Pyrolysis mechanism of the n-octane/H2S mixture at 70Â MPa and 603-623Â K

A detailed kinetic model consisting of 3883 free-radical reactions was developed to describe the pyrolysis of the n-octane/H2S mixture at high pressure and relatively low temperature. The model was validated by comparison between the simulation results and the experimental data obtained at 603 and 623 K, 70 MPa, from 3 to 13 days, in gold cells. The main products, which are alkanes and sulfur compounds, i.e., C8-thiols, alkylthiacycloalkanes, light thiophenes (thiophene, C1-, C2-thiophenes) and C4-thiophenes, are correctly simulated by the model. Nevertheless there are some discrepancies which are discussed in the paper. The kinetic analysis of the model showed that H2S had a slight inhibition effect on the n-octane pyrolysis. This behavior results from different antagonistic effects, i.e., new terminations with HS
- which decrease the pyrolysis rate; new bimolecular initiations with H2S which increase the pyrolysis rate; and a new parallel propagation loop which also increases the pyrolysis rate. Moreover, the inhibition effect of H2S on n-octane pyrolysis decreases when the temperature decreases and the pyrolysis duration increases. This evolution is due to the relative importance of the three antagonistic effects that depends on the temperature and the reaction duration.