Method for Converting Demetallization Products into Dispersed Metal

Article pubs.acs.org/EF

Method for Converting Demetallization Products into Dispersed Metal Oxide Nanoparticles in Heavy Oil Amr E. Abdrabo and Maen M. Husein* Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB, Canada T2N 1N4 ABSTRACT: Metallic heteroatoms deactivate expensive catalyst and, thus, should be removed at early stages during crude oil processing. Electro- and biological demetallization are examples of two emerging techniques which remove the metallic heteroatomsmainly nickel and vanadiuminto ions or ionic complexes ultimately residing in the aqueous phase of a twophase water/oil system. This work investigates the conversion of the aqueous metallic species into metal oxide nanoparticles, which are effective upgrading catalysts, dispersed in the oil phase. The conversion step commenced in situ within a water-in-oil emulsion structure, and the resultant nanoparticles remain very well dispersed in the heavy oil phase. The product nanoparticles were characterized, after successful collection from the oil phase, using X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). Despite the complexity of the heavy oil system, results confirmed the in situ formation of NiO and V2O5 nanoparticles with mean sizes of 20 and 15 nm, respectively. Some aggregates have, nevertheless, formed, due to the relatively high temperature requirement of the method. oxide is known to be a good hydrocracking catalyst.15,16 Dispersed nanocatalysts have been reported to effectively enhance upgrading reactions.17 The most common method of preparing bulk V2O5 is the thermal decomposition of ammonium meta vanadate (AMV) according to the following reaction.

1. INTRODUCTION Most crude oils contain different metals with concentrations varying from a few ppm to 1000 ppm depending on the origin of the crude. Examples of these metals are sodium, potassium, lithium, calcium, strontium, copper, silver, vanadium, manganese, tin, lead, cobalt, titanium, gold, chromium, and nickel.1 Nickel and vanadium are the most common metals in heavy crude. They exist in the form of organo-metallic compounds having a porphyrinic structure2 or, to a lesser extent, in the form of naphthenic acid salts.3 Metal porphyrins are oil-soluble and tend to concentrate in the heavy fractions. It is crucial to eliminate the metallic heteroatoms as early as possible during refining and upgrading in order to reduce the environmental impact of oil processing4,5 and protect downstream catalysts from poisoning.6 Although hydro-demetallization is the most widely employed process,2,7 many new techniques have been developed to remove metallic heteroatoms.8 These techniques help overcome the high operating temperature and pressure as well as the high hydrogen demand associated with hydrodemetallization. Even with the technical challenges hindering their field application, the new techniques may serve as an effective predemetallization step leading to an overall cost reduction and prolonging the life cycle of the hydrodemetallization catalyst.1 Among these, electrochemical, microbial, photochemical coupled with liquid−liquid extraction, and oxidative demetallization have shown promising results.1,6,9−13 All of these techniques require the existence of a two phase water/oil system and are based on breaking the metal−carbon bond by oxidation followed by extracting the metal ions into the aqueous phase. The current work takes advantage of the dispersed nature of water pools stabilized by asphaltenes inside a continuous oil phase, which are practically similar to (w/o) microemulsion systems,14 and converts the ionic form of the resultant metal into dispersed metal oxide nanoparticles. Vanadium pentoxide is known to be a good hydrogenation catalyst, while nickel © 2012 American Chemical Society

2NH 4VO3 → V2O5 + 2NH3 + H2O

(R1)

The NH4VO3 precursor provides a very good starting material, since the ions formed upon the dissolution of this compound in water are identical to the ones produced from the different demetallization techniques referred to above. Reaction R1 has been studied by many researchers under atmospheres of air, inert, vacuum, and ammonia, and the effect of reaction temperature and time on the form of the metal oxide product has been detailed.18−21 It was concluded that bulk V2O5 forms upon thermal decomposing of NH4VO3(aq) at 300 °C under an atmosphere of air and 12 h of reaction time. Bulk nickel oxide, on the other hand, can be prepared by the thermal decomposition of nickel nitrate hexahydrate following reaction R2. 1 Ni(NO3)2 ·6H2O → NiO + 6H2O + 2NO2 + O2 2 (R2)

As per literature reports, decomposition took place at 350 °C under atmospheric conditions22 and at 300 °C under N2 atmosphere.23

2. EXPERIMENTAL METHODS 2.1. Chemicals. Ammonium meta vanadate (AMV), NH4VO3 (>99.0%, Sigma Aldrich, ON, Canada), was used as the vanadium precursor, and nickel nitrate hexahydrate, Ni(NO3)2·6H2O (99.99% Received: November 18, 2011 Revised: January 21, 2012 Published: January 23, 2012 810

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Figure 1. XRD pattern of the powders collected from the thermal decomposition of bulk aqueous (a) Ni(NO3)2 and (b) NH4VO3 solutions. bulk aqueous phases.24 A quick visual test showed that the solubility of NH4VO3 in water is approximately 0.085 M at 25 °C. The formation of vanadium oxide was carried out by heating a 25-mL sample of nearly saturated NH4VO3 aqueous solution at 300 °C for 12 h in a furnace (Gravity Convection Oven model DX300, Yamato Scientific America Inc., CA, USA). The formation of nickel oxide followed the same procedure, however, the initial concentration of Ni(NO3)2 was fixed at 3.4 M. The resultant powder was ground and introduced to XRD for characterization. 2.2.2. Formation of Dispersed Metal Oxide Nanoparticles. A volume of 1 mL of the aqueous NH4VO3 precursor or 2 mL of the aqueous Ni(NO3)2 precursor was added to 50 mL of heavy oil composed of 20 wt % Arabian vacuum residue (VR) and 80 wt %

pure, Alfa Aesar, ON, Canada), was used as the nickel precursor. Toluene (BDH 99.8%, VWR International, PA, USA) was used to separate the particles from the heavy oil, while methanol (99.9% pure, Alfa Aesar, MA, USA) was used as the medium to disperse the particles for the electron microscopy imaging. Sodium hydroxide (5.0N, Sigma-Aldrich, MO, USA) was used to adjust the pH. 2.2.1. Particle Formation. Formation of Bulk Metal Oxides. The formation of the dispersed metal oxide nanoparticles in heavy oil started with carrying out reactions R1 and R2 in bulk aqueous systems in order to establish the appropriate conditions for the oxides formation. The importance of the bulk aqueous experiments is better appreciated knowing that, far from the interfacial region, water pools dispersed in a (w/o) microemulsion structure display properties similar to those of 811

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Figure 2. XRD pattern of the powder collected upon thermal decomposition of bulk aqueous NH4VO3 solution adjusted to pH 10 by addition of NaOH. Arabian vacuum gas oil (VGO) followed by vigorous mixing. The amount of the aqueous precursor was limited to volumes that caused no apparent phase separation. A macroscopically single-phase system ensures very fine dispersion of water droplets and, subsequently, product particles. Following the mixing step, the system was placed in a furnace at 300 °C for 12 h. The sample containing the NH4VO3 precursor flashed and self-ignited, even at a low content of NH4VO3 solution. Therefore, the sample was introduced to a PARR reactor (model 4590 Micro Bench Top Reactor, PARR Instrument Company, USA) vented to the atmosphere and was heat treated at 300 °C and 160 rpm for 24 h. It should be noted that when the sample was left for 12 h, V2O3 mainly formed. After the heat treatment, the resultant particles were collected, as detailed below, and characterized using Xray diffraction. Control samples composed of the heavy oil matrix without the precursor salts were heat treated for the same time duration at the same conditions. The product particles were separated by mixing 1 volume of the heavy oil system with 4 volumes of toluene, followed by sonication for 3 h at 40 °C. The sample was then centrifuged for 45 min at 5000 rpm. The solid phase was washed several times with toluene in order to remove adsorbed organics and left to dry in an incubator shaker at 80 °C overnight. It should be noted that no precipitation took place when toluene was mixed with the control samples. 2.3. Particle Characterization. X-ray diffraction patterns of the final powders were collected using Ultima III Multi Purpose Diffraction System (Rigaku Corp., The Woodlands, TX, USA). The instrument employs Cu Kα radiation operating at 40 kV and 44 mA with a θ−2θ goniometer. Each scan used a 2° step size from 0 to 90° with a counting time of 2 s/step. The structure was identified by comparison to spectra in the JADE program, Materials Data XRD Pattern Processing Identification & Quantification. Particle size distribution and elemental analysis of the powder were determined using a Philips Tecni transmission electron microscopy (TEM) (FEI USA Inc., Hillsboro, OR, USA) equipped with 200-kV field emission gun, and an energy dispersive X-ray (EDX) capability. A small amount of the powder was dispersed into 5 mL of methanol and one drop of the methanol dispersion was deposited onto a copper grid covered with carbon and left to dry overnight. Photographs were collected from different locations on the grid using a slow scan CCD camera equipped with Gatan Imaging Filter (GIF).

3. RESULTS AND DISCUSSION 3.1. Bulk Metal Oxides. The XRD results patterns of the powders collected following the thermal decomposition of bulk aqueous Ni(NO3)2 and NH4VO3 are depicted in Figure 1a and b. All the peaks perfectly match the database of the JADE software and confirm the formation of NiO and V2O5. Jorge et al.9 indicated that the aqueous product of the electrochemical demetallization of vanadyl porphyrin is in fact HVO42−, while Shiraishi12 indicated that VO3− is the form of vanadium produced by photochemical demetallization. The form of the vanadium ion in aqueous solutions is heavily dependent on the pH of the solution. For example, VO2+ is the dominant form for pH < 3, VO3− is dominant in a pH range between 6 and 9, HVO42− dominates between pH 9 and 12.5, while VO43− is dominant for pH > 12.5.18,25,26 In case of nickel, Ni2+ is dominant at pH 1.5−7 and NiOH+, Ni(OH)3−, Ni4(OH)44+, and Ni(OH)2 complexes are dominant at pH higher than 7.11,25 The XRD fingerprint of the powder collected upon thermal decomposition of NH4VO3(aq) solution adjusted to pH 10 by addition of NaOH is shown in Figure 2. Comparing Figure 2 patterns with the JADE database indicates that the product powder is majorly composed of V2O5 and V2O3. It should be noted that no sodium salt or oxide could be detected, since the amount of NaOH used to adjust the pH was minor. 3.2. Dispersed Metal Oxides in Heavy Oil Matrix. NiO nanoparticles can be prepared in (w/o) microemulsions starting from the nickel chloride,27−29 nickel nitrate,30,31 or nickel oxalates32 precursors. Even though NiO nanoparticles have been claimed to form,30 it is in fact nanoparticles of an intermediate compound of nickel (e.g., Ni(OH)2) that were precipitated within the microemulsion structure. NiO nanoparticles were prepared ex situ upon further calcination of the intermediate particles following their collection from the (w/o) microemulsions. On the other hand, the formation of V2O5 nanoparticles has not been considered in the literature. To the best of our knowledge, the current study is the first to report on 812

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Figure 3. (a) XRD pattern, (b) TEM photograph, (c) particle size distribution histogram, and (d) EDX spectroscopy for the powder collected from the thermal decomposition of Ni(NO3)2(aq) in heavy oil at 300 °C for 12 h.

The TEM photograph and the particle size distribution histogram show the formation of nanoparticles with 13-nm mean diameter. Large aggregates can also be seen in the TEM image of Figure 4b, which are believed to have resulted from the longer time duration of the heat treatment and TEM preparation step. The mean particle size calculated from the XRD peak at 2θ = 25.88 using Scherrer equation is 25 nm, which is not very different from the value reported by the TEM measurement.

the formation of dispersed nickel and vanadium oxide particles in situ in heavy oil phases. Figure 3a−d shows the XRD, EDX, TEM images, and the particle size distribution histogram of the powders collected following the thermal decomposition of Ni(NO3)2(aq) in heavy oil. The XRD and EDX patterns confirm the formation of NiO. The TEM photographs confirm the formation of nanoparticles of 20-nm mean diameter as well as some aggregates consisting of nanoparticles with clear borders. These aggregates are believed to form during the sample preparation step. The mean particle size calculated from the XRD peak at 2θ = 43.25 using Scherrer equation33 is 10 nm which is in the same order of magnitude as the mean diameter evaluated from the TEM photographs. The distortion appearing in Figure 3a is attributed to some adsorbed material that could not be completely removed by toluene washing. This is also confirmed by the trace elements appearing in the EDX image of Figure 3d. It is worth noting that, while the EDX image indicates the presence of appreciable amount of sulfur, no nickel sulfide formed as confirmed by the XRD patterns of Figure 3a. The XRD, EDX, and TEM images and the particle size distribution histogram of particles collected upon thermal decomposition of NH4VO3(aq) in heavy oil are shown in Figure 4a−d. The XRD results of Figure 4a confirm the formation of V2O5 mainly. Although pH of the NH4VO3(aq) was not adjusted some minor peaks for VO3− also appear.

4. CONCLUSION This work considered converting the aqueous products of electro-, photochemical, and biological demetallization techniques into dispersed nickel and vanadium oxide nanoparticles in heavy oil. Such particles have been reported to have high catalytic activity toward heavy oil upgrading. Thermal decomposition of representative aqueous precursors was employed, and bulk aqueous tests helped identify the temperature and time requirements for the metal oxides formation. XRD, EDX, and TEM results confirmed that the decomposition of Ni(NO3)2(aq) at 300 °C and 12 h, following its intimate dispersion in heavy oil, resulted in the in situ formation of nanoparticles of NiO of 20-nm mean diameter, while the decomposition of intimately dispersed NH4VO3(aq) in heavy oil at 300 °C and 24 h resulted in the in situ formation of dispersed V2O5 nanoparticles with 13-nm mean diameter. 813

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Figure 4. (a) XRD pattern, (b) TEM photograph, (c) particle size distribution histogram, and (d) EDX spectroscopy for the powder collected from the thermal decomposition of NH4VO3(aq) in heavy oil at 300 °C for 24 h.

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(11) Dedeles, G. R.; Abe, A.; Saito, K.; Asano, K.; Saito, K.; Yokota, A.; Tomita, F. J. Biosci. Bioeng. 2000, 90 (5), 515−521. (12) Shiraishi, Y.; Hirai, T.; Komasawa, I. Ind. Eng. Chem. Res. 2000, 39, 1345−1355. (13) Salehizadeh, H.; Mousavi, M.; Hatamipour, S.; Kermanshahi, K. Iran. J. Biotechnol. 2007, 5 (4), 226−231. (14) Nassar, N. N.; Husein, M. M. Fuel Process. Technol. 2010, 91, 164−168. (15) Takahashi, T.; Higashi, H.; Kai, T. Catal. Today 2005, 104, 76− 85. (16) Bartholomew, C. H.; Farrauto, R. J. Fundamentals of Industrial Catalytic Processes; AICHE-Wiley Interscience: Hoboken, NJ, 2008; pp 671−674. (17) Tian, K.; Mohamed, A.; Bhatia, S. Fuel 1998, 77 (11), 1221− 1227. (18) Khulbe, K. C.; Mann, R. S. Can. J. Chem. 1975, 53, 2917−2921. (19) Taniguchai, M.; Ingraham, T. R. Can. J. Chem. 1964, 42, 2467− 2473. (20) Brown, M. E.; Stewart, B. V. J. Therm. Anal. 1970, 2, 287−299. (21) Brown, M. E.; Glasser, L.; Stewart, B. V. J. Therm. Anal. 1974, 6, 529−514. (22) Estellé, J.; Salagre, P.; Cesteros, Y.; Serra, M.; Medina, F.; Sueiras. J. E. Solid State Ionics 2003, 156, 233−243. (23) Brockner, W.; Ehrhardt, C.; Gjikaj, M. Thermochim. Acta 2007, 456, 64−68. (24) Rabie, H. R..; Helou, D.; Weber, M. E.; Vera, J. H. J. Colloid Interface Sci. 1997, 189, 208−215. (25) Larson, J. W. J. Chem. Eng. Data . 1995, 40, 1276−1280. (26) Baes, C. F.; Mesmer, R. E. The Hydrolysis of Cations; WileyInterscience: New York, 1976; pp197−247. (27) Han, D.; Yang, H.; Wang, F. Nanoscience 2006, 11 (2), 146− 149.

AUTHOR INFORMATION

Corresponding Author

*Tel: (403) 220-6691; fax: (403) 282-3945; e-mail: maen. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Alberta Innovates-Technology Futures (AITF) and the Faculty of Graduate Studies, University of Calgary for the Nanotechnology recruitment fellowship awarded to A.A.

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REFERENCES

(1) Ovalles, C.; Rojas, I.; Acevedo, S.; Escobar, G.; Jorge, G.; Gutierrez, L. B.; Rincon, A.; Scharifker, B. Fuel Process. Technol. 1996, 48, 159−172. (2) Agrawal, R.; Wel, J. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 505−514. (3) Valkovic, V. Trace Elements in Petroleum; Petroleum Publishing Company: Tulsa, OK, 1978; pp 40−100. (4) Larbey, R. J. Sci. Total Environ. 1994, 146/147, 19−26. (5) Cohen, D. D.; Gulsonb, B. L.; Davis, J. M.; Stelcer, E.; Garton, D.; Hawas, O.; Taylor, A. Atmos. Environ. 2005, 39, 6885−6896. (6) Gould, K. A. Fuel 1980, 59, 733−736. (7) Leliveld, R. G.; Eijsbouts, S. E. Catal. Today. 2008, 130, 183−189. (8) Ali, M. F.; Saeed, A. Fuel Process. Technol. 2006, 87, 573−584. (9) Jorge, G. A.; Garcia, E.; Scott, C. E. J. Appl. Electrochem. 2002, 32, 569−572. (10) Welter, K.; Salazar, E.; Balladores, Y.; Márquez, O. P.; Márquez, J.; Martínez, Y. Fuel Process. Technol. 2009, 90, 212−221. 814

dx.doi.org/10.1021/ef201819j | Energy Fuels 2012, 26, 810−815

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Article

(28) Han, D. Y.; Yanga, H. Y.; Shen, C. B.; Zhou, X.; Wang, F. H. Powder Technol. 2004, 147, 113−116. (29) Palanisamy, P.; Raichur, A. M. Mater. Sci. Eng., C 2009, 29, 199− 204. (30) Mihaly, M.; Comanescu, A. F.; Rogozea, A. E.; Vasile, E.; Meghea, A. Mater. Res. Bull. 2011, 46, 1746−1753. (31) Bumajdad, A.; Eastoe, J.; Zaki, M. I.; Heenan, R. K.; Pasupulety, L. J. Colloid Interface Sci. 2007, 312, 68−75. (32) Ahmad, T.; Ramanujachary, K. V.; Lofland, S. E.; Ganguli, A. K. Solid State Sci. 2006, 8, 425−430. (33) Gharagozlou, M. Chem. Cent. J. 2011, 5−19.

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