Practical Microwave-Assisted Recirculated Flow Esterification at Atmospheric Pressure.

In our previous publications, we reported on esterifications carried out in a circulating flow MW system. It was found that circulation enables direct insight into the reactions from both chemical and energy perspectives. We examined productivity and scalability in terms of substrate, temperature, flow rate, and catalyst, and also analyzed the processes from the point of view of energy. Compared to the conventional linear setup, the circulation resulted in a significantly higher reaction rate, and thus a higher productivity, due to a drastic increase in flow rate. However, it also became clear that higher flow rates impose a substantially higher load on both the MW equipment and the overall system, which may easily lead to pipe perforations or instantaneous seal wear due to the higher operating pressure generated by the back pressure regulator (BPR) control unit. As higher pressures are associated with elevated temperatures, this raises considerable safety concerns. In this article, we aimed to eliminate the BPR unit. While this approach sacrifices a key advantage typically associated with the MW technology by restricting the operation to atmospheric pressure, the capabilities offered by the circulation solution may compensate for the inherent limitations of the new system, and, in turn, the safety risk may be reduced.