Hydroxyl-functionalized CAU-1 based mixed matrix membranes with enhanced interfacial compatibility for ethane/ethylene separation

A novel Pebax-based ternary MMM was rationally designed with PEG serving as a dual-functional additive. • Interfacial regulation via PEG modification effectively boosts membrane gas diffusion performance and improves filler dispersion. • The optimized membrane exhibits enhanced C 2 H 6 /C 2 H 4 separation performance with balanced permeability and selectivity. Ethylene (C 2 H 4 ) purification from ethylene-ethane (C 2 H 6 ) mixtures is a crucial process in the petrochemical industry, and membrane separation technology offers a promising solution to overcome the limitations of traditional separation technologies. In this work, a Pebax/PEG/CAU-1-OH ternary mixed matrix membranes (MMMs) was rationally designed and fabricated by incorporating poly(ethylene glycol) (PEG) as a functional additive and CAU-1-OH (a hydroxyl-functionalized ultra-microporous aluminum-based MOF) into the Pebax matrix. The structural properties of CAU-1-OH and the resultant membranes were systematically characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and gas adsorption measurements. CAU-1-OH exhibited preferential adsorption for C 2 H 6 over C 2 H 4 with an ideal adsorption solution theory (IAST) selectivity of 3.15, along with a C 2 H 6 adsorption capacity of 91.76 cm 3  g −1 . PEG played a dual role: it disrupted the crystalline structure of Pebax to increase free volume, and acted as a molecular bridge between Pebax and CAU-1-OH via hydrogen bonding interactions, thereby improving the dispersion of CAU-1-OH and enhancing interfacial compatibility. The gas separation performance of the ternary MMMs was evaluated using a C 2 H 6 /C 2 H 4 (50:50, v /v) mixture at 25 °C and 2 bar. Gas permeation tests showed that the Pebax/PEG/CAU-1-OH (20) ternary MMM exhibited a C 2 H 6 permeability of 1533.6 barrer and C 2 H 6 /C 2 H 4 selectivity of 4.76. The hydroxyl groups in CAU-1-OH can form strong hydrogen bonds with C 2 H 6 , leading to a stronger adsorption preference for C 2 H 6 , as supported by DFT calculations. Additionally, the ternary MMM exhibited outstanding long-term stability and pressure resistance, with stable separation performance maintained over 10 days and under various pressures. These results indicate that the Pebax/PEG/CAU-1-OH ternary MMM offers a viable strategy for developing an efficient C 2 H 6 /C 2 H 4 separation materials.