A novel approach for characterizing carbon catalysts by tap experiments

Two samples were used in this study: a coal based carbon obtained by carbonisation and a gas-phase oxidized sample from the raw carbon. These samples were extensively characterized and their NO removal capacity was also determined. TAP-2 (Temporal Analysis of Products) reactor was used to obtain adsorption parameters and diffusion coefficients of the system NO-carbon catalyst. The diffusivity of NO as well as the enthalpy of adsorption does not change after increasing the number of functional groups by an oxidative pretreatment of the carbon.Peer reviewe

Nitric oxide removal from flue gases by carbon-enriched coal fly ash

The aim of this work is to evaluate the characteristics of activated and non-activated carbons obtained from carbon-enriched coal fly ash (CECFA) from two different power stations in order to be used in the low temperature reduction of NO from stack gases. Carbon-rich fractions were obtained by mechanical sieving of fly ashes and by oil agglomeration. Activation of some samples was carried out in steam at 900ºC in order to develop porosity onto the samples. The obtained activated and non-activated samples were characterized by several techniques and their nitric oxide removal capacity at low temperature using ammonia as reducing agent was evaluated (gas conditions: 150 ºC, 1000 µL/L NO, 1200 µL/L NH3 , 60 mL/L O2, Ar as balance). CECFA obtained only by sieving had carbon contents varying from 1 % to 47 % and NO reduction levels varying from 3 % to 29%. CECFA L2A and E2A, obtained by sieving, agglomeration and further activation, contained 66 % and 57 % of carbon respectively, and their NO conversion was 36 % and 48%. BET surface areas of CECFA samples before activation were in all case below 20 m2/g. In the case of activated samples, L2A and E2A, the surface area increased to 217 and 395 m2/g respectively. In all cases, and comparing samples with the same carbon content, CECFA coming from Escucha fly ash demonstrated higher NO conversion capacity. The obtained results show that carbon content, surface area and parent coal type are the main parameters that influence the NO removal capacity of the obtained CECFA.The Spanish Ministry of Science and Innovation and the European Community (European Regional Development Fund) (Project No. CTM2004- 04252C02).Peer reviewe

Assessment of hydrogen storage in activated carbons produced from hydrothermally treated organic materials

12 activated carbons (ACs) were prepared by KOH activation using hydrochars as precursors. These hydrochars were prepared by hydrothermal carbonisation (HTC) of sucrose solutions at concentrations ranging from 0.2 to 1.6 mol L-1. The KOH to hydrochar weight ratio (W) was varied from 1 to 5, and the activation temperature was set to 1023K. ACs texture was assessed by nitrogen and carbon dioxide adsorption at 77 and 273 K, respectively; pore size distribution was calculated by using both isotherms and the SAIEUS© software. ACs with surface areas between 790 and 2240 m2 g-1 were obtained. Hydrogen excess adsorption was determined at 298K and pressures up to 10 MPa in a volumetric device, and the isosteric heat of adsorption (Qst) was calculated for four ACs, using hydrogen isotherms obtained at 278, 298 and 308K. Potassium intercalation between graphitic planes was assumed to account for the high Qst values, 7-8 kJ mol-1. Hydrogen uptake at 2 MPa was compared with hydrogen adsorption data of 38 other ACs reported in the open literature. Hydrogen adsorption fundamentally depends on micropore volume and preliminary HTC did not enhance hydrogen storage although it could be a good strategy for doping carbon with heteroelements.The authors gratefully acknowledge the financial support of the CPER 2007-2013 “Structuration du Pôle de Compétitivité Fibres Grand’Est” (Competitiveness Fibre Cluster), through local (Conseil Général des Vosges), regional (Région Lorraine), national (DRRT and FNADT) and European (FEDER) funds. Part of this work was supported by CHEERS project (FEDER funds) and the COST Action MP1103 “Nanostructured materials for solid-state hydrogen storage”.Peer reviewe

Estudio preliminar de captura de mercurio con sorbentes regenerables basados en Au/C

El presente trabajo se ha realizado en el Instituto de Carboquímica, CSIC y está enmarcado dentro del Proyecto del Ministerio de Ciencia e Innovación CTQ2008-06860-C02-02 titulado “Monolitos de carbono para aplicaciones medioambientales: captura de mercurio con sorbentes regenerables”. El origen de esta investigación surge de la necesidad de desarrollar nuevas tecnologías de captura de mercurio que sean efectivas, de bajo coste y que no generen un gran volumen de residuos tóxicos. Por lo tanto, el objetivo del presente Trabajo Fin de Máster es el desarrollo de sorbentes regenerables, basados en nanopartículas de oro, que sean capaces de retener el mercurio mediante un proceso de amalgamiento con el oro y que sean capaces de desorberlo mediante un calentamiento ligero del propio sorbente. Para alcanzar el objetivo citado, se han preparado y caracterizado diferentes soportes de material carbonoso a partir de monolitos de carbono comerciales, a los cuales se les aplicó diferentes tratamientos que permitieron la modificación de su química superficial. La deposición de oro sobre los soportes se ha llevado a cabo a partir de sal de oro siguiendo dos metodologías diferentes: i) reducción directa del Au3+ sobre el soporte y ii) deposición de oro coloidal. Se pretende conseguir la deposición de partículas de oro de tamaño nanométrico. Una vez depositado el oro nanoparticulado, los sorbentes se caracterizaron mediante diferentes técnicas. Más concretamente, se utilizó la microscopía electrónica de barrido (SEM) de emisión de campo (FE) para conocer la distribución de nanopartículas de Au en los sorbentes y la espectroscopía de emisión óptica por plasma de acoplamiento inductivo, (ICP-OES) para determinar su contenido en oro. Además, también se estudiaron los estados de oxidación del oro, una vez depositado sobre el soporte, de manera tanto cualitativa como cuantitativa, mediante espectrometría fotoelectrónica de Rayos X (XPS) y, de este modo, conocer la fracción de oro no reducido presente en los sorbentes antes y después del tratamiento de reducción. Una vez caracterizados los sorbentes, se evaluó su capacidad de captura del mercurio a distintas temperaturas comprendidas dentro del rango: 50-150 ºC, en atmósfera inerte. Los experimentos de retención se llevaron a cabo por duplicado para los dos tipos de sorbentes estudiados, obteniéndose para el caso más favorable una retención de 19,8 mg Hg/g de Au. Paralelamente, se estudió la variación de la estructura cristalina del oro antes y después de su amalgamiento con el mercurio mediante difracción de rayos X (XRD) comprobando que ésta no varía. Finalmente, se realizó un estudio de regenerabilidad de los sorbentes, llevando a cabo ciclos de captura de mercurio-regeneración. Se observó una elevada repetitividad en los ciclos, indicando que la capacidad de retención del sorbente no se ve afectada de forma significativa después de varios ciclos de retención-regeneración

Carbones activados

págs.: 17-58Capítulo incluido en el libro: Desarrollo y aplicaciones de materiales avanzados de carbón. Miguel Ángel Álvarez Merino, Francisco Carrasco Marín, Francisco José Maldonado Hódar (Editores). Sevilla: Univeridad Internacional de Andalucía, 2014. ISBN: 978-84-7993-247-3. Enlace: http://hdl.handle.net/10334

Influence of activation atmosphere used in the chemical activation of almond shell on the characteristics and adsorption performance of activated carbons

7 pages, 5 figures, 5 tables.The aim of this work was to compare the effect of different activating atmospheres on the final properties and adsorption performance of activated carbons. Almond shell based activated carbons have been obtained by chemical activation with phosphoric acid. Two sets of activated carbons were prepared. First set was prepared under inert atmosphere at different impregnation ratios, temperatures and times of activation. Second set of activated carbons was prepared at the same activating conditions except the activating atmosphere using an oxidant one. Activated carbons prepared under both activation atmospheres were characterized by elemental analysis (EA), thermogravimetry (TGA), temperature programmed desorption (TPD), point zero charge (PZC), Boehm titration and N 2 physisorption. To study the adsorption performance of the activated carbons toluene adsorption – desorption isotherms were determined gravimetrically. The results obtained con fi rm that the activating atmosphere has a strong in fl uence on the fi nal characteristics of the activated carbons. Activated carbons with higher oxygen content and more negative surface charge have been obtained by changing the activatingatmospherebyanoxidantone.Surfaceareaisalsohigherforactivatedcarbonspreparedunderoxidant atmosphere. However toluene adsorption capacity is lower for activated carbons prepared under oxidant atmo- sphere due to their surface chemistry. © 2013 Elsevier B.V. All rights reserved.The financial support from Spanish Ministry of Environment (contracts 439/2006/3- 11.2 and B030/2007/2-11.2) is duly recognized.Peer reviewe

NO removal in the selective catalitic reduction process over Cu and Fe exchanged type Y zeolites synthesized from coal fly ash

The nitric oxide (NO) removal capacity of ion-exchanged zeolite Y obtained from coal combustion fly ash was evaluated in this work. Zeolite Y was exchanged either with Cu2+ or Fe2+ to obtain two different catalysts for the selective catalytic reduction of NOx from flue gas. The selective catalytic reduction experiments were carried out at temperatures ranging from 50°C to 350°C, water content 0% and 5% and 5% O2. In the absence of water, a total conversion of NO is obtained at 200°C for both zeolites, but important differences were found between zeolites LY-Cu and LY-Fe in the reduction of NO at temperatures lower than 200°C, and especially in the presence of water, that could be attributed to the different temperatures at which active species Cu2+ and Fe3+ are available for both ion-exchanged zeolites at the studied conditions. The greater surface area of zeolite LY-Cu can also contribute to its higher activity.The Spanish Ministry of Science and Innovation and the European Community (European Regional Development Fund) provided financial support for this work (Project No. CTM04252C02).Peer reviewe

Influence of temperature and regeneration cycles on Hg capture and efficiency by structured Au/C regenerable sorbents

8 pages, 10 figures, 2 tables.The objective of this work is to evaluate a novel regenerable sorbent for mercury capture based on gold nanoparticles supported on a honeycomb structured carbon monolith. A new methodology for gold nanoparticles deposition onto carbon monolith support has been developed to obtain an Au sorbent based on the direct reduction of a gold salt onto the carbon material. For comparison purposes, colloidal gold method was also used to obtain Au/C sorbents. Both types of sorbents were characterized by different techniques in order to obtain the bulk gold content, the particle size distribution and the chemical states of gold after deposition. The mercury capture capacity and mercury capture efficiency of sorbents were tested in a bench scale facility at different experimental conditions. The regenerability of the sorbents was tested along several cycles of Hg capture-regeneration. High retention efficiencies are found for both types of sorbents comparing their gold content. Moreover, the high retention efficiency is maintained along several cycles of Hg capture-regeneration. The study of the fresh sorbent, the sorbent after Hg exposition and after regeneration by XPS and XRD gives insight to explain those results. © 2013 Elsevier B.V.The financial support from Spanish Ministry of Science and Innovation and European Regional Development Funds (ref: ENE2011-23412) is duly recognized. C. Gómez- Giménez wants to thank CSIC and European Regional Development Funds for JAE grant.Peer Reviewe

Carbon-enriched coal fly ash as a precursor of activated carbons for SO2 removal

Carbon-enriched coal fly ash was evaluated in this work as a low-cost adsorbent for SO2 removal from stack gases. The unburned carbon in coal fly ash was concentrated by mechanical sieving and vegetal oil agglomeration. The carbon concentrates were activated with steam at 900ºC in order to develop porosity onto the samples. The performance of these samples in the SO2 abatement was tested in the following conditions: 100ºC, 1000 ppmv SO2, 5% O2, 6% water vapor. A good SO2 removal capacity was shown by some of the studied samples that can be related to their textural properties. Cycles of SO2 adsorption/regeneration were carried out in order to evaluate the possibility of thermal regeneration and re-use of these carbons. Regeneration of the exhausted carbons was carried out at 400ºC of temperature and a flow of 25 ml/min of Ar. After each cycle, the SO2 removal capacity of the sample decreases.Ministerio de Educación y Ciencia, EU (FEDER) CTM2004-04252-C02Peer reviewe

A critical short review of equilibrium and kinetic adsorption models for VOCs breakthrough curves modelling

Volatile organic compounds emission has important effects over the environment and human beings health. When these substances cannot be substituted, adsorption systems are still a very common solution to VOCs emission, but for their design, previous laboratory work is necessary: adsorption isotherms and breakthrough curves must be obtained. The first ones establish the maximal amount of adsorbate retained over the solid adsorbent for a certain pressure of the adsorbate, and the second ones define the adsorption process kinetics. Once this information is studied, a theoretical breakthrough time model can be built up, and then the scale up of the adsorption system can be developed. This process is rather complex for multicomponent gas mixtures, where a competition between adsorbates happens. Thus, the aim of this paper is to establish a guide for authors willing to develop breakthrough time prediction models for multicomponent systems through a critical review of different adsorption and kinetic models.Peer reviewe