High-Pressure Methane Storage in Porous Materials: Are Carbon Materials in the Pole Position?

Natural gas storage on porous materials (ANG) is a promising alternative to conventional on-board compressed (CNG) or liquefied natural gas (LNG). To date, Metal���organic framework (MOF) materials have apparently been the only system published in the literature that is able to reach the new Department of Energy (DOE) value of 263 cm3 (STP: 273.15 K, 1 atm)/cm3; however, this value was obtained by using the ideal single-crystal density to calculate the volumetric capacity. Here, we prove experimentally, and for the first time, that properly designed activated carbon materials can really achieve the new DOE value while avoiding the additional drawback usually associated with MOF materials (i.e., the low mechanical stability under pressure (conforming), which is required for any practical application).

NaOH and KOH for preparing activated carbons used in energy and environmental applications

Alkaline hydroxides, especially sodium and potassium hydroxides, are multi-million-ton per annum commodities and strong chemical bases that have large scale applications. Some of them are related with their consequent ability to degrade most materials, depending on the temperature used. As an example, these chemicals are involved in the manufacture of pulp and paper, textiles, biodiesels, soaps and detergents, acid gases removal (e.g., SO2) and others, as well as in many organic synthesis processes. Sodium and potassium hydroxides are strong and corrosive bases, but they are also very stable chemicals that can melt without decomposition, NaOH at 318��C, and KOH at 360��C. Hence, they can react with most materials, even with relatively inert ones such as carbon materials. Thus, at temperatures higher than 360��C these melted hydroxides easily react with most types of carbon-containing raw materials (coals, lignocellulosic materials, pitches, etc.), as well as with most pure carbon materials (carbon fibers, carbon nanofibers and carbon nanotubes). This reaction occurs via a solid-liquid redox reaction in which both hydroxides (NaOH or KOH) are converted to the following main products: hydrogen, alkaline metals and alkaline carbonates, as a result of the carbon precursor oxidation. By controlling this reaction, and after a suitable washing process, good quality activated carbons (ACs), a classical type of porous materials, can be prepared. Such carbon activation by hydroxides, known since long time ago, continues to be under research due to the unique properties of the resulting activated carbons. They have promising high porosity developments and interesting pore size distributions. These two properties are important for new applications such as gas storage (e.g., natural gas or hydrogen), capture, storage and transport of carbon dioxide, electricity storage demands (EDLC-supercapacitors-) or pollution control. Because these applications require new and superior quality activated carbons, there is no doubt that among the different existing activating processes, the one based on the chemical reaction between the carbon precursor and the alkaline hydroxide (NaOH or KOH) gives the best activation results. The present article covers different aspects of the activation by hydroxides, including the characteristics of the resulting activated carbons and their performance in some environment-related applications. The following topics are discussed: i) variables of the preparation method, such as the nature of the hydroxide, the type of carbon precursor, the hydroxide/carbon precursor ratio, the mixing procedure of carbon precursor and hydroxide (impregnation of the precursor with a hydroxide solution or mixing both, hydroxide and carbon precursor, as solids), or the temperature and time of the reaction are discussed, analyzing their effect on the resulting porosity; ii) analysis of the main reactions occurring during the activation process, iii) comparative analysis of the porosity development obtained from different activation processes (e.g., CO2, steam, phosphoric acid and hydroxides activation); and iv) performance of the prepared activated carbon materials on a few applications, such as VOC removal, electricity and gas storages.

Gasification and Pyrolysis of Posidonia oceanica in the Presence of Dolomite

Resumen del p��ster presentado en Symposium on Renewable Energy and Products from Biomass and Waste, CIUDEN (Cubillos de Sil, Le��n, Spain), 12-13 May 2015

Retrofit of heat exchanger networks with pressure recovery of process streams at sub-ambient conditions

This paper presents a new mathematical programming model for the retrofit of heat exchanger networks (HENs), wherein the pressure recovery of process streams is conducted to enhance heat integration. Particularly applied to cryogenic processes, HENs retrofit with combined heat and work integration is mainly aimed at reducing the use of expensive cold services. The proposed multi-stage superstructure allows the increment of the existing heat transfer area, as well as the use of new equipment for both heat exchange and pressure manipulation. The pressure recovery of streams is carried out simultaneously with the HEN design, such that the process conditions (streams pressure and temperature) are variables of optimization. The mathematical model is formulated using generalized disjunctive programming (GDP) and is optimized via mixed-integer nonlinear programming (MINLP), through the minimization of the retrofit total annualized cost, considering the turbine and compressor coupling with a helper motor. Three case studies are performed to assess the accuracy of the developed approach, including a real industrial example related to liquefied natural gas (LNG) production. The results show that the pressure recovery of streams is efficient for energy savings and, consequently, for decreasing the HEN retrofit total cost especially in sub-ambient processes.

La interdependencia hispano-argelina en cuestiones energ��ticas

Desde los a��os 1980 Espa��a y Europa importan una parte creciente de sus hidrocarburos de Argelia. Esta situaci��n ha llevado a una interdependencia que puede resultar peligrosa por ambas partes. Espa��a no consigue reducir su consumo de hidrocarburos, pero en su esfuerzo por diversificar e independizarse del petr��leo ha incrementado significativamente el consumo de gas natural procedente de Argelia. Por su parte este pa��s ha aumentado sus reservar en divisas lo que le ha permitido mejorar extraordinariamente su situaci��n desde la guerra civil de los a��os 1990 y garantizar a corto plazo el estatus quo social y pol��tico. Sin embargo esa misma dependencia de los hidrocarburos le impide resolver los graves problemas estructurales de su juventud y de una econom��a rentista. Esta comunicaci��n estudia estas dependencias analizando la creciente complejidad del mercado de los hidrocarburos, los esfuerzos espa��oles por diversificar sus fuentes de abastecimiento y las apuestas de Argelia por continuar suministrando energ��a primaria.

Radiactividad natural de los materiales de construcci��n. Aplicaci��n al hormig��n. Parte II. Radiaci��n interna: el gas rad��n

El presente art��culo analiza aspectos relacionados con los tipos de radiactividad natural presentes en el interior de las edificaciones, sus fuentes y sus influencias. M��s concretamente, desarrolla el estudio de la radiactividad ambiental en el interior de los espacios construidos debida a la presencia del gas rad��n, as�� como sus fuentes de origen y los niveles recomendados. Este es un art��culo que se presenta como la segunda parte de un trabajo sobre radiactividad natural en los materiales de construcci��n, cuya primera parte hace referencia a la radiaci��n externa de dichos materiales y se publica por los mismos autores, en esta misma revista. Al mismo tiempo, se realiza un recorrido por el marco normativo, tanto internacional como nacional, relativo al rad��n y a sus descendientes de vida media corta. El presente trabajo es parte de la tesis doctoral de la primera autora del mismo, Beatriz Piedecausa Garc��a, a quien el resto de autores agradece su esfuerzo para preparar el texto que ahora se publica y la autorizaci��n y las facilidades ofrecidas para acceder a su trabajo.

Radiactividad natural de los materiales de construcci��n. Aplicaci��n al hormig��n. Parte I. Radiaci��n externa: ��ndice de riesgo radiactivo

El presente art��culo analiza aspectos relacionados con el concepto de radiactividad natural, profundizando en los tipos de radiactividad existente en los materiales naturales radiactivos NORM (���Naturally Occurring Radioactive Materials���) utilizados en la construcci��n, as�� como sus fuentes e infl uencias. Este es un art��culo que se presenta como la primera parte de un trabajo sobre la radiactividad natural de los materiales de construcci��n, cuya segunda parte hace referencia a la radiaci��n interna debida al gas rad��n emitido de manera natural por dichos materiales y se publica por los mismos autores, en esta misma revista. Se aborda la necesidad de establecer criterios de control en este tipo de materiales y se analiza el establecimiento de diferentes ��ndices de riesgo seg��n los distintos pa��ses. Al mismo tiempo, se realiza un recorrido por el marco normativo, tanto internacional como nacional, relativo a estos materiales NORM. El presente trabajo es parte de la tesis doctoral de la primera autora del mismo, Beatriz Piedecausa Garc��a, a quien el resto de autores agradece su esfuerzo para preparar el texto que ahora se publica y la autorizaci��n y las facilidades ofrecidas para acceder a su trabajo.

Radon gas. Environmental concentration measures and remediation actions in exposed buildings

The main contribution to the radiological impact from natural radiation received by general population is due to the emission of radon (222Rn). The objective of this project is the study of radon gas as a radioactive element in our buildings (existing and future constructions) to avoid its influence in interior rooms. The proposed methodology reflects different aspects of natural radioactivity in buildings, their sources, their control criteria and regulatory framework; aspects related to the presence of radon in our constructions, entryways, measurement methodology for indoor environmental concentration are studied; other protection solutions and remediation measures in both existing buildings and new construction projects are analyzed. In conclusion, the paper presents previous evaluation tools, the analysis of existing concentration and the choice of the most appropriate mitigation / remediation measures depending on each case, through the establishment of different architectural proposals to plan actions against radon where necessary.

Applications for CO2-Activated Carbon Monoliths: I. Gas Storage

Carbon monoliths with high densities are studied as adsorbents for the storage of H2, CH4, and CO2 at ambient temperature and high pressures. The starting monolith A3 (produced by ATMI Co.) was activated under a CO2 flow at 1073 K, applying different activation times up to 48 h. Micropore volumes and apparent surface areas were deduced from N2 and CO2 adsorption isotherms at 77 K and 273 K, respectively. CO2 and CH4 isotherms were measured up to 3 MPa and H2 up to 20 MPa. The BET surface area of the starting monolith (941 m2/g) could be significantly increased up to 1586 m2/g, and the developed porosity is almost exclusively comprised of micropores <1 nm. Total storage amounts take into account the compressed gas in the void space of the material, in addition to the adsorbed gas. Remarkably, high total storage amounts are reached for CO2 (482 g/L), CH4 (123 g/L), and H2 (18 g/L). These values are much higher than for other sorbents with similar surface areas, due to the high density of the starting monolith and of the activated ones, for which the density decreases only slightly (from 1.0 g/cm3 to 0.8 g /cm3 upon CO2 activation). The findings reveal the suitability of high density activated carbon monoliths for gas storage application. Thus, the amounts of stored gas can be increased by more than a 70 % in the case of H2 at 20 MPa, almost 5.5 times in the case of CH4 at 3 MPa, and more than 7.5 times in the case of CO2 at 3 MPa when adsorbents are used for gas storage under the investigated conditions rather than simple compression. Furthermore, the obtained results have been recently confirmed by a scale-up study in which 2.64 kg of high density monolith adsorbent was filled a tank cylinder of 2.5 L (Carbon, 76, 2014, 123).