Mercury porosimetry and its application to the analysis of coal pore structure

Abstract

Mercury porosimetry, gas adsorption, helium and mercury densities and small angle X-ray scattering were the methods used for studying porosity characteristics of a number of Czechoslovak coals ranging from lignite to semi-anthracite. Total pore volumes were measured in the pore radii range 0.1 – 7500 nm and then divided into the following groups: micropores (smaller than 1.8 nm), mesopores (1.8 – 30 nm) and macropores (over 30 nm). Coal porosity values ranged from 1.3 up to 43%. With low and medium-rank coals (carbon content under 76%), porosity is mostly due to mesopores. Micropores and mesopores account for a substantial share of the porosity of bituminous coals (carbon content over 80.6%). The distribution of mesopores was determined for an identical pore radii interval on the basis of data obtained independently by means of mercury penetration, gas adsorption and small angle X-ray scattering. High-pressure mercury penetration is an effective method of obtaining the coal porosity spectrum within a broad interval of pore radii, provided that a correction is made for the coal compressibility when evaluating the measured data. The recommended value of the mercury—coal contact angle is 135† for brown coal and 130° for bituminous coal.