The nanoscale pore characteristics of coking coals: Part 1 – Optimization of the experimental conditions and calculation methods of specific surface area and micropore volume

Key Laboratory for Chemical Metallurgy Engineering of Liaoning Province, University of Science and Technology Liaoning, Anshan, Liaoning 114051, P.R. China
e-mail: wangqi8822@sina.com

Received: 27 February 2016
Accepted: 2 September 2016

Abstract

The current evaluation system of the properties of coking coals is not sufficient since the so-called “abnormal coal” appears out control in some cases. In this study, in order to obtain reliable nanoscale pore structural parameters (specific surface area and micropore volume) to supplement and perfect the current evaluation system, a middle rank coking coal was investigated using low-temperature nitrogen physisorption technique to optimize the experimental conditions and calculation methods. the experimental conditions were listed as follows: sample evacuation times 4, 8, and 16 h; target temperatures 125, 150, 175 and 200 °C; sample weights 2000, 3500, and 5000 mg; sample particle size ranges <0.5, 0.5–1.0, and 1.0–2.0 mm; the Brunauer-Emmett-Teller (BET), t-plot, and Dubinin-Radushkevich (DR) methods only within the adsorption isotherm branch were adopted. The optimal experimental conditions were found to be as follows: 8 h sample evacuation time, 150 °C target temperature, 5000 mg sample weight, and <0.5 mm sample particle size range. In the BET, t-plot, and DR methods, BET method is more accurate to calculate total specific surface area compared with t-plot method; t-plot method can distinguish between micropore and external specific surface areas; besides, t-plot method based on Magee’s equation is more applicable to the coking coal sample than that based on de Boer’s equation. DR method is more sensitive to evaluate micropore volume than t-plot method. In order to obtain reliable and comprehensive pore parameters, these three methods should be combined with each other.