PERGAMON Carbon 39 (2001) 751–759 Preparation of activated carbons from Spanish anthracite II. Activation by NaOH * ´ ´ ´ M.A. Lillo-Rodenas, D. Lozano-Castello, D. Cazorla-Amoros, A. Linares-Solano ´ ´ Departamento de Quımica Inorganica, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain Received 8 March 2000; accepted 24 July 2000 Abstract This paper complements the previous one (activation with KOH) analysing the development of porosity of a Spanish anthracite by chemical activation with NaOH. The preparation method has been optimised through the analysis of diverse experimental variables. Among them, activating agent / coal ratio, drying process, method of mixing of the activating agent and coal, nitrogen flow during pyrolysis and mineral matter content of the coal, have been studied. The results obtained confirm the importance of the activating agent to coal ratio and the flow of gas during carbonisation on the development of porosity. In addition, it shows that chemical activation with NaOH can be successfully used to develop activated carbons 2 3 with high surface area and micropore volumes (i.e., up to 2700 m / g and 1 cm / g). Comparing chemical activation using an impregnation method and physical mixing we conclude that physical mixing of NaOH and coal, which is a very easy preparation method, renders the best results. Therefore physical mixing has been also applied in this work to KOH with rather interesting results. Although impregnation produces a higher development of porosity for KOH, activated carbons with high micropore volumes can be synthesised through a much simpler method. Physical mixing produces larger pore volumes by KOH activation than by NaOH activation.  2001 Elsevier Science Ltd. All rights reserved. Keywords: A. Anthracite, Activated carbon; B. Activation; C. Adsorption; D. Microporosity 1. Introduction advantages over KOH. The most important ones are lower price and less corrosive behaviour, what are interesting Part I of this work analysed the activation of a Spanish points from an industrial point of view. anthracite by KOH [1]. The effect of different experimen- tal parameters was extensively studied to optimise the development of porosity. In this way, activated carbons 2. Experimental essentially microporous were prepared with micropore 3 volumes up to 1.45 cm /g. The influence of gas flow rate, Two Spanish anthracites (UA and UAb) with different parameter hardly studied in the literature, was evaluated, ash contents, coming from the same ore but from different showing that it has an important effect on porosity layers, have been used. Elemental analysis and the mineral development. matter content for the two anthracites are shown in Table The second part of this study extends the preparation of 1. Chemical activation, using a particle size smaller than activated carbon from the same raw material to an activat- 0.6 mm, has been carried out with sodium hydroxide (p.a. ing agent like NaOH, analysing two preparation methods 98%) following two different processes: impregnation or (impregnation and physical mixing). This hydroxide, an physical mixing. Fig. 1 summarises the steps of the two activating agent scarcely used in literature [2,3], has some preparation methods used. In the impregnation, the first stage consists of mixing by stirring the anthracite with different volumes of a sodium *Corresponding author. Tel.: 134-96-590-3545; fax: 34-96- hydroxide solution. This solution contains 2 g of the 590-3454. E-mail address: linares@ua.es (A. Linares-Solano). hydroxide per each 10 ml of water. The temperature of the 0008-6223 / 01 / $ – see front matter  2001 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(00)00186-X