Intensified Microwave Reactor Technology

Lead Team Members: Dion Vlachos (PI), Raul Lobo

Supporting Team Members: Raja Busigari, Stavros Caratzoulas, Weiqing Zheng, Abhinav Malhotra, Weiqi Chen, Panagiotis Dimitrakellis

We develop the fundamentals of microwave (MW) reactors and materials for highly endothermic, high temperature processes. We focus primarily on the conversion of hydrocarbons due to the shale gas availability and the huge demand for ethylene and propylene and on methane upgrade to syngas, hydrogen, and liquids. These are inherently very energy demanding processes requiring furnaces whose energy efficiency is typically < 47%.

The objectives of the project have been to develop high energy efficiency, rapid, and selective heating; understand the principles of operation and scale up of MW reactors; develop materials from the molecular scale to structured reactors for MW application, and demonstrate operation over extended times.

Research Highlights

Multiscale modeling of microwave-heated multiphase systems

Homogenization theory

Modeling of microwave heating of multiphase systems requires resolving the electromagnetic field from the single particle to the entire cavity. We introduce a multiscale methodology for computationally affordable simulations of microwave heating of multiphase systems consisting of one phase dispersed in a continuum phase. The methodology homogenizes the original multiphase system, by taking advantage of the large separation of length scales, to calculate the effective permittivity, effective thermal conductivity, and volumetric power absorbed in each phase. The methodology is rigorously assessed against particle-resolved detailed numerical simulations of model systems. We demonstrate a significant reduction in computational cost while retaining the accuracy of detailed simulations. The present methodology enables high throughput exploration of novel multiphase system designs utilizing microwave heating.

Publication: Goyal, and D. G. Vlachos, Multiscale modeling of microwave-heated multiphase systems. Chem. Eng. J. 397, 10 (2020). DOI:10.1016/j.cej.2020.125262.

Intra-particle temperature profiles obtained from the detailed simulations of microwave-heating of spherical particles.

CFD simulations

Overview/abstract

Publication(s):

Machine learning-enabled reactor optimization

Microwave (MW) technology can be powerful for electrification and process intensification but limited fundamental understanding of scalability and design principles hinders its effective use. In this work, we build a continuous-flow microreactor inside a commercial single-mode MW applicator and the corresponding computational fluid dynamics model to simulate the temperature profile. The model is in good agreement with experiments for various microreactor dimensions and operating conditions. The model indicates that MW heating is greatly influenced by reactor geometry as well as the operating parameters. We observe a strong correlation between parameters and develop a gradient boost regression tree model to predict the outlet temperature accurately. This model is then applied to optimize the dimensions and operating conditions to maximize the outlet temperature and energy efficiency, resulting in a Pareto optimal. We demonstrate computationally and experimentally that it is possible to surpass the Pareto optimal and achieve an energy efficiency of ∼90% or greater at temperatures relevant for liquid-phase chemistry via salting of the solvent. The present methodology can be applied to other complex MW reactors. The combined numerical and experimental approach provides insights into and a framework for scale-up and optimization.

Publication: Y. Chen, M. Baker-Fales, and D. G. Vlachos, Operation and Optimization of Microwave-Heated Continuous-Flow Microfluidics. Ind. Eng. Chem. Res. 59(22), 10418-10427 (2020). DOI:10.1021/acs.iecr.0c01650.

CFD-predicted contour plot of outlet temperature vs the combined effect of the distance of the microchannel from the cavity bottom and between the legs.

Heat Transfer