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

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Title: NaOH and KOH for preparing activated carbons used in energy and environmental applications
Authors: Linares-Solano, Angel | Lillo-Rodenas, Maria Angeles | Marco Lozar, Juan Pablo | Kunowsky, Mirko | Romero Anaya, Aroldo José
Research Group/s: Materiales Carbonosos y Medio Ambiente
Center, Department or Service: Universidad de Alicante. Departamento de Química Inorgánica
Keywords: NaOH | KOH | Activated carbons | Energy applications | Environmental applications
Knowledge Area: Química Inorgánica
Issue Date: 2012
Publisher: Nova Science Publishers
Citation: International Journal of Energy, Environment and Economics. 2012, 20(4): 59-91
Abstract: 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 318ºC, and KOH at 360ºC. Hence, they can react with most materials, even with relatively inert ones such as carbon materials. Thus, at temperatures higher than 360ºC 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.
Sponsor: The authors thank Spanish MICINN (MAT 2009-07150), Generalitat Valenciana (project Prometeo/2009/047) and FEDER for financial support.
ISSN: 1054-853X
Language: eng
Type: info:eu-repo/semantics/article
Rights: © Copyright 2012 Nova Science Publishers, Inc.
Peer Review: si
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Appears in Collections:INV - MCMA - Artículos de Revistas

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