介孔材料吸附气相多环芳烃实验及分子模拟研究
发布时间：2019-06-17 20:29
【摘要】：论文基于吸附净化气相多环芳烃(PAHs)对高效吸附、低耗再生的实际需求与技术发展趋势,采用介孔吸附剂,针对吸附热力学与动力学、脱附再生特性和微观吸附机制三大关键问题,展开了系列的实验与分子模拟研究。搭建了气相PAHs准平衡吸附实验,分别对三种PAHs(萘、菲、芘)在三种典型介孔吸附剂(硅基MCM-41、SBA-15和碳基CMK-3)上的吸附相平衡与吸附动力学进行了研究,获取了吸附等温线与不同浓度下的穿透曲线,确立了 Freundlich、Langmuir模型分别对大、小吸附质的适用关系,以及准确的恒定浓度波穿透曲线模型。研究结果表明,内扩散为PAHs吸附的主要控速步骤,介孔材料较传统吸附剂具有更高的吸附速率,并存的微孔结构有助于在低浓度下提高PAHs吸附量,且微-介交联孔结构利于吸附传质,但无序微孔结构会增加大分子(菲、芘)的内扩散阻力。提出了优化后的脱附热分析方法,基于程序升温(TPD)实验确立了各吸附体系的脱附峰值温度及脱附动力学三因子,发现了随机成核增长模型为PAHs脱附的主流机理函数,菲/SBA-15与芘/CMK-3则分别由于二维扩散与π-π作用而呈现特殊机理。MCM-41 一维介孔中的PAHs脱附行为基本一致,SBA-15微-介交联孔可促进脱附传质,CMK-3富含微孔的碳棒阵列虽强化吸附但会抑制脱附扩散。合理的微孔分布是优选高效PAHs吸附剂的关键因素。基于多尺度分子模拟方案,构筑了 MCM-41与SBA-15模型,采用蒙特卡洛法与分子动力学法模拟了 PAHs的吸附效果及吸附状态,结合实验印证了微-介交联孔是提高平衡吸附量、稳定吸附热及均衡吸附质分布的关键因素;随分子量增大,吸附质相对介孔表面的平铺性、有序度与稳定性增大。采用第一性原理进一步模拟研究了 PAHs在硅基表面上的吸附构型、相互作用能及各作用力贡献等微观特性,揭示了对于以物理吸附为主的PAHs吸附,色散力占主导作用且对疏水表面上的吸附促进尤为显著,PAHs分子离域π电子起到静电吸引作用,氢键则主要起到侧向约束PAHs吸附质的作用。论文研究成果可为介孔材料吸附净化气相PAHs提供理论和技术参考,具有重要的科学意义和应用价值。
[Abstract]:Based on the actual demand and technical development trend of adsorption and purification of gas phase polycyclic aromatic hydrocarbons (PAHs) for high efficiency adsorption and low consumption regeneration, a series of experiments and molecular simulation studies were carried out by using mesoporous adsorbents to solve the three key problems of adsorption thermodynamics and kinetics, desorption regeneration characteristics and micro adsorption mechanism. The adsorption phase equilibrium and adsorption kinetics of three kinds of PAHs (Naphthalene, phenanthrene, pyrene) on three typical mesoporous adsorbents (silicon-based MCM-41,SBA-15 and carbon-based CMK-3) were studied by gas phase PAHs quasi-equilibrium adsorption experiments. the adsorption isotherms and penetration curves at different concentrations were obtained, and the applicable relationships of Freundlich,Langmuir models for large and small adsorbents were established. And an accurate constant concentration wave penetration curve model. The results show that internal diffusion is the main rate control step of PAHs adsorption. Mesoporous materials have higher adsorption rate than traditional adsorbents. The coexisting microporous structure is helpful to increase the adsorption capacity of PAHs at low concentration, and the micro-mesocrosslinked pore structure is conducive to adsorption and mass transfer, but the disordered microporous structure increases the internal diffusion resistance of macromolecules (phenanthrene, pyrene). The optimized desorption thermal analysis method was proposed. Based on the temperature programmed (TPD) experiment, three factors of desorption peak temperature and desorption kinetics of each adsorption system were established. It was found that the random nucleation growth model was the mainstream mechanism function of PAHs desorption, while phenanthrene / SBA-15 and pyrene / CMK-3 showed special mechanisms due to the interaction of two-dimensional diffusion and 蟺-蟺, respectively. the desorption behavior of PAHs in one-dimensional mesoporous SBA-15-41 was basically the same. SBA- 15 micro-dielectric crosslinked pores can promote desorption mass transfer. CMK-3 carbon rod arrays rich in micropores enhance adsorption but inhibit desorption diffusion. Reasonable micropore distribution is the key factor to optimize high efficiency PAHs adsorbents. Based on the multi-scale molecular simulation scheme, the MCM-41 and SBA-15 models are constructed. Monte Carlo method and molecular dynamics method are used to simulate the adsorption effect and adsorption state of PAHs. Combined with experiments, it is proved that micro-dielectric crosslinked pores are the key factors to improve the equilibrium adsorption capacity, stabilize the adsorption heat and the distribution of equilibrium adsorbents. With the increase of molecular weight, the flatness, order and stability of the adsorbents relative to the mesoporous surface increase. The adsorption configuration, interaction energy and contribution of various forces of PAHs on silicon surface were further simulated by first principle. It is revealed that dispersion force dominates the adsorption of PAHs based on physical adsorption and promotes the adsorption on hydrophobic surface. PAHs molecule delocalized 蟺 electrons play an electrostatic attraction, while hydrogen bonds mainly act as lateral binding PAHs adsorbents. The research results of this paper can provide theoretical and technical reference for adsorption and purification of gas phase PAHs of mesoporous materials, and have important scientific significance and application value.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.4;O647.3
本文编号：2501245
[Abstract]:Based on the actual demand and technical development trend of adsorption and purification of gas phase polycyclic aromatic hydrocarbons (PAHs) for high efficiency adsorption and low consumption regeneration, a series of experiments and molecular simulation studies were carried out by using mesoporous adsorbents to solve the three key problems of adsorption thermodynamics and kinetics, desorption regeneration characteristics and micro adsorption mechanism. The adsorption phase equilibrium and adsorption kinetics of three kinds of PAHs (Naphthalene, phenanthrene, pyrene) on three typical mesoporous adsorbents (silicon-based MCM-41,SBA-15 and carbon-based CMK-3) were studied by gas phase PAHs quasi-equilibrium adsorption experiments. the adsorption isotherms and penetration curves at different concentrations were obtained, and the applicable relationships of Freundlich,Langmuir models for large and small adsorbents were established. And an accurate constant concentration wave penetration curve model. The results show that internal diffusion is the main rate control step of PAHs adsorption. Mesoporous materials have higher adsorption rate than traditional adsorbents. The coexisting microporous structure is helpful to increase the adsorption capacity of PAHs at low concentration, and the micro-mesocrosslinked pore structure is conducive to adsorption and mass transfer, but the disordered microporous structure increases the internal diffusion resistance of macromolecules (phenanthrene, pyrene). The optimized desorption thermal analysis method was proposed. Based on the temperature programmed (TPD) experiment, three factors of desorption peak temperature and desorption kinetics of each adsorption system were established. It was found that the random nucleation growth model was the mainstream mechanism function of PAHs desorption, while phenanthrene / SBA-15 and pyrene / CMK-3 showed special mechanisms due to the interaction of two-dimensional diffusion and 蟺-蟺, respectively. the desorption behavior of PAHs in one-dimensional mesoporous SBA-15-41 was basically the same. SBA- 15 micro-dielectric crosslinked pores can promote desorption mass transfer. CMK-3 carbon rod arrays rich in micropores enhance adsorption but inhibit desorption diffusion. Reasonable micropore distribution is the key factor to optimize high efficiency PAHs adsorbents. Based on the multi-scale molecular simulation scheme, the MCM-41 and SBA-15 models are constructed. Monte Carlo method and molecular dynamics method are used to simulate the adsorption effect and adsorption state of PAHs. Combined with experiments, it is proved that micro-dielectric crosslinked pores are the key factors to improve the equilibrium adsorption capacity, stabilize the adsorption heat and the distribution of equilibrium adsorbents. With the increase of molecular weight, the flatness, order and stability of the adsorbents relative to the mesoporous surface increase. The adsorption configuration, interaction energy and contribution of various forces of PAHs on silicon surface were further simulated by first principle. It is revealed that dispersion force dominates the adsorption of PAHs based on physical adsorption and promotes the adsorption on hydrophobic surface. PAHs molecule delocalized 蟺 electrons play an electrostatic attraction, while hydrogen bonds mainly act as lateral binding PAHs adsorbents. The research results of this paper can provide theoretical and technical reference for adsorption and purification of gas phase PAHs of mesoporous materials, and have important scientific significance and application value.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.4;O647.3
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