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/Al2O3 catalysts
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.
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