Helium recovery from LNG waste stream using two-dimensional nanostructured MXene membranes

氦(He)是一种战略性工业气体，在各种高科技应用中发挥着越来越重要的作用。目前全球对他的需求是惊人的。每年2亿立方米(STP)，价值60亿美元。从氮气和微量的甲烷和二氧化碳中分离氦的主要目标是通过低温蒸馏实现的-这是一个高度耗能和资本密集型的过程-然后在木炭上吸附，将氦的纯度提高到99.95%。本项目旨在开发无机中空纤维支撑的纳米二维MXene膜，作为先进的功能材料，用于从液化天然气(LNG)工厂的混合气体中分离He和微量CH4、CO2，用于回收He。这项研究的关键概念是材料科学，旨在合成孔径可控的层状2D MXene膜，将其组装在多孔无机中空纤维支撑体上，在室温下提供&gt；1000 Barrer的高氦渗透率和对&gt；30的其他气体的选择性。这些渗透参数允许在一段渗透过程中获得99%的纯He，从而为最终的吸附过程提供了合适的原料。科学上的挑战将是直接合成MXene纳米片材或通过多层MXene粉末的分层来制备MXene纳米片。另一个关键步骤是将纳米薄片沉积在载体上，以获得可控的孔径。在实际应用中，MXene膜将被制备在无机中空纤维载体上，如陶瓷或不锈钢材料，因为中空纤维几何结构可以提供最大的单位体积的膜面积。具体地说，该项目的目标是(1)合成MXene纳米片并使其功能化；(2)通过优化MXene膜的层间距和MXene纳米片的片状尺寸来最大化选择性和通量；(3)了解通过组装的二维纳米结构MXene膜的气体传输行为。

Helium (He) is a strategic industrial gas which becomes increasingly important within a wide range of high-tech applications. The current global demand for He is appr. 200 Mio m3 (STP) per annum with a value of US$ 6 billion. The primary objective of the separation of He from N2 and trace amounts of CH4 and CO2 has been accomplished solely by cryogenic distillation - a highly energy and capital intensive process - followed by an adsorption on charcoal increase the He purity up to > 99.95%. This project aims to develop inorganic hollow-fiber supported nanostructured 2D MXene membranes as advanced functional material for He separation from its mixture with N2 and trace amounts of CH4, CO2 for He recovery in liquefied natural gas (LNG) plants. The key concept of the research is material science-oriented and aims at the synthesis of layered 2D MXene membranes with controlled pore sizes to be assembled on porous inorganic hollow-fiber support, delivering high He permeability of > 1000 Barrer with a selectivity of He against other gases of > 30 at room temperature. These permeation parameters allow to produce 99% pure He in a 1-stage permeation process instead of the cryo-distillation thus giving a suitable feed for the final adsorption process. The scientific challenges will be the direct synthesis of MXene nanosheets or their preparation by delamination of multilayer MXene powder. Another crucial step will be the deposition of the nanosheets on supports to get a controllable pore size. For practice application, the MXene membrane will be prepared on inorganic hollow-fiber supports like ceramic or stainless steel material as the hollow fibre geometry can provide the largest membrane area per unit volume. Specifically, the objectives of this project are to (1) Synthesise and functionalise MXene nanosheets; (2) Maximize He selectivity and flux by optimizing the interlayer spacing of the MXene membranes and the flake size of the MXene nanosheets; (3) Understand the gas transportation behaviour through the assembled two-dimensional nanostructured MXene membranes.