Asphaltenes isolation

Yen, T. F. Structural Differences Between Asphaltenes Isolated from Petroleum and from Coal Liquid, Chemistry of Asphaltenes-, Bunger, J. W. Li, N. C., Eds. Advances in Chemistry Series No. 195 American Chemical Society Washington, D.C., 1981, p 39. 

Asphaltene Structure by Spectroscopic Methods. Much of the information available on the carbon skeleton of asphaltenes has been derived from spectroscopic studies of asphaltenes isolated from various petroleums and natural asphalts (I, 2). The data from these studies support the hypothesis that asphaltenes, viewed structurally, are condensed polynuclear aromatic ring systems bearing alkyl sidechains. The number of rings apparently varies from as low as six in smaller systems to fifteen to twenty in more massive systems (13,14). 

Structural Differences Between Asphaltenes Isolated from Petroleum and from Coal Liquid... 

Asphaltene is an essential component of any dark-colored, heavy, viscous and nonvolatile oil, regardless of the oil source. Asphaltene can be obtained from the oil extracted from a naturally occurring organic-rich fossil material by a simple solvent fractionation. Asphaltene also can be obtained from the chemical conversion product of a solid fuel, such as pyrolysis or catalytic hydrogenation of coal or shale. The former is an example of the asphaltene isolated from native petroleum oil. An example of the latter is the asphaltene obtained from a synthetic crude, such as shale oil or coal liquid. 

It is possible that a cause-and-effect relationship between molecules comprising the asphaltene fraction and difficulty in processing does not exist and that these relationships are largely fortuitous in that the chemistry involved in asphaltenes isolation is only secondarily related to chemistry of processing. If such is the case, much of the ambiguity surrounding asphaltenes derives from the incorrect assumptions about the chemistry of complex hydrocarbon mixtures inferred from empirical correlations. 

Hydrocarbon Structures. Early postulates of asphaltene structure centered around a variety of polymer structures based on aromatic systems (36, 37). More recent information has related to the structural parameters and carbon skeleton of petroleum fractions, and asphaltenes structures have been derived from spectroscopic studies of asphaltenes isolated from various petroleum and bitumen (38-46). 

Teixeira, M. a. G. Gonsalves, M. L. A. 2000. Evaluation of paraffinic material in asphaltenes isolated by precipitation with light alkanes. Petroleum Science and Technology, 18, 273—286. 

We have performed experiments in which asphaltenes isolated from Safaniya due (also known as Arab Heavy) have been subjected to ion-exchange chromatography (66). The neutral fraction in our experiments - i.e., that fraction which binds neither to cationic or anionic resin—is clearly... 

Pineda-Flores, G. Boll-Arguello, G. Lira-Galeana, C., and Mesta-Howard, A. M., A microbial consortium isolated from a crude oil sample that uses asphaltenes as a carbon and energy source. Biodegradation, 2004. 15(3) pp. 145-151. 

Mansuy et al. [97] investigated the use of GC-C-IRMS as a complimentary correlation technique to GC and GC-MS, particularly for spilled crude oils and hydrocarbon samples that have undergone extensive weathering. In their study, a variety of oils and refined hydrocarbon products, weathered both artificially and naturally, were analyzed by GC, GC-MS, and GC-C-IRMS. The authors reported that in case of samples which have lost their more volatile n-alkanes as a result of weathering, the isotopic compositions of the individual compounds were not found to be extensively affected. Hence, GC-C-IRMS was shown to be useful for correlation of refined products dominated by n-alkanes in the C10-C20 region and containing none of the biomarkers more commonly used for source correlation purposes. For extensively weathered crude oils which have lost all of their n-alkanes,it has been demonstrated that isolation and pyrolysis of the asphaltenes followed by GC-C-IRMS of the individual pyrolysis products can be used for correlation purposes with their unaltered counterparts [97]. 

Furby (12) has developed a method for evaluating stocks in the lubricating oil range that results in a breakdown of components into asphaltenes, resins, wax, and dewaxed oil and provides a yield-viscosity index relationship for the dewaxed oil. The author has found such analyses very useful and inexpensive for evaluating a large number of potential lubricating oil stocks. Furby s method utilizes petroleum ether to precipitate asphaltenes, a fuller s earth-petroleum ether fractionation to isolate resins, methyl ethyl ketone-benzene dewaxing on the deasphalted-deresinified material to separate wax, and an adsorption fractionation to provide cuts from which the yield-viscosity index relationship for dewaxed, solvent-refined oil is obtained. 

The soil contained hydrocarbon-degrading Pseudomonas, Rbodococci, Acinetobacter, Mycobacterium, and Arthrobacter. Only the isolated Mycobacterium was able to degrade the asphaltene fraction. 

Petroleum can be fractionated into four generic types of materials representing general chemical properties. These include saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes. The standard ASTM separation procedure (D2007) for isolating the asphaltenes and the other components in petroleum is based on solubility behavior and chromatography, as shown in Fig. 5. Commerically, many refineries utilize solvent separations to produce a solvent deasphalted oil which has lower impurity levels. 

Yen et al. (1961) examined the structure of isolated petroleum asphaltenes by using XRD. From the diffraction pattern they were able to calculate the aromaticity, defined as the number of aromatic carbon atoms over the total carbon atoms. The aromaticity ranged from 0.26 to 0.53 for petroleum asphaltenes. In addition, the characteristic dimensions of an asphaltene were obtained by the XRD method. The asphaltene model developed by Yen et al. (1961) from these observations is presented in Fig. 6 with characteristic molecular dimensions. The model consists of... 

Although the residuum is a mixture too complex for isolating chemically pure components, asphaltene investigators in recent years have developed techniques that separate residuum molecules on the basis of compound class rather than solubility class. These studies, discussed next, have greatly modified the concepts of asphaltene structure. 

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. 

A spectrum of metal compound reactivities in petroleum could arise for several reasons. Nickel and vanadium exist in a diversity of chemical environments. These can be categorized into porphyrinic and non-porphyrinic species vanadyl and nonvanadyl or associated with large asphaltenic groups and small, isolated metal-containing molecules. Each can be characterized by unique intrinsic reactivity. Reaction inhibition which occurs between the asphaltenes and the nonasphaltenes, as well as between Ni and V species, can also contribute to reactivity distributions. The parallel reaction interpretation of the observed reaction order discrepancy is therefore compatible with the multicomponent nature of petroleum. Data obtained at low conversion could appear as first order and only at higher conversions would higher-order effects become obvious. The... 

After removal of the asphaltene fraction, further fractionation of petroleum is also possible by variation of the hydrocarbon solvent. For example, liquehed gases, such as propane and butane, precipitate as much as 50% by weight of the residuum or bitumen. The precipitate is a black, tacky, semisolid material, in contrast to the pentane-precipitated asphaltenes, which are usually brown, amorphous solids. Treatment of the propane precipitate with pentane then yields the insoluble brown, amorphous asphaltenes and soluble, near-black, semisolid resins, which are, as near as can be determined, equivalent to the resins isolated by adsorption techniques. 

In this paper organically-bound sulfur in three types of high-molecular-weight organic matter (kerogen, asphaltenes and resins) obtained from three organic sulfur-rich sedimentary rock samples has been studied. Kerogen, asphaltene and resin fractions were isolated and characterised by the two described techniques. 

Separation methods. Extraction and fractionation (Figure 1) methods have been described elsewhere (16). The kerogen from Jurf ed Darawish-156 was concentrated by decarbonating the extracted whole rock followed by reextraction. The kerogen from the Monterey-25 was fully isolated using standard HC1/HF techniques. Asphaltene fractions were obtained and purified from bitumens by repeated precipitations with n-heptane. 

Asphaltene and resid pyrolysis provide two relevant examples of global pyrolysis models. The pyrolysis of an isolated asphaltene feedstock typically yields the type of data summarized in Figure 2, a plot of the temporal variation of weight based product fractions as a function of time (7). This figure illustrates the exponential disappearance of asphaltene accompanied by the formation of coke, maltene and gas product fractions. Consideration of the initial slopes for the formation of coke, maltene and gas fractions led to the type of reaction network shown in Figure 3. Since resid and its reaction products can likewise be defined in terms of the solubility and volatility-based product groups asphaltene,... 

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