Effect of acid-thermal coupling on the chemical structure and wettability of coal: An experimental study

Coal is the primary fossil fuel in China's energy sector. As the amount of mining continues to increase, the high concentration of dust generated poses a severe threat to equipment and frontline workers. The coupling influence of HCl and temperature on the structure and wettability of coal were conducted by experiments. The phenomenon indicates that the contact angle between coal treated with HCl of different temperatures and water is reduced, the settling distance in an aqueous solution is longer, and the effect is significant with the increase of temperature, demonstrating the acid-thermal coupling solution improves the wettability of coal. Secondly, detailed analysis of coal functional groups and surface element, shows that the percentage of hydrophilic groups increased, such as OH⋯O, free –OH, and hydrophobic groups were destroyed, such as the asymmetric deformation vibration of adjacent H. The L, ‘C', and DOC show an increasing trend, while I first increase and then decrease by analyzing the trends of IR indices of coal. The conclusions prove that the degree of coal deterioration changed after treatment with acid-thermal coupling conditions. The influence mechanism of acid-thermal coupling solution on coal was explored to provide ideas for improving the wettability of coal from the source.