Performance of a versatile variable‐volume permeability cell. Comparison of gas permeability measurements by the variable‐volume and variable‐pressure methods

Abstract

An improved cell which permits the measurement of permeabilities of membranes to gases over a wide range of temperatures and gas pressures is described. The measurements are made by the variable volume method, under constant pressure differential across the membrane. The cell lends itself particularly well to routine tests, because it does not require calibration or the use of vacuum techniques. The performance of the cell is discussed, and typical experimental results are presented. A modified permeability cell of the same type for high‐pressure studies is also described. Measurements with this apparatus show that the rate of gas permeation obeys, in some cases, a single from of Fick's law, even under pressure differentials across the membrane as high as 800 psi (54 atm.). The paper also compares permeability data obtained by the variable volume and the variable pressure methods. The permeability of 0.002 in.‐thick Alathon 15 polyethylene to oxygen and nitrogen was determined between 0 and 50°C. by the two methods, using the same sample of membrane in situ, and the measurements were found to agree within experimental error. Permeabilites of 0.010 in.‐thick samples of Alathon 15 polyethylene to nitrogen, oxygen, helium, and carbon dioxide obtained in the same temperature range by the variable volume method were 15–30% higher than the corresponding data determined by the variable pressure method. This discrepancy could be due to the fact that the variable pressure measurements with the thicker membrances may not have been made under true steady‐state conditions, although permeabilities were determined from apparently linear sections of permeated gas pressure vs. time curves. A critical re‐examination of the methods used to determine permeability constants is suggested.

Gas transport behavior of mixed-matrix membranes composed of silica nanoparticles in a polymer of intrinsic microporosity (PIM-1)

“…The pure-gas permeability was measured using a constant pressure/variable volume apparatus [29]. The feed gas pressure was maintained at 50 psig while the permeation side was kept at atmospheric pressure (0 psig).…”

Sorption and transport of hydrocarbon and perfluorocarbon gases in poly(1-trimethylsilyl-1-propyne)

“…26 The surface area of the membrane used in these experiments was 13.8 cm 2 . For all penetrants except C 3 H 8 and C 3 F 8 , the upstream pressure was varied between 2 and 17 atm, whereas the downstream pressure was atmospheric.…”

“…Over a similar range of penetrant sizes, diffusion coefficients in PVC vary by more than 8 orders of magnitude. 63 The diffusivity data for both PTMSP and PVC are well represented by the following empirical relation, which is often used to correlate gas diffusion coefficients in liquids: (26) where and are adjustable parameters. The lines through the experimental data in Figure 16(b) represent least squares fits of this model to the data.…”

Preparation, characterization and gas permeation study of PSf/MgO nanocomposite membrane

“…Permeation tests of pure gases (H 2 , N 2 , CH 4 and CO 2 ) in PSf and PSf/MgO membranes were carried out by a constant pressure method Stern et al, 1963). The film was displayed to the test gases and the data were collected from the steady-state permeate flow rate through a bubble flow meter.…”