纯硅MFI型分子筛膜的原位合成及其CO2/N2混合气体分离性能研究

摘要

通过多孔α-Al2O3载体的处理或修饰改变其表面物化性质,并采用原位水热晶化法合成纯硅MFI分子筛(silicalite-1)膜.SEM、XRD和接触角的检测结果表明,未经处理、经过H2O2处理或带有氧化锆中间层的α-Al2O3载体为亲水性表面,其上不能形成连续的分子筛膜层;而经过3-氯丙基三甲氧基硅烷(3-CP-TMS)、十二烷基三甲氧基硅烷(DMS)修饰或带有壳聚糖中间层的α-Al2 O3载体为疏水性表面,其上可以形成连续、致密的分子筛膜层,用DMS修饰或带有壳聚糖中间层的α-Al2 O3载体上形成的分子筛膜有一定的择优取向.疏水性的载体表面是形成连续纯硅MFI分子筛膜层的先决条件,而合理的H2O/Si比是保证分子筛完全覆盖载体表面形成致密膜层的重要因素.将载体经DMS修饰后原位水热合成的纯硅MFI分子筛膜应用于CO2/N2混合气体分离过程表明,合成的膜对CO2具有分离选择性.%The porous α-Al2O3 substrates were treated or modified to change the surface properties.The silica-MFI zeolite membranes were synthesized on treated or modified α-Al2O3 substrates by in-situ crystallization.The experimental results by SEM,XRD and contact angle revealed that the untreated porous α-Al2O3 substrate,and that treated by using H2O2 or with a zirconia intermediate layer were hydrophilic,on which the continuous zeolite membrane could not be formed.While the porous α-Al2 O3 substrate modified by using (3-chloropropyl)trimethoxysilane (3-CP-TMS) and dodecyltrimethoxysilane (DMS) or covered with a chitosan layer was hydrophobic,on which the continuous and dense zeolite membrane could be formed.The synthesized zeolite membrane on the porous α-Al2O3 substrate modified with DMS or covered with a chitosan layer were preferentially oriented.The hydrophobic nature of the substrate surface should be the prerequisite for synthesizing continuous zeolite membranes,at the same time,a proper H2O/Si ratio would be a critical factor for the formation of a dense silica-MFI membrane.After being applied in separation of CO2/N2 gas mixture,the MFI membrane synthesized on DMS-modified α-Al2O3 substrate had an increased selectivity for CO2.