Gas transport properties of novel mixed matrix membranes made of titanate nanotubes and PBI or PPO

Abstract

Titanate nanotubes (TiNTs) for enhancing the gas separation performance of mixed matrix membranes (MMMs) are addressed in this work. The incorporation of different amount of TiNT into commercially available polymers such as polybenzimidazole (PBI) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was successfully carried out. The structure and properties of the MMMs were examined using scanning electron microscope (SEM), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). From SEM studies, it was found that the membranes are homogenous and the nanotubes are well distributed in the polymer matrix. The IR spectra showed that PBI interacts with the nanotubes, whereas interaction of PPO with TiNT has not been observed. TGA measurements of PBI–TiNT membranes showed an increase of thermal stability with a higher content of TiNT, whereas no influence of TiNT in PPO membranes is ascertainable. The content of TiNT in membranes affects also the gas transport properties which were investigated with a time lag permeation apparatus and a sorption balance. It is shown that the presence of the TiNT increases the permeability coefficients of H2, CO2, O2, N2, and CH4 in the PPO–TiNT membranes and decreases these values in the PBI–TiNT membranes. The obtained results of the separation showed that 6 wt.% of TiNT in PBI gave a rise to H2/N2 and CO2/N2 selectivities of 603 and 62 with H2 and CO2 permeabilities of 0.92 and 0.068 Barrers, respectively. PPO–TiNT MMM declined the CO2/CH4 selectivity to a value of 13 with a CO2 permeability of 156 Barrer. Sorption isotherms exhibited nonlinear “dual-sorption” behavior for all gasses. The presence of TiNT in PBI matrix increases CO2 sorptions, whereas influence on other gasses is less noticeable.