Effect of acetic acid concentration and dissolution time on the evolution of coal phases: A case report of bituminous coal

Abstract

In the environment of high in-situ stress, the closing-up of coal seam pores and fractures has a great influence on the flow of coalbed methane. The acidification method can effectively expand fractures and generate new fractures, which is of great significance to improve the efficiency of coalbed methane mining. In order to investigate the correlation between the components in coal and the time and concentration of acetic acid dissolution, in this paper, Fourier infrared spectroscopy, X-ray diffraction and scanning electron microscopy experiments were performed on bituminous coal after 1, 3, 5, 12, 24, 48 and 72 h of dissolution to obtain the changes of coal components, organic functional group parameters and coal crystal structure. The results show that when acetic acid reacts with coal, kaolinite is recrystallized within 24 h of dissolution, and the recrystallized crystals are corroded by acetic acid within 24–72 h. The sensitivity of different functional groups to acetic acid is different, and the content of C=O and aliphatic group in acidified coal increases. The surface morphology of dissolved coal samples was observed by scanning electron microscope. It was found that the dissolution effect of acetic acid on coal surface cracks increased with the increase of acetic acid concentration. Combined with the specific experimental results, the best effect of 75% acetic acid on the coal samples was obtained after 72 h of dissolution.