Thermal cracking of n-butylcyclohexane at high pressure (100 bar)—Part 2: Mechanistic modeling

• Exhaustive primary mechanism of BCH pyrolysis based on free-radical reactions was built.
• Partial secondary mechanism includes reactions involving aromatics.
• Pyrolysis mainly leads to n-alkanes, alkylcyclohexanes and alkylbenzenes.
• Breaking of alkyl side chain reactions prevail on dehydrogenation and ring opening.

A detailed kinetic model consisting of 833 reactions has been developed to describe the thermal cracking of n-butylcyclohexane at high pressure (100 bar). A primary mechanism was written in an exhaustive manner whereas a partial secondary mechanism was considered to describe the formation and the consumption reactions of aromatic compounds. The model was tested against our experimental data for BCH pyrolysis at 100 bar in the temperature range 375–425 °C. A global agreement was reached for BCH conversion up to 50% for both conversion and product yields e.g. propane, cyclohexane and toluene. Flow analysis of the proposed mechanism at a conversion of 35% shows that both alkanes (i.e. methane, ethane, propane and n-butane) and cycloalkanes (i.e. cyclohexane, methylcyclohexane and ethylcyclohexane) mainly come from the breaking of the side alkyl chain. The production of butylbenzene is due to the direct dehydrogenation of BCH whereas other alkylaromatic compounds i.e. benzene, toluene and ethylbenzene seem to come from the breaking of the side alkyl chain of butylbenzene rather than aromatization of cycloalkanes or alkylcyclohexenes. At 100 bar and around 400 °C, breaking of alkyl side chain reactions prevail on dehydrogenation reactions and ring opening.

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