Asphaltenes degradation

The incorporation of Sb and As into the asphaltenes may involve a different mechanism from that of the metals as these elements may replace S in the asphaltenes. Degradation of the asphaltenes would possibly reduce alkyl or aryl arsines RxAsHa x or stibines, RxSbHa-x/ several of which are water soluble. 

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

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. 

The soil contained hydrocarbon-degrading Pseudomonas, Rbodococci, Acinetobacter, Mycobacterium, and Arthrobacter. Only the isolated Mycobacterium was able to degrade the asphaltene fraction. 

It appears that the high molecular weight species originally present in the feedstock (or formed during the process) are not sufficiently mobile (or are too strongly adsorbed by the catalyst) to be saturated by the hydrogenation components and, hence, continue to condense and eventually degrade to coke. These deposits deactivate the catalyst sites and eventually interfere with the hydrodesulfurization process. Thus, the deposition of coke and, hence, the rate of catalyst deactivation, is subject to variations in the asphaltene (and resins) content of the feedstock as well as the adsorptive properties of the catalyst for the heavier molecules. 

Composition of H-Coal Asphaltenes and Preasphaltenes Acid-Base Separations and Oxidative Degradation... 

Figure 2. Degradation products from asphaltene fractions separated by phos-...

Figure 4. Degradation products from asphaltene fractions separated by Triton-B acids I, acidic fraction from water-soluble salts acids II, acidic fraction from water-insoluble salts...

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. 

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. 

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