Microscopic adsorption properties of methyl acrylate on lignite surface: Experiment and molecular simulation study

Quality improvement of low-rank lignite is highly desirable for sustaining the increasing demand for primary fossil fuel. In order to characterize the microscopic adsorption behavior of nonionic methyl acrylate (MA) on the low-rank lignite, the Fourier transform infrared (FTIR) experiments, contact angle instruments, Grand Canonical Monte Carlo (GCMC), and molecular dynamics (MD) simulations were adopted in this study. The FTIR results suggested that the MA can be adsorbed in the oxygen-containing functional group region of lignite during the adsorption process. The adsorption performance of the hydrophilic organic matter of lignite to methyl acrylate was better than that of ash minerals. Contact angle results showed that the adsorption of methyl acrylate can improve the hydrophobicity of lignite. The adsorption of MA on lignite can be divided into monolayer adsorption stage (0-0.8 g/L), towards the critical micelle concentration (CMC) adsorption stage (0.8 g/L-CMC), micellar adsorption stage (CMC-1.6 g/L). From the perspective of saving the dosage of surfactant and improving the hydrophobicity of lignite, 0.8 g/L is the most suitable MA concentration. Finally, molecular simulations demonstrated that the adsorption isotherm of methyl acrylate on lignite surface conformed to the type-I Langmuir model, and the adsorption of methyl acrylate on lignite belongs to physical adsorption. Polar water molecules have advantages in the competitive adsorption process between water molecules and MA, while water molecules are greatly affected by temperature.