Abstract
We showed the potential of poly(ethylene-co-propylene) (EPR)/silver metal/p-benzoquinone composite membranes for propylene/propane mixtures, i.e., a selectivity of 10 and a mixed gas permeance of 0.5 GPU (1 GPU = 1 × 10−6 cm3 (STP)/(cm2 s cmHg) in a previous study. In this study, we additionally found that the incorporation of fumed silica nanoparticles into EPR/silver metal/p-benzoquinone (p-BQ) composite membranes exhibited much higher permeance and selectivity for propylene/propane mixtures. The positive polarity of silver metal continuously increased with the increasing silica content up to the 0.1 weight ratio, as revealed by x-ray photoelectron spectroscopy (XPS). This increase in the polarity of silver metal was attributed to the enhanced interaction of p-BQ with the surface of Ag nanoparticles by the increased dispersion of p-BQ by fumed silica nanoparticles. Differential scanning calorimetry (DSC) also presented that the glass transition temperature (Tg) of the membranes was almost invariant. Therefore, the improvement of the permeance and selectivity with the silica nanoparticles was attributable to the increased polarity of the silver metal rather than the structural change.
Highlights
The solvents in composites containing fumed silica nanoparticles were removed in an oven at room temperature, and the composites were dried in a vacuum oven for 2 days
The flow rates for composite membranes were checked by mass flow controllers (MFC) and represented the permeance using a mass flow meter (MFM)
Above the 0.15 weight ratio of fumed silica nanoparticles, the membranes resulted in a significant increase of permeance to give essentially no selectivity of propylene/propane mixtures, which was due to the interfacial defects by the aggregation of silica nanoparticles with EPR polymer chains
Summary
There has been growing research interest in the fabrication of nanoparticles and nanocomposite materials due to their intriguing optical, electrical, and mechanical properties [1,2,3,4,5,6,7,8,9,10,11,12,13]. We reported on the novel application of silver nanoparticles as an olefin carrier for olefin/paraffin separation [17,18,19,20] The electron acceptors, such as p-benzoquinone (p-BQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and ionic liquids, such as 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIIMBF4 ), could modify the surface energy on silver nanoparticles as the electron-insufficient state, complexing reversibly with olefin molecules [17,18,19,20]. The poly(ethylene-co-propylene) (EPR)/Ag nanoparticles/p-BQ composite membranes demonstrated a propylene/propane selectivity of 11 for mixture [17] These membranes showed long-term stable separation performance for more than 100 h [17]. 12 GPU, the EPR/Ag nanoparticles/electron acceptor composite membranes showed the only 0.5 GPU (1 GPU = 1 × 10−6 cm (STP)/(cm s cmHg) [21] These low mixed-gas permeances were attributable to the barrier effect of nanoparticles, resulting in the increase of transport path. The membranes were further characterized using x-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC)
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