Evolutions of nanoscale pore and chemical structures of tectonically deformed coals after supercritical CO<SUB align="right">2 treatment

Abstract

Supercritical CO2 treatments were carried out for four coal samples with different deformation degrees at around 35°C and 10 MPa for 5 h. Nanoscale pore and chemical structures of coals before and after treatments were studied via liquid nitrogen adsorption and X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) tests. The results showed that coal deformation induced more spaces and contact areas, and thus supercritical CO2 treatment presents improved effects on pore volume and specific surface area with increasing coal deformation degree. Moreover, supercritical CO2 treatment mainly induced increased pore volumes of pore types I (< 10 nm) and II (10-50 nm) and specific surface area of pore type I. In addition, supercritical CO2 treatment exerts substantial effects on chemical structures, including increased aromatic layer spacing, decreased the aliphatic compound or ethers, alcohols, and lipids, which is also related to coal deformation degrees. The experiments revealed that treated tectonically deformed coals present greater growths in gas adsorption and diffusion spaces and more obvious changes in chemical structure than the undeformed coal, which can improve CO2 storage and seepage. [Received: June 2, 2017; Accepted: February 10, 2018]