Effects of low and high molecular mass PEG incorporation into different types of poly(ether-b-amide) copolymers on the permeation properties of CO₂ and CH₄

Blend membranes were prepared by incorporating two types of polyethylene glycol (PEG) (molecular masses of 400 and 1000 g mol⁻¹) into three grades of poly(ether-block-amide) (PEBAX), namely PEBAX 1074, PEBAX 1657, and PEBAX 2533. The PEGs, which were used as blending agents, were employed at mass fractions ranging from 10 to 40 wt.% based on the mass of PEBAX. The gas separation performance of each neat or blend membrane, comprising its CO₂ and CH₄ permeabilities and its ideal CO₂/CH₄ selectivity, was studied at room temperature (25 °C) and at pressures of 2–8 bar. X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analyses were used to determine the crystallinities of and the chemical bonds in the prepared membranes, respectively. Scanning electron microscopy (SEM) was also utilized to observe the morphologies of the membranes. The results obtained from experimental investigations showed that the incorporation of low molecular mass PEG significantly increased the permeability but only slightly affected the ideal CO₂/CH₄ selectivity, while the incorporation of high molecular mass PEG decreased the permeability considerably but sharply increased the ideal CO₂/CH₄ selectivity. This behavior intensified as the polyether content of the PEBAX was decreased.