Investigation of the Adsorption Behavior of Organic Sulfur in Coal via Density Functional Theory (DFT) Calculation and Molecular Simulation

In
this paper, we have investigated the chemical adsorption behavior
of O2 on five types of organic sulfur (thiol, sulfoxide,
thioether, sulfone, and thiophene) in polycyclic aromatic hydrocarbon
(PAH) sheets using density functional theory (DFT) calculations. Here,
the adsorption energy of O2-organic sulfur exceeds that
of O2-PAH. Sulfone tends to be more favorable for oxidation
reactions than other organic sulfur compounds and PAH by energy gap
and deformation charge density analyses. A large charge transfer occurs
between O2 and organic sulfur compounds by charge analysis.
A radical distribution function (RDF) analysis shows that O2/CO2/N2 is preferentially adsorbed on nitrogen/sulfur/oxygen-containing
functional groups in coal. To inhibit the reaction of sulfur-containing
coal with oxygen, the physical adsorption of pure gas (CO2/O2/N2) and binary mixed gases (CO2 + O2/N2 + O2/CO2 + N2) is conducted at different temperatures and geological depths
using molecular dynamics (MD) and grand canonical Monte Carlo (GCMC)
simulations. The adsorption capacities of five types of organic sulfur
with respect to the pure gases decrease with increasing temperature
and increase with increasing depth. For O2/CO2, CO2/N2, and O2/N2 binary
gas systems, the order with respect to adsorption amount is CO2 > O2 > N2. The factor of adsorption
capacities is also evaluated, and the results show that pore volume
plays a key role in adsorption behavior.