Autogenous atmosphere

The nanostructure of a solid, also referred to in terms such as "defects," "real structure," and "mosaic structure," depends strongly on its environment. As all aspects of the nanostructure may be relevant to catalytic functions, it is common to infer such properties from static determinations of the nanostructure, often carried out at about 300 K and in laboratory or autogeneous atmospheres. This approach neglects the dynamics and assumes incorrectly that the surface catalysis process should not modify the rigid crystalline bulk of a solid. 

Figure 1. Apparatus for pyrolysis under an autogenous atmosphere.

Pilot and Field Retort Oil Samples. The data we have presented to this point are for oil cracking at relatively low temperatures (500 to 610°C) and long residence times (2 to 11 seconds) under an essentially autogenous atmosphere. These conditions exist in at least two aspects of oil shale retorting ... 

Autogenous. Figure 5 shows the rate of H2S evolution in an autogenous atmosphere from Anvil Points samples of 9-, 22-,... 

Figure 5. Rate of H2S evolution from Anvil Points (AP) samples of varying grades (e.g., Sample AP61 is 61 gal/ton). The samples were heated in an autogenous atmosphere at 4.8°C/min. The temperature of the peak evolution rate increases as grade decreases.

Figure 6. Demonstration of the increase in H2S evolution in an autogenous atmosphere with added pyrite...

The amount of H2S evolved in argon and autogenous atmospheres is comparable, although the evolution profiles are different. The amount of H2S evolved in the presence of steam is substantially greater. Within the accuracy of the results, we conclude that 75 + 25% of the initial sulfur ends up as H2S in a steam atmosphere. 

In an autogenous atmosphere, the temperature of the peak evolution rate varies from 440 to 475°C. The peak temperature increases with a decrease in sample grade (Figure 5). A possible explanation for this effect is that the greater availability of hydrocarbons in the rich shale enables the pyrite to react at a lower temperature. 

Most of the sulfur in oil shale occurs in pyrite and a smaller amount is contained in the kerogen. The major source of H2S during oil shale pyrolysis appears to be the reaction of pyrite with organic matter. In an autogenous atmosphere, most of the H2S evolves between 400 and 500°C. Addition of finely ground pyrite increases the amount of H2S evolved but does not change the evolution profile. In an argon atmosphere, however, added pyrite causes a substantial increase in H2S evolution... 

The rates of ethene and ethane evolution, the ratio of ethene to ethane, and the partial pressure of hydrogen (relative evolution rate of hydrogen to total gas) are shown in Figure 2 for oil shale heated at 1.5°C/min under an autogenous atmosphere. The ethene/ethane ratio reaches a first minimum before the peak rate of C2 evolution. It then increases slightly before reaching a second minimum at about 540°C. A more pronounced variation in the propene/propane ratio was observed at l°C/min (Figure 3). 

Figure 2. Product measurements for oil shale heated at 1.5°C/min under an autogenous atmosphere (a) rate of C2 evolution (b) ethene/ethane ratio (c) partial pressure of hydrogen released.

Figure 4. Arrhenius plot for the time and temperature dependence of [H2][C2H ]/ [C2H6] evolved from 22 gal/ton oil shale heated at 1.5 °C/min under an autogenous atmosphere. The maximum rate of gas evolution, which corresponds to the minimum residence time, is shown.

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