Abstract
Polydimethylsiloxane (PDMS) membranes with different concentrations of multi-walled carbon nanotubes were prepared in order to evaluate their gas separation performances. Mixed matrix membranes were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transformed infrared, positron annihilation lifetime and Raman spectroscopies and X-ray diffraction. The permeabilities to CO2, CH4, N2 and O2 were determined. No phase separation was noticed. For carbon nanotubes content of 1 wt%, it was shown a decrease in membrane permeability with slight increase in ideal selectivity, compared to pure PDMS. However, the increase in the filler load up to 6.7 wt% increased the free volume average size of the membranes, improving the contribution of the diffusion to the transport and decreasing ideal selectivities of CO2/CH4, CO2/N2 and O2/N2.
Highlights
The use of synthetic membranes for gas separation reached an industrial level in the 1980s
The results showed that PDMS profile governed the thermal decomposition
The transport was mainly governed by sorption, low nanotubes load caused a decrease in membrane free volume fraction, with increased selectivity
Summary
The use of synthetic membranes for gas separation reached an industrial level in the 1980s. Ordinary membranes show a trade-off behavior between permeability and selectivity, as reported by Robeson[2,3]. In order to circumvent such limitation, mixed matrix membranes have been investigated as an alternative aiming the increase in both permeability, which allows high productivity, and selectivity, leading to the improvement of process yield[4]. The objective is the use of the solid phase in order to overcome the trade-off behavior reported by Robeson[4]. There are still some issues that remain unsolved in order to launch the technology, such as the material compatibility regarding their permeabilities, particle size to prepare a thin membrane and optimization of the contact between the two phases, for instance[4]
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