Enhancement of the gas separation properties of polybenzimidazole (PBI) membrane by incorporation of silica nano particles

Abstract

In the present work, the effect of silica nano particles on the permeability of CO 2, CH 4 and N 2 gases in polybenzimidazole (PBI) membranes has been studied. Silica particles were prepared via the sol–gel method through the hydrolysis of tetraethoxysilane (TEOS). PBI and PBI–silica hybrid membranes were prepared by thermal phase inversion method. Scanning electron microscopy (SEM), X-ray diffraction and FTIR analyses were employed in order to characterize the PBI and PBI–silica composite membranes. The obtained SEM micrographs confirmed the nano-scale distribution of silica particles in the polymer matrix. Gas permeation experiments showed an increase in the solubility and a corresponding reduction in the diffusivity of the gases through the membranes by increasing the silica content in the polymer matrix; consequently, the permeability of the condensable CO 2 and CH 4 gases were enhanced whereas that of non-condensable N 2 gas significantly decreased upon increasing the silica content of the nano-composite membranes. The permeability of CO 2 and its selectivity over N 2 was increased from 0.025 Barrer and 3.5 in pure PBI to 0.11 Barrer and 71.3 in the nano-composite containing 20 wt% of the silica particles. There was a strong correlation between the solubility coefficients and condensability of the gases, as well as the diffusion coefficient of the penetrants and their kinetic diameter. Higuchi model fitted fairly well with the experimental results concerning the permeability of nitrogen gas in nanocomposite membranes, supposing the K H = 3.8.