• Energy Research

Ionic liquids and deep eutectic solvents (a new class of ionic liquids obtained by complexation of quaternary ammonium salts with hydrogen bond donors such as acids, amines, and alcohols among others) have been recently used as solvents and even as precursors in the synthesis of carbonaceous materials. The use of long-alkyl-chain derivatives of ionic liquids that, playing the role of structure directing agents, were capable of designing the mesoporous structure of the resulting carbons is of particular interest. Meanwhile, deep eutectic solvents proved efficient in tailoring the structure comprised between large mesopores and small macropores, but the control over the smaller ones (e.g. small mesopores and micropores) is still a challenge as compared to ILs. Herein, we have used deep eutectic solvents composed of resorcinol, 4-hexylresorcinol and tetraethylammonium bromide for the synthesis of carbon monoliths with a tailor-made narrow microporosity. Behaving as molecular sieves, these carbons exhibited not only good capacities for CO2 adsorption (up to 3 mmol g−1) but also an outstanding – especially at low pressures – CO2–CH4 selectivity. This work was supported by MINECO (MAT2009‐10214 and MAT2011‐25329). DC acknowledges MINECO for a JdelaC research contract. JP acknowledges MINECO for a FPI fellowship. COA and JBP thank the financial support of FICYT (EQUIP08‐36, file num. 04010208000281). Peer reviewed

Deep eutectic solvents (DESs) have been used in the synthesis of nitrogen-doped carbons exhibiting a hierarchical porous structure. The CO2 sorption capacity of these solid sorbents was extraordinary because of their relatively high nitrogen content and their bimodal porous structure where micropores provide high surface areas (ca. 700 m2 g−1) and macropores provide accessibility to such a surface. DESs were composed of resorcinol, 3-hydroxypyridine and choline chloride in 2 : 2 : 1 and 1 : 1 : 1 molar ratios. Polycondensation of resorcinol and 3-hydroxypyridine (with formaldehyde) promoted DES segregation in a spinodal-like decomposition process by the formation of a polymer rich phase and a depleted polymer phase. Thus, DESs played a multiple role in the synthetic process; the liquid medium that ensured reagents homogenization, the structure-directing agent that is responsible for the achievement of the hierarchical structure, and the source of carbon and nitrogen of the solid sorbent obtained after carbonization. Interestingly, the homogeneous incorporation of nitrogen at the solution stage of the synthetic process (rather than by post-treatment of the preformed carbon) allowed the achievement of significant nitrogen contents even in carbons obtained at relatively high temperatures (e.g. 8–12 at% for 600 °C and ca. 5 at% for 800 °C). It is worth noting that, despite thermal treatments at high temperatures tend to decrease the nitrogen content, the high surface area of the solid sorbents obtained at 800 °C contributed to a significant enhancement of CO2 capture while providing superior selectivity, recyclability and stability.

The preparation of activated carbons from bean pods waste by chemical (K(2)CO(3)) and physical (water vapor) activation was investigated. The carbon prepared by chemical activation presented a more developed porous structure (surface area 1580 m(2) g(-1) and pore volume 0.809 cm(3) g(-1)) than the one obtained by water vapor activation (258 m(2) g(-1) and 0.206 cm(3) g(-1)). These carbons were explored as adsorbents for the adsorption of naphthalene from water solutions at low concentration and room temperature and their properties are compared with those of commercial activated carbons. Naphthalene adsorption on the carbons obtained from agricultural waste was stronger than that of carbon adsorbents reported in the literature. This seems to be due to the presence of large amounts of basic groups on the bean-pod-based carbons. The adsorption capacity evaluated from Freundlich equation was found to depend on both the textural and chemical properties of the carbons. Naphthalene uptake on biomass-derived carbons was 300 and 85 mg g(-1) for the carbon prepared by chemical and physical activation, respectively. Moreover, when the uptake is normalized per unit area of adsorbent, the least porous carbon displays enhanced naphthalene removal. The results suggest an important role of the carbon composition including mineral matter in naphthalene retention. This issue remains under investigation.

The aim of this study was to investigate the influence of coal rank and operating conditions during coal pyrolysis on the resultant char texture properties, morphology and reactivity. A range of bituminous coals were pyrolysed in a fixed bed reactor at different heating rates. It was found that the higher the heating rate and the lower the coal rank, the more microporous chars were obtained. Isothermal (500 °C) gasification in 20% oxygen in argon of the chars was carried out using a differential thermogravimetric system (DTG). The results of this work indicated that the increase in the availability of char-active surface sites led to an increase in char reactivity, not only for oxygen but also for other reactive gases, in particular NO, diminishing emissions during the combustion process.

Peer reviewed

9 pages, 8 figures.-- Printed version published on Jul 18, 2007. In this work, the textural properties of a series of whole anthracitic-derived fly ashes sampled in eight hoppers from the electrostatic precipitators and their sized fractions (from >150 to <25 μm) are investigated. Data from N2 adsorption isotherms at 77 K, helium density, and mercury porosimetry have contributed to establish a relationship between the Brunauer−Emmett−Teller (BET) surface areas, VTOT, porosity, carbon content (the type of fly ash carbons), and Hg retention in these fly ashes. The unburned carbons in these ashes are macroporous materials, and they are different from the carbons in fly ashes from classes C and F (the latter derived from the combustion of bituminous coals) and show different textural properties. These ashes represent the end member of the fly ash classes C and F with respect to certain textural properties. Although the BET surface area and VTOT values for the studied samples are the lowest reported, they increase with the increase in carbon content, anisotropic carbon content, and particle size of the ashes. Thus, a positive relationship between all these parameters and Hg capture by the coarser ash fractions was found. The finest fraction of carbons (<25 μm) represented an exception. Although it makes a significant contribution to the total carbon of the whole fly ashes and shows relatively higher surface areas and VTOT values, its Hg concentration was found to be the lowest. This suggests that the type of unburned carbons in the finest fraction and/or other adsorption mechanisms may play a role in Hg concentration. Because the textural properties of anisotropic carbons depend on their subtype and on their origin, the need for its differentiation has been evidenced. The financial support for this work was provided by the Spanish Ministerio de Educación y Ciencia (MEC) Grant of the Programa de Movilidad to I.S.-R. (ref PR2005-0168). The authors thank the Spanish power plant for providing the samples and CAER at the University of Kentucky (Lexington, KY) for providing facilities for developing this research work. Dr. B. Ruiz Bobes and E. I. González Suárez (INCAR-CSIC, Spain) are also thanked for their analytic work. Peer reviewed

The results presented in this work are part of a more extensive research programme aimed at assessing the impact of coal porous structure on density-based process evaluation and modelling. The coal samples used were obtained from two different density-based cleaning processes, a Vorsyl dense medium separator for treating an anthracite (TW) with a size fraction of 0.5–8.0 mm and a spiral concentrator for treating a bituminous coal (DH) with a size of less than 2 mm. Textural characterisation of the samples was carried out by measuring true (helium) and apparent (mercury) densities and mercury porosimetry up to a maximum pressure of 200 MPa. Adsorption isotherms in CO2 at 273 K were also determined for both coal series. In the case of the bituminous coal series a linear relationship between porosity and ash level was found. This may have important implications if coal porosity and/or textural parameters need to be incorporated into new density-based simulation models. Work carried out with a financial grant from the European Coal and Steel Community (ECSC Project 7220 – EA/132). Peer reviewed

Abstract Investigations for the utilization of olive stones and solvent-extracted olive pulp are carried out. Tar, solid and gas products are obtained by pyrolysis of both precursors under vacuum and atmospheric pressure. Vacuum pyrolysis causes a decrease in the solid yield and an increase in the liquid and gas yields. The identified compounds of the liquid products are predominantly oxygen-containing structures (derivatives of phenol, dihydroxybenzenes, guaiacol, syringol, vanilin, veratrol, furan, acids). Activated carbons with a developed porous structure and alkaline character of the surface are produced by steam activation of the solid product and steam pyrolysis of the raw material. Oxidation treatment with air leads to the formation of a large number of oxygen functional groups with different chemical characters on the carbon surface. Chemical activation with K2CO3 allows the preparing of carbon adsorbents with a high surface area and alkaline character of the surface.