Molecular Interactions between a Biodegradable Demulsifier and Asphaltenes in an Organic Solvent

Abstract

A surface forces apparatus (SFA) was used to measure the intermolecular forces between a biodegradable demulsifier (ethyl cellulose, EC) and asphaltenes immobilized on two molecularly smooth mica surfaces in an organic solvent. A steric repulsion on approach between the immobilized EC layers and asphaltenes was measured, despite strong adhesion during retraction. The measured adhesion was attributed to the interpenetration and tangling of aliphatic branches of swollen asphaltenes and solvated chains of EC macromolecules. Competitive adsorption of EC on/in immobilized asphaltene layers was confirmed by combining SFA force measurements and atomic force microscopy (AFM) imaging. Following the injection of EC-in-toluene solution, an immediate (< 5 min) increase in the confined layer thickness of the immobilized asphaltenes layers was measured. Irreversibly adsorbed asphaltenes were displaced by EC macromolecules through binding with unoccupied surface sites on mica, followed by the spreading of EC across the mica substrate due to increased surface activity governed by the higher number of hydroxyl groups per EC molecule. AFM imaging confirmed that the increase in confined layer thickness resulted from the formation of larger asphaltene aggregates/clusters protruding from the mica substrate.Molecular level topographical images showed that the asphaltenes were not re-solvated in the -2 -organic phase but more self-associated as the EC macromolecules spread across the hydrophilic mica substrate. The results from this study provide not only fundamental insights into the basic interaction mechanisms of asphaltenes and EC macromolecules as a demulsifier in organic media, but also directions towards enhancing demulsification of water-in-oil emulsions.

Foaming Behavior of Polymer-Coated Colloids: The Need for Thick Liquid Films

“…The resulting polymer overlap leads to an increase in osmotic pressure and repulsive interaction energy. Applying the Derjaguin approximation, the total interaction force is given by where k is the Boltzmann constant, T is the temperature, D is the surface separation distance, s is the mean distance between anchoring sites on the surface, and L is the uncompressed brush layer thickness. Since the absolute surface separation distance is unknown, the fully compressed layer thickness was estimated and used to offset the data.…”

Demulsifier Performance and Dehydration Mechanisms in Colombian Heavy Crude Oil Emulsions

“…One of the most complex problems encountered in the petroleum industry is the formation of highly stable water-in-crude oil emulsions and, in fewer cases, multiple emulsions. , The formation and stabilization of such systems are mainly attributed to the presence of the naturally occurring surface active species such as asphaltenes, resins, naphthenic acids, and solid particles such as clays. − The mechanisms involved in the long term stability of these colloidal systems is commonly attributed to the formation of an elastically dominated solid-like interface that hinders coalescence and retards film drainage. Asphaltene crowding, self-association, multilayer buildup, and resin co-adsorption are some of the key parameters that dominate this phenomenon besides their ability to reduce the interfacial tension. − Another particular aspect of the rigid asphaltene layer is that it exhibits a yield stress that is significantly greater than the stress typically prompted by droplet–droplet interactions during flocculation.…”

“…One of the most complex problems encountered in the petroleum industry is the formation of highly stable water-incrude oil emulsions and, in fewer cases, multiple emulsions. 1,2 The formation and stabilization of such systems are mainly attributed to the presence of the naturally occurring surface active species such as asphaltenes, resins, naphthenic acids, and solid particles such as clays. 3−5 The mechanisms involved in the long term stability of these colloidal systems is commonly attributed to the formation of an elastically dominated solid-like interface that hinders coalescence and retards film drainage.…”

Effect of Ethylcellulose on the Rheology and Mechanical Heterogeneity of Asphaltene Films at the Oil–Water Interface

“…That EC has the ability to displace and disrupt asphaltene interfacial layer agrees with the literature studies. 55,56 The recovery of the interface-dominated region implies that bulk C7 might adsorb back into the soft region created by EC, or that a restructuring of the interfacial layer occurs, increasing the film stiffness.…”