Analysis of the evolution of the pore size distribution and the pore network connectivity of a porous carbon during activation M.V. Navarro a , N.A. Seaton a, * , A.M. Mastral b , R. Murillo b a Institute for Materials and Processes, School of Engineering and Electronics, University of Edinburgh, EH9 3JL, United Kingdom b Instituto de Carboquimica, CSIC, M Luesma Castan 4, 50018 Zaragoza, Spain Received 26 December 2005; accepted 21 February 2006 Available online 18 April 2006 Abstract The development of the microporosity, pore size distribution and pore network connectivity has been studied in the production of activated carbons from lignite char. Grand Canonical Monte Carlo simulation of adsorption was applied to the characterisation of a set of activated carbons produced at a sequence of times. The pore size distributions obtained from nitrogen at 77 K and ethane at 264 K were used as inputs to a method based on percolation theory to study the changing connectivity of the system. The incorporation of percolation concepts in the study of the porosity development gives an insight into the processes involved. The analysis is applied to a particular environmental application, the adsorption of phenanthrene. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Activated carbon; Activation; Adsorption; Molecular simulation; Microporosity 1. Introduction In general, microporosity in carbons is created by removal of solid material by an activation process. How- ever, after the evolution of microporosity to a certain optimum degree, further activation to increase the micro- porosity is accompanied by mesopore and macropore evo- lution, which is disadvantageous for many applications [1]. The possibility of modifying the activation process to cre- ate pores of a particular size, tailored to adsorb a group of specific molecules, makes activated carbon an important class of industrial adsorbent [2]. The evolution of the struc- ture of carbons during the activation process is, as yet, incompletely understood [3]. The pore structure of the activated carbon may be modified by either chemical or physical activation. In this work, we have studied physical activation, involving firstly a carbonisation step to reduce the volatiles content, and secondly a partial gasification step at high temperature with an oxidant gas in order to enhance the porosity in the solid [4]. The micropore structure can be determined by several methods [5] among which probably the most widely used is gas adsorption. The pore structure of activated carbons is usually characterised in terms of the pore size distribu- tion (PSD), perhaps the most important aspect of the char- acterisation of the structural heterogeneity of porous solids used in industrial applications. For a local isotherm one may choose classical models (e.g., the Langmuir isotherm), statistical mechanical methods such as density-functional theory, or, most accurate for micropores, methods based on Monte Carlo simulation [5]. A second important struc- tural characteristic of activated carbons is the connectivity of the pore network, which can be determined using an analysis based on percolation theory [6]. The connectivity is conveniently defined in terms of the mean coordination number of the network. The aim of the current study is to model the changes produced in the PSD and coordination number of lignite coal char during physical activation with carbon dioxide and how these changes influence the adsorption of different 0008-6223/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.02.029 * Corresponding author. Fax: +44 131 650 6551. E-mail address: n.seaton@ed.ac.uk (N.A. Seaton). www.elsevier.com/locate/carbon Carbon 44 (2006) 2281–2288