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

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.