Internal Temperature Estimation in Microwave Flow Reactors

Microwave irradiation is a very effective tool in the field of synthesis because of its rapid heating, etc., based on its energy savings and improvement of selectivity as compared to conventional external heating. In particular, flow-type microwave devices in organic synthesis are suitable for difficult synthesis processes in that the synthesis can be performed under rapid heating and cooling and pressurized conditions. On the other hand, estimating the internal temperature profile during chemical synthesis is important for proper synthesis control. However, it is difficult to directly measure the internal temperature in the target device. This paper focuses on Fischer indole synthesis. A dynamic equation was established from the heat energy balance of the reaction tube. The internal temperature profile was estimated taking into account the correlation between the microwave absorption and temperature. This method could accurately estimate the temperature profile within a relative error of 3.4-6.3% under low power microwave conditions. By clarifying the internal temperature profile, it can be used for future control of organic synthesis.