面向乙烯/乙烷分离高性能SSZ-13分子筛薄膜构筑与分离机理的研究

The benchmark cryogenic distillation for ethylene/ethane separation is extremely energy-intensive. In this program, we propose an ethylene-selective zeolite membrane process for this separation with significant energy and cost savings. From the perspective of the matching between pore properties and separation target, SSZ-13 membrane is considered as an ideal membrane material for ethylene/ethane separation due to its perfect pore structure and high process stability. Recently, we have prepared the highly ethylene-selective SSZ-13 membranes with good resistance to impurity heavier hydrocarbons; meanwhile the ethylene permeance should be improved compared with the engineering index. In this program, we propose to optimize systematically the microstructures and morphologies of the asymmetric substrates, seed crystals and membrane layers based on our previous work. The important parameters to be regulated include the orientation and thickness of the zeolite layer, the permeated growth of zeolites into the substrate and the creation of π-complex sites in the surface and cages. The transport behaviors of ethylene and ethane molecules in zeolite channel and the separation mechanism through SSZ-13 membrane will be also explored in depth by the ways of modeling and experimental. Through the proposed fundamental research, <200-nm-thick SSZ-13 membranes with the ethylene-permeable hyperchannel will be accurately constructed, and the construction methods of the microporous membranes and the confinement mass transfer theories will be developed. The resulting membranes are expected to possess ethylene permeances that are more than one order of magnitude higher than our current membranes while still maintaining the same high ethylene/ethane selectivity.

现有用于乙烯/乙烷分离的低温精馏技术能耗非常高。本项目提出采用乙烯选择透过的分子筛膜过程用于乙烯/乙烷分离，预期将显著降低分离能耗。从孔道属性与分离任务匹配性出发，筛选出了具有优良孔道结构和高稳定性SSZ-13分子筛膜作为乙烯/乙烷分离的理想膜材料。在预研工作中，已制备出了抗高碳烃污染和高乙烯选择性的SSZ-13分子筛膜，乙烯渗透速率还有待提高。本项目拟基于前期研究，在支撑体、晶体和晶体层三个层面精确控制其微观形貌与结构，重点调控晶体层的取向生长、厚度、渗入撑体深度和在膜表面或笼内构造π键络合位点。将模拟计算与实验相结合，深入探究乙烯和乙烷在微孔通道内的传递行为和分离机理。通过上述基础性研究，以期精密构筑厚度小于200 nm且具有乙烯选择透过快速通道的SSZ-13分子筛膜，丰富和发展微孔膜的构筑方法和限域传质理论。乙烯渗透速率预期比现有水平提高1个数量级以上，并保持高的乙烯/乙烷选择性。

乙烯和乙烷的动力学直径仅相差3%且沸点接近，现有的低温精馏技术能耗非常高，采用膜分离替代低温精馏可以显著降低能耗。SSZ-13分子膜具有规整均一的三维孔道，孔径大小与乙烯和乙烷动力学直径相当。项目从骨架Si/Al比值调控出发，制备了不同骨架硅铝比、不同金属阳离子配对的SSZ-13分子筛膜，由于孔道大小和极性的细微区别而对膜分离性能参数了较大影响。首次报道了分子筛膜在乙烯/乙烷中的分离性能，在高硅铝比分子筛膜中具有更高的乙烯渗透速率，而在适中的硅铝比条件下具有更高的乙烯/乙烷选择性。首次开发了“seeded gel”、“multi-template”和“gel-less”等3种创新性制备方法用于SSZ-13分子筛膜制备。采用吸附、SEM、XRD和XPS等表征技术表征了SSZ-13晶体和膜，对分子筛在支撑体上非均相晶化成膜的过程与机理进行了系统研究，并通过麦克斯韦-史蒂芬方程对各种气体分子在膜孔中的传质行为进行了模拟预测，对分子筛膜筛分机理进行了研究。通过4年的基础性研究，膜分离乙烯/乙烷的分离选择性大于10，且乙烯的渗透速率比其它膜材料高出5倍以上。在J. Membrane Sci., J. Mater. Chem. A等杂志上发表SCI科研论文12篇，授权发明专利4项，其中发明专利（ZL201710312285.6）已转让给企业。各项指标均达到项目预期。. 项目成功实施对石化领域的基础研究产生非常积极的影响，具有较为深远的科学意义。精馏技术经过一百多年的发展已经遇到技术瓶颈——分离的能耗非常高。本项目以极为挑战的乙烯/乙烷分离为应用背景，通过对膜孔道设计和分离机理等系列基础性研究，解决乙烯选择透过快速通道构筑和限域传质的两大关键科学问题，首次实现微孔膜高效分离该混合物，首次报道选择性超过10的膜材料。项目实施将为石化产品分离提供新的膜法节能分离的解决方案，为膜法工业应用于同碳数烃等石化产品分离提供理论指导和基础数据，具有较强的科研价值。