Preparo e caracterização de membranas isotrópicas de matriz mista contendo nanotubo de carbono de parede múltipla dispersos em polidimetilsiloxano para utilização em separação de gases

Abstract

Over the past three decades, polymeric gas separation membranes have become widely used for a variety of industrial gas separation applications. Removal of CO2 from natural gas is a growing area for membrane technology. Penetration through polymeric membranes in which a filler has been embedded is known as mixed matrix membranes (MMMs). Polydimethylsiloxane (PDMS) films with different weight concentrations of multi-walled carbon nanotubes (MWCNT) removed CO2 from CH4 gas streams. Incorporation of carbon-based fillers into polymer increased the chances of the permeate gas molecule to interact with their surfaces, which could increase selectivity and gas permeability. Permeability and selectivity of these membranes were measured by using a time-lag constant volume variable pressure apparatus. Positron annihilation lifetime spectroscopy (PALS) was applied to assess free volume of the membranes and the chemical structure was determined by Fourier transform infrared (FTIR) and Raman spectroscopies. Scanning electron microscopy (SEM) was used in order to examine the morphology of the membranes as well as the distribution of the MWCNT nanoparticles into the polymer. Membranes average thickness was 150 m. No phase separation of MWCNT and PDMS was noticed. It was obtained a high permeability for H2, N2, CO2, O2 and CH4. The average diameter of the cavities (free volume) responsible for molecular motion in the polymer matrix were not affected by the addition of carbon nanotubes to the weight concentration of 1.6%, as characterized by PALS. An increase in weight concentration of MWCNT from 3.0% to 6.7% caused an increase on both CO2 permeability of 1069 Barrer and selectivity from 1.71 to 1.91, respectively. The free volume increased 2.70%.