Effect of acidification on micro structure and adsorption characteristics of coal

To investigate the changes in the microstructure of coal under acidification and the mechanism of their impact on coal adsorption characteristics, low-temperature nitrogen adsorption experiments, infrared spectroscopy experiments, and isothermal adsorption experiments were conducted on coal samples before and after hydrofluoric acid treatment. The influence of acid solution on the pore structure and molecular structure of coal was analyzed, and the evolution mechanism of coal adsorption characteristics under acidification was explored based on the experimental results. The results showed that after acid treatment, the average pore size and total pore volume of the coal sample increased, while the specific surface area decreased. The acid solution has the effect of expanding pores and increasing capacity of pores. Acidification can change the micro molecularstructure of coal. After acidification, the benzene ring structure of coal samples gradually developed towards multi substituted benzene rings, and the longer fatty chains and weaker hydrogen bond structures were destroyed. Besides, the content of oxygen-containing functional groups increased. In the isothermal adsorption experiment, the maximum adsorption capacity and adsorption rate of methane on coal samples decreased by 14.02% and 23.58% respectively after acidification. Furthermore,the adsorption potential theory indicated that the adsorption capacity of coal samples for methane decreased and the adsorption space for methane decreases after acidification.