Influence of Asphaltene Aggregation on the Adsorption and Catalytic

Subscriber access provided by UNIVERSITY OF MICHIGAN LIBRARY

Article

Influence of asphaltene aggregation on the adsorption and catalytic behavior of nanoparticles Camilo A Franco, Nashaat N. Nassar, Tatiana Montoya, Marco A Ruíz, and Farid B. Cortés Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 19 Feb 2015 Downloaded from http://pubs.acs.org on February 19, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Influence of asphaltene aggregation on the adsorption and catalytic behavior of nanoparticles Camilo A. Franco1, Nashaat N. Nassar*,2,3, Tatiana Montoya1, Marco A. Ruíz1, Farid B. Cortés*,1 1. Grupo de Investigación en Yacimientos de Hidrocarburos, Facultad de Minas, Universidad Nacional de Colombia Sede Medellín, Kra 80 No. 65-223, Medellín, Colombia. 2. Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada. e-mail: [email protected] 3. Department of Chemical Engineering, An-Najah National University, Nablus, Palestine ABSTRACT This study is a continuation of our previous works on the use of metal-based nanoparticles for the adsorption of asphaltenes and its subsequent catalytic thermal decomposition. In this study, we evaluated the effects of asphaltene aggregation on the adsorption process and the subsequent catalytic oxidation using fumed silica and nanoparticles of NiO and/or PdO supported on fumed silica. Adsorption isotherms were constructed through batch adsorption experiments at 25°C by using mixtures of n-heptane and toluene in amounts of 0, 20 %v/v (heptol 20) and 40 %v/v (heptol 40) of n-heptane to obtain different aggregate sizes of asphaltenes. Subsequently, asphaltene oxidation in the presence and absence of the nanoparticles was carried out in a TGA/FTIR system to investigate the impact of adsorbed asphaltene aggregates on the catalytic activity of the selected nanoparticles. The adsorption isotherms were described by the solid-liquid equilibrium (SLE) model, and the catalytic behavior of the nanoparticles was compared based upon the trend of effective activation energies using the isoconversional method of Ozawa−Flynn−Wall (OFW). The results showed that the K parameter of the SLE model for both nanoparticles followed the trend of heptol 40 > heptol 20 > toluene, indicating that as the amount of precipitant in the solution increases, a higher degree of asphaltene self-association on the active site of the catalysts is found. On the other hand, the H parameter revealed higher adsorption affinities as the nheptane in the solution increased. However, when different adsorbents were compared at a fixed asphaltene concentration from the same solution it was found that the use of functionalized nanoparticles led to a lower degree of asphaltene self-association and a higher affinity. A correlation between the effective activation energies from the OFW model and the SLE parameters was developed, finding that for a fixed adsorbent, the Eα increases as the affinity and the degree of self-association of asphaltenes increases. However, when the same asphaltenes were compared using different adsorbents, it was observed that the Eα increases as the affinity decreases and the degree of asphaltene selfassociation increases. Consequently, this work shows the effect of the adsorption process on the catalytic activity of the nanoparticles. The reported results should give a better context for the use of such nanoparticles for the upgrading of heavy and extra-heavy oil. KEYWORDS Adsorption, isotherm, self-association, asphaltenes, SLE, nanoparticles, oxidation, catalytic activity, OFW, effective activation energy.

ACS Paragon Plus Environment

1

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 40

1. INTRODUCTION With the rapid increase in world population and industrialization, the demand for energy is increasing worldwide. Consequently, with the limited sources of conventional oil, the production of oil from unconventional resources is growing. According to the International Energy Agency (IEA), the demand for fossil fuels will increase by one-third between 2011 and 2035.1,

2

Actually, with the gradual depletion of conventional oil resources, such as

light and medium crude oil, the rise of unconventional oil exploitation is changing the way that we understand the distribution of the world’s energy resources.1 In the current context, these unconventional resources duplicate those of conventional crude oils, thus special attention has been paid to unconventional oils, such as heavy and extraheavy crude oils with API gravities less than 20° and 10°; respectively.

2-4

However, these

types of crude oil have large amounts of heavy polar hydrocarbons, such as asphaltenes, that lead to a high viscosity and specific gravity. Consequently, the presence of such heavy hydrocarbons can strongly affect production, transportation and refinery processes, in addition to having high capital and operational costs, because the conventional recovery techniques cannot be used effectively.5 Therefore, new cost-effective and environmentally friendly technologies that enhance heavy oil recovery from unconventional resources with lower operational and capital costs are of paramount importance. To this end, nanotechnology-in the form of nanoparticles-has recently become an area of research interest for the oil industry.5-21 Because of their special and unique properties, nanoparticles are able to improve the mobility of oil under reservoir conditions and may be used as adsorbents/catalysts for


2

Page 3 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

enhancing the upgrading and recovery of heavy oil.5, 11,

13, 14, 22, 23

The small size of the

nanoparticles (between 1 and 100 nm) allows these particles unimpeded transport and a good dispersion ability through porous media, without risk of blocking the pores.13 Further, the high ratio of the surface area/volume of the nanoparticles as well as their surface functionality makes them good adsorbents for heavy polar hydrocarbons in crude oils, such as asphaltenes. Asphaltenes, the most aromatic of the heaviest compounds of crude oil, do not have a chemical identity and typically are defined by their solubility, that is, the heaviest fraction of crude oil is insoluble in low-molecular-weight paraffin, such as n-pentane, n-hexane or n-heptane, while it is soluble in light aromatic hydrocarbons, such as toluene, pyridine, or benzene.24, 25 The structure of a typical asphaltene molecule is complex and, even for the same reservoir, it could vary from one well to another. It is widely accepted that the chemical structure of asphaltenes is generally based on one polycyclic aromatic hydrocarbon (PAH) or many cross-linked PAHs attached to alkyl chains forming island, archipelago, continental or rosary-type structures.25-27 Furthermore, asphaltenes contain heteroatoms, such as N, O, S, V, Fe and Ni.28 Hence, the presence of the polar molecules, nonpolar molecules, and functional groups with heteroatoms in the asphaltene structure results in the amphiphilic behavior of the asphaltenes. These lipophilic and hydrophilic parts of the asphaltene structure,

29,30

in addition to a number of interactions, such as

hydrogen bonds, dispersion forces, induction forces and electrostatic forces29,

31-33

would

facilitate asphaltene nucleation and growth and enhance the subsequent formation of colloidal nanoaggregates, with a size approximately between 2 and 5 nm.25, 26, 34-36


3

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 40

Further, the presence of asphaltenes in crude oil can impact a number of catalytic processes in the refinery, such as hydrocracking, hydrodesulfurization, hydrodenitrogenation and hydrodemetallization, as they are the precursors of heteroatoms and high coke yield that lead to inefficient catalysis and thus reduce the distillable fraction of crude oil.36, 37 Accordingly, removal or in-situ cracking of asphaltenes would enhance the crude oil quality and improve its mobility through the reservoir, making production and transporting processes easier, resulting in a higher distillable fraction. To this end, our research group has paid special attention to the adsorption and subsequent catalytic oxidation,11, 14-16, 38-40 pyrolysis

41

and gasification

5, 42

of asphaltenes using different types of supported and

unsupported metal oxide nanoparticles. Our results showed that asphaltene adsorption and post-adsorption catalytic decomposition is strongly dependent on the type of asphaltene, its origin, type of solvent and the chemical structure and surface chemistry of the nanoparticles.8, 14, 15, 40 Nassar et al.10, 15 reported on the adsorption of n-C7 asphaltenes originated from Athabasca vacuum residue onto nanoparticles of NiO, Co3O4, Fe3O4, TiO2, CaO, CeO2, and ZiO2. These authors reported a correlation between the adsorption affinity and the catalytic activity of the transition-metal-oxide nanoparticles of the same group, suggesting that the higher the affinity for adsorption, the better the catalytic activity for asphaltene decomposition. Further, in their recent study, Nassar et al15 showed that the mechanism function of Athabasca n-C7 asphaltene oxidation is strongly dependent on the type of nanoparticle, which is attributed to the different extent of chemisorption between asphaltenes and the nanoparticle surface. CeO2 showed the lowest values of effective activation energy and change in Gibbs free energy of activation owing to its ability to


4

Page 5 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

follow the Mars-Van Krevelen (MvK) mechanism.43 In similar studies using Iranian n-C7 asphaltenes, Hosseinpour et al44, reported by Nassar et al.

45

used metal oxide nanoparticles similar to the ones

8, 14-16, 38-40, 46

for the adsorption and subsequent oxidation or

pyrolysis of Iranian n-C7 asphaltenes. It was also found that the gases released in the decomposition process are particle-type dependent,44 confirming the catalytic role of the selected metal oxide nanoparticles. Recently, Franco et al47 showed that incorporating 1 wt% of nickel and palladium oxide onto fumed silica nanoparticles significantly enhanced the adsorption and subsequent oxidation of Colombian n-C7 asphaltenes, owing to the synergistic effect that would be achieved upon the incorporation of these metal oxides. Furthermore, the authors also found that these types of supported nanoparticles do not allow the formation of multilayer adsorption, facilitating later processes of asphaltenes, such catalytic thermal cracking and the inhibition of formation damage.12, 42, 47 In general, most of the adsorption isotherms of asphaltenes onto solid surfaces are either described by the Langmuir or Freundlich models, confirming an “effective” monolayer or multilayer of asphaltene adsorption, respectively.35, 48-52 Other adsorption models have been reported as well.20, 53, 54 The catalytic activity of the nanoparticles is typically confirmed by a significant shift in the decomposition temperature or a decrease in the effective activation energy of asphaltenes decomposition, as typically estimated by the isoconversional method.5,

7, 11, 14-16, 38, 39, 41

Most of the reported nanoparticles used for adsorption of

asphaltenes and subsequent decomposition of the adsorbed asphaltenes were believed to be effective adsorbents and catalysts. However, it is very well accepted that asphaltenes have the ability to self-assemble onto various aggregates and colloids.25,

55, 56

Therefore, the

changes in the colloidal state of asphaltenes can impact the catalytic activity of the


5

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 40

nanoparticle surfaces after adsorption. However, none of the aforementioned studies correlates the self-association of asphaltenes with the adsorption affinity or catalytic activity of the nanoparticle surfaces. Although adsorption isotherms for “effective” multilayers of asphaltene have been reported in the literature, there was no evidence about the effect of the size of the adsorbed asphaltene monomers, dimers, i-mers or nanoaggregates on the catalytic activity of the nanoparticle surface.11 Hence, a study of the impact of asphaltene aggregates on the nanoparticle surface adsorption affinity and catalytic activity is of paramount importance. To this end, our research group has recently developed a novel three-parameters solid-liquid equilibrium (SLE) model for describing the behavior of the adsorption of self-associating asphaltene molecules onto solid surfaces based on the self-association theory.54 In addition to predicting the affinity and ability of asphaltenes to be adsorbed onto the nanoparticles surface, this novel SLE model provides, at the macro level, an insight on the extent of the asphaltene aggregates on the nanoparticle surface. Hence, this study continues our previous works, aiming to investigate the impact of asphaltenes monomers, dimers, i-mers or nanoaggregates on the catalytic activity of the nanoparticles. Accordingly, we employed fumed silica and nanoparticles of NiO and/or PdO supported on fumed silica for the adsorption and post-adsorption oxidation of n-C7 asphaltenes using different ratios of heptol (n-heptane and toluene). A correlation between the adsorption affinity, the extent of asphaltene aggregation and catalytic activity is developed using the parameters of our previous SLE model, and the values of effective activation energies are estimated by the isoconversional method.


6

Page 7 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

2. EXPERIMENTAL SECTION 3.1 Materials Virgin solid n-C7 asphaltenes were extracted from a Colombian crude oil sample of 7.2°API and viscosity of 5.9 × 105 cP at 15.5°C, with an approximate asphaltene content of 11.5 wt%. n-C7 asphaltenes extraction was carried out following a standard procedure described in previous works.8, 11 n-Heptane (99%, Sigma-Aldrich, St. Louis, MO) was used as a precipitant for asphaltene extraction, and in the preparation of the heavy oil model solution with toluene (99.5%, MerkK GaG, Germany). The ratio of n-heptane to toluene (heptol) was varied from 0 to 40 %v/v to obtain different sizes of asphaltene nanoaggregates. Fumed silica nanoparticles that were 7 nm in size were obtained from Sigma Aldrich and were used as adsorbents. In addition, nanoparticles of NiO and/or PdO supported on fumed silica were used as an adsorbent as well. The detailed preparation and characterization techniques can be found in our previous study.11 In brief, dried fumed silica nanoparticles were exposed to aqueous solutions of Ni(NO3)2•6H2O or Pd(NO3)2 (MerkK GaG, Germany) to obtain 1 wt% (percent by mass) of each metal. The mixture was mixed for 3 h and then further dried at 120°C for 6 h. The obtained solid was calcined at 450°C for 6 h to obtain the hybrid nanoparticle support. The synthesized supported nanoparticles were labeled as SNi1Pd1. Table 1 shows the characteristics of the virgin fumed silica and fumed silica supported nanoparticles. Table 1. Estimated values of NiO and PdO crystallite size and surface areas of selected nanoparticles.


7

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 40

SBET

NiO crystallite size

PdO crystallite size

± 0.01 m2/g

± 0.2 nm

± 0.2 nm

S

389.00

-

-

SNi1Pd1

201.50

1.3

2.2

Material

3.2 Methods 2.2.1

Preparation of model solutions

Heavy oil model solutions were prepared by exposing Colombian n-C7 asphaltenes, extracted from Colombian crude oil, to a mixture of different ratios of n-heptane and toluene (heptol) at 25°C. Three different ratios of n-heptane to toluene were considered in this study, namely, 0, 20 and 40 %v/v of n-heptane. Before adding the n-C7 asphaltenes, the heptol mixtures were mixed at 300 rpm for 2 h. Then, a specified mass of n-C7 asphaltenes was added to the corresponding solution to obtain a stock solution of 6000 mg/L. The mixture was stirred for 6 h at 300 rpm to ensure that the system was homogenous and the size of the asphaltene aggregate remained constant.57 As asphaltenes precipitation is timedependent process,58 the stability of asphaltene in solution was monitored through the Oliensis Spot Test Number59, 60 and Polarized Light Microscopy61 for 72 h and it confirms that no significant precipitation of asphaltenes could be observed for the selected heptol ratios during the time of adsorption experiment. 2.2.2

Batch Adsorption Experiments

Batch adsorption experiments were conducted at room temperature 25°C by exposing 100 mg of nanoparticles to a set of 10 mL solutions of prepared heavy model oil having


8

Page 9 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

different initial concentrations of n-C7 asphaltenes from 100 to 6000 mg/L. The mixtures were then stirred at 200 rpm for 24 h, to ensure adsorption equilibrium is attained. After that, the nanoparticles containing adsorbed asphaltenes were separated by centrifugation at 4000 rpm for 30 min with the purpose of recovering all of the nanoparticles suspended in solution and avoiding overestimation of the remaining asphaltene concentration in the supernatant. Then, the supernatant was decanted and the remaining concentration of n-C7 asphaltenes in the supernatant was measured using a Genesys 10S UV-vis spectrophotometer (Thermo Scientific, Waltham, MA). The solvent (i.e., toluene or heptol) identical to that used for preparing model heavy oil solution was used as a blank in UV analysis. A calibration curve of absorbance against asphaltene concentration was constructed at a fixed wavelength of 290 nm. Hence, the amount adsorbed of n-C7 asphaltenes per surface area of nanoparticles could be determined by mass balance analysis.9, 11, 12 2.2.3

Thermogravimetric Analysis Nanoparticles containing adsorbed n-C7 asphaltenes were dried overnight in a vacuum oven at 65oC. Approximately 5 mg of dried nanoparticles with adsorbed asphaltenes was taken for thermogravimetric analysis. Thermogravimetric analyses were performed using a fixed amount of adsorbed asphaltenes using a Q50 thermogravimetric analyzer (TGA, TA Instruments, Inc., New Castle, DE) coupled with an IRAffinity-1 FTIR device (Shimadzu, Japan) that was equipped with a gas cell to analyze the effluent gases. The samples (nanoparticles with adsorbed asphaltenes) were heated in an air atmosphere from 30 to 800°C at three different heating rates of 5, 10 and 20°C/min in separate experiments and constant airflows of 100 mL/min. For comparison purposes, thermogravimetric


9

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 40

measurements of virgin asphaltenes were also carried out in the TGA/FTIR system. Prior to the experiments, the TGA instrument was calibrated for mass and heat changes using nickel as a reference material. The profiles of gas production were normalized based on the highest signal in the FTIR spectra that corresponded to CO2. More details on the FTIR analyses are provided in the Supporting Information. 2.3 Modeling The obtained experimental data of adsorption isotherms were described by the solid-liquid equilibrium model (SLE) that was recently developed by our research group.54 The catalytic behaviour of the nanoparticles towards n-C7 asphaltenes was described by the isoconversional method of Ozawa−Flyn−Wall (OFW).62-64 2.3.1

SLE Model Recently, our research group54 developed a three-parameter isotherm model for describing the adsorption isotherms of asphaltenes onto solid surfaces. The model is based on a theoretical framework of adsorption of self-associated molecules onto solid surfaces. The SLE model equation is expressed as follows. More details on the derivation of the model were presented in the previous study.54

CE =

 ψ  ψH exp   1 + Kψ  qm ⋅ A 

(1)

where,

ψ=

−1 + 1 + 4 K ξ 2K

(2)

and

 qm ⋅ q  A  qm − q 

ξ =


(3)

10

Page 11 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

q (mg/m2) is the amount of asphaltenes adsorbed onto the nanoparticle surface, qm (mg/m2) is the maximum adsorption capacity of the nanoparticles, A (m2/mg) is the measured surface area per mass of nanoparticles and C E (mg/g) is the equilibrium concentration of asphaltenes in the supernatant. K (g/g) is the reaction constant related to the degree of association of the asphaltenes on the nanoparticles surface and H (mg/g) is the Henry’s law constant related to the preference of the asphaltenes for being in the liquid phase or in the adsorbed phase.54 Higher values of K indicate that the degree of association of the asphaltenes is higher. On the other hand, a lower value of H indicates that asphaltenes would have a high adsorption affinity to be in the adsorbed phase rather than in the liquid phase. The H, K and qm SLE parameters were estimated by model fitting. 2.3.2

OFW Model The isoconversional equation of OFW62,

63

was mainly used to estimate the effective

activation energy for n-C7 asphaltenes oxidation in the presence and absence of nanoparticles. Using this equation one can compare the catalytic activity of the selected nanoparticles. Using the Doyle approximation,64-66 the OFW equation is expressed as follows: K E  E log( β ) = log  α α  − 2.315 − 0.4567 α RT  Rg (α ) 

(4)

where the heating rate, β = dT / dt , Kα (1/s) is the pre-exponential factor, Eα (kJ/mol) is the activation energy, R (J/mol·K) is the ideal gas constant, T (K) is the reaction temperature and α is the reaction conversion ranging between 0 and 1.0 and is expressed as:


11

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

α=

m0 − mt m0 − m f

Page 12 of 40

(5)

where, m0 , m f and mt are the initial sample mass, the sample mass at a given time and the final mass of the sample, respectively. Hence, the effective activation energy is obtained from the slope of the best-fit line of the plot of log( β ) against 1/ T . All estimated model parameter values and their standard errors were determined by Excel package using the correlation coefficient R2 and the non-linear chi-square analyses.67 3

RESULTS AND DISCUSSION

3.1 n-C7 asphaltenes adsorption isotherms Figure 1 shows the experimental isotherm data obtained together with the fit of the SLE model for Colombian n-C7 asphaltene adsorption from different heptol solutions onto nanoparticles of fumed silica and NiO and PdO supported on fumed silica (SNi1Pd1) at a temperature of 25°C. The estimated SLE model parameters are listed in Table 2. As anticipated, for both cases, the n-C7 asphaltene adsorption increases with an increase in the n-heptane to toluene volume ratio. These results are in excellent agreement with previous studies reported in the literature for asphaltene adsorption from oil solutions with different precipitants onto different solid surfaces, such as hydrophilic and hydrophobic silica particles,68

clay minerals (like kaolinite, illite, montmorillonite and mineral oil

reservoir rocks),69 coated quartz crystals70 and metals.54, 71 It is well known that by adding an asphaltene precipitant to a heavy oil solution, the solubility of asphaltenes will decrease and hence asphaltene aggregation and self-association will be enhanced.8 Accordingly, asphaltenes will be adsorbed on solid surface as large aggregates. 72, 73 Furthermore, Figure 1 also shows that SNi1Pd1 nanoparticles clearly adsorbed more n-C7 asphaltenes than S


12

Page 13 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

nanoparticles across the entire range of n-C7 asphaltene concentrations; the difference was more significant at higher concentrations (200 mg/L). This indicates that asphaltene adsorption is surface specific and that the induced selectivity of the included metal oxides apparently enhances the adsorption capacity of the nanoparticles. These results are also in agreement with the previous results reported on the adsorption of Capella n-C7 asphaltenes onto fumed silica nanoparticles functionalized with NiO and/or PdO.11 To further understand this adsorption behavior, the experimental isotherm data are fitted to the SLE model. As seen in Figure 1 and indicated by the values of the regression coefficient and χ 2 in Table 2, the SLE model fits the experimental data well. The results in Table 2 also show that the adsorption capacity of both nanoparticles, represented by qm, followed the order heptol 40 > heptol 20 > toluene. A similar trend is obtained for the adsorption affinity, represented by the reciprocal of the H parameter of the SLE model. In addition, based on the values of qm and the reciprocal of H, it is very clear that the SNi1Pd1 nanoparticles have a higher adsorption affinity and capacity than the S nanoparticles. On the other hand, lower K values were observed for the SNi1Pd1 nanoparticles than for S, indicating that the inclusion of NiO and PdO on the fumed silica surface allows the inhibition of the self-association of the asphaltenes. The differences in ranking the SLE model parameters (i.e., qm, H, and K) between the two types of nanoparticles with different volume ratios of n-heptane to toluene can be attributed to the different degree of interactions between the nanoparticle surface and the n-C7 asphaltenes molecules or aggregates. It is noteworthy that the SLE model is based on the assumptions that the adsorption process is mainly divided into three regions, namely:54 the first region, which corresponds to low uptake, here the adsorption will likely occur in the high-energy sites and


13

Energy & Fuels

asphaltenes molecules would be possibly adsorbed as monomers; the second region is at medium uptake and here the asphaltene will form aggregates around the high-energy sites; and the last region is at high uptake, in this region it is assumed that the finite volume available for adsorption will become crowded with asphaltene molecules, which are expected to be in the form of i-mers, nanoaggregates, etc.

These findings are interesting, as asphaltene self-association and aggregation can cause formation damage and consequently impact the oil recovery efficiency.12 In addition, large n-C7 asphaltene aggregates might block some of the active sites of the nanoparticles, and hence they, could impact the catalytic activity in the case of the catalytic decomposition of the adsorbed asphaltenes.54,15 Heptol 40 - SNi1Pd1 Heptol 20 - SNi1Pd1 Toluene - SNi1Pd1 Heptol 40 - S Heptol 20 - S Toluene - S SLE model

3 2.5 q (mg/m2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 40

2 1.5 1 0.5 0 0

500

1000 CE (mg/L)

1500

2000

Figure 1. Adsorption isotherms of Colombian n-C7 asphaltenes onto fumed silica and SNi1Pd1 nanoparticles at 25°C and different heptol ratios. The symbols are experimental data and the solid lines are from the SLE model (eq. 1).


14

Page 15 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 2. SLE model parameters of Colombian n-C7 asphaltenes adsorption from different heptol mixtures onto fumed silica and SNi1Pd1 nanoparticles at 25°C. Material

Solvent

H (mg/g)

K (g/g) x 10-4

qm (mg/m2)

R2

χ2

Toluene

2.02

4.51

2.89

0.99

1.03

Heptol 20

1.59

4.96

2.97

0.99

1.65

Heptol 40

1.12

5.47

3.15

0.99

1.45

Toluene

1.77

2.16

6.36

0.99

0.36

Heptol 20

1.18

2.74

6.40

0.99

0.56

Heptol 40

1.07

3.29

6.58

0.99

0.77

Fumed silica

SNi1Pd1

3.2 Asphaltene oxidation in presence and absence of nanoparticles 3.2.1 Oxidation of virgin n-C7 asphaltenes Thermogravimetric oxidation tests of asphaltenes were carried out to investigate the effect of the asphaltene aggregates and the incidence of the adsorption process on the catalytic activity of the nanoparticles. The mass loss and evolution of gaseous products during asphaltene oxidation, in the presence and absence of nanoparticles, were monitored by TGA/FTIR instruments. Panels a-c in Figure 2 show a) the rate of mass loss, b) profiles of CO and CO2 production and c) conversion for oxidation of virgin asphaltenes. Clearly, asphaltene oxidation starts approximately at 300°C and ceases at approximately 520°C, where the conversion to gaseous products was completed. From the rate of mass loss plot, it can be observed that there are three peaks located at 425, 460 and 480°C, indicating that the asphaltene decomposition occurs in different steps, where the first peak could correspond to thermal cracking with low


15

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 40

temperature oxidation and the second and third peaks are attributed to complete oxidation to gaseous products. Before 450°C, the mass loss could correspond to the oxidation of the aliphatic moieties of asphaltenes, and the two peaks observed after 450°C may correspond to the oxidation of the PAH core.44

In addition, in Figure 2b it is observed that the CO and CO2 production also starts at approximately at 300°C. In this order, it can be observed that there was a higher production of CO2 than CO, which is in agreement with the finding of Hosseinpour et al.,44 who evaluated the oxidation of Iranian asphaltenes and followed the production of gases through Temperature-Programmed Oxidation tests (TPO). The CO2 profile shows two peaks at 422 and 471°C, similar to the plot of rate of mass loss from the TGA.38 This is due to the oxygen chemisorption that occurs at low temperatures in the active sites of the stacked clusters. As the temperature is increased, light hydrocarbons are released and the exposure of the aliphatic moieties in the bulk of the cluster is enhanced, so the oxygen chemisorption is also enhanced.38

From the conversion curve in Figure 2c, it can be noticed that approximately 50% of the asphaltenes are converted into gaseous products at approximately 450°C. In addition, the percentage of conversion increases as the heating rate decreases, resulting in a clear gap, with no overlapping of the three curves, which prevents miscalculations of the effective activation energies by the OWF method.


16

a

1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 100 200 300 400 500 600 700 800 Temperature (°C) 1 8.0E-05

Normalized area

b

0.8

CO2 CO

6.0E-05

0.6 4.0E-05 0.4 0.2

2.0E-05

0

0.0E+00

Normalized area

100 200 300 400 500 600 700 800 Temperature (°C)

c

100 Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Rate of mass loss (%/°C)

Page 17 of 40

80 60

5°C/min

40

10°C/min

20

15°C/min

0 100 200 300 400 500 600 700 800 Temperature (°C)

Figure 2. a) Plot of rate of mass loss, b) the evolution of the production of CO and CO2 at a heating rate = 10°C/min and c) conversion at heating rates of 5, 10 and 20°C/min for oxidation of virgin asphaltenes; air flow =100 cm3/min.


17

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 40

3.2.2 Effect of asphaltenes aggregation and nanoparticle type on the catalytic oxidation of asphaltenes Panels a-c in Figure 3 show a) the plot of rate of mass loss, b) the evolution profiles of the production of CO and CO2 and c) the degree of conversion for asphaltene oxidation from toluene, heptol 20 and heptol 40 in the presence of fumed silica nanoparticles for a fixed amount of asphaltenes adsorbed at 0.67 ± 0.03 mg/m2. As is shown in Table 2, according to the K parameter, the degree of asphaltene self-association increases as the amount of nheptane in the solvent increases, indicating that large aggregates can be found over the adsorbent surface.

Figure 3a shows two peaks for the three asphaltenes adsorbed onto S nanoparticles from different solvents. The first peak is found at approximately 359°C for the three systems, and no significant shift was observed. On the other hand, the second peak is observed at 509, 519 and 536°C for toluene, heptol 20 and heptol 40, respectively, confirming a delay in the oxidation of asphaltenes due to an increase in the size of the aggregate. In any case, the first peak for asphaltene oxidation in the presence of fumed silica nanoparticles is lower than for virgin asphaltenes. However, the second peak is found at a higher temperature than for the virgin asphaltenes. This could be due to the high asphaltene loading that leads to addition reactions, which probably occur due to the reaction mechanism of free radical chains.74 After the O2 stabilizes the radical species, heavier compounds that are more difficult to decompose are expected to be produced by the radial recombination at termination step of the chain reactions.75 Also, heavier compounds than the starting specie


18

Page 19 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

can be produced from addition reactions that occur by the addition of free radicals to olefins,76 cross-linking reactions between aromatic clusters74 or reactions between aromatics joined by alkyl bridges.77 As was observed for the virgin asphaltenes, the profile of production of CO2 is similar to the rate of mass loss plot. Although in the rate of mass loss there was no clear evidence of the temperature shifting for the first peak, for the gas analyses in Panel c in Figure 3, it can be observed that there is a delay in the CO2 peaks as the heptol ratio increases. In the second peak of Figure 3b it is observed that the production of CO2 is shifted to a lower temperature in the order toluene < heptol 20 < heptol 40. In addition, it is observed that the ratio CO/CO2 increases as the degree of the self-association of asphaltenes decreases. This could be attributed to the fact that the higher asphaltene aggregates tend to hinder some active sites that are then released as asphaltenes are oxidized. Therefore, the CO could be chemisorbed onto the liberated active sites of the nanoparticles to form CO2; as oxides (like SiO2) are active catalysts for the oxidation of the CO by its reaction with the subsurface oxygen.78 Figure 3c shows that the conversion of asphaltenes occurs at a lower temperature in the order of toluene < heptol 20 < heptol 40, indicating that as the asphaltene aggregate increases, the temperature needed for the oxidation of asphaltenes increases. For instance, the temperatures at a fixed degree of 50% conversion are 447, 456 and 485°C for toluene, heptol 20 and heptol 40, respectively.


19

a

Page 20 of 40

0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

Toluene Heptol 20 Heptol 40

100 200 300 400 500 600 700 800 Temperature (°C) CO2 Toluene CO2 Heptol 20 CO2 Heptol 40 CO Toluene CO Heptol 20 CO Heptol 40

1 Normalized area

b

0.8 0.6

0.01 0.008 0.006

0.4

0.004

0.2

0.002

0

Normalized area

0 100 200 300 400 500 600 700 800 Temperature (°C)

100

c Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Energy & Fuels

80 60

Toluene

40

Heptol 20

20

Heptol 40

0 100 200 300 400 500 600 700 800 Temperature (°C) Figure 3. a) Plot of rate of mass loss, b) the evolution profiles of the production of CO and CO2 and c) conversion for oxidation of virgin asphaltenes from different solvents in presence of fumed silica nanoparticles; asphaltenes adsorbed = 0.67 ± 0.03 mg/m2, air flow =100 cm3/min, heating rate = 10°C/min.


20

Page 21 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

According to the values observed for the K parameter of the SLE model (Table 2), the degree of asphaltene self-association is lower for the supported nanoparticles than for the fumed silica support; hence, it is expected that the catalytic activity towards asphaltene oxidation will be enhanced by the SNi1Pd1 nanoparticles. Panels a-c of Figure 4 show a) the plot of rate of mass, b) the evolution profiles of production of CO and CO2 and c) the degree of conversion for asphaltene oxidation from different solvents in presence of SNi1Pd1 nanoparticles at an amount of adsorbed asphaltenes of 0.67 mg/m2.

Panels a and b in Figure 4 show two peaks for the three samples from different solvents, but at a much lower temperature than for fumed silica nanoparticles (Figure 3b-c), confirming the higher catalytic activity of the SNi1Pd1 nanoparticles. It can be noticed that for the fumed silica support, the second peak for toluene, heptol 20 and heptol 40 were about 27, 29 and 31 % higher than the first peak of each sample, respectively. In the case of SNi1Pd1 nanoparticles, the second peaks are about 13, 20 and 26% higher than the first peak for toluene, heptol 20 and heptol 40, respectively. These results indicate that for SNi1Pd1 nanoparticles higher amount of asphaltenes are decomposed in the region where the first peak appears in comparison to the fumed silica support, confirming their higher catalytic activity. In the first peak observed in Figure 4a, a small shift can be noticed due to the solvent evaluated at temperatures 332, 341 and 394°C. This could be due to higher adsorbed aggregates of asphaltenes that lead to higher temperatures of oxidation. However, in the second peak, there is no clear shift regarding the heptol ratio, and this could be due to the catalytic effect of the nanoparticles, leading to additional reactions occurring to the


21

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 40

same degree for toluene and both systems with heptol. In addition, it is observed that the production of both CO and CO2 starts earlier with the supported nanoparticles and that the first peak of CO2 production is found at 344, 367 and 399°C for toluene, heptol 20 and heptol 40, respectively. This again proves that the size of the asphaltene aggregate influences the catalytic activity of the nanoparticles.

As was seen for the fumed silica nanoparticles, for SNi1Pd1, higher degrees of conversion are obtained in the order of toluene > heptol 20 > heptol 40. However, for the SNi1Pd1 samples the asphaltene oxidation occurred much earlier than for the fumed silica support. Figure 4c shows that for toluene, heptol 20 and heptol 40 a 50% degree of conversion is reached at 397, 422 and 429 °C, respectively. These temperatures are approximately 50, 34 and 56°C lower than for the fumed silica nanoparticles, indicating that the SN1Pd1 nanoparticles are able to inhibit the self-association of the asphaltenes on the active sites and hence have better catalytic activity than the fumed silica support.


22

Page 23 of 40

0.12 Rate of mass loss (%/°C)

a

0.1 Toluene

0.08

Heptol 20

0.06

Heptol 40

0.04 0.02 0 100

Normalized area

b

200

300 400 500 600 Temperature (°C)

700

800

CO2 Toluene CO2 Heptol 20 CO2 Heptol 40 CO Toluene CO Heptol 20 CO Heptol 40

1 0.8 0.6

0.0006

0.0004

0.4

0.0002

0.2 0

Normalized area

0 100

200

300 400 500 600 Temperature (°C)

700

800

c 100 Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

80 60

Toluene

40

Heptol 20

20

Heptol 40

0 100

200

300 400 500 600 Temperature (°C)

700

800

Figure 4. a) Plot of rate of mass loss, b) the evolution profiles of the production of CO and CO2 and c) conversion for oxidation of virgin asphaltenes from different


23

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 40

solvents in presence of SNi1Pd1 nanoparticles; asphaltenes adsorbed = 0.67 ± 0.03 mg/m2, air flow =100 cm3/min, heating rate = 10°C/min.

3.2.3 Effect of asphaltene loading The effect of the asphaltene loading was also evaluated in this work using SNi1Pd1 nanoparticles. Panels a-c in Figure 5 show a) the plot of the rate of mass loss, b) the evolution profiles of production of CO and CO2 and c) the degree of conversion for asphaltene oxidation from different solvents in presence of SNi1Pd1 nanoparticles at a fixed amount of adsorbed asphaltenes of 0.17 ± 0.02 mg/m2. In contrast to what was observed for a higher amount of adsorbed asphaltenes, in the plot of rate of mass loss in Figure 5a, three peaks are observed for the three asphaltenes from different solvents. These were observed over three different temperature ranges, namely, a low-temperature range (LTR) between 200 and 270°C, a mid-temperature (MTR) between 271 and 460°C and a high-temperature range (HTR) between 461 and 800°C. These results are in agreement with our previous study,11 in which we studied the catalytic activity of SNi1Pd1 nanoparticles towards the catalytic oxidation of Colombian Capella asphaltenes at an adsorbed amount of 0.2 mg/m2, and three peaks were also observed in the plot of the rate of mass loss at low, medium and high temperatures. In this case, none of the peaks showed a clear shifting for different heptol ratios, and this observation could be due to both low asphaltenes loading and the catalytic effect of the nanoparticles that would have a higher amount of active sites for the reaction.

11, 38

These facts make the nanoparticles able to oxidize asphaltenes of

different sizes at approximately the same temperature. The first peak in Figure 5a appeared in the LTR at approximately 240°C for toluene and both systems with heptol and was due


24

Page 25 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

to a lower asphaltene loading. This results in less hindering of active sites and a subsequent enhancement of the catalytic activity of the catalyst. Asphaltenes are adsorbed on the nanoparticle surface via diﬀusive processes in which smaller asphaltene aggregates or monomers at low concentrations, are adsorbed first, followed by larger asphaltenes.11 In this order, finding that the first peak in the LTR means that for a lower asphaltene loading the first-adsorbed asphaltenes in the first layer retained a lower degree of self-association and are more easily cracked than those for a larger amount adsorbed. On the other hand, the MTR peak appears at approximately 375°C for the three solvents evaluated, approximately 15°C greater than the peak observed for the SNi1Pd1 nanoparticles in the same region for an amount adsorbed of 0.67 mg/m2. This increase in the temperature can be explained because the oxidation of the asphaltenes in the LTR led to the formation of heavier compounds. The same situation is observed for the peak in the HTR, where the peak of asphaltene oxidation is found at a temperature 35°C greater than for the sample with more adsorbed asphaltene. This shift to a higher temperature in the MTR and HTR was also seen in our previous work, where the effect of the asphaltene loading was evaluated for 0.2, 0.05 and 0.03 mg/m2.11 The CO and CO2 evolution in Figure 5b confirms that a higher degree of asphaltene selfassociation leads to lower catalytic activity of the nanoparticles. It is observed that the production of CO2 starts at lower temperatures as the heptol ratio decreases. A wide first peak is observed for the CO2 for toluene, heptol 20 and heptol 40 and is due to the oxidation of asphaltenes in the LTR and MTR. In addition, a shift of the peak to the right in the MTR is observed in the order of toluene < heptol 20 < heptol 40, indicating that the catalytic oxidation of asphaltenes occurs earlier for the systems with a lower degree of self-


25

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 40

association. Additionally, as seen in Figure 5c, higher degrees of conversion are obtained as the amount of n-heptane in the solvent decreases.


26

Page 27 of 40

0.02


a

Normalized area

b

Toluene Heptol 20

0.016

Heptol 40

0.012 0.008 0.004 0 100 200 300 400 500 600 700 800 Temperature (°C) CO2 Toluene CO2 Heptol 20 CO2 Heptol 40 CO Toluene CO Heptol 20 CO Heptol 40

1 0.8 0.6

0.0016 0.0012

0.4

0.0008

0.2

0.0004

0

0 100

c 100 Conversion (%)

0.002

80 60

Normalized area

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

200

300 400 500 600 Temperature (°C)

700

800

Toluene Heptol 20 Heptol 40

40 20 0 100 200 300 400 500 600 700 800 Temperature (°C)

Figure 5. a) Plot of rate of mass loss, b) the evolution profiles of the production of CO and CO2 and c) conversion for oxidation of virgin asphaltenes from different solvents in presence of SNi1Pd1 nanoparticles; asphaltenes adsorbed = 0.17 ± 0.02 mg/m2, air flow =100 cm3/min, heating rate = 10°C/min.


27

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 40

3.3. Estimation of the Effective Activation Energies The Ozawa−Flynn−Wall (OFW) equation was used to estimate the effective activation energies (Eα) needed for the catalytic oxidation of asphaltenes in the presence and absence of the selected nanoparticles. Figure 6 shows the estimated Eα for virgin asphaltenes and asphaltenes from different solvents in the presence of fumed silica nanoparticles. It is observed that for virgin asphaltenes the effective activation energy ranged between 200 and 125 kJ/mol and decreased as the percentage of conversion increases. The variation in the activation energy as a function of the degree of conversion is because the oxidation of asphaltenes is not a single-mechanism process, but one that occurs in more than one step without considering the effect of the aggregate size. For asphaltenes adsorbed on fumed silica nanoparticles, the Eα trend was the opposite of that for virgin asphaltenes; as the percentage of conversion increases, the Eα increased, indicating that the oxidation mechanism is different than for virgin asphaltenes and that different factors, such as addition reactions, steps involved and reaction order, must be considered in future work. These results are also in excellent agreement with our previous study of the oxidation of Capella asphaltene, both in the presence and absence of fumed silica nanoparticles.11 For the three asphaltenes from different solvents, the trend followed by Eα was heptol 40 > heptol 20 > toluene, indicating that for larger asphaltene aggregates, more energy is needed to oxidize the adsorbed asphaltenes. It is also observed that for the three asphaltenes adsorbed, the pathway followed by the Eα is similar with an upward shift as the amount of


28

Page 29 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

n-heptane increases, suggesting that the mechanisms involved are similar for the three

samples. Figure 7 shows the estimated Eα for asphaltenes adsorbed onto SNi1Pd1 nanoparticles at adsorbed amounts of 0.17 and 0.67 mg/m2. In our evaluation of these two amounts adsorbed, the trend followed by Eα was also heptol 40 > heptol 20 > toluene, and for the asphaltenes adsorbed at a concentration of 0.67 mg/m2 from the same solvent, the Eα was always higher than for those at a concentration of 0.17 mg/m2. These results indicate that the larger asphaltene aggregates can block the active sites and strongly affect the catalytic activity of the nanoparticles. It is worth mentioning that the pathway followed by the Eα for both amounts of asphaltenes adsorbed on SNi1Pd1 is similar. However, when a comparison is made for different nanoparticles, it is seen that the trend is different and the oxidation mechanism and reaction order is specific to the type of nanoparticle. The mechanism for the asphaltenes oxidation is highly dependent on the way asphaltenes are adsorbed on the nanoparticles surface. In fact, depending on the nanoparticles chemical nature, selectivity towards asphaltenes adsorption could change from one type of nanoparticle to another. In this order, asphaltenes can be adsorbed in perpendicular or parallel ways depending on the nanoparticles selectivity towards different functional groups in the asphaltenes structure, affecting the degree of asphaltenes self-association. Thus, the synergistic effect of NiO and PdO on the fumed silica surface alters the selectivity towards different species present in the asphaltenes structure and hence, the way asphaltenes are adsorbed. Then, the disposition of asphaltenes over the nanoparticle surface is different and is in agreement with the values of the K parameter of the SLE model (Table 2). Also, the activated state will be different for the oxidation of asphaltenes in presence of both fumed


29

Energy & Fuels

silica and SNi1Pd1 nanoparticles, being less disordered for the one presenting lower effective activation energies. 15

220 Eα (kJ/mol)

200 180

Virgin asphaltenes Heptol 40 Heptol 20 Tolene

160 140 120 100 0

25

50 75 100 Conversion (%)

125

150

Figure 6. Effective activation energies by the OFW method as function of the conversion for fumed silica nanoparticles.

Eα (kJ/mol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 40

170 150 130 110 90 70 50 30

Virgin asphaltenes Heptol 40 - 0.67 mg/m2 Heptol 20 - 0.67 mg/m2 Toluene - 0.67 mg/m2 Heptol 40 - 0.17 mg/m2 Heptol 20 - 0.17 mg/m2 Toluene - 0.17 mg/m2

0

25

50 75 100 Conversion (%)

125

150

Figure 7. Effective activation energies by the OFW method as function of the conversion for SNi1Pd1 nanoparticles at two different amounts of asphaltenes adsorbed.


30

Page 31 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

3.4.Correlation between the SLE model parameters and the effective activation energy As the application of nanoparticles for asphaltene adsorption and catalytic decomposition has gained interest in the oil industry, a better understanding of the relation of the adsorption behavior and the catalytic activity of the nanoparticles is needed. In this regard, we proposed a correlation between the SLE model parameters (i.e., H and K) that give information about the adsorptive behavior of the nanoparticle surface and the Eα estimated by the OFW model that provides the catalytic behavior of the nanoparticle surface. It is worth remembering that the SLE parameters and Eα are obtained for the adsorption isotherms of asphaltenes from different solvents as shown in the previous sections. Panels a and b in Figure 8 show the relation between the H parameter and the effective activation energy for a) fumed silica and b) SNi1Pd1 nanoparticles at the three different degrees of asphaltene conversion of 20, 50 and 80%. As seen in Figure 8 for both nanoparticles, Eα decreases as the H value increases, i.e., as the adsorption affinity decreases. This observed trend is different from the trend obtained in previous works for asphaltene oxidation, pyrolysis and gasification, where the activation energy decreased as the adsorption affinity increased.38, 41, 42 Nevertheless, our previous studies focused on changing the type of adsorbents for the same asphaltene molecular/aggregate feature, which is different from the current study, where the asphaltene aggregate feature is changing as the heptol ratio changes. The difference between the correlations can be explained because the different adsorbent surfaces would inhibit the asphaltene self-association over the surface of the nanoparticles, directly


31

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 40

affecting the catalytic activity.42, 54 In addition, one has to keep in mind that the increase in the adsorption affinity as the amount of n-heptane increase, is due to the increasing aggregate size and that it could lead to a greater attachment of the asphaltene aggregates that will affect the catalytic activity of the nanoparticles. This finding is in good agreement with the behavior observed in Figure 7, where Eα increased with an increase in the heptol ratio, with larger asphaltene aggregates. On the other hand, Figure 9a and b show the relation between the constant K from SLE model and the estimated activation energy from the OFW model for asphaltene oxidation in the presence of a) fumed silica and b) SNi1Pd1 nanoparticles. Clearly, for both fumed silica and SNi1Pd1 nanoparticles, there is a linear trend between the K parameter and the Eα whereby increasing the degree of asphaltene selfassociation, the activation energy needed for the asphaltene oxidation increases because the higher aggregates are more prone to have buried or hidden functional groups that could interact with the catalyst surface.79 Additionally, when different adsorbents are compared using the same asphaltenes from the same solvent, it is observed that Eα decreases as the adsorption affinity increases and as the degree of self-association of the asphaltenes decreases. For example, in the case of asphaltenes adsorbed from toluene onto SNi1Pd1 nanoparticles the H parameter takes value of 2.02 mg/g and Eα=50% of 42.17 kJ/mol; while for the fumed silica nanoparticles the values of H and Eα=50% are 1.77 mg/g and 86.21 kJ/mol, respectively, indicating that for higher affinities the effective activation energy will decrease. Same observations can be seen for both heptol 20 and heptol 40 mixtures, and effective activation energies at values of α of 20 and 80%. However, the higher affinity of the SNi1Pd1 nanoparticles towards asphaltenes adsorption from same solvent is related to the synergistic effect of NiO and


32

Page 33 of 40

PdO. That synergistic effect enables different unified selectivities, changing intermolecular forces between heteroatoms and functional groups of asphaltenes, and enhancing the surface electronegativity for a more efficient catalytic process. This trend of the effective activation energies as function of adsorption affinity does agree with our previous works where same trend was obtained.38, 41, 42 For the fumed silica nanoparticles, it is observed that the slope of the trend line is similar for conversions of 20 and 50%, but for 80%, the slope is lower, indicating that at this value of conversion there is probably a switch in the oxidation mechanism. Additionally, when different adsorbents are compared using the same asphaltenes from the same solvent, it is observed that Eα decreases as the adsorption affinity increases and as the degree of selfassociation of the asphaltenes increases.

b 160

190 180 170 160 150 140 130

140 Eα (kJ/mol)

a 200 Eα (kJ/mol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Eα 80 Eα 50 Eα 20

1

120 100 80

Eα 80 Eα 50 Eα 20

60 1.4 1.8 H (mg/g)

2.2

40 1

1.3 1.6 H (mg/g)

1.9

Figure 8. Relation between the Henry’s law constant from SLE model and the estimated activation energy from the OFW model for asphaltenes thermo oxidation in presence of a) fumed silica and b) SNi1Pd1 nanoparticles. Degrees of conversion of the activation energy of 20 (■), 50 (●) and 80% (▲).


33

Energy & Fuels

160

Eα 80 Eα 50 Eα 20

a 200 190 180 170 160 150 140 130

Eα 80 Eα 50 Eα 20

140 Eα (kJ/mol)

Eα (kJ/mol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 40

120 100 80 60 40

4

4.5 5 5.5 K (g/g) x 10-4

6

2

2.5 3 K (g/g) x 10-4

3.5

Figure 9. Relation between the constant K from SLE model and the estimated activation energy from the OFW model for asphaltenes thermo oxidation in presence of a) fumed silica and b) SNi1Pd1 nanoparticles. Degrees of conversion of the activation energy of 20 (■), 50 (●) and 80% (▲).

4

CONCLUSIONS

This study investigates the impact of asphaltene self-association on the adsorption affinity and catalytic activity of fumed silica and nanoparticles of NiO and/or PdO supported on fumed silica (SNi1Pd1) towards the adsorption of Colombian n-C7 asphaltenes and their subsequent thermo-oxidative decomposition. The SLE model was used to fit the adsorption isotherms of asphaltene from different solvents with different volume ratios of nheptane/toluene. The inclusion of NiO and PdO over the fumed silica surface greatly enhanced the asphaltene adsorption. The results showed that the H parameter followed the trend of toluene > heptol 20 > heptol 40, indicating that the adsorption affinity increased as the amount of precipitant increased. It was also observed, according to the K parameter, that the asphaltene self-association over the adsorbent surface increased in the order heptol 40 >


34

Page 35 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

heptol 20 > toluene. For the case of the SNi1Pd1 nanoparticles the affinity towards asphaltene adsorption increased compared to the fumed silica support alone and also the degree of self-association of the asphaltenes was lower, indicating that the supported nanoparticles are able to inhibit the self-association of asphaltenes. In addition, TGA/FTIR tests were performed to investigate the effect of the asphaltene aggregate on the catalytic oxidation and the outcome of CO and CO2 gases. These TGA/FTIR tests provided useful information and revealed that as the extent of asphaltene aggregation increased, the temperature of asphaltene oxidation increased. The results showed that nanoparticles portray different reaction mechanisms in the catalytic oxidation of asphaltenes and that the pathway followed is specific to the type of nanoparticle. It was observed that the temperature of asphaltene oxidation decreased in the order heptol 40 > heptol 20 > toluene, indicating that for larger aggregates, the catalytic activity of nanoparticles is reduced. The SNi1Pd1 nanoparticles also reduced the temperature of asphaltene oxidation. The OFW model was used to estimate the effective activation energies in the asphaltene oxidation process, and it was found that as the extent of asphaltene aggregate increased, higher Eα are needed. Finally, a correlation between the SLE parameters and the Eα from the OFW model was found. As the parameter H decreased, i.e., the affinity increases, the Eα increased. However, it was shown that the Eα greatly decreased as the degree of asphaltene self-association decreased. This study should provide a better insight on the influence of the adsorption process on the catalytic activity of the nanoparticles and give a better understanding about the use of nanotechnology for in situ upgrading of heavy and extra-heavy oils.


35

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

5

Page 36 of 40

ACKNOWLEDMENTS

The authors acknowledge COLCIENCIAS and ECOPETROL for the support provided in the agreement 264 of 2013. We also want to acknowledge Universidad Nacional de Colombia for logistical and financial support and to Dr. Pedro Pereira-Almao for fruitful discussions and assistance. 6

REFERENCES

1. Agency, I. E., World Energy Outlook 2013. Internationl Energy Agency: 2013. 2. Shah, A.; Fishwick, R.; Wood, J.; Leeke, G.; Rigby, S.; Greaves, M., A review of novel techniques for heavy oil and bitumen extraction and upgrading. Energy & Environmental Science 2010, 3, (6), 700-714. 3. Castaneda, L. C.; Muñoz, J. A.; Ancheyta, J., Current situation of emerging technologies for upgrading of heavy oils. Catalysis Today 2014, 220, 248-273. 4. Fan, C.; Zan, C.; Zhang, Q.; Ma, D.; Chu, Y.; Jiang, H.; Shi, L.; Wei, F., The oxidation of heavy oil: Thermogravimetric analysis and non-isothermal kinetics using the distributed activation energy model. Fuel Processing Technology 2014, 119, 146-150. 5. Nassar, N. N.; Hassan, A.; Pereira-Almao, P., Application of Nanotechnology for Heavy Oil Upgrading: Catalytic Steam Gasification/Cracking of Asphaltenes. Energy & Fuels 2011, 25, (4), 1566-1570. 6. Hamedi Shokrlu, Y.; Babadagli, T., In-Situ Upgrading of Heavy Oil/Bitumen During Steam Injection by Use of Metal Nanoparticles: A Study on In-Situ Catalysis and Catalyst Transportation. 7. Nassar, N. N.; Hassan, A.; Pereira-Almao, P., Effect of surface acidity and basicity of aluminas on asphaltene adsorption and oxidation. Journal of colloid and interface science 2011, 360, (1), 233-238. 8. Nassar, N. N., Asphaltene Adsorption onto Alumina Nanoparticles: Kinetics and Thermodynamic Studies. Energy & Fuels 2010, 24, (8), 4116-4122. 9. Cortés, F. B.; Mejía, J. M.; Ruiz, M. A.; Benjumea, P.; Riffel, D. B., Sorption of Asphaltenes onto Nanoparticles of Nickel Oxide Supported on Nanoparticulated Silica Gel. Energy & Fuels 2012, 26, (3), 1725-1730. 10. Franco, C.; Patiño, E.; Benjumea, P.; Ruiz, M. A.; Cortés, F. B., Kinetic and thermodynamic equilibrium of asphaltenes sorption onto nanoparticles of nickel oxide supported on nanoparticulated alumina. Fuel 2013, 105, (0), 408-414. 11. Franco, C. A.; Montoya, T.; Nassar, N. N.; Pereira-Almao, P.; Cortés, F. B., Adsorption and Subsequent Oxidation of Colombian Asphaltenes onto Nickel and/or Palladium Oxide Supported on Fumed Silica Nanoparticles. Energy & Fuels 2013, 27, (12), 7336-7347. 12. Franco, C. A.; Nassar, N. N.; Ruiz, M. A.; Pereira-Almao, P.; Cortés, F. B., Nanoparticles for Inhibition of Asphaltenes Damage: Adsorption Study and Displacement Test on Porous Media. Energy & Fuels 2013, 27, (6), 2899-2907.


36

Page 37 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

13. Hashemi, R.; Nassar, N. N.; Pereira-Almao, P., Transport behavior of multimetallic ultradispersed nanoparticles in an oil-sands-packed bed column at a high temperature and pressure. Energy Fuels 2012, 26, (3), 1645. 14. Nassar, N. N.; Hassan, A.; Pereira-Almao, P., Metal oxide nanoparticles for asphaltene adsorption and oxidation. Energy Fuels 2011, 25, (3), 1017. 15. Nassar, N. N.; Hassan, A.; Vitale, G., Comparing kinetics and mechanism of adsorption and thermo-oxidative decomposition of Athabasca asphaltenes onto TiO2, ZrO2, and CeO2 nanoparticles. Applied Catalysis A: General 2014, 484, (0), 161-171. 16. Nassar, N. N.; Hassan, A.; Pereira-Almao, P., Effect of the particle size on asphaltene adsorption and catalytic oxidation onto alumina particles. Energy & Fuels 2011, 25, (9), 3961-3965. 17. Zabala Romero, R. D.; Acuna, H. M.; Cortes, F.; Patino, J. E.; Cespedes Chavarro, C.; Mora, E.; Botero, O. F.; Guarin, L., Application and Evaluation of a NanoFluid Containing NanoParticles for Asphaltenes Inhibition in Well CPSXL4. In Offshore Technology Conference. 18. Kedir, A. S.; Seland, J. G.; Skauge, A.; Skauge, T., Nanoparticles for Enhanced Oil Recovery: Influence of pH on Aluminum-Crosslinked Partially Hydrolyzed Polyacrylamide-Investigation by Rheology and NMR. Energy & Fuels 2014. 19. Giraldo, J.; Benjumea, P.; Lopera, S.; Cortés, F. B.; Ruiz, M. A., Wettability alteration of sandstone cores by alumina-based nanofluids. Energy & Fuels 2013, 27, (7), 3659-3665. 20. Giraldo, J.; Nassar, N. N.; Benjumea, P.; Pereira-Almao, P.; Cortés, F. B., Modeling and Prediction of Asphaltene Adsorption Isotherms Using Polanyi’s Modified Theory. Energy & Fuels 2013, 27, (6), 2908-2914. 21. Mera, C. M.; ARIZA, C. A.; Cortés, F. B., Uso de nanopartículas de sílice para la estabilización de finos en lechos empacados de arena Ottawa. Informador Técnico 2013, 77, (1). 22. Olvera, J. N. R.; Gutiérrez, G. J.; Serrano, J.; Ovando, A. M.; Febles, V. G.; Arceo, L. D. B., Use of unsupported, mechanically alloyed NiWMoC nanocatalyst to reduce the viscosity of aquathermolysis reaction of heavy oil. Catalysis Communications 2014, 43, 131-135. 23. Hashemi, R.; Nassar, N. N.; Pereira-Almao, P. R., In situ Upgrading of Athabasca Bitumen Using Multimetallic Ultra-Dispersed Nanocatalysts in an Oil-Sands-Packed Bed Column: Part 1, Produced Liquid Quality Enhancement. Energy & Fuels 2013. 24. Mullins, O. C.; Sheu, E. Y.; Hammami, A.; Marshall, A. G., Asphaltenes, Heavy Oils, and Petroleomics. 2007. 25. Mullins, O. C., The asphaltenes. Annual Review of Analytical Chemistry 2011, 4, 393-418. 26. Mullins, O. C.; Sabbah, H.; Eyssautier, J. l.; Pomerantz, A. E.; Barré, L.; Andrews, A. B.; RuizMorales, Y.; Mostowfi, F.; McFarlane, R.; Goual, L., Advances in asphaltene science and the Yen– Mullins model. Energy & Fuels 2012, 26, (7), 3986-4003. 27. Acevedo, S.; Castro, A.; Negrin, J. G.; Fernández, A.; Escobar, G.; Piscitelli, V.; Delolme, F.; Dessalces, G., Relations between asphaltene structures and their physical and chemical properties: The rosary-type structure. Energy & fuels 2007, 21, (4), 2165-2175. 28. Groenzin, H.; Mullins, O. C., Asphaltene molecular size and structure. J. Phys. Chem. A 1999, 103, 11237. 29. Witthayapanyanon, A.; Harwell, J.; Sabatini, D., Hydrophilic–lipophilic deviation (HLD) method for characterizing conventional and extended surfactants. Journal of colloid and interface science 2008, 325, (1), 259-266. 30. Mittal, K. L.; Shah, D. O., Adsorption and aggregation of surfactants in solution. CRC Press: 2002. 31. Spiecker, P. M.; Gawrys, K. L.; Kilpatrick, P. K., Aggregation and solubility behavior of asphaltenes and their subfractions. Journal of colloid and interface science 2003, 267, (1), 178-193.


37

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 40

32. Spiecker, P. M.; Gawrys, K. L.; Trail, C. B.; Kilpatrick, P. K., Effects of petroleum resins on asphaltene aggregation and water-in-oil emulsion formation. Colloids and surfaces A: Physicochemical and engineering aspects 2003, 220, (1), 9-27. 33. Prausnitz, J. M.; Lichtenthaler, R. N.; de Azevedo, E. G., Molecular thermodynamics of fluidphase equilibria. Pearson Education: 1998. 34. Sheu, E.; Long, Y.; Hamza, H., Asphaltene self-association and precipitation in solvents—AC conductivity measurements. In Asphaltenes, Heavy Oils, and Petroleomics, Springer: 2007; pp 259277. 35. Acevedo, S.; Ranaudo, M. a. A.; Garcı ́a, C.; Castillo, J.; Fernández, A.; Caetano, M.; Goncalvez, S., Importance of asphaltene aggregation in solution in determining the adsorption of this sample on mineral surfaces. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2000, 166, (1), 145-152. 36. Chianelli, R. R.; Siadati, M.; Mehta, A.; Pople, J.; Ortega, L. C.; Chiang, L. Y., Self-assembly of asphaltene aggregates: Synchrotron, simulation and chemical modeling techniques applied to problems in the structure and reactivity of asphaltenes. In Asphaltenes, Heavy Oils, and Petroleomics, Springer: 2007; pp 375-400. 37. Benito, A. M.; Callejas, M. A.; Martínez, M. T., Kinetics of asphaltene hydroconversion: 2. Catalytic hydrocracking of a coal residue. Fuel 1997, 76, (10), 907-911. 38. Nassar, N. N.; Hassan, A.; Pereira-Almao, P., Comparative oxidation of adsorbed asphaltenes onto transition metal oxide nanoparticles. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2011, 384, (1), 145-149. 39. Nassar, N. N.; Hassan, A.; Luna, G.; Pereira-Almao, P., Kinetics of the catalytic thermooxidation of asphaltenes at isothermal conditions on different metal oxide nanoparticle surfaces. Catalysis today 2013, 207, 127-132. 40. Nassar, N. N.; Hassan, A.; Carbognani, L.; Lopez-Linares, F.; Pereira-Almao, P., Iron oxide nanoparticles for rapid adsorption and enhanced catalytic oxidation of thermally cracked asphaltenes. Fuel 2012, 95, 257-262. 41. Nassar, N. N.; Hassan, A.; Pereira-Almao, P., Thermogravimetric studies on catalytic effect of metal oxide nanoparticles on asphaltene pyrolysis under inert conditions. Journal of thermal analysis and calorimetry 2012, 110, (3), 1327-1332. 42. Camilo A. Franco, N. N. N., Tatiana Montoya, Farid B. Cortés, NiO and PdO Supported on Fumed Silica Nanoparticles for Adsorption and Catalytic Steam Gasification of Colombian C7 Asphaltenes. In Handbook on Oil Production Research, Ambrosio, J., Ed. Nova Science Publishers, Inc.: 2014. 43. Mars, P.; Krevelen, D. W. v., Oxidations carried out by means of vanadium oxide catalysts. Chem. Eng. Sci. Spec. Suppl. 1954, 3. 44. Hosseinpour, N.; Mortazavi, Y.; Bahramian, A.; Khodatars, L.; Khodadadi, A. A., Enhanced pyrolysis and oxidation of asphaltenes adsorbed onto transition metal oxides nanoparticles towards advanced in-situ combustion EOR processes by nanotechnology. Applied Catalysis A: General 2014, 477, 159-171. 45. Hosseinpour, N.; Khodadadi, A. A.; Bahramian, A.; Mortazavi, Y., Asphaltene Adsorption onto Acidic/Basic Metal Oxide Nanoparticles toward in Situ Upgrading of Reservoir Oils by Nanotechnology. Langmuir 2013, 29, (46), 14135-14146. 46. Nassar, N. N.; Hassan, A.; Pereira-Almao, P., Clarifying the catalytic role of NiO nanoparticles in the oxidation of asphaltenes. Applied Catalysis A: General 2013, 462, 116-120. 47. Franco, C. A.; Cortés, F. B.; Nassar, N. N., Adsorptive Removal of Oil Spill From Oil-in-Fresh Water Emulsions by Hydrophobic Alumina Nanoparticles Functionalized with Petroleum Vacuum Residue. Journal of Colloid and Interface Science 2014.


38

Page 39 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

48. González, G.; Moreira, M. B., The wettability of mineral surfaces containing adsorbed asphaltene. Colloids and surfaces 1991, 58, (3), 293-302. 49. Marczewski, A. W.; Szymula, M., Adsorption of asphaltenes from toluene on mineral surface. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2002, 208, (1), 259-266. 50. Marlow, B.; Sresty, G.; Hughes, R.; Mahajan, O., Colloidal stabilization of clays by asphaltenes in hydrocarbon media. Colloids and Surfaces 1987, 24, (4), 283-297. 51. Gaboriau, H.; Saada, A., Influence of heavy organic pollutants of anthropic origin on PAH retention by kaolinite. Chemosphere 2001, 44, (7), 1633-1639. 52. Lowell, S.; Shields, J. E., Powder surface area and porosity. Springer: 1991; Vol. 2. 53. Castro, M.; de la Cruz, J. L. M.; Buenrostro-Gonzalez, E.; López-Ramírez, S.; Gil-Villegas, A., Predicting adsorption isotherms of asphaltenes in porous materials. Fluid Phase Equilibria 2009, 286, (2), 113-119. 54. Montoya, T.; Coral, D.; Franco, C. A.; Nassar, N. N.; Cortés, F. B., A Novel Solid-Liquid Equilibrium Model for Describing the Adsorption of Associating Asphaltene Molecules onto Solid Surfaces Based on the “Chemical Theory”. Energy & Fuels 2014. 55. Groenzin, H.; Mullins, O. C., Molecular Size and Structure of Asphaltenes from Various Sources. Energy & Fuels 2000, 14, (3), 677-684. 56. Mullins, O. C., The Modiﬁed Yen Model†. Energy & Fuels 2010, 24, (4), 2179-2207. 57. Rahmani, N. H.; Masliyah, J. H.; Dabros, T., Characterization of asphaltenes aggregation and fragmentation in a shear field. AIChE journal 2003, 49, (7), 1645-1655. 58. Maqbool, T.; Balgoa, A. T.; Fogler, H. S., Revisiting asphaltene precipitation from crude oils: A case of neglected kinetic effects. Energy & Fuels 2009, 23, (7), 3681-3686. 59. Asomaning, S., Test methods for determining asphaltene stability in crude oils. Petroleum science and technology 2003, 21, (3-4), 581-590. 60. Oliensis, G. In THE OLIENSIS SPOT TEST--WHAT JUSTIFICATION IS THERE FOR ITS USE?, Association of Asphalt Paving Technologists Proceedings, 1935; 1935. 61. Mohammadi, M.; Akbari, M.; Fakhroueian, Z.; Bahramian, A.; Azin, R.; Arya, S., Inhibition of asphaltene precipitation by TiO2, SiO2, and ZrO2 nanofluids. Energy & Fuels 2011, 25, (7), 31503156. 62. Flynn, J. H.; Wall, L. A., A quick, direct method for the determination of activation energy from thermogravimetric data. Journal of Polymer Science Part B: Polymer Letters 1966, 4, (5), 323328. 63. Ozawa, T., A new method of analyzing thermogravimetric data. Bulletin of the chemical society of Japan 1965, 38, (11), 1881-1886. 64. Nassar, N.; Hassan, A.; Luna, G.; Pereira-Almao, P., Comparative study on thermal cracking of Athabasca bitumen. Journal of Thermal Analysis and Calorimetry 2013, 114, (2), 465-472. 65. Doyle, C., Synthesis and evaluation of thermally stable polymers. II. Polymer evaluation. Appl Polym Sci 1961, 5, 285-292. 66. Doyle, C. D., Series approximations to the equation of thermogravimetric data. 1965. 67. Montgomery, D. C., Applied Statistics and Probability for Engineers 6th edition. Wiley: 2013. 68. Tu, Y.; Kingston, D.; Kung, J.; Kotlyar, L. S.; Sparks, B. D.; Chung, K. H., Adsorption of pentane insoluble organic matter from oilsands bitumen onto clay surfaces. Petroleum science and technology 2006, 24, (3-4), 327-338. 69. Pernyeszi, T.; Patzko, A.; Berkesi, O.; Dékány, I., Asphaltene adsorption on clays and crude oil reservoir rocks. Colloids and Surfaces A: Physicochemical and Engineering Aspects 1998, 137, (1), 373-384.


39

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 40

70. Bennion, D. B., An overview of formation damage mechanisms causing a reduction in the productivity and injectivity of oil and gas producing formations. Journal of Canadian Petroleum Technology 2002, 41, (11). 71. Alboudwarej, H.; Pole, D.; Svrcek, W. Y.; Yarranton, H. W., Adsorption of asphaltenes on metals. Ind. Eng. Chem. Res. 2005, 44, 5585. 72. Dudášová, D.; Simon, S.; Hemmingsen, P. V.; Sjöblom, J., Study of asphaltenes adsorption onto different minerals and clays: Part 1. Experimental adsorption with UV depletion detection. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2008, 317, (1), 1-9. 73. Zahabi, A.; Gray, M. R.; Dabros, T., Heterogeneity of Asphaltene Deposits on Gold Surfaces in Organic Phase Using Atomic Force Microscopy. Energy & Fuels 2012, 26, (5), 2891-2898. 74. Habib, F. K.; Diner, C.; Stryker, J. M.; Semagina, N.; Gray, M. R., Suppression of Addition Reactions during Thermal Cracking Using Hydrogen and Sulfided Iron Catalyst. Energy & Fuels 2013, 27, (11), 6637-6645. 75. Sanford, E. C., Molecular approach to understanding residuum conversion. Industrial & engineering chemistry research 1994, 33, (1), 109-117. 76. Gray, M. R.; McCaffrey, W. C., Role of chain reactions and olefin formation in cracking, hydroconversion, and coking of petroleum and bitumen fractions. Energy & fuels 2002, 16, (3), 756-766. 77. Alshareef, A. H.; Scherer, A.; Tan, X.; Azyat, K.; Stryker, J. M.; Tykwinski, R. R.; Gray, M. R., Formation of archipelago structures during thermal cracking implicates a chemical mechanism for the formation of petroleum asphaltenes. Energy & Fuels 2011, 25, (5), 2130-2136. 78. Guczi, L.; Beck, A.; Horvath, A.; Koppány, Z.; Stefler, G.; Frey, K.; Sajo, I.; Geszti, O.; Bazin, D.; Lynch, J., AuPd bimetallic nanoparticles on TiO 2: XRD, TEM, in situ EXAFS studies and catalytic activity in CO oxidation. Journal of Molecular Catalysis A: Chemical 2003, 204, 545-552. 79. Toulhoat, H.; Prayer, C.; Rouquet, G., Characterization by atomic force microscopy of adsorbed asphaltenes. Colloids and Surfaces A: Physicochemical and Engineering Aspects 1994, 91, 267-283.


40

Influence of Asphaltene Aggregation on the Adsorption and Catalytic

Recommend Documents