【作者】 李振杰；

【导师】 韦奇；

【作者基本信息】 北京工业大学 ， 材料学， 2010， 硕士

【摘要】 微孔SiO2膜具有高温稳定性好、机械强度高、耐各种酸碱性介质腐蚀的特点,在涉及高温和腐蚀性气体的分离过程中具有其它膜材料无可比拟的优越性。但因为SiO2膜具有较强的亲水性,不能应用于湿热环境下,通过表面改性的方法制备水热稳定性良好的微孔SiO2膜是当前的研究方向。本论文主要采用含有疏水基团苯基的硅烷前驱体苯基三乙氧基硅烷(PTES)与正硅酸乙酯(TEOS)在酸性条件下进行共水解缩聚反应,通过调节修饰基团的添加量以及水的加入量制备苯基修饰的SiO2溶胶,在洁净室条件下利用dip-coating技术,将修饰后的溶胶涂覆到γ-Al2O3/α-Al2O3多孔陶瓷载体上,得到以γ-Al2O3/α-Al2O3为支撑体的微孔SiO2膜。应用原子力显微镜(AFM)、扫描电镜(SEM)、红外光谱(FT-IR)、N2吸附、光学接触角测量仪、核磁共振(NMR)以及热重分析(TG)等测试手段表征载体以及膜材料的形貌、孔结构和疏水性能,探讨苯基修饰的微孔SiO2膜疏水机理,并在自制的气体渗透装置上,研究了H2和CO2在疏水微孔SiO2膜中的输运和分离行为。实验结果表明,α-Al2O3多孔陶瓷的孔径在62nm左右,孔隙率达到39%,符合气体渗透的要求;苯基修饰对SiO2膜的孔结构没有产生太大影响,膜材料依然为典型的微孔结构,孔径分布在0.4-0.5nm之间,分布狭窄;接触角测量结果显示修饰后SiO2膜表现出良好的疏水性能,并且材料的疏水性随着PTES添加量的增加而增强,且n(PTES)/n(TEOS)=0.6时膜材料对水的接触角增大到115±0.5o。FT-IR结果证明随着PTES加入量的增大,SiO2膜的Si-OH吸收峰明显逐渐减弱,苯基吸收峰逐渐增强,而且出现单取代吸收峰,表明苯基基团成功修饰到膜材料表面;NMR结果证明修饰后样品表面存在Si-C6H5基团,浓度达到4.64mmol/g,而表面羟基的浓度从8.87mmol/g下降到5.84mmol/g。将修饰前后的膜材料置于潮湿环境下陈化30d,发现修饰后膜材料的孔结构几乎没有发生改变,保持了良好的微孔结构,而未修饰的膜材料孔结构由典型微孔结构转变为介孔结构,表明修饰后的膜材料具有较好的水热稳定性。在室温、膜两端压差为0.1MPa的条件下,通过自制的气体分离装置对气体渗透性能进行测试。结果表明氢气在修饰后SiO2膜的输运既遵循发生在微孔孔道的表面扩散机理也遵循发生在较大孔道或者微缺陷的努森扩散机理,膜材料的H2渗透率达到1.49×10-6mol·m-2·Pa-1·s-1,H2/CO2和H2/SF6的理想分离系数分别达到4.64和365.59。更多还原

【Abstract】 Silica membranes have many advantages over other materials when they used at high temperatures and corrosive environments as material for gas separation because of their high mechanical strength, high thermal stability, and high resistance to various acid-base medium corrosion. However, silica membranes can not be used at humid environments due to their poor hydrothermal stability. Therefore, it is of great significance to prepare hydrothermally stable microporous membranes via surface modification.The present thesis focuses on the preparation of hydrophobic silica membranes and the investigation on their gas transport behavior and hydrothermal stability. Phenyl groups modified silica sols were prepared by the acid-catalyzed hydrolysis and condensation of phenyltriethoxysilane(PTES) and tetraethylorthosilicate (TEOS) in an ethanol (EtOH) medium. The supported silica membranes were prepared on the top ofγ-Al2O3/α-Al2O3 ceramic by the dip-coating technology under clean room condition. The pore structure, morphology and hydrophobic property of silica membranes were studied by means of AFM, N2 adsorption, SEM, water contact angle measurement, FT-IR,TG and solid state 29Si MAS NMR. Gas permeation experiment of the supported membranes was performed with a home-made setup.The results show that the modified membranes display a typical type I isotherms, indicating a microporous structure. The modified silica membranes have a narrow pore size distribution centered at 0.4-0.5nm. Such a microporous structure can be stabilized after exposured to humid atmosphere for 30d, in contrast to the collapse of micropores in the unmodified silica membranes. The successful modification with phenyl groups can be confirmed by FT-IR spectra and solid state 29Si MAS NMR. The water contact angle measurement indicates that a hydrophobic membrane is obtained upon the phenyl group modification and the hydrophobic property is gradually enhanced with increasing PTES concentration. It is reasonable that the presence of hydrophobic phenyl group on the pore surface and the decrease of the amount of hydrophilic silanols are responsible for the enhancement of the hydrophobicity of the modified membranes.The modified silica membranes conform to a combination of a surface diffusion mechanism associated with micropores and a Knudsen diffusion mechanism related to the larger pores or microcracks, with a H2 permeance of 1.49×10-6mol·m-2·Pa-1·s-1 and a permselectivity of 4.64 for H2/CO2 and 365.69 for H2/SF6.更多还原