离子型表面活性剂对低阶煤润湿性的调控机制

Regulation mechanism of ionic surfactant on the wettability of low rank coal

表面的强亲水性制约了低阶煤(LRC)的加工和利用,而表面活性剂吸附是调控LRC润湿性的有效方法之一。采用傅里叶变换红外光谱(FTIR)、接触角测定和密度泛函理论(DFT)计算探究了阴离子型表面活性剂和阳离子型表面活性剂对LRC表面润湿性的调控机制。阴离子型表面活性剂为十二烷基苯磺酸钠(SDBS),阳离子型表面活性剂为十烷基三甲基溴化铵(C_(10) TAB)、十二烷基三甲基溴化铵(DTAB)、十六烷基三甲基溴化铵(CTAB)。研究结果表明:表面活性剂对LRC润湿性的调控效果主要受表面活性剂亲水基电荷分布、疏水基长度和药剂吸附量的影响。表面活性剂亲水基的电荷分布影响了吸附的难易程度,在水相中,电离后LRC的-COO^(-)、DTAB的-N^(+)(CH_(3))_(3)和SDBS的-SO^(-)3基团的Mulliken电荷分别为-0.415e,0.483e和-0.69e;DTAB与LRC间的相互作用能为负(-345.36 kJ/mol),而SDBS与LRC间的相互作用能为正(14.88 kJ/mol),说明阳离子型表面活性剂更易吸附于LRC表面。-N^(+)(CH_(3))_(3)与-COO^(-)作用区域的电荷比未吸附前-COO^(-)的电荷减少了-0.341e,正电荷的亲水基与LRC表面负电荷相互中和,减弱了亲水位点的亲水性。表面活性剂疏水基的长度越长越有利于对亲水位点的覆盖,润湿性调控效果越好。当表面活性剂初始浓度过大时,将导致吸附量过量,上层表面活性剂的亲水基与水接触,对亲水性的减弱不利。

The strong hydrophilicity of the surface restricts the processing and utilization of low rank coal(LRC),and surfactant adsorption is one of the effective methods to control the wettability of LRC.Fourier transform infrared spectroscopy(FTIR),contact angle measurement and density functional theory(DFT)calculation were used to explore the regulation mechanism of anionic surfactants and cationic surfactants on the surface wettability of LRC.The anionic surfactant was sodium dodecyl benzene sulfonate(SDBS),and the cationic surfactants were decyl trimethyl ammonium bromide(C_(10) TAB),dodecyl trimethyl ammonium bromide(DTAB)and cetyl trimethyl ammonium bromide(CTAB).Results showed that the control effect of surfactant on the wettability of LRC was mainly affected by the charge distribution of hydrophilic group,the length of hydrophobic group and the adsorption capacity of surfactant.The charge distribution of hydrophilic groups of surfactants affected the ability of adsorption.In the aqueous phase,the Mulliken charges of-COO^(-)of LRC,-N^(+)(CH_(3))_(3)of DTAB and-SO^(-)3 of SDBS after ionization were-0.415e,0.483e and-0.69e,respectively.The interaction energy between DTAB and LRC was negative(-345.36 kJ/mol),while that between SDBS and LRC was positive(14.88 kJ/mol),indicating that cationic surfactants were easier to adsorb on the surface of LRC.The charge in the interaction region of-N^(+)(CH_(3))_(3)and-COO^(-)was-0.341e lower than that of-COO^(-)before adsorption,indicating that the hydrophilic group with positive charge neutralized with the negative charge on the surface of LRC,weakening the hydrophilicity of the hydrophilic point.The longer of the hydrophobic group of surfactants,the better coverage of hydrophilic points,and the better effect of wettability regulation.When the initial concentration of surfactant was too large,it would lead to excessive adsorption,and the hydrophilic group of the upper surfactant contacted with water,which was unfavorable to the weakening of hydrophilicity.