Process intensification for improving the uniformity and efficiency of microwave heating reactor by bubbles-enhanced flow method

Microwave-assisted reaction is a recent trend due to its high reaction rate, yields and selectivity compared with conventional reaction. The temperature non-uniformity and low utilization efficiency are, however, still challenging due to the unreasonable electric field distribution. A model of coupled electromagnetic field, heat transfer, and fluid flow is developed. The comparison of cases with and without bubbles in the reactor is discussed, and the equipment parameters are optimized to improve the microwave utilization efficiency simultaneously. The results showed that the bubbles have a significant improvement on temperature uniformity. The difference between maximum and minimum temperature can decrease from 36 K to 5 K. Furthermore, the natural convection is also effective in some cases for improving temperature uniformity. The electric field distribution is significantly affected by the structure of the cavity, including cavity sizes and shapes, which directly determines the efficiency of microwave energy utilization. The microwave utilization efficiency values with different cavity structures fluctuate greatly (from 7% to 99%). What's more, the method that microwave waveguide is directly connected with the reactor is not a good choice due to the penetration depth. The maximum microwave utilization efficiency can only achieve approximately 50%.

Automated summary

Microwave-assisted reactions have high reaction rates and selectivity compared to conventional reactions, but face challenges such as temperature non-uniformity and low utilization efficiency. By optimizing equipment parameters and introducing bubbles, temperature uniformity can be improved.