Abstract
Amorphous glassy perfluorinated polymers have high gas permeability, are chemically inert, thermally stable and known for their superior separation performance for several gas pairs. In the current study, the gas separation performance of copolymers of perfluoro(butenyl vinyl ether) (PBVE) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) with two different monomer ratios, commercially known as CyclAFlor™, was studied for the first time, both at 35 °C and at higher temperatures below their glass transition temperature. For comparison, the temperature dependence of Cytop® (a homopolymer of PBVE) was studied. The higher the mole percentage of PBVE, the lower gas permeability and the higher selectivity for all gas pairs of interest. All permeability coefficients in Cytop® were lower than those reported in the literature except for helium and hydrogen due to the annealing protocol used, enhancing He/gas and H2/gas selectivity. The poly(PBVE-co-PDD) copolymers exhibited separation performance in the vicinity of the Robeson 2008 upper bound for many gas pairs, including He/H2, He/CH4, He/N2 and N2/CH4. In particular, poly(50%PBVE-co-50%PDD) was more permeable than Hyflon® AD 60 but more selective for most gas pairs of interest. Both copolymers showed increasing H2/CO2 selectivity with temperature. While permeability was stable with pressure up to 10 bar at 35 °C, a change in the activation energy of permeation of CO2 at higher temperatures suggested that changes to the polymer structure had occurred, possibly reducing the glass transition temperature. Mixed gas measurements confirmed the suitability of CyclAFlor™ copolymers for CO2/CH4 separation compared to Cytop®.
Highlights
With population growth and economic expansion, global problems such as water shortages and climate change are growing and are ex pected to exacerbate in the few decades [1]
We report for the first time the permeability of a series of gases in CyclAFlorTM random copolymers of perfluoro(butenyl vinyl ether) (PBVE) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) (Fig. 1) with two different monomer ratios: 0.12/0.88 and 0.5/0.5 at 35 ◦C and temperature ranges below their glass transition temperatures (Tg)
The density and fractional free volume (FFV) measurements for Cytop® are consistent with the reported values in the literature [10,24] (Table 2)
Summary
With population growth and economic expansion, global problems such as water shortages and climate change are growing and are ex pected to exacerbate in the few decades [1]. The synthesis and commercialization of amorphous perfluorinated polymers in the early 1990s, such as Teflon® AF [11], Cytop® [12] and Hyflon® AD [13], was the breakthrough in the use of this class of polymers in gas separation applications These amorphous glassy polymers exhibit high permeability, physical aging resistance and hydrocarbon phobicity which renders these materials significantly more resistant toward plasticization by condensable hydrocarbons than con ventional glassy polymers [1,9,10,13]. Mixed gas measurements were performed to test the CO2/CH4 separation performance of the CyclAFlorTM copolymers compared to Cytop®
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