Asphaltene Solutions Research Articles

Supported and Free-Standing Non-Noble Metal Nanoparticles and Their Catalytic Activity in Hydroconversion of Asphaltenes into Light Hydrocarbons

The hydroconversion of asphaltenes into light hydrocarbons catalyzed by supported and free-standing non-noble metal nanoparticles was studied. The activity of Ni or Co immobilized on microspherical oxide carriers and Co nanoparticles dispersed in a hydrocarbon solution of asphaltene was found to be higher than that of a comparative Pt-Pd/Al2O3 catalyst. The yield of light products (C5+) reached up to 91% on cobalt nanoparticles supported onto alumina microspheres.

Structural Rheology in the Development and Study of Complex Polymer Materials.

The progress in polymer science and nanotechnology yields new colloidal and macromolecular objects and their combinations, which can be defined as complex polymer materials. The complexity may include a complicated composition and architecture of macromolecular chains, specific intermolecular interactions, an unusual phase behavior, and a structure of a multi-component polymer-containing material. Determination of a relation between the structure of a complex material, the structure and properties of its constituent elements, and the rheological properties of the material as a whole is the subject of structural rheology-a valuable tool for the development and study of novel materials. This work summarizes the author's structural-rheological studies of complex polymer materials for determining the conditions and rheo-manifestations of their micro- and nanostructuring. The complicated chemical composition of macromolecular chains and its role in polymer structuring via block segregation and cooperative hydrogen bonds in melt and solutions is considered using tri- and multiblock styrene/isoprene and vinyl acetate/vinyl alcohol copolymers. Specific molecular interactions are analyzed in solutions of cellulose; its acetate butyrate; a gelatin/carrageenan combination; and different acrylonitrile, oxadiazole, and benzimidazole copolymers. A homogeneous structuring may result from a conformational transition, a mesophase formation, or a macromolecular association caused by a complex chain composition or specific inter- and supramolecular interactions, which, however, may be masked by macromolecular entanglements when determining a rheological behavior. A heterogeneous structure formation implies a microscopic phase separation upon non-solvent addition, temperature change, or intense shear up to a macroscopic decomposition. Specific polymer/particle interactions have been examined using polyethylene oxide solutions, polyisobutylene melts, and cellulose gels containing solid particles of different nature, demonstrating the competition of macromolecular entanglements, interparticle interactions, and adsorption polymer/particle bonds in governing the rheological properties. Complex chain architecture has been considered using long-chain branched polybutylene-adipate-terephthalate and polyethylene melts, cross-linked sodium hyaluronate hydrogels, asphaltene solutions, and linear/highly-branched polydimethylsiloxane blends, showing that branching raises the viscosity and elasticity and can result in limited miscibility with linear isomonomer chains. Finally, some examples of composite adhesives, membranes, and greases as structured polymeric functional materials have been presented with the demonstration of the relation between their rheological and performance properties.

Different effects of resins and asphaltenes concentration of crude oil on sandstone wettability

The influence of asphaltenes in crude oil on sandstone wettability is widely acknowledged. Although asphaltenes are recognized for their stronger polarity compared to resins, resins also contain the similar acidic and nitrogen-containing compounds to those found in asphaltenes. Nevertheless, the impact of resin adsorption on altering sandstone wettability, the different effects of vary concentrations of resins and asphaltenes, and their microscopic mechanisms influencing sandstone surfaces remain ambiguous. Thus, in this study, resins and asphaltenes were isolated from crude oil individually to investigate the different effects of their concentrations on sandstone wettability and the specific reasons. The contact angle measurements, atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and Cryo-environmental scanning electron microscopy (ESEM) were used to examine and explain the wettability changes of Berea sandstone slices before and after exposure to varying concentrations kerosene solutions of resins and asphaltenes. The results reveal that sandstone wettability could not be changed from strongly water-wet to oil-wet, even at resin concentrations as high as 50.0 mg/mL kerosene. In contrast, lower concentrations of asphaltenes, equivalent to a 5.0 mg/mL kerosene threshold, can facilitate the wettability transition process. After the adsorption of resins and asphaltenes, the roughness of the clay surface changes much more significantly than that of the quartz surface. Combined with the observation of ESEM and the results of EDS, it is believed that the resins and asphaltenes preferentially adsorb to clay surfaces, especially chlorite, rather than quartz surfaces. Clay could provide favorable sites for the accumulation of oxygen-containing compounds, leading to enduring clay-organic complexes that serve as anchor molecules for the adsorption of other compounds, ultimately causing the sandstone surface to an oil-wet state. These results may provide theoretical support for better core aging process in the laboratory, surfactant development and enhanced oil recovery procedure optimization in the oilfield.

Investigation of the Interfacial Tension at the Interface Between Water and Asphaltene Solution in Toluene

Investigation of the Interfacial Tension at the Interface Between Water and Asphaltene Solution in Toluene

CHANGES IN THE COMPOSITION AND COLLOIDAL STABILITY OF HEAVY OIL IN THE PRESENCE OF QUINOLINE

The influence of low molecular weight nitrogenous bases (by the example of quinoline) on the composition and colloidal stability of asphaltenes in solutions and oil dispersed systems is investigated. The objects of study were model oil systems with the basic nitrogen content of 1.0-3.0 wt. %, obtained by mixing the original oil and quinoline. The content of basic nitrogen (Nbas) was determined using the method of non-aqueous potentiometric titration. Analysis of the colloidal stability of asphaltenes in solutions and oil systems was carried out by spectrophotometry. It is shown that the content of asphaltenes in oil systems is reduced by 0.22 wt. % with an increase in the content of basic nitrogen (quinoline) up to 3 wt. %. At the same time, the content of resins increases by almost 8 wt. %. With an increase in the content of quinoline in oil systems, the proportion of basic nitrogen in the asphaltenes isolated from them increases from 1.71 to 3.60 wt. %, which indicates the active participation of quinoline in the formation of supramolecular structures of asphaltenes during their precipitation with n-hexane. The presence of low molecular weight nitrogenous bases (quinoline) in oil contributes to a significant increase in the growth rate of aggregates and a decrease in the colloidal stability of oil systems.

Asphaltenes: Aggregates in Terms of A1 and A2 or Island and Archipielago Structures.

In this work several issues related to asphaltenes and asphaltene aggregates such as isolation of real asphaltene molecules and comparison of these with average structures obtained using regular analytics laboratory techniques are presented. Several molecular organic models were used to simulate asphaltene in solution and aggregates formation in the two solvents toluene and THF employed. The results, obtained from simulation calculations using molecular dynamics were compared with experimental chromatography results obtained using the micro gel permeation chromatography (μGPC), inductively coupled plasma (ICP) mass spectra (MS) combined technique (GPC ICP MS for short). In this case reasonable hydrodynamic ratios and size distribution were obtained for asphaltenes and their corresponding subfractions A1 and subfraction A2. Comparison between experimental sample profiles, transmission of electron microscopy (TEM) data, and molecular dynamics allows for estimation of hydrodynamic ratios of around 8 nm. Highly aromatic and island type molecular model A30 and continental type molecular model A40 were employed in the molecular dynamics to built colloids. In this case open-like colloids (A40) and compact-like colloids A30 were obtained. Subjects such as trapped compounds (TC), metallic porphyrins, and colloidal dipole moments were also studied. Studies of the adsorption behavior of asphaltenes on several macroscopic and nanoscopic surfaces are presented and show the tendency of the asphaltene to adsorb in aggregate form.

Cancellation of dipole moment of models of asphaltene aggregates as a mean for their dispersion in toluene and THF calculated using molecular dynamics

The study of the behavior of asphaltenes in solution has focused on their tendency to form aggregates and less importance has been given to describing and understanding what allows the formation of asphaltene aggregates that remain stably dispersed. Using molecular dynamics simulations, we calculated that the dipole moment of models for asphaltene aggregate tends to zero when the number of molecules in the aggregate tends to large values. In other words, such dipole moment cancellation would be an important contributor to the dispersion of these aggregates.

Asphaltene precipitation under controlled mixing conditions in a microchamber

Solvent exchange is a controlled process for dilution-induced phase separation. This work utilizes the solvent exchange method to reveal the effect of the mixing dynamics on the asphaltene precipitation process under 20 different mixing conditions using a model system of n-heptane and asphaltene in toluene. The external mixing between the asphaltene solution and the paraffinic solvent is strictly controlled. We employed high-spatial resolution total internal reflection fluorescence microscope to detect asphaltene precipitates with a resolution up to ∼ 200 nm. A multiphysics model is used to simulate the evolution of oversaturation pulse in the solvent exchange process. Based on the simulation results, we predicted the effect of the flow rate, dimension, orientation of the microfluidic chamber, and temperature on the surface coverage and size distribution of asphaltene precipitates. The model predictions of all factors corroborate with the experimental observations. Local concentration of the solvent and shear forces are found to be the two main reasons for the change of asphaltene precipitation caused by mixing dynamics. However, the influence of thermodynamics is more critical than the mixing dynamics as temperature changes. Through a combination of experimental and simulation studies, this work illuminates the significance of the transportation process for the final morphology of asphaltene precipitates and provides a in-depth insight into the mechanism of mixing dynamics on the asphaltene precipitation. A smart mixing may be to boost new phase formation without excessive solvent consumption.

Influence of Asphaltene Modification on Structure of P3HT/Asphaltene Blends: Molecular Dynamics Simulations.

Further development and commercialization of bulk heterojunction (BHJ) solar cells require the search for novel low-cost materials. The present study addresses the relations between the asphaltenes’ chemical structure and the morphology of the poly(3-hexylthiohene) (P3HT)/asphaltene blends as potential materials for the design of BHJ solar cells. By means of all-atom molecular dynamics simulations, the formation of heterophase morphology is observed for the P3HT-based blends with carboxyl-containing asphaltenes, as well as the aggregation of the asphaltenes into highly ordered stacks. Although the π–π interactions between the polyaromatic cores of the asphaltenes in solutions are sufficient for the molecules to aggregate into ordered stacks, in a blend with a conjugated polymer, additional stabilizing factors are required, such as hydrogen bonding between carboxyl groups. It is found that the asphaltenes’ aliphatic side groups may improve significantly the miscibility between the polymer and the asphaltenes, thereby preventing the formation of heterophase morphology. The results also demonstrate that the carboxyl-containing asphaltenes/P3HT ratio should be at least 1:1, as a decrease in concentration of the asphaltenes leads to the folding of the polymer chains, lower ordering in the polymer phase and the destruction of the interpenetrating 3D structure formed by P3HT and the asphaltene phases. Overall, the results of the present study for the first time reveal the aggregation behavior of the asphaltenes of varying chemical structures in P3HT, as well the influence of their presence and concentration on the polymer phase structure and blend morphology, paving the way for future development of BHJ solar cells based on the conjugated polymer/asphaltene blends.

Size distribution of primary submicron particles and larger aggregates in solvent-induced asphaltene precipitation in a model oil system

Asphaltene precipitation is a crucial phase separation phenomenon in the oil industry, especially in paraffinic froth treatment to extract bitumen from oil sands ores. This work reveals the ubiquitous presence of particles at 0.2 to 0.4 μm in radius, defined as primary sub-micron particles (PSMPs) at early stage asphaltene precipitation from diffusive mixing with solvents. We observed PSMPs in a quasi-2D chamber where asphaltene solution (the model oil) is displaced by 3 paraffinic solvents, the blends of solvents, and solvents containing inhibitor at low concentrations. The yield and size distribution of asphaltene particles are affected not only by the Hildebrand solubility parameter of the precipitants but also by the diffusion coefficients of the asphaltene solution and the precipitant. Even though n-pentane is a stronger solvent than n-heptane, the yield of asphaltene in the diffusive mixing chamber is close because of the difference in the diffusion coefficient between n-pentane and n-heptane in asphaltene solution. The results of n-heptane and n-decane blends reveal that the increase of the ratio of PSMPs compared with pure n-heptane or n-decane. The inhibitors significantly decrease the aggregation rate of PSMPs, displayed as a higher ratio of PSMPs compared to a non-inhibitor group. The population balance model (PBM) with the Hildebrand solubility parameter has been used to model particle size distribution. Good agreement has been achieved between numerical predictions and the experimental data. It indicates that the colloid theory can describe the size distribution of PSMPs and larger aggregates in early stage of asphaltene precipitation. This study illustrates the importance of mixing dynamics on the size distribution in asphaltene precipitation. The findings can be useful for accurate modeling of the hydrocarbon separation or asphaltene precipitation.

Investigation of the interfacial tension at the interface between water and asphaltene solution in toluene

The dynamics of the interfacial tension coefficient at the interface between water and model solutions of asphaltenes of different concentrations in toluene has been studied. It has been shown that, over time, the interfacial tension decreases due to the adsorption of asphaltene molecules at the interface. With an increase in the concentration of asphaltenes in the solution, the decrease in interfacial tension occurs more intensively. The results of a study of the elongation of a water drop in a solution under the influence of an electric field are presented. It is shown that after the formation of an adsorption film, a higher electric field must be applied to stretch the droplet, and the relative elongation depends nonlinearly on the applied voltage. Keywords: interfacial tension coefficient, asphaltenes, adsorption film, drop elongation.

Исследование межфазного натяжения на границе воды и раствора асфальтенов в толуоле

The dynamics of the interfacial tension coefficient at the interface between water and model solutions of asphaltenes of different concentrations in toluene has been studied. It has been shown that, over time, the interfacial tension decreases due to the adsorption of asphaltene molecules at the interface. With an increase in the concentration of asphaltenes in the solution, the decrease in interfacial tension occurs more intensively. The results of a study of the elongation of a water drop in a solution under the influence of an electric field are presented. It is shown that after the formation of an adsorption film, a higher stress must be applied to stretch the droplet, and the relative elongation depends nonlinearly on the applied stress. The studies were carried out using the suspended drop method.

Model Asphaltenes Adsorbed onto Methyl- and COOH-Terminated SAMs on Gold.

Petroleum asphaltenes are surface-active compounds found in crude oils, and their interactions with surfaces and interfaces have huge implications for many facets of reservoir exploitation, including production, transportation, and oil-water separation. The asphaltene fraction in oil, found in the highest boiling-point range, is composed of many different molecules that vary in size, functionality, and polarity. Studies done on asphaltene fractions have suggested that they interact via polyaromatic and heteroaromatic ring structures and functional groups containing nitrogen, sulfur, and oxygen. However, isolating a single pure chemical structure of asphaltene in abundance is challenging and often not possible, which impairs the molecular-level study of asphaltenes of various architectures on surfaces. Thus, to further the molecular fundamental understanding, we chose to use functionalized model asphaltenes (AcChol-Th, AcChol-Ph, and 1,6-DiEtPy[Bu-Carb]) and model self-assembled monolayer (SAM) surfaces with precisely known chemical structures, whereby the hydrophobicity of the model surface is controlled. We applied solutions of asphaltenes to these SAM surfaces and then analyzed them with surface-sensitive techniques of near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). We observe no adsorption of asphaltenes to the hydrophobic surface. On the hydrophilic surface, AcChol-Ph penetrates into the SAM with a preferential orientation parallel to the surface; AcChol-Th adsorbs in a similar manner, and 1,6-DiEtPy[Bu-Carb] binds the surface with a bent binding geometry. Overall, this study demonstrates the need for studying pure and fractionated asphaltenes at the molecular level, as even within a family of asphaltene congeners, very different surface interactions can occur.

Molecular Dynamics and Proton Hyperpolarization via Synthetic and Crude Oil Porphyrin Complexes in Solid and Solution States.

The use of vanadyl porphyrins either in synthetic compounds or naturally occurring in asphaltenes is investigated as a source of proton hyperpolarization via dynamic nuclear polarization (DNP) in nuclear magnetic resonance (NMR) experiments. The features of dynamics and location of the vanadyl VO2+ complex in aggregates within the oil asphaltene molecules are studied by means of DNP, electron paramagnetic resonance (EPR), and NMR field cycling relaxometry. Both the solid effect and Overhauser DNP were observed for the asphaltene solution in benzene, as well as in the solution and solid states for synthetic compounds. By comparison with a solution of synthetic vanadyl porphyrins, it is shown that vanadyl porphyrins in asphaltene aggregates are localized outside of the interface of the asphaltene aggregates and more exposed to the maltene molecules than "free" carbon-centered radicals associated with the core of asphaltene molecules. The perceptible contribution of scalar interaction is observed in solutions for both synthetic and asphaltene vanadyl porphyrins.

Impedance response of asphaltene solutions: Effect of solvation

The present work uses a combination of X-ray diffraction (XRD) analysis and dielectric spectroscopy (DES) to study asphaltene aggregation and interactions between these aggregate and maltene phases, with the variations in solvency power of the maltenes, at different asphaltene concentrations. The ability of the dielectric spectroscopy to quantify the interaction of the asphaltenes with the maltene phase lead to the development of a correlation with respect to the solution viscosity.It was seen that the combination of the data obtained from the XRD and DES accounted for differing asphaltene molecular structures, variations in the maltene phase with respect to its solvency power as well as the asphaltene concentration in the solution. This is the first step in developing the ability to predict solution viscosity, as well as eventually explaining rheological behavior, of asphaltene containing compositions.The future application of this work will be to assess if the findings of the methodology used in this paper,i.e. the combination of DES and XRD to predict asphaltene aggregation behavior and solvation, is applicable for asphaltenes from crude oils and heavy oil sands. In addition the use of the DES technique for online insitu monitoring of viscosity of crude oils/ refinery bitumen formulations will also be explored.

Derivative UV-Vis Spectroscopy of Crude Oil and Asphaltene Solutions for Composition Determination

The determination of the first and second derivatives in the UV spectra of crude oil and asphaltene solutions allows the identification of signals attributed to compounds in the crude oil that cannot be seen in the normal spectrum. This processing of the crude oil UV-Vis spectrum to determine first and second derivatives allowed the identification of five maxima. The maxima observed in the first derivative spectrum can be related to different types of compounds in crude oil: ~230 nm for benzene compounds, 259 nm for naphthalene compounds and their derivatives, 295 nm for pure phenanthrene, 328 nm for aromatic chromophores with three or four aromatic rings, and 401 nm for the Soret electronic absorption band of vanadyl porphyrins. The shape of the spectra was analyzed to predict the presence of colloids or particles in the solutions.

The study of asphaltene desorption from the iron surface with molecular dynamics method

In this work, we use molecular dynamics method to estimate the effects of various physical parameters such as: temperature, pressure and TiO2 nanoparticle in the desorption of asphaltene from the iron surface. To calculate the effect of these parameters in the desorption of asphaltene, the iron matrix is simulated at various temperatures (300 K, 325 K and 350 K), pressures (1.00 bar, 1.25 bar and 1.50 bar) and TiO2 atomic rate. In the first step of our simulations, the effect of temperature variation on the desorption of asphaltene molecules from iron matrix was investigated. In the second step, the effects of simulation box pressure were examined. Finally, TiO2 nanoparticles were added to the asphaltene solution and simulations done. In this step, the nanoparticles were added with various volume ratios at 300 K, and the asphaltene molecules distances from the iron matrix were reported. The study of TiO2 nanoparticles effect on the interaction of asphaltene molecules and iron matrix is the novelty of this research and includes practical hints. Our results show that the atomic force between asphaltene and iron surface would decrease with an increase in temperature and pressure of the simulation box. Further, TiO2 nanoparticles atomic rate is another important parameter in separation of asphaltene molecule from the iron surface. Numerically, a separation distance of asphaltene molecules from the iron surface in simulated structures with 1%, 2.5% and 5% nanoparticle rates are 13.6 Å, 17.8 Å and 15.2 Å, respectively.

Effect of resin/asphaltene ratio on the rheological behavior of asphaltene solutions in a de-asphalted oil and p-xylene: A theoretical–experimental approach

This study focuses on understanding the effect of the resin/asphaltene mass ratio (R/A) on the rheological behavior of asphaltene solutions. To this aim, two cases were evaluated experimentally and theoretically. The first case comprised asphaltenes dissolved in a de-asphalted oil (DAO) at asphaltene concentrations of 2, 10, and 16.5% of mass fraction, with R/A ratios of 3, 6, and 31 being obtained. The second case consisted of asphaltenes dissolved in p-xylene, at an asphaltene mass fraction of 1 and 18%, and adding resins to obtain low R/A ratios (0, 0.125, 0.5, 1, and 1.5). The viscosities measured experimentally were reproduced by molecular dynamics (MD) simulations, using the Green-Kubo method and non-equilibrium MD (NEMD) for estimating the viscosity of solutions with Newtonian and non-Newtonian behavior, respectively. In all cases, the experimental measurements were accurately reproduced by MD. Further, the asphaltene-asphaltene and asphaltene-resin coordination number (CN), the asphaltene-asphaltene and asphaltene-solvent interaction energies, the radius of gyration, and the volumetric fraction for asphaltene aggregates were calculated. Theoretical results evidence that the asphaltene molecules dissolved in DAO exhibited repulsive interaction energies between them, whereby the asphaltene is mainly dispersed for R/A ratios higher than 3 in DAO. This result indicates that the viscosity of the heavy oil is not only dependent on the asphaltene aggregation, but that the resin plays a key role in the rheological behavior of this type of crude oil. This latter suggestion was evidenced in the viscosity measurements due to the DAO viscosity (1776 cP) being considerably higher compared to the individual viscosity of the other compounds of the mixture (i.e., saturates and aromatics), which were at least two orders of magnitude lower. In the experimental evaluations of rheological behavior, varying the resin amount in asphaltene dissolved in p-xylene, a minimum viscosity point was obtained for a specific R/A ratio. The MD results indicated that the resins inhibit the asphaltene aggregation, reducing the volumetric fraction and, therefore, the viscosity decreased. Understanding the physical principles of the effect of the resin on the asphaltenes' aggregation, from an atomistic point of view, is a valuable contribution for designing inhibitors that can be used for the specific molecular characteristics of any crude oil.

Effect of solvent polarity during electrodeposition of asphaltenes from a Colombian oil in the presence of a magnetic field and magnetic nanoparticles

This work focuses on analyzing the electrokinetic behavior of asphaltenes of extra heavy oil. For this, electrodepositions were carried out in asphaltene solutions (4 %w/w) with two solvents of different polarities: toluene and chloroform. In addition, we worked with different magnetic fields, and the effect of adding 1% w/w of magnetic nanoparticles was analyzed. The asphaltenes were extracted with heptane and were characterized by infrared and ultraviolet visible spectroscopy. In the case of toluene, the initial adsorption (without fields) was 4 mg in both anode and cathode. By using an electric field (100 V/m) the deposits increased to 6 mg (anode) and 5 mg (cathode). However, when using a static magnetic field of 0.1 mT, no changes were observed. But, by modifying said field by a dynamic one (0.1 mT and 60 Hz), 15 mg (anode) and 19 mg (cathode) were obtained. Moreover, the addition of nanoparticles (previously characterized by scanning electron microscopy and X ray diffraction) changed the behavior, worsening in the absence of fields, and improving only in the presence of the dynamic field (104 mg, 26 mg in anode and cathode, respectively). Similar results were obtained when using chloroform. Thus, the best performance was obtained by using a dynamic magnetic field. By not considering the nanoparticles, total deposits increased more than 14 times (102 mg versus 7 mg). However, considering them, the increase was greater than 30 times (302 mg versus 10 mg). Therefore, we consider that adding nanoparticles, and supporting the electrodeposition process with a dynamic magnetic field, is an alternative that must be included to improve process performance.

Asphaltene Solutions Are Not Adequately Described by Popular Models of Solid Suspensions

The structural parameters of asphaltene nanoparticles are analyzed by employing theoretical models for the properties of solid suspensions in ideal fluids with unvarying composition. This approach ...