Tubular <scp>EVA</scp> copolymer/ <scp> SiO ₂ </scp> / <scp>PEG</scp> composite membrane for <scp> CO ₂ </scp> removal from household biogas

Abstract

Abstract The fuel efficiency of household biogas is generally regulated by its CO 2 content (25%–50%). To improve its heating value, atmospheric CO 2 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 2 and polyethylene glycol (PEG), was fabricated by blown film extrusion. Model biogas containing CO 2 /CH 4 (40/60 v/v) was separated in an in‐house continuous gas separation module, in which CO 2 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 4 permeation, leading to enhanced CO 2 /CH 4 selectivity (from ~2.3 to 2.9). Well‐dispersed SiO 2 particles (0.5 wt%) increase the membrane modulus and suppress CH 4 loss. However, adding more SiO 2 (0.75–1.0 wt%) leads to higher total gas permeation flux with lower CO 2 /CH 4 selectivity due to particle agglomeration. Incorporation of PEG (0.5–1.5 wt%) increased the membrane polarity and CO 2 permeability. The CO 2 /CH 4 selectivity was also improved (~5.3), only up to 1.0 wt% PEG content. Highlights Composite EVA/SiO2/PEG membrane separates CO 2 /CH 4 at atmospheric pressure. The concentration gradient across the membrane drives CO 2 /CH 4 permeation. Adding SiO 2 hinders CH 4 permeability and enhances CO 2 /CH 4 selectivity. Increasing PEG content enhances membrane polarity and interaction with CO 2 .