Effect of volatile matter release on optical properties of macerals from different rank coals

Abstract Ever since the recognition that macerals behave differently during the coking process, their thermal behaviour and its relationship with coke properties have become research topics of widespread interest. The present study is focused on the characterization of six bituminous coals of different rank from Upper Silesia (Poland) and their carbonized products obtained in a relatively high-capacity thermogravimeter under inert atmosphere and well-controlled heating conditions. A combined maceral–reflectance analysis was performed on samples carbonized at temperatures of 400, 450, 550, 750 and 1000 °C. Under such conditions, only coals with a reflectance of over 1.0% passed through a fluid stage as a result of which the coal particles lost their integrity. The reflectance of all the macerals was observed to increase with the pyrolysis temperature, temperature being the most relevant factor in determining the reflectance of inertinite macerals. The amount of unreactive inertinite exhibited a wide range of variation, with the lowest rank coals showing the smallest proportion of unreactive inertinite. The reflectance cut-off values separating reactive and unreactive inertinite decreased with coal rank to a stable value of ca. 1.5% for the highest rank coal. A 67–75% volatile matter release was required to cause a significant increase in the reflectance of the components.