Study on the mechanism of the influence of HNO3 and HF acid treatment on the CO2 adsorption and desorption characteristics of coal

In order to cooperate with the application of acid fracturing enhanced permeability technology, this paper proposes using CO2 adsorption and desorption system and low-temperature nitrogen adsorption method to conduct experimental research on the changes in the CO2 adsorption and desorption characteristics of coal after treatment with HF solution and HNO3 solution. In addition, Combined with X-ray diffraction experiments, the indirect relationship between mineral dissolution and adsorption and desorption characteristics is analyzed. The research results show that: The acid solution transforms the pore structure of coal through the dissolution of mineral impurities. In the microporous stage, hydrofluoric acid is mainly used for pore formation and nitric acid for pore expansion. Acid treatment changed the adsorption characteristics of the coal sample, reduced the saturated adsorption capacity a, and increased the adsorption constant b. And a and b were linearly related to the specific surface area and pore volume, respectively. This paper has determined that adsorption equilibrium pressure 1.91 MPa and 2.57 MPa are the enhanced adsorption thresholds of hydrofluoric acid and nitric acid, respectively. After exceeding the threshold, acid treatment will no longer play a role in increasing CO2 adsorption. In addition, the acid treatment also changed the desorption characteristics of the coal sample, increased the initial desorption amount and the final desorption amount, shortened the desorption time. The effect of hydrofluoric acid was more evident than that of nitric acid.