Understanding the multiple interactions of inertinite during pyrolysis/carbonisation with vitrinite: A study of two Australian coals of different rank

Abstract

Macerals (vitrinite and inertinite) were separated from two Australian coals to study interactions during coking. Macerals were blended in various ratios, and their viscoelastic properties and expansion/contraction behaviour measured using rheometry. The minimum viscosity of a vitrinite concentrate (VC) from a high-rank coking coal (vitrinite reflectance Rvo = 1.54%) increased according to an expected exponential trend with increasing amounts of added inertinite concentrate (IC), suggesting no interaction. Volatile release rates (VRR), obtained from thermogravimetric analysis, were the same as that predicted based on the assumption that vitrinite and inertinite behave independently. For a medium-rank coal (Rvo = 1.19%), increasing proportions of its corresponding inertinite also increased viscosity, but the extent that it increased was much less than expected. VRR from these blends were lower than expected from a mass average of the components. When the IC from the high-rank coal blended with the VC of the medium-rank coal, a dramatic increase in viscosity occurred along with retention of volatile matter. These observations have been attributed to inertinite displaying varying degrees of volatile adsorption and softening/deformation. It is evident that inertinite and vitrinite interact in multiple ways during pyrolysis, which could have competing influences on viscosity and, therefore expansion behaviour.