Effect of binder addition on the mechanical and physicochemical propertiesof low rank coal char briquettes

A series of chars obtained from a low rank coal by N-2 pyrolysis at differe nt temperatures was blended in different proportions with a commercial bind er pitch and pressed at 125 MPa in a mould-and-plunger press. The briquette s obtained (1.5 cm long, 1 cm diameter) were subjected to a heat treatment consisting of a curing stage at 200 degrees C in air followed by a carboniz ation stage in N-2, at 500 degrees C or 700 degrees C depending on the star ting char. A further stage of activation in steam was performed on the briq uettes as well as on the chars. The mechanical properties of the briquettes were assessed by means of their impact resistance index and compressive st rength, and their surface properties were determined by N-2 B.E.T. surface 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) impro ves significantly the impact and compressive resistance of the briquettes. Whatever the amount of pitch used, the mechanical resistance of the briquet tes decreases after activation. Tn both cases (before and after activation) the mechanical resistance of the briquettes depends on the starting char a nd the pitch content used. The changes, with respect to parent chars, found in surface properties of the briquettes were explained in relation to text ural and acidic-basic properties of the pitch added, as well as to the chan ges undergone by the char itself during heat treatment. The effect of steam activation on these properties of the briquettes depends on the parent cha r, pitch content and the temperature of activation. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.