Heavy Oil Based Mixtures of Different Origins and Treatments Studied by Atomic Force Microscopy

Abstract

Heavy oil molecular mixtures were investigated on the basis of single molecules resolved by atomic force microscopy. The eight different samples analyzed include asphaltenes and other heavy oil fractions of different geographic/ geologic origin and processing steps applied. The collected AFM data of individual molecules provide information about the molecular geometry, aromaticity, the content of nonhexagonal rings, typical types and locations of heterocycles, occurrence, length and connectivity of alkyl side chains, and ratio of archipelago-vs island-type architectures. Common and distinguishing structural motifs for the different samples could be identified. The measured size distributions and the degree of unsaturation by scanning probe microscopy is consistent with mass spectrometry data presented herein. The results obtained reveal the complexity, properties and specifics of heavy oil fractions with implications for upstream oil production and downstream oil processing. Moreover, the identified molecular structures form a basis for modeling geochemical oil formation processes.

Direct Visualization of Individual Aromatic Compound Structures in Low Molecular Weight Marine Dissolved Organic Carbon

“…Compared to other complex organic molecular mixtures found in nature, such as asphaltenes (Schuler et al, ) and heavy oil fractions (Schuler, Fatayer, et al, ), the molecules present in LMW DOC are smaller and less planar. Moreover, the DOC imaged also shows a higher incidence of methyl groups attached to the molecules and an increased occurrence of aliphatic groups in comparison to the asphaltenes.…”

“…We resolved the molecular characteristics of the LMW North Pacific DOC (Broek et al, ) from the surface (S, 7.5 m) and deep (D, 2,500 m). To obtain a measure of the average sizes of the evaporated molecules, we measured 46 molecules in the surface sample S and 48 in the deep sample D by STM (Schuler, Fatayer, et al, , and the supporting information). The average area size of the surveyed molecules S and D is quantified as (112 ± 60) Å 2 and (120 ± 60) Å 2 , respectively.…”

“…All AFM images were obtained in the frequency‐modulation mode (Albrecht et al, ; oscillation frequency of f 0 = 30 kHz and amplitude of A = 0.5 Å) in constant‐height mode and at sample bias V = 0 V. The tip was functionalized with a CO molecule prior to molecular imaging (Bartels et al, ; Gross et al, ). Previously, AFM with CO‐functionalized tips have been used to identify individual molecules of heavy oil fractions (Schuler et al, ; Schuler, Fatayer, et al, ). For these complex molecular mixtures, the comparison between the AFM‐identified molecular structures and the distribution of carbon atom number and double‐bond equivalent obtained by mass spectrometry demonstrated the representativeness of the AFM measurements (Schuler, Fatayer, et al, ).…”

“…Previously, AFM with CO‐functionalized tips have been used to identify individual molecules of heavy oil fractions (Schuler et al, ; Schuler, Fatayer, et al, ). For these complex molecular mixtures, the comparison between the AFM‐identified molecular structures and the distribution of carbon atom number and double‐bond equivalent obtained by mass spectrometry demonstrated the representativeness of the AFM measurements (Schuler, Fatayer, et al, ). However, this representativeness is only given up to a maximum molecular weight lower than 1,000 g/mol, because of the preparation method used, which is by flash‐heating a silicon wafer (Schuler et al, ).…”

“…These samples were collected with a combined ultrafiltration and solid‐phase extraction (SPE) approach (Broek et al, ), thus allowing for unambiguous isolation and characterization of LMW DOC. Chemical structure assignment of individual molecules was based on previous AFM image studies of model molecules with different planar aromatic hydrocarbon cores and diverse moieties (Gross et al, ; Kawai et al, ; van der Lit et al, ; de Oteyza et al, ; Riss et al, ; Schuler et al, , ; Schuler, Fatayer, et al, ; Schuler, Zhang, et al, ).…”