Asphalt asphaltenes

In industry, the elimination of asphaltenes from oil involves using propane or butane. The utilization of a lighter paraffin results in the heavier paraffins precipitating along with the asphaltenes thereby diminishing their aromatic character. The oil removed from its asphaltene fraction is known as deasphalted oil or DAO. The precipitated portion is called asphalt. 

Vacuum distillation of the atmospheric residue complements primary distillation, enabli r.ecoyery of heavy distillate cuts from atmospheric residue that will un r o further conversion or will serve as lube oil bases. The vacuum residue containing most of the crude contaminants (metals, salts, sediments, sulfur, nitrogen, asphaltenes, Conradson carbon, etc.) is used in asphalt manufacture, for heavy fuel-oil, or for feed for others conversion processes. 

Asphalt makes up the residue of the deasphalting operation and concentrates the major portion of the impurities such as metals, sediment, 1 salts and asphaltenes. Asphalt fluidity decreases as the molecular weight of... 

Proceedings of the 1992 International Conference on Microbial Enhanced Oil Recovery 40a Asphaltenes and Asphalts, I... 

Asphalt additives Asphalt emulsions Asphaltene Asphaltenes... 

Asphalts characteristically contain very high molecular weight molecular polar species, called asphaltenes, which are soluble in carbon disulfide, pyridine, aromatic hydrocarbons, chlorinated hydrocarbons, and tetrahydrofiiran. 

However, for the past 30 years fractional separation has been the basis for most asphalt composition analysis (Fig. 10). The separation methods that have been used divide asphalt into operationally defined fractions. Four types of asphalt separation procedures are now in use ( /) chemical precipitation in which / -pentane separation of asphaltenes is foUowed by chemical precipitation of other fractions with sulfuric acid of increasing concentration (ASTM D2006) (2) solvent fractionation separation of an "asphaltene" fraction by the use of 1-butanol foUowed by dissolution of the 1-butanol solubles in... 

The fractions obtained in these schemes are defined operationally or proceduraHy. The amount and type of asphaltenes in an asphalt are, for instance, defined by the solvent used for precipitating them. Fractional separation of asphalt does not provide well-defined chemical components. The materials separated should only be defined in terms of the particular test procedure. 

Asphaltenes seem to be relatively constant in composition in residual asphalts, despite the source, as deterrnined by elemental analysis (6). Deterrnination of asphaltenes is relatively standard, and the fractions are termed / -pentane, / -hexane, / -heptane, or naphtha-insoluble, depending upon the precipitant used (5,6,49). After the asphaltenes are removed, resinous fractions are removed from the maltenes-petrolenes usually by adsorption on activated gels or clays. Recovery of the resin fraction by desorbtion is usually nearly quantitative. 

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. 

Many attempts have been made to characterize the stabiUty of the colloidal state of asphalt at ordinary temperature on the basis of chemical analysis in generic groups. For example, a colloidal instabiUty index has been defined as the ratio of the sum of the amounts in asphaltenes and flocculants (saturated oils) to the sum of the amounts in peptizers (resins) and solvents (aromatic oils) (66) ... 

Many investigations of relationships between composition and properties take into account only the concentration of the asphaltenes, independendy of any quality criterion. However, a distinction should be made between the asphaltenes which occur in straight mn asphalts and those which occur in blown asphalts. Remembering that asphaltenes are a solubiUty class rather than a distinct chemical class means that vast differences occur in the make-up of this fraction when it is produced by different processes. 

Bitumen Insoluble in Paraffin Maphtha (AASHPO T46). This test designated by the American Association of State Highway and Transportation Officials (AASHTO) is used to indicate the content of naphtha-insoluble asphaltenes in an asphalt. Other solvents such as / -heptane (ASTM D3279), / -hexane, and / -pentane have been substituted for the naphtha solvent. 

Asphaltic—contain relatively a large amount of polynuclear aromatics, a high asphaltene content, and relatively less paraffins than paraffinic crudes. 

Residues containing high levels of heavy metals are not suitable for catalytic cracking units. These feedstocks may be subjected to a demetallization process to reduce their metal contents. For example, the metal content of vacuum residues could be substantially reduced by using a selective organic solvent such as pentane or hexane, which separates the residue into an oil (with a low metal and asphaltene content) and asphalt (with high metal content). Demetallized oils could be processed by direct hydrocatalysis. 

Solvent extraction may also be used to reduce asphaltenes and metals from heavy fractions and residues before using them in catalytic cracking. The organic solvent separates the resids into demetallized oil with lower metal and asphaltene content than the feed, and asphalt with high metal content. Figure 3-2 shows the IFP deasphalting process and Table 3-2 shows the analysis of feed before and after solvent treatment. Solvent extraction is used extensively in the petroleum refining industry. Each process uses its selective solvent, but, the basic principle is the same as above. 

Furthermore, the injection of organic aromatic solvents and soaking is a feasible method to remove the precipitates [924]. The precipitation of asphalt from crude oil can be reduced by adding an N,N-dialkylamide of a fatty acid [1525,1527]. When asphaltenes are precipitated out, they can be removed from the walls of a well, pipeline, and so forth by washing with a hydrocarbon solvent. However, it has been shown that isopropyl benzoate is exceptionally useful as a solvent for asphaltene removal [1583]. 

Dispersants for Asphalts. Asphalt and asphaltene components can produce difficulties in various processes in recovering crude petroleum oils and preparing them for transportation through pipelines or in refining separation. 

Certain alkyl-substituted phenol-formaldehyde resins can act as dispersants for asphalts and asphaltenes in crude oils [1681]. The dispersants help keep asphalt and asphaltenes in dispersion and inhibit fouling, precipitation, and buildup in the equipment. 

The classic definition of asphaltenes is based on the solution properties of petroleum residua in various solvents. The word asphaltene was coined in France by J.B. Boussingault in 1837. Boussingault described the constituents of some bitumens (asphalts) found at that time in eastern France and in Peru. He named the alcohol insoluble, essence of turpentine soluble solid obtained from the distillation residue "asphaltene", since it resembled the original asphalt. 

Asphaltene precipitation, in many instances, carries from the well tubing to the flow lines, production separators, and other downstream equipment. It has also been reported (19) that asphaltic bitumen granules occured in the oil and gas separator with oil being produced from certain oil fields. 

The downtime, cleaning, and maintenance costs are a sizable factor in the economics of producing a field prone to asphaltene deposition. Considering the trend of the oil industry towards deeper reservoirs, heavier and as a result asphaltic crudes, and the increased utilization of miscible gas injection techniques for recovering oil, the role of asphaltene deposition in the economic development of asphaltene containing oil discoveries will be important and crucial. 

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