Molecular Simulation Study On The Hydrophobic Modification Of Lignite Surface By Surfactants

With the increasing consumption of coal resources,the utilization rate of lignite mining has gradually increased.However,due to the high oxygen content of lignite and strong surface hydrophilicity,the floatability of lignite is poor,which will cause a lot of waste of resources in the development and utilization of lignite.Therefore,surfactants are often used in coal preparation plants to modify lignite to improve its surface hydrophobicity,thereby increasing the yield of flotation clean coal.However,there are still few studies on the two scales of quantum chemistry and molecular dynamics.Therefore,this article intends to explore the mechanism of action of different agents through a combination of experiment and simulation.Different concentration gradients of Gemini surfactants,DTAB and SDS were used for adsorption tests with lignite test coal samples.Using XPS and FT-IR to compare and analyze the adsorption mechanism of different kinds of surfactants on the surface of lignite.And studied the changes of lignite pores under the action of different agents.Subsequently,the molecular structure of lignite was studied using ¹³C-NMR spectroscopy.Finally,quantum chemistry,ab initio molecular dynamics and classical molecular dynamics simulation are used to study the water absorption mechanism of lignite and reveal the phenomenon of water molecule displacement on the surface of lignite.The adsorption mechanism of surfactants on the surface of lignite and the influence mechanism on the water absorption process of lignite were explored from the molecular level.The adsorption test shows that the surfactant can be adsorbed on the surface of the lignite,covering the polar groups on the surface of the lignite.In addition,surfactant molecules will also enter the pores of the lignite.Analyzing the 13C-NMR spectrum of lignite,it can be found that the aromatic carbon and aliphatic carbon content of lignite are 52.67%and 47.33%,respectively.Among them,carboxyl,ether oxygen,hydroxyl and carbonyl are the main polar functional groups in lignite.The extreme value area of the surface electrostatic potential of lignite molecules mainly appears near the N and O atoms containing lone pairs of electrons.The positive value area of electrostatic potential of DTAB and Gemini agents is mainly located in the head base part,while SDS is just the opposite.The interactions between different polar functional groups and water molecules mainly exist in the form of hydrogen bonds,accompanied by different sizes of dispersion and steric hindrance effects.There is a substitution phenomenon between water molecules and polar groups,and this substitution phenomenon is mainly manifested in the formation and breaking of hydrogen bonds.In the adsorption model,the number of hydrogen bonds formed between water molecules will be reduced by the influence of surfactants.At the same time,the lifetime of hydrogen bonds formed between water molecules and lignite will be reduced,and the orientation distribution of water molecules will also be affected.Surfactants will be adsorbed on the surface of lignite in the form of different order parameters,and exist in a form closer to and parallel to XOY.In addition,the surfactant will spontaneously enter the pores of the lignite along with the flow of water molecules,and be adsorbed on the inner surface of the pores of the lignite.The addition of surfactants will inhibit the diffusion of water molecules in the pores,resulting in a significant decrease in the number of water molecules in the pores of lignite.The paper has 60 pictures,15 tables,and 113 references.