面向丙烯/丙烷高效分离的超薄ZIF-8膜的制备

The separation of propylene/propane mixtures is one of the most energy-intensive processes in petrochemical industry, and now is always conducted through the cryogenic distillation method. To reduce energy cost, membrane-based processes have been considered as one of viable alternatives. Recently, metal-organic framework ZIF-8 polycrystalline membranes were demonstrated to effectively separate propylene/propane mixtures. However, the state-of-the-art propylene permeance still can’t satisfy the requirement for industrial separation of propylene/propane mixtures. Therefore, this project is focus on the preparation of ultrathin ZIF-8 polycrystalline membranes through the oriented growth of ZIF-8 nanosheets. The propylene permeance is significantly improved to 1000 GPU, and the separation factor is still keeping higher than 35. We will systematically study the effect of Gemini surfactant on the morphology of ZIF-8 nanocrystals, followed by the exploration of possible growth mechanism of ZIF-8 nanosheets. At the same time, we also examine how seed-orientation affect the microstructure of the ZIF-8 polycrystalline membrane, and explore the effect of membrane thickness on the separation performance and long-term stability for propylene/propane mixtures. The overall goals of this project is to provide a novel strategy for effective separation propylene/propane mixtures.

分离丙烯/丙烷混合气体是目前石油工业中最耗能的过程之一，目前主要采用低温精馏法来分离；而膜分离技术被认为是实现低能耗、低成本分离丙烯/丙烷的潜在手段之一。金属有机骨架材料ZIF-8膜被证明可用于丙烯/丙烷的有效分离，但是丙烯的渗透通量还未能达到工业分离的要求。本项目在申请人前期制备ZIF-8聚晶膜的基础上，提出以纳米片状ZIF-8晶体为晶种，通过调控晶体的取向生长，制备出近似单层的超薄ZIF-8聚晶膜用于丙烯/丙烷混合气体的高效分离（丙烯的通量接近1000 GPU，分离选择性>35）的研究思路。研究Gemini表面活性剂对ZIF-8纳米片状晶体形成过程的影响，揭示纳米片状晶体的形成机理；调控纳米片状晶种的取向生长，制备出近似单层的超薄ZIF-8聚晶膜，进而揭示聚晶膜厚度对丙烯/丙烷分离性能和膜稳定性的关系，为实现丙烯/丙烷的高效分离提供一种新方法。

本项目针对现有的高能耗分离丙烯/丙烷混合气的低温精馏工艺，提出用金属有机骨架ZIF-8膜作为新一代的分子筛材料高效分离丙烯/丙烷混合物，而较厚的膜层显著影响了丙烯气体的渗透率。通过制备ZIF-8超薄膜改善丙烯的渗透率是目前最有效的策略之一。本项目揭示了表面活性剂对ZIF-8晶体形貌和尺寸的影响规律，阐明了二维纳米片状ZIF-8晶体的形成机理。获得了高度单分散的纳米片状ZIF-8晶体悬浮液，阐明了晶体与溶剂匹配性的机理，进而优化出单层纳米片状晶体的沉积工艺。同时调控了纳米片状晶种各个晶面的生长速率，促进其在多孔陶瓷表面的横向生长和扼制其纵向生长，制备出了近似单层的超薄ZIF-8聚晶膜，确定了聚晶膜厚度对丙烯/丙烷分离性能和膜稳定性的定量关系，指导超薄聚晶膜在其它气体分离体系中的制备及应用。在Chem. Mater., J. Membr. Sci., Chem. Eng. Sci., Mater. Horiz., Sep. Purif. Technol., Green Chem. Eng.和化工进展等化学化工主流期刊发表论文12篇，申请中国发明专利3项（已公开），参加国内外重要学术会议5次。