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

Abstract

A series of chars obtained from a low rank coal by N2 pyrolysis at different temperatures was blended in different 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 200°C in air followed by a carbonization stage in N2, at 500°C or 700°C depending on the starting char. A further stage of activation in steam was 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 N2 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) 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.