Microwave Irradiation Power Research Articles

Production of renewable alkyl-phenols from catalytic pyrolysis of Douglas fir sawdust over biomass-derived activated carbons

The catalytic conversion of Douglas fir sawdust into bio-phenols on activated carbons (AC) obtained by chemical activation of corn stover with H3PO4 was investigated. Taguchi experimental design was used to optimize the preparation of AC using microwave assisted pyrolysis. Based on an overall consideration of AC yield, bio-oil yield, and phenols content, the optimized conditions were phosphoric acid to biomass ratio of 0.8, microwave power of 600 W and reaction time of 20 min. The bio-oils were rich in phenolic compounds (up to 90 area %) that mainly comprised phenol, methyl and ethyl phenol. During the catalytic pyrolysis of biomass with AC, phenolic compounds could either be derived from decomposition of lignin, followed by deoxygenation, or derived from furfurals, which were degradation products of carbohydrates. The catalytic activities of ACs were mainly owing to the well-developed porosity and abundant acidic surface functional groups. The porous structures of ACs were characterized by N2 isotherms, showing a strong dependence on the acid impregnation ratio and microwave irradiation power. The presence of acidic phosphoric-containing surface functional groups was confirmed by SEM/EDX, FTIR and NH3-TPD.

An improved method to obtain essential oil, flavonols and proanthocyanidins from fresh Cinnamomum japonicum Sieb. leaves using solvent-free microwave-assisted distillation followed by homogenate extraction

An efficient solvent-free microwave-assisted distillation followed by homogenate extraction method (SFMD-HE) was established to separate the essential oil, non-volatile flavonols and proanthocyanidins from Cinnamomum japonicum Sieb. leaves. In the SFMD-HE technology applied in this work, no excessive water was introduced into the system, which can reduce the loss of flavonols and proanthocyanidins in the subsequent extraction process, avoid the generation of hydrosol and improve essential oil yield. Furthermore, no drying was required, which can reduce the energy consumption. The homogenate process can reduce the production of dust and environmental pollution, meanwhile, avoid the degradation and deterioration of some thermo-sensitive compounds. Through comparison, solvent-free microwave distillation was selected as the optimal method, and the 71% ethanol volume fraction was chosen for homogenate extraction. Based on the yields of essential oil, flavonols and proanthocyanidins, the process parameters (microwave irradiation power and time for essential oil distillation; homogenate time, liquid-solid ratio, and ethanol volume fraction for flavonol and proanthocyanidin extraction) were optimized. Due to the combined effects of these parameters, greater advantages were found for the proposed process compared with traditional methods. Therefore, the proposed technique is a good alternative for distilling essential oil and extracting non-volatile components from edible plants.

Flash Sintering of Oxide Ceramics under Microwave Heating

We report on the results of the analysis of the effect of flash sintering, which is observed upon heating compacted powder materials by high-intensity microwave radiation. Ceramic samples of Y2O3, MgAl2O4, and Yb: (LaO)2O3 were sintered to a density exceeding 98–99% of the theoretical value during 0.5–5 min without isothermal hold. The specific microwave power absorbed volumetrically in the samples was 20–400 W/cm3. Based on the analysis of the experimental data (microwave radiation power and heating and cooling rates) and of the microstructure of the obtained materials, we propose a mechanism of flash sintering based on the evolution of the thermal instability and softening (melting) of the grain boundaries. The proposed mechanism also explains the flash sintering effect observed when a dc or a low-frequency ac voltage is applied to the samples. The microwave heating makes it possible to implement flash sintering without using electrodes for supplying energy to the articles being sintered.

Engineering of ZnO nanostructures for efficient solar photocatalysis

Highly photoactive metal oxide catalyst can be developed by engineering the nanostructure of the material. The present study reports the engineering of ZnO nanostructures using the microwave technique. The physicochemical characterization reveals the role of microwave irradiation power and reaction temperature on ZnO nanostructure engineering. The structural and surface analyses of the samples prepared at room temperature and 180 °C, in various microwave power, confirms the formation of nanorods. The higher reaction temperature has favored the nanorods to a flower like structures and increase in microwave power leads to the formation of denser, uniform nanoflowers, with enlarged petal diameter. The photocatalytic performance of the samples was evaluated using Methylene Blue (MB) as probe pollutant under solar irradiation. All the samples showed relatively high photocatalytic performance in terms of rate constant and photonic efficiency. However, the sample prepared at 180 °C and 360 W showed superior photocatalytic performance than the rest, which can be attributed to the effective photon absorption along with reduced charge carrier recombination. This study opens a new low-cost method for engineering the nanostructure for improving the photocatalytic performance.

Removal of Hexavalent Chromium by Adsorption on Microwave Assisted Activated Carbon Prepared from Stems of Leucas Aspera

Abstract This study reports adsorption of Cr(VI) ions from aqueous solution using activated carbon that was prepared from stems of Leucas aspera. Eight hundred and fifty watts power of microwave radiation, 12 min of radiation time, 60% of ZnCl2 solution and 24 h of impregnation time are the optimal parameters to prepare efficient carbon effective activated carbon. It was designated as MWLAC (Microwave assisted Zinc chloride activated Leucas aspera carbon). Various adsorption characteristics such as dose of the adsorbent, agitation time, initial Cr(VI) ion concentration, pH of the solution and temperature on adsorption were studied for removal of Cr(VI) ions from aqueous solution by batch mode. Also the equilibrium adsorption was analyzed by the Langmuir, Freundlich, Tempkin and D-R isotherm models. The order of best describing isotherms was given based on R2 value. The pseudo-second-order kinetic model best fitted with the Cr(VI) adsorption data. Thermodynamic parameters were also determined and results suggest that the adsorption process is a spontaneous, endothermic and proceeded with increased randomness.

Isolation of essential oil from the leaves of Polygonum viscosum Buch-ham. using microwave-assisted enzyme pretreatment followed by microwave hydrodistillation concatenated with liquid–liquid extraction

Microwave-assisted enzyme pretreatment followed by microwave hydrodistillation concatenated with liquid–liquid extraction (MEP-MHDE) was developed in this work for the efficient separation of essential oil from the leaves of Polygonum viscosum Buch-ham. The modified hydrodistillation concatenated with liquid–liquid extraction apparatus included conventional oil-water separation process and another extraction process for essential oil components from the hydrosol using an organic solvent. A comparison of the types of enzymes implied that the composite enzyme of cellulase and pectinase (1/1, w/w) performed better than the others. The optimum conditions derived were a microwave irradiation time of 17 min, a microwave irradiation power of 503 W, and an incubation temperature of 42 °C, which were evaluated through single factor experiments and Plackett–Burman design for selecting significant parameters as well as Box–Behnken design for optimizing the conditions. Based on these conditions, high yields of essential oil in the first separation column (3.66 ± 0.11 g/kg) and second separation column (1.02 ± 0.03 g/kg) were achieved. The developed MEP-MHDE method performed better regarding obtaining a higher yield of essential oil using a shorter time than other methods, which was mainly attributed to the influence of the combination of microwave irradiation, enzyme pretreatment and the hydrodistillation concatenated with liquid–liquid extraction apparatus. Through GC–MS analysis, more oxygenated compounds of the essential oil were achieved in the second separation column than in the first one, thus providing more valuable essential oil. Thus, the developed MEP-MHDE method is an efficient method for separation of high-value essential oils from natural plants and crops.

Point-like neutron source based on high-current electron cyclotron resonance ion source with powerful millimeter wave plasma heating

A possibility of an intense deuterium ion beam creation for a compact powerful point-like neutron source is discussed. The fusion takes place due to bombardment of deuterium (or tritium) loaded target by high-current focused deuterium ion beam with energy of 100 keV. The ways of high-current and low emittance ion beam formation from the plasma of quasi-gasdynamic ion source of a new generation based on an electron cyclotron resonance discharge in an open magnetic trap sustained by powerful microwave radiation are investigated.

Effect of barium loading on CaO derived from waste egg shell heterogeneous catalyst for canola oil biodiesel

The purpose of this research was to investigate the catalytic activity of Ba loading on calcium oxide (CaO) catalyst by varying the amount of barium added during the synthesis: 5-15 wt%. The waste egg shells were utilized as a CaO heterogeneous catalyst by calcined at 900 °C for 2 h. The Ba/CaO catalysts were prepared by impregnation method and were used as a catalyst in transesterification reaction of canola oil via microwave irradiation under microwave power 300 W. The characterization of catalyst and FAME composition of biodiesel were determined by X-ray fluorescence (XRF), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), and gas chromatography (GC-FID). The conditions of biodiesel production were operated at 60 °C, 3 wt% of catalyst loading, 9:1 methanol-to-canola oil ratio, and microwave irradiation power was 300W for 2 min. The experimental results found that, the waste egg shells consist mainly of CaCO3, which was decomposed to CaO more than 88 wt% after cacination step. The 15 wt% Ba/CaO catalysts exhibited the best catalytic performance with the FAME conversion higher than 97.68%.

Degradation of recalcitrant organics in landfill concentrated leachate by a microwave-activated peroxydisulfate process.

A microwave (MW)-activated peroxydisulfate (PDS) process was applied to remove recalcitrant organics in concentrated leachate. In this study, the optimum activation conditions were studied using the absorbance at 254 nm (UV254) and color number removal efficiencies and by comparison of the different processes. The inner oxidation mechanism was investigated by ultraviolet-visible (UV-vis) spectrophotometry and three-dimensional (3D) excitation–emission matrix (EEM) tests. The results show that oxidation effects followed the order MW/PDS > MW/H2O2 > heat/PDS. The efficiencies of chemical oxygen demand (COD) removal, UV254, and color number were 45.50%, 48.95%, and 88.35%, respectively. The biodegradability was enhanced to 0.23 under optimum conditions (initial pH of 3, MW irradiation power of 450 W, PDS dosage of 3.5 g L−1, and reaction time of 10 min). The UV-vis spectra suggest that the humification degree and aromaticity of organics in the concentrated leachate greatly declined in the MW/PDS process. 3D EEM spectra indicate that the molecular weight of organic substances in the concentrated leachate decreased markedly and that the constitution of the organics became simpler after the MW/PDS process. In a word, the MW/PDS process is a promising method for concentrated leachate treatment.

Research on the honeycomb restrain layer application to the high power microwave dielectric window.

Dielectric window breakdown is an important problem of high power microwave radiation. A honeycomb layer can suppress the multipactor in two directions to restrain dielectric window breakdown. This paper studies the effect of the honeycomb restrain layer on improving the dielectric window power capability. It also studies the multipactor suppression mechanism by using the electromagnetic particle-in-cell software, gives the design method, and accomplishes the test experiment. The experimental results indicated that the honeycomb restrain layer can effectively improve the power capability twice.

Dry reforming of methane over Co–Mo/Al2O3 catalyst under low microwave power irradiation

In this work, microwave (MW) irradiation was used to activate Co/Al2O3, Mo/Al2O3, and Co–Mo/Al2O3 catalysts for dry reforming of methane (DRM) reactions.

Efficient microwave-assisted diastereoselective synthesis of indole-based 4,5-dihydrofurans via a one-pot, three-component reaction in water

The combination of two or more different heterocyclic moieties in a single molecule would enhance biological activity significantly. The indole and furan scaffolds are promising candidates in drug design, and they have been widely found in natural products and therapeutic agents. Owing to their pharmaceutical importance, there is an urgent need to design rapid, efficient and environmentally benign protocols for the synthesis of indole–dihydrofuran biheterocycles. Herein, we have developed a novel ecofriendly approach for the diastereoselective synthesis of indole-based 4,5-dihydrofurans through a three-component reaction of 3-cyanoacetyl indoles with various aldehydes and N-phenacylpyridinium bromides in the presence of potassium carbonate as an inexpensive and non-toxic base in water under low power microwave irradiation. The findings show that aromatic and heteroaromatic aldehydes tolerated well in this reaction. The products were obtained in 85–98% yields in 4–20 min. The advantages of this method consist of the environmental friendly reaction conditions, use of green solvent and safe base, availability of raw materials, wide range of usable substrates, short reaction times, excellent yields and absence of any tedious workup or purification.

Improvement of multi-level resistive switching characteristics in solution-processed AlOx-based non-volatile resistive memory using microwave irradiation

We fabricated a resistive random access memory (ReRAM) device on a Ti/AlOx/Pt structure with solution-processed AlOx switching layer using microwave irradiation (MWI), and demonstrated multi-level cell (MLC) operation. To investigate the effect of MWI power on the MLC characteristics, post-deposition annealing was performed at 600–3000 W after AlOx switching layer deposition, and the MLC operation was compared with as-deposited (as-dep) and conventional thermally annealing (CTA) treated devices. All solution-processed AlOx-based ReRAM devices exhibited bipolar resistive switching (BRS) behavior. We found that these devices have four-resistance states (2 bits) of MLC operation according to the modulation of the high-resistance state (HRSs) through reset voltage control. Particularly, compared to the as-dep and CTA ReRAM devices, the MWI-treated ReRAM devices showed a significant increase in the memory window and stable endurance for multi-level operation. Moreover, as the MWI power increased, excellent MLC characteristics were exhibited because the resistance ratio between each resistance state was increased. In addition, it exhibited reliable retention characteristics without deterioration at 25 °C and 85 °C for 10 000 s. Finally, the relationship between the chemical characteristics of the solution-processed AlOx switching layer and BRS-based multi-level operation according to the annealing method and MWI power was investigated using x-ray photoelectron spectroscopy.

A modified approach for separating essential oil from the roots and rhizomes of Asarum heterotropoides var. mandshuricum

To efficiently separate essential oil from the roots and rhizomes of Asarum heterotropoides var. mandshuricum, a modified dynamic nitrogen-protected microwave-assisted hydrodistillation connected liquid-liquid extraction (DNMHDLLE) technique was developed. In addition to collect essential oil at the bottom of hydrosol in the conventional oil-water separation process, another extraction process was realized for extracting some essential oil components from the hydrosol using a small amount of organic solvents, which can significantly enhance the essential oil yield, effectively reduce the organic content in wastewater and its further disposal burden. The addition of glass beads as the packing in the second separation column had a positive influence on the essential oil yield. After the investigation using a single factor experiment and a response surface analysis, the optimum conditions were determined to be 28 min microwave irradiation time, 11 mL/g liquid-solid ratio, and 550 W microwave irradiation power. Under the optimum conditions, the yields of A. heterotropoides var. mandshuricum essential oil obtained in the first and second separation columns were 1.92 ± 0.07% and 0.50 ± 0.02%, respectively. Using GC-MS analysis, the essential oil containing oxy-compounds with a higher relative content was separated in the second separation column. In addition, the proposed method was compared with other techniques, including efficiency, environmental impact and economic effect, which indicated that the developed technique can effectively improve the essential oil yield, and take full advantage of raw material resources.

An improved approach for the isolation of essential oil from the leaves of Cinnamomum longepaniculatum using microwave-assisted hydrodistillation concatenated double-column liquid-liquid extraction

Abstract In this work, an improved method was developed to isolate essential oil from the leaves of Cinnamomum longepaniculatum, i.e., microwave-assisted hydrodistillation concatenated double-column liquid-liquid extraction, including the traditional essential oil-water separation process and the extraction process of essential oil components dissolved in water using an organic solvent in the second and third separation columns. The selection of extraction solvent indicated that ethyl ether performed better than other solvents, and the addition of glass beads as the filter in the separation columns had great advantage for extraction of essential oil components because of the larger contact area. The investigation on the number of separation column indicated that double liquid-liquid extraction column was better for improving the essential oil yield. After detailed optimization, the optimum conditions were homogenate time of 2.9 min, microwave irradiation time of 23 min and microwave irradiation power of 540 W (specific absorbed power: 1.27 W/g). Satisfactory yields of essential oil in the three separation columns (29.04 ± 0.87, 2.03 ± 0.07 and 0.90 ± 0.03 g/kg) were obtained under these conditions. The kinetic curves of various microwave irradiation powers based on the total yield of essential oil versus time were described. In addition, the kinetics curves of the developed method and other traditional methods were fitted by first-order model for comparison. The essential oil extracted in the second and third separation columns mainly contained oxy-compounds through GC–MS analysis, which could provide special values for application.

Copper(II) complexes with an arylhydrazone of methyl 2-cyanoacetate as effective catalysts in the microwave-assisted oxidation of cyclohexane

Abstract Reaction of sodium (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzene-sulfonate (NaHL) with copper(II) nitrate hydrate in the presence of imidazole (im) in methanol affords [CuL(im)(H2O)] (1). Complex 1 is characterized by IR spectroscopy and ESI-MS spectrometry, elemental and single crystal X-ray crystal structural analyses. The coordination environment of the central copper(II) is nearly intermediate between ideal square-based pyramidal and trigonal bipyramidal geometry, three sites being occupied by the L2− ligand, which chelates in the O, N, O fashion, while two other sites are filled with the water and imidazole molecules. Extensive intermolecular hydrogen bonds between the L2−, water and imidazole ligands lead to a 3D supramolecular network. 1 and known Cu(II) complexes [Cu(H2O)2L]·H2O (2), [Cu(H2O)(py)L]·H2O (3) and [Cu3(µ3-OH)(NO3)(CH3OH)(µ2-X)3(µ2-HL)] (4) act as effective catalysts in the oxidation of cyclohexane to cyclohexanol and cyclohexanone, using low power microwave (MW) irradiation, under mild conditions. Without a promoter, the activity of the catalyst reached a turnover number of 1.44 × 103 and a turnover frequency of 1.98 × 103 h−1, after 2 h, at 50 °C.

Research on microwave pad dyeing process for wool fabric

PurposeThis paper aims to study microwave pad dyeing process for wool fabric. Influences of various dyeing process conditions including galactomannan dosage, urea dosage, sodium bisulphite dosage, pH value, microwave irradiation power, treating time and cold batching time before microwave fixation on K/S values were analysed. The colour yield, fixation and levelness were compared between microwave fixation and cold batching fixation.Design/methodology/approachColour yield (K/S values) was calculated using a Datacolor SF650 colour measuring and matching instrument (10° standard observer, CIE D65 light source Measuring; Datacolor, USA) and was used to determine the depth of the shade of dyed wool fabrics. Levelness of dyeing was evaluated also using the Datacolor SF650 colour measuring and matching instrument by measuring average deviation (S), range (P) of the maximum and the minimum for lightness (L), chroma (C) and hue (h), and balanced colour difference (ΔE) at 20 specified uniform locations on the wool fabrics. The colour difference was calculated as per the equationΔE=(ΔL2+Δa2+Δb2)1/2as appearing in the Experimental section. Fixation was determined using a Datacolor SF650 colour measuring and matching instrument by measuring ratio the of K/S for wool fabrics that were rinsed, washed, neutralised and then dried, and wool fabrics that were dried after fixation without washing. The pH of the padding solution was evaluated using a PHSJ-4A PH meter (Datacolor, USA). SEM analysis was done on JEOL JSM-5600LV machine (JEOL Ltd, Japan).FindingsThis study is based on application of microwave technology in the processing of silk.Originality/valueIt was found in laboratory experiments that uniform dyeing and deeper colour can be achieved throughout the microwave pad dyeing process for wool by using galactomannan. The novel process could reduce the dyeing time and the energy consumption of the traditional cold pad-batch dyeing process for wool fabric.

Dy2O3/CuO nanocomposites: microwave assisted synthesis and investigated photocatalytic properties

Dy2O3/CuO nanocomposites were synthesized by rapid and fast microwave method in polyol solvent. Effect of time and power of microwave irradiation and type of solvent on size and morphology were investigated. Synthesized Dy2O3/CuO is characterized with X-ray diffraction (XRD) analysis, Transmission Electron Microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM) and UV–Visible absorption spectroscopy. Photocatalytic properties for two color, methylene blue and rhodamin b under ultraviolet light irradiation were done and 54 and 47.7% degradation for MB and RB respectively.

Optimization of Ammonia Removal from Aqueous Solution by Microwave-Assisted Air Stripping

In this study, the optimum conditions for the ammonia removal from aqueous solution by microwave-assisted air stripping have been investigated at pH 11. Ammonia solution with five different initial ammonia concentrations was prepared synthetically. The Taguchi method was applied to optimize the ammonia removal conditions. Initial ammonia concentration, air flow rate, temperature, stirring speed, microwave radiation power, and radiation time were defined as the optimization parameters. Experiments were carried out at five different levels for each operational parameter. The results of the experiments revealed that 1800 ppm of initial ammonia concentration, 7.5 L min−1 of air flow rate, 60 °C of temperature, 500 rpm of stirring speed, and 500 W of microwave radiation power for 180 min. of microwave radiation time are optimum conditions for complete ammonia removal. In addition to present experimental data, the optimum operational conditions predicted by the balanced characteristics of orthogonal array were confirmed experimentally. Finally, the effect of optimization parameters was discussed in detail.

A cathode unit of a pulse-periodic relativistic magnetron

The construction of a cathode unit of a pulse-periodic relativistic magnetron that contains an alignment adjuster for axial-symmetric installation of a cathode along the full length of anode block is described. The alignment adjuster makes it possible to rapidly adjust the relativistic magnetron to the maximum output power of microwave radiation. In this case, the process of assembling the device becomes considerably simpler.