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.