Kerogen proposed

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... 

It has been proposed that sulfur-carbon bonds break at lower thermal stress than carbon-carbon bonds in sulfur-rich kerogens (24). Scission of sulfur-carbon bonds provides one explanation for the observed depletion of organosulfur compounds in the pyrolysates of high rank coals. The sulfur groups present in low rank coals are broken from the coal matrix to produce low molecular weight sulfur compounds which are not measured by the techniques used in this study. 

Figure 5. Proposed structures of alkylthiophene moieties in kerogens and asphaltenes and their presumed flash pyrolysis products. Examples are give for alkylthiophene moieties with (a) linear, (b) isoprenoid, (c) branched and (d) steroidal side-chain carbon skeletons. Carbon skeletons are indicated with bold lines.

Figure 1 Kerogen is a key intermediate in the formation of oil and gas. Numerous schemes have been proposed both for the formation and structure of kerogen. This diagram shows one of the schemes which favors the selective...

Two proposed mechanisms were tested a single-step mechanism kerogen - products and a two-step mechanism kerogen bitumen products. 

This proposed silicate mineral catalytic effect is further demonstrated by TG measurements of the kerogen concentrate, Sample D, which show a decrease in the net pyrolysis yield from 68.8 wt% for the bitumen-, carbonate-free Sample C to 57.6 wt% for the now silicate-free sample. These results suggest that the optimum pyrolysis oil yield is achieved for Green River oil shales which are carbonate-free, but still retain their original silicate mineral concentration or, possibly, an increased silicate concentration. 

A frequent characteristic of past investigations is excessive complexity of the proposed kerogen pyrolysis models. The works of Fausett et al. (6 ) and Johnson et al. (3) belong in this category. A goal of the present investigation is to keep the model as simple as possible. 

First-order rate expressions are proposed in Table I for the three principal steps light hydrocarbon production (equals kerogen decomposition), primary heavy oil production, and coking. 

As part of this investigation, kerogen pyrolysis models different from the one proposed here were considered. One such model of theoretical appeal is similar in structure to the one given in Figure 9 but with a pure diffusion process for the heavy oil production. However, this alternative model is incompatible with some experimental findings It predicts lower coke concentrations on the surface of the particle than in the interior, whereas microprobe results indicate a uniform coke distribution. Further, this diffusion model predicts zero coke yield for infinitely small particles, whereas the limited amount of data available for small particle sizes suggest a leveling-off of the coke yield below a particle size of 0.4 mm. 

The proposed model can be compared with both the model of Allred ( ) and that of Campbell et al. (8). Allred s model does not have the feature of competing parallel reactions that is essential to the pyrolysis model proposed here. It does, however, have the intermediate product bitumen which reaches a maximum level almost identical to the one in this work. Allred postulates that all kerogen decomposes into bitumen, whereas bitumen in the present work is the remainder of the kerogen after the light hydrocarbon fraction has been stripped off. 

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