Effect of ionic liquid treatment on pore structure and fractal characteristics of low rank coal

In order to study the variation of pore characteristics and fractal dimensions, coal samples are treated by ionic liquid with different concentrations. Then the N-2 isotherm adsorption/desorption experiment is carried out. The results show that water treatment caused a decrease in total pore volume. While the total pore volume in ionic liquid treated coal samples are larger than that in water treated coal sample. In comparison with water treated coal sample, the volumes of micropores in ionic liquid treated coal samples are reduced and the specific surface areas are increased. However, the volume and specific surface area of the mesopores are opposite to those in the water treated coal sample. The fractal dimensions D-1 and D-2 are calculated. The results show D-1 decreases in water treated coal sample while increases in ionic liquid treated coal samples. D-2 decreases obviously in water treated coal sample. Besides, it is lower than that in ionic liquid treated coal samples. Those indicate single water treatment will decrease the surface roughness and structural complexity of pores, while ionic liquid treatment will increase it. This study is of great significance to enhance the CBM exploitation and reduce the water block effect.