PERGAMON Carbon 37 (1999) 1833–1841 Effect of binder addition on the mechanical and physicochemical properties of low rank coal char briquettes * B. Rubio , M.T. Izquierdo, E. Segura ´ ´ ´ Instituto de Carboquımica ( CSIC), Departamento de Energıa y Medio Ambiente, Marıa de Luna, 12. 50015, Zaragoza, Spain Received 7 August 1998; accepted 11 February 1999 Abstract A series of chars obtained from a low rank coal by N pyrolysis at different temperatures was blended in different 2 proportions with a commercial binder pitch and pressed at 125 MPa in a mould-and-plunger press. The briquettes obtained (1.5 cm long, 1 cm diameter) were subjected to a heat treatment consisting of a curing stage at 2008C in air followed by a carbonization stage in N , at 5008C or 7008C depending on the starting char. A further stage of activation in steam was 2 performed on the briquettes as well as on the chars. The mechanical properties of the briquettes were assessed by means of their impact resistance index and compressive strength, and their surface properties were determined by N B.E.T. surface 2 area and pore volume measurements, as well as by acidic–basic titration. An increase in pitch content within the range tested (10–25% by weight) improves significantly the impact and compressive resistance of the briquettes. Whatever the amount of pitch used, the mechanical resistance of the briquettes decreases after activation. In both cases (before and after activation) the mechanical resistance of the briquettes depends on the starting char and the pitch content used. The changes, with respect to parent chars, found in surface properties of the briquettes were explained in relation to textural and acidic–basic properties of the pitch added, as well as to the changes undergone by the char itself during heat treatment. The effect of steam activation on these properties of the briquettes depends on the parent char, pitch content and the temperature of activation.  1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Char; Pitch; B. Mixing; D. Mechanical properties; Surface properties 1. Introduction The strength of the carbon or coke formed by briquet- ting has been studied from many angles, with the industrial Active cokes or activated carbons are industrially used briquetting process having been extensively reviewed by for the removal of SO and NO from flue gases at Schinzel [8] and by Rhys-Jones [9]. There have been, 2 relatively low temperatures [1–3]. The economy of the however, few systematic studies aimed at gaining a basic process, which is one of its main disadvantages, can be understanding of the briquetting process, due in part to the improved by the use of inexpensive carbons obtained from large number of process variables involved. According to lower rank coals. The lack of hardness of these coals Clarke and Marsh [10], in addition to the porosity of the limits, however, their use as precursors of a suitable starting carbon being critical, pore shape, pore size and activated carbon, despite their good surface properties and pore wall characteristics influence the strength of the final ´ their well-contrasted catalytic activity [4,5]. As Rodrıguez- product. Given that solid coke is a composite (inert Reinoso showed in a recent review [6], the study of carbon material plus optically isotropic and anisotropic material), not only as catalyst support but also as a catalyst by itself its strength will depend on the strength of its individual is a topic of growing interest, given the special features of components. Moreover, the interface between components carbon in general [7]. is of importance, especially under gasification, which usually occurs in a preferential way at the boundaries between coke components [11]. In studies dealing with the strength of briquettes pro- *Corresponding author. Tel.: 134-9-76-733-977; fax: 134-9- duced from lignite char, Taylor et al. [12–14] concluded 76-733-318. E-mail address: brubio@carbon.icb.csic.es (B. Rubio) that the strength of the briquettes is determined by the 0008-6223 / 99 / $ – see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(99)00057-3