Gas transport properties of some fluorine-containing polyethers

Abstract:

A set of five polyethers containing the highly fluorinated monomer, 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenylmethoxy-2-propyl)benzene (12F-FBE), were obtained by polycondensation with the monomers: biphenol, bisphenol F, bisphenol A, bisphenol AF, and a biphenol-substituted spirodilactam. Significant physical properties to characterize their application as membranes for gas separations processes were measured. They exhibit little crystalline domains (below 8%), very similar cohesive energy densities (CED) (with differences smaller than 1.8 (cal/cm³)^1/2), glass transition temperatures (T<inf>g</inf>) above 94 °C, good thermal resistance (T<inf>d</inf> > 350 °C), low specific volumes (V ≤ 0.6516 cm ³/g), and fractional free volumes (FFV) above 0.170. Their permeabilities, at 35 °C and 2 atm, to He, H<inf>2</inf>, O<inf>2</inf>, N<inf>2</inf>, CH<inf>4</inf>, and CO<inf>2</inf> exceed those of commercial polysulfone (PSF) membranes. 12F-BISAF, the most permeable polyether with permeability coefficients (in Barrers) of 51 for He, 28 for H<inf>2</inf>, 3.8 for O<inf>2</inf>, and 12 for CO<inf>2</inf>, is also the material with the highest FFV. However, the observed relation between permeability and FFV confirms that besides FFV other features need to be taken into consideration to determine permeability-especially for the smaller permeants He and H <inf>2</inf>. Concerning the ideal selectivity factors of these materials, they are in the same order of magnitude as those of PSF. The material identified as 12F-SDL is the most selective member of this series with selectivity factors to H<inf>2</inf>/CH<inf>4</inf>, O<inf>2</inf>/N<inf>2</inf>, and CO <inf>2</inf>/CH<inf>4</inf> of 84, 4.8, and 28, respectively. Such superior selectivity of 12F-SDL could be related mainly to inhibited segmental movements. These results are interpreted in terms of CED, FFV, and T<inf>g</inf> together with their respective contribution of gas solubility and diffusivity to the overall selectivity coefficients. © 2010 American Chemical Society.

Año de publicación:

2010

Keywords:

Fuente:

scopus