Influence of pressure (100 Pa-100 Mpa) on the pyrolysis of an alkane at moderate temperature (603 K-723 K): Experiments and kinetic modeling

- The pyrolysis of n-octane was studied from 1 MPa to 70 MPa and from 603 to 723 K.
- At 603 K-623 K the conversion of n-octane as a function of pressure is bell-shaped.
- A previous study focused on the very low concentration (100 Pa diluted in inert gas).
- Both studies underline the crucial role of pressure in the reaction paths and products.
- A mechanism consisting of 182 free-radical reactions is proposed and validated from low (100 Pa) to high pressure (70 MPa).

Confined pyrolysis of n-octane was performed in a closed, constant-pressure gold reactor at pressure ranging 1 MPa-70 MPa, temperature between 603 K and 723 K and residence times from 1 h to 1 month. The main products of reaction are n-alkanes of molecular weight lower than n-octane and branched alkanes of molecular weight higher than n-octane. Alkenes are minor products. At moderate temperature (603 K-623 K) the conversion of n-octane increases with pressure up to a maximum and then decreases (at constant duration of pyrolysis). For higher temperature (723 K) the conversion increases continuously with increasing pressure. A mechanism consisting of 182 free-radical reactions is set up and used to model these experimental results (1-70 MPa) as well as those obtained in a previous study at very low concentration (100 Pa diluted in inert gas, total pressure 0.15 MPa). The agreement between the experimental data and simulation results is satisfactory in terms of product distribution and conversion of n-octane in a wide range of pressure (100 Pa to 70 MPa). Some mechanistic explanations concerning the effect of pressure are proposed.

91