Microwave Heating

Measured influence of microwave heating on time dependencies of component temperatures for two immiscible liquids in a mixture shows differences for polar (water) and non-polar (cyclohexane or carbon tetrachloride) liquids. The rate of increase for the temperature of water with time of microwave heating is larger than other liquids in the mixture (maximum rate of temperature growth for water is 8 times larger than corresponding rate for carbon tetrachloride and 2 times larger than cyclohexane). This leads to creating, for a considerable time period, a unique environment where there is a significant temperature difference between two liquids in a mixture. The maximum value of the difference between water and carbon tetrachloride temperatures in the mixture was 107 °C at 300 sec of microwave heating. While the maximum value of the difference between water and cyclohexane temperatures in the mixture was 57 °C at 135 sec microwave heating. This suggests that electromagnetic waves lose most of their energy to polar liquids (water), while the difference in rates of temperature growth for carbon tetrachloride and cyclohexane can be explained by different mechanisms of heat transfer from water to cyclohexane (conduction and convection) and to carbon tetrachloride (conduction only). Semi-empirical mathematical models for the time dependencies of temperature growth for components of the mixtures gave good correlation with experimental data (relative error less than 9%). These results can be used to model the temperature kinetics of components for other multi-phase immiscible liquid mixtures.

Introduction. Enzyme inactivation is a major objective in orange juice production. Conventional heating in elevated temperature causes adverse effects on the final products such as color alterations, flavor damages, ascorbic acid losses. For this, microwave heating (MW) was used in this study as thermal treatment on orange juice production for pectin methylesterase (PME) inactivation, and response surface methodology (RSM) was used for optimization of MW conditions. Materials and methods. Oranges (Citrus sinensis Osb.) of Navel variety were used as raw material in this study. The effects of flow rate and power on PME activity were investigated. After optimization orange juice was produced with using optimized conditions and compared with untreated control juices and conventional thermally heated juices on the aspect of PME inactivation and some quality characteristics. Results and discussion. The linear effects of flow rate (x 1 ) and power (x 2 ), as well as the quadratic effect of flow rate (x 1 2 ), power (x 2 2 ) and the interaction effect of flow rate-power (x 1. x 2 ) were significant for PME inactivation by MW. Lack of fit of experimental data was not significant (P>0.05) for model. The coefficient of variation (C.V.) was 6.27%. The model showed an adequate precision of 6.788x10 -3 . The determination coefficient (R²) was 0.9793, while the adjusted determination coefficient (adjusted R²) value was 0.9645. R 2 and adjusted R values for the models did not differ dramatically indicating non-significant terms have not been included in the model. Reduction of PME activities was found approximately 93-95% in MW groups. The PME inactivation rate was described satisfactorily as a function of microwave heating conditions. The PME can be inactivating in moderate temperatures by MW (40 mL/min-900W-83 °C) and MW (50 mL/min-900W-75 °C). D values were calculated for two optimum conditions of MW and CH treatments and found as 39.24 sec for MW (40 mL/min-900W), 38.76 sec for MW (50 mL/min-900W) and 70 sec for CH (95 ºC-60 sec). Total pectin content was increased 17.2% after MW application. And the loss of ascorbic acid content for MW sample was found lower than other applications. Conclusions. A synergistic effect of microwave energy and temperature on orange juice PME inactivation was found under microwave heating conditions. It was determined that MW (50 mL/min-900W) can be applied as a thermal treatment on orange juice production in moderate temperatures (75 °C) for PME inactivation and may improve functional properties of orange juice. And this result is extremely important in terms of cloud stability of orange juices.

Introduction. Enzyme inactivation is a major objective in orange juice production. Conventional heating in elevated temperature causes adverse effects on the final products such as color alterations, flavor damages, ascorbic acid losses. For this, microwave heating (MW) was used in this study as thermal treatment on orange juice production for pectin methylesterase (PME) inactivation, and response surface methodology (RSM) was used for optimization of MW conditions. Materials and methods. Oranges (Citrus sinensis Osb.) of Navel variety were used as raw material in this study. The effects of flow rate and power on PME activity were investigated. After optimization orange juice was produced with using optimized conditions and compared with untreated control juices and conventional thermally heated juices on the aspect of PME inactivation and some quality characteristics. Results and discussion. The linear effects of flow rate (x 1 ) and power (x 2 ), as well as the quadratic effect of flow rate (x 1 2 ), power (x 2 2 ) and the interaction effect of flow rate-power (x 1. x 2 ) were significant for PME inactivation by MW. Lack of fit of experimental data was not significant (P>0.05) for model. The coefficient of variation (C.V.) was 6.27%. The model showed an adequate precision of 6.788x10 -3 . The determination coefficient (R²) was 0.9793, while the adjusted determination coefficient (adjusted R²) value was 0.9645. R 2 and adjusted R values for the models did not differ dramatically indicating non-significant terms have not been included in the model. Reduction of PME activities was found approximately 93-95% in MW groups. The PME inactivation rate was described satisfactorily as a function of microwave heating conditions. The PME can be inactivating in moderate temperatures by MW (40 mL/min-900W-83 °C) and MW (50 mL/min-900W-75 °C). D values were calculated for two optimum conditions of MW and CH treatments and found as 39.24 sec for MW (40 mL/min-900W), 38.76 sec for MW (50 mL/min-900W) and 70 sec for CH (95 ºC-60 sec). Total pectin content was increased 17.2% after MW application. And the loss of ascorbic acid content for MW sample was found lower than other applications. Conclusions. A synergistic effect of microwave energy and temperature on orange juice PME inactivation was found under microwave heating conditions. It was determined that MW (50 mL/min-900W) can be applied as a thermal treatment on orange juice production in moderate temperatures (75 °C) for PME inactivation and may improve functional properties of orange juice. And this result is extremely important in terms of cloud stability of orange juices.

We report the use ofmicrowave-hydrothermal processing to synthesire various ceramic powders. Microwave-hydrothermal processing is compared with conventional hydro thennal processing in the crystallisation of MoO 2 • The presence of microwave fi eld leads to accelerated kinetics of crystallization of the finely divided molybdenum dioxide particles. Existing microwave heated pressure vessels for chemical synthesis cannot be used above 250 MPa and 270 °C because they contain parts made of polymeric materials. The objective ofthis work is to associate a microwave source to a high pressure vesse! in a way such that it might be used to carry out reactions in acqueous media at pressures around IOOMPa and temperatures above the critical point of water.

Over the past decade, use of microwave energy, to heat chemical reactants on a laboratory scale, has evolved as a well-demonstrated alternative to traditional heating. Clean chemistry, reduction in reaction times, improved yields, and applicability to wide range of reactions, greatly improved efficiency with better quality, safety and tremendous scope for automation are some of the benefits of this emerging technology. Association of biological activity with heterocyclic motifs is well known and is important from drug discovery viewpoint. This article gives an account of the recent applications of microwaves in the synthesis of biologically active heterocyclic compounds with synthesis schemes and/or comprehensive review of reaction conditions and biological importance of over 50 such applications.

Herein, novel nitrogen-doped nanoporous carbons possessing 2.63 at.% N and high porosity were prepared using nitrogen-rich carbon quantum dots (N-CQDs) via a facile chemical activation. To this end, after performing the hydrothermal process on the raw materials, chemical activation was carried out by various KOH/N-CQDs ratios (2:1 to-4:1), resulting in unique micro-mesoporous structures (i.e., HNAC samples). In this approach, a large surface area (1477 m 2 g-1) and pore volume (1.05 cm 3 g-1) were obtained, where the micropore volume was increased by decreasing the KOH/N-CQDs ratio, activation time and augmenting the activation temperature, that caused considerable adsorption at 1 bar. It is worth mentioning that mesopores could be generated by condition optimization that led to higher adsorption at high pressure. Due to their large surface area and high nitrogen loading, the HNAC samples demonstrated excellent H 2 S and CO 2 adsorption capacity at ambient conditions (9.28 mmolg-1 for H 2 S and 4.28 mmolg-1 for CO 2 at 1 bar and 25 • C) and at higher pressures (18.0 mmolg-1 for H 2 S and 6.20 mmolg-1 for CO 2 at 10 bar and 25 • C). According to the significant performance of the prepared nanosorbents along with stable cyclic adsorption-desorption performance, the HNACs are proposed as promising adsorbents with outstanding adsorption.

In this work, various carbon materials were studied as catalysts/microwave receptors for the CO 2 reforming of the CH 4 reaction. Carbon materials with a different textural development (metallurgical coke, activated carbons, re-activated carbon) were selected as catalysts in order to determine the role of porosity and pore size in dry reforming. Microporosity was found to be necessary for a good performance of the carbon catalysts. An activated carbon and an oxidized activated carbon were compared in order to evaluate the influence of oxygen surface groups on the catalytic activity of carbons for the dry reforming reaction. Oxidized carbons were found to be bad catalysts, especially under microwave heating. The importance of CO 2 reactivity for carbon materials to be able to act as acceptable catalysts was also established.

Energy storage is a topic of great importance for the development of renewable energy, since it appears to be the only solution to the problem of intermittency of production, inherent to such technologies. In this paper, a new technology for energy storage, based on microwave-induced CO 2 gasification of carbon materials is proposed. The tests carried out in this study on different carbon materials showed that charcoal consumes the least amount of energy. Two microwave heating mechanisms, a single-mode oven and a multimode device, were evaluated with the latter proving itself to be the more efficient in terms of energy consumption and recovery. The initial results obtained showed that this technology is able to achieve energy efficiencies of 45% at laboratory scale with every indication that these results can be improved upon to make this approach highly competitive against other energy storage technologies.

Microwave heating is one of the most attractive cooking methods for food preparation, commonly employed in households and especially in restaurants for its high speed and convenience. The chemical constituents of oils that degrade during microwave heating do so at rates that vary with heating temperature and time in a similar manner to other type of processing methods. The rate of quality characteristics of the oil depends on the fatty acid composition and the minor components during heating. Addition of oxidative-stable palm olein (PO) to heat sensitive canola oil (CO), may affect the quality characteristics of CO during microwave heating. The aim of this study was to evaluate how heat treatments by microwave oven affect the quality of CO in presence of PO. The blend was prepared in the volume ratio of 40:60 (PO:CO, PC). Microwave heating test was performed for different periods (2, 4, 8, 12, 16 and 20 min) at medium power setting for the samples of CO and PC. The changes in qualit...

1-(1-alkylsulfonic)-3-methylimidazolium chloride Brönsted acidic ionic liquids are shown as excellent catalysts and reaction mediums for Skraup synthesis of quinolines under microwave conditions without the use of nitrobenzene as an oxidant and metal catalysts.

The Activated charcoal AC is a carbonaceous material with high carbon content in its structure, it can be obtained from biomaterials such as: coconut shell, wood, bamboo, etc. Its pores are highly developed, have high adsorption capacity and have a microcrystalline form capable of selectively purifying liquids or gases. All the ACs have micro, meso and macro pores in their structure, but the relative proportion depends on the precursor and production process. In carrying out this work, activated carbon was produced from the charcoal of the babassu endocarp prepared via microwave radiation. The physical activation process took place in the atmosphere of CO2 via microwave radiation at room temperature 235 °C and activation time corresponding to 50 minutes. The characterizations of the AC were performed with the following techniques: Scanning electron microscopy SEM; Surface area analysis BET and porosity; Thermogravimetric analysis TGA; Analyzes of methylene blue adsorption in the reg...

The effect of microwave susceptor design on the heating profiles of co-pyrolysis between waste truck tyre and empty fruit bunch was studied. Carbonaceous susceptor was used to elevate the pyrolysis temperature along with increased heating rate. Different design of microwave susceptor and its effect towards the heating profiles of the studied co-pyrolysis process was examined. The aim is to determine the effect of heating rates on the pyrolytic-oil yield, calorific value and energy recovery. From the study, it was revealed that the microwave susceptor design (D1) with a horizontal-layer single-bed, located at the bottom (SB-HL-B) of the feedstocks, showed higher heating rate (83 °C min−1). Higher heating rates were observed to significantly increase pyrolytic-oil (39.0 wt%) and energy yield (59.0%). Such heating rate also upgraded the pyrolytic-oil properties, producing oil with higher calorific value (42.20 MJkg−1). Thus, the present study demonstrated a viable method to optimise py...

Starting from a Cl-trytyl linked hydroxylamine, a hydroxamic dipeptide having serine in the second position was prepared by using DMTMM as the coupling agent. Mitsunobu cyclization carried out under microwave heating gave very good yields of a 3,6-disubstituted-perhydro-diazepin-2,5-dione. This heterocycle can be used as a new platform for combinatorial chemistry or as a constraint to rigidify a small peptide.

Syntheses of structurally varied densely functionalized olefins have been accomplished (23 examples) through microwave-assisted ammonium formate-mediated Knoevenagel condensation of differently substituted aromatic aldehydes with ethyl cyanoacetate, cyanoacetamide, malononitrile, and malonic acid under solvent-free condition in good yield (76Á95%) and high purity. The said reactions occur within very short period of time (0.75Á3 min) in eco-friendly conditions involving an operationally simple procedure, eliminating any kind of inorganic support, toxic reagent and organic solvent.

This paper deals with a circular double‐ridged waveguide (CDRW) as a key element of traveling‐wave systems for microwave thermal processing. Approximate formulas for estimation of basic characteristics of CDRW partially filled with dielectric are derived with the use of the equivalent circuit technique. For accurate analysis, 3D FDTD models are developed and used for computation of coupling, electric field, and dissipated power in a coaxially excited five‐section CDRW applicator with three spherical loads. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1708–1713, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22539

Purpose: Simultaneous polymerization of maxillary and mandibular complete dentures with teeth in occlusion through investing in a double special flask has been described as a more rapid and efficient method to polymerize prostheses than the conventional method; however, no study has been done to verify important properties of resin, including superficial porosity, surface roughness, and hardness, when processed by this technique. The purpose of this study was to verify if the simultaneous polymerization associated with microwave heating may alter the superficial porosity, surface roughness, and Knoop hardness of acrylic resin. Materials and Methods: Resin specimens processed in single and double dental flasks were compared using microwave energy and warm water methods. Four groups were tested according to the investing flask and the method of resin cure: Group I control specimens (n = 15) were invested in single metal flasks and cured by warm water at 74 • C for 9 hours. Group II (n = 15) specimens were invested in single polyvinyl chloride flasks and cured by microwave energy at 90 W for 20 minutes plus 450 W for 5 minutes. Group III (n = 30) and Group IV (n = 30) specimens were processed by simultaneous polymerization in double flasks and cured by the same warm water and microwave energy protocols, respectively. Results: No significant differences were found in mean superficial porosity (8.06 ± 2.28 pore/cm 2 ), surface roughness (0.14 ± 0.03 μm), or Knoop hardness (19.66 ± 2.25 kgf/mm 2 ) between the control group (GI), and the other three experimental groups (p > 0.05). Processing acrylic resin in a double flask heated by either warm water or microwave energy does not alter the resin's superficial porosity, surface roughness, or Knoop hardness; however, other properties of resin should be analyzed using this denture processing technique. * Warm water or microwave energy. * * Single or double investing flask. (ns) No significant difference; p = 0.05.

This study aims to convert composite textile structures composed of nonwoven and woven fabrics produced from cotton-jute wastes into activated carbon textile structures and investigate the possibilities of using them for electromagnetic shielding applications. To this end, the novel contribution of this study is that it shows that directly carbonized nonwoven textile via self-purging microwave pyrolysis can provide Electromagnetic Interference (EMI) shielding without any processing, including cleaning. Textile carbonization is generally achieved with conventional heating methods, using inert gas and long processing times. In the present study, nonwoven fabric from cotton-jute waste was converted into an activated carbon textile structure in a shorter time via microwaves without inert gas. Due to its polar structure, FeCl 3 has been used as a microwave absorbent, providing homogeneous heating in the microwave and acting as an activating agent to serve dual purposes in the carbonization process. The maximum surface area (789.9 m 2 /g) was obtained for 5% FeCl 3 . The carbonized composite textile structure has a maximum of 39.4 dB at 1 GHz of EMI shielding effectiveness for 10% FeCl 3 , which corresponds to an excellent grade for general use and a moderate grade for professional use, exceeding the acceptable range for industrial and commercial applications of 20 dB, according to FTTS-FA-003.

Teoretická část bakalářské práce zhodnocuje metody a trendy recyklace polyuretanových materiálů s důrazem na tvrdé polyuretanové pěny používané jako termoizolace ve stavebnictví. Experimentální část práce je zaměřena na ověření využitelnosti glycerolu jako alkoholyzačního činidla v procesu regenerace polyolu v kombinaci s perspektivním mikrovlnným ohřevem reakční směsi. V závěru práce jsou navrženy další kroky k rozvoji uvedeného procesu s cílem převedení metody do technické praxe.The theoretical part of the bachelor thesis evaluates methods and trends of recycling polyurethane materials with the emphasis on rigid polyurethane foams used as thermo isolation building material. The experimental part is focused on glycerol process verification as an alcoholization agent in the regenerative process of polyol, together with perspective microwave heating of reaction mixture. The final part of the work suggests further steps in the development of above mentioned process with the aim of its...

Microwave-assisted organic synthesis (MAOS) provides a novel and efficient means of achieving heat organic reactions. Nevertheless, the potential arcing phenomena via microwave (MW) interaction with solid metal catalysts has limited its use by organic chemists. As arcing phenomena are now better understood, new applications of Pd/C-catalyzed reactions under MW dielectric heating are now possible. In this review, the state of the art, benefits, and challenges of coupling MW heating with heterogeneous Pd/C catalysis are discussed to inform organic chemists about their use with one of the most popular heterogeneous catalysts.

Microwave-assisted organic synthesis (MAOS) provides a novel and efficient means of achieving heat organic reactions. Nevertheless, the potential arcing phenomena via microwave (MW) interaction with solid metal catalysts has limited its use by organic chemists. As arcing phenomena are now better understood, new applications of Pd/C-catalyzed reactions under MW dielectric heating are now possible. In this review, the state of the art, benefits, and challenges of coupling MW heating with heterogeneous Pd/C catalysis are discussed to inform organic chemists about their use with one of the most popular heterogeneous catalysts.

Controlled microwave heating has found many important applications in organic synthesis. Almost all kinds of reactions have been tested using microwaves. Major successes in carrying out rapid organic transformations have been achieved when high temperatures are required and substrates or reagents do not survive to prolonged heating. On the other hand, very few reports deal with the use of gas as reagent inside a microwave oven, even though many organic transformations that employs gas are carried out under heating and could take advantage of the use of microwaves. This review collects all the contributions reported until now on microwave-assisted reaction using gas reagents. Except for a few examples, all the reactions selected have been carried out using commercially available instruments for synthesis with minor modifications.

The allylation of indigo results in the one-step synthesis of two unique complex heterocyclic systems: a spiroindoline-pyridoindolone arising from the addition of three allyl moieties and a fused pyridoindoloazepinoindolone generated from the addition and subsequent cyclisation of two allyl moieties. The structures of these novel heterocycles are assigned unambiguously using extensive NMR experiments and by X-ray crystallographic analysis. The distribution of the products is influenced by the use of thermal versus microwave heating.

The aim of this work was to improve microwave heating in white sauces using different polysaccharides in their formulation; ι-, λ-and κ-carrageenan and native and modified starches were used as thickeners. Five model systems were prepared, each one with a different polysaccharide, salt, and water. Dielectric loss factor (ε'') was measured and penetration depth of the electric field was calculated at 20 and 40°C at 2450 GHz. The results showed that ε'' increased significantly (P < 0.05) when temperature rose in all the model systems. Moreover, ε'' decreased significantly (P < 0.05) when the polysaccharide concentration rose in the systems elaborated with starch (both native and modified). The penetration depth increased significantly at 40°C when native starch concentration rose. Not significant differences due to the thickener concentration were found in the depth penetration values in the other model systems, both at 20 and 40°C.

In the recent years, interactive relations between various branches of science and technology have improved interdisciplinary fields of science. In fact, most of the research activities take place somewhere among these branches. Therefore, a specialist from one branch usually can propose novel methods, whenever enters a new field, based on his previous knowledge. Taking a look at the extensive problems in the field of agriculture, an expert in the field of Electromagnetic waves can easily suggest some innovative solutions to solve them. The major suffering problems with which a farmer faces are the damages caused by the harmful pests as well as the product freezing in unexpected cold weather. The promising available biological methods of treatment have decreased the need for new treatment methods effectively. However, some advantages of electromagnetic treatment is still without competitor. The environment-friendly methods we introduce in this chapter are to use electromagnetic waves to kill pest insects without killing the taste or texture of the food they infest. Electromagnetic waves as tools in the field of agriculture have been used in many applications such as remote sensing, imaging, quality sensing, and dielectric heating in a pre-harvest or post-harvest environment. However, the goal here is to discuss about applications which are directly related to the main electromagnetic wave effect which is warming. Among variable methods applicable in the agriculture section, Radio frequency (RF) power has been known as physical (non-chemical) thermal method. In this method, the general idea is the same as heating food products to kill bacteria. It can be used to disinfest various foods and non food materials including soil. On the other hand, there are applications of using radio frequency to measure soil parameters and soil salinity, as well.

Microwave re-heating of a surimi gel may change its mechanical properties by introducing defects into the protein gel matrix. These defects result from the localized hot spots that are generated due to the non-uniform nature of microwave heating, especially at high output power. When the temperature at these hot spots is above the boiling point, the resulting high water vapor pressure may overcome the gel cohesion forces and create structural defects. This phenomenon will not take place in the absence of loci having a temperature above boiling point. The latter is the case when re-heating is done by hot water, steam, low power microwave, and even by high-power microwave, as long as the temperature is well below the boiling point. The structural changes due to these defects seem to weaken the gel structure, which is opposite to the eect caused by moisture lost.

The authors report on the results of the second phase of a four-phase program at Oak Ridge National Laboratory to develop a system to decontaminate concrete using microwave energy. The microwave energy is directed at the concrete surface through the use of an ...

Five new C-C bonded steroidal homodimers derived from deoxycholic acid, pregnenolone, and progesterone were synthesized by an olefin metathesis reaction assisted by microwave heating. Microwave improved the yield and accelerated the reaction allowing the use of less catalyst with good results (2.5 mol %). Due to the bulky nature of the steroidal skeleton the more favorable E-dimers were formed as the sole or major products depending on the linker length.

The present article deals with the influence of microwave treatment on the properties of glass-fiber reinforced composites. The cement used in the matrices of the composites was either plain ordinary portland cement or metakaolin-blended cement. Two levels of microwave power were investigated: 40 W and 80 W for 1 hour 30 minutes. The behavior of such composites was compared to that of specimens cured at ambient conditions (20°0 and at 60°C and 90°C. The mechanical behavior was assessed by means of three-point flexure tests. The microstructure was investigated using differential thermal analysis, infrared spectrometry, and scanning electron microscopy. The results obtained show that microwave treatment enhanced the pozzolanic reaction between ordinary portland cement and metakaolin and the bond between the fibers and the matrix. Interfaces between fibers and matrix were also modified. The mechanical performances of the microwave-processed composites were very interesting at early ages, but microwave heating degraded some long-term properties, such as work of fracture and toughness.

This work aims to develop a numeric model using FDTD in order relate the microwave spread, with the dielectric material heating on industry applications, standing as a base to future development of a software, which can study the microwave effects on these applications. Initially the basic issues involving the propagation of electromagnetic waves are discussed, as well as the equation that govern it. Then the mathematical treatment is performed, in order to related the known parameters to those obtained on the simulation. Lastly, experiments based in the simulated medium were performed, for the purpose of verify the error presented on the developed model. Those experiments allowed to conclude that the results numerically given, serve as a reference to situations where high precision is not necessary on the final temperature of the dielectric medium.

In order to study the heating process of water by the microwaves of 2.5-20GHz frequencies, we have performed molecular dynamics simulations by adopting a non-polarized water model that have fixed point charges on rigid-body molecules. All runs are started from the equilibrated states derived from the I c ice with given density and temperature. In the presence of microwaves, the molecules of liquid water exhibit rotational motion whose average phase is delayed from the microwave electric field. Microwave energy is transferred to the kinetic and inter-molecular energies of water, where one third of the absorbed microwave energy is stored as the latter energy. The water in ice phase is scarcely heated by microwaves because of the tight hydrogenbonded network of water molecules. Addition of small amount of salt to pure water substantially increases the heating rate because of the weakening by defects in the water network due to sloshing large-size negative ions.

The sol-gel process is a commonly used methodology for producing silica gels with tailored textural properties. However, the full conventional procedure involves several steps and is complicated and time-consuming, preventing production on a large scale. In the present study, as a more practical approach, microwave heating was applied via the acid-base synthesis of different precursor mixtures. By evaluating the effect of microwaves at each synthesis step, optimal pathways were established resulting in considerable time-saving. Mesoporous gels with porosities of around 70 per cent were obtained with a reduction in time consumption of more than 90 per cent compared to conventional methods. Strict control of the production stages has led to a much better understanding of the contribution of each stage to the overall process, making it possible to much more accurately evaluate the effects of applying microwave technology on the final properties of the materials with a view to optimizing their production.

Synthesis of silica gels with tailored textural properties using the sol-gel process has been extensively studied. However, even with the inclusion of several steps and special techniques, the entire conventional procedure is still complex and time-consuming for their large scale production. The use of microwave heating could be an effective alternative. Until now, this technology has been only used for the drying step, but it could be applied to the whole process in order to reduce the synthesis time. In the present study, silica xerogels were prepared via acid-basic synthesis from different mixtures of TEOS, ethanol and HCl (used as silica precursor, solvent and catalyst respectively). Conventional and microwave heating were applied to the precursor solutions at different exposure configurations to evaluate the effect of this technology at each step on the sol-gel process. Porosity characterization showed a positive effect of microwaves on the silica gel structure. The analysis of these porosity results evidence for the first time interactions between microwave radiation and functionalities of the reactants, offering not only a reduction around 90% of the synthesis time, but also the possibility of using moderate operating conditions and a simple process for the synthesis of silica gels.

The crystallization of the microporous AIPO, phase VPI-5 using conventional boiling and refluxing systems (CR), conventional hidrothermal reactors (CH), microwave-activated refluxing systems (MR), and microwave hydrothermal reactors (MH) have been explored. The MR synthesis yielded amorphous materials or pure VPI-5, depending of the synthesis times. The MH and CH synthesis yielded pure VPI-5 and mixtures (VPI-5+AIPO,-H3 and VPI-5+AIPO,-1 I), respectively. The CR synthesis yielded mixtures of VPI-5+AIPO,-H2. A reduction in the minimum time necessary to crystallize VPI-5 was observed when microwaves activation was used. The performances of the microwave activation techniques are explained in terms of the influence of microwaves in the change of coordination of Al in the gel, from octahedral AI(O) to tetrahedral, AI(T) to yield the specific AI(O)/AI(T) ratio in the gel precursor necessary to direct the crystallization of VPI-5, and in terms of the rapid heating obtained using microwaves, necessary to reduce the probability of formation of intermediate metastable phases.

Biodiesel has been commercially produced by transesterification of triglyceride with homogeneous base catalyst, where the separation of catalysts, glycerol and biodiesel from the product is troublesome. The solid catalyst can be used to resolve the separation problem and available to be reused. In this study metal oxide catalysts (PbO 2 , MnO 2 , Bi 2 O 3 , Fe 3 O 4 , TiO 2 , Fe 2 O 3) were selected for the transesterification. Purity of fatty acid methyl ester (FAME) in the products, which is equivalent of FAME yield, was determined for these catalysts under pressurized microwave heating condition (200 o C and 1.9 MPa). More than 89% of FAME purity was achieved with PbO 2 and MnO 2 catalyst for 30 minutes.

Numerical simulation of heat transfer during the microwave heating process of a one-dimensional (1-D) magnetite slab subjected to convective, radiative boundary conditions was performed. The governing equations representing the heating process in the slab were discretized using an explicit finite-difference approach, and a computer code was developed to predict the temperature distributions inside the slab. The heat generation from microwave irradiation dominates the initial temperature rise in the heating and the heat radiation heavily affects the temperature distribution, giving rise to a temperature peak in the predicted temperature profile. As heating continues, the temperature peak migrates inward. The microwave power level is crucial to obtain a high temperature increase rate in the initial heating period (i.e. < 60 s for magnetite). Microwave heating at 915 MHz exhibits better heating homogeneity than 2 450 MHz due to larger microwave penetration depth. To minimize/avoid temperature non-uniformity during the microwave heating the optimization of the object dimension should be considered. KEY WORDS: heat transfer; microwave processing; magnetite; heating homogeneity. * Value calculated based on the data reported in Ref. 19. ** Value calculated based on the data reported in Ref. 20. *** Values taken from Ref. 21. **** Value taken from Ref. 22.

A synthesis of novel benzimidazo[1,2-a]quinolines, substituted with piperidine, pyrrolidine and piperazine nuclei has been accomplished using an uncatalyzed amination protocol under microwave heating. All compounds were characterized by means of 1 H, 13 C NMR, IR, UV/Vis and fluorescence spectroscopy. Crystal and molecular structures of 2-chloro-and 2-piperidinyl-benzimidazo[1,2-a]quinoline-6-carbonitrile were determined by X-ray diffractometry. These molecules are essentially planar. Their molecular assembly is characterized by the existence of weak intermolecular hydrogen bonds of CeH,,,N type and pep aromatic interactions. The pep aromatic stacking observed in the solid state structures of the 2-chloroand 2-piperidinyl-derivatives are not analogous. The spectroscopic properties of these amino substituted benzimidazo[1,2-a]quinolines as their hydrochloride salts in the presence of ct-DNA were studied by means of fluorescence spectroscopy. Comparison of binding properties of amino substituted benzimidazo [1,2-a]quinoline hydrochloride salts to ct-DNA revealed significantly enhanced fluorescence emission intensity and thus offer the potential applications as a DNA-specific fluorescent probes.

To develop an in-line microwave fluid warming system that eliminates the difliculties of uneven heating that are characteristic of batch-mode microwave fluid warmers. Methods. Using a commercial microwave oven, we developed a method for warming fluid as it flowed through tubing along a defined path in the oven's cavity. Algorithms utilizing either proportional or adaptive control were used to control microwave heating cycles by varying the heating pulsewidth during 3-second epochs. Methods of fluid entry and exit were devised to minimize microwave leakage. Heating performance was tested using icewater at multiple flow rates from 18 mL/min to 105 mL/min. Results. In all warming tests, the system achieved temperature control without exceeding the maximum temperature allowable based on American Association of Blood Banks requirements. The adaptive control maintained the set temperature, with peak-to-peak oscillations of 2°C or less. Microwave leakage was below the commercially required limit for home microwave appliances. Conclusions. The combination of proportional and adaptive control is successful in controlling the permanent magnet magnetron microwave energy to heat the icewater tested. The in-line microwave warmer has the potential to become a successful medical fluid warmer. More study is needed to determine the stability of the control system under clinical conditions, and to evaluate its utility for warming blood.

Braking of emulsion is necessary in many practical applications such as the petroleum industry, agrochemical industry, food industry, pharmaceutical industry, painting and waste-water treatment in environmental technology. Chemical demulsification is the most widely applied method of treating water-in-crude oil emulsions and involves the use of chemical additives to accelerate the emulsion breaking process. The effect of chemical demulsification operations on the stability and properties of water-in-crude oil emulsions was assessed experimentally at various crude oil pH. Three different demulsifiers, BE-027, QIT-007 and WAMCO-2 demulsifiers were used for the studies. Result showed that WAMCO-2 gave the best performance with clean produced water and clean oil phase combined with sharp water-oil interphase at pH of 7.68.

This work deals with a numerical study of the potential use of microwave radiation as a heating mode for the thermoforming of wood-plastic composites (WPC). It also shows the comparison between the infrared and microwave heating modes for polypropylene (PP) and PP-based bio-composite sheets. The latter contain PP with 30% wood-based reinforcements. The differentiating parameters between the investigated bio-composite sheets were their thicknesses and the size of their reinforcements. Their thicknesses were 1, 2, 5 and 10 mm, and the size of their reinforcements were 10 0, 20 0 and 50 0 μm. The target heating temperature is 140 °C on the outer surfaces of the sheets. The results indicate that the microwaves generate a closely uniform temperature distribution in the sheets. Meanwhile, the minimum heating time is found for the bio-composites, which is 1 mm thick for the infrared mode, and the bio-composites whose reinforcements are 200 μm for the microwave mode.

Practical and simple techniques are described for using no modified domestic microwave ovens as safe and convenient laboratory devices to obtain numerous esters. In this work, an optimization of the solvent-free acetylation of natural product (diterpenoids) with acetic anhydride under microwave heating with iodine as a catalyst was performed in an eco-friendly process. The reactions were carried out under solvent-free conditions and the acetates were obtained in nearly quantitative yields with dramatic reduction of reaction time compared to standard oil-bath heating at room temperature. A complete theoretical study of the reaction has also been carried out using density functional methods (B3LYP/6-31G*)

Two kinds of typical Activated Carbons (coal based AC and coconut shell based AC) were modified in a flow of N 2 gas has been carried out using a microwave device operating at 2450 MHz and different input power, instead of a conventional furnace. The samples were analyzed by means of low temperature N 2 adsorption, elemental analysis and Boehm titration. The results show that microwave heating is an effective means of activated carbon modification. The temperature of activated carbon increases rapidly under microwave heating and then gradual increase to a quasi-stationary temperature. The pore texture of activated carbon changes slightly after microwave treatment and the two activated carbons still keep rich pore structure. The oxygen functional groups decompose and evolve with the form of CO and CO 2. This in turn gives rise to a significant decrease in oxygen content. These changes of oxygen contents increase as the microwave input power increases. During microwave treatment, a gradual decrease in the surface acidic functional groups is observed. More important, with the removal of the surface acidic groups, the number of the basic group increased gradually, the activated carbon with oxygen functional groups become basic properties material.

Microwave dielectric heating of the gas phase decomposition of H 2 S catalysed by metal sulfides on a g-Al 2 O 3 support results in significant apparent shifts in the equilibrium constant, which have been attributed to the development of hot-spots in the catalytic beds; X-ray diffraction and electron microscopy measurements have indicated the formation of hot-spots with dimensions of 90-1000 mm and which involve not only the active phase, but also the support.

wide range of coordination compounds of substitutionally-inert transition metal ions have been rapidly and conveniently synthesized using microwave dielectric loss heating effects. The compounds were synthesized in good yields in a Teflon autoclave, which can sustain temperatures up to 250°C and pressures up to 80 atm. With microwave techniques, reactions requiring 24 h take place in approximately 1 min.