With the increasing importance of renewable electricity as a primary source of energy on the planet, the importance of electricity–based technologies in process industries is expected to rise as well. Microwave heating is a well–known electricity–based industrial technology that is used in a variety of commercial applications.

This work addresses challenges and explores opportunities for industrial–scale utilization of microwave heating in heterogeneous catalytic gas-phase reactors. Through critical analysis of microwave applicators, the thesis highlights the limitations of traditional cavity–based reactors and underscores the potential of traveling–wave systems for achieving uniform heating profiles in heterogeneous catalytic flow reactors. The contribution of the thesis lies primarily in the design and optimization of traveling microwave reactors (TMRs). Challenges associated with catalyst heating profiles and process scale–up are addressed by introducing a coaxial waveguide structure and a tailored catalyst loading pattern. The TMR model demonstrates its effectiveness in accurately predicting temperature profiles and reaction dynamics along the reactor through simulation studies and experimental validation. Furthermore, the thesis introduces the Reverse Traveling Microwave Reactor (RTMR) as a novel reactor concept aiming to minimize temperature gradients along the catalyst bed by periodic reversal of microwave irradiation. Simulation–based studies showcase the RTMR’s potential in achieving temperature uniformity within the catalyst bed, offering new insights into reactor design and scale–up considerations for microwave–assisted catalytic flow processes.@en

Microwave heating presents a potentially green alternative for energy supply to chemical and catalytic reactors as it can be based on the electricity from renewable sources. The Reverse Traveling Microwave Reactor (RTMR) is a novel heterogeneous catalytic reactor concept, based on the coaxial waveguide structure. The reactor has two microwave ports on both ends, and microwave irradiation is periodically switched between those ports to minimize the temperature gradients along the catalyst bed. In the current paper, COMSOL MULTIPHYSICS® simulation environment has been used to develop a 3D multiphysics model of the RTMR. Based on the model, operational characteristics of the reactor including electric field distribution and transient temperature profiles have been studied. Simulation results show that periodically reversed microwave irradiation improves the homogeneity of the temperature distribution inside the catalyst bed. The study provides new insights into the design and scale-up of microwave-assisted catalytic flow processes.

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Microwave irradiation can intensify catalytic chemistry by selective and controlled microwave-catalytic packed-bed interaction. However, turning it to reality from laboratory to practical applications is hindered by challenges in the reactor design and scale-up. Here, we present a novel, rectangular traveling-wave microwave reactor (RTMR) and provide an easy-to-handle, 3-step design procedure of such reactor. The multiphysics model couples the electromagnetic field, heat transfer, and fluid dynamics in order to optimize the geometrical parameters and operational conditions for the microwave-assisted heterogeneous catalysis. The results show that the microwave energy input/output ports should be well-positioned and matched; otherwise, it would significantly decrease energy efficiency. In terms of microwave transmission, the RTMR presents a mix between the standing wave and the traveling-wave systems. Gas space velocity and input temperature significantly affect the temperature profile, and gas–solid temperature can present no significant difference under certain gas–solid contact.

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Microwave chemistry applications have been investigated for more than three decades. Contrary to common cavity-based microwave applicators, the traveling-wave microwave reactor has the potential to enable the process scale-up, a better coupling of microwave energy with microwave-susceptible catalysts, and consequently highly uniform microwave heating. In this work, the engineering challenges entailed with the design of a traveling-wave microwave waveguide are explained and appropriate solutions developed. A new traveling-wave microwave reactor with a coaxial waveguide structure is presented. Simulation results show that there is no standing wave generated along the structure. Furthermore, in order to keep the impedance matching and minimize the microwave reflections while the reactor is loaded with catalyst samples, new reactor's loading patterns are introduced. Simulation results showed that for the proposed method, microwave-susceptible catalytic fixed-bed could interact more efficiently with microwave energy and produce a uniform heating profile.

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The paper discusses the currents status and future perspectives of the utilization of microwaves, as a selective and locally controlled heating method, in heterogeneous catalytic flow reactors. Various factors related to the microwave-catalyst interaction and the design of microwave-assisted catalytic reactor systems are analyzed. The analysis clearly shows the superiority of the traveling-wave systems over the mono-mode and multi-mode cavity-based systems when it comes to the design and application of microwave flow reactors at relevant production scales.

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In this paper, a novel adaptive Takagi-Sugeno (TS) fuzzy observer-based controller is proposed. The closed-loop stability and the boundedness of all the signals are proven by Lyapunov stability analysis. The proposed controller is applied to a flexible-transmission experimental setup. The performance for constant payload in the presence of noisy measurements is compared to a controller based on a classical extended Luenberger observer. Simulation and real-time results show that the proposed observer-based feedback controller provides accurate position tracking under constant and varying payloads.@en