The efficient enrichment of Helium (He) from low concentrated natural gas seems the only way to balance the He shortage. However, to reinforce this process, one of the biggest challenges is the membrane with both high He permeability and He/CH₄ selectivity. Here, we applied a direct fluorination technique to in-situ modify two intrinsic microporous polyimides (SPI and TPI) with different surface areas. The fluorine reacted with the polyimide backbone at the membrane skin and inner surface that were proved by FT-IR, XPS and EDS analysis. The resulting fluorinated SPI (FSPI) and TPI (FTPI) manifested significantly enhanced He/CH₄ separation properties by huge improved He/CH₄ diffusion selectivity. The overall performance of He/CH₄, He/CO₂, H₂/CO₂ and H₂/CH₄ were much better than their precursor membranes. In which, the FSPI-60 demonstrated a state-of-the-art He permeability of 590 Barrer combined with He/CH₄ selectivity of 634. This figure-of-merit outperformed most of polymer membranes and beat the latest perfluorinated trade-off line. Notably, the FSPI-60 with higher BET surface area precursor demonstrated simultaneously larger He permeability and He/CH₄ selectivity than the corresponding FTPI-60 from low surface area precursor. The higher permeability of FSPI originated from its larger concentration of micropores that provides more pathways for He transport. The higher selectivity of FSPI-60 derived from its much larger He/CH₄ diffusion selectivity, that is, 6375 vs 2334. Additionally, this FSPI-60 membrane also showed plasticization resistant and excellent He/CH₄ (1/99) mixed-gas separation performance, which provides great perspective in He recovery from natural gas applications.

从低浓度天然气中有效富集氦（He）似乎是平衡氦短缺的唯一途径。然而，为了加强这一过程，最大的挑战之一是具有高 He 渗透性和 He/CH ₄选择性的膜。在这里，我们应用直接氟化技术对两种具有不同表面积的本征微孔聚酰亚胺（SPI 和 TPI）进行原位改性。FT-IR、XPS和EDS分析证明，氟与膜皮和内表面的聚酰亚胺骨架发生反应。得到的氟化 SPI (FSPI) 和 TPI (FTPI)通过极大改进的 He/CH ₄扩散选择性表现出显着增强的 He/CH ₄分离性能。He/CH _{4的整体性能}、He/CO ₂、H ₂ /CO ₂和H ₂ /CH ₄比它们的前体膜好得多。其中，FSPI-60 展示了 590 Barrer 的最新 He 渗透率以及 634 的 He/CH ₄选择性。这一品质因数优于大多数聚合物膜，并击败了最新的全氟权衡线。值得注意的是，具有较高 BET 表面积前体的 FSPI-60 同时表现出较大的 He 渗透率和 He/CH ₄选择性高于来自低表面积前体的相应 FPI-60。FSPI 的较高渗透性源于其较大浓度的微孔，为 He 传输提供了更多途径。FSPI-60 更高的选择性源于其更大的 He/CH ₄扩散选择性，即 6375 vs 2334。此外，该 FSPI-60 膜还表现出抗塑化性和优异的 He/CH ₄ (1/99) 混合-气体分离性能，这为从天然气应用中回收 He 提供了很好的前景。