Use Of Microwave Heating Research Articles

Upgrading Biomass Wastes to Graphene Quantum Dots with White-Light-Emitting Features in the Solid State

The emergence of bio-based carbonaceous materials for various applications has attracted significant attention during the last few years. Here, we report a rapid, efficient, and reproducible microwave-assisted synthesis of graphene quantum dots (GQDs) with identical features irrespective of the nature of biomass waste investigated. The synthesized GQDs were fully characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy, and dynamic light scattering. The nanoparticles displayed narrow sizes of 1–2 nm and high solubility in polar solvents such as water and ethanol. The protocol described herein is advantageous in comparison to dealing with the synthesis of GQDs from biomass waste previously reported since our protocol is faster owing to the use of microwave heating and the avoidance of dialysis for the purification step. Furthermore, in solution, the water-soluble particles showed excitation-dependent photoluminescence ranging from blue to orange emission wavelengths. Interestingly, thin films displayed white-light emission under 325 nm UV-light excitation, while aggregation-induced quenching was usually observed, opening the way for their potential use as a phosphor in white-light-emitting diodes.

Two complementary examples of electrification in the cement industry

The European “Horizon 2020” LEILAC and DESTINY projects are two examples of electrification in the cement industry. LEILAC shows how resistance heating can be applied as a substitution of an existing gas-supplied process. The use of microwave heating in the DESTINY project illustrates the downscaling of the production paradigm towards small on-site-of-demand cement production, allowing a further reduction in CO2 emission.

Microwave Assisted Grafting Technique for Modification of Polysaccharides

Abstract: A natural and renewable substrate for the synthesis of high-performance macromolecules is polysaccharides. Grafting with the use of microwaves of synthetic polymers onto natural polysaccharides is a common, adaptable, and practical method of creating materials based on polysaccharides. It eliminates all drawbacks of the traditional grafting technique, including the need for hazardous solvents and longer reaction times. Grafting yield is also increased by microwave irradiation. In fact, the employment of microwaves in polysaccharide grafting modification for diverse applications has been prompted by the growing interest in clean and environment-friendly chemistry. Furthermore, compared with their traditionally synthesized counterparts, microwave-synthesized polysaccharide copolymers frequently have greater characteristics for commercial exploitation. Moreover, for many traditional grafting processes, the necessity for an inert environment is an additional drawback, which can be overcome by microwave grafting techniques. This study focuses on the current use of microwave heating in polysaccharide grafting modifications and its further use in pharmaceutical formulations.

Effect of microwave method on jasminaldehyde synthesis using solvent-free over Mg–Al–NO3 hydrotalcite catalyst

Jasminaldehyde is a widely used starting material in the chemical industry. One method for synthesizing jasminaldehyde is through the aldol condensation of benzaldehyde with 1–heptanal, using a heterogeneous catalyst called hydrotalcite Mg–Al–NO3. The synthesized catalyst was characterized using various techniques, including XRD, FT–IR, TGA, DTA, SEM, EDX, and N2 adsorption–desorption isotherm (BET) to determine its structure, morphology, thermal stability, and properties. This catalyst was tested in the studied reaction under solvent-free conditions, using both microwave and conventional heating methods (in an oil bath) to evaluate the efficiency of each method in producing jasminaldehyde. The results showed that the use of microwave heating in this reaction is particularly advantageous. It allowed for the highest conversion (>99%) of 1–heptanal, with a good selectivity (80%) towards jasminaldehyde, after only 50 min of reaction time. In contrast, conventional heating required a longer reaction time of about 8 h to achieve similar conversion and selectivity values. Furthermore, Mg–Al–NO3 demonstrated nearly sustained activity in three consecutive reuse experiments, and the durability of this catalyst was characterized using several techniques.

Screening of Oligomeric (Meth)acrylate Vaccine Adjuvants Synthesized via Catalytic Chain Transfer Polymerization.

This report details the first systematic screening of free-radical-produced methacrylate oligomer reaction mixtures as alternative vaccine adjuvant components to replace the current benchmark compound squalene, which is unsustainably sourced from shark livers. Homo-/co-oligomer mixtures of methyl, butyl, lauryl, and stearyl methacrylate were successfully synthesized using catalytic chain transfer control, where the use of microwave heating was shown to promote propagation over chain transfer. Controlling the mixture material properties allowed the correct viscosity to be achieved, enabling the mixtures to be effectively used in vaccine formulations. Emulsions of selected oligomers stimulated comparable cytokine levels to squalene emulsion when incubated with human whole blood and elicited an antigen-specific cellular immune response when administered with an inactivated influenza vaccine, indicating the potential utility of the compounds as vaccine adjuvant components. Furthermore, the oligomers' molecular sizes were demonstrated to be large enough to enable greater emulsion stability than squalene, especially at high temperatures, but are predicted to be small enough to allow for rapid clearance from the body.

TECHNOLOGICAL ASPECTS OF MICROWAVE HEATING EQUIPMENT IN THE FOOD INDUSTRY

The article describes the features of the interaction of microwave energy with food raw materials and food products and conducts an analytical review of the application of microwave processing for various technological processes in the food industry and hotel and restaurant business. The paper examines the peculiarities of the interaction of microwave energy with food raw materials and food products and gives an overview of the application of microwave processing for various technological processes in the food industry and the hotel and restaurant business. Despite the number of scientific works devoted to the topic of technological equipment, in particular, microwave heating, in Ukraine this is an insufficiently illuminated topic that requires research, taking into account the current conditions in the national economy. To create more rational technological processes, a combination of microwave heating with other energy carriers is used: steam, hot air, infrared heating, heated fat, vacuum, ultrasound. Heat treatment of food products in the cooking mode is divided into two stages: heating to a set temperature and maintaining this temperature until complete culinary readiness. The stepwise microwave heating method is also used, which ensures a high heating rate and avoids uneven heating of individual areas of the processed products. In this way, the possibility of temperature redistribution is ensured through the thermal conductivity of the material during its thermostating. One of the features of microwave processing is the possibility of rapid and relatively uniform heating of the product throughout the entire volume, which by its nature depends not so much on the thermophysical characteristics of the heated object, but on the presence of moisture in it and the nature of its distribution by volume. The ability of dielectric heating is effectively used in the food industry when defrosting products. Defrosting in the microwave field allows you to speed up the process tenfold and to a large extent preserve the quality of food products. Good results are given by combined methods of defrosting microwave heating with ultrasound, as well as with the method of blowing the product with cold air. The use of microwave heating with other physical methods and energy carriers makes it possible to intensify technological processes, reduce the cost of finished products, as well as increase the nutritional and biological value of raw materials, semi-finished products and finished products

Microwave Heating for the Conservation of Cultural Heritage Assets: A Review of Main Approaches and Challenges

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Objectives:</i> The cultural heritage (CH) represents the proof of human achievements from the past in terms of historical and technological progress. One of the main issues regarding CH preservation is the bio-deterioration phenomenon which arises from biological colonization of artistic materials with consequent aesthetic, chemical and structural damage. The most common disinfestation methods are based on mechanical, chemical, biological or physical treatments. Among the physical methods, microwave heating has high potentialities, but its application is not a standard. Here we reviewed relevant literature on the use of microwave heating for the disinfestation of artworks from biodeteriogens. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Method:</i> We performed a systematic literature search, identified twenty relevant publications, and extracted relevant information. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Results:</i> Microwave heating resulted effective for total disinfestation of various infesting agents on several materials, rapid, safe for operators and the environment. However, we highlighted the lack of a systematic approach to the planning of artworks treatment with microwave heating and developed operative guidelines that include dielectric characterization of materials, prediction and control of electric field distribution in the artwork, identification of lethal doses for infesting agents. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Impact:</i> The proposed approach might contribute to boost the use of this promising, non-invasive, and safe technology for artworks conservation.

FEATURES OF THE USE OF ROASTING AND BAKERY EQUIPMENT IN THE HOTEL AND RESTAURANT BUSINESS

The article describes the features of the interaction of thermal energy with food raw materials and food products and conducts an analytical review of the use of heat treatment for various technological processes in the food industry and hotel and restaurant business. The paper examines the peculiarities of the interaction of thermal energy with food raw materials and food products and provides an overview of the use of heat treatment for various technological processes in the food industry and hotel and restaurant business. Despite the number of scientific publications dedicated to the topic of technological equipment, in particular thermal heating, in Ukraine this is an insufficiently illuminated topic that requires research, taking into account the current conditions in the national economy. To create more rational technological processes, a combination of thermal heating with other energy carriers is used: steam, hot air, infrared heating, heated fat, vacuum, ultrasound. Heat treatment of food products in the cooking mode is divided into two stages: heating to a set temperature and maintaining this temperature until complete culinary readiness. The stepwise thermal heating method is also used, which ensures a high heating rate and avoids uneven heating of individual areas of the processed products. In this way, the possibility of temperature redistribution is ensured through the thermal conductivity of the material during its thermostating. One of the features of heat treatment is the possibility of rapid and relatively uniform heating of the product over the entire volume, which by its nature depends not so much on the thermophysical characteristics of the heated object as on the presence of moisture in it and the nature of its distribution by volume. The ability of dielectric heating is effectively used in the food industry when defrosting products. Defrosting in the microwave field allows you to speed up the process tenfold and to a large extent preserve the quality of food products. Good results are given by combined methods of defrosting microwave heating with ultrasound, as well as with the method of blowing the product with cold air. The use of microwave heating with other physical methods and energy carriers makes it possible to intensify technological processes, reduce the cost of finished products, as well as increase the nutritional and biological value of raw materials, semi-finished products and finished products.

Heating performance of microwave ovens powered by magnetron and solid-state generators

Magnetrons are the most common microwave power sources. However, variation of output frequencies of magnetrons makes heating patterns of foods in multi-mode microwave cavities random and unpredictable. It is desirable to find effective alternatives, such as solid-state microwave generators. Here, we compared the frequency spectra of magnetrons and solid-state generators to evaluate their influence on the heating performance of microwave ovens. Results showed that the spectrum (i.e., peak frequency and bandwidth) of microwaves from the magnetron varied depending on the food and food position and varied considerably between individual ovens of the same model. In contrast, the solid-state microwave generator provided microwaves not only at exactly the set frequency but also within a narrow band, regardless of food loads. That is, solid-state generators had better spectral quality than that from magnetrons. As a result, solid-state generators would provide predictable and stable heating patterns of foods that cannot be achieved with magnetrons. Therefore, solid-state generators create new opportunities in designing next-generation microwave systems with high heating performance. Industrial relevanceHeating patterns of foods in magnetron-powered multi-mode cavities are random and unpredictable, limiting the use of microwave heating to address food safety issues. Solid-state microwave generators have the potential to overcome this drawback by providing better spectral quality than magnetrons, as shown in this study. In addition, the methodology developed in this work to measure the frequency spectrum of microwave generators is helpful in improving the accuracy of computer simulations. This study provides fundamental information and useful guidance to the food industry on designing and mathematically modelling solid-state powered microwave heating systems.

Potential of Microwave Heating and Plasma for Biosecurity Applications

This review explores the use of microwave heating and microwave-generated plasma for biosecurity applications. Microwave heating has been shown to rapidly heat and kill a wide range of pests and pathogens. Examples of microwave thermal disinfestation of soils, grains, hay, and timber are presented and discussed. Microwave energy can also ionize various gasses, including air, to create plasma. Plasmas are described by many characteristics, such as temperature, degree of ionization, and density. In the “after glow” (cold plasma) of a plasma discharge, there are sufficient charged particles and excited atoms to generate elevated UV levels and ionize the surfaces of objects. Examples of cold plasma and plasma-activated water disinfestation of grains and other commodities are also presented and discussed. Brief comments on the scale-up of this technology have also been presented.

Adsorption of Organic Compounds on Adsorbents Obtained with the Use of Microwave Heating.

Activated carbons were obtained by physical and chemical activation of the residue of supercritical extraction of green tea leaves. All the adsorbents obtained were characterized by: elemental analysis, low-temperature nitrogen adsorption, and the contents of acidic and basic oxygen functional groups on the surface of activated carbons by the Boehm method. The activated carbons were micro- or micro-mesoporous with well-developed surface area ranging from 520 to 1085 m2/g and total pore volume from 0.62 to 0.64 cm3/g. The physical activation of the precursor led to the strongly basic character of the surface. Chemical activation with 50% solution of H3PO4 of the residue of supercritical extraction of green tea leaves promoted the generation of acidic functional groups. All adsorbents were used for methylene blue and methyl red adsorption from the liquid phase. The influence of the activation method, pH of the dye solution, contact time of adsorbent with adsorbate, the temperature of adsorption, and rate of sample agitation on the effectiveness of organic dyes removal was evaluated and optimized. In the process of methylene blue adsorption on adsorbents, an increase in the sorption capacity was observed with increasing pH of the adsorbate, while in the process of methyl red adsorption, the relation was quite the reverse. The adsorption data were analyzed assuming the Langmuir or Freundlich isotherm models. The Langmuir model better described the experimental results, and the maximum sorption capacity calculated for this model varied from 144.93 to 250.00 mg/g. The results of the kinetic analysis showed that the adsorption of organic dyes on activated carbon was following the pseudo-second-order model. The negative values of the Gibbs free energy indicate the spontaneous character of the process.

Microwave‐supported synthesis of pyridocarbazoles

AbstractWe developed a microwave‐assisted preparation of pyrido[2,3‐c]carbazole from 3‐amino‐9‐ethylcarbazole. The use of microwave heating resulted in shorter response times and higher yields. This process is atom‐efficient and can be used in a variety of multi‐component reactions.

Rapid temperature swing adsorption using microwave regeneration for carbon capture

The use of microwave heating for the thermal regeneration of a porous carbon adsorbent in adsorptive carbon capture was evaluated. In this Microwave Swing Adsorption (MSA) process, a multimode microwave oven has been used to accelerate the desorption of CO2 after the adsorption of a CO2 / N2 (15/85 v/v) mixture. Starting from a commercial activated carbon (AC) material (MSP-20X), sorbent extrudates were prepared and loaded in a Teflon column. The heating of the sorbent bed inside the microwave (MW) cavity was characterised at different locations. Although the adsorption bed is not heated uniformly due to hot spots in the multimode MW cavity, flowing a purge gas reduces the non-uniform heating during the regeneration step. This study also reports that MSA regeneration achieves extremely fast total desorption (in 56 to 79 s), the quickest regeneration reported up to date in MSA, and very rapid desorption rates allowing swift adsorption–desorption cycles. This fast desorption is associated with the extremely high heating rates achieved (100 to 400 °C/min). We show that the desorption rate is faster when using higher powers at practically identical MW energy inputs. Complete CO2 desorption can be achieved at slightly longer durations when using 2-step MW heating. When comparing the MSA results with a reference TSA process, MSA outperforms TSA, due to the higher heating rates achieved by MSA. During eleven adsorption–desorption cycles, it is evidenced that the MSA process can regenerate the adsorption bed at a high reproducibility. The microporosity of the material remained intact during the MSA, revealing that localised heating and the high heating rates are not damaging the sorbent material.

Microwave‐assisted torrefaction and pyrolysis of rice straw pellets for bioenergy

The highlights of this study involve the use of microwave heating for torrefaction and pyrolysis of pelletized rice straw for the generation of high-quality bio-char pellets, and thorough energy assessment of the process. The effects of microwave power and final temperature on the product yields and their quality were thoroughly assessed. At 600 W power, the bio-char yield followed the trend: 33.7 wt.% (800°C) < 35.5 wt.% (600°C) < 55.6 wt.% (300°C). Bio-char yield was unaffected by microwave power at the final temperature of 300°C. High yield of moisture (23.5 wt.%) with a minimal amount of bio-oil (10.5 wt.%) and gases (10.7 wt.%) were obtained at 600 W and 300°C. The major functional groups in the bio-oil were phenols (∼40%), cyclic oxygenates (∼16%), furan derivatives (∼20%) and aliphatic oxygenates (16%). Bio-char obtained from torrefaction at 600 W and 300°C possessed a calorific value of 17.2 MJ/kg with limiting oxygen index of 36.7%, and power generation potential of 4.8 kWh/kg. Overall, microwave-assisted torrefaction is shown to be a promising process intensification strategy to derive high-quality bio-char in a short time of 5–10 min with high process efficiency (51–56%) and comparable biomass conversion efficiency (∼83%) with respect to conventional pyrolysis.

Delignification efficiency of various types of biomass using microwave-assisted hydrotropic pretreatment

The use of a method of an effective delignification of lignocellulosic biomass is a key stage of designing processes of its microbiological conversion e.g. for the purposes of the production of cellulosic ethanol. The study was aimed at evaluating the effectiveness of microwave-assisted hydrotropic pretreatment using sodium cumene sulfonate (NaCS) for the delignification of pine and beech chips and wheat straw. Research results presenting the impact of process parameters of microwave-assisted hydrotropic delignification confirm a high effectiveness of this method of pretreatment of lignocellulosic biomass. The observed effects included changes in the composition of the biomass and an increased susceptibility of cellulose to the subsequent enzymatic hydrolysis. The use of microwave heating combined with an addition of hydrotrope of 40% w/v NaCS and 117 PSI for 60 min enabled a reduction of the absolute concentration of lignins by 36.58% in pine chips, by 57.68% in beech chips, and by 74.08% in wheat straw. After enzymatic hydrolysis was conducted, the highest concentration of glucose: 463.27 ± 11.25 mg glucose/g (hydrolysis yield 46.76 ± 1.14%) was obtained from the wheat straw, while 327.70 ± 22.15 mg glucose/g (hydrolysis yield 35.13 ± 2.37%) was acquired from the beech chips, and only 50.77 ± 0.75 mg glucose/g (hydrolysis yield 6.63 ± 0.10%) was obtained from the pine chips. Microwave-assisted hydrotropic delignification in the optimum process conditions additionally allows a complete removal of hemicellulose from biomass, which improves the effectiveness of enzymatic hydrolysis. Due to a significant reduction of lignin and hemicellulose concentration in biomass, cellulose—which is susceptible to enzymatic hydrolysis and a source of carbon in biosynthesis processes—becomes the main biomass component.

Hybrid RF-Si Xerogels: A Cost-Effective Proposal for Insulator Materials.

Hybrid xerogels RF/Si were synthesized by controlling the chemical variables involved in the polymerization process (i.e., molar ratios, dilution ratio, catalysts, etc.) and evaluated as insulator materials. Higher insulating performances were recorded for these hybrids compared with their counterparts made from only one of their components (i.e., RF or Si xerogels with similar porous characteristics). The analysis of chemical and structural features correlated with heat transfer methods was useful in understanding the sum of contributions involved in the thermal conductivity of RF/Si xerogels. Variables such as roughness and tortuosity can be used to improve the performance of xerogels from a different perspective. In this way, thermal conductivities of 25 mW/mK were achieved without lengthy process steps or special drying methods. Knowledge of material design and the use of microwave heating during the synthesis allowed us to approach a simple and cost-effective process. These results suggest that the hybrid materials developed in this work are a good starting point for the future of the massive production of insulation materials.

Optimization of synthesis conditions for carboxymethyl cellulose from pineapple leaf waste using microwave-assisted heating and its application as a food thickener

Pineapple leaf waste, with its high cellulose content, can serve as alternative starting material for the production of carboxymethyl cellulose (CMC). In this study, synthesis conditions of CMC from pineapple leaves via the use of microwave heating were optimized. Box-Behnken design and response surface methodology were applied to schedule the experiments and to optimize the synthesis condition, respectively. Preparation of CMC was investigated by varying three factors, namely, sodium hydroxide (NaOH) concentration, monochloroacetic acid (MCA) dose, and etherification time. The process of carboxymethylation was optimized to produce CMC with high degree of substitution (DS). Optimal condition for CMC synthesis was noted to be 50% (w/v) NaOH solution, 8 g of MCA/g cellulose, and etherification time of 16 min; such optimal condition resulted in the maximum DS of 0.78. Synthesized CMC was utilized as a thickener for liquid foods (water, orange juice, milk, and mushroom cream soup) where 2% (w/v) as-synthesized CMC increased the viscosity of the foods and changed their characteristics from thin to nectar-like liquids.

Optimization of synthesis conditions for carboxymethyl cellulose from pineapple leaf waste using microwave-assisted heating and its application as a food thickener

Pineapple leaf waste, with its high cellulose content, can serve as alternative starting material for the production of carboxymethyl cellulose (CMC). In this study, synthesis conditions of CMC from pineapple leaves via the use of microwave heating were optimized. Box-Behnken design and response surface methodology were applied to schedule the experiments and to optimize the synthesis condition, respectively. Preparation of CMC was investigated by varying three factors, namely, sodium hydroxide (NaOH) concentration, monochloroacetic acid (MCA) dose, and etherification time. The process of carboxymethylation was optimized to produce CMC with high degree of substitution (DS). Optimal condition for CMC synthesis was noted to be 50% (w/v) NaOH solution, 8 g of MCA/g cellulose, and etherification time of 16 min; such optimal condition resulted in the maximum DS of 0.78. Synthesized CMC was utilized as a thickener for liquid foods (water, orange juice, milk, and mushroom cream soup) where 2% (w/v) as-synthesized CMC increased the viscosity of the foods and changed their characteristics from thin to nectar-like liquids.

Full-Scale Use of Microwave Heating in Construction of Longitudinal Joints and Crack Healing in Asphalt Pavements.

Asphalt pavement construction technology is an industry branch that undergoes constant development. Analyzing the directions of the development, one can divide it into two mainstreams: the development of roadworks equipment and the development of roadworks technology. Microwave heating technique has been mentioned in the road industry from the early ‘70s, but research records from practical full-scale use are very rare. This article presents the evaluation of the possible use of microwave heating technique during a particular aspect of the construction process, namely, the formation of longitudinal joints and the potential repair process of the cracked asphalt pavement. Research results showed that joints constructed using microwave-assisted heating performed the same or even better with regards to tensile characteristics comparing to other techniques. Also, the highest level of compaction was reached among the other tested techniques applied to the wearing course level. The second part of the research experiment showed the large potential of the microwave crack healing technique. The asphalt pavement was healed on its full depth of 10 cm with the single healing operation applied. Although some limitations may occur in the practical use of microwave heating, the test results suggest that it is a very promising technique and should be further developed (for, e.g., shielding concerns, electricity supply). The microwave heating technique is powered with electricity, which is important when there is a constant need for further reductions of CO2 emissions. It can be reached in parallel with clean energy or clean electricity sources.

Size-controlled one-pot synthesis of viologen nanoparticles via a microwave heating technique

We report a size-controlled one-pot synthesis of redox-active organic nanoparticles consisting of viologen units via precise temperature control afforded by the use of microwave heating. A DMF solution of 4,4′-bipyridine and 1,3,5-tris(bromomethyl)benzene (TBMB) corresponding to monomers and ethyl bromide corresponding to a terminator was subjected to microwave heating at 80 °C for 20 min as the first stage corresponding to the growth reaction, which was then followed by heating at 150 °C for 5 min as the second stage corresponding to the termination reaction. 1H NMR analysis of the reaction mixture at each step confirmed that at 80 °C, 4,4′-bipyridine primarily reacts with TBMB, leading to an increase in molecular weight and that a termination reaction with ethyl bromide occurs due to the increase in temperature to 150 °C. Moreover, the size of the nanoparticles can be controlled by varying the first stage reaction time; the nanoparticle diameter was determined to be 142 ± 15 nm for the first stage reaction time of 10 min, which increased to 269 ± 67 nm at 20 min, as evidenced by dynamic light scattering measurements. The microwave heating technique has been widely used in various organic and inorganic syntheses, and it has been reported that this technique provides the desired compounds quickly and easily. In this work, we applied microwave heating to synthesize redox-active organic nanoparticles consisting of hyperbranched viologen units. By the precise temperature control afforded by use of microwave irradiation, we succeeded in controlling the growth and termination reactions kinetically and preparing viologen nanoparticles in one-pot. We also demonstrated that the size of the nanoparticles can be controlled by varying the temperature program.