Study of porous development in pyrolysis chars obtained from a low-volatile coal

Oxidation produces important transformations in the chemical composition an d textural properties of bituminous coals. A higher-rank coal - semianthrac ite, 14.7% volatile matter - was oxidised in an oven with a forced air circ ulation, at 473 and 543 K, for periods of 1-7 days. The pyrolysis of fresh and oxidised coal samples was performed under nitrogen up to 1123 K at a he ating rate of 60 K min(-1) without a soaking time. As oxidation progressed, increases in volatile matter and oxygen content were observed for all the coals. Preoxidation led to a densification of carbonaceous matter with an i ncrease in the true and apparent densities, the increase being most pronoun ced for the series oxidised at 543 K. The pyrolysis of raw material and oxi dised coals caused a decrease in oxygen and hydrogen contents and an increa se of up to 93% in carbon content. The true density of the chars was higher than that of the oxidised coals. Total pore volume and porosimetry values show that oxidation has a strong influence on pore-size distribution in the chars, a longer oxidation favouring a pronounced microporous character. Bo th BET-N-2 and DR-CO2 surface areas of the chars increase correspondingly, showing the positive effect of oxidation on the evolution of the solid text ure. (C) 2001 Elsevier Science B.V. All rights reserved.