Thermal Decomposition Kinetics and Mechanism of 1,1′-Bicyclohexyl

Abstract

Thermal decomposition of 1,1′-bicyclohexyl, a potential surrogate component of high-density hydrocarbon fuels, was performed in a batch-type reactor to investigate its thermal stability. A first-order kinetic equation is supposed to correlate the decomposition process, and the apparent rate constants, ranging from 0.0223 h^–1 at 683 K to 0.1979 h^–1 at 713 K, are determined. The Arrhenius parameters are determined with the pre-exponential factor <i>A</i> = 6.22 × 10²⁰ h^–1 and the activation energy <i>E</i>_a = 293 kJ·mol^–1. Compared with four typical hydrocarbon compounds, the thermal stability trend is observed in the order of <i>n</i>-dodecane ≈ 1,3,5-triisopropylcyclohexane > bicyclohexyl > <i>n</i>-propylcyclohexane > decalin. Cyclohexane and cyclohexene are found to be the primary products due to the relatively low energy of the C–C bond connecting the two cyclohexyl rings. Bicyclohexyl decomposes into cyclohexane and cyclohexene equivalently at the beginning of the reaction. A probable mechanism on the basis of quantum calculation and GC-MS analyses for the decomposition of bicyclohexyl is proposed to explain the product distribution. It is shown that the formation of decomposition products is mainly obtained through hydrogen transfer, β-scission, isomerization, or dehydrogenation