Microwave Irradiation Heating Research Articles

Synthesis pathways of (HfZrTiCe/La/Y)O2-x nanoparticles via benzyl alcohol route at critical temperature

The controllable synthesis of high-entropy fluorite oxide (HEO) having large ionic radius mismatch remains a challenging due to poor understanding on nucleation. The (HfZrTiLn)-5HEO nanoparticles with 15 % ionic radius mismatch were synthesized via benzyl alcohol route at 220 °C-5 min in presence of PtCl4 and Fe(acac)3, exhibiting novel optical, electrical and magnetic properties. Nucleation pathways of the 5HEO at the critical temperature were elucidated by using a comparison study of conventional heating and microwave irradiation heating. Consistency of XRD patterns and STEM-EDX observation indicate that the resultant Hf-OBn monomers acted as the nucleation center of the 5HEO, determined by diffusion kinetics. The nucleation rate depended on the metal monomers assembly and esterification reaction, which was accelerated by water vapor pressure produced in-situ by 0.5×10−4mol/l PtCl4 catalyst. The Fe-metal organic cages derived from 1.5×10−4mol/l Fe(acac)3 additive served as the structure stabilizer of Zr/Ti monomers, and prevented early hydrothermal reaction route.

Effect of microwave irradiation and conventional heating on high pressure modified white finger millet starch hydrogel properties

High pressure modified (200 MPa and 400 MPa for 10 min) white finger millet starch hydrogels were prepared with three starch concentrations (12 %, 15 % and 18 % (w/v)), by conventional heat treatment (75 °C for 12 min) and microwave treatment (50 s at 900 W, surface temperature 75 °C). The prepared hydrogels were compared to native white finger starch hydrogels for understanding the effect of modification as well as the gel synthesis method. Effect of the storage period on physical stability was evaluated for ten days by evaluating weight loss, water activity, and color. The whiteness index of the prepared hydrogel intensified during the storage period, and water activity was reduced (0.99–0.976). While stored at 4 °C, the hydrogel weight decreased due to moisture migration. The results emphasize that treatment conditions, starch modification, and concentration significantly affected water absorption. The maximum gel strength was identified for conventional heat-induced 400 MPa high-pressure modified hydrogel stored for ten days. 1H NMR relaxation time showed microwave-induced gel synthesis had a shorter relaxation time. The gel microstructure helped to correlate the swelling and gel strength increment in the modified gel sample, as it had a higher wall thickness and a smaller pore size than heat-induced hydrogels. These findings help to conclude high pressure modified white finger millet starch hydrogel synthesised by microwave irradiation can be alternative to conventional heat gelatinisation method.

High-efficient microwave-assisted conversion of fructose to 5-hydroxymethylfurfural over rice straw-derived sulfonated porous carbonaceous catalyst

5-Hydroxymethylfurfural (HMF) has emerged as a pivotal platform chemical derived from biomass, attracting considerable attention for its renewable applications. In this study, sulfonated rice straw biochar (RSBC-SA) catalysts were developed and employed for microwave-assisted catalytic conversion of fructose to HMF. The RSBC-SA catalysts, synthesized by pyrolyzing rice straw biomass at different temperatures and subsequent functionalization with sulfonic acid groups, were characterized using X-ray photoelectron spectroscopy (XPS), elemental analysis, temperature programmed desorption (TPD) and Fourier-transform infrared spectroscopy (FT-IR). A comparative analysis of catalytic performance between microwave irradiation and conventional oil bath heating revealed a substantial enhancement in efficiency with the former. Notably, the 700 ℃ pyrolyzed RSBC-SA catalyst demonstrated the highest HMF yield of 92.6 % within just 5 min of reaction time under a microwavehydrothermal condition, surpassing the conventional oil bath heating method. In addition, moderate to high yields of HMF were achieved from different carbohydrates in our developed microwave reaction system, demonstrating significant catalytic activity. This superior catalytic effect under microwave irradiation can be attributed to the responsive dipole polarization of sulfonic acid groups, selective heating of the RSBC carrier via microwave absorption, and synergistic interactions among these factors. Overall, this study highlights the innovative use of agricultural waste and introduces a new method for creating microwave-responsive catalysts with biochar. This strategy enables efficient fructose conversion to HMF, promotes sustainable biomass transformation, and offers value-added uses for agricultural residues in chemical production.

Improved Operation of Chloralkaline Reversible Cells with Mixed Metal Oxide Electrodes Made Using Microwaves.

This study focuses on the synthesis of mixed metal oxide anodes (MMOs) with the composition Ti/RuO2Sb2O4Ptx (where x = 0, 5, 10 mol) using hybrid microwave irradiation heating. The synthesized electrodes were characterized using scanning electron microscopy, X-ray energy-dispersive analysis, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. These electrodes were then evaluated in both bulk electrolytic and fuel cell tests within a reversible chloralkaline electrochemical cell. The configurations using the electrodes Ti/(RuO2)0.7-(Sb2O4)0.3 and Ti/(RuO2)66.5-(Sb2O4)28.5-Pt5 presented lower onset potential for oxygen and chlorine evolution reactions and reduced resistance to charge transfer compared to the Ti/(RuO2)63-(Sb2O4)27-Pt10 variant. These electrodes demonstrated notable performance in reversible electrochemical cells, achieving Coulombic efficiencies of up to 60% when operating in the electrolytic mode at current densities of 150 mA cm-2. They also reached maximum power densities of 1.2 mW cm-2 in the fuel cell. In both scenarios, the presence of platinum in the MMO coating positively influenced the process. Furthermore, a significant challenge encountered was crossover through the membranes, primarily associated with gaseous Cl2. This study advances our understanding of reversible electrochemical cells and presents possibilities for further exploration and refinement. It demonstrated that the synergy of innovative electrode synthesis strategies and electrochemical engineering can lead to promising and sustainable technologies for energy conversion.

Enhancing Biodiesel Production: A Review of Microchannel Reactor Technologies

The depletion of fossil fuels, along with the environmental damages brought by their usage, calls for the development of a clean, sustainable and renewable source of energy. Biofuel, predominantly liquid biofuel such as biodiesel, is a promising alternative to fossil fuels, due to its compatible direct usage within the context of compression ignition engines. However, the industrial production of biodiesel is far from being energy and time efficient, which contributes to its high production cost. These inefficiencies are attributed to poor heat and mass transfer of the transesterification reaction. The utilisation of microchannel reactors is found to be excellent in escalating heat and mass transfer of the reactants, benefitting from their high surface area-to-volume ratio. The microchannel also intensifies the mixing of reactants via the reactor design, micromixers and the slug flow patterns within the reactor, thus enhancing the contact between reactants. Simulation studies have aided in the identification of mixing regimes within the microchannel reactors, induced by various reactor designs. In addition, microwave irradiation heating is found to enhance biodiesel production by localised superheating delivered directly to the reactants at a molecular level. This enables the reaction to begin much earlier, resulting in rapid biodiesel production. It is postulated that the synergy between microchannel reactors and microwave heating would catapult a pathway towards rapid and energy-efficient biodiesel production by enhancing heat and mass transfer between reactants.

New insights into the role of color extraction from (Aegle Marmelos leaf) using a non-traditional heating source

Purpose Due to herbs and plants’ therapeutic properties and simplicity of availability in nature, humans have used them to treat a variety of maladies and diseases since ancient times. Later, as technology advanced, these plants and herbs gained significant relevance in some industries due to their suitable chemical composition, abundant availability and ease of access. Aegle marmelos is a species of plant that may be found in nature. Yet, little or very little literature was located on the coloration behavior of this plant’s leaves. This study aims to focus on the effect of different parameters on the extraction of colorant from Aegle marmelos leaves. Design/methodology/approach Some factors that affected on the extraction processes were examined and found to have significant impacts on the textile dyeing such as the initial dye concentration, extracted temperature, extracted bath pH and extracted time were all changed to see how they affected color extraction. The authors report a direct comparison between three heating methods, namely, microwave irradiation (MWI), ultrasonic waves (USW) and conventional heating (CH). The two kinetic models have been designed (pseudo-first and pseudo-second orders) in the context of these experiments to investigate the mechanism of the dyeing processes for fabrics under study. Also, the experimental data were analyzed according to the Langmuir and Freundlich isotherms. Findings From the result, it was discovered these characteristics were found to have a substantial effect on extraction efficiency. Temperature 90°C and 80°C when using CH and USW, respectively, while at 90% watt when using MWI, period 120 min when using CH as well as USW waves, while 40 min when using MWI, and pH 4, 5 and 10 for polyamide, wool and cotton, respectively, were the optimal extraction conditions. Also, the authors can say that wool gives a higher absorption than the other fabric. Additionally, MWI provided the best color strength (K/S) value, and homogeneity, at low temperatures reducing the energy and time consumed. The coloring follows the order: MWI > USW > CH. The adsorption isotherm of wool could be well fitted by Freundlich isotherm when applying CH and USW as a heating source, while it is well fitted by the Langmuir equation in the case of MWI. In the study, it was observed that the pseudo-first-order kinetic model fits better the experimental results of CH with a constant rate K1 = −0.000171417 mg/g.min, while the pseudo-second-order kinetic model fits better the experimental results of absorption of both MWI (K2 = 38.14022572 mg/g.min) and USW (K2 = 12.45343554 mg/g.min). Research limitations/implications There is no research limitation for this work. Dye was extracted from Aegle marmelos leaves by applying three different heating sources (MWI, ultrasonic waves [USWW] and CH). Practical implications This work has practical applications for the textile industry. It is concluded that using Aegle marmelose leaves can be a possible alternative to extract dye from natural resource by applying new technology to save energy and time and can make the process greener. Social implications Socially, it has a good impact on the ecosystem and global community because the extracted dye does not contain any carcinogenic materials. Originality/value The work is original and contains value-added products for the textile industry and other confederate fields.

Effect of the Ferrocene Nucleus on the Microwave-Accelerated Esterification Reaction

Microwave irradiation has been utilized in the syntheses of a wide variety of organic compounds due to its shorter reaction times and improved selectivities. Since ferrocene is an organometallic compound consisting of an iron center sandwiched between two cyclopentadienyl rings, the iron moiety was expected to efficiently absorb microwave irradiation, thereby resulting in the ferrocene molecules exhibiting an antenna effect. Thus, we herein confirmed this antenna effect by employing an esterification reaction as a model reaction, using both ferrocene and benzene derivatives under microwave irradiation and conventional heating conditions for comparison purposes. It was also found that the reaction could be carried out at lower temperature using ferrocene derivatives.

Promoting Effect of Microwave Field on Gas Phase Diffusion Limited Magnetite Reduction in Carbon Monoxide

To investigate the effect of microwave irradiation on the rate of magnetite reduction while increasing the gas phase diffusion rate limit, the microstructure and kinetics of CO reduction of magnetite powder were studied. The investigation was conducted through microwave irradiation and conventional heating at 900~1100 °C. Under the two heating methods, the iron crystal is selectively reduced and gradually expanded along the direction normal to the length of the ore powder, forming a strip of iron crystal that penetrates the powder and expands outward across the width. The microwave field can effectively improve the sintering of minerals. The changes in Avrami exponents m and k in the reduction process were determined by combining the Johnson–Mehl–Avrami (JMA) model with the lnln method. The microwave field did not change the limiting step. Microwave irradiation proves to be the most effective means to enhance both the initial reduction rate and the rate during the primary iron crystal precipitation phase. The morphology of the iron crystal takes on a dense punctate shape, influenced by the rate of diffusion control.

An Economical and Eco‐Efficient Ammonium Chloride Promoted Friedländer Condensation: A Study of Microwave‐Assisted Versus Conventional Heating.

AbstractA new approach to Friedländer hetero‐annulations reaction is presented here for the synthesis of polysubstituted quinolines and polycyclic quinolines by the use of an inexpensive, nontoxic and readily available NH4Cl promoter. As a promoter, it shows good compatibility with various substrates, its easy removal, no side product, enhances the atom economy and makes the reaction eco‐friendly. Both microwave irradiation and conventional heating accomplished the reaction. The present method provides a comparative study of microwave irradiation versus conventional heating.

Preparation and properties of multifunctional eco-friendly slow-release urea fertilizer encapsulated by diatomite filter aid waste-based superabsorbent

Due to the high cost, incomplete degradation, and limited raw material sources of traditional slow-release fertilizers, the development of environmentally friendly slow-release urea based on waste filter aids is of great significance in modern agriculture. In this study, beer diatomite filter aid waste-based superabsorbent resin (BDWSA)11beer diatomite filter aid waste (BDW), beer diatomite filter aid waste-based superabsorbent resin (BDWSA), acrylic acid (AA),N, N-methylenebisacrylamide (MBA), potassium persulfate (KPS), ethyl cellulose (EC), monolayer-coated slow-release urea (MSRU), double-coated slow-release urea (DSRU). was synthesized by free radical grafting copolymerization through microwave radiation heating with beer diatomite filter aid waste (BDW), acrylic acid (AA), N, N-methylenebisacrylamide (MBA), and potassium persulfate (KPS). Then, BDWSA was used as the outer coating material, along with ethyl cellulose (EC) and Kaolin as the inner coating, urea and Phellinus igniarius biochar as the fertilizer core, to form a multifunctional eco-friendly double-coated slow-release urea (DSRU) for water-retaining and slow-release functionalities. The performance of slow release behavior of nitrogen was investigated, and showed that urea in soil released 86.02 % of nitrogen during 3 days, monolayer-coated slow-release urea (MSRU) released 94.02 % of nitrogen in 30 days, and DSRU released a total of 74.66 % of nitrogen in 30 days, indicating that DSRU can improve fertilizer utilization by delaying nutrient release. The biodegradation experiment showed that DSRU degraded 86.65 % wt% in 90 days, not only indicating a good biodegradation effect but also beneficial to the growth of soybeans under drought conditions in growth experiments. Therefore, the eco-friendly DSRU product with excellent slow-release capacity has broad application prospects in agriculture.

APPLICATION OF UHF INSTALLATIONS FOR THE MANUFACTUREOF MOLDED THERMAL INSULATION PRODUCTS BASED ON LIQUID GLASS

The article investigates the processes of swelling of liquid-glass compositions and the production of heat-insulating materials based on them under convective and microwave heating. In the work, it was established that the nature of the swelling curves of liquid-glass compositions under the conditions of microwave radiation and convective heating are significantly different. Thus, during convection heating, there is an induction period, but then the speed increases sharply and then the process gradually slows down. In the case of microwave radiation, there is no induction period, and the process proceeds at a high speed from the very beginning, and then slows down as the concentration of gas-forming substances decreases. In contrast to the swelling process under the influence of microwave radiation, during convective heating, the process proceeds uniformly with gradual release of water, as a result of which the material is mostly dried, and not swollen. A comparative analysis of the processes of swelling of liquid-glass compositions under convective and microwave heating showed a higher efficiency of swelling with the help of microwave radiation. The necessary duration of such heat treatment is 8-10 minutes. The materials obtained by convective heating at a temperature of 300 0C are the closest to such materials in terms of the swelling coefficient, the duration of such heating lasts more than 15 minutes. In addition, the calculated efficiency of the microwave installation is almost two times higher than the efficiency of the drying installation, for example, it is 0.79 for the microwave installation, and only 0.46 for the drying installation. Therefore, under the influence of microwave radiation, it is possible to produce effective heat-insulating materials based on liquid glass at lower temperatures and during a significantly shorter heat treatment time, compared to traditional convective heating. The work presents industrial microwave installations that can be used for the swelling process. These are chamber microwave installations of periodic action, which are used mainly for drying or heating large-sized products.

The Effect of Microwave Radiation on the Self-Healing Performance of Asphalt Mixtures with Steel Slag Aggregates and Steel Fibers.

Self-healing in asphalt mixtures is a property that can be enhanced by external heating, which causes a thermal expansion that increases the flow of bitumen with reduced viscosity through the cracks. Therefore, this study aims to evaluate the effects of microwave heating on the self-healing performance of three asphalt mixtures: (1) conventional, (2) with steel wool fibers (SWF), and (3) with steel slag aggregates (SSA) and SWF. After evaluating the microwave heating capacity of the three asphalt mixtures with a thermographic camera, their self-healing performance was determined with fracture or fatigue tests and microwave heating recovery cycles. The results demonstrated that the mixtures with SSA and SWF promoted higher heating temperatures and presented the best self-healing capacity during the semicircular bending test and heating cycles, with significant strength recovery after a total fracture. In contrast, the mixtures without SSA presented inferior fracture results. Both the conventional mixture and that containing SSA and SWF presented high healing indexes after the four-point bending fatigue test and heating cycles, with a fatigue life recovery of around 150% after applying two healing cycles. Therefore, the conclusion is that SSA greatly influences the self-healing performance of asphalt mixtures after microwave radiation heating.

Microwave- and Thermally Promoted Iminyl Radical Cyclizations: A Versatile Method for the Synthesis of Functionalized Pyrrolines.

A detailed study of iminyl radical cyclizations of O-aryloximes tethered to alkenes is reported. The reactions can be triggered by either microwave irradiation or conventional heating in an oil bath. A variety of radical traps can be employed, enabling C-C, C-N, C-O, C-S, or C-X bond formation and producing a diverse array of functionalized pyrrolines. Substrates containing an allylic sulfide furnish terminal alkenes by a tandem cyclization-thiyl radical β-elimination pathway. Cyclizations of hydroxylated substrates exhibit moderate diastereoselectivity that in some cases can partially be attributed to intramolecular hydrogen bonding. Computational studies suggested a possible role for thermodynamics in controlling the stereochemistry of cyclizations. The reaction temperature can be lowered from 120 to 100 °C by employing O-(p-tert-butylphenyl)oximes instead of O-phenyloximes as substrates, and these second-generation iminyl radical precursors can be used in a one-pot oxime ether formation-cyclization that is promoted by conventional heating. The functionalized pyrrolines obtained from these reactions can be conveniently transformed in several different ways.

Comparison of microwave irradiation and conventional thermal heating on volatile profiles and degree of oxidation in corn oil

SummaryVolatile profiles and degree of oxidation in corn oils after microwave treatment for 50 min were compared to oils with conventional heating at 180°C for 4 h. Oil microwaved for 10 and 50 min showed a similar degree of oxidation compared to the oil heated at 180°C for 1 and 3 h, respectively, based on the primary and secondary oxidation products. However, the total volatile contents of 50 min‐microwaved oil were significantly lower than that of corn oil heated for 1 h at 180°C (P < 0.05). Microwave treatment accelerated the rates of lipid oxidation by 4.6 times compared to 180°C thermal oxidation. Relatively short treatment with microwave irradiation may not provide sufficient time to generate volatiles from oil. Microwaved corn oil for 50 min had higher contents of hexanal and t‐2‐heptenal and lower contents of 2,4‐decadienal and nonanal than the oils heated at 180°C for 3 h. Reactive oxygen species may be involved in volatile formation in microwave‐irradiated oils.

Pd-Supported Co3O4/C Catalysts as Promising Electrocatalytic Materials for Oxygen Reduction Reaction

This paper describes the activity of PdCo3O4/C obtained by wet impregnation towards the oxygen reduction reaction (ORR). For this purpose, the Co3O4/C substrate was synthesized using the microwave irradiation heating method with further annealing of the substrate at 400 °C for 3 h (Co3O4/C-T). Then, the initial Co3O4/C substrate was impregnated with palladium chloride (Pd-Cl2-Co3O4/C), and then part of the obtained Pd-Cl2-Co3O4/C catalyst was annealed at 400 °C for 3 h (PdOCo3O4/C). The electrocatalytic activity of the prepared catalysts was investigated for the oxygen reduction reaction in alkaline media and compared with the commercial Pt/C (Tanaka wt. 46.6% Pt) catalyst. It was found that the annealed PdOCo3O4/C catalyst showed the largest ORR current density value of −11.27 mA cm−2 compared with Pd-Cl2-Co3O4/C (−7.39 mA cm−2) and commercial Pt/C (−5.25 mA cm−2).

Sensitivity analysis on the microwave irradiation enhancing coal seam gas recovery: A coupled electromagnetic-thermo-hydro-mechanical model

Microwave irradiation (MI) technology is a potential effective method to improve the efficiency of coal seam gas recovery. However, the research on how to increase coal seam gas production by microwave heating is rare. In this paper, microwave stimulation technology is introduced in coal seam gas extraction area for the first time. Based on the gas extraction technology with directional long borehole, a new coupled electromagnetic-thermo-hydro-mechanical model for coal seam gas recovery is established. The heat and gas transfer characteristics of coal seam under MI heating is analyzed. What's more, the impacts of key parameters on gas production, temperature distribution, gas pressure distribution and permeability ratio are discussed. Under the MI power 1000 W, numerical simulation results show that the cumulative gas production increased by 80%, which indicating the great effective of microwave heating for improving gas extraction rate. Furthermore, it reveals that the daily gas production will decrease rapidly with the attenuation coefficient λ. And with the greater of attenuation coefficient λ, the faster the permeability ratio decays. Comparing with the case of λ = 1 × 10−8, the permeability ratio decreases by 26% when λ = 5 × 10−8. And we also found that the initial permeability k0 is negatively correlated with the peak pressure in matrix. Overall, microwave heating can effectively reduce the methane adsorption capacity of the coal matrix and significantly increase the gas extraction production from coal seam.

MICROWAVE IRRADIATION AND CONVENTIONAL HEATING: A COMPARISON USING IN SILICO EXPERIMENTS WITH WATER AND ETHYLENE GLYCOL

MICROWAVE IRRADIATION AND CONVENTIONAL HEATING: A COMPARISON USING IN SILICO EXPERIMENTS WITH WATER AND ETHYLENE GLYCOL

Microwave Radiation Influence on Dairy Waste Anaerobic Digestion in a Multi-Section Hybrid Anaerobic Reactor (M-SHAR)

Whey is a primary by-product of dairy plants, and one that is often difficult to manage. As whey processing units are costly and complicated, only 15–20% of whey is recycled for use in the food industry. The difficulties in managing waste whey are particularly pronounced for small, local dairy plants. One possible solution to this problem is to use advanced and efficient digesters. The aim of this study was to present an innovative multi-section hybrid anaerobic bioreactor (M-SHAR) design and to identify how microwave radiation heating (MRH) affects methane fermentation of liquid dairy waste (LDW) primarily composed of acid whey. The MRH reactor was found to perform better in terms of COD removal and biogas production compared with the convection-heated reactor. The heating method had a significant differentiating effect at higher organic load rates (OLRs). With OLRs ranging from 15 to 25 kgCOD∙m−3∙d−1, the M-SHAR with MRH ensured a 5% higher COD removal efficiency and 12–20% higher biogas yields.

Microwave irradiation treatment improved the structure, emulsifying properties and cell proliferation of laccase-crosslinked α-lactalbumin

Influence of microwave irradiation heating (MH) and water bath heating (WH) pretreatments (70, 80 and 90 °C) on the structure, emulsifying properties and cell proliferation of laccase-crosslinked α-La was investigated. Compared with WH pretreatment, MH pretreatment can further promote the formation of polymers in laccase-crosslinked α-La. Also, MH treatment further unfolded the secondary structure, increased the surface hydrophobicity, and induced more formation of dityrosines in laccase-crosslinked α-La solution than that of WH pretreatment. Compared with untreated laccase-crosslinked α-La, its emulsifying activity index (EAI) was increased by 28.87% and 25.01% after MH and WH pretreatment at 90 °C. Gel hardness and water holding capacity of laccase-crosslinked α-La was increased by 30.20% and 18.37% after MH at 90 °C compared to untreated laccase-crosslinked α-La. Cell viability of laccase-crosslinked α-La (2 mg/mL) was increased by 18.12% at 90 °C with MH pretreatment. These findings indicated that MH pretreatment could ameliorate the crosslinking degree of α-La and laccase, thus improving its emulsifying, gel properties, and cell viability.

Effect of Microwave Irradiation on the Fries Rearrangement Reactions of Acetyloxy- and Benzoyloxybenzenes

The Fries rearrangement reactions of acetyloxy- and benzoyloxybenzenes were carried out both under microwave irradiation and conventional heating conditions, and the effect of microwave irradiation was examined. Acceleration of the reaction for the acetyloxy derivatives could not be confirmed, but was successfully demonstrated for the benzoyloxy derivatives. On the Fries rearrangement, the Lewis acid coordinates to the ester oxygens, but also coordinates to the aromatic rings. The microwave is efficiently absorbed by such an adduct between the Lewis acid and substrate, resulting in acceleration of the reaction.