Degradation of asphaltene

The open literature does not show any report on microbial conversion of metal prophyrins although degradation of asphaltenic fractions has been eluted. The technical... 

The results of the depolymerization studies such as metal reductions and low temperature solvolysis have shown that the mechanism and the rate of degradation of asphaltene depend to a large extent on the chemical environment. 

Figure 1. Degradation of asphaltene with molten AlCl3...

Figure 2. Degradation of asphaltene with molten Lewis acids (H2 850 psig) heteroatom removal (1) AlCl3 (220° C) (2) ZnCl2 (300° C)...

Table VIII. Product Distribution from the Catalyzed and Noncatalyzed Degradation of Asphaltene...

Rojas-Avelizapa, N. G. Cervantes-Gonzalez, E. Cruz-Camarillo, R., and Rojas-Avelizapa, L. I., Degradation of aromatic and asphaltenic fractions by Serratia liquefasciens and Bacillus sp. Bulletin of Environmental Contamination and Toxicology, 2002. 69(6) pp. 835-842. 

Lewis Acids Assisted Degradation of Athabasca Asphaltene... 

To obtain a more clearly defined picture of these structural features and to establish the relationship between the chemical structure of asphaltene and its reactivity under a variety of conditions, the potential of chemical and thermal degradation reactions as diagnostic tools has been studied. The specific subject of this investigation was the high molecular weight, sulfur rich asphaltene from the Athabasca bitumen. 

The pentane-soluble portion of asphaltene thermolyzed at 300° C has been found to contain a full complement of n-alkanes, acyclic isoprenoids, small ring saturated and small ring aromatic compounds, typical of unbiodegraded conventional crude oil (8). However, in all cases only a small fraction of the degraded asphaltene can be analyzed in this manner, and therefore the question of the size and homogeneity of the remaining hydrocarbon units remains unresolved. 

In the absence of tin less asphaltene is produced which manifests itself as Increased yields of THF insolubles and preasphaltenes. At this time the activity of iron is not completely certain as no effects have been observed on the reactions of the coal derived products. However the proven ability of iron to both catalyze the reactions of some ethers while suppressing propagation reactions of phenoxy radicals suggests that its major activity is probably restricted to the first minutes of reaction (reactions 1,2) and to the slow catalytic degradation of polymerized material. The iron-tin synergism (1) can be interpreted as a co-operative action... 

Yields of Preasphaltenes and Asphaltenes. Subbituminous coal is converted very rapidly to soluble products in tetralin at 427°C. Figure 1 shows the yields of THF-soluble but pentane-insoluble, benzene-soluble and pentane-soluble products vs. reaction time. These fractions correspond respectively to a mixture of preasphaltenes and asphaltenes, asphaltenes and oils. Of the 78% ultimate yield of THF-soluble products based on the dry coal containing 8.6% ash, 55-60% are formed within 5 to 10 min of reaction time. By 35 min of reaction time, conversion of coal to soluble products is essentially complete. In contrast to the extremely rapid process of conversion of the parent coal to preasphaltenes, the further degradation of preasphaltenes occurs only very gradually, the yield of asphaltenes increasing from 10 to only 25% over a 1-hr reaction time. 

The fractions obtained in these schemes are defined operationally or procedurally. 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 (Fig. 15.5). However, these fractions are generated by thermal degradation or by oxidative degradation and are not considered to be naturally occurring constituents of asphalt. The test method for determining the toluene-insoluble constituents of tar and pitch (ASTM D-4072, ASTM D-4312) can be used to determine the amount of carbenes and carboids in asphalt. 

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