Figure 1: Flow diagram of gas permeation rig.
All pure gas membrane permeation tests were performed in a variable feed
pressure and constant volume permeation system, as shown in Figure 1.
All gas permeation tests were performed at room temperature. The
membrane module utilizes a sealing o-ring directly onto the selective
polymeric membrane surface. The membranes were secured in the gas
permeation module before tests. The membranes were held under vacuum for
approximately 5 minutes before being exposed to selected gas on the feed
side at a selected pressure of around 2 bars. The permeate side of the
membrane (including the buffer tank) was left in a vacuum before the
start of the gas permeation test. The pressure of the feed and permeate
side of the membrane were measured at intervals of 5 s, and the steady
rate of pressure increase on the permeate side was calculated. The
effective membrane area for each test was also recorded.
The permeation coefficient was calculated using the following equation:
\begin{equation}
P=\ \frac{273.15\ \times 10^{10}}{760\times A\times T}\frac{V\times L}{\frac{P_{0}\times 76}{14.7}}\frac{\text{dp}}{\text{dt}}\nonumber \\
\end{equation}Where \(P\) is the permeation coefficient in barrer (1 barrer =1 ×
10-10 cm3 (STP) cm
cm-2 s-1 cm Hg-1),\(A\) is the effective area of the membrane (cm2),\(T\) is the absolute temperature (K), \(V\) is the dead-volume of the
permeate side (cm3), \(L\) is the membrane thickness
(cm), \(P_{0}\) is the feed pressure (psi), and\(\frac{\text{dp}}{\text{dt}}\) is the steady rate of pressure increase
in the permeate side (mm Hg s-1). All permeation
values and error bars were obtained from multiple measurements of the
samples.
The ideal selectivity for different gas pairs was calculated using the
following equation:
\begin{equation}
\alpha=\ \frac{P_{A}}{P_{B}}\nonumber \\
\end{equation}Where \(P_{A}\) and \(P_{B}\) are the permeation coefficient of pure gas
A and B, respectively.