Experimental investigation on combined modification for micro physicochemical characteristics of coal by compound reagents and liquid nitrogen freeze-thaw cycle

Abstract

To meet urgent demands for efficient resources and sustainable development, an experimental study on combined physicochemical modification of coal was carried out. After 49 tests analyzed of single-factor experiment and orthogonal experiment, it was found that MW (mine water), 6% SLS (sodium N-lauroyl sarcosinate), 10% HNO3 and 3% [Bmim]Cl (1-Butyl-3-methylimidazole chloride), freeze-thaw cycle 8 times, and freeze-thaw time of 1.25 h each time was the best physicochemical modification scheme. Compared with raw coal, the wettability, porosity and permeability of the treated coal are significantly increased. Under the synergy of the combined physicochemical modification (including hydrogen bonding and tight filling) and the multi-field coupling (including temperature field, stress field and deformation field), the porosity is at an increase rate of 335.65%; the permeability is at an increase rate of 882.24%; while surface tension of the compound reagent is reduced to 16.24 mN/m. Furthermore, the relative content of C–C bonds and C–H bonds on coal surface increases greatly, while the relative content of C-O and COO decreased gradually, with a decrease rate of 57.61%. The results of this paper are beneficial to achieve efficient co-mining of coal and coalbed methane, and further improve safety and efficient production levels of coal mines.