Microwave-assisted regeneration of activated carbons loaded with pharmaceuticals

8 pages, 4 figures, 2 tables.-- PMID: 17572468 [PubMed].-- Printed version published Aug 2007.The purpose of this work was to explore the application of microwaves for the regeneration of activated carbons spent with salicylic acid, a metabolite of a common analgesic frequently found in wastewater from the pharmaceutical industry. The exhausted carbon was treated in a quartz reactor by microwave irradiation at 2450 MHz at different temperatures and atmospheres, the regeneration efficiency being highly dependent on the operating conditions. Quantitative desorption of the pollutant was achieved at high temperature and oxidizing atmosphere, with regeneration efficiencies as high as 99% after six cycles. The stripping efficiency was superior to 95% at high temperatures and decreased at 450ºC. The incomplete desorption of the adsorbate at low temperature was further confirmed by the changes in the porosity observed by N2 and CO2 adsorption isotherms. Hence, micropores remain blocked which results in a reduction in loading capacities in successive cycles.The authors thank Química Farmacéutica Bayer for kindly providing the adsorbent and for financial support. COA thanks the CSIC I3P Program, co-financed by the European Social Fund, for a postdoctoral contract.Peer reviewe

Effect of microwave and conventional regeneration on the microporous and mesoporous network and on the adsorptive capacity of activated carbons

The effect of different heating mechanisms on the porous network of activated carbons (AC) previously exhausted with phenol has been studied. To this end, thermal treatment of the exhausted AC was performed using two experimental devices: a single mode microwave device operating at 2450 MHz and a conventional electric furnace. By employing microwave energy, the regeneration time was considerably shortened compared to conventional thermal heating. Moreover, microwave heating preserved the porous structure of the regenerated AC more efficiently than treatment in a conventional device. In both cases successive regeneration cycles reduced the microporosity of the activated carbons. However, conventional heating shifted the micropore size distribution to pores of narrower sizes. The apparent BET surface areas were also reduced significantly over the regeneration cycles. A loss of the adsorptive capacity of the carbon material was observed after six adsorption–desorption cycles in both systems. The phenol adsorption capacities decreased to a greater extent in the samples regenerated in the electric furnace.Work carried out with a financial grant from the European Coal and Steel Community (Project 7220-PR-139). The authors wish to thank Dr. Martín-Gullón for his considerate and helpful assistance with the software tool used for the DRS calculation.Peer reviewe

Comparison between the reactivity of coal and synthetic coal models

A mixture of carbon compounds was pyrolysed under an inert atmosphere at different temperatures in a fixed bed reactor. The resultant chars were characterised in terms of texture and thermal behaviour. Textural characterisation of the chars was carried out by N2 and CO2 adsorption isotherms at −196 and 0 °C, respectively. Char isothermal reactivity in air at 500 °C, and in CO2 at 1000 °C, was performed in a thermogravimetric analyser (TGA). Temperature-programmed combustion tests under 20% oxygen in argon were also performed in the TGA linked to a mass spectrometer (TGA/MS). The results showed that char textural properties do not always relate well to their reactivity. Not only do physical properties (e.g. surface area, porosity) but also chemical properties (e.g. active sites concentration and distribution) play an important role in the reaction of carbonaceous material and oxidant. On the other hand, in terms of chemical composition the chars obtained from the mixture of carbon compounds were very similar to the chars produced under the same experimental conditions by a high volatile bituminous coal. The fact that carbon compounds are well known makes it easier to obtain knowledge about the functional groups present in synthetic char, and to study the mechanisms of heterogeneous reactions such as the reduction of NO with carbon.Peer reviewe

Kinetic models comparison for non-isothermal steam gasification of coal–biomass blend chars

The non-isothermal thermogravimetric method (TGA) was applied to a bituminous coal (PT), two types of biomass, chestnut residues (CH) and olive stones (OS), and coal–biomass blends in order to investigate their thermal reactivity under steam. Fuel chars were obtained by pyrolysis in a fixed-bed reactor at a final temperature of 1373 K for 30 min. The gasification tests were carried out by thermogravimetric analysis from room temperature to 1373 K at heating rates of 5, 10 and 15 K min−1. After blending, no significant interactions were detected between PT and CH during co-gasification, whereas deviations from the additive behaviour were observed in the PT–OS blend. However, for the two coal–biomass blends, the gasification behaviour resembled that of the individual coal, as this component constituted the larger proportion of the blend. The temperature-programmed reaction (TPR) technique was employed at three different heating rates to analyze noncatalytic gas–solid reactions. Three nth-order representative gas–solid models, the volumetric model (VM), the grain model (GM) and the random pore model (RPM) were applied in order to describe the reactive behaviour of the chars during steam gasification. From these models, the kinetic parameters were determined. The best model for describing the reactivity of the PT, PT–CH and PT–OS samples was the RPM model. VM was the model that best fitted the CH sample, whereas none of the models were suitable for the OS sample.This work was carried out with financial support from the Spanish MICINN (Project PS- 120000-2006-3, ECOCOMBOS), and co-financed by the European Regional Development Fund, ERDF.Peer reviewe

CO2 capture by adsorption with nitrogen enriched carbons

9 pages, 7 figures, 3 tables.-- Printed version published Sep 2007.-- Issue title: The 6th European Conference on Coal Research and its Applications.The success of CO2 capture with solid sorbents is dependent on the development of a low cost sorbent with high CO2 selectivity and adsorption capacity. Immobilised amines are expected to offer the benefits of liquid amines in the typical absorption process, with the added advantages that solids are easy to handle and that they do not give rise to corrosion problems. In this work, different alkylamines were evaluated as a potential source of basic sites for CO2 capture, and a commercial activated carbon was used as a preliminary support in order to study the effect of the impregnation. The amine coating increased the basicity and nitrogen content of the carbon. However, it drastically reduced the microporous volume of the activated carbon, which is chiefly responsible for CO2 physisorption, thus decreasing the capacity of raw carbon at room temperature.This work was carried out with financial support from the Spanish MEC (Project CTM2005-03075/TECNO). M.G.P. and C.P. acknowledge the support from the CSIC I3P Program co-financed by the European Social Fund.Peer reviewe

Proceso asistido por microondas para la obtención de materiales carbonosos de naturaleza básica y dispositivo

Describe un dispositivo y proceso para modificar la química superficial de de materiales carbonosos utilizando un horno microondas.Peer reviewe

Oxygen-induced Decrease in the Equilibrium Adsorptive Capacities of Activated Carbons

Special attention was paid in this work to the role of surface chemistry in the adsorption of phenol and salicylic acid onto activated carbons. To this end, two commercial activated carbons (granular and powdered) were oxidised using ammonium peroxodisulphate [(NH4) 2S2O8] and nitric acid in different concentrations. The structural and chemical properties of the oxidised adsorbents were characterised via nitrogen adsorption isotherms measured at –196 ° C and Boehm titrations. Phenol adsorption from solution at low concentration was studied at room temperature without specific pH control of the solution. The results showed a significant reduction in the adsorptive capacities towards phenol of the activated carbons as the oxygen content of the latter increased. However, very little effect was observed towards the retention of salicylic acid. The decrease in adsorptive capacity depended not only on the amount of oxygen per unit mass of activated carbon, but also on the textural properties of the latter.The authors wish to thank the European Commission and the Spanish Ministry of Science and Technology (Research Project 1FD 1997-0400-CO2-01) for financial support. The SEM micrographs were obtained with the help of D. Álvarez (INCAR-CSIC, Spain).Peer reviewe

Simultaneous thermogravimetric–mass spectrometric study on the pyrolysis behaviour of different rank coals

Simultaneous thermogravimetry–mass spectrometry was used to study the pyrolysis behaviour of an anthracite and three bituminous coals of different volatile matter content. This system was optimised by using calcium oxalate as a reference for calibration. A normalisation method that permitted a semiquantitative comparison between the volatile species of the coals was also developed. The instantaneous evolution of the volatile compounds was studied by means of temperature-programmed pyrolysis experiments. The peaks varied in shape, temperature and size, and showed a marked dependence on coal rank. This can be attributed to the varying amounts of the different functional groups in the coals studied. Special attention was paid to the nitric oxide released during pyrolysis, together with its precursor species.Work carried out with a financial grant from the European Coal and Steel Community (Project 7220-ED/094). Fellowship support to A.Arenillas by DGICYT is also acknowledged.Peer reviewe

Combustibility behaviour of coal and biomass blends under O2-CO2 mixtures

Oxy-fuel combustion is a GHG abatement technology in which coal is burned using a mixture of oxygen and recycled flue gas to obtain a rich stream of CO2 ready for sequestration. A thermobalance and an entrained flow reactor (EFR) were used in this work to study the combustibility of coals and blends with biomass under oxy-fuel conditions. Mixtures of CO2/O2 of different concentrations were used and compared with air as reference. Combustion profiles were performed in the thermobalance and burnout temperatures were calculated from these results. During these tests, it was observed that CO2 concentration exerts a low effect on the combustibility of the samples. In addition, interactions between coal and biomass were negligible. In the EFR tests it was observed that the burnout of coals and blends with a mixture of 79%CO2-21%O2 was lower than in air. However, an improvement in the burnout was achieved when the oxygen concentration was higher than 30%. The results of this work indicate that coal burnout can be improved by blending biomass with coals under CO2/O2 mixtures.Spanish MEC (Ministerio de Educación y Ciencia), Project: “Procesos avanzados de generación, captura y almacenamiento de CO2. Oxicombustión”). CSIC, I3P Program co-financed by the European Social Fund.Peer reviewe

Microwave-assisted regeneration of activated carbons loaded with pharmaceuticals

8 pages, 4 figures, 2 tables.-- PMID: 17572468 [PubMed].-- Printed version published Aug 2007.The purpose of this work was to explore the application of microwaves for the regeneration of activated carbons spent with salicylic acid, a metabolite of a common analgesic frequently found in wastewater from the pharmaceutical industry. The exhausted carbon was treated in a quartz reactor by microwave irradiation at 2450 MHz at different temperatures and atmospheres, the regeneration efficiency being highly dependent on the operating conditions. Quantitative desorption of the pollutant was achieved at high temperature and oxidizing atmosphere, with regeneration efficiencies as high as 99% after six cycles. The stripping efficiency was superior to 95% at high temperatures and decreased at 450ºC. The incomplete desorption of the adsorbate at low temperature was further confirmed by the changes in the porosity observed by N2 and CO2 adsorption isotherms. Hence, micropores remain blocked which results in a reduction in loading capacities in successive cycles.The authors thank Química Farmacéutica Bayer for kindly providing the adsorbent and for financial support. COA thanks the CSIC I3P Program, co-financed by the European Social Fund, for a postdoctoral contract.Peer reviewe