Asphaltene isolating from maltenes

The discovery of HMWHCs in the asphaltene fraction clearly necessitated the development of a new method that would eliminate the presence of HMWHCs from the asphaltene fractions. In 1999, Thanh et al. successfully developed a method involving adsorption of the oil on alumina, and extraction with wo-octane to recover the maltene fraction followed by extraction with dichloromethane/methanol to recover the asphaltenes from the alumina. This method produced an asphaltene fraction devoid of HMWHCs and a maltene fraction devoid of asphaltenes, permitting a far more accurate indication of the gross compositional characteristics of the oil. Furthermore, asphaltene-free waxes could be isolated from the maltenes and, if required, further divided into macro- and micro-crystalline fractions providing additional and useful information of interest to the production engineers. 

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]. 

Boduszynski et al. (1980) also employed the more conventional separation procedure based on solubility properties (Corbett, 1969) to provide asphaltene and maltene samples from the 675°C+ residuum. Asphaltenes are isolated by precipitation in an alkane solvent, with further separation of maltenes by chromatography in solvents of increasing elution strength. The FIMS results in Fig. 9 illustrate, significantly, that asphaltenes are not necessarily the highest-molecular-weight components in residuum. Asphaltenes have, rather, a relatively low but broad distribution of molecular weights. 

The structure and chemistry of tar sand bitumen asphaltenes were studied indirectly by inference from processing and characterization of virgin bitumen and deasphaltened bitumen (maltenes). Results differ significantly from those derived from characterization of asphaltenes as isolated... 

Figure 33.9 shows the LD mass spectrum of the NMP-insoluble fraction of the sample, with maximum ion intensity at m/z 3000 and an upper mass limit of m/z 10,000. Table 33.3 lists the maximum intensity masses (m/z) and upper mass limits of the mass spectra of the whole sample, the maltene and asphaltene fractions, and several TLC fractions from each of them. It is clear that the Syncrude contains some material of relatively high mass that can only be defined by fractionation to isolate it from low-mass components. 

Klein et al. " investigated the pyrolysis kinetics of resids, isolated asphaltenes and maltenes from Hondo, Arabian heavy, Arabian light, and Maya oils. At 400°C and 425°C, isolated asphaltenes reacted selectively to form maltenes. At higher temperatures (450°C), asphaltenes reacted... 

Acevedo, S., Escobar, G., Gutierrez, L. Rivas, H. (1992). Isolation and characterization of natural surfactants from extra heavy crude oils, asphaltenes and maltenes. Interpretation of their interfadal tension-pH behaviour in terms of ion p>air formation. Fuel Vol.71 619-623. 

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