Polyurethane Mixed Matrix Membranes for Gas Separation: A Systematic Study on Effect of SiO2/TiO2 Nanoparticles

In this study, the effect of SiO2 and TiO2 nanoparticles on the gas separation performance of the polyurethane (PU) membranes has investigated. Polyurethanes were synthesized by bulk two step polymerization of polytetramethyleneglycol (PTMG)/polycaprolactone (PCL): isophorone diisocyanate (IPDI)/hexamethylene diisocyanate (HMDI): 4,4'-methylenebis(2-chloroaniline) (MOCA) in mole ratios of 1:3:2. Silica nanoparticles were synthesized using the sol-gel method by hydrolysis of tetraethoxysilane (TEOS) while commercial TiO2 nanoparticles were used. The neat PU membrane and PU-SiO2, PU-TiO2 and PU-SiO2-TiO2 flat sheet asymmetric mixed matrix membranes (MMMs) were fabricated by phase inversion and characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses. Although SEM observation showed uniform distribution of SiO2 and TiO2 nanoparticles inside the polymer matrix, agglomerated nanoparticles were observed at high silica contents in the MMMs of different SiO2/TiO2 ratios. Permeability of membrane samples were measured using pure CO2, CH4, N2 and O2 as test gases. The experimental results revealed that SiO2 and TiO2 could increase permeability of all gases when used separately or in combination. It was shown that when SiO2 and TiO2 were added in combined form, the separation performance of MMMs could be improved signifcantly; either permeability increased up to 120 barrer or CO2/N2 selectivity up to 34, although the individual effect of SiO2 and TiO2 on the selectivity of gas pairs was different.