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

Abstract

Oxidation produces important transformations in the chemical composition and textural properties of bituminous coals. A higher-rank coal — semianthracite, 14.7% volatile matter — was oxidised in an oven with a forced air circulation, 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 heating 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 increase in the true and apparent densities, the increase being most pronounced for the series oxidised at 543 K. The pyrolysis of raw material and oxidised coals caused a decrease in oxygen and hydrogen contents and an increase 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. Both BET-N 2 and DR-CO 2 surface areas of the chars increase correspondingly, showing the positive effect of oxidation on the evolution of the solid texture.