Liquid-Phase Hydrogenation of Phenol in an Advanced Gas-Liquid Concurrent Upflow Fixed-Bed Reactor with Membrane Dispersion

Phenol hydrogenation is an environmentally friendly route to produce cyclohexanone, an important intermediate for manufacturing nylon-6 and nylon-66. Herein, a gas-liquid cocurrent upflow fixed-bed reactor with an external multichannel ceramic membrane as the dispersion medium was developed for continuous liquid-phase hydrogenation of phenol to cyclohexanone over Pd/Al₂O₃catalysts in aqueous media. The pipeline between the membrane module and fixed-bed reactor was designed and optimized after examination of the influence of the bubble size and solubility of hydrogen quasi in situ and the corresponding phenol conversion and cyclohexanone selectivity. Results highlight that only a suitable pipe height can effectively improve the gas-liquid mass transfer, so as to improve the phenol conversion. A phenol conversion of ∼98% and a cyclohexanone selectivity of ∼95% can be achieved in a 52 h continuous run. In particular, the phenol conversion is significantly increased by 14.5% compared with that without a pipeline connection. This work will pave an efficient route to the optimal design of a fixed-bed reactor coupled with a membrane distributor for green cyclohexanone production.