Study of dual Filler Mixed Matrix Membranes with acid-functionalized MWCNTs and Metal-Organic Framework (UiO-66-NH2) in Cellulose Acetate for CO2 Separation

Biogas upgradation is vital for enhancing its calorific value and reducing corrosion. Membrane-based CO2 separation is an alternative to conventional separation techniques. Polymer membranes such as cellulose acetate have low CO2 permeability. Mixed matrix membranes (MMMs), incorporating nanofillers, either single or dual, in a polymer matrix, are explored to enhance CO2 separation. This work investigates the CO2 separation from model biogas employing dual filler MMMs prepared using acid-functionalized multi-walled carbon nano-tubes (f-MWCNTs) and amine-functionalized metal-organic framework (UiO-66-NH2) as nanofillers and cellulose acetate (CA) as the polymer matrix. MMMs were fabricated by varying the f-MWCNTs loading from 0.01 wt% to 1 wt% with a constant loading of 10 wt% UiO-66-NH2. The morphology, chemical structure, and thermal stability were analyzed using scanning electron microscopy (FESEM), X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). The MMMs 0.01wt% f-MWCNTs@10wt%UiO-66-NH2/CA showed enhanced gas separation performance with CO2 permeability of 31.65 Barrer and CO2/CH4 selectivity of 16.78, compared to the base polymer (CO2 permeability of 6.44 Barrer and CO2/CH4 selectivity of 20.72) and single filler UiO-66-NH2 MMM (CO2 permeability of 10.18 Barrer and CO2/CH4 selectivity of 10.43). The permeability of 0.01wt% f-MWCNTs@10wt%UiO-66-NH2/CA is enhanced by 391% compared to the pure CA membrane and 210% compared to UiO-66-NH2/CA MMMs. A comparison was made with dual filler MMMs fabricated with non-functionalized MWCNTs and UiO-66-NH2, and it was observed that the acid-functionalized MWCNTs-based dual filler MMMs performed better.