A perfectly mixed membrane module is used to concentrate helium in the retentate. The feed

stream is $5$mol$\%$ of helium $(He)$ and $95$mol$\%$ of hydrogen $(H_2)$ at $5\mathrm{.}0$atm. The membrane is

natural rubber and operates at $25C.$ The membrane permeability for $H_2$ and $He$ are $90\mathrm{.}8{10}^{-10}$

and $-$s