Pore volume and surface area of the Carboniferous coals from the Zonguldak basin (NW Turkey) and their variations with rank and maceral composition

Abstract

The macropore volume, micropore volume and surface area of Carboniferous bituminous coals from the Zonguldak basin in northwestern Turkey have been determined. Furthermore, variations of these coal properties with rank and maceral composition have been investigated. Helium density, mercury porosimetry and low-pressure CO 2 gas adsorption measurements were performed in order to determine the pore volumes and the surface area of coals. Helium and mercury densities of the coals vary between 1.28–1.41 and 1.11–1.32 g/cm 3, respectively. The macropore volume determined by mercury porosimetry varies between 0.0065 and 0.0687 cm 3/g. For the interpretation of the adsorption mechanism and for the determination of the respective pore volumes and surface areas, Langmuir and Dubinin–Radushkevich (D–R) equations were applied. The micropore volume and respective micropore surface area values are ranging from 0.0139 to 0.0524 cm 3/g and from 42 to 160 m 2/g, respectively. The Langmuir monolayer volume, which can be considered as an estimate of the gas adsorption capacity varies between 14 and 37 cm 3/g. The corresponding specific surface area values range from 80 to 216 m 2/g. A comparison of pore volumes with rank and maceral composition of coals indicated that micropore volume decreases with increasing maturity up to a value of 1.0% R o and then increases with further increase of coal rank. A similar trend is also observed with Langmuir monolayer volume and specific surface area. In general, an indicative correlation could not be observed between maceral composition and pore volume and surface area. However, a weak correlation does exist between Langmuir monolayer volume and vitrinite content.