Asphaltenes, depolymerization

ASM-5, alkane sorption on, 42 71 Asphaltenes, depolymerization, 40 63 Association constants, 32 446-447 Associative mechanism... 

Flo. 31. Proposed mechanism for asphaltene conversion (a) destruction of asphaltene micelle (b) depolymerization due to heteroatom removal (Asaoka a al1983). 

A combination of triflic acid with iodine was shown to be effective to liquefy three types of coal in toluene or tetralin under hydrogen pressure.141 The major role of acid was found to enhance coal depolymerization to asphaltenes, whereas the main function of iodine was to hydrogenate and hydrocrack asphaltenes to oils. The combined catalytic system removed 50% of the nitrogen and 90% of the sulfur of the coals (Illinois No. 6 and Pittsburg seam samples). 

The thermal instability of hydrorefined SRC creates another parameter which requires careful consideration. If, for example, topping operations reverse some of the depolymerization occurring in the SRC process, this equates to a hydrogen penalty. Additional work needs to be done to characterize the asphaltenes generated thermally vs. the starting asphaltenes from coal. 

The ratio of aliphatic protons to aromatic protons for the heavy oil was 4.01/1 and of methylene to methyl 1/1.75. For the asphaltenes, the ratio of aliphatic protons to aromatic protons was 3.49/1 and of methylene to methyl 1/1.1. The asphaltenes were observed to melt at HG C. Molecular weights obtained by vapor phase osmometry (o-xylene solvent) were 407 for the heavy oil and 638 for the asphaltenes. There appears to be little difference in the relative yield of heavy oils and asphaltenes from depolymerized coal as compared with the "as received" coals. Acknowledgements... 

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. 

In the presence of a high pressure of hydrogen, tin metal facilitates the stabilization of radicals formed by initial coal depolymerization leading to the formation of preasphaltenes and asphaltenes (reactions 5 and 6). The stronger pressure dependence of the tin catalyzed reactions compared with other systems investigated here may be linked... 

Figure 3. Model of Hydrocracking of Asphaltene. A De-agglomeration of Asphaltene due to demetallation, B Depolymerization due to desulfurization. means heteroatom...

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