Chemical Modification Effect of Compound Solutions of Surfactants with Acetic Acid on Coal Pores

Abstract

Coal seam pores are the major places for coalbed methane storage, diffusion, and seepage, and changes in the pore structure cause changes in the porosity. The porosity of coal seams can be effectively improved by applying strongly corrosive and oxidative chemical reagents to coal seam pores, but these reagents may pose threats to coal workers, corrode mining equipment, and pollute the environment. In this study, coal samples were treated with solutions compounded by acetic acid and anionic, cationic, and non-ionic surfactants. The variations of pores in coal samples after the compound modification of surfactants and acetic acid were investigated. Experimental methods of SEM, MIP, LTNA, PAC, and FTIR and fractal theory are applied in this work. The results reveal that the compound modification of surfactants and acetic acid conduces to the transformation of pore shape and affects a wider pore size range. The anionic and cationic surfactants can increase the hydrophilicity and can promote the connection of larger pores. The non-ionic surfactant reduces the hydrophilicity and capillary effect yet increases the porosity. Thus, it promotes the connection of pores and makes the pore surface smooth and the pore structure simple. Comparing the three kinds of surfactants, non-ionic surfactants are more conducive to coal seam pore reconstruction.

A comprehensive insight into the effects of acidification on varied-sized pores in different rank coals

“…Therefore, welldeveloped pore and fracture network is essential for the fast and efficient gas extraction (Liu et al, 2023). However, for coal seams with high mineral content, the pores and fractures are often blocked by minerals (such as calcite, kaolinite and pyrite), which seriously hampers the desorption and migration of CBM (Chen S. et al, 2021). Aiming at this problem, many studies have demonstrated that acidizing treatment can effectively remove the minerals and link the blocked channels (Turner and Steel, 2016;Wang et al, 2020;Chen Q. et al, 2021;Guo et al, 2021).…”

“…In recent years, many scholars have performed studies on the variation of coal pore structure under acidification. In these studies, the pore structure was commonly characterized by nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), gas adsorption method (GA), and highpressure Mercury intrusion (MIP) (Zhang et al, 2016;Zhao et al, 2018;Ni et al, 2020;Wang et al, 2020;Liu et al, 2021;Xie et al, 2021;Yi et al, 2021). For example, Ni et al explored the changes in pore structure under nitric acid treatment by SEM and LTGA-N 2 .…”

“…In the work reported by Xie et al, SEM was used to qualitatively evaluate the changes in surface morphological characteristics caused by acetic acid acidification, and the combination of MIP and LTGA-N 2 methods was used to quantitatively analyze the overall evolution characteristics of pore structure. They found that acidification helped to form cylinders pores and parallel plates pores, thus improving the pore connectivity (Xie et al, 2021). Taking acid solution with different components as treatment agents, Li et al carried out NMR and SEM tests on the raw and acidified coal samples and explored the pore evolution characteristics, showing that different acid solutions affected macropores (1-100 µm), mesopores (0.1-1 µm) and micropores (<0.1 µm) differently .…”

Microstructure Study of High-Rank Coal in an Alkaline Solution at the Chengzhuang Mine

“…At present, many scholars are using different surfactants to change the wettability of the coal surface, which in turn affects the pore structure and adsorption properties of coal. − Meng et al and Liu et al formed an effective directional closely aligned adsorption layer after surfactant treatment of lignite, which facilitates coal adsorption. Ma et al concluded that SPAN80 can change the wettability of the coal surface and attenuate the effect of oxygen-containing functional groups on the coal surface through hydrogen bonding adsorption by the surfactant SPAN80 on the promotion of coal slurry flotation.…”