Asphaltene formation

Figure 6. Asphaltene formation upon air-blowing of asphalt...

Many questions concerning the nature of petroleum asphaltenes remain unresolved (1) What is the chemical composition of petroleum asphaltenes (2) What are the molecular weights of asphaltene components (3) Why are asphaltenes precipitated from solution in petroleum by the addition of a hydrocarbon solvent such as n-pentane In this chapter we attempt to answer these questions. In addition, we suggest that asphaltene formation is a general phenomenon that is pertinent to the chemistry of coals, tar sand bitumens, shale oil, and other complex solutions of organic compounds. 

In oil bearing formations, the presence of polar chemical functions of asphaltenes probably makes the rock wettable to hydrocarbons and limits their production. It also happens that during production, asphaltenes precipitate, blocking the tubing. The asphaltenes are partly responsible for the high viscosity and specific gravity of heavy crudes, leading to transport problems. 

The refining industry generally seeks either to eliminate asphaltenes or to convert them to lighter materials because the presence of heteroelements cause pollution problems, e.g., sulfur and nitrogen, catalyst poisoning, and corrosion (formation of metal vanadates during combustion). 

Excessive asphaltene and aromatics in the feed are precursors to carhon formation on the catalyst surface, which substantially reduces its activity and produces gasolines of lower quality. 

A solids-stabilized water-in-oil emulsion may be used either as a drive fluid for displacing hydrocarbons from the formation or to produce a barrier for diverting the flow of fluids in the formation. The solid particles may be formation solid particles or nonformation solid particles, obtained from outside the formation (e.g., clays, quartz, feldspar, gypsum, coal dust, asphaltenes, polymers) [228,229]. 

Cap Gas. Both crude and asphaltene-free oil were used to determine the consequences of low-temperature oxidation. It was found that the oxygen content in an artificial gas cap was completely consumed by chemical reactions (i.e., oxidation, condensation, and water formation) before the asphaltene content had reached equilibrium. 

Formation of asphaltenes during solubilization of low-rank bituminous coals has been attributed to cleavage of open ether-bridges (6). But while the presence of such configurations in high- and medium-rank bituminous coals is well established (7), their existence in less mature coals remains to be demonstrated. From reactions of low-rank bituminous coals with sodium in liquid ammonia or potassium in tetrahydrofuran, it has, in fact, been concluded that open ether-bonds are absent (8) or only present in negligible concentrations (9). 

A most striking result from the work described above is that the composition of the bottoms product and residues from the dissolution reaction did not depend on the chemical structure of the original coal material only their relative quantities differed. This supports the view of a mechanism involving the stabilisation of reactive fragments rather than an asphaltene-intermediate mechanism. The formation of a carbon-rich condensed material as a residue of the reaction and the fact that hydrogen transfer occurred largely to specific parts of the coal further supports this view. 

Residue HDP is complicated by the quality of the feed high nitrogen concentration, asphaltenes and metals are the complicating factors. A large number of parallel and simultaneous reactions occur, both thermal and catalytic. Besides contributing to conversion, the thermal reactions contribute to coke formation, as well. 

An additional mechanism affects the deposits formation from the H-Oil reactor, rejection of vanadium and nickel sulfides from the catalyst. In the vacuum tower, asphaltene precipitation was found to be the prevalent fouling mechanism. In asphaltene... 

Pore size optimization is one area where developmental efforts have been focused. Unimodal pore (NiMo) catalysts were found highly active for asphaltene conversion from resids but a large formation of coke-like sediments. Meanwhile, a macroporous catalyst showed lower activity but almost no sediments. The decrease of pore size increases the molecular weight of the asphaltenes in the hydrocracked product. An effective catalyst for VR is that for which average pores size and pore size distribution, and active phase distribution have been optimized. Therefore, the pore size distribution must be wide and contain predominantly meso-pores, but along with some micro- and macro-pores. However, the asphaltene conversion phase has to be localized in the larger pores to avoid sediment formation [134],... 

However, for the heavier resides, zeolite pore structure may preclude their use in HCK. We have introduce the effect of the pore size and distribution on the conversion and coke formation of asphaltene containing feeds (Section 5.2.1), but we should also point out that they also affect the dispersion of the hydrogenation metals on the catalyst surface. A poor dispersion will also lead to poor hydrogenation and indirectly favor coke formation. 

Stanislaus, A., Absi-Halabi, M., Khan, Z., Influence of Catalyst Pore Size on Asphaltenes Conversion and Coke-Like Sediments Formation During Catalytic Hydrocracking of Kuwait Vacuum Residues, In Catalysts in Petroleum Refining and Petrochemical Industries. Studies in Surface Science and Catalysis. 1996, Elsevier New York, USA. pp. 189-197. 

Asphalt chemicals, ethyleneamines application, 8 500t, 506 Asphalt emulsifier amine oxides, 2 473 fatty acid amides, 2 458 Asphalt emulsions, 10 131 Asphaltenes, in petroleum vacuum residua, 18 589-590 Asphyxiants, 21 836 Aspirating aerators, 26 165-169 compressed, 26 168-169 propeller driven, 26 168 submersible, 26 169, 170t subsurface, 26 168 Aspiratory, 11 236-237 Aspirin, 4 103-104, 104t, 701 22 17-21. See also Acetylsalicylic acid as trade name, 22 19 for cancer prevention, 2 826 Aspirin resistance, 4 104 ASP oil recovery process, 23 532-533 Assay format, competitive, 14 142 Assay limits, in Investigational New Drug Applications, 18 692 Assays, for silver, 22 650. See also... 

Petroleum is typically described in terms of its physical properties (such as density and pour point) and chemical composition (such as percent composition of various petroleum hydrocarbons, asphaltenes, and sulfur). Although very complex in makeup, crude can be broken down into four basic classes of petroleum hydrocarbons. Each class is distinguished on the basis of molecular composition. In addition, properties important for characterizing the behavior of petroleum and petroleum products when spilled into waterways or onto land and/or released into the air include flash point, density (read specific gravity and/or API gravity), viscosity, emulsion formation in waterways, and adhesion to soil. 

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