Gas permeation unit

The permeability of gases through membranes is most commonly measured in Barrer, defined as 10-10 cm3(STP)/cm2 s cmHg and named after R.M. Barrer, a pioneer in gas permeability measurements. The term ji/ pio — pit), best called the pressure-normalized flux or permeance, is often measured in terms of gas permeation units (gpu), where 1 gpu is defined as 10 6 cm3(STP)/cm2 s cmHg. Occasional academic purists insist on writing permeability in terms of mol m/m2 s Pa (1 Barrer = 0.33 x 10-15 mol m/m2 s Pa), but fortunately this has not caught on. 

The common unit of P, is Barrer (IBarrer = 10 10cm3 (STP)-cm/ cm2scmHg = 0.76-10 17m3 (STP) m/m2 s Pa). The ratio P,/l is referred to as the permeance, and its common unit is the gas permeation unit (GPU), which is 10 scm3 (STP)/(cm2 s cmHg). If the downstream pressure is negligible compared with the upstream pressure, the selectivity can be expressed as... 

Degassing involves chemical, physical and/or electrolytic procedures, as well as the use of gas permeation units [127,128]. Addition of nitrogen and the use of reduced pressure permit a faster and more efficient degassing. These procedures are not however permanent, as there is always a tendency for the solutions to re-equilibrate with the environment. To date, no single efficient and completely safe approach for solution degassing in flow analysis has been reported. 

Built and operated our in-house light gas permeation unit ... 

A perfectly mixed gas permeation unit is separating a mixture that is 20 mol% carbon dioxide, 5 mol% oxygen and 75 mol% nitrogen using a poly(dimethylsiloxane) membrane at 25°C. Feed flow rate is 20,000 cm (STP)/s. The membrane thickness is 1 mil (0.00254 cm). Pressure on the feed side is 3.0 atm and on the permeate side is 0.40 atm We desire a cut fraction = 0.225. Find the membrane area needed, and the outlet mole fracs of permeate and retentate. 

The permeability (permeance) P is defined as the gas flow rate multiplied by the thickness of the membrane, divided by the area and by the pressure difference across the membrane (Equation 1). The permeability is given in the unit barrer or gas permeation unit (GPU) (Equations 2 and 3). 

CNT = carbon nanotube GPU = gas permeation unit MMM = mixed-matrix membrane MOF = Metal organic framework ODA = 4,4-oxydianiline PFG = pulsed field gradient PLO = porous layered oxide PMDA = pyromellitic dianhydride PPEES = poly-( 1,4-phenylene ether-ether-sulfone) ... 

The development of membranes with improved permeance is more important than the development of more selective materials. For polymeric materials with a physical separation process, the best performances reported up to now can be defined as a CO2/N2 selectivity of 50-70 and a permeance of 1000 GPU (gas permeation unit). 

Fluxes through integrally skinned asymmetric membranes and TFC membranes are expressed as permeances that are reported in gas permeation units, GPU, where ... 

Such a unit was originally defined for convenience because many polymer membranes had permeabilities around 1 barrer. In the cases where the membrane thickness is not known, the permeance Pjl) becomes the operating parameter. In its simplest form, the permeance is just the mass transfer coefficient for the membrane, with dimensions of velocity. Like the permeability, however, more common dimensions are gas permeation units (GPU), defined as... 

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