Microporous activated carbon prepared from coconut shells using chemical activation with zinc chloride Diana C.S. Azevedo a , J. Ca ´ssia S. Arau ´jo a , Moise ´s Bastos-Neto a , A. Eurico B. Torres a , Emerson F. Jaguaribe b , Ce ´lio L. Cavalcante a, * a Grupo de Pesquisas em Separac ¸o ˜es por Adsorc ¸a ˜o (GPSA), Departamento de Engenharia Quı ´ mica, Universidade Federal do Ceara ´ (UFC), Campus Universita ´ rio do Pici, Bl. 709 60.455-760 Fortaleza, CE, Brazil b Laborato ´ rio de Carva ˜ o Ativado (LCA), Departamento de Engenharia Meca ˆnica, Universidade Federal da Paraı ´ ba (UFPB), Campus I, Bloco F, 58059-900 Joa ˜o Pessoa, PB, Brazil Received 12 March 2006; received in revised form 8 September 2006; accepted 17 November 2006 Abstract Microporous activated carbon samples were prepared from coconut shells (low-cost lignocellulose waste), using chemical activation with zinc chloride followed by physical activation. Textural characterization was performed using nitrogen adsorption at 77 K. The sam- ple that presented the best characterization results was then evaluated for methane adsorption at pressures between 0.1 MPa and 7 MPa and temperatures in the range 283–333 K. At 298 K and 40 bar, a capacity of ca. 122 mg of methane/g of carbon (80 v/v) was observed, just short of the target established in Brazil for ANG in remote sites transportation (100 v/v). These results suggest that activated carbons prepared from coconut shells, using chemical activation followed by physical activation, may be further developed as potential adsor- bents for natural gas storage applications. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Microporous activated carbon; Adsorption properties; Zinc chloride chemical activation 1. Introduction The increase in natural gas (NG) usage in the Brazilian energy matrix is one of the main guidelines set by energy policy makers in the country, due to high availability of NG associated with offshore oil production. One of the main difficulties in large-scale NG usage is the large distance between oil fields and consumption sites, which sometimes do not justify constructing pipelines and pumping accesso- ries. As alternatives to transporting and storing natural gas to develop new large-scale markets, two options can be used: compressed natural gas (CNG) or adsorbed natural gas (ANG). Natural gas storage has been attracting interest among researchers in the materials and adsorption field. According to the US Department of Energy, a capacity of 150 v/v would be desirable for the practical application of ANG in vehicular use in the USA [1]. In Brazilian condi- tions the target for ANG in remote sites transportation has been established as 100 v/v [2]. Microporous activated carbons have been found to be suitable materials for natural gas storage [3]. They may be prepared by pyrolysis of a large number of different carbon-containing source materials. The carbonization process is usually conducted by heating the carbonaceous material in the absence of air at temperatures between 400 °C and 900 °C. Chemical agents, such as zinc chloride, potassium hydroxide or phosphoric acid, may be mixed with the source material prior to carbonization so as to ensure the formation of micropores [4,5]. Micropores should be predominantly present in the pore size distribu- tion of AC, since they are the ones that contribute more significantly to adsorption of methane, which is the major 1387-1811/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2006.11.024 * Corresponding author. Tel.: +55 85 3366 9611; fax: +55 85 3366 9601. E-mail address: celio@gpsa.ufc.br (C.L. Cavalcante). www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 100 (2007) 361–364