Gas permeation test
The gas permeation tests were conducted at different temperatures and pressures on self-designed equipment, which was based on constant pressure and variable volume (Figure. S1), and gas permeation testing details are given in supplementary information. In this work, we measured gas transportation across the membrane in “permeance” as it is independent of the membrane thickness and membrane module. Simple flat sheet membranes were used in this work for the separation of butadiene and nitrogen, while different membrane modules widely used in industries for getting better results than the flat sheet membranes. Gas permeance of both the gases was measured, and all the readings were repeated at least five times and reported an average value of it. The gas permeance (J ) was calculated by using the following equation,
\(J=\frac{q}{p\times A}\) (2)
where q represents the flow rate (cm3/sec), which was measured by a bubble flow meter, \(p\) used for the trans-membrane pressure (cm Hg), and A is used for active membrane surface area (cm2). The unit used for permeance was GPU (gas permeation unit) (1×10-6cm3 cm-2 sec-1cmHg-1).
The permeance is related to the permeability by using the following equation,
\begin{equation} P=J\times l\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (3)\nonumber \\ \end{equation}
here, P is used for permeability (1×10-10cm3 cm cm-2 sec-1cmHg-1), and l is for membrane active thickness (cm).
The ideal permeation selectivity (а P) was measured by the permeation ratios of pure gases,
\(\alpha_{P}=\frac{P_{\text{BD}}}{P_{N2}}\) (4)
here P BD and P N2 showing the permeabilities of butadiene and nitrogen, respectively.