Effects of Chemical Components and Structure on the Pore Properties of Lignite Treated by Acidification and...

Acid-tetrahydrofuran (THF) treatment could change the soluble components and chemical structure of coal, enhancing the gas extraction performance. Gas chromatography-mass spectrometry (GC-MS) was adopted to analyze the changes in the soluble organic matter in lignite after acid-THF treatment. Based on Fourier transform infrared (FTIR) testing, parameter variations including degrees of hydrogen enrichment (I₁), oxygen enrichment (I₂), aromatization (I₃), and aromatic condensation (I₄) of coal were quantitatively analyzed. Meanwhile, the pore structure changes were analyzed through the N₂-BET experiment and FHH fractal model. The effects of lignite chemical components and structure on the pore structure were discussed. With the combined acid-THF treatment, lignite extracts are dominated by aliphatic and aromatic compounds, promoting the transformation of micropores and mesopores into macropores. The values of I₁, I₂, I₃, and I₄ of the acidified coal are smaller than those of the original coal samples. I₁, I₂, and I₄ further decrease with an increased THF concentration. After the combined treatment, the maximum gas adsorption amount of coal decreases from 14.1439 cm³/g to 9.6635 cm³/g and 6.5026 cm³/g. Acid-THF treatment could lead to a decrease in I₁, with a subsequent reduction in the specific surface area (SSA) and pore volume (PV) and an increase in the average pore size (APS). Moreover, significant solubilization of oxygen-containing functional groups results in a decrease in SSA and PV and an increase in APS with decreasing I₂. Relationships between I₄ and pore structure parameters are similar to those of I₁ and I₂, reflecting a decrease in aromatic condensation that increases the pore size.