【作者】 刘剑；

【导师】 张会平；

【作者基本信息】 华南理工大学 ， 化学工程， 2012， 博士

【摘要】 随着社会经济的飞速发展，人们对环境保护的要求日益提高。大气污染防治是环境保护的主要任务之一，挥发性有机化合物（VOCs）是一类最典型的大气污染物。目前，VOCs净化方法有很多种，包括吸附、吸收、冷凝、催化燃烧和热力燃烧等。其中，吸附法是最常见的净化方法之一。传统固定床吸附装置通常采用粒径相对较大颗粒活性炭作为吸附剂，其吸附速率相对较慢，传质阻力较高。如何制备一种新型吸附材料应用在传统固定床中，提高其吸附速率，降低固定床传质、传热阻力是一个前沿性研究课题。本文较详细地综述了国内外微纤复合材料的制备、表征和应用研究进展，研究了微纤包覆活性炭复合材料和不锈钢微纤复合纯硅分子筛膜材料的制备、表征及其在VOCs净化中的应用，分析探讨了结构化固定床吸附动力学及传质机理。首先，本文研究了微纤包覆活性炭复合材料的制备工艺。以不锈钢纤维、针叶木纤维和颗粒活性炭（150200m）为原料，采用湿法造纸和烧结工艺制备了微纤包覆活性炭复合材料，分别考察了不同工艺参数对微纤复合材料性能的影响规律，确立了最优制备工艺参数。结果表明在活性炭和不锈钢纤维的质量比为13:6，烧结温度1050℃，烧结时间20min，加水量2L，解离时间10min，烧结压片质量212g的条件下，所制备的微纤复合材料炭包覆率达到64.3%。采用扫描电子显微镜观察了在最优条件下制备的微纤复合材料烧结前后的微观结构，结果表明不锈钢纤维的连接处能被很好地融合在一起，形成具有大的空隙率、烧结锁定的三围网络结构，微米尺度的颗粒活性炭能良好地被包覆其中。采用氮气吸附法测定了两种活性炭在包覆前后的比表面积和孔径分布，结果表明包覆前后活性炭的孔径分布基本相同，其中柱状111型活性炭包覆前后的比表面积分别为678和769m~2/g，0960型活性炭为976和955m~2/g。其次，本文研究了微纤复合分子筛膜的制备技术。以正硅酸乙酯(TEOS)为硅源，四丙基氢氧化铵（TPAOH）为模板剂，采用二次生长法制备了不锈钢微纤复合纯硅分子筛膜材料，考察了不同工艺参数对分子筛膜性能的影响规律。结果表明采用二次生长法能在不锈钢微纤表面合成连续致密的MFI型分子筛膜，膜厚度约为2.3m。膜的比表面、总孔容和微孔孔容分别为93.24m~2/g、0.06545cm~3/g和0.03826cm~3/g。采用阳极氧化法预处理载体所制备的膜较采用高温煅烧法预处理的膜表观形态更为连续规整。同时，随着晶化温度增加或晶化时间延长，膜表面更加致密，晶体颗粒尺寸增加。在二次生长的基础上进行三次生长对分子筛膜性能影响相对很小。再次，本文研究了基于微纤复合材料的结构化固定床吸附动力学。通过在固定床的进口端和出口端分别装填颗粒活性炭和微纤包覆活性炭复合材料组成结构化固定床，研究了苯、甲苯单组份气体以及苯和甲苯、甲苯和对二甲苯双组分气体在结构化固定床上的吸附动力学，并与传统颗粒炭固定床的实验结果进行比较。结果表明，在相同条件，相对较低的透过浓度下，苯、甲苯在结构化固定床上的吸附透过时间较在传统颗粒炭固定床上的延长了约20min。随着床层高度降低，气体流量或入口浓度增加，苯、甲苯在结构化固定床上的吸附透过时间缩短。苯和甲苯、甲苯和对二甲苯双组份气体在结构化固定床和传统颗粒炭固定床上的吸附透过曲线均体现竞争吸附特性。甲苯吸附性能强于苯，对二甲苯吸附性能强于甲苯。在相同条件下，苯、甲苯和对二甲苯在结构化固定床上的吸附透过时间均较在传统颗粒炭固定床上的显著延长。最后，本文通过吸附动力学模型研究了结构化固定床传质机理。采用LUB方程计算了结构化固定床和传统颗粒炭固定床吸附苯、甲苯的无效层厚度和床层利用率；同时，采用Bohart Adams、Yoon Nelson和Bed Depth Service Time（BDST）模型对吸附透过曲线进行线性回归分析。结果表明，结构化固定床的无效层厚度相对传统颗粒炭固定床的降低26%47%，床层利用率提高9%18%。Bohart Adams模型能很好地预测苯、甲苯在结构化固定床上的透过曲线中C/C0小于0.5的初始部分；当C/C0超过0.5时，预测值和实验值出现较大偏差。Yoon Nelson模型能用来考察结构化固定床的吸附速率常数k ’和50%透过时间τ，在相同的条件下，结构化固定床的吸附速率常数相对传统颗粒炭固定床的增大约50%；同时，Yoon Nelson模型适用于预测苯、甲苯在结构化固定床上的吸附透过曲线中C/C0大于0.05的部分。BDST模型能用来考察结构化固定床吸附苯、甲苯的吸附容量N0和吸附速率常数k a。更多还原

【Abstract】 The demand for environmental protection has received increasing attention with therapid development of both the society and economy. The removal of pollutants from air is oneof the important environmental protection tasks. Volatile organic compounds (VOCs) are themajor air pollutants. There are much more techniques for treating VOCs including adsorption,absorption, condensation, catalytic combustion and thermal combustion. Adsorption is one ofthe domain technologies for VOCs removal. Conventional fixed bed adsorber with relativelylarger granular activated carbons is of low adsorption rate and high mass transfer resistance.How to prepare a novel material for the application in the conventional fixed bed which canincrease adsorption rate and decrease mass/heat transfer resistance is a cutting edge researchtopic. In this paper, the research progress on the preparation, characterization and applicationof microfibrous composite was reviewed. The preparation, characterization and application ofboth microfibrous entrapped activated carbon composite and silicalite1zeolite membrane onstainless steel microfibrous for VOCs purification were investigated. The adsorptiondynamics and mass transfer mechanism in the structured fixed bed were analyzed anddiscussed.First, the preparation process of microfibrous entrapped activated carbon composites wasstudied. Microfibrous entrapped activated carbon composites were prepared by wet layuppapermaking and sintering process from stainless steel fibers, coniferous wood fibers andactivated carbon particles (150200m). The effects of a variety of operation parameters onthe properties of microfibrous composites were investigated and the optimum processparameters were obtained. The experimental results showed that the carbon entrapment ratioof the microfibrous composites prepared with a ratio of13:6(W/W, carbon/fibers) is64.3%under the conditions of adding2L water, stirring for10min, and then sintering at1050C for20min with the sintering material mass of212g. The microstructure of microfibrouscomposites before and after sintering prepared under the optimized condition was measuredby means of SEM, the results showed that the junctures of stainless steel fibers are wellwelded together to form a sintered locked three dimensional network with large voidage, which entrap the micron size activated carbon particles very well. The pore size distributionsand specific surface areas of activated carbons before and after entrapment were measured bynitrogen adsorption method. The pore size distributions of the activated carbons before andafter entrapment are basically the same, and the specific surface areas are678and769m~2/gfor type111activated carbon,976and955m~2/g for type0960activated carbon respectively.Second, the preparation technique of zeolite membrane on microfibrous support wasinvestigated. The silicalite1zeolite membrane on stainless steel microfibrous support wasprepared by secondary growth from TEOS as Si source and TPAOH as a template. Theeffects of a variety of operation parameters on the properties of zeolite membrane wereinvestigated. The experimental results showed that it is feasible to prepare continuous anddense MFI zeolite membrane on the surface of stainless steel microfibrous by secondarygrowth method, and the thickness of the membrane is about2.3m. The specific surface areas,total pore volume and micropore volume of the membrane are93.24m~2/g,0.06545cm~3/g and0.03826cm~3/g, respectively. The membrane by treating support with anodic oxidation methodis more continuous and denser than that with calcinations. The surface of membrane is muchdenser and the size of crystal grains increased as increasing the crystallization temperature orcrystallization time. The effect of third growth based on secondary growth on the propertiesof zeolite membrane is not very clear.Then, the adsorption dynamics of the structured fixed bed with microfibrous compositeswere studied. The structured fixed bed was filled with granular activated carbons andmicrofibrous entrapped activated carbon composites in the inlet and outlet of the fixed bed,respectively. The adsorption dynamics of benzene, toluene, benzene/toluene andtoluene/p xylene binary mixtures in the structured fixed bed were measured, and comparedwith that in the conventional GAC fixed bed. The results showed that the breakthrough timeof benzene and toluene in the structured fixed bed increases about20min compared with thatin the conventional GAC fixed bed at relatively low breakthrough concentration. Thebreakthrough time of benzene and toluene in structured fixed bed decreases as decreasing beddepth or increasing gas flow rate and inlet concentration. The breakthrough curves of bothbenzene/toluene and toluene/p xylene binary mixtures in both structured fixed bed andconventional GAC fixed bed is of completive adsorption characteristics. Toluene is more easily adsorbed than benzene, and p xylene is more easily adsorbed than toluene. Thebreakthrough time of benzene, toluene and p xylene in the structured fixed bed clearlyprolongs than that in the conventional GAC fixed bed at the same conditions.Finally, the mass transfer mechanism in the structured fixed bed by adsorption dynamicsmodels was investigated. The length of unused bed and bed utilization for benzene andtoluene in both structured fixed bed and conventional GAC fixed bed were determined byLUB equation. The adsorption breakthrough curves were fitted according to three fixed bedadsorption models of Bohart Adams, Yoon Nelson and BDST models by the linear regressionanalysis. The results showed that the LUB value in the structured fixed bed decreases26%47%compared with that in the conventional GAC fixed bed, and bed utilizationincreases9%18%. Bohart Adams model is valid for the C/C0up to0.5, and largediscrepancies are found between the experimental and predicted values above this value forbenzene and toluene adsorption in the structured fixed bed. The adsorption rate constant k’and50%breakthrough timeτcan be obtained by Yoon Nelson model, the k ’value in thestructured fixed bed increases about50%compared with that in the conventional GAC fixedbed at the same conditions. The experimental breakthrough curves are very agreement withthose predicted by the Yoon Nelson model when the C/C0is above0.05for the adsorption ofbenzene and toluene in the structured fixed bed. The adsorption capacity N0and adsorptionrate constantk aof benzene and toluene in the structured fixed bed can be obtained by BDSTmodel.更多还原