Self-Association of Asphaltenes

Sheu, Eric Y.

doi:10.1007/978-1-4899-1615-0_4

Cited by 24 publications

(23 citation statements)

References 65 publications

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“…This enhances in consequence the probability of reencounters between proton hydrocarbons and paramagnetic species, not necessarily in first neighbor, for maintaining the pairwise dipolar correlations for a much longer time and thus causing the dispersion of NMRD at low frequency. The fractal character of these macroaggregates, evidenced by conductivity 28 and SAXS 4 measurements, favors the presence of such cavities. The plateau observed in the 2D NMR D−T 2 spin correlation spectra of samples 1 and 3, for long T 2 , gives another evidence that hydrocarbons with small chains can transiently wet the asphaltene nanoaggregates.…”

Section: Theory and Discussion Of Nmrd Data In Bulk And Confined Crud...mentioning

confidence: 95%

Probing Structure and Dynamics of Bulk and Confined Crude Oils by Multiscale NMR Spectroscopy, Diffusometry, and Relaxometry

2013

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We propose using a set of noninvasive multiscale NMR techniques for probing the structure and dynamics of bulk and confined crude oils with and without asphaltene. High-field 1D (1)H and (13)C NMR spectroscopies evidence the proton species and the amount of asphaltene and give an average chain length for the hydrocarbon aliphatic chains. Two-dimensional (1)H diffusion-ordered NMR spectroscopy (DOSY) spectra allow us to identify two populations of hydrocarbons characterized by two distributions of translational diffusion coefficients in the presence of asphaltene and a single one without asphaltene. A detailed analysis of the distributions of longitudinal, T1, relaxation times measured at different magnetic fields is proposed in terms of highly skewed bimodal (or monomodal) log-normal distributions, confirming the two environments in the presence of asphaltene and a single one without asphaltene. We show that these distributions are similar to the gas and gel permeation chromatography distributions, thus showing a connection of the hydrocarbon dynamics with their chain lengths. The remarkable observed features of the nuclear magnetic relaxation dispersion (NMRD) profiles of <1/T1> for bulk and confined crude oils with and without asphaltene are interpreted with an original relaxation model of intermittent surface dynamics of proton species at the proximity of asphaltene nanoaggregates and bulk dynamics in between clusters of these nanoaggregates. This allows us to probe the 2D translational diffusion correlation time and the time of residence of hydrocarbons in the proximity of the asphaltene nanoaggregates. Provided that the diffusion of the hydrocarbons close to the asphaltene nanoaggregates is three times smaller than the bulk diffusion, as the DOSY experiments show, this time of residence gives an average radius of exploration for the 2D hydrocarbon diffusion, r2D ≈ 3.9 nm, of the same order of magnitude as the aggregate sizes found by J. Eyssautier with SAXS and SANS in asphaltene solutions and by O. C. Mullins with the observation of gravitational gradients of asphaltenes in oilfield reservoirs.

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Section: Theory and Discussion Of Nmrd Data In Bulk And Confined Crud...mentioning

confidence: 95%

Probing Structure and Dynamics of Bulk and Confined Crude Oils by Multiscale NMR Spectroscopy, Diffusometry, and Relaxometry

2013

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“…The intra- and intermolecular potentials are assigned to the atoms and molecules based on the selected force-field, and the coordination and velocity changes are calculated based on the Newton motion law. MD has been successfully employed to model asphaltene precipitation ,− and asphaltene deposition on calcite − and silica. , Also, MD is able to model the interfacial properties in the presence of different substances such as asphaltene, ,− asphaltene and resin, emulsifier, and demulsifier of water/oil emulsion . MD has been used to estimate the solubility parameter for asphaltenes in different solvents, , diffusion coefficients, ,,, and hydrate stability and dissociation. − Recently, the MD approach has been used to model asphaltene aggregation during enhanced oil recovery (EOR) processes such as water injection − and gas injection .…”

Section: Theory Of Computational Approachmentioning

confidence: 99%

New Molecular Insights into Aggregation of Pure and Mixed Asphaltenes in the Presence of n-Octylphenol Inhibitor

2020

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Asphaltene stability can be perturbed during the oil production and transportation, leading to asphaltene precipitation and deposition. Chemical inhibitors are usually added to the oil phase to postpone asphaltene deposition. The chemical bonding between asphaltene and inhibitor molecules, and the steric hindrance are the key mechanisms of aggregation inhibition. Nevertheless, the interaction mechanisms between asphaltenes and chemical inhibitors still need more research investigations. In this paper, we use an advanced computational chemistry tool, molecular dynamics (MD), to analyze the inhibitory effect of noctylphenol (OP) on three different asphaltene structures at 1 bar and 300 K. To meet the objectives, the asphaltene aggregation and aggregate characterization in both cases of pure and mixed asphaltenes are studied. It is concluded that the archipelago asphaltene (A1) does not aggregate appreciably in the absence of OP; nevertheless, OP reduces the aggregation. The addition of OP is more effective in reducing the aggregation rate for the continental asphaltene, containing hydroxyl and pyridine groups (A2), which is due to the formation of strong hydrogen bonds between the asphaltene and OP, compared to the aromatic stacking between asphaltene and asphaltene. The presence of hydrogen bonds significantly changes the characteristics of aggregates in both scenarios: in the absence and presence of OP. Hence, OP exhibits less efficiency for the continental asphaltene case without hydrogen bond potential (A3). For the mixed asphaltene systems, OP considerably lowers the aggregation rate when A2 and A3 are simultaneously present; the higher relative portion of OP to A2 is the main reason for this behavior. This study reveals that the OP can be an effective inhibitor, depending on the distribution of different types of asphaltenes in the crude oil. The same strategy can be used to screen proper inhibitors or inhibitor mixtures for various types of asphaltenes.

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“…We further assume that the asphaltenes in the oils and diluents occur as some form of macromolecularlike structures that are not visible using the microscope 25 but would interact with other structures in a manner analogous to particles in suspensions. 11,17,18,[26][27][28] The viscosity (η) versus volume fraction (Φ) of the toluene-diluted heavy oils is presented first, followed by similar curves for the viscosity versus volume fraction of residual heavy oils in heptol (n-heptane + toluene) supernatant, i.e., after the precipitated asphaltenes were removed. All data are evaluated using four selected viscosity predictive models for Newtonian fluids.…”

Section: Introductionmentioning

confidence: 99%

“…The high concentrations of these high-molecular-weight organic structures in heavy oils make significant contributions to the high viscosity of heavy oils. Thus, in the pursuit of understanding the behaviors of these materials in the crude oils, researchers have invoked thermodynamic arguments that include the regular solution approach, as well as macromolecular arguments, − as are discussed in proteins, colloidal, or nanoparticle dispersions. In heavy oil processing, the viscosity of the oil diluted in toluene would indicate limits for viscous resistance to turbulent deformation stresses by the droplet in water.…”

Section: Introductionmentioning

confidence: 99%

Viscosities of Heavy Oils in Toluene and Partially Deasphalted Heavy Oils in Heptol in a Study of Asphaltenes Self-Interactions

et al. 2005

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Interparticle interactions of the soluble asphaltenes in partially deasphalted heavy oils in toluene-heptane (heptol) mixtures are compared to those of several heavy oils diluted in toluene only. Viscosity-volume fraction (η-Φ) relationships for the heavy oils and bitumen in toluene were almost identical. However, the asphaltenes in toluene associated and scaled differently from its source oil. Four classical viscosity models were used to describe the data, and scaling was interpreted on the basis of asphaltenes association, as in macromolecular interactions. The Pal-Rhodes model showed deviation from sphericity with solvation constants for heavy oils in toluene and C-5 asphaltenes in toluene, at 1.4-1.6 and 3.7, respectively. The Krieger-Dougherty (K-H) model indicated high interparticle interaction factors, and maximum packing factors of ∼1 suggested polydispersity. Neither models fit the data for deasphalted oils. The Leighton-Acrivos model showed that (i) the maximum packing fraction (Φ max ) for all oils was similar, (ii) the asphaltenes alone in toluene had the highest self-associations, and (iii) the deasphalted oils showed Φ max values close to the theoretical values (0.58). From the Einstein equations, intrinsic viscosities [η] of deasphalted oils in heptol gave aspect ratios (length to radius, L/R) of the asphaltenes at 10 (i.e., rodlike molecules). The K-H model gave [η] of ∼4 and L/R ≈ 3.5 for heavy oils in toluene; however, for asphaltenes in toluene, the model gave [η] ≈ 10.6 and L/R ≈ 5.8 (i.e., less-rodlike molecules).

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Self-Association of Asphaltenes

Cited by 24 publications

References 65 publications

Probing Structure and Dynamics of Bulk and Confined Crude Oils by Multiscale NMR Spectroscopy, Diffusometry, and Relaxometry

Probing Structure and Dynamics of Bulk and Confined Crude Oils by Multiscale NMR Spectroscopy, Diffusometry, and Relaxometry

New Molecular Insights into Aggregation of Pure and Mixed Asphaltenes in the Presence of n-Octylphenol Inhibitor

Viscosities of Heavy Oils in Toluene and Partially Deasphalted Heavy Oils in Heptol in a Study of Asphaltenes Self-Interactions

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