In this work, N-doped hierarchical porous carbon has been successfully fabricated by KOH activation of waste wool. The optimal sample exhibits good CO₂ adsorption capacity under atmospheric pressure (1 bar), as well as excellent CO₂/N₂ selectivity.

A laboratory test was conducted to investigate the effect of the freeze‐thaw action of liquid nitrogen on the pore structure and permeability of coal rock. First, coal rock samples with similar sound velocities and permeabilities were selected. These samples were prepared in different water saturation levels and subjected to nuclear magnetic resonance (NMR) test before and after the freeze‐thaw action. Furthermore, the freeze‐thaw cycle of liquid nitrogen, freezing time, and water saturation of coal rocks were controlled in permeability test. Results showed that the pore diameter, porosity, and permeability of the coal rocks increase after the freeze‐thaw action of liquid nitrogen. These characteristics increase further with the increase of water saturation. The fracturing mechanisms of the freeze‐thaw action of liquid nitrogen were summarized in two aspects, phase change of pore water and cold shock, and cold shock was mainly discussed. The results indicate that the effect of cold shock is still crucial at low water saturation, but it is limited by the degree of temperature drop. In general, freeze‐thaw action of liquid nitrogen can cause damage to pore structure, promote the formation of fracture networks, and consequently improve the permeability of coal rock.

To understand the effects of thermal shock on microcrack propagation and permeability in coal, thermal shock tests were conducted on coal specimens by using a constant temperature drying oven (105 °C) and a SLX program controlled cryogenic tank. The growth and propagation of microcracks were measured with computer tomography (CT) scanning and scanning electron microscope (SEM) tests. Results showed that thermal shocks improved the permeability of coal significantly. Notably, the permeability of coal after thermal shocks increased from 211.31% to 368.99% and was positively correlated with temperature difference. CT scanning images revealed that thermal shocks increased the crack number, crack volume and crack width as well as smoothened and widened the gas flow paths, thereby enhancing coal permeability. Moreover, SEM images showed that heating-cooling shocks created more new microcracks, forming more complex crack propagation paths and better connectivity among microcracks in coal compared to cooling shocks. We proposed a crack propagation criterion for coal to explain the mechanism of crack failure and propagation during thermal shocks. Our experiment results and theoretical analysis indicate that the heating-cooling shock is more effective in damaging and breaking coal than the cooling shock. Thus, it can be used as an alternative approach to enhance coal permeability in the production of coalbed methane (CBM).

Experimental system for investigating gas-desorption characteristics of deformed coal was established. The gas desorption law of deformed coal with different damage extent was investigated. The desorption characteristics of deformed coal having different size under different equilibrium pressures were determined. This provides a theoretical basis for the prediction of coal and gas outburst, the measurement of pressure and content of coal seam gas, and the estimation of gas emission of coal mining fell.