Conversion of hydrocarbons over an Ni-Al 2O 3 catalyst II: Study of the mechanism of the conversion of cyclohexene

Abstract

The catalytic conversion of cyclohexene on an Ni-Al 2O 3 catalyst was studied using a flow technique. The catalytic activity was measured in the temperature range 360–450 °C at space velocities of 11.93 × 10 -4 − 48.13 × 10 -4 min -1 under normal pressure. The gaseous and liquid products of the disproportionation reaction were analysed chromatographically. The gaseous products were methane, ethane, propane and hydrogen, and the liquid products were cyclohexane, methylcyclopentane, cyclohexadiene, benzene, toluene and p-xylene together with unreacted cyclohexene. The kinetics of the gaseous products and of cyclohexadiene, toluene, p-xylene and cyclohexane revealed a zero-order reaction. However, this was not the case for benzene. The apparent activation energy was calculated to be 16.39±0.5 kcal mol -1 independent of the space velocity. Artificial cyclohexene-benzene and cyclohexene-cyclohexene mixtures were prepared. It was shown that benzene can be obtained directly from cyclohexene and/or indirectly from the cyclohexane produced by the disproportionation reaction. The formation of different products and the gain in the mass of the catalyst after participation in cyclohexene conversion are explained in terms of the formation of condensation products on the catalyst surface which may decompose in different ways giving reaction products.