Use Of Microwave Heating Research Articles

Application of Kalman filter to determination of coal liquefaction mechanisms using discrete time models

Seven different liquefaction mechanisms that consist of reversible and irreversible steps are suggested for a Turkish lignite (Tunçbilek) in tetralin with the use of microwave heating. Compliance of the proposed mechanisms are determined by forming first order linear Discrete-time models with the experimental data and reaction rate constants are determined with the program written in MATLAB with the use of the Kalman filter. The most appropriate suggested model is determined by looking at the sum of the experimental data and squared differences of the values calculated with the model. The magnitude of the reaction rate constants is examined for the models that best fit. The obtained results show that majority of the oil is formed directly from coal. Furthermore, whereas coal:oil reaction step has maximum reaction rate constant, coal:asphaltene and coal:preasphaltene reaction steps have minimum rate constant. Models containing parallel and reversible steps are seen to provide a better fit to the experimental data. The best fit was obtained with model that has both reversible (between asphaltene:coal, asphaltene:oil, and asphaltene:preasphaltene) and irreversible (coal:oil, coal:preasphaltene and preasphaltene:oil) reaction steps. The model also evidenced that the reversible reactions are critical on the liquefaction of Tunçbilek coal.

EFFECT OF MICROWAVE IRRADIATION ON ARABINOGALACTAN AND ITS INTERACTION WITH BETULIN DIACETATE

Betulin diacetate (BDA) has a variety of biological activities, but poor solubility in water limits its application. The use of arabinogalactan (AG) as a complexing agent is a promising method for solving the problem of solubilization of drugs. In this work, influence of microwave (MW) irradiation on the properties of AG and BDA and their interaction in the aqueous suspension with formation of a water-soluble supramolecular complex was studied. It is shown that the MW heating of AG under hard conditions can lead to degradation of the biopolymer. The use of MW heating allowed significantly reducing the complex preparation time compared to the conventional synthesis in a water bath. The preliminary mechanical treatment of the mixture of components, leading to the formation of mechanocomposites, inhibited the reaction between the components in the aqueous suspension under MW irradiation. The IR spectroscopy method has shown that a supramolecular complex formed under MW irradiation similar to that formed by conventional heating. BDA-AG complex was isolated from a MW heated solution as a thin film, which may be a promising material for pharmaceutical applications.

Scalable continuous production of high quality HKUST-1 via conventional and microwave heating

Metal Organic Frameworks (MOFs) are materials with large surface areas and internal volumes, which result in a number of useful properties for applications such as catalysis, separations and gas storage. However, MOFs are challenging to produce at a large scale creating a barrier to becoming truly viable alternatives to current technologies. As a first step towards industrial scale manufacture, we demonstrate here the first scalable, continuous synthesis of high-quality HKUST-1 using ethanol as the solvent, resulting in a greener and potentially much more economical process (as solvent does not decompose and thus can be recycled). We also show that microwave heating can be used to produce HKUST-1 continuously, in timescales several orders of magnitude faster than by conventional heating. We demonstrate a novel approach to microwave assisted synthesis of HKUST-1, based on a recycle loop with microwave irradiation, which is scalable under both batch and continuous conditions and allows an independent control of microwave irradiation regime and the overall reaction time. The use of microwave heating for continuous production of HKUST-1 enabled STY of 400,000kgm−3d−1, which is higher than any production rates reported to date, even when using the preferred high yield solvent, DMF, and is 17 times more than the highest production rates reported to date for HKUST-1 in ‘ethanol-only’ systems.

Exemplification of catalyst design for microwave selective heating and its application to efficient in situ catalyst synthesis

The use of dielectric property monitoring to develop an underpinning understanding of the molecular transformations involved in achieving the successful, rapid in situ synthesis of a catalytic chain transfer polymerisation (CCTP) catalyst using microwave heating is reported. The hypothesis behind the molecular design of this catalyst, such that it was tailored towards the application of microwave heating (MWH), is discussed, reviewed relative to the empirical results and compared to the performance of a benchmark pre-formed catalyst. The overall number/type of function group present in the catalyst, the degree of flexibility exhibited by its organic ligand system and level of solvation achieved are shown to be key factors affecting the interaction between the catalyst and the applied microwave energy. Use of microwave heating leads to fast, in situ formation of the catalyst (approximately 32s) within the polymerisation mixture, rendering pre-preparation steps unnecessary and ensuring it is generated prior to the polymerisation reaction commencing. Thus potentially presenting an enormous opportunity to intensify current industrial processes.

Enhanced ionic conductivity of scandia-ceria-stabilized-zirconia (10Sc1CeSZ) electrolyte synthesized by the microwave-assisted glycine nitrate process

Scandia-stabilized-zirconia is a potential zirconia-based electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this study, the properties of zirconia co-doped with 10mol% Sc and 1mol% Ce (scandia-ceria-stabilized-zirconia, 10Sc1CeSZ) electrolyte synthesized by the microwave-assisted glycine nitrate process (MW-GNP) were determined. The effects of microwave heating on the sintering temperature, microstructure, densification and ionic conductivity of the 10Sc1CeSZ electrolyte were evaluated. The phase identification, microstructure and specific surface area of the prepared powder were investigated using X-ray diffraction, transmission electron microscopy and the Brunauer-Emmett-Teller technique, respectively. Using microwave heating, a single cubic-phase powder was produced with nanosized crystallites (19.2nm) and a high specific surface area (16m2/g). It was found that the relative density, porosity and total ionic conductivity of the 10Sc1CeSZ electrolyte are remarkably influenced by the powder processing method and the sintering temperature. The pellet sintered at 1400°C exhibited a maximum ionic conductivity of 0.184S/cm at 800°C. This is the highest conductivity value of a scandia-stabilized-zirconia based electrolyte reported in the literature for this electrolyte type. The corresponding value of the activation energy of electrical conductivity was found to be 0.94eV in the temperature range of 500–800°C. Overall, the use of microwave heating has successfully improved the properties of the 10Sc1CeSZ electrolyte for application in an IT-SOFC.

PERBANDINGAN METODE MICROWAVE HYDRODISTILLATION (MH) DAN MICROWAVE HYDRODIFFUSION AND GRAVITY (MHG) UNTUK MENGEKSTRAK MINYAK ATSIRI DARI KULIT JERUK

One source of essential oil that has long been popular is a citrus fruit (Citrus aurantium). Results waste citrus peel around 500,000 tonnes per year. So the prospects for the utilization of waste orange peel are big enough to extract the essential oil. However, conventional extraction methods have drawbacks in terms of product quality, so to find solutions to these shortcomings, it is necessary to use the extraction method by Microwave Hydrodiffusion and Gravity (MHG). This method combines the use of microwave heating and physical phenomena (hydrodiffusi and earth gravity) at atmospheric pressure, without addition of organic solvents or water. In this study used fresh orange peel material 400 and 500 grams, two variable microwave power of 100 and 300 Watt and the extraction time for 15, 30, 45 and 60 minutes. To know the processing time and the microwave power effective method of MHG, oil composition was analyzed by GCMS to determine the amount of the fraction of oxygenated compounds. The larger of installed microwave power, the higher of operating temperature, so the %yield increases in a shorter time. From the comparison of energy consumed, the MHG method is give 30% more energy efficient than the Microwave Hydrodistillation (MHD) method. The use of microwaves does not change the physical properties of oil. The oil produced from the MHG method has a good quality because it has specific gravity and refractive index values that meet the EOA quality standard and has a greater oxygenated compounds content than the MHD method

Metal-Assisted and Microwave-Accelerated Decrystallization: An Alternative Approach to Potential Treatment of Crystal Deposition Diseases.

Gout is a painful and prevalent crystal deposition disease caused by the overproduction of Uric Acid (UA) in the body and the atypical deposition in human synovial joints as Monosodium Urate Monohydrate (MSUM). Conventional treatments, such as NSAIDs, cyclooxygenase-2 inhibitors, and systemic glucocorticoids often present harmful side-effects and are short-lived. Long-term therapies including xanthine oxidase inhibitors and the use of uricosuric agents have been developed and aim to lower the UA serum levels in the body. As regards to post-crystals deposition, our research laboratory recently proposed and demonstrated the use of the Metal-Assisted and Microwave-Accelerated Decrystallization (MAMAD) technique for the breakdown of organic and biological crystals on planar surfaces. The MAMAD technique is based on the combined use of microwave heating and Au NPs in solution. The interactions of the Au NPs with microwave’s electromagnetic field result in an increase in the kinetic energy of Au NPs, and subsequently, an increase in the collisions with target crystals placed on planar surfaces leading to rapid crystal breakdown. In this regard, our laboratory aims to develop the MAMAD technique as an alternative treatment for crystal deposition diseases, particularly gout, with minimal invasion and side-effects as compared to current treatments. In this review article, we will summarize our previous findings and provide additional data detailing the effectiveness of the MAMAD technique as a rapid and efficient method for the breakdown of gout related crystals and L-alanine crystals (a model crystal).

Effect of different home-cooking methods on acrylamide formation in pre-prepared croquettes

This study compared the effects of different heating methods such as roasting, pan-frying, deep-frying and microwave treatment on the formation of acrylamide (AA) in ready-to-eat croquettes. The experiment was performed with ten commercially available pre-cooked flour-based croquettes with meat filling for home-cooking reheated according to the information on the labels. The AA content was determined by the reversed phase-high performance liquid chromatography (RP-HPLC) method coupled to a diode array detector (DAD). Browning development and water activity along with free asparagine and sugar content were also monitored. Before preparation, all products showed the lowest (190μg/kg) acrylamide content. The highest acrylamide content was found when microwave heating was used. The mean AA content in all samples prepared in this way was significantly higher (420μg/kg) than that of roasting (360μg/kg), deep-frying (298μg/kg) or pan-frying (285μg/kg) (p<0.05). The manner in which heat is transmitted to a food appears to have a significant impact on the rate of acrylamide formation. Among the domestic methods used, microwave treatment was more favourable for AA formation in products. The use of microwave heating for thermal processing of carbohydrate-rich food should be limited by consumers to prevent excessive acrylamide formation.

Microwave pretreatment of lignocellulosic agroindustrial waste for methane production

This study focuses on the use of microwave heating as a pretreatment for lignocellulosic agroindustrial waste prior to anaerobic digestion for methane production. Four materials were investigated, namely winery waste, cotton gin waste, olive pomace and juice industry waste. Results showed different effects of microwave heating on the solubilization and methane potential of the studied substrates. The variations were attributed to the specific characteristics of each substrate combined with the pretreatment conditions. In the cases of winery waste and juice industry waste, microwave pretreatment resulted in relatively high solubilization levels for both materials. Nevertheless, the portion retained on the solid fraction after pretreatment was larger and less biodegradable for winery waste, while for juice industry waste it was smaller but with a higher biodegradability degree. As far as cotton gin waste and olive pomace are concerned, microwave pretreatment seems not to cause high organic matter solubilization, while it most likely induced structural changes in the materials matrices. This resulted in methane production levels that indicate the presence of recalcitrant or/and inhibitory compounds on the pretreated samples. Moreover, the increased moisture and hydrogen contents for pretreated samples suggested that additional changes were made to the substrates. Ultimately, although microwave pretreatment did not improve methane production, results indicated that at temperatures between 125 and 150°C, such a process could eventually provide samples which are more suitable for methane production. Moreover, an improved energy balance could be obtained by combining these temperatures with lower exposure times and higher solid to liquid ratios.

Pyrolysis Recovery of Waste Shipping Oil Using Microwave Heating

This study investigated the use of microwave pyrolysis as a recovery method for waste shipping oil. The influence of different process temperatures on the yield and composition of the pyrolysis products was investigated. The use of microwave heating provided a fast heating rate (40 °C/min) to heat the waste oil at 600 °C. The waste oil was pyrolyzed and decomposed to form products dominated by pyrolysis oil (up to 66 wt. %) and smaller amounts of pyrolysis gases (24 wt. %) and char residue (10 wt. %). The pyrolysis oil contained light C9–C30 hydrocarbons and was detected to have a calorific value of 47–48 MJ/kg which is close to those traditional liquid fuels derived from fossil fuel. The results show that microwave pyrolysis of waste shipping oil generated an oil product that could be used as a potential fuel.

Graphene/Na carboxymethyl cellulose composite for Li-ion batteries prepared by enhanced liquid exfoliation

In the present work, we report a sonication-assisted exfoliation method of graphene preparation enhanced by the use of microwave heating and “green” exfoliant – sodium carboxymethyl cellulose (NaCMC). Introducing microwave heating during sonication of graphite dispersions in aqueous solutions of NaCMC results in the formation of graphene dispersions with concentration as high as 4.29mg/ml. It is found that drying the dispersions results in the formation of graphene/NaCMC composites with graphene content up to 38.65wt%. A study of the composite with High Resolution Transmission Electron Microscopy and Raman Spectroscopy reveals the formation of few-layer graphene approximately below five layers. The as-prepared graphene/NaCMC composite shows higher capacities than commercial graphite in Li-ion half cells reaching 397mAh/g(graphene). Also, when the composite is used with a nanosilicon (33wt%) in a Li-ion half cell high initial reversible capacities of 1611mAh/g(Si) with good cyclability and rate capability have been reached.

The Use of Microwave For One-pot Reductive Amination

A variety of reactions can now be conducted in microwave ovens. Generally, equal or better yields are obtained when microwave heating is being utilized for a reaction compared to the use of conventional heating. One area of organic synthesis where microwave conditions is being used more is in the formation of secondary and tertiary amines. This review will highlight the use of microwave heating in one-pot formation of primarily secondary aryl amines with a few examples of formation of primary and tertiary amines being descussed. Keywords: Aryl amines, catalysis, microwave, one-pot reactions, reductive amination.

Ionic Thiourea Organocatalysis of the Morita–Baylis–Hillman Reaction

An ionic thiourea based organocatalyst has been shown to promote a 1,4-diazabicyclo[2.2.2]octane, (DABCO) catalysed Morita-Baylis-Hillman reaction between benzaldehyde and cyclohex-2-en-1-one. The ionic thiourea catalyst was easily prepared from a pyrrolidinium salt containing an arylamine moiety and 3,5-di(trifluoromethyl)phenylisothiocyanate. X-ray crystallographic analysis of the ionic thiourea catalyst shows an acetone molecule doubly hydrogen bonded to the Lewis acidic thiourea N-H protons. Entrainment of the ionic thiourea co-catalyst in the ionic liquid N-butyl-N-methylpyrrolidinium bistriflimide, [BMPyr][N(Tf)2], facilitates catalyst recycling and affords very good yields with reaction times reduced through use of microwave heating.

Molecular Differentiated Initiator Reactivity in the Synthesis of Poly(caprolactone)-Based Hydrophobic Homopolymer and Amphiphilic Core Corona Star Polymers.

Macromolecules that possess three-dimensional, branched molecular structures are of great interest because they exhibit significantly differentiated application performance compared to conventional linear (straight chain) polymers. This paper reports the synthesis of 3- and 4-arm star branched polymers via ring opening polymerisation (ROP) utilising multi-functional hydroxyl initiators and Sn(Oct)2 as precatalyst. The structures produced include mono-functional hydrophobic and multi-functional amphiphilic core corona stars. The characteristics of the synthetic process were shown to be principally dependent upon the physical/dielectric properties of the initiators used. ROP’s using initiators that were more available to become directly involved with the Sn(Oct)2 in the “in-situ” formation of the true catalytic species were observed to require shorter reaction times. Use of microwave heating (MWH) in homopolymer star synthesis reduced reaction times compared to conventional heating (CH) equivalents, this was attributed to an increased rate of “in-situ” catalyst formation. However, in amphiphilic core corona star formation, the MWH polymerisations exhibited slower propagation rates than CH equivalents. This was attributed to macro-structuring within the reaction medium, which reduced the potential for reaction. It was concluded that CH experiments were less affected by this macro-structuring because it was disrupted by the thermal currents/gradients caused by the conductive/convective heating mechanisms. These gradients are much reduced/absent with MWH because it selectively heats specific species simultaneously throughout the entire volume of the reaction medium. These partitioning problems were overcome by introducing additional quantities of the species that had been determined to selectively heat.

ChemInform Abstract: Microwave‐Assisted Synthesis of Novel 2,3‐Disubstituted Imidazo[1,2‐a]pyridines via One‐Pot Three Component Reactions.

An expeditious one-pot, metal-free, three-component reaction of arylglyoxals, cyclic 1,3-dicarbonyls and 2-aminopyridines in the presence of molecular iodine under microwave irradiation is reported. A wide variety of 2,3-disubstituted imidazo[1,2-a]pyridine derivatives can be synthesized in good to very good yields using this methodology. The salient features of this methodology are: metal-free, short reaction time, good yields, use of microwave heating and no harmful by-products.

Study of Two Catalyst Configurations under Microwave Irradiation for the Selective Benzaldehyde Production over Co-ZSM-11 and Fe-ZSM-11

Abstract Intensification process by the use of microwave heating was investigated by testing two catalyst configurations on the selective styrene oxidation for benzaldehyde production. The oxidation reaction was studied over Co-ZSM-11 and Fe-ZSM-11 catalysts. Their catalytic activity was evaluated by using these catalysts in two different forms: compacted pellets and fine particles. Thus, two reaction systems were studied under microwave: a batch system with fine particles in suspension (system 1) and a recirculating batch liquid through a fixed bed system comprising the compact catalyst pellets (system 2). Despite a better microwave interaction with the catalyst in the pellet form, the fixed bed configuration did not lead to a significant intensification of the process. At 60°C, the styrene molar conversions by using Co-ZSM-11 catalyst were found to be 33% and 3% for systems 1 and 2, respectively. With fine particles, the catalytic activity was higher since the styrene oxidation was able to occur without significant internal diffusional resistance of the reagents toward the active acid sites of the zeolite structure.

Microwave-Assisted Synthesis of Azines and their Condensed Derivatives

In recent years, numerous reports concerning the synthesis of azines and their fused derivatives under microwave irradiation condition have appeared. The use of microwave heating is a valuable tool for synthetic chemists. Being able to reduce reaction times and to increase product yield, this methodology offers to organic chemists the potential to optimize reaction processes. Additionally, application of microwave irradiation leads to many advantages, like the use of non-corrosive and inexpensive reagents, in addition to the eco-friendly and quot; green chemistry and quot; economical and environmental impacts. In this review, we report the important role of microwave activation and their advantages in the synthesis of medically important azines and their fused derivatives. Keywords: Azines, biginelli synthesis, dihydropyridines, dihydropyrimidinones, green synthesis, hantzsch synthesis, heteroatom, microwave-assisted organic synthesis, microwave-assisted synthesis, microwave irradiation, multi-component reaction, pyridine, pyridine dicarbonitriles, pyrimidine, triazines.

Manufacturing of Kevlar/Polyester Composite by Resin Transfer Moulding using Conventional and Microwave Heating

Microwave heating was incorporated into the resin transfer moulding technique. Polytetrafluoroethylene (PTFE) mould was used to cure the composite panel. Through the use of microwave heating, the mechanical and physical properties of produced Kevlar fibre/polyester composites were compared to those manufactured by conventional resin transfer moulding. The flexural modulus and flexural strength of 6-ply conventionally cured composites was 45% and 9% higher than the flexural modulus and flexural strength of 6-ply microwaved cured composites, respectively. However, 19% increase in interlaminar shear strength (ILSS) and 2% increase in compressive strength was observed in 6-ply microwave cured composites. This enhancement in ILSS and compressive strength is attributed to the better interfacial bonding of polyester resin with Kevlar fibres in microwaved cured composite, which was also confirmed via electron microscopy scanning. Furthermore, the microwave cured composite yielded maximum void contents (3%).

Preparation of activated carbon from Xinjiang region coal by microwave activation and its application in naphthalene, phenanthrene, and pyrene adsorption

Coal-based activated carbons (CAC) were prepared from coal in Xinjiang China by microwave-assisted activation. The effects of preparation conditions on adsorption capabilities of CAC for methylene blue (MB) and iodine were investigated. The microwave activation was carried out with coal activator ratio of 1:3 for 12 min at 700 W of power, the adsorption capacities of the prepared CAC achieved the maximal values of 312 and 1048.19 mg/g for MB and iodine. The increasing of CAR, activation time, and microwave power reduced the surface functional groups and improved the pHPZC of CAC. The BET surface area and total pore volume of CAC prepared were identified as 1770.49 m2/g and 0.99 cm3/g, respectively. Hence, the work demonstrates that the use of microwave heating for preparing CAC is more rapid, cheaper and efficient. The adsorption behaviors of typical polycyclic aromatic hydrocarbons (PAHs) in ethanol aqueous solution on CAC were also explored. Equilibrium data were favorably described by the Langmuir and Freundlich isotherms, and adsorption kinetics was fitted to the pseudo-second-order model well. The equilibrium adsorption amounts were 117.17 mg/g for pyrene, 111.39 mg/g for phenanthrene, and 78.18 mg/g for naphthalene. Thus, CAC prepared by microwave activation could have a very effective application in removal of these PAHs.

Fast and tunable synthesis of ZrO2 nanocrystals: mechanistic insights into precursor dependence.

In this work, ZrO2 nanocrystals (NCs) are synthesized via a solvothermal treatment in benzyl alcohol, which is an established method for the synthesis of many metal oxide nanocrystals. We found that the use of microwave heating allows for a reduction in reaction time from 2 days in the autoclave to merely 4 h in the microwave. Furthermore, we were able to tune the crystallographic phase from pure cubic to pure monoclinic zirconia by changing the reaction mechanism through the use of a different zirconium precursor. Via GC-MS measurements, we found that the release of a strong acid during synthesis controls the key mechanism behind the control over crystal phase formation. The as-synthesized ZrO2 NCs (cubic or monoclinic) are small in size (3-10 nm), yet aggregated. However, aggregate-free NCs are generated through a surface-functionalization with carboxylic acid ligands, providing stabilization in apolar solvents via steric hindrance. Solution (1)H NMR was used to study the details of this post-modification step and the surface chemistry of the resulting aggregate-free NCs. This led to the conclusion that not only a different crystal structure but also a different surface chemistry is obtained, depending on the precursor composition.