Separation from maltene fraction

Figure 1. Flow diagram for the separation of the sulfide and thiophene classes of compounds from the maltene fraction of petroleum. (Reproduced from Reference 34. Copyright 1989, American Chemical Society.)...

Fractionation by solubility is used to isolate asphaltenes from maltenes, and the standard method (ASTM-3279-97) has been used in this work. Crude petroleum is mixed with 40 volumes of heptane, heated, stirred, and left to cool. The asphaltenes form a precipitate that can be removed by filtration. Normal practice is to clean the asphaltene fraction by Soxhlet in heptane. The proportions of asphaltene in crude petroleums vary widely, from less than 0.1% in the best crudes to over 10% in the heavy crudes. In general, the heavy crudes such as Maya are of most interest. The solubility of petroleum asphaltene in NMP is of interest since the NMP-insoluble material has no fluorescence [61] and was initially assumed to be aliphatic. However, it has UV absorbance and must be aromatic [62]. The separation into NMP soluble and insoluble was achieved for several asphaltenes. A Kuwaiti asphaltene was separated into NMP-soluble and -insoluble fractions [63]. Seven crude oils were fractionated into heptane solubles and asphaltenes for comparison with an asphaltene from a heavy oil [64]. 

Formation of Asphaltenes in Straight-Reduced Asphalt. The straight-reduced 125-penetration asphalt (SR-125) has been separated into fractions using two separation procedures illustrated in Figures 2 and 3. The results of the separations are compared in Figure 5. The comparison of the amounts of fractions generated from the asphaltene-free (maltene) portion of SR-125 asphalt (Method 1) and acid- and base-free portion of SR-125 asphalt (Method 2) by chromatography on alumina shows that the amounts of saturates plus aromatics-1, often called oils, remain constant (53 wt %). Differences can be observed in the amounts of polar fractions (resins) defined as aromatics-2 and aromatics-3. The prior separation of acids and bases directly from the asphalt... 

Equations (2) and (3) were fit to experimental data using nonlinear regression to obtain values of the first-order reaction rate constants and the stoichiometric coefficients at each temperature. The conversion data from the 400°C thermal run and the best fit of the kinetic model are shown in Figure 1. It is interesting to note that at the time of incipient coke formation ( 60 minutes) the asphaltene and maltene data deviate from predicted first-order behavior. From this we concluded that both asphaltenes and maltenes were participating in secondary coke-forming reactions. Further separation of the maltenes into resins (polar aromatics) and oils confirmed this to be true and showed that it was the resin fraction that was involved in coke formation. 

A major problem associated with the characterization of the HMWHCs is the quantitative and qualitative separation of waxes from asphaltenes. Thanh et al. (1999) developed a method, subsequently modified (Hsieh et al. 2000), which involved the adsorption of the crude oil on alumina, followed by extraction of the alumina to remove the maltenes, including the HMWHCs, leaving the asphaltenes adsorbed to the alumina. The maltenes were subsequently separated into wax and non-wax fractions via acetone precipitation (Burger et al. 1981) and the asphaltenes were recovered by secondary extraction of the alumina. Characterization of the respective fractions demonstrated that the waxes were asphaltene-free and the asphaltenes were wax-free. 

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