Molecular simulation of alkyl glycoside surfactants with different concentrations inhibiting methane diffusion in coal

The injection of surfactant solutions into coal seams is one of the most critical technical means of preventing coal mine disasters. It can effectively prevent coal and gas outburst disasters by reducing the gas concentration at the coal mining face. The Wiser model of coal was utilized to establish the initial CH4-containing coal. Different concentrations (0%, 0.2%, 0.4%, 0.8%, 1.2%, and 1.6%) of alkyl poly glucoside surfactant (APG) were injected into CH4-containing coal to investigate the microkinetic mechanism of inhibiting gas desorption. The diffusion parameters of CH4 (i.e., diffusion coefficient, relative concentration, interaction radius), the gyration radius of APG, and the interaction energy between surfactant solution and CH4-containing coal were analyzed on the basis of the kinetic results. Results showed that with the increase in APG concentration, the diffusion coefficient of CH4 decreased gradually. The distribution of CH4 in coal molecules and the change rate of diffusion coefficient increased remarkably. When the concentration of APG was 0%, the diffusion coefficient was 12.00 x 10-7 m2 s- 1, and that of 1.6% was 5.65 x 10-7 m2 s- 1, a reduction of 52.91% compared with the concentration of 0%. With the increasing concentration of APG, the gyration radius increased, and the interaction energy between APG and CH4-containing coal molecules decreased. The CH4 diffusion coefficient was negatively correlated with the APG gyration radius, and the number of hydrogen bonds was positively correlated with the interaction energy. With the increase in the gyration radius of APG molecule, more hydrogen bonds were formed between APG surfactant and coal molecules, resulting in a decrease in the interaction energy. The system gradually stabilized to effectively inhibit the diffusion of CH4 in coal, which can provide a basis to prevent coal and gas outburst disasters.