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The Use of Microwave Radiation in Preparationof the Carbonaceous Adsorbents
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A new technology of obtaining activated carbons by physical and direct activation of biomass with the use of microwave radiation is described. The effect of activation temperature (700 and 800 °C) and two periods of time (15 and 30 min) on the textural parameters, acid–base character of the surface and sorption properties of activated carbons was tested. The resulting carbons were characterized by low-temperature nitrogen sorption and determination of pH as well as the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide adsorption in dry and wet conditions as well as by iodine removal from aqueous solution. The final products were adsorbents of surface area ranging from 291 to 368 m2/g and pore volume from 0.20 to 0.26 cm3/g, showing basic character of the surface. The results obtained in our study have proved that suitable choice of the pyrolysis and activation procedure for hay with the use of microwave radiation permit producing adsorbents with good capacity toward toxic gases of acidic character as well as inorganic pollutants of molecules of size similar to that of iodine molecules.
Microwave heating, in which ZnCl2 was used as activation agent and heating carrier, has been successfully used to prepare activated carbon from wood. The process is simple and only takes a few minutes. The pore structure and surface area of the as-prepared carbon materials can be tuned by simply changing the ratio of ZnCl2 to wood and the microwave heating time.
This paper describes a new method for pyrolyzing sewage sludge using a microwave furnace. It was found that if just the raw wet sludge is treated in the microwave, only drying of the sample takes place. However, if the sludge is mixed with a small amount of a suitable microwave absorber (such as the char produced in the pyrolysis itself) temperatures of up to 900 degrees C can be achieved, so that pyrolysis takes place rather than drying. Microwave treatments were also compared with those carried out in a conventional electric furnace, as well as the characteristics of their respective carbonaceous solid residues.
Pyrolysis is a promising bioconversion technique for energy recovery, waste management, and converting biomass into useful energy products which has attracted considerable attention during the past decades. Char/carbonaceous residue, bio-oil, and syngas are the three main products of the pyrolysis process. The pyrolysis technique is one of the major barriers for large-scale commercialization of this method. This study strives to extensively review the recent work on microwave-assisted technology applied to the pyrolysis process as a way of cost reduction. The fundamentals of microwave irradiation and a brief background of pyrolysis are presented. Additionally, biomass resources which can be the raw material for pyrolysis process have been categorized and reviewed in this paper. The effectual parameters of the microwave-assisted pyrolysis process and advantages of this technique have been summarized. It is concluded that microwave-assisted technology is an effectual method to reduce the pyrolysis reaction time and increases the quality of value-added products from different kinds of feedstocks. In addition, this technique can overcome the needs of feedstock shredding and improves the quality of heating as well. Therefore, it can be a suitable method for decreasing the pyrolysis processing cost and a pathway out of poverty for developing countries.
Cherry stones were used as a precursor for the preparation of activated carbons by physical and chemical activation with CO2 and KOH, respectively. The effect of pyrolysis temperature (500 and 800 °C) and activation method on the acid–base character of the surface, textural parameters as well as sorption properties of adsorbents prepared toward gas and liquid impurities was tested. Depending on the method of preparation, the final products were microporous activated carbons of surface area ranging from 361 to 1173 m2/g and pore volume from 0.21 to 0.74 cm3/g, with very diverse acid–base character of the surface. The results obtained in our study proved that a proper choice of cherry stone pyrolysis and activation procedure can produce adsorbents with high capacity for nitrogen dioxide as well as different contaminants from the liquid phase.
A new method, microwave pyrolysis, has been investigated to dispose the paper mill sludge. Microwave pyrolysis is a new fast pyrolysis technology for biomass. The effects of various different factors on paper mill sludge’s microwave pyrolysis were mainly discussed. The results showed that the mass of the paper mill sludge reduced very rapidly within the first 6 min and then flattened out with the microwave reaction time increasing; The greater the microwave power was, the faster the sludge’s pyrolysis and the more the smell and concentration of diesel smoke was; The pyrolysis performance was better when the dosage of the paper mill sludge was increased and of 5% NaOH was added as microwave absorbers; Under CO2 atmosphere, the pyrolysis performance was the best when of 5% NaOH was added, while under N2 atmosphere, the pyrolysis performance was the best when of 5% ZnCl2 was added.
This paper presents a review of microwave heating applications in environmental engineer-ing. A number of areas are assessed, including contaminated soil remediation, waste processing, minerals processing and activated carbon regeneration. Conclusions are pre-sented, which identify the areas of potential commercial development as contaminated soil vitrification, volatile organic compounds (VOC) treatment and recovery, waste sludge processing, mineral ore grinding and carbon in pulp gold recovery. Reasons are detailed why other areas have not seen investment into and implementation of microwave heating technology. These include difficulties associated with the scaling up of laboratory units to industrial capacities and a lack of fundamental data on material dielectric properties. This has meant that commercialisation of microwave heating processes for environmental engi-neering applications has so far been slow. In fact, commercialisation is only deemed viable when microwave heating offers additional process-specific advantages over conventional methods of heating. © 2002 Elsevier Science B.V. All rights reserved.
This study presents the production of activated carbon from waste tea. Activated carbons were prepared by phosphoric acid activation with and without microwave treatment and carbonisation of the waste tea under nitrogen atmosphere at various temperatures and different phosphoric acid/precursor impregnation ratios. The surface properties of the activated carbons were investigated by elemental analysis, BET surface area, SEM, FTIR. Prior to heat treatment conducted in a furnace, the mixture of the waste tea and H3PO4 was treated with microwave heating. The maximum BET surface area was 1157 m2/g for the sample treated with microwave energy and then carbonised at 350 °C. In case of application of conventional method, the BET surface area of the resultant material was 928.8 m2/g using the same precursor and conditions. According to the Dubinin–Radushkevich (DR) method the micropore surface area for the sample treated with microwave energy was higher than the sample obtained from the conventional method. Results show that microwave heating reasonably influenced the micropore surface area of the samples as well as the BET surface area.The samples activated were also characterised in terms of the cumulative pore and micropore volumes according to the BJH, DR and t-methods, respectively.
Activated carbons (ACs) prepared from peat were used for benzene adsorption (5 ppmv) from dry and humid (relative humidity (RH) 70%) air streams. Benzene uptake by the ACs was lower in the presence of water vapor due to competition between benzene and water molecules for the adsorption sites. Adsorption of benzene from dry and humid air on the ACs with low content of surface oxygen groups was attributed to the presence of narrow micropores (size <0.7 nm). A linear correlation between the amount of adsorbed benzene and micropore volume calculated from CO2 adsorption isotherms was found. The coefficients of determination R2 were 0.87 for benzene adsorption in the absence of water vapor and 0.83 for adsorption at relative humidity 70%. It was shown that the presence of surface groups in the ACs reduces benzene uptake more profoundly in the presence of moisture than in the dry conditions.
Bituminous coal-based activated carbon was modified by impregnation with melamine and heat treatment at 850 °C. Another sample was impregnated with melamine and urea and heat treated at 650 and 850 °C. Chemical and physical properties of the materials were determined using Boehm titration, thermal analysis, sorption of nitrogen and SEM with EDX. Then the H2S breakthrough capacity tests were carried out and the sorption capacity was calculated. The results revealed that carbons modified with nitrogen-containing species and heat-treated at 850 °C have a hydrogen sulfide removal capacity exceeding more then 10 times the capacity of unmodified sample. H2S on the surface of these materials is oxidized to sulfuric acid and elemental sulfur and stored in the pore system. New carbons are hypothesized to act as catalytic reactors promoting two different pathways of hydrogen sulfide oxidation in two different locations. In small micropores, where water is present, hydrogen sulfide dissociate to HS− ions and those ions are oxidized to sulfur radicals and sulfur dioxide leading to the formation of sulfuric acid. In larger pores with incorporated nitrogen, basic sites promote dissociation and formation of sulfur polymers, which are resistant to further oxidation.
In microwave processing, energy is supplied by an electromagnetic field directly to the material. This results in rapid heating throughout the material thickness with reduced thermal gradients. Volumetric heating can also reduce processing times and save energy. The microwave field and the dielectric response of a material govern its ability to heat with microwave energy. A knowledge of electromagnetic theory and dielectric response is essential to optimize the processing of materials through microwave heating. The fundamentals of electromagnetic theory, dielectric response, and applications of microwave heating to materials processing, especially fiber composites, are reviewed in this article.
In this study, the drying of wood by microwave energy using a continuous microwave belt drier was compared to that by conventional method. By using a continuous microwave belt drier, the microwave power was generated by means of 14 compressed air-cooled magnetrons of 800 W each that gives a maximum of 11.2 kW. The power setting could be adjusted individually in 800 W steps. Most importantly, this work focuses on the investigation of drying phenomena under microwave environment. In this analysis, the effects of the irradiation time and microwave power level on overall drying kinetics and mechanical properties were studied. The results showed that using the continuous microwave applicators technique has several advantages over the conventional method such as shorter processing times, volumetric dissipation of energy throughout a product, high energy efficiency as well as improvements in product quality. The results presented here provide a fundamental understanding of microwave-heating of various kinds of dielectric materials.
The present study attempts to utilize coconut shell to prepare activated carbon using agents such as steam, CO(2) and a mixture of steam-CO(2) with microwave heating. Experimental results show that the BET surface area of activated carbons irrespective of the activation agent resulted in surface area in excess of 2000 m(2)/g. The activation time using microwave heating is very much shorter, while the yield of the activated carbon compares well with the conventional heating methods. The activated carbon prepared using CO(2) activation has the largest BET surface area, however the activation time is approximately 2.5 times higher than the activation using steam or mixture of steam-CO(2). The chemical structure of activated carbons examined using Fourier transformed infra-red spectra (FTIR) did not show any variation in the surface functional groups of the activated carbon prepared using different activation agents.
Wykorzystanie promieniowania mikrofalowego w technologii adsorbentów węglowych
- L Czepirski
- B Łaciak
- E Komorowska-Czepirska
Czepirski L., Łaciak B., Komorowska-Czepirska E., Wykorzystanie promieniowania mikrofalowego w technologii adsorbentów węglowych, [w:] Węgiel aktywny w ochronie środowiska
i przemyśle, Wydawnictwo Politechniki Częstochowskiej, Częstochowa 2006.
Zastosowanie promieniowania mikrofalowego w technologii adsorpcyjnej
- M Rumian
- L Czepirski
Rumian M., Czepirski L., Zastosowanie promieniowania mikrofalowego w technologii adsorpcyjnej, Przemysł Chemiczny 2005, 85, 329-332.