Dual-mode Mobility Model Research Articles

Sorption and permeation behavior for a gas in glassy polymer membrane near the glass transition temperature

The deviation from the conventional dual-mode sorption and mobility model for a gas in glassy polymer membranes has separately been studied thus far, and to simulate sorption and diffusion behavior, an extended dual-mode sorption model and a modified dual-mode mobility model, respectively, have been proposed independently. However, simultaneous deviation from the conventional dual-mode sorption and mobility model was observed in cases of CO2in poly-4-methyl-1-pentene membrane at 20°C and in polystyrene membrane at 60 and 70°C. The plasticization effect of sorbed CO2 on both the sorption and diffusion processes tends to be brought about in glassy polymer membranes near the glass transition temperature. The behavior was simulated based on the concept that only one population of sorbed gas molecules exists. © 1996 John Wiley & Sons, Inc.

Permeation of carbon dioxide in glassy poly(ether imide) and poly(ether ether ketone) membranes

Sorption equilibria and permeation rates for CO 2, O 2 and N 2 in poly(ether imide) (PEI) membrane which has a glass-transition temeperature of 216°C and in poly(ether ether ketone) (PEEK) (a typical crystalline polymer, crystallinity=0.4) membrane, whose glass-transition temperature is 143°C, were measured at 25, 30 and 40°C and at pressures up to 3 MPa. The pressure dependence of the mean permeability coefficients of PEEK membrane to O 2 and CO 2 obeyed conventional dual-mode mobility model, whereas that of PEI membrane to CO 2 did not follow the conventional dual-mode mobility model. A modified dual-mode mobility model which takes into account four kinds of diffusive movements was satisfactorily used to simulate the pressure dependence.

Transport phenomena in gas permeation through glassy polymer membranes with concentration-dependent sorption and diffusion parameters

The modified dual-mode mobility model for permeation of a gas in glassy polymer membranes was combined with the extended dual-mode sorption model to take account of the plasticization effect of sorbed gas molecules on both sorption and diffusion processes. The combined model was further simplified by the introduction of a concentration of the mobile gas species. However, the observed pressure dependence of mean permeability coefficients of carbon dioxide in methylmethacrylate-n-butyl acrylate copolymer and polymethylmethacrylate films at 30°c and also that of oxygen in a polycarbonate film at 50°C and 60°C showed that a plasticization action of sorbed gas species has an influence on the diffusion process rather than on the sorption process, that is, were simulated by the modified dual-mode mobility model combined with the conventional dual-mode sorption model.

Transport of oxygen and carbon dioxide through polycarbonate membrane

Sorption equilibria and permeation rates for oxygen and carbon dioxide in polycarbonate membrane were measured at different temperature between 30 and 60°C and at pressures up to 2.5 MPa. The pressure dependence of mean permeability coefficient to oxygen obeyed the conventional dual-mode mobility model, whereas that to carbon dioxide followed a modified dual-mode mobility model with concentration-dependent diffusivities, as that of polystyrene to the same gas did.

Gas permeation through glassy polymer membranes with relatively low glass-transition temperature

When the glass-transition temperature of the polymer is not so much higher than the experimental temperature, the pressure dependence of the mean permeability coefficient of the poly-mer membrane to a gas is apt to deviate from the prediction by the conventional dual-mode mobility model, and to obey a similar model with concentration-dependent diffusivities because of the plasticization action of sorbed gas in the polymer membrane. In this work, sorption and permeation for oxygen and carbon dioxide in a membrane of polystyrene whose glass-transition temperature is 95°C, were measured to discuss the mechanism of gas diffusion in glassy polymer membranes with relatively low glass-transition temperature at 30, 40 and 50°C respectively.

Separation of carbon dioxide by asymmetric hollow fiber membrane of cellulose triacetate

AbstractPermeation behavior of pure CO2, O2, and N2 and separation characteristics of CO2–air mixtures were examined using hollow fiber modules of asymmetric cellulose triacetate membrane at 30°C. The ideal separation factor for CO2 relative to N2 ranged from 21 to 24. Permeation behavior for pure CO2 was interpreted in terms of the total immobilization model, i.e., a limiting case of the dual‐mode mobility model for glassy polymer, where the diffusion coefficient for Henry's law mode is not assumed to be constant and depends on gas pressure via a modified free‐volume model. Based on pure gas permeabilities to CO2, O2, and N2, simulation for the separation of CO2–air mixtures was made using a counter‐current plug flow model, and the result fitted the corresponding experimental data fairly well. Membrane plasticization induced by CO2 had negligible effect on permeation to mixture of CO2 and air in the range of CO2 composition up to 50% and upstream total pressure up to 1.5 MPa.

Sorption and diffusion of carbon dioxide in polyimide films

The sorption isotherms of carbon dioxide in a polyimide film sample were measured by a pressure decay method at 30, 40, 50, and 60°C and pressures up to 1.7 MPa. The mean permeability coefficients at the same temperatures were measured by a variable volume method at applied upstream pressures up to 3 MPa. The sorption equilibria at these temperatures were found to be well described in terms of a dual-mode sorption model. The pressure dependences of the mean permeability coefficients at these four levels of temperatures did not satisfactorily follow a dual-mode mobility model, but could be well simulated by a modified mobility model that both the Henry's law (D) and Langmuir (H) populations execute four kinds of diffusive movements such as D D, D H, H D, and H H. The diffusion coefficients of D D, D H, and combined H H and H D steps were determined by comparing the experimental permeability data with those predicted via this modified mobility model. The temperature dependences of such diffusion coefficients were consistent with Arrhenius-type equations within the covered temperatures.

Mechanism of gas permeation through glassy polymer films

The observed pressure dependence of the mean permeability coefficients of carbon dioxide and methane in glassy polymer films such as polycarbonate, Kapton® polyimide and polysulfone, taken from existing papers, was compared with the predictions in terms of a dual-mode mobility model and a modified mobility model in which both the Henry's Law and Langmuir populations execute four kinds of diffusive movement. The pressure dependence is simulated better by the modified model than by the original model. The mean permeability coefficients and sorption isotherms for carbon dioxide and methane in commercially available polysulfone films were measured at four temperature levels between 30 and 45°C and at gas pressures up to 33 atm and 61 atm, respectively. The pressure dependence of the mean permeability coefficients for the above systems is also described well by the modified mobility model, whereas the sorption isotherms are described well by the dual-mode sorption model.