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.

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A new method to evaluate the colloidal stability of crude oils and related products was developed on the basis of the evaluation of the solubility profile or solubility distribution of asphaltenes in these materials. The new method uses an on-column precipitation coupled with an evaporative light scattering detector (ELSD). The new method requires a small amount of sample, takes only 35 min to perform, and can work for asphaltene concentrations as low as 500 ppm. Using this method, different patterns for asphaltene solubility profile distributions were found depending upon the origin and processing history of the samples. Extracted asphaltenes from virgin and processed materials exhibit uni- and bimodal distributions, respectively. On-column precipitated asphaltenes usually have bimodal distributions, where the separation between the peaks is related to the colloidal stability of the asphaltenes. In general, asphaltenes from unstable materials are characterized by wider solubility profile distributions than asphaltenes from stable materials. A characteristic parameter of the solubility profile distribution, ΔPS, can be obtained and correlated to the colloidal stability of the samples.

Rather recently, a new technique called the “asphaltene solubility profile” was developed to analyze the stability of asphaltenes. In this technique, a distribution of the asphaltenes in terms of their respective solubilities is provided, allowing for a more comprehensive view of how the different molecules comprising asphaltenes behave and interact. In the present work, maltenes and asphaltenes are preparatively separated according to the classification established by the asphaltene solubility profile analysis, i.e., “transitional material” or easy-to-dissolve asphaltenes (EDA) and difficult-to-dissolve asphaltenes (DDA). The results obtained for blends of DDA and EDA show that the latter fraction has a peptizing effect on the former. EDA help in the solubilization of DDA, as shown by the asphaltene solubility profile of the blends, and also decreases aggregation, as shown by the size-exclusion chromatography experiments. These findings support the following: (a) the idea that this so-called “transitional fraction or EDA” plays a key role in the stabilization of asphaltenes similar to the fraction known as “resins” in the literature, (b) the use of solubility profile analysis as a valid test to evaluate asphaltene stability, and (c) the model of crude oils as a continuum of molecules in which their properties vary gradually.

Pipelining of heavy crudes can be facilitated by preparing oil-in-water (O/W) emulsions of the crude, but separation of the oil from the water after pipelining is problematic if conventional surfactants are used. Long-chain acetamidines are CO 2 -triggered switchable surfactants, being surface-active when CO 2 is present but not when CO 2 is absent. Unfortunately, in the presence of CO 2 , they stabilize water-in-oil (W/O) emulsions of heavy crude rather than the desired O/W emulsions. However, in the absence of added CO 2 , several compounds (Na 2 CO 3 , three of the long-chain acetamidines, and two other amidines) stabilize O/W emulsions. These low-viscosity emulsions can later be broken by the addition of CO 2 . The residual oil content in the recovered water is lowest if the compound used to stabilize the original emulsion was a long-chain acetamidine.

An improved method for the separation of asphaltene solubility fractions is presented and has been proven useful for the characterization of heavy crude oils and their fractions. Mixtures of heptane, dichloromethane, and methanol are used to obtain four different and well-defined asphaltene fractions with increasing solubility parameter. A good correlation (0.95) is found between the solubility fraction method and the gravimetric asphaltenes for virgin materials. For processed samples, the correlation depends upon the type of conversion process chosen [fluidized catalytic cracking, thermal cracking, or hydroprocessing]. The characterization of asphaltenes by the asphaltene solubility fraction method for a heavy oil feed and its visbroken products indicated that the low solubility parameter asphaltenes are processed first (“easy-to-react”) and then the higher solubility parameter counterparts (“hard-to-process”). Preparative separations and characterization of Mexican vacuum residue asphaltenes and a thermally cracked residue were carried out using an automatic solvent extractor (ASE) apparatus and the same set of solvents as the solubility fraction method. The results indicated that the H/C ratio of the extracted asphaltene fractions decreased and the aromaticity increased with the solubility parameter of the solvent. However, small differences in the distributions of asphaltene fractions were observed and were attributed to the larger precipitant/sample ratio used in the asphaltene solubility fraction method (>50:1) compared to the ASE preparative separation (20:1).

Asphaltenes, resins and maltenes physical isolation procedures involving different alkane precipitants and solvent/sample ratios were applied in this work to Athabasca bitumen vacuum residue. Samples were characterized by Solubility Profiling, Size Exclusion Chromatography, Fluorescence Spectroscopy, X-ray Photoelectron Spectroscopy and density-viscosity analyses. Isolated fractions were found to display systematic property changes. Thus, it was found that denser, more polar, higher molecular weight (MW), more viscous, red shifted fluorescence materials were sequentially ranked as follows: Solvent extracted asphaltenes -C7 (unwashed) asphaltenes -C5 (unwashed) asphaltenes -resins -maltenes. Intermolecular aggregation for these fractions was determined to follow the same order. Decreasing contents of resins in the same order were found to increase aggregation phenomena.This work further reported on aspects of possible practical interest, i.e., the liquid nature of asphaltenes at 300°C and, possible existence of oxidative reactions affecting fractions isolation that follow standard methods which do not contemplate inert atmospheres. Preliminary assessment of chemical functionalities within isolated fractions highlighted on the possible enrichment of pyrrolic compounds within resins and oxygen functionalities in asphaltenes.

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