Effect of soluble organic matter in coal on its pore structure and methane sorption characteristics

In order to study the effect of soluble organic matter within coal on its characteristics of gas adsorption, the organic matters in coal seam 7＃ (Linhuan) and coal seam 3＃ (Qinan) were extracted with THF at 30 ℃ under atmospheric pressure by microwave-assistant extraction. Adsorption isotherm experiments and low temperature nitrogen adsorption test were made for raw coal and their residues. The gas adsorbance, specific surface area and pore size distribution were analyzed. Gas adsorbance of soluble organic matter was theoretically calculated. The results show that CH₄-adsorption capacity of raw coal is stronger than those of their residues. After extraction, the specific surface area and total pore volume increase and average pore size decreases. Meanwhile, methane adsorption capacity is mainly influenced by 1.7~5.0 nm pores. Methane adsorbances of soluble organic matter are 0.45~4.22 and 0.69~4.99 mL/g, which account for 30% and 38% of the maximum adsorption capacity of raw coal under 0.1~5.0 MPa. Soluble organic matter occupies part of pores of coal, which influences structure of pores in coal. At the same time, the methane can be dissolved and adsorbed in soluble organic matter of coal under pressure.