Energy Efficiency of Microwave- and Conventionally Heated Reactors Compared at meso Scale for Organic Reactions

This study reports on the energy efficiency of microwave heating at the largest currently accessible scale in commercial microwave reactors (∼1−3 L). The energy consumptions of four microwave reactors, each with different operating principles, were compared against one another and against a conventionally heated jacketed reaction vessel for four pharmaceutically relevant organic reactions under identical conditions using a commercial wattmeter. In addition, several scales of reaction were investigated in one microwave reactor. The results show that microwave heating can be more energy-efficient than conventional heating under many conditions. However, these results are highly dependent upon the design of the microwave reactor (manufacturer and operating principle), with significant differences being observed between them. They are also dependent upon the scale applied, with multimode microwave reactors being more efficient at larger scales. Shorter reaction times were also more efficient in microwave reactors, but the benefits were completely lost for long reactions. Overall, these results show that, <i>at this scale</i>, microwave heating is generally more energy-efficient than conventional heating