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    Enhanced CO2/CH4 Permselectivity in Partially Hydrolyzed EVA Membranes via Synergistic PEG Plasticization and Amine-Functionalized Silica Incorporation
    (2026-03-27) ;
    Wisatsuvan, Patchnakan
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    The separation of carbon dioxide (CO2) from methane (CH4) in biogas is essential for increasing the fuel quality. However, conventional membrane-based separation under high pressure is not suitable for household biogas systems due to operational cost and complexity. This study aims to develop low-pressure gas separation membranes based on partially hydrolyzed ethylene vinyl acetate (p-E) copolymers by incorporating poly(ethylene glycol) (PEG) as a plasticizer and amine-functionalized silica (APTES-modified SiO2) as a polar filler. The hydrolysis of EVA improves mechanical strength by increasing hydrogen bonding. PEG addition enhances the free volume and CO2 affinity, while the well-dispersed surface-treated SiO2 increases membrane polarity and suppresses CH4 permeation. Among the tested membranes, the optimal formulation (p-EP400(15)-S0.6) containing 15 wt % PEG400 and 0.6 wt % APTES-SiO2 achieves the highest CO2/CH4 selectivity (∼22) and a high CO2 permeability (∼1400 g/m2·day). These findings demonstrate a promising strategy to develop effective membranes for biogas upgrading under ambient conditions.
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    Tubular EVA copolymer/SiO2/PEG composite membrane for CO2 removal from household biogas
    (2025-03-01)
    Watasit, Prachya
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    Ausavasukhi, Artit
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    The fuel efficiency of household biogas is generally regulated by its CO<inf>2</inf> content (25%–50%). To improve its heating value, atmospheric CO<inf>2</inf> removal of household biogas using a polymeric membrane was attempted to avoid a complicated separation process. A tubular membrane of poly(ethylene-co-vinyl acetate), composed of 28% and 18% vinyl acetate (E28 and E18) modified with SiO<inf>2</inf> and polyethylene glycol (PEG), was fabricated by blown film extrusion. Model biogas containing CO<inf>2</inf>/CH<inf>4</inf> (40/60 v/v) was separated in an in-house continuous gas separation module, in which CO<inf>2</inf> was mainly permeated out of the tubular membrane at atmospheric pressure. Blending the E28 matrix with E18 (10 wt%) improves the membrane processability and inhibits the CH<inf>4</inf> permeation, leading to enhanced CO<inf>2</inf>/CH<inf>4</inf> selectivity (from ~2.3 to 2.9). Well-dispersed SiO<inf>2</inf> particles (0.5 wt%) increase the membrane modulus and suppress CH<inf>4</inf> loss. However, adding more SiO<inf>2</inf> (0.75–1.0 wt%) leads to higher total gas permeation flux with lower CO<inf>2</inf>/CH<inf>4</inf> selectivity due to particle agglomeration. Incorporation of PEG (0.5–1.5 wt%) increased the membrane polarity and CO<inf>2</inf> permeability. The CO<inf>2</inf>/CH<inf>4</inf> selectivity was also improved (~5.3), only up to 1.0 wt% PEG content. Highlights: Composite EVA/SiO2/PEG membrane separates CO<inf>2</inf>/CH<inf>4</inf> at atmospheric pressure. The concentration gradient across the membrane drives CO<inf>2</inf>/CH<inf>4</inf> permeation. Adding SiO<inf>2</inf> hinders CH<inf>4</inf> permeability and enhances CO<inf>2</inf>/CH<inf>4</inf> selectivity. Increasing PEG content enhances membrane polarity and interaction with CO<inf>2</inf>.