Experimental study on modification of physicochemical characteristics of acidified coal by surfactants and ionic liquids

To study the modification of the physicochemical characteristics of acidified coal by surfactants and ionic liquids, N-2 adsorption, scanning electron microscopy and so on, combined with fractal theory were used. The results show that when the coal sample is treated with HNO3, a large number of corrosion pores can be generated, and the aromaticity of the coal can be improved. [Bmim]Cl (1-Butyl-3-methylimidazolium chloride) can reduce the proportion of oxygen-containing functional groups. Both HNO3 and [Bmim]Cl can effectively reduce the mineral content of coal. Neither HNO3 nor [Bmim]Cl is conducive to the wettability of coal, they increase the surface tension by 10.79 mN/m and 2.66 mN/m, respectively; SLS (Sodium N-lauroyl sarcosinate) reduces it by 20.79 mN/m. So SLS is added to improve the wettability. The combined action of HNO3 and SLS not only decreases the surface tension to 22.16 mN/m, which is 39.16% of that of HNO3 and can improve the wettability of the coal; but also, greatly increase the injectable water porosity of coal to 9.28%, which is 2.15 times of that of coal sample #1 and beneficial to coal seam water injection. HNO3, SLS and [Bmim]Cl have a strong synergistic effect, which severely breaks the pore size distribution of coal but can enlarge the average pore size of the coal and increase the porosity by 1.58 times. This approach can provide a new way to improve the efficiency of coalbed methane mining.