Supercritical ethylene processing of ZIF-8 membranes towards practical electronic-grade propylene production

Supercritical ethene was employed in MOF membrane processing for the first time. • Pre-deposition of a zinc nitrate hydroxide nanosheet buffer layer was proven effective in enhancing the C 3 H 6 /C 3 H 8 separation performance. • Supercritical ethene-processed ZIF-8 membrane enabled one-step purification of polymer-grade C 3 H 6 to electronic-grade C 3 H 6 . • Much higher C 3 H 6 permeance with no compromise in product purity was achieved on supercritical ethene-processed ZIF-8 membrane. ZIF-8 membranes exhibit great promise for high-efficiency C 3 H 6 /C 3 H 8 separation. Nevertheless, maintaining superior performance from pressurized C 3 H 6 -rich feed streams remains a significant challenge, considering its specific application scenarios (e.g., electronic-grade C 3 H 6 production). In this work, we innovatively utilize supercritical ethylene (scC 2 H 4 ) as medium to synthesize ZIF-8 membranes capable of tolerating pressurized high-C 3 H 6 -ratio feed under sub-freezing temperature. Owing to a wider supercritical operation window of scC 2 H 4 , both nucleation and growth kinetics of ZIF-8 crystallites can be readily optimized over a broad temperature and pressure range; through combing with moderate reversible π-coordination between unique C C double bond of scC 2 H 4 and Zn 2+ ions during membrane processing, an unprecedented platform for microstructure optimization of ZIF-8 membranes was established. The introduction of zinc nitrate hydroxide-based buffer layer prior to scC 2 H 4 processing further contributed to their superior performance. Under practical electronic-grade C 3 H 6 production conditions (i.e., −40 °C, 3 bar, polymer-grade C 3 H 6 feed, and vacuum on the permeate side), our membrane achieved C 3 H 6 /C 3 H 8 selectivity of 169.5 with C 3 H 6 flux of 3.6 × 10 −3  mol m −2  s −1 , allowing efficient removal of C 3 H 6 content from 2998 ppm down to below 50 ppm, which completely fulfilled the purity requirement of electronic-grade C 3 H 6 (>99.99%). Through combining with unique advantages of supercritical processing featuring zero waste emission and complete ligand recycling, our research paves an avenue for eco-friendly fabrication of various MOF membranes with tailored microstructures to achieve outstanding separation performance under practical operation conditions. Download: Download high-res image (432KB) Download: Download full-size image