Helium recovery from LNG waste stream using two-dimensional nanostructured MXene membranes
Chemical and Thermal Process Engineering
Solid State and Surface Chemistry, Material Synthesis
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
We successfully synthesized a series of MXene (Ti3C2) nanosheets with different methods, including simultaneous etching and intercalation using HCl-LiF mixture, etching using HCl-HF mixture followed by interaction using LiCl or dimethyl sulfoxide, delamination via hand-shaking or ultra-sonication. All methods can deliver MXene nanosheets, the main differences are the yield, size distribution, and thickness of nanosheets. Furthermore, in-plane pores can be formed on MXene nanosheets by using Cu (II) ions as catalysis. MXene nanosheets have abundant surface groups such as -OH, which endow the nanosheets with high stability in water. MXene nanosheets can also be stably dispersed in some commonly used organic solvents (e.g. ethanol, dimethyl sulfoxide, dimethylformamide) by exchanging solvents when necessary. MXene membranes were prepared using aforementioned nanosheets with various parameters. The interlayer free spacing between two adjacent nanosheets is extremely sensitive to the duration of vacuum filtration and drying conditions. While the interlayer free spacings of entire nanosheets inside a MXene membrane may be retained or increased by solvent molecules during applications such as ion sieving, the spacing near the surface of a MXene membrane may be decreased during the gas separation due to the pressure difference between feed and sweep sides and losing of intercalated water molecules. As a result, we do not observe He/N2 and He/CH4 selectivities higher than the corresponding Knudsen selectivities. A high amount of cations can be adsorbed and intercalated in MXene membranes. These cations promote the heterogeneous nucleation and crystal growth of zeolitic imidazolate frameworks (ZIFs) and lead to well-intergrown membranes. The ZIF-67 membranes prepared by the assistance of MXene show excellent He/N2 and He/CH4 separation performance with a He permeance greater than 6.6 x 10^-8 mol·m-2·s^-1·Pa^-1 and selectivities above 13. The membranes also have good long-term chemical (against CO2 and H2O) and thermal stabilities.
Publications
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MXene assisted preparation of well-intergrown ZIF-67 membrane for helium separation. Journal of Membrane Science, 652, 120432.
Zhao, Zhijun; Ding, Li; Hinterding, Richard; Mundstock, Alexander; Belke, Christopher; Haug, Rolf J.; Wang, Haihui & Feldhoff, Armin
