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In the present study, the dielectric heating option was investigated for various dry materials: USY zeolite, ZSM-5 zeolite, and α- & γ-alumina. These materials are characterized by low effective dielectric loss factors; therefore they are often considered as not accessible for direct dielectric heating. Applying technically relevant volumes up to 20 L, dielectric heating could be demonstrated for all these materials when employing radio waves (RW) whereas heating with microwaves (MW) was difficult or even impossible. Dielectric heating experiments were also simulated with the CST electromagnetic simulation software. It could be shown that for all tested materials RW heating is more suitable than MW heating with regard to heating rates, temperature rise (both at equal power input) and homogeneity of the temperature pattern. The comparison of experimental data and simulation shows an excellent agreement. Thus, dielectric heating utilizing frequencies in the MHz range (radio-frequencies, RF) was demonstrated to be well applicable, even for materials with low loss factors, up to technically relevant temperatures and scales. This study also includes the evaluation of the energy efficiency for RW heating on the basis of the heating and power input data. Reasons for lower efficiencies, even under optimal fitting conditions applying an electronic matching network, are discussed and interpreted using literature and own experimental results, namely temperature-programmed desorption (TPD). [ABSTRACT FROM AUTHOR]

In the present study, the dielectric heating option was investigated for various dry materials: USY zeolite, ZSM-5 zeolite, and α- & γ-alumina. These materials are characterized by low effective dielectric loss factors; therefore they are often considered as not accessible for direct dielectric heating. Applying technically relevant volumes up to 20 L, dielectric heating could be demonstrated for all these materials when employing radio waves (RW) whereas heating with microwaves (MW) was difficult or even impossible. Dielectric heating experiments were also simulated with the CST electromagnetic simulation software. It could be shown that for all tested materials RW heating is more suitable than MW heating with regard to heating rates, temperature rise (both at equal power input) and homogeneity of the temperature pattern. The comparison of experimental data and simulation shows an excellent agreement. Thus, dielectric heating utilizing frequencies in the MHz range (radio-frequencies, RF) was demonstrated to be well applicable, even for materials with low loss factors, up to technically relevant temperatures and scales. This study also includes the evaluation of the energy efficiency for RW heating on the basis of the heating and power input data. Reasons for lower efficiencies, even under optimal fitting conditions applying an electronic matching network, are discussed and interpreted using literature and own experimental results, namely temperature-programmed desorption (TPD). [ABSTRACT FROM AUTHOR]

In the present study, the dielectric heating option was investigated for various dry materials: USY zeolite, ZSM-5 zeolite, and α- & γ-alumina. These materials are characterized by low effective dielectric loss factors; therefore they are often considered as not accessible for direct dielectric heating. Applying technically relevant volumes up to 20 L, dielectric heating could be demonstrated for all these materials when employing radio waves (RW) whereas heating with microwaves (MW) was difficult or even impossible. Dielectric heating experiments were also simulated with the CST electromagnetic simulation software. It could be shown that for all tested materials RW heating is more suitable than MW heating with regard to heating rates, temperature rise (both at equal power input) and homogeneity of the temperature pattern. The comparison of experimental data and simulation shows an excellent agreement. Thus, dielectric heating utilizing frequencies in the MHz range (radio-frequencies, RF) was demonstrated to be well applicable, even for materials with low loss factors, up to technically relevant temperatures and scales. This study also includes the evaluation of the energy efficiency for RW heating on the basis of the heating and power input data. Reasons for lower efficiencies, even under optimal fitting conditions applying an electronic matching network, are discussed and interpreted using literature and own experimental results, namely temperature-programmed desorption (TPD). [ABSTRACT FROM AUTHOR]

The influence of electrical heating on microbiological processes in soil has been studied to evaluate the potential for enhancing biodegradation of pollutants by controlling the temperature. A frequency of 50 Hz (power line frequency) was applied for resistive heating. Dielectric heating was realized using a frequency of 13.56 MHz (radio frequency). Both techniques were compared with conventional heating in a water bath. For experiments in laboratory and full scale, a model soil and a contaminated original soil were used. It was shown that under conditions capable for heating soil to 35 °C or even 60 °C, soil respiration as a measure for microbial activity was not hindered by electrical heating when temperature and moisture content were comparable with conventional heating. The variations of soil respiration were reversible upon temperature changes. Under certain conditions, periodical fluctuations of microbiological activity were observed. Several possible explanations including chronobiology are discussed without being able to provide an unambiguous interpretation for this effect. [ABSTRACT FROM AUTHOR]

By utilizing the specific influence of water adsorption on the dielectric loss factor and, consequently, selective heating of the zeolite NaY in a radio-frequency (RF) electromagnetic field, a hot zone moving through the packed bed can be realized initiated by water injection. While the effect of water adsorption on RF heating and the phenomenon of the thermo-chromatographic pulse (TCP) itself were described in a previous paper, the present study presents a detailed model for the description and explanation of this effect. It involves the complex dependence of dielectric loss on temperature and moisture content, a diffusion model considering both hopping and Knudsen mechanisms and a power balance for a representative segment of the packed bed. The developed model was successfully applied to adequately describe various experimental situations observed for selective RF heating in a NaY zeolite bed. [ABSTRACT FROM AUTHOR]

In the present study, the astonishing influence of water dosage on a purged dry packed bed of NaY zeolite in the presence of an electric field with a frequency of 13.56 MHz was investigated. The injection of a small amount of water to the inlet of the bed led to pronounced selective heating of the inlet zone by more than 150 K. Thus, water represented a very effective coupling medium for dielectric heating. The selectively heated zone then slowly moved through the whole packed bed and a water pulse finally left the zeolite. This effect correlated with a coupled water and heat flux was called thermo-chromatographic pulse (TCP) emphasizing its analogy to chromatography. The phenomenon could not be performed by using conventional (convective) or microwave heating. It was demonstrated under various conditions and explained by a new model based on own experimental results as well as data from literature. The model will be the objective of a forthcoming publication. [ABSTRACT FROM AUTHOR]

Two types of iron-containing zeolites, Fe-ZSM5 and Fe-Beta, were tested as catalysts for wet peroxide oxidation of organic groundwater contaminants such as trichloroethene (TCE) and methyl tert-butyl ether (MTBE) at nearly neutral pH. Adsorption of TCE is more favorable on the ZSM5 zeolite whereas MTBE is effectively adsorbed on Beta zeolite. Batch experiments showed that the efficiency of utilization of H2O2 for contaminant degradation is more favorable for the catalyst with the higher adsorptive enrichment of the respective contaminant. Laboratory-scale column experiments, including the use of contaminated groundwater, were conducted in order to test the stability of the Fe-zeolites under flow-through conditions. [ABSTRACT FROM AUTHOR]

Selective dielectric heating using the influence of a coupling medium such as water can lead to the formation of combined temperature-mass transport pulses moving through a packed bed. Depending on the dielectric and sorption properties of the material these so-called thermo-chroma- tographic pulses (TCP) can cause large temperature differences between the starting temperature and the peak temperature in the pulse. The impregnation of porous substances with various salts was shown to be a simple method for improving material properties leading to the formation of stable TCP. This procedure was proven to only slightly reduce the specific surface area and the sorption capacity towards organic compounds of the investigated sorbents. Consequently, a wide spectrum of silica gels, zeolites and porous alumina can be applied as matrices for TCP-based processes in chemical engineering and environmental technology. [ABSTRACT FROM AUTHOR]

The occurrence and extent of selective dielectric heating with microwaves (MW) and radio waves (RW) was studied with a variety of model systems using temperature-programmed desorption (TPD). Over a wide pressure and temperature range, selectivity effects were neither found for polar adsorbates (compared to non-polar compounds) nor expressed by an overheating of metal clusters" supported on a nearly MW- and RW-transparent support. In contrast, significant temperature gradients between particles consisting of materials with various dielectric losses could be established under certain conditions. The utilization of adsorbates significantly modifying the dielectric properties of a material was investigated as a further approach to initiate selective dielectric heating. Applying water as a coupling medium, a combined heat and mass transport, which we call a thermo-chromatographic pulse, can be created in a packed-bed column consisting of various zeolites. In this case, selective heating of bed zones by more than 100 K was observed. The suitability of a material for the creation of thermo-chromatographic pulses depends on its" dielectric properties as well as on its sorption properties with respect to water or other coupling media. The study provided further insight into not only the potential but also the limitations of selective dielectric heating of solid materials relevant to chemical engineering, environmental technology and sorption processing. [ABSTRACT FROM AUTHOR]

In general, soils without the vegetation growing on them are regarded as sources of CO 2 . However, there are indications that CO 2 is also fixed by soil microorganisms. Although this process is not significant from a quantitative point of view, it may change the isotopic composition of soil organic matter. Therefore, we conducted an incubation study with soil and 13 C-labeled CO 2 to investigate this process. We found that the label was transferred from CO 2 into organic compounds in soil. At the end of a 61-day incubation period, 1.3 µmol C g -1 soil, corresponding to ~0.08% of the soil organic carbon, had been fixed. CO 2 may, therefore, be an additional source of soil organic carbon. Compound-specific analysis of amino sugars, amino acids, and fatty acids indicated that the label is incorporated into microbial, mainly bacterial, biomass. All groups of microorganisms were involved in the assimilation of CO 2 , but the relatively high enrichment of mono-unsaturated and mid-chain branched fatty acids indicates that gram negative bacteria and actinomycetes may be slightly more important in this process than other groups of microorganisms. [ABSTRACT FROM AUTHOR]