【作者】 刘峥；

【导师】 李立清；

【作者基本信息】 中南大学 ， 土木工程， 2014， 博士

【摘要】 随着生存环境的日益恶劣和人们环保意识的不断增强,空气污染控制技术已成为研究热点,活性炭(Activated Carbon)吸附净化气态污染物被越来越多的学者和环保人士所研究。尽管诸多研究显示对挥发性有机污染物(VOCs)和二氧化硫的控制工艺技术已经相对成熟,但是在活性炭吸附微尺度分析理论对吸附作用影响机理研究上仍处于探索阶段。本文以活性炭为吸附剂,以丙酮为代表的VOCs和以二氧化硫(S02)为代表的无机气态污染物为吸附质,在活性炭多孔材料微尺度分析的理论上,定量系统地分析有机和无机气态污染物与微尺度材料表面物理化学性质之间的关系,从宏观和微观不同角度深入探讨丙酮和二氧化硫气体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,从而科学地揭示吸附的微尺度构效关系。本课题的研究内容和结论主要包括：(1)利用元素分析、扫描电镜、BET、傅立叶红外光谱(FTIR)等一系列分析测试方法对活性炭表面物理化学等结构特征数据进行测试分析,量化关联有机和无机气态污染物在活性炭中的吸附基础物性数据、吸附性能数据,热力学实验数据,建立活性炭物理化学性质与吸附行为之间的关系,系统地分析活性炭的微观结构对有机和无机气态污染物的吸附性能的影响。同时研究活性炭对气态污染物的吸附过程中的传热传热耦合规律。结果表明：用Langmuir吸附等温线模型可较好地描述丙酮在样品活性炭上的吸附。丙酮吸附量随着微孔孔容的增大而增大。丙酮在活性炭上的表面覆盖率随丙酮浓度的增大而明显增大。活性炭孔结构影响吸附能,吸附能大的活性炭表面覆盖率小。在活性炭吸附丙酮的过程中,传热系数的变化对传质影响不大,传质系数对传热有一定影响,与浓度差异引起的传热效应相比,温度差异引起的传质过程更加明显。在S02吸附研究中,活性炭的总比表面积和微孔比表面积与S02吸附量的线性相关系数随进气浓度的增加而增大；在较高进气浓度和较低吸附温度时,活性炭的总孔容和微孔孔容均与SO2吸附量呈现良好的线性关系。在相同的吸附温度和进气浓度下,活性炭的物性与SO2吸附量影响排序为：次微孔孔容>微孔孔容>微孔比表面积>总比表面积>总孔容。当吸附温度一定时,四种商业活性炭的微孔极限吸附容积排序为山西活性炭(AC-SX)最大,广州活性炭(AC-GZ)最小,而吸附能的排序为AC-GZ>AC-NX>AC-HN>AC-SX。AC-SX极限微孔孔容最大,吸附能最小,最易与SO2进行吸附反应。(2)采用微波热处理,无机和有机化学试剂等三种方法对商业活性炭进行改性,借助Boehm滴定法、透射电镜、BET、FTIR等分析方法对改性活性炭的表面物理化学等结构特征数据进行表征,考察改性活性炭吸附丙酮规律。结果表明：Langmuir方程更加适合描述丙酮在改性活性炭上的吸附；经微波辐照加热和碱性溶液浸渍改性后,活性炭的总比表面积、孔容均减小,但微孔比表面积显著增大；在微波辐照加热改性中,随着温度升高,酸性基团大量分解,碱性基团逐渐形成；在碱性溶液浸渍改性后,酸性基团被完全去除。随着活性表面碱性基团的增加,丙酮吸附量呈现递减的趋势；利用酯类试剂浸泡-真空干燥法改性活性炭,可以定向改变活性炭结构,促使中孔比表面积减小,微孔比表面积增大,提高了活性炭捕获吸附质分子的能力。酯改性活性炭吸附丙酮气体初期,会出现酯类改性试剂被丙酮气体少量置换脱附的现象,采用乙酸乙酯改性的活性炭(AC-ethy)在处理高湿度、低浓度丙酮气体过程中对丙酮具有良好的吸附性能,与宁夏商业活性炭(AC-NX)相比较,在维持对丙酮具有一定吸附量的同时,吸附能力基本不受水蒸汽含量的影响。(3)采用两床五步式变压吸附工艺,研究了固定床的两床变压吸附处理SO：与空气的混合气体的动态过程,理论分析了商业活性炭变压吸附SO2过程中的传热传质规律和脱附状态下脱附气的浓缩率的变化规律。结果表明：吸附床内的压力呈周期性变化。不同吸附高度的温度曲线随变压吸附循环的周期数改变而变化。在实验条件下,传质区主要集中在H=0.08m-0.15m处。随着吸附柱高度的增加,气相组分物质浓度逐渐降低,并且在400个周期以后开始达到稳定。在床层高度0.6m以上没有SO2气体的存在。SO2在吹扫脱附阶段和真空脱附阶段的不同脱附时刻的脱附气浓缩率均随变压吸附过程先快速升高,然后趋于稳定。当达到稳定时,SO2的脱附气浓缩率随脱附时刻的增加而降低。所以在实验条件下,变压吸附各阶段的最佳时长分别设为,均压段3s,吸附段为170s,吹扫脱附设为15s,真空脱附为180s；脱附气的SO2平均浓缩率为2。(4)利用烟草工业废弃物(烟梗)采用化学法制备高比表面积活性炭,并对活性炭进行物性表征,探讨了不同活化实验条件下对制备活性炭性能的影响,通过利用孔结构参数分析所制备的活性炭的大孔、中孔及微孔的分布特征,同时采用所制备活性炭对丙酮进行吸附效果的实验研究,考察其对丙酮为代表的有机气态污染物的吸附效果。结果表明：在活性炭制备实验中,活化剂种类和用量对所制备的活性炭的孔结构和吸附性能产生重要影响。采用ZnCl2为活化剂所制备出的活性炭具有较高的比表面积；采用三种活化剂所制备的活性炭的氮吸附等温线基本符合Ⅰ型吸附等温线,采用D-A方程和H-K方程分别研究活性炭微孔分布可知,以ZnCl2为活化剂制备的活性炭H-K法微孔分布较宽,呈多峰分布的状态,这也说明了其形成的微孔极为丰富其且形成比表面积最大。采用BJH方程研究活性炭中孔和大孔分布可知,以KOH为活化剂制备的活性炭所形成的中孔及大孔最为丰富,而在相同活化剂的情况下,高活化剂用量有利于中孔和大孔的形成。通过活性炭固体表面分形维数的计算得到以K2C03为活化剂制备的活性炭表面是三类活化剂中最粗糙,说明该类活性炭极小微孔<0.6nm含量最多。在所研究的温度和浓度范围内,采用K2C03活化剂用量为2：1时制备的活性炭对丙酮吸附能用Langmuir和Temkin模型进行较好的拟合。本课题的研究成果对活性炭吸附法净化有机和无机工业气态污染物吸附处理的工业化应用和乡村废弃生物质资源综合利用将具有重大的指导意义。更多还原

【Abstract】 Because of the increasing public awareness of pollution and environmental protection, gaseous pollutants control technology as a hot topic, has been widely studied. Although control technologies of volatile organic compounds (VOCs) and sulfur dioxide (SO2) have been conducted, researches on the mechanism as well as micro structure-function of activated carbons (ACs) are still in exploration. In this thesis, commerial ACs were selected as a adsorbent for acetone and SO2adsorption, the relationship between gaseous pollutants and micro structure-function material surface physicochemical properties was systematically and quantificationally analyzed. The inherent correlation between acetone and SO2adsorption activity and the AC’s surface physicochemical properties and complex interaction mechanism was studied from the micro/macro point of view. The primary contents and conclusions are listed as follows:(1) Series of analysis methods such as elemental analysis, scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) surface area analyser, fourier transformed infrared (FTIR) were used to study the surface physicochemical properties and structure of ACs. And these gaseous pollutant adsorption performance by AC in association with basic physical property data, adsorption performance data and thermodynamic test data were systematically and quantificationally investigated. The relationship between physicochemical properties of ACs and adsorption behavior was set up. The effect of microstructure of ACs on organic and inorganic gaseous pollutants adsroption performance was also analysed. The coupled effects of heat and mass transfer in gaseous pollutants adsorption process by AC was theoretically studied. The received findings were that the Langmuir adsorption isotherm model described the adsorption of acetone onto ACs very well. Adsorption of acetone increased positively-linearly with the increases of micropore volume. Acetone surface coverage in the ACs increased obviously with the increase of acetone concentration. Smaller acetone surface coverage resulted in higher ACs adsorption energy for acetone. Heat transfer coefficients exhibited insignificant effect on mass transfer. In contrast, mass transfer coefficients exhibited more impact on heat transfer. The mass transfer effects caused by a temperature gradient were more obvious than heat transfer effects caused by a concentration gradient.For SO2adsorption on ACs, the linear correlation coefficient of specific surface area and micropore specific surface area and SO2adsorption capacity increased with the increasing of SO2inlet concentration. In the higher inlet concentration and lower adsorption temperature, total pore volume and micropore volume of ACs have both a well linear fitting with the SO2adsorption capacity. With the same adsorption temperature and inlet concentration, the impact of textural properties of ACs on SO2adsorption were in order as narrow pore volume> micropore volume> micropore surface area> BET surface area> total pore volume. When the adsorption at a certain temperature, the maximum adsorption capacity of micropore volume performed as AC-SX> AC-NX> AC-HN> AC-GZ, the order of adsorption energy were AC-GZ> AC-NX> AC-HN> AC-SX, it was explained that the larger the maximum adsorption capacity of micropore volume, the lower the adsorption energy, so absorption of AC-SX was occurred easily.(2)Commerial ACs were modified with microwave thermal treatment, inorganic and organic chemical reagents. The structure characteristics parameters such as physicochemical properties of modified ACs were obtained by the characterizations of Boehm titration, transmission electron microscope (TEM), BET and FTIR to investigate the adsorption performance of acetone by modified ACs. The research shows that the Langmuir adsorption isotherm model described the adsorption of acetone onto modified ACs. The specific surface area and total pore volume of modified ACs decreased slight, but the micropore specific surface area increased remarkably. With an increase of temperature, large number of surface acidic functional groups resolve and surface basic functional groups were formed gradually in thermal treatment. After alkaline solutions modification, with an increase of alkaline of solutions, surface basic functional groups increased remarkably and surface acidic functional groups were removed completely, which resulted in a dercease of acetone adsorption capacity. Esters modification could directional modified pore structure of ACs. It decreased the mesopore specific surface area, prompted micropore specific surface area, and improved the ability of the modified ACs capture adsorbate molecule. In early stage of adsorption of acetone on modified ACs, a small amount of ester reagents was replaced by acetone. The modified AC-ethy has a good performance on the treatment of high humidity and low density of acetone. Compared with the AC-NX, the acetone adsorption capacity of AC-ethy was not affected by water vapor.(3) The heat and mass transfer in a fix bed of AC and the variation of the ratio of desorption gas condensability was investigated on a double bed five steps pressure swing adsorption (PSA) for the first time. The results show that the pressure inside the adsorption bed was changed periodically, the temperature curve of different height was changed according to the changing periodicity, the mass transfer area was mainly in0.08-0.15m. The concentration of gas phase composition was decreased gradually with the increase of adsorption column height. It begin into a stability stage after400cycles. No SO2was detected when the bed height was higher than0.6m. During the purge desorption and vacuum desorption stage, the ratio of desorption gas condensability was increased, then tends to stable, finally bring down with desorption time increasing. In our experiment conditions, the best operation time for each stage were adsorption with170s, purge desorption with15s, vaccum desorption with180s, balance pressure with3s. The avarge condensability of SO2in desorption gas can achieved2.0.(4) Self-made AC was prepared by a chemical activation method using an tobacco industry waste. Experiments were conducted to study the influence of AC properity, The pore distribution of different ACs by using the pore structure parameter and the different of AC on acetone adsorption efficiency were investigated. The results show that the AC pore structure and adsorption properties were determined by the activation agent types and dosage. AC prepared by ZnCl2exhibited the highest specific surface area. Nitrogen adsorption isotherm for the three ACs in line with type I adsorption isotherm. Micropore distribution of ACs was illustrated by D-A equation and H-K equation, respectively. ACs exhibited the most wide pore distribution was prepared by ZnCl2, which appeared muti-peak distribution. Meso and macropore distribution of ACs was displayed by BJH equation. Most abundant meso and macropore structure were formed on the AC treated by KOH. Higher dosage of activation agent resulted in more meso and macropore when the same activation agent was used. The solid surface fractal dimensions of ACs was calculated. AC with K2CO3as a activation agent is the most rough, it was illustrated that the content of tiny micropore (<0.6nm) was the maximum. Adsorption of acetone has been measured for AC with two times dosage of K2CO3as a activation agent. The result shows that the Langmuir and Temkin model fitted experimental data well.This research provides a reasonable basis in industrial application of purification of gaseous pollutants by adsorption of AC, and also a new comprehensive utilization method by rural waste biomass resources.更多还原