Microwave Heating Technology Research Articles

Microwave-Assisted Pyrolysis of Pine Wood Sawdust Mixed with Activated Carbon for Bio-Oil and Bio-Char Production

Pyrolysis of pine wood sawdust was carried out using microwave-heating technology in the presence of activated carbon (AC). Experimental conditions were of 20 min processing time, 10 wt.% of AC, and a microwave power varying from 100 to 800 W. The results obtained showed that the microwave absorber allowed increasing the bio-oil yield up to 2 folds by reducing the charcoal fraction. The maximum temperature reached was 505 °C at 800 W. The higher heating values (HHV) of the solid residues ranged from 17.6 to 30.3 MJ/kg. The highest HHV was obtained for the sample heated at 800 W with 10 wt.% of AC, which was 33% higher than the non-charged sample heated at the same power. Furthermore, the addition of AC allowed showing the probable catalytic effect of the AC in the charged sample pyrolysis bio-oils.

Regionally Tunable Microwave Heating Technology Using Time-Frequency-Space Domain Synthesis Modulation Method

In this article, we present a new microwave system with the tunable ability of the heating region and heating effect. The heating region is changed by choosing different antennas above different heating region, which leads to larger heating range. And this system can be utilized in precise temperature control in ammonia synthesis phase. The frequency-space domain modulation technology is ingeniously suggested in our heating system. The different antennas above different heating region is then selected by changing the input working frequency. Based on the frequency-space domain modulation, we further add time domain modulation to increase the tunability of heating effect at different heating regions. By adjusting the frequency distribution of the input microwave source in time domain, where we named as time-frequency-space domain synthesis modulation method, the tunable heating region and effect is finally achieved. A simple microwave system is fabricated, and different heating effects are measured. The proposed heating method and system has benefits as following, simple structure, low cost, uniform heating, and controllable heating effect, which results in great improvement in microwave heating.

Three-dimensional numerical simulation on the thermal response of oil shale subjected to microwave heating

Microwave heating technology has received significant attention as an alternative to conventional heating methods for oil shale upgrading. To investigate the thermal response of oil shale such as temperature distribution, product migration, pressure generation, and thermal stress under microwave irradiation, numerical simulations were conducted based on a fully coupled three-dimensional electromagnetic-thermal-chemical-hydraulic-mechanical model by COMSOL Multiphysics software. The influence of microwave frequency and power on the temperature distribution of oil shale sample is investigated. The results reveal that the temperature distribution of oil shale sample is not uniform under microwave heating due to the nonuniform distribution of electric field. Microwave heating is most efficient at a frequency of 2.45 GHz because of the size and shape of rectangular waveguide. The temperature rise of oil shale is characterized by “slow-fast”, because the dielectric property of oil shale is temperature-dependent. Once the reaction temperature is over 500 °C, the heating rate increases significantly, and this phenomenon can be more obvious under high microwave power. Under 800 W, kerogen decomposition starts at 120 s in the sample center, the highest temperature region. The migration of products is dominated first by diffusion and then by convection, because the production of oil and gas forms a significant pressure gradient within oil shale over time. Compared with electrical heating, microwave heating accelerates the generation of pressure gradient and thermal stress, enlarging the porosity and enhancing the permeability of oil shale. In addition, the stepwise microwave heating mode is proposed to avoid excessive temperature and proved to be feasible during the oil shale retorting process. The outcomes show great potential of microwave heating in replacing conventional electrical heating for oil shale upgrading.

Phase stability and microstructure morphology of microwave-sintered magnesia-partially stabilised zirconia

In this work, microwave heating approach was introduced into the preparation process of zirconia materials to overcome the tricky technical defects during the traditional electric arc furnace method. Magnesia-partially stabilised zirconia (MgO-PSZ) with enhanced stability and a uniform microstructure was prepared via microwave heating of a ZrO2 sample manufactured by the electric arc furnace method. The effects of microwave heating on the phase stability properties, microstructure, and surface morphology of the prepared MgO-PSZ sample were evaluated via X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and Scanning electron microscopy, and the obtained results suggested that the stability rate of the MgO-PSZ sample improved from the initial value of 81.19%–94.82% after microwave heating at 1300 °C for 1 h. As a result of the martensitic conversion of ZrO2 material, the m-ZrO2 diffraction peaks were suppressed at the same time. Additionally, a similar changing trend was noticed in the XRD pattern, Raman spectrum, and FT-IR spectrum, indicating a decrease in the m-ZrO2 phase content in the microwave treated products. Furthermore, the microstructure on the surface of the microwave-sintered MgO-PSZ sample was improved in contrast to the raw MgO-PSZ sample, and became relatively more uniform and smooth. This study determined the optimal microwave heating conditions for the preparation of MgO-PSZ material with enhanced performance, and can provided as a good foundation for developing the further related research on zirconia materials preparing by microwave heating technology.

Kinetics characteristics and microwave reduction behavior of walnut shell-pyrolusite blends

Combining biomass pyrolysis with microwave heating technologies provides a novel and efficient approach for low-grade pyrolusite reduction. The microwave reduction behavior and pyrolysis kinetic characteristics of walnut shell-pyrolusite blends were explored. Results indicated the optimal reduction parameters were: reduction temperature of 650 °C, holding time of 30 min, Mbio/More of 1.8:10, and microwave power of 1200 W. The co-pyrolysis characteristics of the blends included four stages: dehydration, pre-pyrolysis, intense pyrolysis and reduction, and slow pyrolysis and reduction. Fitting analysis based on Coats-Redfern method revealed that chemical reaction was the control step of the process of reducing pyrolusite by biomass, which the finding matched to the isothermal kinetic analysis results determined through unreacted shrinking nuclear model. The activation energies and pre-exponential factors were determined at 5.62 kJ·mol−1–16.69 kJ·mol−1 and 0.0426 min−1–0.515 min−1. The work provides sound references for promoting the industrial application of the combined method on minerals reduction.

Investigation on Microwave Heating Technology for Rutting Maintenance in Asphalt Pavement

Abstract As one of the major diseases of asphalt pavement, rutting has become an important research topic. The current treatment method of rutting generally requires the milling of asphalt layers and construction of a new overlay, which is time-consuming and costly. Microwave heating is a promising technology for asphalt pavement maintenance. This research aimed to introduce microwave heating into the in situ rutting rehabilitation. The effects of microwaves on the aging of asphalt and mechanical properties of asphalt mixtures were discussed. The mechanism and effects of microwave maintenance were explored at the macroscopic and microscopic scale with the British Pendulum Test, X-ray Computed Tomography, Asphalt Extraction Test, and Discrete Element Method. The experiments showed that the microwaves have little negative effect on the performance of asphalt and asphalt mixtures. The analysis of the formation process of rutting showed that asphalt or asphalt cement shows bottom-up migration while the coarse aggregates move down. Overall, the research indicates that the general effect of microwave maintenance is an improvement in the rutting resistance of asphalt pavement, suggesting that rutting maintenance using microwave heating is feasible in practice.

Investigation on the mechanism of micro-cracks generated by microwave heating in coal and rock

Abstract In the coalbed methane (CBM) exploration and development, microwave treatment technology can be used to improve the reservoir permeability and enhance coalbed methane recovery. In this paper, the mechanism of microwave heating on micro-cracks in coal and rock is studied. And to research the interactions between microwave and coal, a mathematical model of electromagnetic field and heat transfer in solid coupling is established. Combined with numerical simulation and experimental research, the electromagnetic field distribution and the temperature changing law in coal samples collected from Ordos basin of China during microwave heating process are analyzed. Through the comparisons of appearance identification and internal CT scanning before and after microwave treatment, there are a large number of obvious cracks generated by microwave heating on the surface and inside of coal samples. Three main generation mechanisms of micro-cracks in coal and rock are obtained by SEM analysis. Finally, a new microwave heating technology for CBM recovery is proposed and the structure of waveguide antennas (coaxial) for heating is designed. The simulation results show that the reservoir temperature has been greatly improved and the temperature change rates in the top half of the reservoir are larger which can easily cause the generation of micro-cracks.

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphoslogies.

Zinc oxide (ZnO) is a multifunctional material due to its exceptional physicochemical properties and broad usefulness. The special properties resulting from the reduction of the material size from the macro scale to the nano scale has made the application of ZnO nanomaterials (ZnO NMs) more popular in numerous consumer products. In recent years, particular attention has been drawn to the development of various methods of ZnO NMs synthesis, which above all meet the requirements of the green chemistry approach. The application of the microwave heating technology when obtaining ZnO NMs enables the development of new methods of syntheses, which are characterised by, among others, the possibility to control the properties, repeatability, reproducibility, short synthesis duration, low price, purity, and fulfilment of the eco-friendly approach criterion. The dynamic development of materials engineering is the reason why it is necessary to obtain ZnO NMs with strictly defined properties. The present review aims to discuss the state of the art regarding the microwave synthesis of undoped and doped ZnO NMs. The first part of the review presents the properties of ZnO and new applications of ZnO NMs. Subsequently, the properties of microwave heating are discussed and compared with conventional heating and areas of application are presented. The final part of the paper presents reactants, parameters of processes, and the morphology of products, with a division of the microwave synthesis of ZnO NMs into three primary groups, namely hydrothermal, solvothermal, and hybrid methods.

Investigations on the microwave absorption properties and thermal behavior of vanadium slag: Improvement in microwave oxidation roasting for recycling vanadium and chromium

Vanadium slag contains high contents of vanadium and chromium with complex and dense structures, hence microwave heating instead of conventional methods is expected to destroy the dense structure and further to improve the extraction rate of vanadium and chromium, and exploring its dielectric properties is the prerequisite work. Microwave absorption properties and thermal behavior of vanadium slag were investigated. Results indicated that vanadium slag endowed excellent microwave absorption properties, with minimum εr′ value of 34.447 (F/M). Dielectric properties of vanadium slag varied with temperature, which changing trend was matched to the three stages of microwave heating characteristics identified by heating rates. Meanwhile, the changing process of dielectric properties also corresponded to the three processes of thermogravimetric characteristics: dehydration stage (30 °C–280 °C), oxidation decomposition of olivine phase and normal spinel phase (280 °C–650 °C), and oxidation decomposition of vanadium chromium spinel (650 °C–950 °C). Moreover, the maximum dielectric constant and highest microwave heating rate of vanadium slag both appeared at the temperature regime of 500 °C–550 °C, which was also the main temperature regime for oxidation decomposition of olivine phase and normal spinel phase in vanadium slag, demonstrating the appropriate process temperature for microwave heating technology to recycle vanadium slag.

Comparative evaluation of microwave-assisted acid, alkaline, and inorganic salt pretreatments of sugarcane bagasse for sugar recovery

Microwave heating technology has attracted great attention in biorefineries to generate biofuels and biomass-derived chemicals. NaOH and H2SO4 pretreatments are often applied to improve the process efficiency. Traditional heating pretreatments require long reaction times and contribute to rapid sugar degradation. Although effective, H2SO4 pretreatment suffers from the disadvantages of equipment corrosion, inhibitors generation, and waste water production. Herein, we performed NaOH, H2SO4, and FeCl3 pretreatments on sugar cane bagasse under microwave heating, and compared their effects on the biomass physical features, chemical compositions, and sugar release during pretreatment process. Our results showed that high amounts of sugar were obtained, and xylose and glucose were selectively recovered in the pretreatment liquor within 5–10 min of microwave heating by changing pretreatment media. NaOH efficiently fractionated biomass, generated xylose as the major product in pretreatment liquor, and left the solid residue more digestible. H2SO4 and FeCl3 effectively degraded both the hemicellulose and cellulose, producing glucose as the major product in the pretreatment liquor. Compared with H2SO4, FeCl3 pretreatment more efficiently removed lignin and recovered 48% glucose within only 5 min. Biomass chemical composition and morphological characteristics were studied and compared, confirming that microwave assisted FeCl3 pretreatment is a new and feasible approach to replace H2SO4 for biofuel and biomass-derived chemicals production.

Efficient Preparation of Si3N4 by Microwave Treatment of Solar-Grade Waste Silicon Powder.

In this study, the waste silicon powder generated in the production of solar-grade polysilicon scrap was used as the raw material, and silicon nitride (Si3N4) was directly efficient prepared by the microwave heating nitridation. The temperature raising characteristics of silicon powder by microwave heating and the influencing factors of the nitridation reaction process were studied. The thermogravimetric analysis was performed, and the temperature raising dielectric properties of silicon powder were studied. The electromagnetic field and temperature distributions of the microwave heating-induced silicon powder nitridation process were simulated using COMSOL software. The nitridation reaction of silicon powder induced by microwave heating has better temperature raising characteristics: the average heating rate can reach 135 °C/min, and the reaction time is significantly shortened (only 10–20 min). Microwave heating decreases the nitridation reaction temperature by more than 100 °C and greatly shortens the reaction time. With the increase of nitrogen pressure and reaction time, the nitridation reaction is better. In addition, the conversion of the nitridation reaction is more than 97%, and the products are mainly β-Si3N4 with the uniform and columnar morphology. Finally, it is proved that the efficient recovery and utilization of industrial waste silicon powder are realized, and there is lower energy consumption by microwave heating technology.

Preparation of WC-TiC-Ni3Al-CaF2 functionally graded self-lubricating tool material by microwave sintering and its cutting performance

AbstractWith the concern of the environment, green dry cutting technology is getting more and more attention and self-lubricating tool technology plays an important role in dry cutting. Due to the demand for high temperature performance of tools during dry cutting process, cemented carbide with Ni3Al as the binder phase has received extensive attention due to its excellent high temperature strength and high temperature oxidation resistance. In this paper, WC-TiC-Ni3Al-CaF2graded self-lubricating material and tools were prepared by microwave heating method, and its microstructure, mechanical properties and cutting performance were studied. Results show that gradient self-lubricating material can be quickly prepared by microwave heating technology, and the strength is equivalent to that of conventional heating technology. CaF2not only plays a role in self-lubrication, but also refines the grain of the material. A reasonable gradient design can improve the mechanical properties of the material. When the gradient distribution exponent is n1= 2, the material has high mechanical properties. Cutting experiments show that the WC-TiC-Ni3Al-CaF2functional gradient self-lubricating tool has better cutting performance than the homogeneous WC-TiC-Ni3Al hard alloys.

Microwave processing of carbon fibre polymer composites: a review

Microwave processing of carbon fibre-reinforced polymer (CFRP) composites is gaining increasing attention as an alternative to conventional thermal processing techniques. It has the potential to reduce part processing times and alleviate the bottleneck that often exists in composite component production. The present study reviews the current research and the state-of-the-art of microwave processing of CFRP composites. The benefits and limitations of microwave processing compared with traditional thermal processing methods are examined. The mechanical properties of microwave-cured composites are compared against conventionally-cured counterparts with varying levels of success. Current industrial microwave heating technologies are also examined. It is evident that microwave processing of polymer composites is promising but has notable limiting factors which have stunted its uptake in industry. Due to their prevalence in literature, CFRP composites with thermosetting matrices are the focus of this review. However, potential applications to carbon fibre-reinforced thermoplastics are also briefly described.

Microwave Heating Characteristics of Emulsified Asphalt Repair Materials Incorporated with Steel Slag

Emulsified asphalt needs to be cured for a certain age after demulsification to produce strength, which seriously affects the traffic opening time. In this work, microwave heating technology was applied for emulsified asphalt repair materials. Steel slag with high microwave activity was adopted to improve the performance of emulsified asphalt repair materials by microwave heating. Effects of steel slag sizes and contents on the heating rate, temperature distribution, and thermal performance of emulsified asphalt repair materials were analyzed by close microwave heating, open microwave heating, and repair simulation tests. Results show that the temperature of emulsified asphalt repair materials presents three different heating stages under microwave irradiation. The “critical point of phase transition” in the three stages is gradually advanced with the increase in steel slag content. The core temperature and maximum temperature of emulsified asphalt repair materials with different steel slag sizes are basically the same; however, the heat distribution of emulsified asphalt repair materials is significantly different. In contrast to conventional asphalt mixture, there exists a smaller temperature difference. The temperature of repairing materials can reach above 80°C. The interface area can form an embedded interface structure. Incorporation of steel slag and adoption of microwave heating are effective to improve the performance of emulsified asphalt repair materials.

Effect of Fe-modified ZSM-5 catalyst during microwave assisted pyrolysis of Mengdong lignite for the oil production

Microwave catalytic pyrolysis of Mengdong lignite by Fe-modified ZSM-5 catalysts was studied. The effects of pyrolysis method and the ZSM-5 molecular sieves loading different amounts of Fe2O3 on the total tar yield were investigated. The results show that the microwave heating technology could effectively improve the yield of lignite pyrolysis tar; In the conventional pyrolysis, the total yield of raw coal pyrolysis oil was 2.19%. When the Fe2O3 loading was 5%, the catalyst had the best effect with the yield of 3.56%, and the increase rate was 62.56%; Under microwave condition, the pyrolysis oil yield of raw coal is 6.43%. When the Fe2O3 loading increased from 0 to 10%, the total yield of tar increased from 7.02% to 9.47%. When the Fe2O3 loading was 10%, the catalyst had the best effect with the increase rate of 62.56%.

Discovery of N-(1-(3-fluorobenzoyl)-1H-indol-5-yl)pyrazine-2-carboxamide: a novel, selective, and competitive indole-based lead inhibitor for human monoamine oxidase B

Herein, two new series of N-substituted indole-based analogues were rationally designed, synthesized via microwave heating technology, and evaluated as noteworthy MAO-B potential inhibitors. Compared to the reported indazole-based hits VI and VII, compounds 4b and 4e exhibited higher inhibitory activities over MAO-B with IC50 values of 1.65 and 0.78 µM, respectively. When compared to the modest selectivity index of rasagiline (II, a well-known MAO-B inhibitor, SI > 50), both 4b and 4e also showed better selectivity indices (SI > 60 and 120, respectively). A further kinetic evaluation of the most potent derivative (4e) displayed a competitive mode of inhibition (inhibition constant (K i)/MAO-B = 94.52 nM). Reasonable explanations of the elicited biological activities were presented via SAR study and molecular docking simulation. Accordingly, the remarkable MAO-B inhibitory activity of 4e (N-(1-(3-fluorobenzoyl)-1H-indol-5-yl)pyrazine-2-carboxamide), with its selectivity and competitive inhibition, advocates its potential role as a promising lead worthy of further optimization.

RESEARCH PROGRESS AND INDUSTRIAL APPLICATIONS OF MICROWAVE HEATING PROCESSING ON ROCK AND CONCRETE

Microwave heating is a green, effective and sustainable technology, with the heating characteristics of immediate, volumetric, selective and low pollution presented. The recent interest in fundamentals and applications of microwave processing of rock and concrete is highlighted by many symposia, scholars and research groups all over the world due to its potential for significant process benefit. Many theoretical analyses, simulations and experimental tests were carried out subject to the heating mechanism and properties. The review systematically summarizes the important research results from previous studies. The mechanism and advantages of microwave assisted breaking and the influence factors relating to the microwave processing efficiency were discussed. The research status and application prospect of microwave assisted rock breaking and drilling, concrete aggregate recycling, and mineral sorting were discussed. The research focus and future research direction in related fields are discussed in order to provide a reference and recourse for promoting the application and development of microwave heating technology in engineering.

Synthesis of Nano/Microsized MIL-101Cr Through Combination of Microwave Heating and Emulsion Technology for Mixed-Matrix Membranes.

Nano/microsized MIL-101Cr was synthesized by microwave heating of emulsions for the use as a composite with Matrimid mixed-matrix membranes (MMM) to enhance the performance of a mixed-gas-separation. As an example, we chose CO2/CH4 separation. Although the incorporation of MIL-101Cr in MMMs is well-known, the impact of nanosized MIL-101Cr in MMMs is new and shows an improvement compared to microsized MIL-101Cr under the same conditions and mixed-gas permeation. In order to reproducibly obtain nanoMIL-101Cr microwave heating was supplemented by carrying out the reaction of chromium nitrate and 1,4-benzenedicarboxylic acid in heptane-in-water emulsions with the anionic surfactant sodium oleate as emulsifier. The use of this emulsion with the phase inversion temperature (PIT) method offered controlled nucleation and growth of nanoMIL-101 particles to an average size of <100 nm within 70 min offering high apparent BET surface areas (2,900 m2 g−1) and yields of 45%. Concerning the CO2/CH4 separation, the best result was obtained with 24 wt.% of nanoMIL-101Cr@Matrimid, leading to 32 Barrer in CO2 permeability compared to six Barrer for the neat Matrimid polymer membrane and 21 Barrer for the maximum possible 20 wt.% of microMIL-101Cr@Matrimid. The nanosized filler allowed reaching a higher loading where the permeability significantly increased above the predictions from Maxwell and free-fractional-volume modeling. These improvements for MMMs based on nanosized MIL-101Cr are promising for other gas separations.

Comparative study of carbide slag autoclaved aerated concrete (AAC) manufactured under thermal oven and microwave pre-curing process: Foaming course, rough body strength and physic-mechanical properties

The substitution of carbide slag to quicklime in carbide slag autoclaved aerated concrete (AAC) preparation caused significant side-effect on stable formation of porosity structure in pre-curing process. With objective of regulating slurry foaming course and rough body strength development during pre-curing process of carbide slag AAC production, microwave heating technology was introduced to control the slurry temperature accurately, and regulate the foaming and thickening process ulteriorly. Therefore, the discrepancy between conventional and microwave pre-curing process in mould and energy were discussed qualitatively. Moreover, to figure out the superiority and effect law of microwave pre-curing process with different curing temperature, the comparison between conventional and microwave pre-curing process on slurry foaming course, rough body development and physic-mechanical properties were investigated. The discrepancy analysis illuminated that with transition from thermal oven curing to microwave pre-curing, mixing water and mould should be changed from warm water (＞50 °C) and metal mould to normal temperature water and microwave penetrable mould respectively, meanwhile, the theoretical energy requirement was significantly reduced. Otherwise, the experimental results indicated that microwave pre-curing technology effectively accelerate the gas foaming rate in early stage and increased ultimate foaming ratio with increasing of curing temperature. However, the gradient temperature of microwave pre-curing between foaming and thickening stage should not exceed 20 °C, so as to avoid the temperature stress on bonding surface of rough body and container, which may cause ring collapse. Moreover, rough body strength development was improved with utilizing of microwave pre-curing technology, the pre-curing duration could be shortened by 0.5–1 h relative to thermal oven pre-curing process. Furthermore, the physic-mechanical performance of thermal oven and microwave pre-cured carbide slag AAC specimens were comparable. Overall, the results indicated that microwave pre-curing technology has great potential to be an alternative curing method for manufacturing carbide slag AAC.

Effects of microwave heating on the carbothermic reduction of steel plant mill scale using lignocellulosic biomass as the reducing agent

ABSTRACT The microwave reduction of a biomass-bearing mill scale composite briquette followed by magnetic separation was investigated in this work to explore the feasibility of using microwave heating technology on steel plant mill scale. The activation energy obtained for pyrolysis of biomass by Freeman-Carroll method was 189.3, 103.26 and 89.82 kJ mol−1 at the temperature ranges of 260–300°C, 330–370°C and 430–480°C, respectively. By comparing the two reducing agents with microwave (MW) heating, the iron content in a magnetic product was approximately 97.15% and 96.46%, respectively, using coal and biomass as the reducing agents. The iron recovery only reached 85.15% with coal. In addition, up to 96.12% of the iron was recycled using biomass fuel as the reducing agent. In particular, the contents of carbon, phosphorus and sulphur using biomass as the reducing agent were far below the content of those using coal as the reducing agent.