Construction of molecular structure of low/middle coal rank and its adsorption mechanism of CO2 after N/S/P doping

There are significant differences in carbon capture capacity of coals with different degrees of metamorphism after doping modification. In this work, we found that with the increase of the degree of coal metamorphism, the degree of aromatic ring condensation gradually increases, and the coalification process is essentially a process of deoxidation and side chain shedding. Pyridine and Pyrrole are the main forms of nitrogen present in the four coal samples, accounting for about 72.80%-74.39% of the total nitrogen. Elemental sulfur in the middle rank coal samples was mainly in the form of thiophene. The S-CYM system had the largest specific surface area (2536.78 m2/g), and the S-JM system had the highest porosity (23.89%).The adsorption capacity of N-low rank coal for CO2 was higher than that of the other low rank coal blending systems (1.21 mmol/g), and the S-modified middle rank coal demonstrated a high carbon capture in the middle rank doping system (2.12 mmol/g). N-doping of low rank coals enhances the diffusion of CO2 in the coal structure, and modification of medium rank coals by sulfur enhances the diffusion process of CO2. These results provide theoretical guidance for the development of novel solid adsorbents for carbon capture technology.