Preparation of CO_2 selective composite membranes using Pebax/CuBTC/PEG-ran-PPG ternary system

Three phase Pebax^® MH 1657/PEG-ran-PPG/CuBTC (polymer/liquid/solid) was successfully deposited as a selective layer on a porous Polysulfone (PSF) support. In fact, the beneficial properties of PEG (high selectivity) with those of PPG (high permeability, amorphous) have been combined with superior properties of mixed matrix membrane (MMMs). The membranes were characterized by DSC, TGA and SEM, while CuBTC was characterized by CO₂ and CH₄ adsorption test. Statistically based experimental design (central composite design, CCD) was applied to analyze and optimize the effect of PEG-ran-PPG (10–50 wt%) and CuBTC (0–20 wt%) mass contents on the CO₂ permeance and CO₂/CH₄ ideal selectivity. Based on the regression coefficients of the obtained models, the CO₂ permeance was notably influenced by PEG-ran-PPG, while CuBTC has the most significant effect on the CO₂/CH₄ ideal selectivity. Under the optimum conditions (PEG-ran-PPG: 32.76 wt% and CuBTC: 20 wt%), nearly 620% increase in the CO₂ permeance and 43% enhancement in the CO₂/CH₄ ideal selectivity was observed compared to the neat Pebax. The effect of pressure (3, 9 and 15 bar) on the pure and mixed gas separation performance of the composite membranes was also investigated. The high solubility of CO₂ in the membranes resulted in the enhancement of CO₂ permeability with increase in gas pressure.