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The hypothesis of microscopic hot spots is widely used to explain the unique microwave (MW) effect in materials science and chemical engineering, but it has not yet been directly measured. Herein we use Eu/Tb mixed‐metal organic complexes as nano thermometers to probe the intrinsic temperature of MW‐absorbing particles in MW fields based on the thermosensitive fluorescent spectra. According to the measurements of the temperature gradient at the solid/liquid interphase, we derive an MW‐irradiated energy transfer model to predict the extent of microscopic hot spots. The fluorescence results agree with the model predictions that the MW‐induced temperature gradient can be enlarged by increasing MW intensity, as well as the dielectric loss and size of particles. Conversely, the increase in the thermal conductivity and the dielectric loss of the liquid lowers the temperature gradient. This study enables control of MW‐assisted synthesis and MW‐responsive techniques. [ABSTRACT FROM AUTHOR]

The application of newly electrified microwave heating to traditional processes of vapor-liquid mass transfer has given rise to many emerging process intensification technologies, such as microwave-induced evaporation separation and microwave-induced reactive (flash) distillation. Many researchers are eager to find suitable application scenarios for microwave technology by deeply understanding the role of microwaves in the separation process of vapor-liquid mass transfer. In this paper, we summarize the role of microwaves in the above processes from prespectives of the driving energy and microwave special effects, and briefly outline the bottlenecks in the current development to point out the research direction for subsequent fundamental investigations and industrial applications. [ABSTRACT FROM AUTHOR]

· The advantages of microwave preparation of adsorptive materials are systematically reviewed. · The mechanism of the microwave intensification adsorptive technique is discussed in depth. · The industrialization development of microwave intensification adsorptive technology was prospected. Compared with the traditional heating modes, microwave technology is promising to intensify adsorption processes, due to its ability to accelerate the production rate of adsorbents and achieve adsorption equilibrium faster. This review paper describes the state-of-the-art field of microwave technology used for the adsorption separation, with a particular focus on microwave assisted preparation of various adsorbents, including metals, high molecular polymers, biology, and composite adsorption materials. The mechanisms of microwave-intensified adsorbents preparation and processes of adsorption separation, as well as the practical applications of microwave techniques in the adsorption/desorption field are explained and discussed. Finally, efforts to promote microwave intensification technology to industrial use in the field of adsorption and open questions in the development of industrial-scale microwave-assisted techniques are outlined. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel MW-VLE model is proposed to facilitate and accurately predict VLE data in microwave fields. • The influence of thermodynamic and dielectric properties of the binary system on MIRVC is discussed in detail. • The empirical correlation equations were established by correlating model characteristics parameters with binary system properties and electric field strength. • The error range between predictive values and experimental results was within ± 10%. Microwave (MW) irradiation can intensify the vapor–liquid separation of polar/non-polar binary system mixtures, but its industrialization requires vapor–liquid equilibrium (VLE) data in microwave field. Therefore, a novel MW-VLE model was proposed to predict the VLE data of binary systems in microwave fields by using system thermodynamic properties, dielectric properties, and electric field strength. For modeling, first, the influence of thermodynamic and dielectric properties on microwave-induced relative volatility change (MIRVC) was investigated experimentally in detail. It indicated that increasing the system dielectric loss difference, boiling temperature difference, and decreasing the thermal conductivity can enhance the effect of MIRVC. Then, the model characteristic parameters were obtained by fitting the VLE curves with/without microwave irradiation. Afterwards, the empirical correlation equations of MW-VLE were derived by correlating model characteristic parameters with mentioned above factors and electric field strength. Finally, the model predictions well agreed with the experimental results of PrOH-PP and IPA-EA systems within 10% error, verifying the model accuracy. [ABSTRACT FROM AUTHOR]

In their Research Article (e202114340), Hong Li, Xin Gao et al. report the detection of microwave-induced hot spots in liquid solutions with a fluorescence thermometer attached on microwave-absorbing carbon particles. Frontispiece: Watching Microwave-Induced Microscopic Hot Spots via the Thermosensitive Fluorescence of Europium/Terbium Mixed-Metal Organic Complexes Keywords: Carbon Particles; Fluorescence; Metal-Organic Complexes; Microwave Energy; Sensors EN Carbon Particles Fluorescence Metal-Organic Complexes Microwave Energy Sensors 1 1 1 01/28/22 20220201 NES 220201 B Microwave Chemistry b . [Extracted from the article]

• Microwave energy is employed to enhance the co-pyrolysis of PET and biomass. • The mechanism of microwave-assisted pyrolysis of PET and biomass is proposed. • The microwave-assisted pyrolysis of PET-biomass blends shows a synergetic effect. • The effect of three microwave susceptors on products composition are evaluated. The present study employs microwave (MW) energy to enhance the co-pyrolysis of polyethylene terephthalate (PET) wastes and biomass. Based on the characterization of raw materials as well as gas and liquid products, we propose a pyrolysis mechanism of PET and biomass during microwave-assisted pyrolysis (MAP). The MAP of PET-biomass blends shows a synergetic effect that the interaction between PET and biomass promotes the yields of value-added products (e.g. aromatic acids and phenols) and suppresses the generation of biphenyls and polycyclic aromatic hydrocarbons, compared to the MAP of individual biomass or plastics. Besides, the blending ratio of PET-biomass has significant effect on the formation of major liquid products. The liquid product from the MAP of PET-biomass 4:1 blends contains above 30 wt.% chain hydrocarbon that can be used as gasoline and kerosene. Moreover, we evaluate the roles of three typical MW absorbing materials during MAP, including carbon powder, ferroferric oxide (Fe 3 O 4) and calcium oxide (CaO). Carbon powder can enlarge the yield of main products from plastics pyrolysis due to its significant dielectric loss. Apart from the MW-absorbing ability, Fe 3 O 4 can accelerate the esterification and decarboxylation reaction; CaO can convert acids into ketones and hydrocarbons through neutralization and catalytic cracking reactions. [ABSTRACT FROM AUTHOR]

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 pervaporation 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. Image 1 • The unique features of microwave heating render the technology a promising tool for Process Intensification. • Application of microwaves to diverse separation processes in the last five years have been summarized. • The underlying mechanisms of microwave-assisted separations are discussed. • The challenges and limitations of microwave-assisted techniques, requiring further research are highlighted. [ABSTRACT FROM AUTHOR]

• A microwave-transparent thermochromic MOF is synthesized as nano-thermometer. • The thermometer has good thermal stability and dispersity in liquid solution. • A color-temperature relationship of the thermochromic MOF is established. • The temperature distribution is directly visualized during microwave heating. Microwave has been widely used as an efficient and clean method for energy supply in chemical engineering, due to its unique heating characteristics. The industrialization of microwave is obstructed by the problem of uneven heating; the inhomogeneous temperature distribution results in inaccurate prediction of reaction kinetics, uncertain product yields, and unstable energy utilization efficiencies. With the aim to overcome this problem, we use a non-contact nano-thermometer to achieve in situ imaging of liquid temperature distribution during microwave heating. A zinc-based metal organic framework material (ZMOF) is employed as the temperature indicator in microwave field, due to its microwave transparency, thermal stability and good dispersibility in solvents. A case study was conducted by dispersing the ZMOF particles in a 95% ethanol solution, where the color of ZMOF changes from yellow to orange with the increase of temperature in the range of 30–120 °C with the sensitivity of 1.512%/°C. By linearly correlating the hue value of ZMOF suspension with the temperature, the color images of liquid heated in microwave cavity were transformed into temperature distribution maps. ZMOF also has shown the advantages of good dispersion, cyclic temperature measurement, continuous linear discoloration, and visible light excitation. This facile route of temperature field imaging can provide experimental validation for numerical simulation and guide the equipment optimization in microwave-assisted chemical engineering. A zinc-based MOF material is fabricated, whose color is sensitive to temperature. By dispersing the material in solvents, the temperature distribution of liquid samples can be directly observed during microwave irradiation. This facile route can calibrate the results of numerical simulation and provide guidance for equipment optimization of microwave-assisted chemical engineering. [Display omitted]. [ABSTRACT FROM AUTHOR]

In this work, nickel oxide/sulfide nanoparticle-embedded porous carbon (NiO-Ni x S y @KC) is successfully constructed using kelp as a starting material by an impregnation and vulcanization method. Such 3D porous structure endows the NiO-Ni x S y @KC-800 electrode with fast ion transport and low interface resistance for supercapacitor application. The NiO-Ni x S y @KC-800 electrode delivers a high specific capacitance of 3160.33 F g−1 at 0.5 A g−1 and a capacitance retention of 83.24 % after 10,000 cycles at 5 A g−1. An asymmetric supercapacitor device assembled by NiO-Ni x S y @KC-800 and kelp-derived porous carbon pyrolyzed at 800 °C (KC-800) exhibits a maximum energy density of 68.58 W h kg−1 at a power density of 375.01 W kg−1. Benefitting from the structural and compositional advantages of NiO-Ni x S y @KC-800, the composite shows a minimum reflection loss (RL) of − 38.2 dB at a thickness of 3.0 mm. The prepared material presents a great potential for supercapacitors and microwave absorbers. [Display omitted] • This work reported a material of nickel oxide/sulfide supported on kelp-derived porous carbon. • The NiO-Ni x S y @KC-800 electrode fulfilled specific capacitance of 3160.33 F g−1 at 0.5 A g−1. • The ASC delivered a maximum energy density of 68.58 W h kg−1 at 375.01 W kg−1. • The composite had a minimum reflection loss of −38.2 dB at 7.28 GHz with a thickness of 3.0 mm. [ABSTRACT FROM AUTHOR]