Abstract
The adsorption of dodecyl trimethyl ammonium bromide (DTAB) on coal can affect the wettability of coal and change the water absorption of coal. After DTAB treatment, the change in the CH4 adsorption capacity of coal is worth further study. To reveal the microscopic mechanism of the influence of DTAB on the CH4 adsorption capacity of coal, we employed the density functional theory (DFT) with the 6-311 G (d, p) basis set. DFT-based computations interpreted the adsorption process of CH4 and DTAB on coal molecules and determined the stable structure, adsorption distance, Mulliken overlapping populations, and adsorption energies of the two adsorption configurations. The results showed that the adsorption energies of CH4 and DTAB on the molecular model of coal were 2.15 and 42.69 kJ/mol and the adsorption stability distances were 0.261 and 0.238 nm, respectively. The DTAB–coal configuration was more stable than the CH4–coal configuration. When there was competitive adsorption between DTAB and CH4 on coal, the coal molecules preferentially adsorb the DTAB. Infrared spectroscopy and adsorption experiments were also carried out, and the calculation results of quantum chemistry are consistent with the experimental results.
Highlights
Underground methane hazards are very dangerous, due to their flammability and explosibility [1,2,3].An increase in mining depth has led to a rise in ground stress and gas pressure
Density functional theory (DFT) with the B3LYP-D3 functional and 6-311 G (d, p) as the basis set was selected based on its combination of relative accuracy and speed
When CH4 or dodecyl trimethyl ammonium bromide (DTAB) adsorbed to the surface of coal molecules, the total energy of the system would be reduced
Summary
An increase in mining depth has led to a rise in ground stress and gas pressure. It should be stressed that methane is one of the most harmful greenhouse gases and constitutes a major risk to the natural environment [5]. The permeability of a coal seam can be enhanced through various forms of coal seam fracturing technology in coal mining sites, to improve the gas extraction effect [6,7]. The hydro-fracturing technique is another pre-drainage method that has been successfully used in the USA. This method is not universally applicable due to the different geology, coal seam characteristics, in-situ gas content, pressure, and saturation, as well as gas sources and the surrounding strata’s low in-situ permeability [9]
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