Fundamentals and applications of microwave heating to chemicals separation processes

The aim of this review is to discuss the applications of microwave heating to separation and purification processes in chemical engineering from the perspective of its three unique features, namely rapid heating, selective heating and specific microscopic effects. These features render microwaves an alternative clean energy source that can replace or complement the conventional heating in various separation processes. The rapid heating and evaporation of water under the influence of microwaves renders the technology valuable in materials drying and organic extraction. The direct and selective heating of materials with high dielectric loss in a mixture enables energy savings in the treatment of petrochemical products. In adsorption processes, microwave heating can selectively heat solid adsorbent material leading to the formation of micro "hot spots" (localized zones of high temperature), increasing the efficiency in adsorbent regeneration. Finally, a deeper understanding of the impact of microwaves on microscopic structure has led to novel separation methods, such as microwave-assisted per-vaporation and microwave-assisted reactive distillation. An overview of the key mechanisms and developments of microwave heating in all these applications during the recent five years is provided and is followed by identification of the associated challenges in scale up. Fundamental research is still required for guiding further industrial application, while numerical simulations considering both heat transfer and distribution of the electromagnetic field in various reactor geometries can be helpful in the design of microwave reactors for large scale applications.