Dynamic Performance Analysis of Swellable Monolithic Hydrogel-Based Catalyst in Continuous Reaction Column

Operation of a reaction column packed with a swellable monolithic catalyst in continuous mode results in interesting transitional properties and a moving boundary. This study simulated the dynamic performance of a hydrogel-based monolithic catalyst in reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), revealing the unique transitional properties associated with swellable catalysts in continuous operation. The effect of feed flow rate and the concentration on conversion, catalyst activity and deactivation, pressure drop, and residence time distribution (RTD) were investigated for three distinct scenarios of completely swollen hydrogel (cSH), nonswellable hydrogel (nSH), and time-dependent swelling hydrogel (tSH). We demonstrated that the tSH configuration is much more interesting, wherein the conversion approaches ∼100%, despite exhibiting catalyst activity comparable to cSH and lower than nSH. For all the scenarios, the conversion decreased with increasing flow rate of the feed at a given concentration. Furthermore, the pressure drop during the reaction for nSH was negligible at a given flow rate. While for the cSH, the highest and constant pressure drop of about 50 kPa was obtained. However, for the tSH, as the reaction proceeded, the pressure drop increased nonlinearly and approached a value slightly higher than 50 kPa. The results suggest that at least for a pseudo-first-order reaction, a bed height with a moving front might be appropriate as the reactor does not always experience the highest pressure drop, and at the same time, the conversion is favorable.