Because of the centrifugal field in rotating packed beds (RPB), a process intensification of gas–liquid mass transfer takes place. While two-rotor RPBs offer a great potential to increase the separation performance, compared to one-rotor RPBs, there is a lack of fundamental understanding of hydrodynamics and mass transfer in two-rotor RPBs. To bridge that gap, systematic experimental approaches are needed to derive correlations for mass transfer and hydrodynamic behavior. The current article presents a detailed analysis of dry pressure drop (Δp total) by measurements with different rotor configurations (one-rotor RPB vs two-rotor RPB) equipped with metal foam as packing and operating conditions at F-factors (F G) up to 4.9 Pa0.5 and rotational speeds (n rot) up to 1200 rpm at T = 293.15 K and p = 1 atm. Based on the Δp total of a one-rotor RPB, a correlation was proposed for Δp total of a two-rotor RPB as a function of F G and n rot. The correlation allows predicting Δp total of two-rotor RPB for F G up to 3.5 Pa0.5, using the data of the one-rotor RPB only.

The transfer of batch processes to continuous flow is a major driver for the application of microreactors. Here, we present a methodology for the transfer of (bio)chemical reactions in batch mode to two-phase continuous flow. For our purposes, the coiled flow inverter (CFI) is a promising reactor design providing enhanced heat and mass transfer, narrow residence time distribution, and rapid mixing. First, this methodology is used for current development of a droplet-based reaction screening system, which was first tested with a Paal−Knorr pyrrole synthesis as model reaction. The reaction was successfully performed in the automated screening system. The yields compared to the batch mode revealed enhanced mass transfer of the product into the continuous phase. Second, we investigated the biocatalyzed oxidation of ABTS by the enzyme laccase in a straight capillary for process development in a CFI. Because of its high flexibility regarding substrate specificity, laccase oxidizes many substrates with a colored product. Hence, an optical evaluation method for determination of reaction rate is used. We compare the Michaelis−Menten kinetic of the batch reaction and the continuous reaction in a capillary. The results show that the batch reaction can be mapped to the capillary setup. However, the capillary in continuous operation enables higher screening capacity of different reaction conditions and simple scale-up procedure.

Multi-rotor RPBs (MR-RPBs) are a promising way to intensify mass transfer by exploiting the centrifugal field while achieving high separation performance. Reaching the full potential of the separation performance of MR-RPBs requires a uniform liquid distribution in each rotor. As conventional liquid distributors like nozzles can only be used at the pressurized inlet of the liquid, a new concept is needed for distribution on additional rotors. For this r eason, a novel liquid distribution concept named rotating baffle distributor (RBD) was developed. It has a compact design and exploits the rotational speed n rot of the rotor. High-speed camera analyses showed that a minimum n rot of 600 r min −1 was required for axial liquid distribution with water at ambient conditions. CT scans revealed a uniform liquid distribution in the circumferential direction using RBD with 36 baffles. Furthermore, RBDs with 12, 24, and 36 baffles were applied to the distillation of ethanol−water at atmospheric pressure under total reflux using a one-rotor RPB (1R-RPB). The F-factor (F G ) was set up to 2.3 Pa 0.5 and n rot up to 1200 r min −1 . The results were compared to the same distillation experiment in the 1R-RPB using the conventional liquid distribution, i.e., spraying the liquid on the packing via a full-jet nozzle. The distillation study revealed that the RBD with 36 baffles showed one theoretical stage higher separation performance at n rot ≥ 900 r min −1 compared to the conventional liquid distribution. Those results suggest that the RBD is not only multi-rotor-compatible but also provides uniform liquid distribution while being easier to adjust and operate than the conventional nozzle setup.

The impact of different sealing types and their wearing on the separation performance in distillation processes in rotating packed beds (RPB) has been investigated, which potentially causes bypass flows inside the unit. In the literature, a maximum separation performance is observed, which can have several possible explanations. Next to the theory that with increasing rotational speed a lower residence time counteracts the mass transfer intensification, one theory is that there are undetected bypasses from the casing of the unit to the eye of the rotor. Besides the effect of the maximum, the latter would indicate the fact that bypasses generally induce lower separation performance in RPBs. However, with a suitable sealing concept, higher separation performances could be achieved in the units. Therefore, the influence of bypass flows on the separation performance was investigated by installing different sealings in the RPB, which has not yet been discussed. For this purpose, two sealing types, a labyrinth and a floating ring sealing, were tested in two different RPBs of similar design. The results showed that the labyrinth sealing was less effective than the floating ring sealing in reducing the bypass mass flow. For the floating ring sealing, the separation performance dropped with increasing operation time due to abrasion and wearing. The results also showed that, in general, with increasing rotational speed, the tightness of the sealings is reduced, leading to the formation of bypass streams that reduce the separation performance of the plant. The study highlights the need for greater awareness of bypasses in RPBs especially concerning the separation performance and emphasizes the demand to develop more efficient and effective sealing systems that are ideally nonabrasive, require no additional fluids, and have higher tightness. These findings could call for re-evaluation of previous results, packing evaluations, and derived models.

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