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.