【作者】 宋剑飞；

【导师】 李立清；

【作者基本信息】 中南大学 ， 土木工程， 2014， 博士

【摘要】 摘要：为了强化活性炭选择性吸附能力以及提高其吸附性能,必须对吸附质和吸附剂的物性差异以及相互作用机理有系统且全面的的认识,需系统地量化分析吸附质在活性炭上的吸附性能与微尺度结构和性质之间的内在关联。本研究从针对活性炭对挥发性有机污染物(VOCs)的吸附现象,以活性炭和VOCs微尺度结构与表面物理化学性质影响有机气体吸附性能这一认识为出发点,利用恒温吸附实验装置,对活性炭吸附VOCs进行实验测试,深入探讨VOCs在活性炭多孔介质内复杂的表面物理化学状态和相互作用机制。借助红外光谱分析、显微观测分析、比表面积及孔隙分析、元素分析、Boehm滴定分析等手段,对活性炭进行表征。利用理论方法分析吸附性能等参数,结合活性炭表征结果,探讨了活性炭吸附性能与吸附质和吸附剂物性的宏观微观构效关系,为新型活性炭制备以及吸附净化回收VOCs工业过程与配套装置优化设计提供技术支撑。研究包括五个部分：(1)VOCs物性对活性炭吸附性能影响的研究。研究表明：活性炭对VOCs的饱和吸附量跟VOCs的分子动力学直径、分子量、密度、沸点、饱和蒸汽压、极性存在着密切关系,跟VOCs前四种物性因素呈现正线性关系；跟后两种物性因素呈现负线性关系。(2)活性炭孔结构特性对吸附VOCs影响的研究。实验研究发现：活性炭内部结构越复杂,传质速率越慢,良好的孔结构梯度分布有助于加强活性炭内部吸附质的扩散。吸附质分子直径越小,在吸附剂中越容易扩散；利用不同孔径区间下的孔容与吸附量之间的相关系数关系可以较好地解释吸附质在活性炭内部的扩散过程。(3)复合氧化改性对活性炭物性及其吸附甲苯性能影响的研究。实验研究发现：强氧化剂预处理活性炭有助于热复合氧化改性中活性炭微孔孔容的增大；活性炭表面含氧基团由化学氧化改性和热复合氧化改性共同作用产生,热改性温度较低时,其主要由化学氧化改性生成,温度较高时,酸性基团则主要来源于氧气与活性炭表面的氧化反应；酸性基团的存在能够促进活性炭吸附甲苯；控制合理的热复合氧化改性条件,既可以增加活性炭表面酸性基团,又可扩充微孔孔容,从而综合提升了活性炭对甲苯的吸附能力。(4)有机酸改性对活性炭物性的影响,探讨了吸附时间、浓度和温度对活性炭吸附二甲苯的动态过程的影响,研究其在不同吸附条件下对二甲苯的气相吸附动力学及吸附平衡。实验发现：有机酸改性活性炭是一种成功的提高活性炭对二甲苯吸附容量的方法。改性后活性炭的孔结构参数均有不同程度的减小,经FTIR验证,改性后活性炭表面生成羟基、酮基、羧基、S=O等官能团。吸附温度降低,二甲苯进气浓度增大,则活性炭的吸附速率增大,平衡吸附量增大。Bangham动力学模型能很好地描述4种活性炭对二甲苯的吸附动力学过程,其拟合的相关系数R2均高于0.997。(5)VOCs吸附性能参数优化及宏观微观构效关系研究。利用正交分析与多元回归分析的方法,通过Design Expert7.0软件对活性炭改性及其吸附VOCs过程进行优化,研究了活性炭在不同改性条件下物性的变化,探讨了活性炭物性对于VOCs吸附性能的作用。通过构建数学模型,研究发现改性温度、改性氧气浓度、改性时间等三种参数均对活性炭的微孔孔容与表面氧含量产生了显著的影响,而对比表面积影响不大；在较高的氧气浓度和较高的改性温度以及较短的改性时间的条件下,可以改性制得具有较大比表面积、较大微孔孔容和较高表面氧含量的活性炭。研究对制备高比表面积、大微孔孔容和高表面氧含量的功能活性炭具有重要的指导意义。更多还原

【Abstract】 Abstract:To improve the adsorption performance of activated carbons and make the adsorption more selective, it is necessary to comprehensively and systematically understand the mechanism of the physical differences between the activated carbons and adsorbates, and their interaction. What’s more, it is of necessity to systematically and quantificationally investigate the inherent correlation between the adsorption performance of adsorbates by activated carbons and the micro structure-function relationship.This is a study from the perspective of interdiscipline, which is based on the adsorption phenomenon of the volatile organic compounds (VOCs) by activated carbons from the micro/macro point of view, and the effect of the micro structures and surface physicochemical properties of VOCs and activated carbons on the adsorption properties of VOCs from the perspective of interdiscipline. The experimental study of the adsorption of was conducted by the isothermal adsorption experimental apparatus. The complicated surface physicochemical properties of VOCs inside the activated carbons and the interaction mechanism between the adsorbents and adsorbates were studied deeply. The activated carbon was characterized by infrared spectroscopy, microscopic observation, specific surface and pore size analysis, elemental analysis and Boehm titration. Theoretical methods were employed to analyze the adsorption performance data, which were then combined with the structure characteristics parameters. The relationship between the adsorption of VOCs by activated carbons and their micro structure properties was examined by combining computer software, mathematical methods and experimental studies, which further renders an effective guidance on the preparation of novel activated carbons and the optimization of the corresponding purifying equipment.This dissertation achievement contains five sections:(1) Studies on the effect of VOCs physical properties on the adsorption performance of activated carbons. It was found that the saturated adsorption of VOCs is closely related to VOCs molecular dynamics diameter, molecular weight, density, boiling point, vapour pressure, polarity, with positive linear relationship between the first four and negative linear relationship between the last two.(2) Studies on the effect of carbon’s pore structure on the adsorption of VOCs. The results shown that the more complex the internal structure of activated carbons is, the lower the mass transfer rate of adsorbates is. The good gradient distribution of pore structure benefits the diffusion of adsorbates inside the activated carbons. The adsorbates with smaller molecular diameters are much easier to diffuse in the adsorbents. The diffusion process inside the activated carbons can be well explained by the correlation between the pore volume and adsorption capacity in different pore diameter ranges.(3) Studies on the effect of the composite oxidation modifications of activated carbons on their physical properties and the adsorption of toluene. The results exhibit that the micropore volume of the hot-composite oxidation modified carbons increases when the carbons are pretreated by strong oxidants. Both the chemical oxidation modification and hot-composite oxidation modification generate the surface oxygenic functional groups. When the temperature of heat modification is low, the surface oxygenic functional groups are mainly from the chemical oxidation modification. When the temperature of heat modification is high, they are mainly from the oxidation reaction between oxygen and the surface of carbons. The modified carbons possess acidic groups, which are in favor of the adsorption of toluene. Suitable hot-composite oxidation modification can not only increase the surface acidic groups on the activated carbons but also enhance the micropore volume, further improving the adsorption of toluene.(4) The granular activated carbons were modified using oxalic acid, formic acid and sulfamic acid respectively. The effects of adsorption time, concentration and temperature on the dynamic adsorption of xylene were then investigated. Test results show that the activated carbons modified using organic acid have high capacity in the adsorption of xylene. The pore structures of the modified carbons were decreased to some extent, which was proved by FTIR to be caused by the production of hydroxyl, ketonic group, carboxyl and S=O groups. With the increase in xylene inlet concentration and the decrease in adsorption temperature, the adsorption rate of the modified carbons increase, the same as equilibrium adsorption capacity. Bangham’s kinetic model well describes the adsorption process of the four modified carbons with correlation coefficients R2above0.997.(5) The optimization of adsorption parameters of VOCs and construction of micro/macro coupled structure-function relationship. Based on orthogonal analysis and multiple regression analysis, activated carbon modification and adsorption process were optimized by Design Expert7.0. The physical properties changes of activated carbon were studied under different modification conditions. The effects of physical properties of activated carbon on adsorption performance were discussed. By developing mathematical model, it has been found that the effects of modification factors, such as temperature, oxygen density and time, on the specific surface areas of activated carbons are not significant, while their effects on the micropore volume and surface oxygen content are pronounced. The activated carbons with large specific surface area, large micropore volume and high surface oxygen content can be obtained under the modification conditions of high oxygen density, high temperature and short time period, which will provide an important guidance on the preparation of activated carbons.The study results of this paper are benefit to develop the new activated carbon materials with high surface area, huge micropore volume and high surface functional groups.更多还原