Relationship of Permeation and Diffusion of Carbon Dioxide and Methane Gases with Fractional Free Volume in the Blend Membranes of Poly(ether-b-amide) and Vinyl Acetate- Based Copolymer

Blend membranes based on the poly(ether-b-amide) and vinyl acetate/ dibutyl maleate copolymer were prepared via solution casting. Results of the gas permeability test showed that the selectivity of carbon dioxide gas (CO2) relative to the methane (CH4) gas in the prepared membranes increases twofold while the permeability of these gases decreases by increasing amount of vinyl acetate/ dibutyl maleate copolymer. Diffusivity and solubility of CO2 in the membranes were calculated, and it was found that decrease in permeability is due to the decrease in the diffusivity of gases in the blend membranes. To further understand this issue, fractional free volumes (FFV) of the membranes were calculated by two different methods, one without and another with considering the permeated gas from membrane. It was observed that by increasing the amount of the vinyl acetate/ dibutyl maleate copolymer in the blend membranes, FFV decreases. By equations at hand for polymers, a relationship between the FFV of membranes and diffusivity and permeability of the gases was established, and a good correlation between them was found.