Asphaltenes association

Asphaltene association factor the number of individual asphaltene species which associate in nonpolar solvents as measured by molecular weight methods the molecular weight of asphaltenes in toluene divided by the molecular weight in a polar nonassociating solvent, such as dichlorobenzene, pyridine, or nitrobenzene. 

The precise mechanism of asphaltene association has not been conclusively established, but hydrogen bonding (66, 95, 96) and the formation of charge-transfer complexes (66) have been cited as the causative mechanisms. Evidence exists that asphaltenes participate in such complexes (97, 98), but the exact chemical or physical manner in which they would form in petroleum is still open to discussion. Intermolecular hydrogen-bonding could also be involved in asphaltene association and may have a significant effect on observed molecular weights (95). 

Thus, data derived from low-frequency dielectric relaxation are important in predicting asphaltene-associated problems. Low frequency measurements can also produce sensor responses that are sensitive to interactions between asphaltenes and surfactants usually... 

Some authors point out that the precipitation techniques may provide an excessively strong interference into the delicate molecular organization of asphaltenes associates (Figure 10), leading to their irreversible transformation, so that the supra-molecular architecture in solutions of the precipitated material may be different from that in native crude. Consequently, studies of aggregation in crude oil solutions may supply valuable information regarding the manner of asphaltenes-asphaltenes interactions in the presence of other crude oil components. 

Bitumen Insoluble in Paraffin Maphtha (AASHPO T46). This test designated by the American Association of State Highway and Transportation Officials (AASHTO) is used to indicate the content of naphtha-insoluble asphaltenes in an asphalt. Other solvents such as / -heptane (ASTM D3279), / -hexane, and / -pentane have been substituted for the naphtha solvent. 

Product yields and qualities obtained from HCK of heavy Safaniya VR are compared in Table 12 [142], As can be seen, higher yields on slurry and ebullated beds are associated with poorer product quality, besides the asphaltene concentration in the hydrocracked VR makes almost impossible any further improvement by further processing. 

Leon, O. Rogel, E. Espidel, J., and Torres, G., Asphaltenes Structural Characterization, Self-Association, and Stability Behavior. Energy Fuels, 2000. 14 pp. 6-10. 

ASM-5, alkane sorption on, 42 71 Asphaltenes, depolymerization, 40 63 Association constants, 32 446-447 Associative mechanism... 

Reduced crystallite size of the zeolite and/or breaking or grinding of clusters of zeolite crystals to individual crystals, also serves to enhance accessibility in the face of asphaltenes, nitrogen-containing molecules, destructive and harmful elements, and other molecular "clutter" associated with the bottom of the barrel. 

Some of the fuel performance problems which can be associated with asphaltenes include ... 

Mack (58, 59) points out that asphaltenes from different sources in the same petro-lenes give mixtures of approximately the same rheological type, but sols of the same asphaltenes in different petrolenes differ in flow behavior. Those in aromatic petrolenes show viscous behavior and presumably approach true solution. Those in paraffinic media show complex flow and are considered to be true colloidal systems. Pfeiffer and associates (91) consider that degree of peptization of asphaltene micelles determines the flow behavior. Thus, a low concentration of asphaltenes well peptized by aromatic petrolenes leads to purely viscous flow. High concentrations of asphaltenes and petrolenes of low aromatic content result in gel-type asphalts. All shades of flow behavior between these extremes are observed. 

Tynan and Yen (1969) have suggested that the association of aromatic sheets in the asphaltene macrostructure may occur through coordination of heterocycles. The aromatic sheets may have defect centers with heteroelements providing coordination centers for metals (Yen, 1974). 

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