Crude oil asphaltenes

The classic definition of asphaltenes is based on the solution properties of petroleum residuum in various solvents. Broadly speaking, asphaltenes are insoluble in paraffin solvents but soluble in aromatic solvents. Structurally, asphaltenes 

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All these problems arise from the sedimentation of asphaltenes. Sedimentation begins when asphaltenes achieve a predetermined size of asphaltene molecules and/or asphaltene particles. The growing of asphaltene molecules is caused by polycondensation reactions. Lowering the solubility of asphaltenes in oil causes polycondensation. This implies that in the case of deep cracking of asphaltene, polycondensation reactions cannot take place. 

The objectives of this chapter are twofold. First is to show the fundamentals of the chemistry and process engineering of asphaltenes during thermal treatment for achieving deep asphaltene cracking to increase and/or improve distillable yields of crude oil. The second is to present the current major processes for utilization of heavy oils and residuum fractions. 

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The stabilization of water-oil emulsions happens as a result of the interfacial layers, which mainly consist of colloids present in the crude oil—asphaltenes and resins. By adding demulsifiers, the emulsion breaks up. With water-soluble... 

Rontani, J. F. Bosser-Joulak, F. Rambeloarisoa, E., et al., Analytical Study of Asthart Crude-Oil Asphaltenes Biodegradation. Chemosphere, 1985. 14(9) pp. 1413-1422. 

Asphaltenes may contain both porphyrin and nonporphyrin metals, depending upon the origin of the crude oil. Yen et al. (1969) characterized the vanadium complexes in a petroleum asphaltene by mass spectroscopy, optical spectroscopy, and ESR. Porphyrins (Etio and DPEP), acid-resistant porphyrin macrocycles of increased aromaticity (Rhodo), and nonporphyrins with mixed donor complexes were identified. Baker (1966) and Baker et al. (1967) extracted porphyrins from Boscan crude oil asphaltenes and also found Etio and DPEP as the two major porphyrin series. These homologous series range in molecular weight by 7 to 18 methylene groups. Gallegos (1967) observed by mass spectroscopy that asphaltenes and maltenes from a Boscan crude oil had nearly identical porphyrins in terms of mass distribution. 

Reactor studies were done in the Catalyst Laboratory at the R D Center of Phillips Petroleum Company in Bartlesville, Oklahoma. More detailed descriptions of the hydroprocessing reactor system and experimental program are given elsewhere (ref, 14,15). The catalyst is laboratory-impregnated Ni-Mo on a commercial 0.156 cm diameter alumina extrudate support provided by Ketjen. The feeds are partially hydrotreated residua from Hondo, Oriente, and Cano Limon crude oils. Asphaltenes were precipitated with a 40 to 1 ratio of n-pentane to oil. Residual oil and hydrogen are pumped upflow through a thermal zone... 

From the title given to part IV of this book, it is obvious that in the next two chapters we will be engaged in studies involving the chemistry of the heaviest compounds of crude oil - asphaltenes. The presence of these compounds in crude oil leads to many problems during crude oil treatment. In this part of the book, these problems and ways to circumvent them are discussed. 

Asphaltenes are derived from the root word "asphalt", a "sticky tar-like substance found naturally in petroleum crude oil." Asphaltenes are complex, high molecular weight aromatic compounds suspended within the fuel. They have high melting points and high carbon/hydrogen ratios with low calorific values. 

The porphyrin metallo complexes in crude oils, asphaltenes and other natural bitumens are chiefly those of vanadium and nickel although copper, iron and even uranium have been suggested. Recently in a Precambrian shale, porphins were found to chelate with iron, zinc and copper in addition to vanadium and nickel.The origin of these complexes is still uncertain, although several theories have been advanced. Some of these theories could be verified or possibly even disproved if the porphyrin type bound to each metal was known. Furthermore, since these heavy metals are harmful to both health and catalysts, a systematic study of demetallation of metalloporphyrins should prove useful. 

The formation of an interfaciai layer consisting of surface-active material present in crude oil (asphaltenes and resins) may provide a physical barrier for droplet-droplet coalescence and improve the stability of emulsions. Numerous researchers have noted the presence of this rigid, viscous interfaciai film in crude oil-water systems with these surface-active components present and have studied it [20,23-27,55,61-67]. The evidence is compelling that the primary mechanism of asphaltene stabilization of w/o emulsions is through the formation of a viscous, cross-linked three-dimensional network with high mechanical rigidity. 

Because the asphalt system is not a true solution, it can be fractionated into saturates, aromatics, resins, and asphaltenes by the solvent fraction method, SARA method, or TLC method. The polarity of these four fractions is increased in the order of saturates, aromatics, resins, asphaltenes. In crude oil, asphaltene micelles are present as discrete or dispersed particles in the oily phase. Although the asphaltenes themselves are insoluble in gas-oil (saturates and aromatics), they can exist as fine or coarse dispersions, depending on the resin content. The resins are part of the oily medium but have a polarity higher than gas-oil. This property enables the molecules to be easily adsorbed onto the asphaltene micelles and to act as a peptizing agent of the colloid stabilizer by charge neutralization. 

When CO2 is mixed with some crude oils, asphaltene may precipitate above a certain concentration. Figure 5.15 depicts the amount of the precipitation vs. CO2 concentration for the Weyburn reservoir fluid at 160 bar and 332 K (Kokal et at, 1992). The composition of the Weyburn oil is given in Table 5.7. Note that the amounts of the asphaltenes and resins in the stock-tank oil are 4.9 and 8.9 weight percent, respectively (see Table 5.7). In Table 5.7, the C28+ composition is 13.75 mole percent which comprises fractions CPI, CP2, resins and asphaltenes. Figure 5.15 shows that when CO2 content in the Weyburn oil is less than 50... 

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. 

The free radical gives rise to a single line corresponding to the transition between the spin + 1/2 and — 1/2. This line is interpreted as resulting from the superposition of the signals of the different species of free radicals with very close values of g-factor in crude oil asphaltenes (Guedes et al., 2001, 2003). 

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