表面活性剂吸附对褐煤润湿性影响及其调控机制研究

发布时间：2018-05-17 04:34

本文选题：表面活性剂 + 亲水性抑制　；参考：《太原理工大学》2017年博士论文

【摘要】：褐煤是重要化石能源之一,随着经济发展对能源需求的日益增长,褐煤在我国煤炭消耗中的比例逐年提高。褐煤的低煤化程度赋予它氧含量高、吸水能力强的特点,在开发利用过程中造成大量的能源浪费,如运输成本高、燃烧热值低等。然而传统低阶煤干燥提质技术对于解决干燥后煤样水分复吸的问题还不够完善,不能满足现阶段对低阶煤高效开发利用的要求。表面活性剂作为调节界面性质的化工产品之一,其双亲分子结构决定了它能够在褐煤表面形成定向的紧密吸附层,疏水基团远离吸附方向,降低褐煤表面亲水性,抑制干燥后煤样水分复吸。本文以芒来褐煤为实验煤样,研究了褐煤润湿性及水分复吸性,考察了表面活性剂亲水基团类型和疏水基团结构(碳链长度、芳香结构、环结构、双子结构等)以及非离子表面活性剂HLB值对褐煤表面亲水性抑制效率的影响,利用微量热、微电泳、表面张力、红外光谱、紫外可见光分光光度计、X射线光电子能谱仪(XPS)和液氮吸附等仪器表征方法和量子模拟计算方法分析了阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)、阴离子表面活性剂十二烷基硫酸钠(SDS)和非离子表面活性剂十二烷基聚氧乙烯醚(C12(EO)15)在褐煤表面的吸附特征和吸附机理,此外还考察了褐煤中有机质、矿物质和煤化程度对褐煤润湿性以及褐煤亲水性抑制效率的影响。得到主要结论如下:褐煤中有机质的润湿热远高于矿物质的润湿热,是褐煤润湿放热的主体。矿物质中高岭石的润湿热高于方解石和石英。芒来褐煤水分复吸符合二级动力学模型,褐煤中复吸水分含量与润湿热负相关,水分含量越高,润湿热越小。芒来褐煤水分复吸过程中在表面形成的单层或团簇吸附水降低润湿热较为显著,在孔隙吸水或毛细凝聚吸水对润湿热影响较小。含氧官能团含量是影响褐煤润湿热的重要因素,随着煤化程度增加,煤中含氧量减少,润湿热降低。极性润湿剂和非极性润湿剂对褐煤润湿放热差异显著,水和无水乙醇对褐煤的润湿热远大于正构烷烃对褐煤的润湿热。褐煤吸附表面活性剂能够降低褐煤润湿热,抑制干燥褐煤水分复吸,二者具有一致性,其本质是表面活性剂吸附降低了褐煤表面的亲水性。表面活性剂对褐煤表面亲水性的抑制依赖于表面活性剂能在褐煤表面形成有效的定向紧密排列吸附层。这与表面活性剂分子结构密切相关。具体表现在:亲水基团中阳离子和非离子表面活性剂对褐煤亲水性抑制效果优于阴离子;疏水基团中,随着疏水基团链长的增加,褐煤表面亲水性抑制效率增加;疏水基团中含有支链和苯环结构的表面活性剂不利于褐煤表面亲水性抑制效率的增加;双子结构的gemini型表面活性剂对褐煤表面亲水性的抑制效率高于单链结构和双疏水基结构的表面活性剂;吐温系列表面活性剂对褐煤表面亲水性抑制效果不明显;烷基糖苷类含多羟基的表面活性剂增强了褐煤表面的亲水性;随着非离子表面活性剂c12(eo)n的hlb值减小,褐煤表面亲水性抑制效果有增加趋势,最小值出现在hlb值为13.6附近。表面活性剂对褐煤亲水性抑制的关键是抑制褐煤中有机质的亲水性。褐煤中矿物质亲水性抑制效率与矿物类型和表面活性剂种类相关,阳离子表面活性剂对高岭石更有效,而阴离子表面活性剂对方解石效果更好,石英表面亲水性随表面活性剂吸附波动较大。阳离子表面活性剂ctab在褐煤表面的吸附为放热过程,可以用freundlich模型描述,其吸附速率较符合二级动力学模型;温度升高、碱性条件和低离子强度对ctab在褐煤表面吸附有促进作用。ctab在褐煤表面吸附与褐煤表面含氧量密切相关,煤中氧含量增加,ctab在煤表面吸附量增加。酸洗脱灰处理后,芒来褐煤中含氧官能团含量减少,ctab吸附量和亲水性抑制效率降低。在低浓度条件下,褐煤中含氧官能团优于矿物质对ctab进行吸附,矿物质中高岭石对ctab的吸附能力高于石英和方解石。含氧官能团中,ctab在羧基组分表面吸附量大于其它含氧官能团组分表面吸附量。量子模拟计算结果表明不同含氧官能团对ctab吸附能力遵循强弱顺序为:酚羟基羧基醇羟基羰基醚基。ctab在褐煤表面的吸附不仅发生在褐煤表面,还能够在褐煤大孔结构内表面发生吸附,二者共同影响了ctab对褐煤亲水性抑制效率。温度升高、酸性条件和低离子强度对阴离子表面活性剂sds在褐煤表面吸附有促进作用。褐煤中矿物质对sds吸附的影响强度高于褐煤中有机质,其中方解石对sds的吸附能力远高于石英和高岭土。不同煤化程度煤样中的矿物质含量对sds吸附的影响很大。由于静电斥力存在,sds在褐煤含氧官能团表面吸附量少,其中羧基组分表现出优于其它含氧官能团组分的吸附能力。芒来褐煤吸附sds后比表面积、平均孔径、孔容均变小,表明了sds能够在褐煤大孔结构中发生吸附。非离子表面活性剂十二烷基聚氧乙烯醚(C_(12)(EO)_(15))在褐煤表面的吸附符合langmuir吸附模型,二级动力学方程可以描述C_(12)(EO)_(15)在褐煤表面的吸附动力学行为;温度升高、碱性条件和高离子强度对C12(EO)15在褐煤表面吸附有促进作用。褐煤脱灰后,C12(EO)15的吸附量降低,但降低幅度不大。随着煤化程度的增加,煤中氧含量降低,C12(EO)15在煤表面的吸附量呈减少趋势。C12(EO)15在褐煤表面吸附覆盖了表面含氧官能团,其中含羧基组分对C12(EO)15的吸附能力高于其它含氧官能团。C12(EO)15在褐煤表面的吸附覆盖了褐煤中的微孔结构,还能在褐煤的大孔结构内表面发生吸附。本研究对应用表面活性剂降低褐煤表面亲水性,抑制干燥提质煤样水分复吸具有一定借鉴作用,为进一步研究表面活性剂在褐煤表面吸附机理和亲水性抑制调控机制提供一些基础数据。
[Abstract]:Lignite is one of the important fossil energy. With the increasing demand for energy in economic development, the proportion of lignite in coal consumption in China is increasing year by year. The low coalification degree of lignite is endowed with high oxygen content and strong water absorption ability, which causes a lot of energy waste in the process of exploitation and utilization, such as high transportation cost and low burning calorific value. The traditional low order coal drying technology is not perfect to solve the problem of moisture absorption of the coal samples after drying. It can not meet the requirements for the high efficiency development and utilization of low order coal at the present stage. As one of the chemical products that regulate the interfacial properties, the amphiphilic molecular structure of the surfactant determines its ability to form the direction of the lignite surface. The adsorption layer, the hydrophobic group is far away from the adsorption direction, reduces the hydrophilicity of lignite surface and inhibits the moisture absorption of coal samples after drying. In this paper, the wettability and water absorption properties of lignite are studied. The type of hydrophilic group and the solidarity structure of the surface active agents (carbon chain length, aromatic structure, ring structure, double structure, etc.) are investigated. The effect of the HLB value of non ionic surfactants on the hydrophilic inhibition efficiency of the lignite surface was investigated by means of microcalorimetry, microelectrophoresis, surface tension, infrared spectroscopy, UV VIS spectrophotometer, X ray photoelectron spectroscopy (XPS) and liquid nitrogen adsorption, and the analysis of the cationic surfactant sixteen. The adsorption characteristics and adsorption mechanism of alkyl three methyl ammonium bromide (CTAB), anionic surfactant twelve alkyl sulfate (SDS) and non ionic surfactant twelve alkyl polyoxyethylene ether (C12 (EO) 15) on the lignite surface, and the wettability of lignite and the hydrophilicity of lignite in lignite were also investigated. The main conclusions are as follows: the wetting heat of organic matter in lignite is far higher than the wet heat of minerals. It is the main body of wetting and exothermic heat of lignite. The moist heat of kaolinite in mineral is higher than calcite and quartz. The moisture absorption of lignite is in accordance with the two stage kinetic model, and the moisture content in lignite is negatively related to the wetting heat. The higher the content, the smaller the moisture and damp heat. The wetting heat of the monolayer or cluster adsorption water formed on the surface of the awn lignite is more significant in the process of water absorption. The effect of water absorption or capillary condensation on moisture and humid heat is less. The content of oxygen containing functional group is an important factor affecting the wet heat of lignite, and the oxygen content in coal decreases with the increase of coal chemical degree. The wetting and releasing heat of brown coal is significantly different from polar wetting agent and non polar wetting agent. The wetting heat of water and anhydrous ethanol on lignite is much greater than that of n-alkanes on lignite. The lignite adsorbing surfactants can reduce the moisture heat of lignite and inhibit the recovery of dry lignite water, and the two are consistent, and the essence is surface. The surfactant adsorption reduces the hydrophilicity of the lignite surface. The inhibition of the surface hydrophilicity of the surface active agent on the surface of the lignite depends on the ability of the surface active agent to form an effective directional close arrangement adsorption layer on the surface of the lignite. This is closely related to the molecular structure of the surfactant. The hydrophilic inhibition effect of lignite is better than that of anions; in the hydrophobic group, the hydrophilic inhibition efficiency of lignite surface increases with the increase of the chain length of the hydrophobic group, and the surface active agent containing the branched chain and the benzene ring structure in the hydrophobic group is not conducive to the increase of the hydrophilic inhibition efficiency of the lignite surface; the gemini type surfactant of the Gemini structure is on the lignite surface. The hydrophilic inhibition efficiency is higher than the surface active agent of single chain structure and double hydrophobic group; Twain series surfactants have no obvious inhibition effect on the surface hydrophilicity of lignite; alkyl glycosides have polyhydroxy surfactant enhanced the hydrophilic property of lignite surface; with the decrease of HLB value of non ionic surfactant C12 (EO) n, lignite meter The inhibition effect of surface hydrophilicity is increasing, the minimum value occurs near the HLB value of 13.6. The key to the hydrophilic inhibition of lignite is to inhibit the hydrophilicity of organic matter in lignite. The hydrophilic inhibition efficiency of lignite is related to the type of mineral and the species of surfactant, and the cationic surfactant is more effective for kaolinite. The effect of the anion surface active agent on the stone solution is better, the surface hydrophilicity of the quartz is more volatile with the surfactant. The adsorption of Cationic Surfactant CTAB on the lignite surface is the exothermic process, which can be described by the Freundlich model, and the adsorption rate is in accordance with the two stage kinetic model; the temperature increases, the alkaline condition and the low ionic strength are higher. The adsorption of CTAB on the lignite surface promotes the adsorption of.Ctab on the lignite surface closely related to the oxygen content of the lignite surface, the oxygen content in coal increases, and the adsorption of CTAB on the coal surface increases. After the acid washing, the content of oxygen containing functional groups in the lignite is reduced, the adsorption capacity of CTAB and the inhibition efficiency of hydrophilicity are reduced. Under the low concentration, the lignite is reduced. Oxygen functional groups are superior to minerals for CTAB adsorption. The adsorption capacity of kaolinite to CTAB in minerals is higher than that of quartz and calcite. In oxygen functional groups, the adsorption capacity of CTAB on the surface of carboxyl groups is greater than that of other oxygen functional group components. The results of quantum simulation show that different oxygen functional groups follow the adsorption capacity of CTAB. The order of strength and weakness is that the adsorption of phenol hydroxyl carboxyl alcohol hydroxyl ether group.Ctab on lignite surface not only occurs on the lignite surface, but also can be adsorbed on the surface of brown coal with large pore structure. The two factors affect the hydrophilic inhibition efficiency of CTAB to lignite. The temperature rises, the acid condition and low ionic strength are on the anionic surface active agent SDS in brown coal. The influence of surface adsorption on the adsorption of SDS in lignite is higher than that of organic matter in lignite. The adsorption capacity of calcite to SDS is much higher than that of quartz and kaolin. The mineral content in coal samples with different degree of coalification has a great influence on the adsorption of SDS. Because of the existence of electrostatic repulsion, SDS is adsorbed on the surface of oxygen functional group of lignite. The carboxyl group showed a better adsorption capacity than other oxygen functional group components. The specific surface area, the average pore size and the pore volume were smaller after the adsorption of SDS, which showed that SDS could be adsorbed in the macroporous structure of lignite. The adsorption character of non ionic surfactant twelve alkyl polyoxyethylene ether (C_ (12) (15)) on the lignite surface Combined with the Langmuir adsorption model, the two stage kinetic equation can describe the adsorption kinetics of C_ (12) (EO) (15) on the lignite surface; the temperature increases, the alkaline condition and the high ionic strength can promote the adsorption of C12 (EO) 15 on the lignite surface. After the lignite deashing, the adsorption capacity of C12 (EO) 15 decreases, but the decrease is not significant. With the increase of coalification degree, The oxygen content in coal is reduced, the adsorption of C12 (EO) 15 on the surface of coal shows a decreasing trend of.C12 (EO) 15 on the surface of lignite covering the surface oxygen functional group, and the adsorption capacity of the carboxyl group on C12 (EO) 15 is higher than that of other oxygen functional groups.C12 (EO) 15 on the lignite surface and covers the microporous structure in lignite, and it can also be in the large pore of lignite. This study has a certain reference effect on reducing the surface hydrophilicity of lignite surface and restraining the moisture absorption of the dry coal sample, and provides some basic data for the further study of surface active agents on the mechanism of lignite surface adsorption and the mechanism of hydrophilic inhibition.
【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD849.2

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