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Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) is a copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) which not only maintains the excellent properties of polytetrafluoro...

A dual-resistance model, in which a barrier resistance confined at the micropore mouth is assumed to act in series with pore diffusional resistance distributed in the micropore interior, has been proposed for multicomponent transport of gases in carbon molecular sieves (CMS). Excellent predictive power of the model has been thoroughly validated by means of extensive unary/binary integral uptake and breakthrough measurements involving large pressure steps on Takeda and Bergbau Forschung (BF) CMS samples. Quantitative agreement between the experimental and predicted results is truly remarkable considering the fact that all the predictions are strictly based on independently measured single-component equilibrium and kinetic parameters. Impact of two mixture isotherms, namely ideal adsorbed solution (IAS) theory and extended Langmuir (E-L) model, on mixture uptakes has also been investigated. This study undeniably establishes the following: (1) effectiveness of a dual-resistance approach for gas transport in CMS micropores, and (2) much stronger concentration dependence of the transport parameters than that predicted from the use of a chemical potential gradient as the driving force for diffusion with constant intrinsic mobility.

In two recent studies from this laboratory, a dual resistance model with chemical potential gradient as the driving force for transport and empirical correlations to account for the strong concentr...

Single component differential uptake of oxygen and nitrogen in three samples of carbon molecular sieve adsorbent and carbon dioxide and methane in one of the samples has been measured volumetrically at different temperatures over a wide range of adsorbent loading. The results seem to suggest that the early part of the uptake is controlled by a barrier resistance confined at the micropore mouth while the later part is controlled by a pore diffusional resistance distributed in the micropore interior. A dual resistance model is able to capture the observed single component uptake behavior for all the four gases, which is assuredly less tentative than what the current literature may suggest. Moreover, the extracted micropore transport parameters have much stronger dependence on adsorbent loading than that expected from chemical potential gradient as the driving force for diffusion and the assumption of a constant limiting transport coefficient based on prevailing evidence. An approximate way of accounting for...

The possibility of distinguishing between barrier and pore diffusional resistances in adsorbent micropores from dynamic column response has been explored. The modeling of transport through a barrier resistance confined at a micropore mouth is mathematically equivalent to the linear driving force (LDF) model. By comparing the pore diffusion and LDF models for dynamic column response for a linear isotherm, it is shown that the extent of agreement between the two models depends on the product of the two parameters α (=(1-e p )K c /e p ) and γ (=D c L/r c 2 v 0 ). By an appropriate choice of operating conditions, it is indeed possible to clearly distinguish between the two mechanisms. The proposed criteria have been verified experimentally for the breakthrough of oxygen and nitrogen in a 4A zeolite and two carbon molecular sieve samples.