Synergy of Parameters Determining the Optimal Properties of Coal as a Natural Sorbent

Abstract

Selection of the optimal properties of coal as a natural sorbent, both as a sample collected from a seam or of the coal seam itself, requires various parameters to be determined and may not be based on the knowledge of metamorphism degree only. In order to improve the predictions of sorption capacity and the kinetics, analyses of correlation and multiple regression based on the results of laboratory studies were performed for 15 coal samples with various coal rank. The maximum vitrinite reflectance (R0) for low-rank coals was 0.78%–0.85%, and 0.98%–1.15% and 1.85%–2.03% for medium- and high-rank coals, respectively. Coal samples were subjected to technical and petrographic analysis. The gravimetric method was used to perform sorption tests using methane, in order to determine the sorption capacity and the effective diffusion coefficient for each of the coals. Pycnometric methods were used to determine the textural parameters of coals, such as the percentage porosity and specific pore volume. The studies were further supplemented with an evaluation of the mechanical properties of the coals, Vickers micro-hardness, and elastic modulus. This work shows that the statistical multiple regression method enables a computational model including the selected petrophysical parameters displaying synergy with the specific sorption property—capacity or kinetics—to be created. The results showed the usefulness of this analysis in providing improved predictions of the optimal sorption properties of coal as a natural sorbent.

Sorption and Micro-Scale Strength Properties of Coals Susceptible to Outburst Caused by Changes in Degree of Coalification

“…there is a notable difference in their microhardness [ 28 ]. Studies conducted in recent years (own and of other researchers) proves that the results of coal microhardness parameter analysis with the changing degree of coalification may be somewhat different than the previous literature data (data from [ 30 ]). However, all study results, both those included in the archival studies and the current ones, presented recently by the authors of this publication show that microhardness properties may be an sign of specific coal behaviour and indicate features responsible for increased coal outburst susceptibility.…”

“…The basic characteristics of coals were obtained via technical analysis, which determined the total moisture content W t , volatile content V daf and ash content A d in the coal [ 30 ].…”

“…The degree of coalification is a parameter determining several coal properties. A higher degree of coalification results in a higher gloss, changes to microscopic properties (e.g., colour or structure), along with changes to strength properties [ 23 , 30 ], accumulation properties [ 24 ], etc. Therefore, assessment of the degree of coalification is the key and the starting parameter required for further studies of coal.…”

“…The Vickers method is the most frequently used method of determining coal microhardness [ 23 , 36 ]; the Knoop method is also sometimes used for this substance [ 43 ]. Microhardness has been used by a number of researchers to examine coal for many years [ 44 , 45 ], including the Upper Silesian Coal Basin [ 23 , 30 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ] and in other coal basins (e.g., Indian coals [ 41 ] or highly volatile, bituminous Kentucky coals [ 53 ]). Some researchers use microhardness tests to solve unusual problems—for example, Hower et al [ 53 ] presented an interesting use of Vickers microhardness tests to distinguish almost identical macerals of the vitrinite group.…”

Macromolecular Structure Controlling Micro Mechanical Properties of Vitrinite and Inertinite in Tectonically Deformed Coals—A Case Study in Fengfeng Coal Mine of Taihangshan Fault Zone (North China)

“…Hou et al [21] determined that the hardness and elastic modulus are in the order of exinite < vitrinite < inertinite by employing depth-sensing nanoindentation. Kožušníková [22] revealed that the Vickers microhardness and elastic modulus of coal sample with higher coalification were lower than of coal sample with lower coalification and also, Godyńand et al [23] found that micro-hardness value decreases with metamorphism degree using Vickers hardness test in Silesian Coal Basin, Poland. Fender et al [24] suggested that thermally immature liptinite macerals have a lower modal modulus than the inertinites and the modal Young's modulus of all macerals increases with maturity, based on atomic force microscopy.…”