Modification And Molecular Simulation Of The Wettability Of Long Flame Coal By Nonylphenol Ethoxylates

Long flame coal is the important part of coal resources in China.However,through the conventional separation process such as flotation,efficient utilization for long flame coal is severely restricted due to low metamorphic grade,a number of oxygen-containing functional groups on surface,strong hydrophily and low floatability.Modifying wettability to improve hydrophobicity is the key of efficient utilization for long flame coal.The wettability of the long flame coal from Daliuta of Shendong Coal Group was modified by nonylphenol ethoxylates(NPEO).The effects of NPEO with different ethylene oxide(EO)adduct number(NPEO-8,NPEO-10 and NPEO-12)on the adsorption property and wettability rule were investigated.The microcosmic regulatory mechanism for wettability of the long flame coal was revealed at molecular level,which provided theoretical foundation and technical support for effective upgrading and utilization of long flame coal.The results of FTIR,XPS and 13C-NMR show that ratio of aromatic carbon and ratio of aromatic bridge carbon to aromatic peripheral carbon of Shendong long flame coal is 0.66 and 0.14,respectively.Aliphatic carbon structure is mainly composed of methylene and methyne.The ratio of-C-O,-COOH and>C=O is 8:2:1.Combining ultimate analysis data,the chemical formula of macromolecutar structure for Shendong long flame coal with C97H92O13 is obtained after optimization and correction.The adsorption isotherms of NPEO were well fitted by the Langmuir equation,which is spontaneous physical adsorption driven by hydrogen bonding.The kinetics of the adsorption conform with quasi-second order kinetics model,which are controlled by intra-particle diffusion and liquid membrane diffusion.As EO adduct number decreases,the spontaneity is improved,and the adsorption process is most likely to occur.The effective regulation of wettability for the Shendong long flame coal can be gained through NPEO.As the concentration of the surfactant gradually increases,the contact angle of long flame coal first increases and then decreases,and the maximum contact angle is obtained at around CMC of NPEO.The similar maximum contact angle of NPEO-8,NPEO-10 and NPEO-12 are achieved when the concentration is 35.32mg/L,45.26mg/L and 60.83mg/L,respectively.It is indicated that the efficiency order of improving hydrophobicity of long flame coal is NPEO-8>NPEO-10>NPEO-12.The adhesive work of coal/water system can be significantly reduced with the order of NPEO-8>NPEO-10>NPEO-12 at the condition of concentration below CMC.Due to interaction of NPEO(below CMC),C/O ratio of coal surface increase,absolute value of zeta potential and the oxygen-containing functional groups decrease.The results reveal the macroscopical mechanism of promoting hydrophobicity of Shendong long flame coal.Based on lacromolecular structure of Shendong long flame coal,the aggregation structure model of Shendong long flame coal is constructed.The results of molecular simulation show that the polar group of NPEO adsorbs at the hydrophilic sites of coal surface,leaving the intertwining hydrophobic portions of NPEO exposed to the solution.The results reveal the microcosmec mechanism of improving hydrophobicity of long flame coal.As EO adduct number decreases,the absolute value of interaction energy between NPEO and long flame coal,the number of hydrogen bond(donor is long flame coal and receptor is NPEO),and diffusion coefficient of water molecular within long flame coal/NPEO/water system gradually increased.The results indicate that adsorption binding capacity between NPEO and long flame coal and hydrophobicity of long flame coal modified by NPEO increase.The simulation results are agreement with experiment results of adsorption and wetting.