Determination of Asphaltene Critical Nanoaggregate Concentration Region Using Ultrasound Velocity Measurements

TL;DR

This study uses ultrasonic velocity measurements to identify a critical nanoaggregation region of asphaltenes, revealing heterogeneity in aggregation behavior linked to molecular structure variations.

Contribution

It introduces a new concept of a critical nanoaggregation region and links molecular heterogeneity to ultrasonic velocity data, advancing understanding of asphaltene aggregation.

Findings

Identification of a critical nanoaggregation region.

Variation in nanoaggregation proximity not explained by existing models.

Correlation between molecular structure and aggregation behavior.

Abstract

Asphaltenes constitute the heaviest, most polar and aromatic fraction of petroleum crucial to the formation of highly-stable water- in-crude oil emulsions. The latter occur during crude oil production as well as spills and cause difficulties to efficient remediation practice. It is thought that in nanoaggregate form, asphaltenes create elastic layers around water droplets enhancing stability of the emulsion matrix. Ultrasonic characterisation is a high-resolution non-invasive tool in colloidal analysis shown to successfully identify asphaltene nanoaggregation in toluene. The high sensitivity of acoustic velocity to molecular rearrangements and ease in implementation renders it an attractive method to study asphaltene phase properties. Currently, aggregation is thought to correspond to an intersection of two concentration-ultrasonic velocity regressions. Our measurements indicate a variation in the proximity of nanoaggregation which is not accounted for by present models. We attribute this uncertainty to physico-chemical heterogeneity of the asphaltene fraction driven by variation in molecular size and propose a critical nanoaggregation region. We treated asphaltenes from North and South American crude oils with ruthenium ion catalysed oxidation to characterise their n-alkyl appendages attached to aromatic cores. Principal component analysis was performed to investigate the coupling between asphaltene structures and velocity measurements and their impact on aggregation.