Tubular EVA copolymer/SiO2/PEG composite membrane for CO2 removal from household biogas

The fuel efficiency of household biogas is generally regulated by its CO2 content (25%-50%). To improve its heating value, atmospheric CO2 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 SiO2 and polyethylene glycol (PEG), was fabricated by blown film extrusion. Model biogas containing CO2/CH4 (40/60 v/v) was separated in an in-house continuous gas separation module, in which CO2 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 CH4 permeation, leading to enhanced CO2/CH4 selectivity (from similar to 2.3 to 2.9). Well-dispersed SiO2 particles (0.5 wt%) increase the membrane modulus and suppress CH4 loss. However, adding more SiO2 (0.75-1.0 wt%) leads to higher total gas permeation flux with lower CO2/CH4 selectivity due to particle agglomeration. Incorporation of PEG (0.5-1.5 wt%) increased the membrane polarity and CO2 permeability. The CO2/CH4 selectivity was also improved (similar to 5.3), only up to 1.0 wt% PEG content.