Maldistribution susceptibility of monolith reactors: Case study of glucose hydrogenation performance

Abstract

In this work an ultrafast electron beam X-ray modality was applied for the first time to characterize the gas-liquid Taylor flow inside each channel of an opaque honeycomb monolith structure (65 cpsi) for u G;S 50:1 . . . 0:5 m=s and u L;S 50:2 m=s. Significant spatial and temporal deviations in the phase holdup as well as in the gas bubble and liquid slug lengths were found. To evaluate the impact of Taylor flow maldistribution on the reactor performance, the data of more than 125; 000 unit cells were used to simulate the reactor productivity in the hydrogenation of glucose. The results verify that a monolith reactor solely designed by using superficial velocities and empirical correlations for gas bubble and liquid slug lengths fails significantly in achieving high product selectivity and the desired conversion. The developed methods are a solid base to design and select proper distributors ensuring the favorable flow configurations for specific chemical processes.

Modeling the Excess Velocity of Low-Viscous Taylor Droplets in Square Microchannels

“…It determines the contact time of the educts and influences the pressure drop of the reactor [19]. Within a parallel reactor, an exact knowledge of the pressure drop is especially necessary since a steady educt supply for each individual single reactor is needed to ensure stable and efficient working conditions [20].…”

Hydrodynamic study of a monolith-type reactor for intensification of gas-liquid applications

“…In the literature, the impact of the distributor is generally investigated for an air-water system. The conventional and widely used measurement method is based on liquid collectors set at the outlet of the channels [32] but some authors have used optical fibre sensors [33] or conductive needle sensors [2], or, more recently, gamma ray computed tomography [34,35,36], ultrafast electron beam X-ray tomography [37] or magnetic resonance imaging (MRI) techniques [38,39,40]. In particular, the last two techniques provide not only the time-averaged liquid distribution over the monolith cross-section but also the dynamic features of Taylor flow within individual channels.…”

“…Behl and Roy [32] observed a better flow distribution when increasing the liquid flow rate in the same range of liquid velocity (u L between 0.04 and 0.085 m s −1 ) with a packed bed distributor and, to a lesser extent, with a pipe distributor. For liquid velocities of up to 0.2 ms −1 and a nozzle injector, Schubert et al [37] mentioned empty channels in the peripheral area, near to channels with high gas hold-up.…”

Effect of phase maldistribution on performance of two‐phase catalytic monolith reactor and its comparison with trickle bed reactor

“…It should be noted that Roy and Al‐Dahhan reported that uniform phase distribution was achieved within the limited range of operating conditions within the Taylor flow regime. Using actual phase distribution data from experiments, Schubert et al and Roy et al reported that the performance of the monolith has a strong dependence on the phase distribution using modelling studies. However, there is no experimental study available that confirms and quantifies the effect of the degree of maldistribution on the performance of the monolith reactor.…”

“…Further, a maldistributed entry (mostly due to the distributor and operating conditions) results in gross underutilization of the monolith catalyst, resulting in reduced productivity. The underutilization of the catalyst might be due to the empty channels, or due to the flow structure or regime change in some of the channels . However, there is no quantitative information available in the literature on the effect of maldistribution on catalyst utilization.…”