Molecular simulation on competitive adsorption characteristics of CH4/O2/N2 gas in lignite

Abstract

This study intends to explore the influence of temperature and molar ratio on the competitive adsorption of CH4/O2/N2 gas in coal. It probed into the competitive adsorption characteristics of CH4/O2 and N2/O2 binary mixed gas in Xiaolongtan lignite of Yunnan under different temperatures (303.15~383.15 K)and pressures (0~480 kPa)through grand canonical Monte Carlo (GCMC)and molecular simulation methods. Results show that : ① Within the range of test temperature and pressure, temperature will inhibit the adsorption of CH4, O2 and N2 by coal, and the adsorption capacity of coal to three gases is CH4>O2>N2. ② The selectivity coefficient of CH4/O2 adsorption is basically independent of the gas molar ratio, and shows decrease with the increase of temperature. The adsorption selectivity of N2/O2 on coal under different molar ratios was not significantly related to temperature and molar ratio. ③ With the increase of adsorption capacity, the isosteric adsorption heat of any component in the binary mixed gas shows linear increase. Under the same adsorption capacity, larger molar ratio of CH4/O2 and N2/O2 would lead to lower adsorption heat. However, when the adsorption capacity of CH4 is less than 0.029 mmol / g, the isosteric adsorption heat of CH4 gas shows little correlation with the molar ratio. The research reveals the influence mechanism of competitive adsorption behavior of CH4 and air on low temperature oxidation of coal.

Keywords

• coal spontaneous combustion
• competitive adsorption
• adsorption selectivity
• adsorption heat
• molecular simulation