Aggregation thermodynamics for asphaltene precipitation

Abstract

in Wiley Online Library (wileyonlinelibrary.com) Asphaltene precipitation has been a major concern for petroleum industry due to its adverse effect on upstream production, midstream transportation, and downstream refining. As a complex phenomenon involving solubility, aggregation, and clustering, asphaltene precipitation has been extensively investigated and correlated with empirical models and equations. Based on the insight regarding hierarchical structure of asphaltenes recently elucidated by Mullins, we present a thermodynamic formulation for asphaltene aggregation, the onset of asphaltene precipitation. The thermodynamic formulation accounts for asphaltene aggregation driving force as a two-step process: (1) molecular asphaltene forming imaginary "nanocrystals", and (2) "nanocrystals" re-dissolving as colloidal nanoaggregates. Applying UNIFAC with this thermodynamic formulation, we show semi-quantitative predictions of asphaltene precipitation in 13 binary solvents with wide varieties of chemical structures and solvent combinations.

Colloidal Asphaltenes—Non-extinct “Dinosaurs” in Native Petroleum

“…Second, in such descriptions, asphaltenes originate from multi-ring “monomers” (Figure a), appearing in expelled crude oils by some unspecified mechanisms; nanocolloidal particles (Figure b) also are formed in expelled crude oils by aggregation of “monomers” via a single type of π–π bonding. Hence, in this scheme, occlusion of biomarkers of the source OM may occur only in “monomers”, which is impossible, as indicated by many geochemists. ,, Indeed, occlusion of a pentacyclic, saturated hydrocarbon, such as hopane [molecular weight (MW) of 412 Da], within an asphaltene “monomer” with a mass of ∼750 Da would not be physically possible . Moreover, it has been repeatedly demonstrated that the very notion of multi-ring “monomers” in asphaltenes may stem from faulty interpretation of some experimental results (cf.…”

“…Inadequate description of the origin and structure of asphaltene colloids [modified with permission from ref . Copyright 2016 American Institute of Chemical Engineers (AIChE)].…”

“…However, in many asphaltene studies, this information is ignored and, clearly, inadequate descriptions are employed. A representative example 41 is illustrated in Figure 4. First, such schemes ignore the presence of macromolecules in both source OM and oil nanocolloids.…”

New Two-Dimensional Particle-Scale Model To Simulate Asphaltene Deposition in Wellbores and Pipelines

“…3 On the basis of asphaltene concentrations in crude oils, the asphaltene molecules are dispersed in the oleic phase with a size range from ∼1.5 to ∼5 nm in width. 4 It is widely believed that the asphaltene nanoaggregates will either flocculate to form larger particles, 5 which can flow through a channel (e.g., pipeline and porous media), or deposit on the surfaces. In many oil reservoirs, asphaltenes are fairly stable in the oil; however, a small variation in the pressure, composition, and temperature can cause asphaltene phase instability and alteration in their solubility parameter, 6,7 and they can precipitate and aggregate out of the crude oil, leading to expensive deposition problems in pipelines, well, valves, and porous media.…”

Characterisation of carbonaceous deposition in oil exposed surfaces at the nanoscale

“…Prior research reveals very little about the mechanisms of aggregation and deposition that occur after the flocculation of the organic molecules and before the fouling of the relevant components [2], [3]. More specifically, the question becomes whether the organic molecules form nanoaggregates and clusters in the liquid phase and then get adsorbed to the surface or whether individual molecules adsorb on the surface, potentially forming a monolayer, and then attract others leading to aggregation at the liquid-solid interface [4].…”