【作者】 金炜阳；

【导师】 王月娟； 罗孟飞；

【作者基本信息】 浙江师范大学 ， 物理化学， 2009， 硕士

【摘要】 挥发性有机气体（VOCs）是一类重要的大气污染物,给环境和人类健康带来严重威胁,其污染控制技术日益引起高度重视。吸附技术是处理VOCs的有效手段,转轮吸附技术解决了低浓度有机气体富集的连续性问题,其吸附性能好坏的关键是吸附剂。SBA-15介孔分子筛具有比表面积高、主孔道尺寸均一、孔壁厚、稳定性较好等特点,自首次合成以来一直受到广泛关注,在催化、吸附和分离等各领域均有潜在应用前景。本文主要通过调变合成条件制备出不同的SBA-15介孔分子筛,并将其用于VOCs（甲苯和乙酸乙酯）吸脱附性能的研究。主要研究内容如下:1、以三嵌段聚合物P123(EO₂₀PO₇₀EO₂₀)为模板剂,TEOS（正硅酸四乙酯）为硅源,酸性条件下合成了常规SBA-15分子筛;以CTAB（十六烷基三甲基溴化铵）为模板剂,TEOS为硅源,碱性条件下合成了MCM-41分子筛。小角X射线衍射、N₂吸脱附表征结果表明,合成的两种分子筛具有典型的二维六方介孔结构,且二者有相似的比表面积。分别用穿透曲线和程序升温脱附考察了甲苯和乙酸乙酯在MCM-41以及SBA-15分子筛上的吸脱附性能。实验表明,和MCM-41相比,甲苯在SBA-15上具有更高的吸附量和较高脱附温度;而乙酸乙酯在两种分子筛上表现出相似的吸脱附性能。两种有机分子与分子筛之间的相互作用强弱用亲性指数表示,结果表明这两种分子筛均呈亲乙酸乙酯、憎甲苯的性能。甲苯在SBA-15分子筛上具有较高的脱附温度是由于SBA-15分子筛中所含的微孔内具有较高吸附势,因而需要更大的脱附活化能。和微孔分子筛TS-1、Silicalite-1等相比,有机气体在介孔分子筛上更容易脱附。2、通过调节合成过程中晶化温度（分别为80℃,100℃,135℃）和晶化时间（分别为0 h,12 h,1 d,2 d,5 d）两种方式调变SBA-15孔道结构。分子筛的孔道性质仍通过小角X射线衍射、N₂吸脱附表征;同时用穿透曲线和程序升温脱附研究甲苯和乙酸乙酯在所合成分子筛上的吸脱附性能。分析结果表明,晶化温度升高,样品的比面表积下降;随晶化时间延长,样品中的介孔含量增多,表明在高温和长时间晶化条件下,更多的微孔向介孔转化。根据不同有机气体在分子筛上的吸脱附行为探讨了晶化过程中有机模板剂和无机物种间脱离逐步形成孔道的可能过程。对有机气体吸脱附实验表明:晶化温度提高,气体吸附量减小,脱附温度降低;分子筛随晶化时间延长,有机气体吸附量先增加后减小。实验结果证实甲苯吸附量和分子筛中微孔含量有关,SBA-15分子筛对甲苯的吸附容量比对乙酸乙酯的吸附容量要小得多。3.用TG-DTG考察了甲苯和乙酸乙酯在SBA-15分子筛上的吸脱附性能,分别用ASTM E698、Friedman与OFW三种经典的动力学方法计算了乙酸乙酯在分子筛样品上的脱附活化能E、指前因子lgA及其随反应进程的变化曲线。有机气体穿透曲线达到平衡后用空气吹扫,根据不同操作条件下的气体脱附浓度与时间的关系,分析了甲苯和乙酸乙酯在分子筛上的扩散过程,表明扩散过程受到介孔孔道的限制。更多还原

【Abstract】 Volatile organic compounds （VOCs） are one of the main air pollutants, which can be a threaten to environment and human health. Its pollution control has attracted more and more attention. Adsorption technologies has been recognized as an efficient way and the thermal swing rotor adsorption technology could condense the low concentration VOCs continuously. The key issue of this technology is the adsorbents. Mesoporous SBA-15 molecular sieve has high specific surface area, large uniform main pore sizes, thick pore wall and good stability, which is potential for catalysis, adsorption, separation etc. In this thesis, a series of mesoporous SBA-15 molecular sieves were prepared and evaluated for its applicability as a sorbent for adsorption of VOCs, using toluene and ethyl acetate as the model compounds. The main contents in this paper are summarized as follows:1. SBA-15 mesoporous molecular sieves were synthesized under acidic condition, using Pluronic P123 (EO₂₀PO₇₀EO₂₀, EO=CH₂CH₂O- and PO = -CH₂（CH₃）₃CHO-) as the template and TEOS （Tetraethylorthosilicate） as the silica source. MCM-41 material was synthesized under alkaline condition, using CTAB （Cetyltrimethylammonium bromide） as the template. SA-XRD （Small-angle X-ray diffraction） and N₂-sorption isotherms results for the two kinds of samples exhibit the P6mm space group mesophases structure properties, with similar BET （Brunauer-Emmett-Teller） surface areas. The adsorption/desorption properties of toluene and ethyl acetate on SBA-15 and MCM-41 have been evaluated using breakthrough curves and TPD （temperature programmed desorption） techniques. A larger amount of toluene adsorption and a higher desorption temperature were observed on the SBA-15; while both samples exhibited similar properties for ethyl acetate sorption. The interaction between organic molecules and adsorbents were evaluated by affinity index. It was found that SBA-15 and MCM-41 are philic to ethyl acetate but phobic to toluene. The larger amount toluene retained and higher desorption temperature of toluene on SBA-15 were also ascribed to the higher adsorption potential existed in the micropores. In contrast to microporous adsorbents such like TS-1 and Silicalite-1, desorption of organic gases from mesoporous molecular sieves could be achieved at lower temperature.2. The pore structures of SBA-15 mesoporous molecular sieves were manipulated by synthesizing at different temperatures （80℃, 100℃, 135℃） and aging at different time （0 h, 12 h, Id, 2 d, 5 d）. All materials were investigated by SA-XRD and N₂-sorption isotherm techniques. The results show that the surface area declined at the higher aging temperature and the mesoporous volume of samples increased with aging time, which was probably due to the fact that a gradual transition from micropore to mesopore under the higher aging temperature and the longer aging time. The sorption properties of toluene and ethyl acetate on the SBA-15 samples were tested by breakthrough curves and TPD techniques. The interactions processes may exist between organic template and inorganic silica species are discussed on basis of sorption results. Less adsorption capacities and easier desorption were observed with increasing aging temperature. When it came to the different aging time, the adsorption capacities of organic gases first increased then decreased. Experiments confirmed that the dynamic adsorption capacities of toluene was proportional to its micropore volume, and the ethyl acetate adsorption capacity on SBA-15 is much higher than that of toluene.3. The sorption properties of methanol and ethyl acetate on SBA-15 materials were investigated by TG-DTG analysis, and three classical dynamics methods （ASTM E698、Friedman and OFW） were used to further analysis. The ethyl acetate desorption properties was evaluated in terms of activation energy for desorption, pre-exponential factor and variation curve with desorption processes. Air purge was operated after the breakthrough curves reached equilibrium. Diffusion coefficients of toluene and ethyl acetate were obtained, based on the gas concentration and desorption time under operating condition. It was found that the diffusion was limited by the pore structure.更多还原