Temperature Homogeneity under Selective and Localized Microwave Heating in Structured Flow Reactors

[EN] Selective heating of different phases of multiphase systems via microwaves can result in energy savings and suppression of side reactions. However, materials properties and operating conditions that maximize temperature gradients are poorly understood. Here we utilize computational fluid dynamics (CFD) computations and temperature measurements in structured flow reactors (monoliths) in a monomodal microwave cavity to assess the temperature difference between the walls and the fluid and develop a simple lumped model to estimate when temperature gradients exist. We also explore the material's thermal and electrical properties of structured reactors for isothermal catalyst conditions. We propose that CFD simulations can be used as a nonintrusive, predictive tool of temperature homogeneity. Importantly, we demonstrate that localized heating in the bed under several conditions rather than selective heating is responsible for the selectivity enhancement. Our results indicate that structured beds made of high thermal conductivity materials avoid arcing and enable temperature homogeneity and low electrical conductivity materials allow microwaves to penetrate the domain.This work was supported by the Department of Energy's Office of Energy Efficiency and Renewable Energy Advanced Manufacturing Office under award no. DE-EE0007888-8.3. The Delaware Energy Institute gratefully acknowledges the State of Delaware's support and partnership toward the RAPID projects. The authors acknowledge fruitful discussions with Prof. Mark Mirotznik, Paul Parsons, and Tai-Ying Chen. The authors thank Keiji Adachi from Ibiden USA for providing the SiC monolith sample and Jaynell Keely for assistance with graphics.Malhotra, A.; Chen, W.; Goyal, H.; Plaza González, PJ.; Julian, I.; Catalá Civera, JM.; Vlachos, DG. (2021). Temperature Homogeneity under Selective and Localized Microwave Heating in Structured Flow Reactors. Industrial & Engineering Chemistry Research. 60(18):6835-6847. https://doi.org/10.1021/acs.iecr.0c0558068356847601