Bitumen Pyrolysis

Sample A, the water-washed 184 L/t shale, is the raw shale against which comparisons on the effect of mineral constituents will be made. Contrary to initial expectations, the net pyrolysis yield after removal of the bitumen, Sample B, is observed to increase by 1.5 wt% with respect to that of Sample A. Although the bitumen component is generally believed to be pyrolyzed quantitatively, the kerogen component appears to be converted more effectively in the absence of bitumen. The secondary TG peak near 520°C, Figure 4, is still present for the bitumen-free sample. Thus, the peak is not associated with bitumen pyrolysis and is, therefore, by inference, associated with the bitunen-free kerogen component. 

FIGURE 17.6 Flow diagram for the purification and stabilization of the products of bitumen pyrolysis. (Reprinted from Hocking [46], with permission.)... 

Numerous kinetic mechanisms have been proposed for oil shale pyrolysis reactions (11—14). It has been generally accepted that the kinetics of the oil shale pyrolysis could be represented by a simple first-order reaction (kerogen — bitumen — oil), or... 

Schimmelmann A, Lewan MD, Wintsch RP (1999) D/H ratios of kerogen, bitumen, oil and water in hydrous pyrolysis of source rocks containing kerogen types I, II, IIS and III. Geochim Cosmochim Acta 63 3751-3766... 

Figure 1 Production rates of bitumen and hydrogen sulfide in pyrolysates of the two types of pyrolysis.

Figure 3 Variation of carbon isotope ratios with H/C ratios in residual kerogens and bitumens generated during pyrolysis. 0 hours denotes starting kerogens and original sedimentary bitumen. 2, 10 and 100 denote heating times.

Virgin Bitumen Vis- breaking Products Maltenes Hydro- pyrolysis Products... 

Indeed, an excellent example of inconsistency between a spectroscopic method (i.e., NMR) and other data is provided by an examination of the asphaltenes from Athabasca bitumen where alkyl sidechains are deduced to contain approximately four carbon atoms (20, 21). The pyrolysis (350°-800°C) of this asphaltene produces substantial amounts of alkanes (< C34) in the distillate (22, 23, 24). The presence of these alkanes in the pyrolysates is thought to reflect the presence of such chains in the original asphaltene (24) but this is difficult to rationalize on the basis of an average structure derived from NMR data. Obviously, recognition of the inconsistencies of the spectroscopic method with respect to the paraffinic moieties must lead to recognition of similar inconsistencies when considering the aromatic nucleus. 

Chapters 10-12 cover important aspects of coke formation in metal tubular reactors during pyrolysis of hydrocarbons. Chapters 13 and 14 are concerned with coal and lignite pyrolysis. Chapters 15 and 16 deal with pitch formation from, respectively, heavy petroleum fraction and tar sand bitumen. Chapters 17 and 18 cover studies on the mechanisms of thermal alkylation and hydropyrolysis. Chapters 19 and 20 on oil shale deal with the properties of oil shale and shale oil as developed by techniques of microwave heating and thermal analysis. 

Thermogravimetric Studies on Catalytic and Noncatalytic Pyrolysis of Pitch Derived from Hydrocracked Athabasca Bitumen... 

Figure 6. Comparison of the normal alkane distribution in shale oil generated by pyrolysis and in bitumen from geological samples with an equivalent stage of thermal...

There are two major causes for the differences observed between shale oil and crude oil. One is due to generation by pyrolysis of compounds unusual in natural bitumens and crude oils, such as unsaturated hydrocarbons (olefins) Figure 10. Nitrogen hetero-compounds are also much more abundant than they are in natural bitumen or crude oils. The other difference is due to the migrated character of pooled oil which results in a preferential migration of hydrocarbons, especially saturates, and a retention of most of the N,S,0 - compounds in the source rock (1 ). Thus natural bitumen has an intermediate composition, separated from shale oil by the conditions of pyrolysis and from pooled oil by migration across sedimentary beds. 

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