Synergistic Mechanism of Ultrasonic-Chemical Effects on the CH Adsorption-Desorption and Physicochemical Properties of Jincheng Anthracite.

Ultrasonic is a new method to enhance coalbed methane recovery. A deeper comprehension of the synergistic mechanisms of combined ultrasonic-chemical modification on the CH adsorption-desorption capability and physicochemical properties of coal is necessary for potential field implementation, as the modification of coal reservoirs frequently necessitates the addition of chemical reagents. This paper evaluated the CH adsorption-desorption properties of anthracite modified by sodium dodecyl sulfate (SDS) solution, ultrasonic modification, and combined ultrasonic-SDS modification. Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, and micro-CT were applied to elucidate the synergistic mechanism of the combined modification. The research results show that the SDS solution reduces the saturated adsorption capacity of anthracite and increases its final desorption rate by dissolving clay minerals and the physical adsorption masking effect of SDS micelles on the coal surface. Some surface groups with low bond energy are broken or evaporated under mechanical vibration and thermal effects generated by ultrasonic. The original fractures are expanded and connected, which changes the adsorption-desorption properties of anthracite. The synergistic effect of the combined modification of ultrasonic-SDS can promote the penetration range and chemical reaction efficiency of the SDS solution, which expands the effective range of ultrasonic. After combined modification, the amount of aromatics, oxygen-containing functional groups, and aliphatic hydrocarbons on the surface of coal is reduced. The connected porosity of coal samples accounts for 91.5% of the total porosity. As a result, the saturated adsorption capacity of anthracite reduces by 26.7%, and the final desorption rate increases by 28.0%. The effect of the combined ultrasonic-chemical modification is better than that of a single modification.