Investigation of mixed matrix membranes of graphene and acid‐treated graphene fillers in cellulose acetate and polyetherimide polymers for <scp>CO</scp>₂ separation from biogas

Abstract Gas separation membranes are crucial for upgrading biogas by separating carbon dioxide (CO 2 ) from biogas, thereby enhancing its calorific value and reducing greenhouse gas emissions. This study aims to improve CO 2 /CH 4 separation using mixed‐matrix membranes (MMMs) by incorporating graphene (Gr) and acid‐treated graphene (AGr) fillers in a cellulose acetate (CA) polymer matrix. Similarly, polyetherimide (PEI) MMMs were also prepared with Gr and AGr fillers to draw a comparison. Various characterization techniques, including Fourier transform infrared spectroscopy, differential scanning calorimetry, field emission scanning electron microscopy, Raman spectroscopy, and X‐ray diffraction, were employed to investigate the structural and morphological properties of the membranes and fillers. Gas permeation tests using a model biogas mixture (40% CO 2 and 60% CH 4 ) revealed that the 0.1%AGr/CA membrane achieved the highest CO 2 permeability of 43 Barrers, which is approximately 307% more than that of the pure CA membrane, and showed a CO 2 /CH 4 selectivity of 14.80. The 0.5%Gr/PEI membrane demonstrated the best performance among PEI‐based MMMs, with a CO 2 permeability of 17.48 Barrers and a CO 2 /CH 4 selectivity of 8.96. These results indicate that the incorporation of Gr and AGr significantly enhances the gas separation performance over pure CA and PEI membranes. Highlights Graphene (G) and acid‐treated Gr‐based cellulose acetate (CA) and polyetherimide (PEI) mixed‐matrix membranes (MMMs) were fabricated. Model biogas was used for testing CO 2 and CH 4 gas permeation. The 0.1% AGr/CA MMM showed 307% higher CO 2 permeability than pure CA. The 0.5% Gr/PEI MMM showed 435% higher CO 2 permeabilit than pure PEI. Structural properties were confirmed by Fourier transform infrared spectroscopy, differential scanning calorimetry, field emission scanning electron microscopy, Raman, and X‐ray diffraction.