Molecular Simulation And Experimental Study On Wettability Regulation Of Bijie Anthracite

Coal plays a"mainstay"role in China’s primary energy,which has its own unique advantages and cannot be completely replaced.As the level of mining mechanization is improved,coal mining efficiency is improved,the frequency of coal dust generation is accelerated,which will put forward stricter prevention and control requirements for the health of miners and the safe and efficient production of mines.In order to reduce the harm of coal dust,the influence of surfactants on the wettability of anthracite was studied comprehensively from both macro and micro perspectives through the combination of molecular simulation and experimental research.Materials Studio software was used to explain the wetting mechanism.The average molecular structure of anthracite was verified by molecular dynamics density simulation.The molecular structure of surfactant was analyzed by the principle of quantum chemistry.Through molecular dynamics,the adsorption configuration,relative concentration distribution,non-bond interaction,hydrogen bond interaction and azimuth shift of water were simulated to explain the wetting mechanism,and the differences and similarities between non-ionic surfactant and anionic surfactant in the wetting of anthracite were compared.Ten surfactants will be selected in the experiment:Fs-3100（fluorosurfactants FS-3100）,NP-10（nonylphenol polyoxyethylene ether 10）,CF-10（Dow triton）,AEO-9（fatty alcohol polyoxyethylene ether 9 carbon chain 12-14）,JFC（fatty alcohol polyoxyethylene ether Carbon chain 6-8）,AES（sodium fatty alcohol polyoxyethylene ether sulfate）,MES（sodium fatty acid methyl ester sulfonate）,Rapid Penetrant T（diisooctyl maleate sulfonate）,AOS（α-enyl sodium sulfonate）,SDBS（sodium dodecylbenzene sulfonate）.The monomer selection of surfactants was carried out by combining dynamic surface tension and dynamic contact Angle experiments.The wetting characterization of anthracite was investigated by Fourier transform infrared spectroscopy.The optimum concentration of optimum monomer to anthracite wettability was obtained by means of improved sedimentation experiment and infiltration experiment,and the compound of optimum monomer was carried out.Finally,the performance of the optimal compound wetting solution was comprehensively evaluated through spray dust removal experiment,scanning electron microscope experiment,specific surface area experiment,corrosion detection experiment,wind resistance test and water retention test:（1）The average molecular structure of Bijie anthracite was verified by molecular dynamics density simulation.The molecular structure of surfactant was analyzed by frontier orbit and electrostatic potential diagram based on quantum mechanics principle.By comparing AES with AEO-9,it can be concluded that AES has similar performance with AEO-9.By comparing AEO-9 with NP-10,it is concluded that the benzene ring rearranges the electron cloud of the structure,thus changing the activity of the surfactant.Combined with the electrostatic potential diagram of surfactant molecules,the four reagents have high activity.The electrostatic potential of ethylene oxide of NP-10 and AEO-9 is relatively small,and the electrostatic potential of AES and SDBS near the hydrophilic group is relatively small.These sites with low electrostatic potential are the best active sites for adsorption with coal molecules,easy to adsorption.Surfactants coat the surface of the coal tightly,forming a network.The surfactants are arranged in a directional manner on the coal surface,the hydrophobic chain is near the coal side,and the hydrophilic chain is near the water side.According to the relative concentration distribution of anionic surfactants and non-ionic surfactants,anionic surfactants have stronger directional arrangement.Van der Waals force is the main force of water adsorption on coal without surfactant.Surfactants have little effect on van der Waals force,but the electrostatic force and hydrogen bond force of water adsorption on coal surface are greatly increased,so the wettability of anthracite is enhanced.However,the increase of non-bond interaction energy of anionic surfactant is higher than that of non-ionic surfactant.Surfactants greatly improve the hydrogen bond between coal and water.Because AEO-9 and NP-10 have more oxygen-containing groups than SDBS and AES,anionic surfactants have less influence on hydrogen bond than non-ionic surfactants.The diffusion coefficient of water molecules in water/coal system is greater than that in water/surfactant/coal system.（2）Through the dynamic surface tension test,the reagents selected（preparation of 0.2%wetting solution）.All surfactants conform to Rosen’s empirical equation（correlation coefficients greater than 0.92）.According to the parameters(n,t*,R_1/2)fitted by dynamic surface tension,the wetting ability of surfactants is in the order of Rapid Penetrant T>AEO-9>SDBS>NP-10>JFC>AES>AOS>MES>FS-3100>CF-10.Through data comparison,the smaller the n value is,the smaller the t*value is,the smaller the R_1/2 value is,and the greater the surfactant activity is.However,the change range of n value is small,and the change range of t*and R_1/2 is large.According to the dynamic contact Angle test and the analysis of wetting factor K,the wetting ability of each reagent on anthracite was as follows:AEO-9>NP-10>Rapid Penetrant T>SDBS>AOS>JFC>AES>MES>FS-3100>CF-10.The wetting results obtained by the two experiments were roughly the same.Two anionic surfactants with the best wetting ability were selected:Rapid Penetrant T and SDBS.Non-ionic surfactants:AEO-9 and NP-10.The four reagents were used as the components of the compound wetting solution for the compound experiment.Through infrared spectrum experimental analysis,the content of oxygen-containing functional groups in anthracite modified by surfactants showed an upward trend,indicating that the content of hydrophilic groups on the surface of anthracite increased,and the wettability of coal was improved.NP-10 and SDBS also have certain effects on benzene ring structure.It is noteworthy that both AEO-9 and NP-10 contain hydroxyl groups,which do not affect the structure of aromatic hydrocarbons,but the introduction of ether bond at 1080 cm^-1 can be obviously observed,indicating that there are also strong chemical modifications on coal molecules.However,the Rapid Penetrant T treatment process is relatively"mild"and only increases the content of some oxygen-containing functional groups,without damaging or affecting any structure of coal molecules.（3）Through the combination of improved settlement experiment and infiltration experiment,considering the settlement rate and economic cost of coal dust,the optimal concentration of AEO-9,Rapid Penetrant T,SDBS and NP-10 for anthracite wetting is 0.4%,0.4%,0.4%and 0.8%,respectively.The combined wettability and infiltration rate of anthracite were greatly improved.There are antagonistic and synergistic effects among each monomer.Through experimental comparison,the best compound wettability of anthracite is AEO-9+NP-10（the mass fraction of AEO-9 is 0.4%,and the mass fraction of NP-10 is0.8%）.（4）Based on the optimum wettability,the properties of the compound wettability were tested comprehensively.Through the spray dust removal experiment,the combined wetting solution greatly improves the dust removal efficiency of anthracite.When the water supply pressure and water consumption increase,the number and initial velocity of dust suppression droplets are increased,and the collision probability and effect of water and coal dust are improved.The wetting agent has a better trapping effect on coal dust.Through scanning electron microscope experiment,the combination of wettability can enhance the bonding effect of coal dust particles in the air.Through specific surface area experiment,the combination of wettability can change the surface characteristics of anthracite,and eventually the specific surface area decreases and wettability improves.Through corrosive test:the PH value of the compound wetting solution is 6.28,which basically has no negative impact on the soil.Through the wind resistance test:the combination of wetting liquid can improve the wind resistance of coal dust,can effectively avoid the secondary dust of coal dust.Through the experiment of water retention performance,the"water retention ability"of coal dust was improved by the combination of wetting liquid,and finally a certain water retention effect was achieved.