fe, and Mo can be explained by the small metal particles sizes, and active phases presented in the material. This method contributes to the decreasing of asphaltenes, and surface tension of HCO, reducing the viscosity and increasing API gravity. This improvement in the oil crude mobility has an impact for future applications within the reservoir.

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4. Conclusion The method of the inverse microemulsion to obtain Ni, Fe and Mo nanocatalysts offers the advantage to get average particle size less than 20 nm for the Ni, and less than 5 nm for Fe and Mo respectively. The application of nanocatalysts showed an increase in the API gravity, reducing substantially the amount of asphaltenes, and improving the naphtha, and distilled fractions. The iron nanocatalysts was the most active material. Particle size, sulfur phases (FeS) play an important role in the hydrocracking process of HCO. This process has the advantage to improve the oil crude physicochemical properties for future applications in where the HCO would be stationary phase, and the nanocatalyst can promote a better diffusional effect. Acknowledgements Mayda Lam Maldonado gratefully acknowledges a scholarship from to National Council of Science and Technology (210240/201608) and would like to thanks for financial assistance from CONACyT-SENERHYDROCARBONS project (No. 177007) and the National Technological of Mexico/ Technological Institute of Madero City, Center for Research in Petrochemistry, Bays Avenue, Tecnia Industrial Park, Altamira, Tamaulipas, México. David Alejandro Dominguez Vargas from Center of Nanoscience and Nanotechnology (CNyN) of the National Autonomous University of México (UNAM) is gratefully acknowledged for performing XPS measurements. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.cattod.2018.05.052.

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