Investigation of Micro- and Mesomixing in a Reaction Mixing Pump and Jet loop Reactor

n many industrial syntheses — particularly in pharmaceutical manufacturing and the production of fine chemicals — the characteristic timescales of the reactions are comparable to, or even shorter than, those of the mixing process. When multiple reactions proceed simultaneously, the local mixing behavior can therefore exert a significant influence on reaction selectivity. The reliable use of such reactions requires a dedicated reactor design. First, extremely short mixing times — particularly micromixing times — are essential to ensure a rapid incorporation of the reactants into the bulk fluid at the point of feed inflow. Achieving such mixing times requires high local energy dissipation rates. Second, a high degree of process control is necessary to maintain reproducible mixing behavior and, consequently, consistent selectivity. Since in the pharmaceutical industry multipurpose plants are commonly used to produce various products in batch mode, additional process flexibility is required. This includes the ability to handle different process conditions such as fluctuating viscosities, varying flow rates, and multiphase systems within the same equipment. Over the past decades, static mixers have become well-established as reactors offering excellent micromixing performance and a high degree of process control. However, due to their inherent design, they provide only limited flexibility with respect to varying process conditions. For this reason, stirred tank reactors continue to be the predominant choice in industrial practice. Yet, their comparatively long mixing times make them only partially suitable for mixing-sensitive reactions. Currently, alternative reactor types that combine the flexibility of stirred tanks with short mixing times characteristic for static mixers are lacking in the pharmaceutical industry. In this work, two innovative reactor concepts for mixing-sensitive reactions are investigated, each aiming to unite the flexibility of stirred tank reactors with short mixing times: 1. the Reaction Mixing Pump (RMP) 2. the Jet Loop Reactor (JLR) To investigate the meso- and micromixing behavior of these reactors, the influence of various process parameters such as feed rates and feed positions on the selectivity of the established Villermaux–Dushman test system was examined under single-phase operating conditions. Based on the experimental results, micromixing times were calculated using the engulfment micromixing model. In addition, this model was used to predict the expected selectivities of this synthesis in the reactors. The experimental results demonstrate that even small changes in process parameters can have a significant impact on reaction selectivity. For both reactors, a reduction in feed rate led to a transition from the mesomixing to the micromixing regime. For example, in the case of the RMP, very low feed rates resulted in an increase of the mixing time, indicating backflow into the feed capillary. Micromixing times in both reactors were determined to lie in the range of 10⁻⁴ to 10⁻² seconds. Using the micromixing model, the reaction selectivity in the micromixing regime could be predicted reliably. The results demonstrate that both the RMP and the JLR can achieve micromixing times comparable to those of specialized static mixers, while offering the process flexibility of stirred tanks. Overall, these findings indicate that the RMP and JLR are highly promising reactor concepts for achieving high selectivities in mixing-sensitive reactions under variable process conditions.