Asphaltene association factor

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. 

Figures 2 and 3 contain yield curves for naphthalene and 1-methylindan as a function of reaction time for tetralin and tetralin plus coal, pyrite, or asphaltene. The asphaltene was a homogenized mixture of several samples isolated from coal liquefaction products during other work in our laboratory (9). This asphaltene sample contained essentially a negligible ash content (<0.1%). Therefore, it contains many organic structures similiar to those found in coal, but unlike coal, its reactions will be free of any complicating factors due to mineral matter. The yields of naphthalene and 1-methylindan are greater in the presence of asphaltene than in its absence, although not quite as high as in the presence of coal. This is additional evidence that these two products arise mainly from reactions associated with the presence of the organic portion of coaly matter. These reactions are quite likely free radical in nature.

To assist in defining the Slope Factors of an unaltered sequence of oils of increasing maturity, pyrolysates of a petroleum asphaltene were employed (data of Thompson 2002). Aliquots of a purified asphaltene from a mature, clastic-sourced, oil were heated in sealed quartz capillaries for a period of 48 h at temperatures of 320, 340, 350 and 360 °C (MSSV method of Horsfield et al. 1989). The two lower temperatures yielded petroleum-like fluids of very low maturity, less that that of a 30° API oil, while the 350 and 360 °C pyrolyses attained the maturity level of mid-range of oils and were strikingly oil-like in their associated values of light end and liquid component Slope Factors, as evidenced in Table 1. 

This preliminary factor analysis leaves many questions unanswered concerning the relations among the trace elements in the total crude oils. But as pointed out previously the fact that most trace elements are associated with the asphaltene fraction of crude oils together with the facts that the contents of asphaltenes vary widely and hence that many elements were below detection limits indicates that examination of trace elements in the asphaltenes should resolve many of the uncertainties posed by the present study. Furthermore, EPR, NMR and elemental (C, H, N, O, S) analysis of the asphaltene fraction may help link the factors controlling the organic and inorganic components in these Alberta crude oils. 

Desmaison et al. conducted studies on Arabian crudes and noted the emulsion formation was correlated with two factors - photo-oxidation exposure and amount of asphaltenes (16). The photo-oxidation was found to occur on the aromatic fractions of the oil. Asphaltenes were found to become structured with time and this was associated with emulsion formation. Miyahara reported that the stability of emulsions was primarily controlled by the composition of the oil, specifically that which resided in flie hexane-insoluble fraction of the oil, but he did not define what fliis content was (17). Miyahara also reported that salt and freshwater emulsions showed relatively similar stabilities, alfliough in one case the salt-water emulsion appeared to be more stable. Payne and Phillips reviewed the subject in detail and reported on their on experiments of emulsification wifli Alaskan cmdes in fire presence and absence of ice (18). Their studies showed fliat emulsion formation could occiff in an ice field, thus indicating that fliere was sufficient energy in this environment and that the process could occur at relatively low temperatures. 

Choice of the solvent system is of great importance, particularly with a complex material like asphalt. The solvent system includes not only the solvent but also the concentration, temperature, sample size, and even the flow rate because of effects apart from the effect on column performance. All these factors interact to determine the solution characteristics on which the column must act. The key factors are the tendency of polar materials in asphalt to associate and to be adsorbed on the column. To a lesser, but still important extent, the results are also affected by interactions with the solvent that affect the apparent hydrodynamic volume. For instance, associating substances, such as asphaltenes, show much higher molecular size in a poor solvent, but a smaller size polar substance, such as a normal... 

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