Asphaltenes In Toluene Research Articles

SYNTHETIC WATER-IN-OIL EMULSIONS: EFFECT OF OIL COMPOSITION ON STABILITY AND DEMULSIFIER PERFORMANCE

Stable water-in-oil (w/o) emulsions are undesirable from an operational standpoint, with the asphaltenes present in petroleum being considered the main stabilizers of these emulsions. Demulsifiers are agents added to destabilize these emulsions. The objective of this work is to evaluate the stability of w/o emulsions formed from an oil phase with different polarities (kerosene and toluene) containing asphaltene fractions C3I, C5I, and C7I, and how these systems affect the action of a demulsifier additive. Systems containing asphaltenes in toluene were more stable when using the C7I fraction due to its greater polarity and, consequently, considerable action at the interface. With the oil phase composed of a less polar solvent (kerosene), the C3I fraction increased the stability of the emulsion by reducing the action of the demulsifying additive, with an upper asphaltenes concentration limit of 1.0% observed where the action of the demulsifying agent was affected.

Study of asphaltene reaggregation in toluene/heptane mixture by dynamic and static light scattering

This paper presents the study of the effect of multiple ultrasonic impacts on submicron asphaltene aggregates in a toluene/heptane solution, conducted with dynamic light scattering technique. The objects of the study were four samples of asphaltenes obtained from four different oils. For all samples, the change in the average size of the asphaltene submicron aggregates with time was measured after the addition of a precipitant (heptane) to a solution of asphaltenes in toluene at an amount above the threshold concentration. Asphaltene aggregates formed in solution after the addition of the precipitant and were subjected to ultrasonic treatment, which led to the destruction of the asphaltene aggregates. Aggregation of destroyed asphaltenes was observed. The kinetics of this aggregation were similar to the kinetics of aggregation of asphaltenes after the addition of a precipitant. Multiple iterations of asphaltene aggregate destruction in the sample led to a significant change in the kinetics of aggregation: the growth of aggregates slowed and stabilized at a size of approximately 200 nm and 30 nm for the different studied samples.

Producing asphaltene fibres from bitumen‐derived asphaltenes for carbon fibre development: Part one–Electrospinning

AbstractBitumen‐derived asphaltenes are rich in carbon but of low value and contain other elements such as nitrogen, sulphur, oxygen, vanadium, and nickel. Their use as a feedstock for producing carbon fibre (CF) is largely under‐investigated. In this study, electrospinning was used to create asphaltene fibres (AFs), which is a pre‐carbon fibre material, from asphaltenes. Various operational parameters were investigated in order to improve the spinning abilities, such as the concentration of asphaltenes in toluene, pumping rate, voltage, and distance between the tip of the needle to the collector. Results indicated that asphaltenes concentrations had the greatest effect on the quality of the produced AFs, with the range of asphaltenes concentrations from 45 to 50 wt.% being suitable for producing the AFs, while voltage, pumping rate, and tip distance had less of an effect on electrospun AF production.

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.

A study on the characteristics of Algerian Hassi-Messaoud asphaltenes: solubility and precipitation

This study focuses on detailed characterizations of asphaltene fractions extracted from the Algerian Hassi-Messaoud oil field. It was found that the extracted asphaltenes are not completely soluble in toluene, instead two fractions of asphaltenes were obtained upon solubilizing the heptane-precipitated neat asphaltenes in toluene. Extensive characterizations of the toluene-soluble and insoluble fractions were carried out using elemental analysis, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (ssNMR). It was suggested that the high oxygen content and uneven compositional structures are the main contributors to asphaltene instability. The toluene-insoluble fractions were found to have higher polarity and aromaticity as well as more oxygen content than the neat asphaltenes and toluene-soluble fractions.

Influence of ultrasonic treatment on kinetic of asphaltene aggregation in toluene/heptane mixture

This article illustrates the results of a study of ultrasonic dispersion’s influence on kinetic of asphaltene aggregation in a toluene/heptane mixture. The study was carried out by the method of dynamic light scattering. This optical method allows to measure the size of nano- and submicron particles in liquid medium. This method allows to measure the dependence of the average size of asphaltene aggregates during primary and secondary asphaltene aggregation. The primary aggregation was studied in a solution of asphaltenes in toluene and was initiated by the addition of heptane. Secondary aggregation of asphaltenes was initiated by ultrasonic dispersion of a mixture of toluene/heptane/asphaltene, in which primary aggregation finished and which contained asphaltene floccules. The effect of stabilization of asphaltene aggregates was experimentally detected after multiple ultrasonic dispersions.

Estimating the asphaltene critical nanoaggregation concentration region using ultrasonic measurements and Bayesian inference

Bayesian inference and ultrasonic velocity have been used to estimate the self-association concentration of the asphaltenes in toluene using a changepoint regression model. The estimated values agree with the literature information and indicate that a lower abundance of the longer side-chains can cause an earlier onset of asphaltene self-association. Asphaltenes constitute the heaviest and most complicated fraction of crude petroleum and include a surface-active sub-fraction. When present above a critical concentration in pure solvent, asphaltene “monomers” self-associate and form nanoaggregates. Asphaltene nanoaggregates are thought to play a significant role during the remediation of petroleum spills and seeps. When mixed with water, petroleum becomes expensive to remove from the water column by conventional methods. The main reason of this difficulty is the presence of highly surface-active asphaltenes in petroleum. The nanoaggregates are thought to surround the water droplets, making the water-in-oil emulsions extremely stable. Due to their molecular complexity, modelling the self-association of the asphaltenes can be a very computationally-intensive task and has mostly been approached by molecular dynamic simulations. Our approach allows the use of literature and experimental data to estimate the nanoaggregation and its credible intervals. It has a low computational cost and can also be used for other analytical/experimental methods probing a changepoint in the molecular association behaviour.

Synthesis and evaluation of a hyperbranched copolymer as viscosity reducer for offshore heavy oil

As is well known, resin and asphaltene greatly increase the viscosity of the oil, which causes difficulty for heavy oil to flow and to be displaced. Therefore, reducing the viscosity of heavy oil effectively is the key to enhance oil recovery. A hyperbranched copolymer named as HVR grafted with hydrophilic surfactant monomers, was synthesized and evaluated in this paper as an alternative to reduce the offshore heavy oil viscosity. The synthesis method of HVR through free-radical copolymerizing using the third generation polyamidoamine dendrimer, acrylamide, acrylic acid and surfactant monomers in deionized water was detailed in this paper. Thereupon the characterization of HVR were described by Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The physical properties of HVR solution including apparent viscosity, oil viscosity reducing ability, interfacial tension were comprehensively studied. Otherwise the effect of HVR on sheet structure of asphaltene aggregate and asphaltene aggregation inhibition-dispersion activity were measured by X-ray diffraction and ultraviolet–visible spectrophotometer, respectively. The results indicate that apparent viscosities of HVR solution is relatively not high. For example, after shearing with a Waring blender at 3500 rpm for 20 s, the viscosity of 2500 ppm HVR solution is only 22.7 cP. However, the HVR solution has a relatively high viscosity remaining rate, which is approximately 58%. On the other hand, HVR solution has a good viscosity reducing ability on heavy oil. For the oil viscosities from 350 cP to 500 cP, the viscosity reduction rate of HVR at 2000 ppm is approximately 97% under the oil-water ratio of 3:7. In addition, the oil-water interfacial tension can be reduced by HVR solution at the concentration of 2500 ppm to 1.61 × 10−2 mN m−1. Comparing the asphaltene aggregates after interacting with HPAM and HVR, it illustrates that the layer spacing, interchain distance and diameter of the aromatic sheets are lager if interacting with HVR; meanwhile height of the aromatic clusters and effective number of aromatic sheets are smaller due to the reaction with HVR. In addition, if compared with the asphaltene treated by HPAM, with the increase of HVR concentration, the absorbance of asphaltene in toluene treated by HVR solution decreased significantly. Overall, this new hyperbranched copolymer shows potential for applications in heavy oil viscosity reduction.

Development of a Methodology Using GPC-ICP HR MS for Analysis of the Adsorption of Asphaltene Aggregates on SiO2 Nanoparticles

The aggregation and adsorption of asphaltenes is of great interest due to their negative effects on the oil industry. Asphaltenes form aggregates, even at low concentrations, producing groups of molecules with different molecular weights in equilibrium. Using GPC ICP HR MS, the different molecular weight fractions are separated. By monitoring the signals of S, V, and Ni ions, typical mass profiles are obtained. The V profile of asphaltene in toluene shows three zones corresponding to low, medium, and high molecular weight fractions in equilibrium. The present study describes the development of a method to study the adsorption of asphaltenes on SiO2 nanoparticles using GPC-ICP HR MS. Samples of asphaltenes in toluene were analyzed before and after adsorption onto nanoparticles (NPs). At low concentrations, the adsorption of larger aggregates predominates. The adsorption onto NPs increases the proportion of vanadium in the low molecular weight fraction of the solution.

Toward Predictive Molecular Dynamics Simulations of Asphaltenes in Toluene and Heptane.

The conventional definition of asphaltenes is based on their solubility in toluene and their insolubility in heptane. We have utilized this definition to study the influence of partial charge parametrization on the aggregation behavior of asphaltenes using classical atomistic molecular dynamics simulations performed on the microsecond time scale. Under consideration here are toluene- and heptane-based systems with different partial charges parametrized using the general AMBER force field (GAFF). Systems with standard GAFF partial charges calculated by the AM1-BCC and HF/6-31G*(RESP) methods were simulated alongside systems without partial charges. The partial charges implemented differ in terms of the resulting electrical negativity of the asphaltene polyaromatic core, with the AM1-BCC method giving the greatest magnitude of the total core charge. Based on our analysis of the molecular relaxation and orientation, and on the aggregation behavior of asphaltenes in toluene and heptane, we proposed to use the partial charges obtained by the AM1-BCC method for the study of asphaltene aggregates. A good agreement with available experimental data was observed on the sizes of the aggregates, their fractal dimensions, and the solvent entrainment for the model asphaltenes in toluene and heptane. From the results obtained, we conclude that for a better predictive ability, simulation parameters must be carefully chosen, with particular attention paid to the partial charges owing to their influence on the electrical negativity of the asphaltene core and on the asphaltenes aggregation.

Mechanism of an asphaltene inhibitor in different depositing environments: Influence of colloid stability

Additives are used to reduce unwanted carbonaceous deposits of asphaltenes on surfaces during petroleum production from natural oil and gas reservoirs. The working mechanism of formulated additive packages can be multifaceted. Additives may be effective in the bulk fluid by preventing asphaltenes aggregation, as well as at the surface by preventing asphaltenes adhesion. In this paper, we investigate the numerous different mechanisms by which an asphaltene inhibitor can interfere with the formation of carbonaceous deposits using a combination of techniques including dynamic light scattering to determine particle size distribution, quartz crystal microbalance with dissipation monitoring to examine deposition behaviour and atomic force microscopy to probe deposit morphology. The tested inhibitor prevents deposition of asphaltenes in toluene, where asphaltenes exist as a stable colloidal dispersion of nanoaggregates, by forming barrier-type films that inhibit asphaltenes adhesion and displacing adsorbed thin films of asphaltenes. However, inhibitor performance in heptane-toluene, where asphaltenes are destabilised, depends on the degree of destabilisation. At low heptane volume fraction, inhibitor slows the rate of deposition and deposition rate decreases with increasing inhibitor concentration. However, at high heptane volume fraction, inhibitor can increase the deposition rate, particularly when used in high concentration. At high heptane volume fraction, inhibitor addition alters the morphology of the deposit from that consisting of large flocculent aggregates to that consisting of smaller, submicrometer aggregates. This is consistent with the finding that inhibitor acts as an anti-agglomerant and prevents the formation of large aggregates in the bulk liquid. This paper shows that the impact of inhibitor addition depends on the environmental conditions encountered and the degree of destabilisation of the asphaltenes. Where inhibitor addition alters the nature of depositing species from large flocculent aggregates to smaller submicrometer aggregates, an increase in deposition rate may be observed.

Brine ions impacts on water-oil dynamic interfacial properties considering asphaltene and maltene constituents

Smart water flooding is one of the most promising methods for Enhanced Oil Recovery (EOR). However, the exact mechanism beyond is still unknown and the comprehensive knowledge for optimization of the composition of the ions needed for an effective flooding process is not available. In this manner, the interactions of different ions present in the aqueous phase with those components of the oil that can have a certain affinity to water (e.g. asphaltene and maltene) are of great importance. In this research work, the effects of monovalent and divalent ions of different charges (Na+, Cl−, Ca2+, Mg2+, and SO42-) on dynamic interfacial properties of the water/oil system have been studied using profile analysis tensiometry (PAT) experimental method. It is demonstrated that participation of the ions from the water phase into the electrostatic interactions with oil, depends on the surface charge of different components of the oil that adsorb at interface. For a better understanding of this matter, separate solutions of the extracted asphaltene in toluene and maltene (de-asphalted oil using heptane) were prepared and used for comparative studies. The results illustrate a major role for the cations, while changes of the anions show negligible effects in our case studies. Among the cations, Mg2+ and Ca2+ show very significant effects on interfacial properties of the related brine-oil interface while Na+ shows negligible effects. The results also demonstrate more significant interaction of the resin components with divalent cations (Mg2+ and Ca2+) in comparison with the asphaltene components. In particular, Mg2+ shows a stronger interaction with both resin and asphaltene molecules in comparison with Ca2+. The measured interfacial elasticity results provide us very helpful complementary data for better understanding of the approximate size and concentration of the adsorbed molecules/aggregates, that support these findings well.

Molecular dynamics simulations of asphaltene aggregation under different conditions

Abstract The formation of organic sediments, especially asphaltene in reservoirs, wells and equipment, has a harmful effect on the oil production economy, which reduces oil production and can block oil production facilities. In order to investigate the asphaltene aggregation and solubility, a series of molecular dynamics simulations in different conditions were performed on two famous asphaltene based model, of M1 and VI. VI asphaltene has two high aliphatic side chains, whereas M1 asphaltene has only two methyl groups on its sides. The simulation results show that the solubility parameter increases with increasing number of aromatic rings and decreasing the number of carbon atoms in the side chain. The aggregation of asphaltene molecules in toluene, heptane and isopropyl benzene solvents and also in the mixture of solvents has been investigated. The results show that the aggregation of M1 asphaltene in toluene and isopropyl benzene is lower than that of VI asphaltene. The mixture isopropyl benzene-heptane is appropriate solvent for both asphaltenes M1 and VI which represents less interaction between asphaltene molecules. The effect of six types of inhibitors on the aggregation of asphaltene was investigated. Based on the simulation results, the aggregation of asphaltene with the presence of DETPMP inhibitor significantly decreases due to the delay in the growth of crystals and by increasing the concentration of all used inhibitors, their inhibitory properties were decreased.

Impact of Asphaltene Surface Energy on Stability of Asphaltene–Toluene System: A Parametric Study

Asphaltene is a complex macromolecule whose abundance strongly affects the physical and interfacial properties of crude oil. Asphaltene molecules may precipitate during crude oil production/transportation, which may lead to plugging/clogging of wellbores, pipelines, and equipment. In this study, the solubility of asphaltene in toluene has been investigated by calculation of noncovalent interaction energies between asphaltenes in toluene medium. The results of this study revealed that the main interactions in the asphaltene-toluene system are Lifshitz-van der Waals and Lewis acid-base interactions, whereas the electrostatic double layer is of lower comparative order of significance specifically at lower separation distances and lower ζ potentials. However, the repulsive electrostatic double-layer interactions may assist in stabilizing the asphaltene-toluene system based on the comparative values of Lifshitz-van der Waals, Lewis acid-base, and electrostatic double-layer interactions. This is the case especially at higher separation distances and/or higher temperatures where asphaltene particles have greater values of ζ-potential. Furthermore, it is illustrated that when asphaltene has a lower electron-donor parameter, i.e., a lower basicity than toluene, then Lewis acid-base interactions between asphaltenes in toluene are repulsive. This repulsive Lewis acid-base interaction may compensate for the attractive van der Waals interactions between asphaltene particles at low asphaltene basicity. Finally, the electron donor/acceptor component of the surface energy strongly determines the fate of asphaltene in crude oil colloidal system.

On Certain Characteristics of Ultrasound Attenuation in Suspensions of High-Molecular Oil Components

The paper presents experimental research data on the frequency and concentration dependences of additional ultrasound attenuation in mixtures of asphaltene in toluene. The results indicate that additional attenuation is determined by several different processes and has a relaxation nature. By juxtaposing the results to the data from several methods for studying similar model disperse systems, we show that changes in the concentration attenuation coefficient and its frequency dependence can provide additional information on structure transformations and phase transitions. The frequency dependence was measured in a range of 10–23 MHz. The concentration dependence was measured in the same frequency range from 0.1 to 10 wt %.

Deposition of Asphaltene from Destabilized Dispersions in Heptane–Toluene

Deposition of carbonaceous materials, such as asphaltene, is a major problem in petroleum production. During production, changing environmental conditions destabilize asphaltene, resulting in dispersions that are out of equilibrium, where asphaltene is aggregating or flocculating. Key to developing the most effective strategies for tackling this problem is a fundamental understanding of asphaltene deposition behavior. A quartz crystal microbalance with dissipation monitoring (QCM-D) is used to study asphaltene deposition from destabilized dispersions generated by in-line mixing of asphaltene in toluene (a solvent) with n-heptane (a precipitant). The effects of heptane:toluene ratio and destabilization time are investigated. At high heptane:toluene ratio, the rate of asphaltene aggregation is faster, and large flocs form by the time the flowing liquid reaches the QCM cell. In this case, the rate of deposition decreases with deposition time. At low heptane:toluene ratio, the rate of asphaltene aggregation i...

Suppression of Phase Separation as a Hypothesis to Account for Nuclei or Nanoaggregate Formation by Asphaltenes in Toluene

Here, the concept of suppression of phase separation is proposed to account for the solubility behavior of asphaltenes at high dilution in toluene under ambient conditions. Nuclei formation at concentrations near 90 mg L–1 is the consequence of reaching A1 fraction solubility, and phase separation is suppressed by the intercalation of sufficient A2 in these nuclei or nanoaggregates. Presumably, such intercalation leads to media penetration of the nuclei periphery, hindering the growth and allowing for nuclei dispersion as a kinetic unit. Trapped compounds (TCs) or compounds trapped by asphaltene clusters were isolated, and their elemental analysis showed that they were neither resins nor asphaltenes. The information available regarding the A1 and A2 asphaltene subfractions is revised and complemented with new thermogravimetric analysis, simulation distillation (SimDis) curves, microcarbon Conradson, softening points, and nanoparticle results involving size-exclusion microchromatography. In general, physical results, such as solubility, SimDis, aggregation, and the softening point, differ substantially, whereas structural results, such as elemental analysis, DBE, and 13C nuclear magnetic resonance spectra, are similar. These results suggest that minor structural differences strongly affect the solubility, softening point, and other physical characteristics.

Gold Core Nanoparticle Mimics for Asphaltene Behaviors in Solution and at Interfaces

Asphaltenes are a poorly defined class of self-assembling and surface active molecules present in crude oils. The nature and structure of the nanoaggregates they form remain subjects of debate and speculation. In this exploratory work, the surface properties of asphaltene nanoaggregates are probed using electrically neutral 5 nm diameter gold-core nanoparticles with alkyl, aromatic, and alkanol functionalities on their surfaces. These custom synthesized nanoparticles are characterized, and their enthalpies of solution at near infinite dilution and the interfacial tensions of solutions containing these nanoparticles are compared with the corresponding values for Athabasca pentane asphaltenes. The enthalpies of solution of these asphaltenes in toluene, heptane, pyridine, ethanol, and water are consistent with the behavior of gold-alkyl nanoparticles. The interfacial tension values of these asphaltenes at toluene–water and (toluene + heptane)–water interfaces are consistent with the behavior of gold-biphenyl...

Relationships between Electrical Conductivity Variation and Coking Characteristics of Residue during Thermal Reaction through Online Equipment

To study the relationship between the electrical conductivity and the coking performance, a device for the online measurement of the conductivity of heavy oil during thermal reaction was constructed. Three samples with different fraction compositions, including Middle East atmospheric residue (ME-AR), Tahe atmospheric residue (TH-AR), and Saudi Arabia vacuum residue (SA-VR), were selected for study. The conductivity of all samples presents the peak value, before or after the end of the coke induction period. The molar conductivity of asphaltenes, resins, or aromatics in toluene solutions was measured, and the fractions were derived from SA-VR thermal reaction samples under hydrogen. The molar conductivity of asphaltenes in toluene was 20 and 2000 times more than that of resins and aromatics, indicating that the asphaltene was the most important conductive fraction in the petroleum residue. The dipole moments of fractions of SA-VR thermal reaction samples were measured. The concentration of asphaltenes went through a maximum during a reaction, which was consistent with the conductivity variation qualitatively. This work indicated that there were certain relationships between the conductivity variation and the coking characteristics of residue during thermal reaction.

The influence of different organic solvents on the size and shape of asphaltene aggregates studied via small-angle X-ray scattering and scanning tunneling microscopy

An influence of various organic compounds on aggregation of asphaltenes separated from Tartar oil was studied by small-angle X-ray scattering and scanning tunneling microscopy methods. The compounds such as cyclohexane, methanol, formic acid, heptane, tetrabutylammonium fluoride, acetonitrile, decane, hexanol-1, furfural, and octene-1, added to the solution of asphaltenes in toluene, were shown to produce a considerable aggregation of asphaltene particles of ∼10–13 nm size and of an oblong ellipsoid shape along the longer axis. Decalin, dimethylformamide, dimethylsulfoxide, nitrobenzene, aniline, cyclohexanol, monoethanolamine, triethanolamine, 1-methylnaphtalene, and dichloroethane cause asphaltene aggregate sizes to decrease essentially. Acetone, glycerin, ethyl acetate, dioxane, benzyl alcohol, oleic acid, limonene, α-pinene, cycloheptatrien, and nitromethane were shown to influence weakly on aggregation/disaggregation processes of asphaltenes. Conceivable reasons of the observed effects are discussed from general physico-chemical properties of the compounds used.