Investigation of the performance and deactivation behavior of Raney-Ni catalyst in continuous dehydrogenation of cyclohexane under multiphase reaction conditions

• Raney-Ni has an excellent catalytic activity for dehydrogenation of cyclohexane.
• The decay of Raney-Ni catalyst is parallel deactivation.
• The multiphase reaction is confined to the outer layers of the catalyst pellet.
• The reaction is controlled by the external mass transfer.

The performance and deactivation behavior of Raney-Ni catalyst in continuous dehydrogenation of cyclohexane under multiphase reaction conditions were investigated in this paper. The experimental results showed that Raney-Ni had excellent catalytic activity for dehydrogenation of cyclohexane. Without assistance of any sweeping or carrier gas, the highest hydrogen evolution rate per unit reaction area could reach 0.20 mmol cm−2 min−1 at 322 °C with a cyclohexane feeding rate of 8.5 mmol min−1 and Raney-Ni catalyst dosage of 3 g. However, the deactivation of Raney-Ni catalyst was also observed during the course of reaction. The deactivation kinetics of Raney-Ni was studied, and the orders of deactivation at different reaction temperatures were determined, which showed that the decay of Raney-Ni catalyst was parallel deactivation. The equations of hydrogen evolution rates at different reaction temperatures were deduced from the deactivation kinetic equations. Due to the strong purging effect caused by the rapid evaporation of liquid organics on the catalyst surface under multiphase reaction conditions, the dehydrogenation reaction was confined to the outer layers of catalyst pallet and an ultralow apparent activation energy of 20.60 kJ mol−1 was obtained.

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