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

Abstract

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.

A Pilot-Scale HiGee-Aided Fixed Bed Reactor: Size Characteristics of Microbubbles in Diesel

“…The increment of the ε b of the catalyst bed would lead to the increment of the free movement space of bubble and low velocity of bubbles. The collision frequency could be calculated by eq . , It could be seen that the lower the velocity of bubbles, the smaller the bubble collision frequency, which led to the lower coalescence frequency probability . Thus, the d 32 of CB-A was larger than that of CB-B. h ij = F C false[ n i n j S i j ( u i 2 + u j 2 ) 1 / 2 false] Here, F C is the collision coefficient; n i and n j are i th and j th bubble number density, respectively.…”

“…29,30 It could be seen that the lower the velocity of bubbles, the smaller the bubble collision frequency, which led to the lower coalescence frequency probability. 28 Thus, the d 32 of CB-A was larger than that of CB-B.…”

“…25 The corresponding pore size was 0.93 mm according to the simplified two-dimensional model of the cross section, 25 and most bubble sizes were less than 0.5 mm in the experiments. So the coalescence effect played a dominant role, 28 resulting in d 32 at the CB-B outlet being greater than that at the CB-B inlet.…”

Microbubbling by Multichannel Ceramic Membranes: Experimental Analysis and Modeling of Gas Flux

“…However, liquid-phase hydrogenation is usually limited by mass transfer. In our previous studies, ,− , multichannel ceramic membranes were used to disperse hydrogen into microbubbles and increase the gas–liquid contact area, thereby improving the mass transfer performance and enhancing the reaction effect, such as glycerol hydrogenation to 1,2-propanediol and phenol hydrogenation to cyclohexanone. − The key factors controlling the size of microbubbles were studied, and the correlation between bubble size and membrane parameters, operating conditions, and liquid properties was established …”

“…have been widely investigated. As a result, novel distributor-type membrane reactors have been developed, and their applications have been expanded, including in the preparation of ultrafine particles, , wastewater treatment, mineral flotation, and heterogeneous catalytic reactions. − …”