Experimental study of influence of natural organic solvent limonene on methane adsorption–desorption behaviors of selected rank coals

For the clean and efficient extraction of coalbed methane (CBM), it is of great significance to understand the mechanism of the interaction between limonene, which is a natural organic solvent, and coal. In this study, the surface groups, nanoscale pore characteristics, and methane (CH4) adsorption–desorption behaviors of selected rank coals were compared and analyzed to explore the effect of limonene leaching-induced evolution of the macromolecular structure of coal on its adsorption–desorption behaviors. The results showed that with the increase in the mass fraction of limonene, the contents of the aliphatic, aromatic hydrocarbons, and the cross-linking degree of the macromolecular structure of the coal decreased. This led to pore volume expansion of the SH and SQ coals, from a range of 0.3–7 nm to 7–36 nm. The pore volume in the 1.5–7 nm range in the LD coal increased significantly under the combined influence of the pore-expanding effect of the 0.3–1.5 nm pores and the porosity-enhancing effect of the 7–36 nm pores. Therefore, the promotion effect of limonene modification on the CH4 adsorption-desorption behaviors of the coal was more evident in the medium- and high-rank coals than in the low rank-coals.