离子液体中AlPO4-n分子筛膜的可控合成及气体分离性能研究

Natural gas and biogas as an important clean energy which can greatly reduce the emissions of sulfides, nitrides and the influence of haze weather. However, the presence of CO2 will not only reduces combustion value, also increases the transportation costs. Membrane separation as a high efficient, energy saving and environment friendly technical route was proposed in this project for the efficient separation of CO2 and CH4 by using AlPO4-n molecular sieving membrane. The membranes were prepared in a green and safe strategy of ionothermal by AlPO-17 (IZA code ERI, pore size of 0.36 nm) and AlPO-18 (IZA code AEI type, pore size of 0.38 nm) which was the most important molecular sieves of the AlPO4-n family with a high stability and selective adsorption of CO2. The secondary growth method and membrane automatic transformation methods were proposed to fabricate the oriented membranes on macroporous α-Al2O3 supports by microwave-assisted, solving the technical bottlenecks like the difficulties in synthesis of AlPO4-n membranes and the large transfer resistance. To understand the growth regularity of AlPO4-n membranes under the ionothermal condition and the structure-activity relationship between the environmental factors of membrane growth and membrane structures, revealing the formation mechanism of the oriented membranes. This study will mainly focus on the microstructure design and controlled synthesis of AlPO4-n molecular sieving membrane and the quantitative evaluation and regulation of membrane channels as well as mass transport mechanism of membranes, leading to solutions to the key issues relating membrane design, preparation, evaluation and separation for the CO2/CH4 system, which are expected to provide a scientific and technologic basis for efficient application of high-performance molecular sieving membrane for CO2 removing.

天然气及沼气作为重要的清洁能源可极大减少硫化物、氮化物的排放及雾霾天气的影响。然而CO2的存在不仅降低了其燃烧值，同时增加运输成本。本研究利用膜分离技术，根据分离条件选用结构稳定及高CO2选择性的AlPO-17(ERI型, 孔径0.36nm)及AlPO-18(AEI型, 孔径0.38nm) 两种AlPO4-n分子筛，在绿色、安全的离子热条件下制备成膜。针对AlPO4-n分子筛膜制备困难且传输阻力大、通量低的技术瓶颈，提出二次生长法及“膜层自发晶化法”，在微波辅助作用下，于大孔α-Al2O3载体上制备具有取向性的AlPO4-n分子筛膜。弄清离子热条件下膜的生长规律，膜生长的环境要素与膜结构之间的构效关系；揭示取向膜的形成机制。通过AlPO4-n分子筛膜的可控合成、微结构设计以及研究分子筛膜物质传输微通道的定量评价与渗透行为规律，解决面向CO2/CH4混合气体分离中高性能分子筛膜的制备难题。

天然气及沼气作为重要的清洁能源可极大减少硫化物、氮化物的排放及雾霾天气的影响。然而CO2的存在不仅降低了其燃烧值，同时增加运输成本。此外，随着CO2“温室气体”排放量的逐年增加，经济有效地实现CO2的高效分离具有非常重要的研究意义。通过对晶体生长规律及分子筛膜制备工艺的研究，揭示膜生长的环境要素与膜结构之间的构效关系及形成机制。一方面探究了分子筛材料的宏观及微观结构与CO2吸附之间的关系，开发出球状多级结构、新型中空、及纳米SSZ-13分子筛，其中中空材料在0.27 bar时CO2的吸附量在吸附压力为量达到了2.53 mmol/g。另一方面，基于对大孔载体表面的修饰方法的研究，得到了具有结构取向性的AlPO-17沸石膜，其CO2通量可达2.8× 10-7 mol·m-2s-1Pa-1，CO2/CH4、CO2/N2选择性分别为33和12。最后，自主开发分子筛膜离子热法的绿色合成路线，针对分子筛膜在离子液体中制备困难、反应物传输阻力大的技术瓶颈。首次设计出“膜层自发晶化法”，在大孔α-Al2O3载体上制备出高质量的AlPO-34分子筛膜，其CO2渗透率为1.15×10-8 mol·m-2s-1Pa-1，H2/CO2理想选择性为8.47。提出了构建对水分子在载体表面形成分子簇或连续的氢键网络以促进晶体的成核、生长及自发迁移的新思路。通过分子筛膜的微结构控制合成，解决离子热条件下高性能分子筛膜的制备难题。本研究中关于膜制备工艺的设计和膜合成机理的研究为离子热等复杂体系下的高质量分子筛膜的可控合成提供重要的技术支撑，同时离子液体的循环及大孔载体的使用有效降低了实际应用中的运行成本和设备成本，可产生较好的经济效益，同时解决了传统无机膜工业化合成中的高温高压安全隐患。