Solutions Of Asphaltenes In Toluene Research Articles

Impedance spectroscopy in asphaltene-toluene and maltene-toluene solutions of crude oils from the Orinoco Belt

In this investigation, an impedance and dielectric spectroscopy study was carried out on Asphaltene-Toluene and Maltene-Toluene solutions, prepared from two oil samples from the Orinoco Oil Belt that presented low resistivity at the depths of the oil well where petrophysical logs were taken. The purpose of this work is to investigate whether the asphaltenes and maltenes would be responsible for the low resistivities found in the logs. A Lock-In amplifier, an impedance analyzer, and a coaxial cylindrical cell were used to obtain the impedance measurements. From the plotting of the impedance and phase angle parameters, it was confirmed Asphaltene-Toluene solutions were the least resistive. A fit of the experimental data based on an electrical circuit was realized, finding good correspondence between the experimental data and the fit line. The AC conductivity values were plotted using the fitting data, and it was observed that the Asphaltene-Toluene solution is more conductive. A remarkable difference in the electrical behavior was found between the maltene solutions of both crude oil samples .

Theoretical-experimental evaluation of rheological behavior of asphaltene solutions in toluene and p-xylene: Effect of the additional methyl group

This study is focused on understanding the effect of the additional methyl group (-CH3) of p-xylene, in comparison with toluene, on the rheological behavior of model solutions of asphaltenes. For this, three concentrations of asphaltenes in both solvents were evaluated experimentally and theoretically. Experimental results show an increase of the viscosity as the asphaltene concentration increase, being up to 739% higher in p-xylene than in toluene. Molecular dynamics (MD) simulations were conducted to understand the difference in the rheological behavior of asphaltene model solutions. The viscosity, volumetric fraction of aggregates, coordination number (CN), as well as the asphaltene-asphaltene and asphaltene-solvent interaction energies were calculated. Experimental viscosities were accurately reproduced by MD simulations, with average deviation lower than 7.4% and 10.9% for toluene and p-xylene solutions, respectively. The volumetric fraction exhibits a similar trend regarding the increase in viscosity, whereby the results obtained are in agreement with the Einstein theory modified for concentrated suspensions, since an increase in the volumetric fraction promotes viscosity increases. On the other hand, from the theoretical evaluation, it was found out that the additional methyl group in the p-xylene structure regarding toluene, promotes significant differences between the interaction energies of asphaltene aggregates. This is a consequence of an increasing of the aggregates size, which contributes to the increase of volumetric fraction and therefore the viscosity. Finally, this study highlights the importance of the asphaltene-solvent relationship, from an atomistic point of view, since small changes in aggregates volume promotes significantly changes in viscosity.

Aggregation of asphaltenes in the presence of dispersant S5A

Aggregation of asphaltenes over time in the presence of dispersant S5A has been studied using photon correlation spectroscopy. The addition of the dispersant to toluene solutions of asphaltenes decreases the size of the aggregates, stabilizes their growth, and reduces the rate of aggregation for a considerably long time. The growth stabilization is achieved at the asphaltenes to dispersant ratio of 0.2–4.

Alkanes Induced Asphaltene Precipitation Studies at High Pressure and Temperature in the Presence of Argon

The continuous increase of petroleum production under adverse subsea conditions and the preeminent need for adequate operational conditions and efficient use of additives to warrant flow assurance makes it interesting to set up experimental procedures to carry out n-alkane precipitation studies under high-pressure (p) and high-temperature (T) conditions. In this contribution, some preliminary experimental studies developed to characterize asphaltene precipitation in model systems consisting of asphaltene solutions in toluene or mixtures of hydrocarbons by the addition of propane, n-heptane, or other alkanes at various pressures and temperatures, using a commercial compact equipment, are reported. In general terms, it was established that these tests follow the same pattern described at ambient p and T conditions and the one single study reported in the literature for a stock tank oil sample at 3000 psi and room T. Four crude oils of different characteristics were tested, using diluted or undiluted samples, and it was possible to detect the asphaltene precipitation onset. However, these results cannot be used to infer the stability of the crude oils because results correlating onset and stability at high p and T are not yet available. The effect of pressure at high pressures was not entirely resolved because argon, used as an assumed inert gas to pressurize the system, dissolves in the hydrocarbons and displaces the precipitation onset toward lower values. The need to develop compact equipment to assess the effect of solvents, inhibitors, and other additives on the phase behavior of crude oil at high pressure and temperature and in the presence of CO2 and other gases, representing a valuable contribution to the petroleum industry in the area of flow assurance, still persists.

Cluster of Asphaltene Nanoaggregates by DC Conductivity and Centrifugation

A model of the dominant molecular and stable colloidal structures of asphaltenes has been proposed, the Yen–Mullins model. The formation of clusters of asphaltene nanoaggregates in toluene was reported elsewhere to occur at a concentration of a few grams per liter with a cluster aggregation number of approximately 8 (Mullins, O. C. Energy Fuels 2010, 24, 2179−2207). Here, we measure the DC-conductivity signal of toluene as a function of asphaltene concentration obtaining support for the critical clustering concentration (CCC) of a roughly 1.7 g/L in toluene. In addition, the small change in the Stokes drag at the CCC indicates that the cluster aggregation number is small, less than 10. The temperature variation of the CCC is measured to be small and within error, suggesting that cluster formation is entropically driven. Centrifugation experiments were also performed on asphaltene–toluene solutions at different concentrations. These experiments confirmed that a significant change in asphaltene aggregation occurs in the concentration range of the CCC. The CCC values from centrifugation and DC-conductivity measurements are roughly the same. The centrifugation experiments confirm a cluster size of ∼5 nm corroborating the small aggregation number found in the DC-conductivity experiments. These results add to the growing body of literature validating the Yen–Mullins model.

Asphaltene Adsorption onto Acidic/Basic Metal Oxide Nanoparticles toward in Situ Upgrading of Reservoir Oils by Nanotechnology

The effects of surface acidity and basicity of metal oxide nanoparticles on the thermodynamics of asphaltene adsorption were studied. Three different categories of metal oxides/salts with acidic (WO3 and NiO), amphoteric (Fe2O3 and ZrO2), and basic (MgO and CaCO3) surfaces were synthesized, and their textural, structural, and acid-base properties were characterized. Asphaltenes were extracted from a dead oil sample and characterized by X-ray powder diffraction and Fourier transform infrared spectroscopy. The acid and base numbers of the asphaltenes were measured. The nanoparticles were added to the asphaltene-toluene solutions, and the amount of adsorbed asphaltene was obtained through centrifugation followed by UV-vis spectroscopy of the supernatant liquid and temperature-programmed oxidation analysis of the precipitated solid. The concentrations of organic acid and base groups in the asphaltenes are 2.75 and 12.34 mg of KOH/g, respectively, indicating that the asphaltenes are more basic in nature. Isotherms of the asphaltene adsorption onto the six metal oxides/salts fit the Langmuir model closely. The asphaltene adsorption capacity of the nanoparticles is 1.23-3.67 mg/m(2) and decreases in the order of NiO > Fe2O3 > WO3 > MgO > CaCO3 > ZrO2, concomitant with the synergetic effects of acidity and the net charge of the surfaces. High-resolution transmission electron microscopy illustrates that the asphaltenes are spread out over the surfaces with no short-range/long-range order. The adsorption of the asphaltenes onto the six samples is exothermic and spontaneous with the Gibbs energy change of -27.80 to -28.79 kJ/mol at 25 °C. The absolute value of the enthalpy change of the adsorption is calculated to be within the range of 5-20 kJ/mol. Acid-base interaction and electrostatic attraction seem to be the dominant forces contributing to the adsorption of the asphaltenes onto the metal oxide/salt surfaces.

Study of Asphaltene Adsorption on Kaolinite by X-ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectroscopy

The interaction between asphaltenes and clay is crucial in understanding wettability changes in petroleum reservoirs and in oilsands production. In this study, we report the changes in surface properties and composition of kaolin clay as a result of exposure to solutions of asphaltenes. Adsorption experiments were conducted at 25 °C with solutions of asphaltenes in toluene at concentrations ranging from 0.05 to 5 mg/mL. The wettability of the modified kaolinite surface was characterized by contact angle measurement. Chemical composition changes of the surface because of asphaltene adsorption were assessed using time-of-flight secondary ion mass spectroscopy (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and elemental analysis. The contact angle data indicated that, upon asphaltene adsorption, the clay particles changed from water-wet to bi-wet. Both ToF-SIMS and XPS measurements indicated that the kaolinite surface was never completely covered by asphaltenes based on the concentration of Al and Si on asphaltene-treated kaolinite surfaces. ToF-SIMS analysis indicated that, with more asphaltenes covered on the kaolinite surface, the relative intensities of C3H5+/Al+ and C3H5+/Si+ increased and an inverse linear correlation between the contact angle and surface Si+ concentration was observed. The maximum thickness of adsorbed asphaltenes, assuming complete surface coverage, was estimated to be 11 nm based on XPS depth profile results on a model silica surface, with a mean value of 3 nm. The XPS depth profile also indicated no preferential adsorption of nitrogen- or sulfur-rich species at the interface between asphaltenes and kaolinite.

Structure and Dynamic Properties of Colloidal Asphaltene Aggregates

The abundant literature involving asphaltene often contrasts dynamic measurements of asphaltene solutions, highlighting the presence of small particle sizes between 1 and 3 nm, with static scattering measurements, revealing larger aggregates with a radius of gyration around 7 nm. This work demonstrates the complementary use of the two techniques: a homemade dynamic light scattering setup adapted to dark and fluorescent solutions, and small-angle X-ray and neutron scattering. Asphaltene solutions in toluene are prepared by a centrifugation separation to investigate asphaltene polydispersity. These experiments demonstrate that asphaltene solutions are made of Brownian colloidal aggregates. The hydrodynamic radii of asphaltene aggregates are between 5 and 10 nm, while their radii of gyration are roughly comparable, between 3.7 and 7.7 nm. A small fraction of asphaltenes with hydrodynamic and gyration radii around 40 nm is found in the pellet of the centrifugation tube. The fractal character of the largest clusters is observed from small angle scattering nearly on a decade length scale. Previous results on aggregation mechanisms are confirmed ( Eyssautier, J., et al. J. Phys. Chem. B 2011 , 115 , 6827 ): nanoaggregates of 3 nm radius, and with hydrodynamic properties also frequently illustrated in the literature, aggregate to form fractal clusters with a dispersity of aggregation number.

Effect of the Particle Size on Asphaltene Adsorption and Catalytic Oxidation onto Alumina Particles

In this study, the adsorption and catalytic oxidation of asphaltenes, problematic heavy hydrocarbons present in heavy oil, onto two aluminas with different particle sizes and comparable surface acidity were investigated. Equilibrium batch adsorption experiments were conducted at 25 °C with solutions of asphaltenes in toluene at concentrations ranging from 100 to 3000 mg/L. Adsorption data were fit to the Langmuir and Freundlich isotherm models. Nano-alumina fit better to the Langmuir model, while micro-alumina fit well to the Freundlich model. On a surface area basis, nano-alumina has higher adsorption capacity for asphaltenes than micro-alumina. Interestingly, micro-alumina has higher catalytic activity toward asphaltene oxidation than nano-alumina, at the same asphaltene loading, thus exhibiting the significance of textural properties during catalytic oxidation of asphaltenes that dominated over the effect of the particle size.

Small-angle scattering study of colloidal particles in heavy crude oils

The structural and dispersion characteristics of samples of heavy crude oils and fractions isolated from them have been studied. A method of in situ analysis of the aggregation of asphaltenes directly in crude oils on the basis of small-angle X-ray scattering is proposed. It has been shown that the maximum size of scattering particles in all crude oil samples is limited to the value on the order of 8.0 nm; the average diameter is ∼2.0 nm. It has been found that the fraction with sizes of 0.8–2.5 nm is mostly composed of resins. Asphaltenes in crude oils form larger aggregated particles with a size up to 8 nm. A comparative study of model dilute solutions of asphaltenes in toluene (0.23 wt %) has shown that the major part of asphaltenes in the liquid (∼94%) is in the form of individual molecules with a size of 0.4–1.2 nm, and only an insignificant remaining part (∼6%) occurs in the form of large aggregates.

Particular features of circular dichroism spectra of resin-asphaltene compounds in solvent and crude oil

The circular dichroism (CD) spectra of solutions of asphaltenes, resins, and crude oils in toluene, as well as of oil residue, which is free of resin-asphaltene compounds (RACs), were studied in the spectral range 400–600 nm. It was demonstrated that, unlike, oil and RACs solutions, oil residue does not show the CD signal. This result proves that, in this spectral range, the occurrence of the CD signal in oil is determined by the presence of RACs. The concentration dependences of CD signal for the solutions under study were obtained for the maximum of the CD band in the considered spectral range. For pure toluene solutions of asphaltenes and resins, these dependences can be approximated with good accuracy by a linear function, whereas, for solutions of crude oils, the concentration curves deviate from the linear dependence at large concentrations of RACs due to the formation of particles of the disperse phase in oil. Therefore, in a certain concentration range, the structure of oil undergoes significant changes and becomes disperse, whereas solutions of molecules of RACs remain molecular.

Effect of surface acidity and basicity of aluminas on asphaltene adsorption and oxidation

This study investigates the effect of surface acidity and basicity of aluminas on asphaltene adsorption followed by air oxidation. Equilibrium batch adsorption experiments were conducted at 25°C with solutions of asphaltenes in toluene at concentrations ranging from 100 to 3000g/L using three conventional alumina adsorbents with different surface acidity. Data were found to better fit to the Freundlich isotherm model showing a multilayer adsorption. Results showed that asphaltene adsorption is strongly affected by the surface acidity, and the adsorption capacities of asphaltenes onto the three aluminas followed the order acidic>basic and neutral. Asphaltenes adsorbed over aluminas were subjected to oxidation in air up to 600°C in a thermogravimetric analyzer to study the catalytic effect of aluminas with different surface acidity. A correlation was found between Freundlich affinity constant (1/n) and the catalytic activity. Basic alumina that has the lowest 1/n value, depicting strongest interactions, has the highest catalytic activity, followed by neutral and acidic aluminas, respectively.

Adsorption of Asphaltenes in Porous Media under Flow Conditions

Asphaltene adsorption on minerals induces wettability alteration in porous media, which, in turn, affects capillary pressure, relative permeability, and residual oil saturations. The majority of existing work addresses the adsorption of asphaltenes on minerals under static conditions, where adsorption isotherms are measured and modeled. Very little work currently exists on the adsorption kinetics of asphaltenes under dynamic conditions, which are more relevant to laboratory-scale experiments, specifically those involving dynamic wettability alteration of minerals. In this study, we propose to investigate the dynamic adsorption of different asphaltenes on various minerals using UV−vis spectroscopy. The experimental setup consists of a core holder containing crushed minerals with comparable mesh size. Asphaltene solutions in toluene are then flown though the mineral pack with a constant flow rate, and their concentrations are recorded with time at the outlet. Preliminary results indicate that adsorption is largely controlled by the type of mineral rather than the asphaltene itself. The highest adsorption amounts per unit area are found on calcite. Furthermore, the effect of several parameters, such as concentration, asphaltene composition, and flow rate, are considered. The theory of activated adsorption/desorption (TAAD) approach (Rudzinski, W.; Plazinski, W. J. Phys. Chem. C 2007, 111, 15100−15110) is incorporated into the convection-dispersion transport equation to model the flow of asphaltenes inside the porous medium. The resulting equation is then solved numerically using Barakat−Clark finite difference technique (Satter, A.; Shum, Y.; Adams, W.; Davis, L. SPE J. 1980, 20, 129−138). We find that kinetics and not equilibrium governs asphaltene adsorption in porous media. Levenberg−Marquardt’s optimization algorithm is used to derive kinetic parameters, such as Γm, ka, and kd. Once these concentration-independent parameters are found, the model is able to predict with reasonable accuracy the effect of concentration on asphaltene adsorption in porous media.

Composition of Asphaltene Solvate Shell at Precipitation Onset Conditions and Estimation of Average Aggregate Sizes in Model Oils

Macroscopic properties of petroleum disperse systems are functions of its particle size. Asphaltene particles in model oils are in fact building agents. Compositional changes of disperse medium have an effect on the internal structure of the dispersed system. Optical methods are informative enough for analysis of structural evolutionary processes. Near-infrared (NIR) spectroscopy was used to determine asphaltene precipitation onset conditions in model oils (asphaltenes were dissolved in binary solvent: toluene and n-alkane precipitant n-hexane/n-heptane). Asphaltene precipitation onset was determined as a point where the deviation from Beer’s law takes place. Solvate shells of asphaltenes in binary solvents are formed according to differences between intermolecular interaction potentials of components of the model oil. The model of non-uniform distribution of components in solvate shells of asphaltene aggregates at the moment of aggregation stability loss (first stage of precipitation onset) is proposed. On the basis of experimentally determined asphaltene precipitation onset conditions, average aggregate sizes in toluene solutions, set of assumptions concerning geometry of solvent and precipitant molecules, and interaction energy of molecule pairs, the proposed model allows for estimation of the precipitant fraction threshold value in solvate shells of asphaltene aggregates at the moment of stability loss. Polarization of fluorescence was used for the determination of the concentration dependence of average sizes of aspahltene aggregates in toluene solution. The linear aggregation model was used for characterization of asphaltene solutions in toluene; the fraction of n-mers was determined. The concentration dependence of the asphaltene aggregation rate constant was calculated within this model.

A combined QCM and XPS investigation of asphaltene adsorption on metal surfaces

To investigate asphaltene–metal interactions, a combined quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS) study of asphaltene adsorption on a gold surface was conducted. Adsorption experiments were conducted at 25 °C with solutions of asphaltenes in toluene at concentrations ranging from 50 to 1500 ppm. QCM measurements yielded information on the kinetics of adsorption and further assessment of the data allowed the estimation of equilibrium adsorption levels. XPS analysis of adsorbed and bulk asphaltene demonstrated the presence of carboxylic, thiophenic, sulfide, pyridinic and pyrrolic type functional groups. The intensity of the main carbon (C–H) peak was related to surface coverage of adsorbed asphaltene as a function of asphaltene concentration by a simple mathematical model. The mass adsorption data from the QCM experiments also allowed estimation of the surface coverage, which was compared to those from XPS analyses. Surface coverage estimates as a function of asphaltene concentration could be described by a Langmuir (type-I) isotherm. The free energy of asphaltene adsorption was estimated to be − 26.8 ± 0.1 and − 27.3 ± 0.1 kJ / mol from QCM and XPS data, respectively assuming asphaltene molar mass of 750 g/gmol. QCM and XPS data was also analyzed to estimate adsorbed layer thickness after accounting for surface coverage. The thickness of the adsorbed asphaltene estimated from both XPS and QCM data analyses ranged from 6–8 nm over the entire range of adsorption concentrations investigated.

Interactions between Asphaltenes and Water in Solutions in Toluene

Binding of water by asphaltenes dissolved in toluene was investigated for two asphaltene samples, OMV1 and OMV2, from the same reservoir deposit. Solubility of water in asphaltene solutions in toluene was found to increase with an increasing asphaltene concentration, indicative of solubilization of water by asphaltenes. Fourier transform infrared (FTIR) spectroscopy of stretching modes of OH groups in the region of 3800−3100 cm−1 was used to obtain insight into the state of water in water-unsaturated asphaltene solutions in toluene. The number of water molecules bound to one asphaltene molecule was determined for water-saturated solutions (OMV1 and OMV2) and for water-unsaturated solutions (OMV1 only). These numbers were found to decrease from several water molecules per asphaltene molecule to below unity upon an increase of the asphaltene concentration in toluene from 0.1 to 20 g/L, suggesting that binding of water by asphaltenes dramatically depends upon the aggregated state of asphaltenes and that the mechanism of water solubilization by asphaltenes differs significantly from water solubilization in reverse micelles formed by conventional surfactants.

Characterization of the Charge Carriers in Bitumen

This work aims to identify the nature of the charge carriers in Athabasca bitumen to better understand the mechanisms of emulsion stabilization and electrically induced separations. A quartz crystal microbalance (QCM) with nanogram sensitivity is used to determine the electrodeposited mass in toluene-based systems. The use of low voltages for the first time allows a small amount of deposited material to be determined accurately. The method consists of applying a DC voltage between two gold-coated QCM crystals immersed in toluene solutions of asphaltenes, maltenes, or solid-free bitumen. Application of a 250 V/cm electric field strength produces an electrocollection of cationic and anionic species at the negatively and positively charged QCM crystals, respectively. A small fraction of the electrocollected material eventually electrodeposits and forms a transparent colorless film at the electrode surfaces. The specific mass (i.e., mass over charge) is found to be higher for the positive species than it is for the negative species. With this method, the characteristic time of relaxation of the bituminous solutions is estimated during the early stage of voltage application. This time could be used to establish a minimum frequency criterion for the critical field methods of water electrocoalescence in oil. Solids separated from bitumen are mainly negatively charged, and their specific mass is relatively high. This study shows that electrodeposition can efficiently separate solids and solid-stabilized water droplets from bitumen. Thus, an electrostatic treatment processes could be successful in removing solids and water from diluted bitumen systems.

Circular dichroism of crude oil and its derivatives. Role of permolecular structures

Petrols with different octane numbers, diesel fuel and solutions of crude oil in toluene have been studied by the methods of absorption spectroscopy, circular dichroism spectroscopy and correlation spectroscopy of scattered light. Circular dichroism signal was registered for crude oil solutions in the spectral ranges corresponding to the measured earlier resonance absorption of asphaltene solutions in toluene. We show that the optical activity of crude oil solutions is due to the aggregation of asphaltene molecules in one spectral range and is intensified with the aggregation of asphaltene molecules in another spectral range. Petrols have no optical activity. The optical activity registered for diesel fuel is possibly due to the aggregation of asphaltene molecules.

05/00565 Absorbance and fluorescence spectroscopy on the aggregation behavior of asphaltene-toluene solutions

05/00565 Absorbance and fluorescence spectroscopy on the aggregation behavior of asphaltene-toluene solutions

Methodology for the Characterization and Modeling of Asphaltene Precipitation from Heavy Oils Diluted with n-Alkanes

A regular solution model, previously used to model asphaltene precipitation from Western Canadian bitumens, was tested on four international heavy oil and bitumen samples. The input parameters for the model are the mole fraction, the molar volume, and the solubility parameter for each component. Heavy oils and bitumens were divided into four main pseudo-components, corresponding to the SARA fractions (saturates, aromatics, resins, and asphaltenes). Asphaltenes were divided into fractions of different molar mass, based on a gamma molar mass distribution. The molar volumes and solubility parameters of the pseudo-components were calculated using solubility, density, and molar mass measurements and previously developed correlations. Model predictions were compared with the measured onset and the amount of asphaltene precipitation for solutions of asphaltenes in toluene and n-heptane and for heavy oils diluted with n-alkanes, all under ambient conditions. The overall average absolute deviations (AAD) of the pr...