Estimation of Pores Distribution in Lignite Utilizing Hg, H2O, CO2, and N2 as Molecular Probes

Pores size distribution (PSD) and surface area (SA) analysis are so important for the description of porous materials, so selection of different pore characterization methods is emphasized, especially nondestruction methods. In this study, N 2, H 2 O, CO 2, and Hg were utilized as molecular probes to estimate the PSD in Shengli lignite (SL). In the N 2 adsorption, traditional degassed sample and wet samples freezing by liquid N 2 were combined to obtain the PSD and moisture distribution in SL. The pores of degassed samples were mainly located in the range of 5–100 nm, and most of the moisture was in the larger macropores in the range of 26–100 nm, peaking at 37 nm. We used two methods of H 2 O as molecular probe: H 2 O dynamic adsorption and low-field nuclear magnetic resonance (LFNMR). The saturation concentration of H 2 O in the pore of SL was 0.29 cm 3 /g from H 2 O adsorption, and the pores located in the range of 1–154 nm and peaked at 42.4 nm from LFNMR. The comparison and combination of different molecule probes were also presented. The surface area (SA) from CO 2 adsorption was the most credible because of the good monolayer adsorption of CO 2 in the micropores. N 2 and CO 2 adsorption would lead to an underestimation of the mesopore and micropore volume, and LFNMR has the most potential for PSD analysis owing to the high accuracy of the equipment and the nondestructive sample (without predrying process).