Related to asphaltenes

Metals distribution, which in some degree should relate to asphaltene distribution, are shown for the actual equilibration temperatures in Table IX. Nickel showed the expected enrichment at all temperatures. Vanadium responded similarly except at 403 and 603°F. Progressive sulfiding (0.6, 0.7, 1.4% S) and coke lay-down (0.8, 1.5, 7.8% C) were observed for the used catalysts and hence represent an experiment complication. 

Two contrasting processes that relate to asphaltenes take place during visbreaking ... 

As mentioned previously, the exponential equations were derived from a process different from hydrotreating/hydrocracking however, it is not surprising that metals and Conradson carbon content are well predicted when they are related to asphaltene concentration since it is well known that metals concentrate in the asphaltene fraction and that asphaltenes are directly associated with coke formation (Ancheyta and Speight, 2007). 

Colloidal State. The principal outcome of many of the composition studies has been the delineation of the asphalt system as a colloidal system at ambient or normal service conditions. This particular concept was proposed in 1924 and described the system as an oil medium in which the asphaltene fraction was dispersed. The transition from a coUoid to a Newtonian Hquid is dependent on temperature, hardness, shear rate, chemical nature, etc. At normal service temperatures asphalt is viscoelastic, and viscous at higher temperatures. The disperse phase is a micelle composed of the molecular species that make up the asphaltenes and the higher molecular weight aromatic components of the petrolenes or the maltenes (ie, the nonasphaltene components). Complete peptization of the micelle seems probable if the system contains sufficient aromatic constituents, in relation to the concentration of asphaltenes, to allow the asphaltenes to remain in the dispersed phase. 

All of these problems are related to the performances of the catalysts used in coal liquefaction. Very active, durable, recoverable, and regenerable catalysts are most wanted in the primary liquefaction stage, where catalyst poisons from asphaltenes and minerals are most severe. Multifunctional catalysts should be designed by selecting supports with specific functions, such as strong but favorable interactions with catalytic species, resistance to poisons, and improved properties to allow easy recovery, while maintaining high activity. 

Yet the statement of Professor Brill s question indicates the importance of flow assurance, particularly related to hydrates, waxes, scale, corrosion, and asphaltenes, in decreasing order of importance. In the Gulf of Mexico, for example, hydrates are considered to be the largest problem by an order of magnitude relative to the others. 

Application of gas chromatographic/mass spectrometric analysis to acidic/basic subfractions of coal-derived asphaltenes has led to the conclusion that the asphaltenes are made up of one-ring and/or two-ring aromatic units that are linked by methylene chains as well as by functional groups (Koplick et al., 1984). Projection of this finding to coal itself is of interest only if it can be assumed that the intemuclear bonds withstood the high temperatures and were not formed as a result of secondary and tertiary (etc.) reaction. In short, the question relates to the relationship of the structural types in the asphaltenes to those in the original coal. 

A first step toward catalyst design is to relate pore structure roughly to asphaltene dimensions. Another step is to consider pore structure of the used catalyst and the probable size of asphaltenes at reactor temperature. 

Very few data have been reported that relate to this aspect of asphaltene separation. There is fragmentary evidence to show that the most polar materials (not necessarily the highest molecular weight material) separate first from the feedstock. This is in keeping with the increased paraffinic character of the feedstock as the hydrocarbon is added. 

To quantify the concepts given above, it is necessary to devise a polarity scale related to solubility theory. Since the precipitating solvents for asphaltene separation are at the low end of the solubility parameter scale, it seems... 

Structural information obtained from various methods can usually be represented by a set of structural parameters, S. These parameters are related to the physical and chemical properties of a given substance. A given set of properties, Pjt is unique to a given substance. Therefore, a given set of structural parameters can be used to characterize a given asphaltene ... 

This calibration does not assume that the n-alkanes and polystyrenes are typical of residual molecules. However, they do provide well-defined size standards in the elution time range of interest. No assumptions can be made concerning the shapes of the asphaltene or maltene molecules. Therefore, the GPC size calculated is defined as the critical molecular dimension, which determines if the asphaltene or maltene molecule will diffuse into the pores of the GPC packing. This size is assumed to be related to the size parameter that determines the molecular diffusion into hydrotreating catalyst pores. 

The high viscosity at ambient temperature of coal liquids derived from hydrogenation processes has been related to the asphaltene (toluene-soluble, pentane-insoluble) and preasphaltene (toluene-insoluble, pyridine-soluble) fractions (1-5). Although the effect of preasphaltene concentration on the viscosity of coal liquids is dramatic, the increase caused by asphaltene materials has been attributed to hydrogen-bonding (6) and acid-base salt... 

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. 

Compound type analysis was not conducted in this work, but it is instructive to look at some literature results. With respect to heteroatoms, tar sand bitumen and petroleum asphaltenes have been variously reported as containing predominantly polar heteroatoms, principally oxygen types (18) or nonpolar heteroatoms, principally nitrogen types (14). The difference in these reported results apparently relates to the method of analysis in which the former is a direct determination, the latter an indirect determination. 

Solvent fractions of coal liquids such as oils, resins, asphaltenes, and carboids may be separated because of their different polarity, molecular weights, and degree of aromatic character. The composition of coal liquids appears to be more closely related to the liquefaction process used rather than to the type of coal used. For example, oils and resins produced in SRC processes appear to have higher molecular weight, more aromatic average molecules than those contained in either pyrolysis or catalyzed hydrogenation coal liquids. This suggests less breakdown of coal and coal liquefaction intermediates to smaller. 

The study of the matrix on pyrolysis result has an additional use besides the understanding of the origin of pyrolysate components. This is related to the influence of the matrix on the generation of specific hydrocarbons from a certain starting organic substrate under the infiuence of heat and of catalysis [46,47]. However, most of these studies are not directly related to analytical pyrolysis. In these studies, furnace pyrolysers were commonly preferred to small sample and flash pyrolysis [46]. These and other pyrolysis appiications for the study of kerogens and also of oil related components such as asphaltenes [47] have been proven extremely useful in practice [19]. 

Crude petroleum contains complex mixtures of hydrocarbons as well as relatively small amounts of nitrogen-, sulfur-, and oxygen-containing organic compounds, asphaltenes, and various trace metals (uncomplexed and complexed forms). The hydrocarbons can be divided into two classes related to their chemical structure the alkanes (normal, branched, and cyclo) and aromatic compounds (mono-, di-, and poly-, i.e., PAH). 

Experimental studies undertaken by Schutte (61) to examine the partitioning of polar constituents of the bitumen to various process streams in the extraction circuit indicated that froth is enriched in asphaltenes. Schutte postulated that asphaltenes play a key role in promoting air attachment to bitumen. Further observations also indicated that the water and solids content of froth is directly related to the asphaltene content of the bitumen. Findings were rationalized in terms of the effect of asphaltenes on the rate of coalescence of aerated bitumen droplets at a froth interface. Schutte believed that rapid coalescence would inhibit the entrainment of water and solids and thereby favor good product quality. Experimentation with a model system using paraffin oil and process water indicated that the presence of asphaltenes substantially increases the time required for coalescence. 

Nonhydrocarbon Solvents, Although an asphaltene fraction can be removed from petroleum by using a wide variety of hydrocarbon liquids (14), the use of nonhydrocarbon solvents as deasphalting media and their influence on asphaltene dispersibility and compatibility has also been investigated. Dispersibility of asphaltenes in petroleum is suggested to be conveniently related to the surface tension of the system components (8, 20, 21, 22, 23). Obviously, asphaltene dispersion and compatibility is complex and is dependent on several factors and varies markedly with the character of the added liquid. 

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). 

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