Asphaltene Molecular Size and Structure

TLDR

Simple theoretical models and model‑independent comparisons with known chromophores yield asphaltene diameters of 10–20 Å. Fluorescence depolarization shows asphaltene molecules have diameters of 10–20 Å, masses of 500–1000 amu, and typically contain one or two aromatic chromophores, with similar patterns observed in the largest aromatics of de‑asphaltened crude oil.

Abstract

The rotational correlation times of individual asphaltene molecules have been determined using fluorescence depolarization techniques, addressing an active, long-standing controversy. Using simple theoretical models and using model-independent comparisons with known chromophores, a range of asphaltene molecular diameters is obtained of 10−20 Å. Comparison with corresponding data of known chromophores indicates a molecular mass for asphaltene molecules of 500−1000 amu. Furthermore, we have performed the first direct measurement correlating molecular size with constituent chromophore size; we establish that the bulk of asphaltene molecules possess 1 or 2 (aromatic) chromophores per molecule. Similar results are found for the largest aromatic molecules of the de-asphaltened crude oil.