Onset Of Flocculation Research Articles

Role of motility and nutrient availability in drying patterns of algal droplets.

Sessile drying droplets in various bio-related systems attracted attention due to the complex interactions between convective flows, droplet pinning, mechanical stress, wettability, and the emergence of unique patterns. This study focuses on the drying dynamics of Chlamydomonas reinhardtii (chlamys), a versatile model algae used in molecular biology and biotechnology. The experimental findings shed light on how motility and nutrient availability influence morphological patterns- a fusion of macroscopic fluid dynamics and microbiology. This paper further discusses the interplay of two competing stressors during drying- nutrient scarcity (quantitative analysis) and mechanical stress (qualitative analysis), where the global mechanical stress does not induce cracks. Interestingly, motile chlamys form clusters under nutrient scarcity due to metabolic stress, indicating the onset of flocculation, a common feature observed in microbial systems. Moreover, non-motile chlamys exhibit an "anomalous coffee-ring effect" in the presence of nutrients, with an inward movement observed near the droplet edge despite sufficient water in the droplet. The quantitative image processing techniques provide fundamental insights into these behaviors in classifying the patterns into four categories (motile+with nutrients, motile+without nutrients, non-motile+with nutrients, and non-motile+without nutrients) across five distinct drying stages- Droplet Deposition, Capillary Flow, Dynamic Droplet Phase, Aggregation Phase, and Dried Morphology.

Effect of temperature on the appearance of flocculated asphaltene in an unperturbed unstable American shale oil: Insights from a colloidal modeling

This work aimed to study the onset of flocculation of asphaltenes using optical microscopy and to evaluate the effect of temperature on the destabilization of an unstable undisturbed American shale oil. After magnetic stirring for 24 h, the flocculated asphaltene was redispersed. Increasing the temperature to 40 °C led to asphaltenes flocculating. After heating, the sample was cooled back to room temperature. We calculated the precipitate volume from microscopy data and found that after cooling the system had a larger precipitate volume than in the previously studied scenarios. When comparing the volumes of precipitates before and after cooling, it is possible to observe that the volume of smaller particles does not vary significantly in each class, but the volume of larger particles increases with cooling, indicating an irreversible phenomenon. Statistical analysis of the optical microscopy results allowed a detailed analysis of the phenomenon. To study the colloidal effect, a theoretical analysis was performed based on Hamaker theory and De Gennes scaling theory, presenting compatible results when the parameters of the repulsive term were adjusted. When the parameters of both the attractive term and the repulsive term of the model were kept constant, greater stability was verified with the increase of temperature. Conversely, it was observed that the reduction of the parameter related to the length of the alkyl chains can explain the experimental macroscopic behavior of the shale oil here studied and also some different behaviors reported in the literature, i. e., increasing of flocculated volume with increasing temperature. This size reduction of the length of the alkyl chains can be attributed to a desolvation effect. Hence, the appropriate parameterization of the model showed great potential to mimic the behavior of increasing and also decreasing stability with the increase of temperature. The sets of parameters were related to reaction-limited aggregation (RLA) and diffusion-limited aggregation (DLA), which allowed to interconnect the discussion on experimental stability of asphaltenes, molecular simulation, and the theoretical discussion. Furthermore, the proper use of this theory seems to be a promising way to represent microscopic interactions in asphaltene systems, including previous results from the literature. This work presents (i) an experimental case that shows reversibility of asphaltene flocculation only with magnetic stirring; (ii) the effect of temperature on the stability of asphaltenes, and also (iii) brings a contribution with the volume of precipitate, making it possible to conclude on the irreversibility in the thermal cycle applied. In addition, the proper use of this modeling can predict the stability changes as a function of temperature, being a promising way to represent microscopic interactions in asphaltene systems, including previous results from the literature.

Prediction of Refractive Index of Petroleum Fluids by Empirical Correlations and ANN

The refractive index is an important physical property that is used to estimate the structural characteristics, thermodynamic, and transport properties of petroleum fluids, and to determine the onset of asphaltene flocculation. Unfortunately, the refractive index of opaque petroleum fluids cannot be measured unless special experimental techniques or dilution is used. For that reason, empirical correlations, and metaheuristic models were developed to predict the refractive index of petroleum fluids based on density, boiling point, and SARA fraction composition. The capability of these methods to accurately predict refractive index is discussed in this research with the aim of contrasting the empirical correlations with the artificial neural network modelling approach. Three data sets consisting of specific gravity and boiling point of 254 petroleum fractions, individual hydrocarbons, and hetero-compounds (Set 1); specific gravity and molecular weight of 136 crude oils (Set 2); and specific gravity, molecular weight, and SARA composition data of 102 crude oils (Set 3) were used to test eight empirical correlations available in the literature to predict the refractive index. Additionally, three new empirical correlations and three artificial neural network (ANN) models were developed for the three data sets using computer algebra system Maple, NLPSolve with Modified Newton Iterative Method, and Matlab. For Set 1, the most accurate refractive index prediction was achieved by the ANN model, with %AAD of 0.26% followed by the new developed correlation for Set 1 with %AAD of 0.37%. The best literature empirical correlation found for Set 1 was that of Riazi and Daubert (1987), which had %AAD of 0.40%. For Set 2, the best performers were the models of ANN, and the new developed correlation of Set 2 with %AAD of refractive index prediction was 0.21%, and 0.22%, respectively. For Set 3, the ANN model exhibited %AAD of refractive index prediction of 0.156% followed by the newly developed correlation for Set 3 with %AAD of 0.163%, while the empirical correlations of Fan et al. (2002) and Chamkalani (2012) displayed %AAD of 0.584 and 0.552%, respectively.

Structure and Flocculation of Ion Associates of Carrageenan and Poly(diallyldimethylammonium chloride) Depending on the Component Ratio.

Carrageenan is a polysaccharide of a plant origin, commonly used as a thickening and gelling agent in the food, pharmaceutical, and cosmetic industries. Due to the negative charges of its sulfate groups, carrageenan macromolecules strongly interact with oppositely charged polyions. The ionic complexes of carrageenan with poly(diallyldimethylammonium chloride) were obtained at the molar ratios 4:1, 2;1, 1:1, 1:2, and 1:4. The structure and characteristics of the polyanion-polycation associates were studied by XRD, IR, optical microscopy, and via sedimentation and particle size measurements. It was found that the suspended particles flocculate and settle fastest when the molar ratio of the polyions is near 1:1. Turbidimetric titration experiments enabled us to measure the molar ratio of cationic to anionic groups at the onset of flocculation, and the value in question was found to be 1:1.32. In other words, a mass of 511 mg carrageenan corresponds to one millimole of ester sulfate (monobasic) groups. The measurement of the onset of flocculation has been employed for the accurate determination of carrageenan in real samples of food products. The color and turbidity of the sample do not interfere with the determination results.

Tuning the Cloud-Point and Flocculation Temperature of Poly(2-(diethylamino)ethyl methacrylate)-Based Nanoparticles via a Postpolymerization Betainization Approach.

The ability to tune the behavior of temperature-responsive polymers and self-assembled nanostructures has attracted significant interest in recent years, particularly in regard to their use in biotechnological applications. Herein, well-defined poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA)-based core–shell particles were prepared by RAFT-mediated emulsion polymerization, which displayed a lower-critical solution temperature (LCST) phase transition in aqueous media. The tertiary amine groups of PDEAEMA units were then utilized as functional handles to modify the core-forming block chemistry via a postpolymerization betainization approach for tuning both the cloud-point temperature (TCP) and flocculation temperature (TCFT) of these particles. In particular, four different sulfonate salts were explored aiming to investigate the effect of the carbon chain length and the presence of hydroxyl functionalities alongside the carbon spacer on the particle’s thermoresponsiveness. In all cases, it was possible to regulate both TCP and TCFT of these nanoparticles upon varying the degree of betainization. Although TCP was found to be dependent on the type of betainization reagent utilized, it only significantly increased for particles betainized using sodium 3-chloro-2-hydroxy-1-propanesulfonate, while varying the aliphatic chain length of the sulfobetaine only provided limited temperature variation. In comparison, the onset of flocculation for betainized particles varied over a much broader temperature range when varying the degree of betainization with no real correlation identified between TCFT and the sulfobetaine structure. Moreover, experimental results were shown to partially correlate to computational oligomer hydrophobicity calculations. Overall, the innovative postpolymerization betainization approach utilizing various sulfonate salts reported herein provides a straightforward methodology for modifying the thermoresponsive behavior of soft polymeric particles with potential applications in drug delivery, sensing, and oil/lubricant viscosity modification.

Determination of Hansen Solubility Parameters of an Algerian Asphaltene and its Sub-Fractions

From near-infrared spectrophotometry measurements, flocculation onset for an Algerian asphaltene in different toluene/non-solvent solutions were detected. The Hansen solubility parameters of the extracted asphaltene and sub-fractions were calculated and compared to ones of a set of good and bad solvents. The ranking of the different solvents according to Hansen solubility sphere method shows that chloroform and quinoline may be the best solvents for dispersing polar asphaltene fractions.

The role of direct asphaltene inhibitors on asphaltene stabilization during gas injection

There are a large number of investigations, which evaluate the impact of the liquid-based inhibitors on the asphaltene stabilization. In those studies, a specific volume of inhibitor was added to the oil sample and the asphaltene precipitation is then studied. However, this method is indirectly applicable to processes like gas injection. For that reason, in this work, the metal oxide nanoparticles (GO, TiO2, SiO2, and MgO) have been considered in the liquid-free mode as direct asphaltene inhibitors (DAIs) on asphaltene stabilization for the duration of miscible CO2 injection. The dissolution of DAIs in CO2 was investigated by measurement of cloud point pressure to evaluate the pressure/temperature conditions, need for certifying that the CO2/DAIs mixtures have the single-phase condition. Afterwards, the impact of DAI was studied on asphaltene precipitation and deposition by static and dynamic approaches. Results show that the total size of asphaltene particles which precipitated during injection of miscible CO2/DAIs mixture is significantly lower than that for immiscible pure CO2 injection. The amount of asphaltene deposition significantly decreased during injection of miscible CO2/DAIs mixtures compared to immiscible pure CO2 injection. Additionally, themetal oxide nanoparticles hinder the phase separation of asphaltenes kinetically and prevent growth. It is conducted by stabilizing the colloidal suspension of the asphaltene particles, which are in sub-micrometre size to significantly slow the asphaltene flocculation onset.

Análisis comparativo de la eficiencia estabilizadora de asfaltenos del aceite de cáscara de Anacardium occidentale y productos comerciales

La investigación tuvo como objetivo comparar la eficiencia inhibidora y estabilizante de asfaltenos, en mezclas de aceite de cáscaras de Anacardium occidentale (CNSL) en diésel y productos dispersantes comerciales, para evaluar el aceite como alternativa de tratamiento químico antiasfalténico del petróleo crudo. Se determinó el umbral de floculación por precipitación con n-heptano y el punto de dispersión por adición de xileno, ambos mediante la observación directa de la formación de flóculos de asfaltenos en un microscopio óptico. El diseño experimental utilizado fue factorial, con cuatro variables respuestas (umbral de floculación, actividad inhibidora, índice de inestabilidad y eficiencia de estabilización) y dos factores experimentales (producto y dosis). Se evaluaron cinco productos con CNSL y tres productos comerciales, todos en dosis 2, 4, 6 y 8 µl en 10 ml de una muestra de petróleo crudo mediano. El análisis estadístico se basó en Anova multifactorial y test de diferencia mínima significativa de Fisher (LSD) con α = 0.05. Se obtuvo que los dos factores experimentales influyeron significativamente en las variables respuestas de forma individual y también sus interacciones. Los productos con CNSL fueron más eficientes como inhibidores y los comerciales más eficientes como estabilizadores.

Effect of asphaltene structure on its aggregation behavior in toluene-normal alkane mixtures

Colloidal behavior of asphaltene in normal alkane-toluene mixture has been under research over the past decades. However, the influence of asphaltene composition and its structure on asphaltene aggregation in such mixtures has not been fully understood yet. In this study, the colloidal behavior of asphaltene in normal alkane-toluene mixture was investigated using image processing approach. Three different types of asphaltenes were extracted from Iranian oil reservoirs. Asphaltenes were characterized by elemental analysis, X-Ray Diffraction (XRD), and Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The effects of asphaltene concentration, type of normal alkane, ratio of normal alkane to toluene, and structure of asphaltene on onset of asphaltene flocculation (OAF) and aggregates size were investigated. The onset of asphaltene flocculation decreases with increasing asphaltene concentration. A mathematical model was developed to predict OAF for different normal alkanes and asphaltenes. The proposed mathematical model has an exponential form with two constants, which should be tuned using experimental data. The results indicate that as asphaltene concentration increases, larger aggregates are formed with an average (AS) size between 8 and 15 μm and some aggregates greater than 100 μm may be formed. Moreover, the structure and composition of asphaltene is determinant of aggregates’ size. The lowest aggregates size refers to asphaltene C with the lowest number of fused rings, polarity, and aromaticity, which is the most stable asphaltene with the smallest aggregates size. Asphaltenes A and B have almost the same size as polarity and aromaticity both contribute to the aggregates size. The aggregates formed by n-C7 (AS≈ 7.5 to 8.5 μm) are larger than those of n-C10 (AS≈ 8.5 to 12 μm) and n-C16 (AS≈ 9 to 14 μm). In addition, increasing the ratio of normal alkane to toluene increases the size of asphaltene aggregates up to a maximum value and then gradually decreases.

Evaluation of Jatropha gossypiifolia oil as a asphaltenes stabilizer in a petroleum sample at the laboratory level

Asphaltenes are condensed polyaromatic solids that are present in oil forming colloidal suspensions in a thermodynamic system that in some cases tends to be unstable producing flocculation and aggregation. In the oil industry, dispersant chemical compounds are used to minimize the flocculation of asphaltenes to avoid clogging problems in pipes and production equipment, which represent an important investment since they are formulated with synthetic resins and oils, in addition to expensive solvents. This research evaluates the use of Jatropha gossypifolia oil as an active stabilizing component of asphaltenes, mixed with diesel as a solvent in laboratory level tests. Five dilutions of oil in diesel (10 to 50%) were evaluated. The procedure consisted of observing the asphaltene aggregates under an optical microscope when applying n-heptane to a crude oil sample from Monagas State, Venezuela, the volume of n-heptane used being the flocculation onset. Successive volumes of each dilution were then applied until the dispersion of the aggregates was achieved, being this volume the point of dispersion. In addition, xylene was used as a standard dispersant to compare the performance of the dissolutions. The tests were performed at two temperatures of 25 and 40 ºC. A factorial statistical design was used with experimental factors dissolution and temperature and dependent variable instability index, with ANOVA analysis and Tukey HSD test with α = 0.05. With the application of the solutions, a greater dispersion of the aggregates was achieved with efficiencies greater than 94% with respect to the dispersion obtained with xylene, being the solution with 40% oil the most efficient. The statistical results showed that stability is dependent on the solution used and independent of the test temperature with a 95% confidence level.

Predicting coke morphology in Delayed Coking from feed characteristics

Currently, there is no well-established methodology to predict coke morphology in Delayed Coking from feed characteristics. We found that for a series of fourteen coking feeds from different parts of the world, coke morphology and shot-coke propensity can be predicted by determining the asphaltene solubility parameter using the asphaltene solubility profile method without further separation and in ~25 min runs. The results are attributed to asphaltenes with higher solubility parameters that favor phase separation from the hydrocarbon matrix and lead to shot coke formation. Similarly, asphaltene peptizability measured by flocculation onset, ΔPS stability parameter determined by asphaltene solubility profile, and surface area measurements of MCRT cokes showed good potential for predicting coke morphology and shot-coke tendency of coking feeds. Conversely, mean particle size measured by cross-polarized light optical microscopy of the MCRT cokes showed a relatively large dispersion of the data and a weak correlation with the shot-coke propensity. Finally, a general scheme for the formation of shot and sponge cokes during Delayed Coking was proposed.

Investigation of the Microstructure and Rheology of Iridium Oxide Catalyst Inks for Low-Temperature Polymer Electrolyte Membrane Water Electrolyzers.

We present an investigation of the structure and rheological behavior of catalyst inks for low-temperature polymer electrolyte membrane water electrolyzers. The ink consists of iridium oxide (IrO2) catalyst particles and a Nafion ionomer dispersed in a mixture of 1-propanol and water. The effects of ionomer concentration and catalyst concentration on the microstructure of the catalyst ink were studied. Studies on dilute inks (0.1 wt % IrO2) using zeta potential and dynamic light scattering measurements indicated a strong adsorption of the ionomer onto the catalyst particles which resulted in an increase in the ζ-potential and the z-average diameter. Steady-shear and dynamic-oscillatory-shear rheological measurements of concentrated IrO2 dispersions (35 wt % IrO2) indicated that the particles are strongly agglomerated in the absence of the ionomer. The addition of even a small amount of the ionomer (2.4 wt % with respect to total solids) caused the rheology to transition from shear thinning to Newtonian because of the reduction in agglomerated structure due to stabilization of the aggregates by the ionomer, consistent with the behavior of dilute inks. At intermediate ionomer loadings, between 2.4 and 9 wt %, the viscosity increased with increasing ionomer wt %, though remained Newtonian, predominantly due to the increasing ionomer volume fraction in the ink. For ionomer loadings greater than 9 wt %, the particles were found to be flocculated, likely induced by a dispersed ionomer. The flocculated inks exhibited strong shear-thinning and gel-like behaviors in steady-shear and oscillatory-shear rheology. The onset of flocculation was found to be sensitive to the catalyst concentration, where below 35 wt % of IrO2, flocculation was not observed. The rheological observations were further verified by ultra-small-angle X-ray scattering.

Inhibition of asphaltene precipitation in blended crude oil using novel oil-soluble maleimide polymers

ABSTRACTAsphaltene deposition can cause serious problems during petroleum refinery. In this paper, oil-soluble MAC series asphaltene dispersants with comblike structure were synthesized by free- radical polymerization and amination. The asphaltene deposition inhibition was investigated by determining the flocculation onset of blended crude oil (Tahe: Northern Xinjiang = 20:80 (w/w)) and conducting dynamic thermal deposition experiment. The results showed that MAC3 had the best performance and the flocculation onset of crude oil increased from −20.5 to 3.89 when the dosage of MAC3 was 150 mg/L. The anti-scaling rate of MAC3 was 60% in dynamic thermal deposition experiment of blended crude oil.

Chemical Prevention of Asphaltene Flocculation in Oil Production System

The change of pressure, temperature or chemical composition of crude oil during oil production constitute the factors that may destabilize the heaviest fraction of crude oil presented in asphaltenes leading to many problems in the production system including the alteration of reservoir rock wettability, permeability reduction, plugging of tubing and production aerial facilities which generate a high production cost because of loss in the well productivity and the need of corrective measures. In this work, a crude oil sample was taken from an Algerian oil field to study the efficiency of two commercial inhibitors. The flocculation onset point of asphaltenes was measured by a solid detection system which is based on the light transmittance of flocculated particles when n-heptane is added. The effectiveness of two inhibitors was evaluated by the solid detection system at different concentration to select the best inhibitor, however, the best additive should provide a good performance at low concentration. Meanwhile, the effect of thermodynamic conditions has been also established in this work, however, the operator conditions of pressure and temperature have affected the efficiency of the added inhibitor on the flocculation of asphaltenes.

Inhibition of asphaltene flocculation in light crude oil: effect of pressure, temperature and inhibitor concentration

In this study, a light crude oil sample was taken from Hassi Messaoud field to characterize its physicochemical properties. The asphaltene flocculation onset was determined in the dead oil by Flocculation Titrimeter equipment. The petroleum resins have been extracted from the same crude oil and tested as an inhibitor of asphaltene flocculation then their efficiency has been studied at different conditions of pressure and temperature. The results point out that the extracted resins may have two different effects on the onset point depending upon the operator conditions and the concentration of the added resins to crude oil.

Laboratory Testing and Prediction of Asphaltene Deposition in Production Wells

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27884, “Laboratory Testing and Prediction of Asphaltene Deposition in Production Wells,” by Kosta J. Leontaritis, SPE, and Efstratios Geroulis, SPE, Asphwax, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. During primary oil production, when the thermodynamic conditions within the well tubing lie inside the asphaltene-deposition envelope (ADE) of the produced fluid, flocculated asphaltene particles could start being deposited on the tubing wall, causing a restriction in the tubing inner diameter that results in loss of production. This paper presents a methodology that begins by determining the ADE in the laboratory. Moreover, asphaltene-deposition rates for the tubing conditions can be measured using high-pressure/high-temperature coaxial-cylinder technology. In-Situ Asphaltene Testing At some thermodynamic states, asphaltenes exhibit a behavior called flocculation—that is, asphaltene particles or micelles aggregate or flocculate into larger particles or flocs. The locus of all thermodynamic points in a phase diagram at which flocculation occurs is called the ADE. Accurate measurement of asphaltene solubility at in-situ conditions inside the ADE is extremely difficult. Many asphaltenic reservoir fluids exhibit irreversible asphaltene flocculation. This means that, once the upper ADE boundary is crossed, some of the asphaltenes will not deflocculate and go back into stable suspension by simply reversing the thermodynamic path. The spectrophotometric near-infrared (NIR) onset method uses the observation that there is a sharp increase in light absorption or attenuation in the NIR region of the electromagnetic spectrum at the onset of asphaltene flocculation. Transmittance of light through a sample of asphaltenic oil has also been used to detect the onset of asphaltene flocculation. There is a sharp decrease in the transmittance of NIR light through a sample of asphaltenic oil at the onset of asphaltene flocculation. Along with the spectrophotometer, an NIR imaging system is also used in the attempt to decipher the asphaltene behavior of a fluid. One can change the thermodynamic conditions in the vessel containing the sample and obtain the oil’s ADE. State-of-the-art high-pressure/high-temperature imaging technology is routinely used in the laboratory to detect asphaltene particles very clearly upon isothermal pressure depletion. The asphaltic heavy-phase-formation phenomenon is indicated in the images to be a consequence of many asphaltene particles forming, aggregating, and settling in the NIR cell under the prevailing thermodynamic conditions. This indicates that the asphaltene-phase behavior responsible for asphaltene-induced formation damage and asphaltene-deposition problems takes two forms—asphaltene flocculation into larger particles or heavy-asphaltic-phase separation.

Flocculation of Clay Colloids Induced by Model Polyelectrolytes: Effects of Relative Charge Density and Size.

Flocculation and its tuning are of utmost importance in the optimization of several industrial protocols in areas such as purification of waste water and civil engineering. Herein, we studied the polyelectrolyte-induced flocculation of clay colloids on a model system consisting of purified clay colloids of well-defined size fractions and ionene polyelectrolytes presenting regular and tunable chain charge density. To characterize ionene-induced clay flocculation, we turned to the combination of light absorbance (turbidity) and ζ-potential measurements, as well as adsorption isotherms. Our model system allowed us to identify the exact ratio of positive and negative charges in clay-ionene mixtures, the (c+/c-) ratio. For all samples studied, the onset of efficient flocculation occurred consistently at c+/c- ratios significantly below 1, which indicated the formation of highly ionene-deficient aggregates. At the same time, the ζ-potential measurements indicated an apparent zero charge on such aggregates. Thus, the ζ-potential values could not provide the stoichiometry inside the clay-ionene aggregates. The early onset of flocculation in clay-ionene mixtures is reminiscent of the behavior of multivalent salts and contrasts that of monovalent salts, for which a large excess amount of ions is necessary to achieve flocculation. Clear differences in the flocculation behavior are visible as a function of the ionene charge density, which governs the conformation of the ionene chains on the clay surface.

Application of response surface methodology for optimization of the stability of asphaltene particles in crude oil by TiO2/SiO2 nanofluids under static and dynamic conditions

ABSTRACTIn this work, the onset of asphaltene flocculation for an Iranian crude oil by titration of samples with heptane in the presence and absence of the TiO2/SiO2 nanofluids was obtained by Near-IR spectroscopy. Nanoparticles and nanocomposites were characterized by BET, FESEM, EDX, XRD, and XRF analysis. Modeling and optimization of inhibition of asphaltene flocculation process by TiO2/SiO2 nanofluids were conducted by response surface methodology (RSM). Under optimum conditions (nanocomposite composition = 0.04 wt% (80%TiO2:20%SiO2), salinity = 4.01 wt%, and pH = 3.42), the onset point increased. For nanofluids stability analysis, the optimum nanofluid was compared with the two other nanofluids (SiO2 and TiO2) by visual observation method. The results indicated that high stability and surface area of the 80%TiO2 nanocomposites increase asphaltene adsorption on the particles surface that subsequently increases the onset point. In addition, the optimum nanofluid performance on the carbonate rocks was evaluated by contact angle and core flooding experiments. The 80% TiO2 nanofluid changed the wettability of carbonate rocks from strongly oil-wet to strongly water-wet condition and also decreased the residual oil saturation and enhanced the oil recovery with an increase in the recovery factor of about 15%.

TiO2/SiO2 nanofluids as novel inhibitors for the stability of asphaltene particles in crude oil: Mechanistic understanding, screening, modeling, and optimization

Determination of the onset of asphaltene flocculation is a key step in studying the asphaltene deposition problems. Therefore, finding an inhibitor to prevent or delay the onset of asphaltene flocculation is inevitable. In this work, first the structural properties of two asphaltene samples extracted from two different Iranian south oilfields were compared. The structural parameters of both asphaltene samples were investigated using elemental analysis, FTIR spectroscopy, and XRD. The onset of asphaltene flocculation for both crude oils A and B was obtained using Near-IR spectroscopy. Asphaltene A from unstable crude oil is characterized by high aromaticity and low hydrogen content, while asphaltene B from stable crude oil shows low aromaticity and high hydrogen content. Then, Near-IR obtains the onset of flocculation by titration of oil samples with n-heptane in the presence of the TiO2/SiO2 nanocomposites at different pH and salinities. Nanoparticles and nanocomposites were characterized using BET, FESEM, EDX, FTIR, XRD and XRF analysis. Modeling and optimization of inhibition of asphaltene flocculation process by TiO2/SiO2 nanofluids were conducted using response surface methodology (RSM). Under optimum conditions (nanocomposite composition=0.04wt% (80%TiO2:20%SiO2), salinity=4.01wt% for crude oil A and B, pH=4.87 for A, pH=3.42 for B), the onset of asphaltene flocculation (the n-heptane volume) increased. For nanofluids stability analysis, one of the optimum nanofluids was compared with the two other nanofluids (SiO2 and TiO2) using visual observation method. The results indicated that high stability and surface area of the 80%TiO2 nanocomposites increase asphaltene adsorption on the particles surface which subsequently increases the onset point. Finally, Polyvinylpyrrolidone (PVP) stabilizer with 1.0 and 2.0wt% concentrations was used for the stability analysis of the optimum nanofluid using DLS measurement. The results showed that 1.0wt% PVP was the optimum concentration.

Asphaltene fractionation based on adsorption onto calcium carbonate: Part 2. Self-association and aggregation properties

The self-association and aggregation properties of asphaltene sub-fractions obtained by adsorption onto CaCO3 (doi:http://dx.doi.org/10.1016/j.colsurfa.2016.02.011) were investigated using a combination of near infrared spectroscopy, isothermal titration calorimetry (ITC) and diffusion-ordered 2D NMR spectroscopy (DOSY). Three asphaltenes sub-fractions were prepared: the bulk fraction that stayed in the bulk solution (i.e., did not adsorb on CaCO3), the adsorbed fraction that was obtained by desorption of asphaltenes adsorbed on CaCO3 using tetrahydrofuran, and the irreversibly-adsorbed fraction that was obtained after dissolution of CaCO3. The irreversibly-adsorbed asphaltene sub-fraction, which contained a higher content of carbonyl, carboxylic acid or derivative groups was found to have a significantly higher tendency to self-associate and to form larger aggregates than other fractions. In addition, the properties of above asphaltene fractions were compared with fractions obtained by stepwise precipitation using various n-hexane/crude oil ratios to study the influence of fractionation procedure. The irreversibly-adsorbed asphaltenes exhibited several similarities in properties with the fraction precipitating first from stepwise precipitation procedure (named as asphaltene 3.5V) including lower flocculation onset, higher tendency to self-associate (based on ITC) and a greater ability to adsorb onto stainless steel (based in QCM-D measurements). However, the size of aggregates determined by NMR differed, with the irreversibly-adsorbed asphaltenes forming aggregates of larger aggregate size (11.3Å) than compared to asphaltene 3.5V fractions (7.2Å). In conclusion, our investigations indicate that the asphaltene precipitation tendency depends on both the aromaticity and polarity of asphaltene fractions, and some of the asphaltene sub-fractions present different properties than the whole (or unfractionated) asphaltene fraction.