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Abanades J.C.,CSIC - National Coal Institute
Applied Energy | Year: 2014

This work presents a comprehensive conceptual design of a Ni-based chemical looping combustion process (CLC) carried out in fixed bed reactors. The process is intended to exploit the well-known advantages of the Ni/NiO redox system for CLC applications in terms of high reactivity, O2 carrying capacity and chemical and thermal stability. Solutions to the problem of heat management in fixed bed reactors at high temperature and high pressure are described, while a continuous flow of nitrogen for driving a gas turbine is produced. Each reactor involved in the process goes through a cyclic sequence of five reaction and heat transfer stages. Cool product gas recirculations are incorporated into the Ni oxidation and NiO reduction stages in order to moderate the maximum temperatures in the beds and control the displacement of the reaction and heat transfer fronts. A preliminary conceptual design of the process has been carried out to determine the minimum number of reactors needed for continuous operation in typical large-scale CO2 capture systems. Basic reactor models and assumptions based on an ideal plug flow pattern have been used in all the reactors during the chemical reactions and the heat transfer operations. This has made it possible to identify reasonable operating windows for the eight fixed-bed reactors that make up the CO2 capture system, and has demonstrated not only its technical viability but also its great potential for further development. © 2014 Elsevier Ltd.

Granda M.,CSIC - National Coal Institute | Blanco C.,CSIC - National Coal Institute | Alvarez P.,CSIC - National Coal Institute | Patrick J.W.,University of Nottingham | Menendez R.,CSIC - National Coal Institute
Chemical Reviews | Year: 2014

The route from coal to chemicals can be simply apportioned into the three processes of coal carbonization, coal gasification, and coal liquefaction. Because of their highly aromatic composition, the chemicals derived from coking processes have a molecular structure that is not easy to find in chemicals obtained from other sources. At the present time, chemicals such as benzene and its derivatives and even naphthalene are mainly manufactured by the petrochemical industry. These chemicals can also be obtained from coal coking fractions, as an alternative source to petroleum. Some recent research has demonstrated the effectiveness of a novel catalyst, in the form of iron nanoparticles embedded in carbon nanotubes, for converting carbon dioxide to a mixture of hydrocarbons.

Sevilla M.,CSIC - National Coal Institute | Fuertes A.B.,CSIC - National Coal Institute
Journal of Colloid and Interface Science | Year: 2012

Highly porous carbons have been prepared by the chemical activation of two mesoporous carbons obtained by using hexagonal- (SBA-15) and cubic (KIT-6)-ordered mesostructured silica as hard templates. These materials were investigated as sorbents for CO2 capture. The activation process was carried out with KOH at different temperatures in the 600-800°C range. Textural characterization of these activated carbons shows that they have a dual porosity made up of mesopores derived from the templated carbons and micropores generated during the chemical activation step. As a result of the activation process, there is an increase in the surface area and pore volume from 1020m2g-1 and 0.91cm3g-1 for the CMK-8 carbon to a maximum of 2660m2g-1 and 1.38cm3g-1 for a sample activated at 800°C (KOH/CMK-8 mass ratio of 4). Irrespective of the type of templated carbon used as precursor or the operational conditions used for the synthesis, the activated samples exhibit similar CO2 uptake capacities, of around 3.2mmolCO2g-1 at 25°C. The CO2 capture capacity seems to depend on the presence of narrow micropores (<1nm) rather than on the surface area or pore volume of activated carbons. Furthermore, it was found that these porous carbons exhibit a high CO2 adsorption rate, a good selectivity for CO2-N2 separation and they can be easily regenerated. © 2011 Elsevier Inc..

Ferrero G.A.,CSIC - National Coal Institute | Fuertes A.B.,CSIC - National Coal Institute | Sevilla M.,CSIC - National Coal Institute
Journal of Materials Chemistry A | Year: 2015

A procedure for the fabrication of N-doped hollow carbon spheres with a high rate capability for supercapacitors has been developed. The approach is based on a nanocasting method and the use of a nitrogen-rich compound (pyrrole) as a carbon precursor. The carbon particles thus produced combine a large BET surface area (∼1500 m2 g-1) with a porosity made up of mesopores of ∼4 nm, a high nitrogen content (∼6 wt%) and a capsule morphology which entails short ion diffusion paths derived from the shell morphology (thickness ∼60 nm). The porous properties of these hollow particles can be enhanced by means of an additional activation step with KOH. The activation process does not alter the hollow structure or spherical morphology, but strongly modifies the pore structure from a mesoporous network to a microporous one. The N-doped carbon capsules were tested in aqueous and organic electrolytes. In an aqueous medium (1 M H2SO4), the mesoporous carbon capsules offer the best performance due to the pseudocapacitive contribution of the N-groups, exhibiting a specific capacitance of ∼240 F g-1 at 0.1 A g-1 and a capacitance retention as high as 72% at 80 A g-1. In contrast, in an organic electrolyte (1 M TEABF4/AN), where the charge storage mechanism is based on the formation of the electric double-layer, the microporous capsules perform better due to the larger specific surface area. Thus, the microporous carbon capsules display a specific capacitance of up to 141 F g-1 at 0.1 A g-1 and an outstanding capacitance retention of 93% for an ultra-high discharge current density of 100 A g-1. © The Royal Society of Chemistry 2015.

Sevilla M.,CSIC - National Coal Institute | Mokaya R.,University of Nottingham
Energy and Environmental Science | Year: 2014

Porous carbons have several advantageous properties with respect to their use in energy applications that require constrained space such as in electrode materials for supercapacitors and as solid state hydrogen stores. The attractive properties of porous carbons include, ready abundance, chemical and thermal stability, ease of processability and low framework density. Activated carbons, which are perhaps the most explored class of porous carbons, have been traditionally employed as catalyst supports or adsorbents, but lately they are increasingly being used or find potential applications in the fabrication of supercapacitors and as hydrogen storage materials. This manuscript presents the state-of-the-art with respect to the preparation of activated carbons, with emphasis on the more interesting recent developments that allow better control or maximization of porosity, the use of cheap and readily available precursors and tailoring of morphology. This review will show that the renewed interest in the synthesis of activated carbons is matched by intensive investigations into their use in supercapacitors, where they remain the electrode materials of choice. We will also show that activated carbons have been extensively studied as hydrogen storage materials and remain a strong candidate in the search for porous materials that may enable the so-called Hydrogen Economy, wherein hydrogen is used as an energy carrier. The use of activated carbons as energy materials has in the recent past and is currently experiencing rapid growth, and this review aims to present the more significant advances. This journal is © the Partner Organisations 2014.

Sevilla M.,CSIC - National Coal Institute | Fuertes A.B.,CSIC - National Coal Institute
ACS Nano | Year: 2014

An easy, one-step procedure is proposed for the synthesis of highly porous carbon nanosheets with an excellent performance as supercapacitor electrodes. The procedure is based on the carbonization of an organic salt, i.e., potassium citrate, at a temperature in the 750-900 °C range. In this way, carbon particles made up of interconnected carbon nanosheets with a thickness of <80 nm are obtained. The porosity of the carbon nanosheets consists essentially of micropores distributed in two pore systems of 0.7-0.85 nm and 0.95-1.6 nm. Importantly, the micropore sizes of both systems can be enlarged by simply increasing the carbonization temperature. Furthermore, the carbon nanosheets possess BET surface areas in the ~1400-2200 m2 g-1 range and electronic conductivities in the range of 1.7-7.4 S cm-1 (measured at 7.1 MPa). These materials behave as high-performance supercapacitor electrodes in organic electrolyte and exhibit an excellent power handling ability and a superb robustness over long-term cycling. Excellent results were obtained with the supercapacitor fabricated from the material synthesized at 850 °C in terms of both gravimetric and volumetric energy and power densities. This device was able to deliver ~13 Wh kg-1 (5.2 Wh L-1) at an extremely high power density of 78 kW kg-1 (31 kW L -1) and ~30 Wh kg-1 (12 Wh L-1) at a power density of 13 kW kg-1 (5.2 kW L-1) (voltage range of 2.7 V). © 2014 American Chemical Society.

Sevilla M.,CSIC - National Coal Institute | Fuertes A.B.,CSIC - National Coal Institute
Carbon | Year: 2013

Macro/mesoporous carbon monoliths with a graphitic framework were synthesized by carbonizing polymeric monoliths of poly(benzoxazine-co-resol). The overall synthesis process consists of the following steps: (a) the preparation of polymeric monoliths by co-polymerization of resorcinol and formaldehyde with a polyamine (tetraethylenepentamine), (b) doping the polymer with a metallic salt of Fe, Ni or Co, (c) carbonization and (d) the removal of inorganic nanoparticles. The metal nanoparticles (Fe, Ni or Co) formed during the carbonization step catalyse the conversion of a fraction of amorphous carbon into graphitic domains. The resulting carbon monoliths contain >50 wt.% of graphitic carbon, which considerably improves their electrical conductivity. The use of tetraethylenepentamine in the synthesis results in a nitrogen-containing framework. Textural characterization of these materials shows that they have a dual porosity made up of macropores and mesopores (∼2-10 nm), with a BET surface area in the 280-400 m2 g-1 range. We tested these materials as electrodes in organic electrolyte supercapacitors and found that no conductive additive is needed due to their high electrical conductivity. In addition, they show a specific capacitance of up to 35 F g-1, excellent rate and cycling performance, delivering up to 10 kW kg-1 at high current densities. © 2013 Elsevier Ltd. All rights reserved.

Velasco L.F.,CSIC - National Coal Institute | Lima J.C.,New University of Lisbon | Ania C.,CSIC - National Coal Institute
Angewandte Chemie - International Edition | Year: 2014

By using monochromatic light the ability of semiconductor-free nanoporous carbons to convert the low-energy photons from the visible spectrum into chemical reactions (i.e. phenol photooxidation) is demonstrated. Data shows that the onset wavelength of the photochemical activity can be tuned by surface functionalization, with enhanced visible-light conversion upon introducing N-containing groups. Scratching the surface: The ability of semiconductor-free nanoporous carbons to absorb low-energy photons from visible light and convert them into chemical reactions (i.e., phenol photooxidation) is demonstrated by using monochromatic light. Data showed the strong dependence of the photochemical activity on the wavelength of the irradiation source and the chemical composition of the nanoporous carbon. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sevilla M.,CSIC - National Coal Institute | Valle-Vigon P.,CSIC - National Coal Institute | Fuertes A.B.,CSIC - National Coal Institute
Advanced Functional Materials | Year: 2011

Highly porous N-doped carbons have been successfully prepared by using KOH as activating agent and polypyrrole (PPy) as carbon precursor. These materials were investigated as sorbents for CO 2 capture. The activation process was carried out under severe (KOH/PPy = 4) or mild (KOH/PPy = 2) activation conditions at different temperatures in the 600-800 °C range. Mildly activated carbons have two important characteristics: i) they contain a large number of nitrogen functional groups (up to 10.1 wt% N) identified as pyridonic-N with a small proportion of pyridinic-N groups, and ii) they exhibit, in relation to the carbons prepared with KOH/PPy = 4, narrower micropore sizes. The combination of both of these properties explains the large CO 2 adsorption capacities of mildly activated carbon. In particular, a very high CO 2 adsorption uptake of 6.2 mmol·g -1 (0 °C) was achieved for porous carbons prepared with KOH/PPy = 2 and 600 °C (1700 m 2·g -1, pore size ≈ 1 nm and 10.1 wt% N). Furthermore, we observed that these porous carbons exhibit high CO 2 adsorption rates, a good selectivity for CO 2-N 2 separation and it can be easily regenerated. N-doped porous carbons exhibiting high surface areas, large pore volumes and a porosity in the micro-/mesopore range are prepared by using a one-step synthesis strategy based on the chemical activation of polypyrrole. The prepared activated carbons exhibit a large CO 2 uptake (up to 3.9 mmol CO 2 g -1 at 25 °C), a good selectivity for CO 2-N 2 separation, and they can be easily regenerated. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Titirici M.-M.,Max Planck Institute of Colloids and Interfaces | White R.J.,Max Planck Institute of Colloids and Interfaces | Falco C.,Max Planck Institute of Colloids and Interfaces | Sevilla M.,CSIC - National Coal Institute
Energy and Environmental Science | Year: 2012

This perspective review paper provides an overview on recently developed carbon material technology synthesised from the hydrothermal carbonisation (HTC) approach, with a particular focus on the carbon formation mechanism, perspectives on large scale production, nanostructuring, functionalisation and applications. Perceptions on how this technology will be developed especially with regard to application fields where the use of HTC-derived materials could be extended will also be introduced and discussed. © 2012 The Royal Society of Chemistry.

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