Separation Athabasca asphaltenes

Structure-Related Properties of Athabasca Asphaltenes and Resins as Indicated by Chromatographic Separation... 

Figure 2. Separation of Athabasca asphaltenes on ion exchangers A - adds (separated on A-27) B - bases (separated on A-15) vertical dashed line represents the end of solvent system described in (3)...

Table II. Separation of Athabasca Asphaltenes on Anion Exchange...

McKay s solvent sequence completely eluted the Wilmington asphaltenes but did not elute all the Athabasca asphaltene samples and had to be extended by additional solvent mixtures to obtain good sample recoveries (cf. Figure 2). For large scale preparative separations of asphaltenes, the asphaltenes were dissolved in benzene and eluted with the same solvent, omitting the cyclohexane step. This accelerated the operation, but at the same time, as expected, the percentage of the neutral fraction now increased from 20%-21% to approximately 28%-30%, in reasonable agreement with the bulk results from the cyclohexane experiments (see Table III). Table III also shows the additional solvent systems used. 

Table III. Preparative Scale Separation of Athabasca Asphaltenes on Ion Exchangers IRA-904 and A-15...

A study of MW distribution for precipitated asphaltenes and the derivation of conclusions about bitumen or asphalt properties from it has severe limitations since this complex mixture exhibits a considerable overlap of GPC curves for all the fractions obtained in a conventional separation procedure. Similarly, the resins separated on clay and the eluted hydrocarbons exhibit overlap, as shown by Figures 5 and 6. Figure 5 demonstrates the GPC profiles of Athabasca asphaltenes (nC5) and resins (Attapulgus clay—total resin eluent)... 

Fractionation of an asphaltene by stepwise precipitation with hydrocarbon solvents (heptane to decane) allows separation of the asphaltene by molecular weight. The structural parameters determined using the x-ray method (Table II) show a relationship to the molecular weight (16). For the particular asphaltene in question (Athabasca), the layer diameters (La) increase with molecular weight to a limiting value similar relationships also appear to exist for the interlamellar distance (c/2), micelle height (Lc), and even the number of lamellae (Nc) in the micelle. 

The separation of resin acids and bases has been described previously (II, 12), see also comments in (14). The percentage of resins, as determined for deasphaltened Athabasca bitumen by their separation on an Attapulgus clay column, was 34%, while combined acids, bases, and Lewis bases amounted to 25.9% of the whole bitumen. Thus, 8.1% of material retained as resins on Attapulgus clay did not interact with the ion exchangers or the complexation column and appeared in the polyaromatic fraction. The distribution of material within the resin fraction was 46.1% acids, 21.9% bases, and 32% neutral compounds. Thus, the pattern of acid and base distribution is similar for the resins and asphaltenes, except for a higher proportion of neutral material present in the resins. 

The separations of resins and asphaltenes under comparable conditions done on the fractions from a common source—Athabasca (in some cases Cold Lake) bitumen—have confirmed a number of postulates that have appeared in the recent literature. 

Asphaltene Separation. Asphaltenes were isolated from bitumen (Athabasca) by using an excess of n-pentane (40 mL of n-C5Hi2 per gram of bitumen) and following... 

Conversion (upgrading) of bitumen and heavy oils to distillate products requires reduction of the MW and boiling point of the components of the feedstocks. The chemistry of this transformation to lighter products is extremely complex, partly because the petroleum feedstocks are complicated mixtures of hydrocarbons, consisting of 10 to 10 different molecules. Any structural information regarding the chemical nature of these materials would help to understand the chemistry of the process and, hence, it would be possible to improve process yields and product quality. However, because of the complexity of the mixture, the characterization of entire petroleum feedstocks and products is difficult, if not impossible. One way to simpHfy this molecular variety is to separate the feedstocks and products into different fractions (classes of components) by distillation, solubility/insolubility, and adsorption/desorption techniques. For bitumen and heavy oils, there are a number of methods that have been developed based on solubility and adsorption. The most common standard method used in the petroleum industry for separation of heavy oils into compound classes is SARA (saturates, aromatics, resins, and asphaltenes) analysis. Typical SARA analyses and properties for Athabasca and Cold Lake bitumens, achieved using a modified SARA method, are shown in Table 1. For comparison, SARA analysis of Athabasca bitumen by the standard ASTM method is also shown in this table. The discrepancy in the results between the standard and modified ASTM methods is a result of the aromatics being eluted with a... 

Asphaltenes from Athabasca bitumen were first separated using n-pentane by Pasternak and Clark in 1951. In most refinery practices, the solvent of choice is n-heptane and asphaltenes are defined as materials soluble in toluene or a solvent having a solubility parameter in the 17.5-21.6 Mpa range. As the carbon number of the extracting solvent increases, the amount of asphaltenes that precipitate decreases. Fundamentally, it is important to note that during asphaltene precipitation by any solvent, smaller asphaltene molecules, as well as some maltene materials, co-precipitate because of... 

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